Volume 1 Number 1 2007

CONTENTS AND ABSTRACTS

Jean-Paul Ducos, Charles Lambot, Vincent Pétiard (France) Bioreactors for Coffee Mass Propagation by Somatic Embryogenesis (pp 1-12)

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Special Feature: Coffee somatic embryogenesis in liquid medium is a powerful alternative to other vegetative propagation techniques for mass propagation of selected Coffea canephora (Robusta) clones and F₁ Coffea arabica hybrids. This review presents the different types of bioreactors used for coffee somatic embryogenesis by Nestl? R&D Centre-Tours and by other scientific teams. Mechanically agitated bioreactors were used for the production of torpedo-shaped embryos. Critical parameters are the inoculation density (0.5 to 1.0 g FW L^-1), medium renewing and the initial oxygen transfer rate (K_La: 5 h^-1). In this system, Robusta embryo concentrations range between 200,000 to 400,000 L^-1 within 2 months. Maturation from the torpedo to the cotyledonary-stage embryos was achieved in various temporary immersion bioreactors (TIB): in 1-L RITA^? system (up to 1,000 cotyledonary embryos per system), in 10-L glass bottles (up to 20,000) and in 10-L flexible disposable bags. The latter one, the so-called “Box-in-Bags”, insures a higher light transmittance to the biomass due to its horizontal design. At the end of the maturation phase, the somatic embryos are green and able to photosynthesize: these pregerminated embryos can be directly transplanted to the greenhouse to get fully germinated plantlets. More recently, a temporary root immersion bioreactor (TRI) has been described for the growth of individualized Arabusta plantlets in photoautautrophic conditions, i.e. in sugar-free medium with enriched CO₂ and high light intensity. The pros and cons of these different bioreactors will be discussed considering how they can be integrated in a mass propagation process. We present a “state of the art” by describing a pilot scale process for the production of pregerminated Robusta embryos and some examples of diffusion of coffee selected genotypes. These last years, two major trends have been developed for industrial micropropagation: i) bulk-cultivation of small propagules in photomixotrophic conditions (with sugar) followed by their selection and transfer to the greenhouse for their conversion to plant, ii) production of singulated and fully developed plantlets in the laboratory under photoautotrophic conditions. Next development in coffee mass propagation by somatic embryogenesis will probably originate from the combination of these two approaches. The usage of the “micro-environment” method, combined with media releasing CO₂, is well adapted for the ex vitro germination of coffee embryos. Particularly, this method can be a relevant alternative to the conventional one, consisting on insufflating CO₂ in the culture rooms or in the greenhouses.

Mark F. Belmonte, Muhammad Tahir, Claudio Stasolla (Canada) Developmental and Molecular Studies of Spruce Embryogenesis in Vitro (pp 13-21)

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Invited Review: Since first described in the mid-eighties somatic embryogenesis of spruce has been extensively utilized both as a tool for mass propagation and as a model system for the investigation of structural, physiological and molecular events occurring during embryo development in conifers. Despite the increased efforts to optimize media composition and culture environment, production of somatic embryos still poses problems, especially for recalcitrant genotypes. Low yield and/or poor quality embryos which are not able to regenerate viable plants are often observed in culture. Improvements to the system have been made possible through the combined applications of developmental, physiological and molecular studies. Cell tracking techniques have defined the different phases of embryo development with great precision and have allowed for comparative structural studies between somatic and zygotic embryos. Physiological work has revealed ways to improve embryo development in culture. Manipulating the embryonic environment during the early phases of development through changes in osmoticum and redox state, or during germination through applications of ascorbic acid, has improved embryo regeneration. Furthermore, recent molecular work has identified several genes involved in embryo development. Advances in spruce transformation have revealed the functional relevance of such genes in regulating the developmental fate of somatic embryos. The focus of this review is to provide an up-date on the current status of spruce embryogenesis and to emphasize developmental and molecular events characterizing the process.

