Volume 1 Number 2 2007

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CONTENTS AND ABSTRACTS

Richard D. Noyes (USA) Apomixis in the Asteraceae: Diamonds in the Rough (pp 207-222)

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Invited Review: The Asteraceae is commonly listed, along with Poaceae and Rosaceae, as one of the principal families within which asexual reproduction by seed, i.e., apomixis, is prolific. A review of the literature indicates that naturally occurring apomixis is robustly indicated for 22 genera in seven tribes of Asteraceae (Lactuceae, Gnaphalieae, Astereae, Inuleae, Heliantheae, Madieae, and Eupatorieae), all but one of which occurs in the subfamily Asteroideae. Apomixis has been proposed for an additional 46 genera. However, consideration of the evidence indicates that the trait is contra-indicated for 30 of these cases in which developmental abnormalities or components of apomixis are recorded for otherwise sexual taxa. Accumulation and perpetuation of these reports through generations of reviews has inflated the actual number of genera in which apomictic reproduction occurs in the family. Data are strongly indicative or equivocal for effective apomixis for the remaining 16 genera, but thorough documentation is wanting. Our state of knowledge of apomixis in the Asteraceae is generally poor. Interpreting the phylogenetic distribution and evolution of the trait in the family will require systematic effort involving cytological documentation and genetic analysis of reproduction for many candidate genera.

Van Cuong Duong, Amitabha Das, Seon-Won Kim, Jae-Yean Kim (South Korea) Recent Advances in Understanding the Regulation of Plant Flavour and Fragrance (pp 223-231)

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Invited Review: Plants emit a number of volatile organic compounds some of which are very attractive for perfume and cosmetic industry which reached about 11.6 billion US dollars in the global market in 2003. To date, about 17,000 plant volatile compounds have been identified. In the last two decades efforts have been made to understand the biosynthesis, functions and regulation of emission of plant volatiles and to target certain volatiles for exploitation at the commercial level. Work is still undergoing in several laboratories in this field by using the most advanced molecular techniques. Plant volatiles are mostly derived from three main classes of compounds: terpenoids, phenyl propanoids/benzenoids and fatty acid derivatives. This review deals with the function and regulation of plant volatiles highlighting the application of new biotechnological approaches to improve the aroma and scent of flowers and fruits with high commercial value.

Youssef Chebli, Anja Geitmann (Canada) Mechanical Principles Governing Pollen Tube Growth (pp 232-245)

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Invited Review: Cellular growth and morphogenesis are central aspects of cellular differentiation. In plants, cellular growth is based on the turgor driven expansion of the cell wall and concomitant addition of new cell wall material. In no plant cell does this process occur as rapidly as in the pollen tube, the carrier of the male gametes. This cell is therefore an excellent model system to investigate the processes governing the dynamics of plant cell growth. This review provides a brief overview of the anatomy of the pollen tube focusing on the structural features that are implicated in the growth process ? the cell wall and the cytoskeleton as well as spatially focused exocytotic events. The mechanics of the growth process is discussed and various theoretical modeling approaches that explain this process are outlined. In pollen tubes from many plant species the growth process is oscillatory or pulsatory and the ions and signalling molecules that form controlling feedback loops in this growth process are analyzed. A model that explains the oscillatory mechanism based on its mechanical components and that results from converging available data and hypotheses is elaborated.

Aya Hatano-Iwasaki, Ken’ichi Ogawa (Japan) Redox Metabolism in Response to Environmental Stimuli for Flowering (pp 246-253)

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Invited Review: It is generally known that flowering is affected by various stresses such as chilling, strong light, drought, wounding, and pathogen infection. Such stresses increase the cellular levels of reactive oxygen species (ROS) altering the cellular redox state of the plant. Recent studies have shown that, in plants, ROS are crucial molecules for signaling responses to biotic and abiotic stresses and for regulation of growth and development, probably including flowering. In this review, we provide information on the regulation of flowering and its relation of the cellular redox state. Based on this information, we discuss how flowering processes are influenced by environmental stimuli.

Yansong Miao, Minghui Yang, Kwun Yee Li, Pui Kit Suen, Junli Shao, Zeng-Fu Xu, Liwen Jiang (China) Molecular Characterization of Plant Vacuolar Sorting Receptor (VSR) Proteins (pp 254-260)

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Invited Mini-Review: Vacuolar sorting receptor (VSR) proteins transport cargoes from Golgi to vacuoles via prevacuolar compartments (PVCs), where VSRs define lytic PVCs as multivesicular bodies (MVBs) in plant cells. The Arabidopsis genome contains seven VSR homologs (AtVSR1-7) but little is known about their subcellular localization and function in plants. Here we summarize studies taken to understand the biology of VSR proteins over the past years and present possible strategies to be used in studying the functional roles of individual AtVSRs in future research, which will serve as a first step for exploring VSR function in plants.