Mads Eggert Nielsen (Denmark) A Transcriptomic View of Barley Embryo Development (pp 22-27)

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Original Research Paper: Due to the agricultural interests in grain crops, there has been a substantial focus on molecular aspects of grain development, particularly related to grain filling. However, only little attention has been on gene regulation in the developing embryo. Recently, array analyses revealed that the transcriptome of the developing barley embryo is quite different from that of the surrounding tissues. In order to generate a general view of the processes involved in embryo development, transcriptome data from previous array analyses of developing embryos of barley, maize, wheat and Arabidopsis are discussed. An interesting aspect is the dual role of abscisic acid, involved in the regulation of storage product synthesis and in the desiccation tolerance of the embryo. The latter phenomenon might involve the transcription factors DREB2A and DREB2B, probably by up-regulating both late embryo abundant proteins and perhaps cysteine protease inhibitors to help the embryo tolerate desiccation and prevent initiation of programmed cell death. In addition, a detailed analysis of changes in the transcriptome of the developing barley embryo is presented with a particular interest in the embryo-specific initiation of at least two forms of developmental defense activations (DDAs), initiated at 21 and 37 days after flowering and termed early and late DDA, respectively. The initiation of both early and late DDA could help explain the protection of the developing embryo against disease and could provide valuable information on the regulation of potential allergens. Combined these data help to elucidate the regulatory networks involved in barley embryo development.

Xing-chun Tang, Meng-xiang Sun (China) Exine-Dehisced Microspores: a Novel Model System for Studying Embryogenesis (pp 28-33)

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Invited Mini-Review: Upon stress of high temperature, Brassica microspores can be switched from their gametophytic development to an embryogenenic pathway. It provides a powerful system for understanding the biological basis of embryogenesis. However, embryos derived from symmetrically divided microspores usually lack a suspensor, which is distinct from normal zygotic embryogenesis. This obviously limits the application of the system in the investigation of the early developmental events of embryogenesis. We have now established a novel system for inducing and studying embryogenesis: the exine-dehisced microspore, in which the exine is ruptured but still envelopes the microspore. Evidence shows that the exine-dehisced microspore shares all the advantages of the traditional androgenesis system and offers a unique chance to examine the role of polarity, asymmetric division, and the cell wall in cell fate determination and apical-basal axis selection in embryos. Thus, the exine-dehisced Brassica microspore system provides a novel and useful alternative model for studying these early events of embryogenesis. In this mini-review, we mainly introduce the system and outline its potential applications.

Alina Morquecho-Contreras, José López-Bucio (Mexico) Cannabinoid-Like Signaling and Other New Developmental Pathways in Plants (pp 34-41)

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Invited Review: Plant growth and development depend on the interplay of a number of chemical regulators. Traditionally, six groups or classes of plant hormones have received the most attention: auxins, cytokinins, ethylene, abscicic acid, gibberellins and brassinosteroids. Recently, it has become clear that additional signaling molecules are used by plants. The alkamides and N-acylethanolamides (NAEs) - a class of small organic compounds related to animal endocannabinoids - appear to play a role in diverse morphogenetic processes including seed germination, alteration of plant architecture and response to pathogen attack. In vertebrates, the endocannabinoid signaling pathway has been found to control cellular and morphogenetic responses including embryo development, cell proliferation, immune responses and apoptosis. The notion that plants use alkamides and NAEs to regulate physiological processes is supported by their occurrence in a wide range of plant species, their selective accumulation and rapid metabolism in response to developmental transitions and by the recent identification of the enzymatic machinery for NAE degradation. Moreover, signal transduction cascades involving glutamate and nitric oxide, partners of NAEs and alkamides in regulating animal physiology, have been found to participate in important developmental processes in plants. This information suggests that endocannabinoid-like compounds and other ancestral signaling pathways might be integral to morphogenetic and adaptive processes in plants.

Laura Ragni, Elisabeth Truernit, Véronique Pautot (France) KNOXing on the BELL: TALE Homeobox Genes and Meristem Activity (pp 42-48)

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Invited Mini-Review: All plant organs are derived from meristems. The shoot apical meristem (SAM) produces the aerial part of the plant. It has two main functions: the maintenance of a group of stem cells at the center of the meristem and the initiation of organs at its periphery. The organs are initiated in a regular spatial pattern, referred to as phyllotaxy, and are separated from the surrounding tissue by a boundary domain. The KNOTTED-like homeobox (KNOX) family of transcription factors plays a key role in the control of SAM activity. These proteins belong to the three amino acid loop extension (TALE) homeodomain superclass and form heterodimers with other TALE proteins belonging to the BEL1-like (BELL) family. The KNOX proteins regulate the different activities of the SAM. They control SAM maintenance, boundary establishment, the correct patterning of organ initiation and the development of axillary meristems. They exert their effects through the regulation of several hormonal pathways. KNOX proteins repress gibberellin (GA) biosynthesis and activate cytokinin (CK) synthesis and signaling. In addition to their role in the SAM, they contribute to leaf form diversity. In plants with simple leaves, KNOX genes are expressed in the SAM and downregulated in leaf primordia, whereas in plants with dissected leaves their expression is reactivated in leaves.

Wun S. Chao, Michael E. Foley, David P. Horvath, James V. Anderson (USA) Signals Regulating Dormancy in Vegetative Buds (pp 49-56)

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Invited Mini-Review: Dormancy in plants involves a temporary suspension of meristem growth, thus insuring bud survival and maintenance of proper shoot system architecture. Dormancy regulation is a complex process involving interactions of various signals through specific and/or overlapping signal transduction pathways. In this review, environmental, physiological, and developmental signals affecting dormancy are discussed. Environmental signals such as temperature and light play crucial roles in regulating development and release of bud dormancy. Physiological signals including phytochrome, phytohormones, and sugar are associated with changes in dormancy status that occur when plants perceive environmental signals. Developmental signals such as flowering and senescence also have an effect on bud dormancy. Currently, many genes and/or gene products are known to be responsive directly or indirectly to these signals. The potential roles for these genes in dormancy progression are discussed.

Maria Filek, Jolanta Biesaga-Kościelniak (Poland), Ivana Macháčková, Jan Krekule (Czech Republic) Generative Development of Winter Rape (Brassica napus L.) - The Role of Vernalization (pp 57-63)

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Invited Mini-Review: Winter rape (Brassica napus L.), a bright yellow-flowering member of the Brassicaceae, is the single most important oilcrop, recognized as an alternative to cereals over the wide range of temperate agricultural regions. Thus, its adaptation to local climatic conditions is of special importance. The timing of flowering is a crucial determinant of the adaptation to the environment. Vernalization, i.e. the exposure of plants to a prolonged period of low temperatures is, beside photoperiodism, considered as most specific primary factor inducing and controlling generative development. Ecological, physiological and molecular aspects of vernalization of winter rape are dealt with in this review.

Muriel Quinet, Jean-Marie Kinet (Canada) Transition to Flowering and Morphogenesis of Reproductive Structures in Tomato (pp 64-74)

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Invited Mini-Review: Flowering in tomato (Solanum lycopersicum L.) has long been investigated by plant physiologists and horticulturists aiming to increase productivity of this important fruit crop. The disruption of the sequence of events which give rise to normal development of the reproductive structures by either the manipulation of the environment, hormones or mutations has provided information useful to unravel the complexity of the implicated mechanisms. In this paper, we focus on the early stages of the flowering process, analysing how flowering time and reproductive morphogenesis are regulated. Development of the reproductive structures up to anthesis, having been reviewed on several occasions in the past, is not considered. Tomato is an autonomously flowering plant with a sympodial growth habit, which means that it flowers repeatedly, at the top of an initial segment and of successive sympodial segments. The nature of its reproductive structure, a raceme or a cyme, is still questioned but available evidence supports the view that the tomato inflorescence is racemose. Flowering time is strongly dependent on the daily light energy integral and is regulated by an array of genes among which SINGLE FLOWER TRUSS (SFT) and SELF PRUNING (SP) play a major role. SFT is a flowering promoter particularly active in the initial segment while SP regulates sympodial development by controlling the regularity of the vegetative-reproductive switch of the different sympodial segments. Many genes specifying the identity of the meristems and floral organs interact to regulate the morphogenesis of the reproductive structures, opening a large field for future investigations.