Francisco J.L. Gordillo (Spain) Ecophysiological Strategies of Arctic Seaweeds in a Changing Environment (pp 261-266)

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Invited Mini-Review: Littoral and sublittoral hardbottom zones of the Arctic are mainly dominated by dense macroalgal communities producing high amounts of biomass, which represent a major trophic contribution to these systems. Research on the ecophysiology of polar macroalgae originally focussed on depth zonation pattern as well as basic photosynthetic, nutritional and growth characteristics at near freezing temperatures. More recently a number of studies have dealt with functional and structural strategies that allow polar species to cope with the long periods of darkness during winter and excess light and nutrient limitation during summer. Lately, research efforts have also devoted to gain knowledge on the effects of excess ultraviolet radiation on these organisms caused by stratospheric ozone depletion. Other threats linked to global change in polar ecosystems are increasing load of nutrients dissolved in seawater, increasing levels of atmospheric CO₂ and occasional episodes of drastic decrease in salinity caused by thawing of large masses of ice. This mini-review aims to update the knowledge on the survival strategies of macroalgae that evolved genetically to inhabit the Arctic, and their mechanisms to overcome predicted environmental changes. From the presence of an internal clock synchronising nutrient assimilation and light harvest operating at species and community levels to mechanisms of defence against high light stress, polar macroalgae appear to be not as fragile as originally thought. However, some predictions on the disturbance of the community species composition are also discussed.

Johann Lavaud (Germany) Fast Regulation of Photosynthesis in Diatoms: Mechanisms, Evolution and Ecophysiology (pp 267-287)

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Invited Review: Diatoms (Bacillariophyceae, Heterokontophytes) are essential aquatic eukaryotes. Their role in the structure and ecology of most of the aquatic ecosystems is crucial. Especially, their photosynthetic activity is responsible for about a quarter of the Earth’s primary productivity as large as the most productive terrestrial ecosystems, even though they represent only few percents of the total plant biomass on the planet. Both planktonic and benthic diatoms tend to dominate in ecosystems characterised by a high turbulence of the water (coasts and estuaries). As a consequence, they have to cope with an underwater light climate with high frequency fluctuations in irradiance coupled with large amplitude. The observation that diatoms grow and dominate under a fluctuating light regime regularly punctuated with excess light exposure, which can be harmful for photosynthesis activity, suggests both an unusual flexibility and ability to protect from light stress. These abilities arise from fast photoprotective processes which allow the diatoms to rapidly regulate the absorption, transfer and use of the light energy used for photochemistry and ultimately for biomass production. While largely studied in higher plants, the function and peculiarities of these mechanisms just start to come to light in diatoms. Here, after a description of the composition and organisation of the photosynthetic apparatus of the diatoms, the main fast photosynthetic regulatory processes are described, their evolution discussed and their possible involvement in the ecophysiology of diatoms in the context of water vertical mixing highlighted.

Gerardo Pérez, Nohora Vega (Colombia) Lamiaceae Lectins (pp 288-299)

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Invited Mini-Review: The Lamiaceae family is widely distributed throughout the world and some species have been used in folk medicine, gastronomy and as a source of essential oils and aromas since ancient times; secondary metabolites from many species from Eurasia and North-America have been characterised during the last 5-6 decades. By contrast, species from the neotropical Calosphace Benth. subgenus have been little explored, despite their great diversity. Studies on seeds have been limited to mucilage distribution, chromosome patterns and, since the 1970s, to the presence of lectins, mainly in Salvia and Sclarea Benth. subgenera from the temperate zone. This review initially summarises the available information concerning the presence of lectins in both temperate and neotropic genera, the former being the subject of the pioneering work of Bird’s group in the 1970s which revealed the presence of seed lectins able to recognise the Tn antigen (GalNAcα Ser/Thr). Later work has contributed to further our knowledge regarding neotropic genera lectins. The various detection methods used for assessing the presence of lectins in Lamiaceae seeds and vegetative tissues are discussed. The biochemical characteristics of lectins isolated from five genera (Salvia, Lepechinia, Moluccella, Glechoma and Clerodendron), their structural features and fine specificity are compared. Recent findings concerning their interactions with cell lines and Tn antigen-containing tumour cells are presented. An overview is given about their potential applications and those research lines which would help us in better understanding these lectins.

Zsolt Pónya (Italy), Beáta Barnabás (Hungary), Mauro Cresti (Italy) In Vitro Fertilisation in Wheat (Triticum aestivum L.) (pp 300-326)

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Invited Review: Studying the early events of fertilisation and the first zygotic cleavage during zygotic embryogenesis in angiosperms requires meticulously designed, complex experimental approaches. In wheat, like in an overwhelming number of crop species, little is known about fertilisation and the early events that ensue concomitantly. Therefore, answering questions such as to what extent the wheat zygote is dependent on the endosperm for its normal development, what morhpogenetic stimuli come from the maternal tissues, what factors are necessary for the accomplishment of embryonic growth from the onset of zygote development, what intertwining pathways ensure egg activation triggered by fertilization is of paramount importance. Towards this goal a brief overview is provided as to the main achievements of in vitro fertilisation (IVF) in the best-described maize system. This paper summarizes experimental data obtained by the application of IVF and the microinjection method adopted in wheat to address some important issues such as the ultrastructural characterization of wheat egg cells isolated at different maturational stages; the competence of the wheat female gamete for transient expression of foreign genes; DNA dynamics during sperm-egg fusion and zygotic development; and cytoskeletal changes occurring during in situ egg cell development and in the course of fertilization. A summary is given about studies conducted to follow up structural changes in the endoplasmic reticulum identified to be the main calcium store in the female gamete in wheat. The present review concludes by depicting some future prospects pertaining to the potential offered by exploiting the sexual route for the improvement of wheat and delineates vistas opened up by the application of plant biotechnology tools in sexual plant reproduction research as well as in developmental biology of angiosperms.