Christopher Ochieng Ojiewo, Kenji Murakami (Japan), Peter Wafula Masinde, Stephen Gaya Agong (Kenya) Floral Genetics of African Nightshade (Solanum section Solanum) (pp 75-81)

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Invited Mini-Review: Solanum section Solanum, centering on the species commonly known as African nightshade, and botanically known as the “Solanum nigrum complex” is composed of a large number of morphogenetically distinct taxa, with certain common features. Their wide tolerance of habitat types, early flowering and prolific fruit production are adaptive features for success in the wild, semi-wild or weedy forms. In most parts of Africa and south-east Asia, their consumption, demand and market value as leafy vegetables have been on the rapid and steady rise in recent years due to their high nutritional and health benefits. However, production of these vegetables has traditionally remained on kitchen-garden scales with very low leaf yields. Notably, competition between vegetative and reproductive functions accounts for this low yield. Accurate manipulation of the switch from vegetative to reproductive development or elimination of the latter would potentially delay, reduce or eliminate competition from excess fruit load. A thermosensitive abnormal floral organ mutant (T-5) with sepaloid, stamenless and indeterminate phases has been induced in the sub-taxon S. villosum. The mutant will form an important basis for understanding reproductive developmental steps, such as floral induction, meristem formation, and organ development in African nightshade. This review explores the established floral genetic models as a basis to elucidate the aspects of floral genetics of African nightshade, with special reference to the T-5 mutant.

Amy Hetrick, Andrew G. McCubbin (USA) Heteromorphy and Flower Development in Primula (pp 82-86)

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Invited Mini-Review: The phenomenon of heterostyly, the possession of floral morphs with differing style lengths within the same plant species, occurs across 28 plant families. One hundred and forty years after its first description in the Primulaceae by Darwin, heterostyly has been studied extensively, but is still not fully understood. Heterostyly functions to maintain sexual diversity by preventing self-fertilization. Primula is distylous, with flowers existing in two forms, “pin” and “thrum,” each having reciprocal placement of the anthers and stigma. Several other morphological differences - such as pollen number and size, stigmatic papillae, and stylar cell length - occur between the two forms, as well as genetic differences of the traits, with pin being homozygous recessive (ss) and thrum heterozygous (Ss). Research on heterostyly in Primula has focused largely on the anatomical and physiological differences between the two floral morphs, and traditional genetic studies of the self-incompatibility (S-) locus that governs this breeding system. The S-locus has been shown to be a "supergene complex" of genes held in linkage disequilibrium and inherited as a single unit. Developing a thorough understanding of this breeding system promises to have a broad impact not only on the knowledge base of the sexual incompatibility systems of plants, but also on the applied industries of agriculture and horticulture. In this article we provide an overview of our current understanding of this system.

Houcheng Liu, Riyuan Chen, Guangwen Sun (China) The Development of Chiehqua Flowers (pp 87-90)

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Invited Mini-Review: Chiehqua (Benincasa hispida Cogn. var. chieh-qua How.) is one of the main vegetable gourds widely grown in South China. Chiehqua begin flower primordia differentiation at the 6^th node in seedlings with only two expanded leaves. There is a positive linear relationship between the nodes of expanded leaves and the nodes of flower bud differentiation and also between the nodes of sexually differentiated flowers. The monoecious sexual type is most prevalent in chiehqua. The flower primordia differentiation and female flowers differentiation in chiehqua seedlings are enhanced by low temperature and short days, and also by lower plant intensity and N fertilizer level. Higher IAA and GA₃ contents, a lower ratio of ABA/IAA, ZT/IAA and higher GA₃/ZT in the stem-tip favor female flower formation in chiehqua. Higher Put, Spd and total polyamine contents and lower Cad content, higher ratio of Spd/Pas and lower ratio of (Put+Cad)/(Spd+Spm) in stem tips favor female flower formation in chiehqua. Exogenous GA₃ application increases the number of male flowers, but silver thiosulphate decrease their presence. The antioxidant enzymes (POD, CAT, SOD, PPO) might influence flower sex expression by influencing ethylene production.

Arlete Santos, Júlio Borlido, Isabel Santos, Roberto Salema (Portugal) Influence of Temperature and Growth Regulators on Anther and Pollen Development During In Vitro Flowering of Narcissus triandrus (pp 91-94)

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Original Research Paper: During the in vitro propagation of Narcissus triandrus the culture conditions for the development of flowers with anthers and pollen comparable to those found in vivo were determined. Flowering was achieved, after 12 weeks of culture, from twin-scales of bulbs initially cultured on a modified Murashige and Skoog medium supplemented with benzyladenine (4 mg l^-1 BA) and naphthaleneacetic acid (0.12 mg l^-1 NAA) or with 2 mg l^-1 BA and indolebutyric acid (1 mg l^-1 IBA), with 3% sucrose, under constant 25°C. Both media were adequate for either foliar primordia or floral bud induction; however, flower organs appeared disorganized both in disposition and structure. In the anthers, a typical callose wall surrounded pollen mother cells but the tapetum had already degenerated and most of the pollen grains had collapsed with a disordered exinic wall. When the cultures were transferred to medium containing only NAA and when sucrose was increased from 3% to 9% and maintained at 25°C, a slight elongation of floral stalks was observed but the further development of flowers failed in 100% of plants. In contrast, at 18°C, flowers morphologically identical to those found in vivo developed, displaying a well-organized tapetal layer and pollen grains with a correctly architectured wall. However, the lower temperature (18°C) did not promote the development of normal flowers when cultures were maintained on induction media with BA and auxins. These results suggest that in this Narcissus species it is possible to induce flowering in vitro albeit conditioned by the composition of the culture media and strongly temperature-dependent.

Jianjun Guo (Canada), Jiansheng Liang (China), and Jin-Gui Chen (Canada) RACK1, a Versatile Scaffold Protein in Plants? (pp 95-105)

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Invited Review: Receptor for Activated C Kinase 1 (RACK1) is a tryptophan-aspartic acid-domain (WD40) repeat protein. Compelling evidence supports the notion that RACK1 is a versatile scaffold protein which binds numerous signaling molecules from diverse signal transduction pathways and plays critical roles in multiple developmental processes in mammals. RACK1 orthologs are present in plants. In particular, the Arabidopsis genome contains genes that encode three RACK1 proteins, all of which are over 75% similar to mammalian RACK1 at the amino acid level. In addition, all functional domains of RACK1 protein including the number and position of WD40 repeats and the protein kinase C binding sites are largely conserved in plant RACK1 proteins. However, no signaling protein has been shown to physically interact with plant RACK1, therefore a scaffolding function of RACK1 protein has not been established in plant cells. Recently, the characterization of the first loss-of-function RACK1 mutant, rack1a, in Arabidopsis has shed lights on a scaffolding function of RACK1 in plants. rack1a mutants display defects in multiple developmental processes and hormone responsivenesses, consistent with a scaffolding role of RACK1. In this article, we provide a comprehensive review of RACK1 in plants, compare its domain structure with mammalian RACK1, and analyze which RACK1-interacting proteins may be conserved in plants. Future studies are expected to lead the discovery of a wide range of RACK1-interacting proteins and the determination of the molecular mechanism of the action of RACK1 in plant cells.

Tohru Ariizumi (USA), Kinya Toriyama (Japan) Pollen Exine Pattern Formation is Dependent on Three Major Developmental Processes in Arabidopsis thaliana (pp 106-115)

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Invited Review: Classical ultrastructural studies have revealed that the architectural structure of the pollen wall is composed of a series of concentric outer layers, although its shape, size and morphology are highly diverged among plant species. These layers are known as the exine, which is formed around the microspore during microsporogenesis. Detailed morphological studies have demonstrated that the exine consists of the simple inner nexine layer and the outer sexine portion, which determines the sculptured exine structure. Biochemical studies have shown that a constituent of the exine precursor, sporopollenin, potentially contains polymers of fatty acid, phenylpropanoids and phenolics derivatives. On the other hand, genetic and molecular studies employing Arabidopsis mutants defective in exine formation have provided new knowledge not only on the critical processes for this pattern formation, but also on the genes involved in the process. Characterization of these mutants has shown that they can be generally classified into three types from a morphological viewpoint: mutants defective in sporopollenin synthesis, primexine formation or callose wall formation. The genetic approach has demonstrated that Arabidopsis mutants lacking any of these three processes show failure in exine pattern formation. In other words, these three processes play critical roles in exine pattern formation in Arabidopsis. Here we review the mutants and genes related to exine pattern formation in Arabidopsis.

Yoshihiro Hosoo (Japan) Development of Pollen and Female Gametophytes in Cryptomeria japonica (pp 116-121)

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Invited Mini-Review: Cryptomeria japonica (Taxodiaceae) is a tall evergreen conifer that is native to Japan and China. It is important as an ornamental tree and as a source of lumber; thus, it has been planted in many regions of Japan. The pollen of C. japonica causes pollinosis, which is becoming a serious problem in Japan. Male-sterile C. japonica that release no pollen have recently gained interest as a potential measure to alleviate this problem. C. japonica is monoecious, and male and female cones usually occur on different branchlets. Both male and female cones begin to develop in summer. In male cones, meiosis of pollen mother cells occurs in October, and mature pollen grains form from late October to late November. Pollen grains are then disseminated in the following spring after winter dormancy. In female cones, ovules with developed integuments and nucelli form in late October, and megaspore mother cells undergo meiosis at the time of pollination. Fertilization occurs in June, and embryo development is completed in August. A better understanding of this reproductive process will contribute not only to breeding and genetic research, but also to measures against pollinosis caused by this species. This mini-review describes the current information available on the process of pollen and female gametophyte development and introduces recent studies of sterility in C. japonica.

Eike H. Rademacher, Dolf Weijers (The Netherlands) Got Root? - Initiation of the Embryonic Root Meristem (pp 122-126)

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Invited Mini-Review: Plant development relies on the activity of meristems, small groups of undifferentiated cells that produce all organs. The first meristems are formed in the embryo, and all subsequent development depends on their proper establishment, making embryonic meristem initiation a key step in plant life. The founder cells of the embryonic meristems are specified early in embryo development after the establishment of the body axis. Initiation of the root meristem in the early embryo is marked by the specification of a single cell, the hypophysis, and hence an attractive model to study meristem initiation. In this review, we will discuss the mechanisms that control embryo axis formation and root meristem initiation.

Dimitris L. Bouranis, Styliani N. Chorianopoulou, Vassilis F. Siyiannis, Vassilis E. Protonotarios (Greece), Malcolm J. Hawkesford (UK) Lysigenous Aerenchyma Development in Roots - Triggers and Cross-talks for a Cell Elimination Program (pp 127-140)

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Invited Review: Aerenchyma, the tissue containing enlarged gas spaces and surrounded by parenchymatous cells, is formed either as part of normal development or in response to hypoxia (oxygen shortage), mechanical impedance, high temperature, nitrogen-, phosphorus- and sulphur-deficiency. Focussed in the root cortex, some cells die to create a lacuna. The diverse stimuli induce a cell elimination program (CEP) result in the same endpoint: a lysigenous aerenchyma formation in the root cortex. CEP occurs as an orchestrated series of events, suggesting a genetically controlled process of active cell death, and can be distinguished in three major processes: the activation process, the execution process and the dissemination and termination process. It seems that perturbations in the energy and the redox status of specific cortex cell stimulate the activation process, which may include the enzymes NADPH oxidase, phospholipase D, protein kinase C, mitochondrial permeability transition pore, cytochrome c, haemoglobin, ACC synthase, ACC oxidase and mitogen-activated protein kinase cascade, as well as the molecules ATP, NADH, reactive oxygen species, calcium, phosphatidic acid, nitric oxide, 1-amino-cyclopropane-1-carboxylate (ACC), and ethylene as CEP activators, organised in various signal transduction modules, while mitochondrion possess a key role in this part of CEP. The coordination of CEP activation modules results in the expression of CEP specific genes. Subsequently, the execution process, may include vacuolar processing enzyme and all the necessary hydrolytic enzymes including proteases, lipases, DNases, RNases, pectinases, cellulases, xyloglucan endo-trans glygosylase, expansins and γ-tonoplast intrinsic proteins as CEP executors and possibly again reactive oxygen species and peroxynitrite, with a key role of the lytic vacuole. Dissemination of CEP produces a tubular structure, the architecture of which is strongly affected by cell packing. Aerenchyma formation is a localised, site-specific CEP, the termination process of which determines the extent of the dissemination, to facilitate either an effective translocation of oxygen, carbon dioxide and ethylene or other gases, or to redirect scarce resources, or to provide a rapid diffusion path for solutes, within the root cortex.

Ella M. Kof, Igor V. Kondykov (Russia) Pea (Pisum sativum L.) Growth Mutants (pp 141-146)

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Invited Mini-Review: This review is devoted to the Pisum sativum L. growth mutants. These mutants are presented by several groups of plants. The first group is characterized by short internodes (dwarf mutants le, na, lk, la, lh, ls) or by elongated internodes (slender mutant sln). The stem growth of mutants of both types (dwarf and slender) is controlled by hormones (GA and IAA) in the stem or in seeds. Mutants characterized by decreased apical bud growth and predominated axillary bud growth belong to another group. They exhibit a multi-branching phenotype. Based on grafting studies with these mutants, several genes have been identified that operate in the shoot and roots in order to moderate the level or transport of graft-transmissible signal involved in branching control (genes rms1, rms2, rms3, rms4, rms5, rms6, rms7). The level and transport of auxins, cytokinins and shoot-multiplicational signal (SMS) take part in the regulation of stem branching. SMS can be surmised to be proteins, among them carotenoid cleavage dioxygenases. The third mutant group is defined as the foliage mutants (genes af, tl, tac, st) characterized by different total leaf weights and areas per plant: high positive correlations of root weight with leaf and stem weight and also of root weight with leaf area are observed. The “chameleon” phenotype is controlled by two recessive genes af and tac, which characterize heterophyllia. The determinate habit mutation is controlled by a recessive allele of the deh gene and result in the reduction of reproductive node number. The recessive det mutant forms an apical raceme, stops growth of the main stem and also exhibits a determinant habit. The lupinoid phenotype is controlled by recessive det and fas genes and determines the apical multi-flower inflorescence which is analogous to a lupine inflorescence. These mutants are important for studying the regulation of plant growth and for progress in improving high productive pea varieties.

Ying Li, Jing-quan Yu (France) Lagenaria leucantha: New Model Plant for Studying Fruit Development (pp 147-150)

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Invited Mini-Review: Lagenaria leucantha, belonging to the Cucurbitaceae family, is an important vegetable crop widely grown in greenhouses throughout Asia. It lacks the ability of natural parthenocarpy and pollination is essential for successful fruiting. Fruit growth of L. leucantha, after anthesis, starts by cell division and is followed by cell expansions that make the greatest contribution to the final fruit size that is characteristic of the growth and development of most fruits. As an important cucurbita crop, L. leucantha is distinct from the model plant Arabidopsis, which belongs to the mustard family, in many aspects of development. CPPU, a synthetic cytokinin, can effectively promote cell division and induce parthenocarpy in L. leucantha. This not only provides an effective solution to ovary abortion, but also provides an experimental system for studying fruit development, in particular, the mechanism of chemical-induced parthenocarpy.

Branka Salopek-Sondi, Volker Magnus (Croatia) Developmental Studies in the Christmas Rose (Helleborus niger L.) (pp 151-159)

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Invited Review: The Christmas rose (Helleborus niger L.) is a herbaceous, winter-green, perennial native to Southern Europe, which is also widely grown as an ornamental. In mild winters, the flowers may indeed appear at Christmas time, resembling wild roses with respect to size and color (white to pink). Reproductive development in the Christmas rose is characterized by an interesting aspect, uncommon in the world of flowering plants: after pollination and fertilization, the perianth develops a photosynthetic apparatus, and persists during fruit development. Unpollinated or depistillated flowers survive almost as long as their fruit-bearing neighbors, but do not pass through the complete greening process. Removal of the gynoecium also affects the shape of the flower and the length of the flower scape. The correlative signals which normally trigger and maintain these morphogenetic processes appear to include plant hormones synthesized in the developing fruit. Because of the size of its flowers, their long lifespan, and the changes induced by fruit development and maturation, the Christmas rose could become a useful research model for disentangling some of the complex interactions between developing seeds and the mother plant.

Kaisa Marjamaa, Eija M. Kukkola, Kurt V. Fagerstedt (Finland) Lignification in Development (pp 160-169)

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Invited Review: Developmental lignification is a process where lignin is deposited to the plant cell wall during the normal cell differentiation. Lignification of cell walls occurs where increased support or water impermeability is needed, such as in tracheary elements and in sclerenchymatic tissues of e.g. fibers and in the endocarp of some fruits. The chemical structure and amount of lignin varies between plant species, cell types, and cell wall layers and as response to environmental conditions. Lignification is apparently regulated by hormonal signaling (e.g. gibberellin) controlling the multiple enzymes via various transcription factors (e.g. MYB and LIM) involved in the monolignol biosynthesis pathway and probably by the level of reactive oxygen species in the apoplast. The most extensively studied area of developmental lignification is the lignification of xylem cells. In this review, two main areas of xylem research are covered: Lignin biosynthesis in xylem cells of trees, and the tracheary element differentiation in the Zinnia elegans cell culture. Knowledge on xylem lignification in trees has increased enormously during the recent years due to development e.g. in histological and in molecular biology methods, whereas the Z. elegans system presents a well characterized model for studying cellular events in xylem differentiation. In addition, studies on other cases of developmental lignin biosynthesis in particular in monocotyledonous species are included.

Noritsugu Terashima (Japan) Non-Destructive Approaches to Identify the Ultrastructure of Lignified Ginkgo Cell Walls (pp 170-177)

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Invited Mini-Review: Information on the lignification mechanism and 3D ultrastructural assembly of lignin and polysaccharides in plant cell walls is essential for better understanding of physical, chemical and biological properties of lignified plant tissue. Ginkgo biloba (ginkgo) is one of the most suitable plant species for lignification studies because it is the oldest still living trees on earth appeared in the early stage of evolution of trees, and it retains primitive characteristic features of lignified plant cell walls. Because conventional destructive analyses can provide only limited information on the 3D assembly of cellulose, pectin, hemicelluloses and lignin in cell walls, we examined the lignification process in ginkgo xylem by various non-destructive approaches: radioisotope tracer methods using ³H and ¹⁴C combined with a scintillation counting technique and microautoradiography; a stable isotope tracer method using ²H, ¹³C, combined with the techniques of mass spectrometry and differential NMR spectrometry; observation of lignifying cell wall under field-emission scanning electron microscopy combined with mild selective removal of lignin or polysaccharides from the cell walls retaining their morphological features. The combined results provided useful information on the ultrastructure of lignified cell walls not only in ginkgo xylem but also in xylems of most coniferous trees.

Henriette Weber, Perdita Hano, Hanjo Hellmann (Germany) The Charming Complexity of CUL3 (pp 178-184)

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Invited Mini-Review: Ubiquitination is a fascinating regulatory tool for various biological processes, mostly for the control of rapid and selective degradation of important regulatory proteins involved in cell cycle and development, among others. The superfamily of cullin-RING finger protein complexes is the largest known class of E3 ubiquitin ligases and several substrates have been described in different organisms. In plants, cullins can be grouped into at least four subfamilies, and each subfamily associates with a specific class of substrate receptors that often belong to larger protein families. Consequentially, the corresponding complex interaction patterns indicate that numerous substrate proteins are ubiquitinated by plant E3 ligases. In this review we recapitulate recent findings on a newly identified plant E3 ligase family that contains class 3 cullins (CUL3) and BTB/POZ proteins as their corresponding substrate adaptors. Here, three main aspects will be described: 1) the molecular composition of CUL3-based E3 ligases, 2) BTB/POZ domain containing proteins and their role in substrate recognition, and 3) comparison of plant and other eukaryotic CUL3-based E3 ligases to provide an outlook on potential roles of this specific E3 ligase family in higher plants. By focusing on these points, the review will provide a perspective on the impact of CUL3-based E3 ligases on plant development.