Marina Belonogova, Galina Raldugina (Russia) Biotechnology of Flax (Linum usitatissimum) (pp 327-346)

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Invited Review: Biotechnology can offer useful tools to complement conventional breeding programs. The techniques of in vitro selection, that exploit phenomenon, called somaclonal variation, by screening cell cultures for resistance to herbicides, different types of stress or diseases, already helped to obtain tolerant lines of flax (Linum usitatissimum), which were used in further commercial breeding programs. The other important techniques in flax biotechnology are anther and immature embryo cultures. Development of haploid or dihaploid lines based on a regeneration capacity of microspores in immature anthers can speed up conventional breeding. Embryo rescue helps to overcome the post-zygotic incompatibility mechanisms after wide crosses for the transfer of desired traits. One of the main objectives of tissue culture studies is to obtain high-frequency shoot regeneration or somatic embryo formation. Age and viability of the explant, the tissue source and genotype of donor plant from which the explant was excised, composition of the culture medium and plant growth regulator supplementation, are very important for the effectiveness and the direction of morphogenic responses. This review highlights main studies devoted to flax biotechnology and the main factors controlling morphogenesis of L. usitatissimum.

Dimitris L. Bouranis, Styliani N. Chorianopoulou, Vassilis E. Protonotarios, Vassilis F. Siyiannis (Greece), Malcolm J. Hawkesford (UK) Localization of Reactive Oxygen Species and Lignification in Leaves of Young Sulphate-Deprived Maize Plants (pp 347-354)

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Original Research Paper: Young maize (Zea mays L., Poaceae) plants were grown in a complete, well-oxygenated nutrient solution and after 15 days were subjected to sulphate deprivation for 12 days. The lamina of the fully expanded 2^nd leaves in sulphate-deprived plants (-S) presented more developed lower sclerenchyma and an intense lignification. Vascular bundles (VB) were more developed in the lamina of the expanding 4^th leaves of -S plants, possessing more and larger xylem vessels compared with the control. Sulphate deprivation also affected the spatial and temporal distribution of reactive oxygen species. Superoxide anions and hydrogen peroxide in 2^nd leaf of control plants were located mainly in the mesophyll, whilst in the 2^nd leaf of -S plants they were located in the parenchymatic sheath of the VB. Addition of the superoxide dismutase inhibitor, N,N-diethyldithiocarbamate (DDC), resulted in an increased level of superoxide anions in -S leaves. The presence of superoxide anions was particularly evident in the cell walls between the VB of leaf 2 of -S plants. In contrast, there was a higher concentration of hydrogen peroxide in control leaves at day 12. Leaf 4 of the -S plants, had less superoxide anions than control plants, and there was no detectable superoxide anion in the VB. Conversely, in control leaves intense presence of superoxide anion was observed inside and around the VB (in the area where the midvein VB develops). There was no appearance of hydrogen peroxide, either in the treatment with DDC or in the treatments with ascorbate or ascorbate plus DDC, for both control and -S leaves.

Kazuhiko Miyanaga, Masumi Yamada, Minoru Seki (Japan) Development of a Micro-Scale Cell Culture System for Strawberry using Microfabricated Devices (pp 355-360)

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Original Research Paper: A microfluidic device for cell-culture systems has been studied. Micro-scale culture systems are expected to be used for a high-throughput screening system for cell selection, micro-bioreactors, environmental monitoring devices for trace hazardous compounds, etc. Selections of highly-producing cell-lines or determinations of optimal culture conditions are time- and labor-consuming processes, especially for slow-growing cell species. Recently, a number of investigations have been reported on cell cultures using microfabricated devices. However, there exist many problems related to the control of culture conditions similar to large-scale cultivation. Also, no research has been done on plant cell culture in microfluidic devices, probably because of difficulties in their cultivation at a lower cell density. In this study, microfluidic devices fabricated using polydimethylsiloxane (PDMS) were developed for the culture of plant cells. Cultured strawberry cells, which produce red pigments, anthocyanins, were introduced into a cultivation chamber in the microfluidic device. This device was composed of cultivation chambers, weir structures to retain plant cultured-cells in them, several inlets and outlets, and connecting micro-channels. The conditioned medium (CM) combined fresh medium and used-medium and was used to facilitate cell growth at a low cell density. In this micro-scale culture system, strawberry cells were successfully proliferated for more than 5 days. Moreover, the cell growth and pigment productivity using CM were compared with those using normal fresh liquid medium. Extending the applications, we examine techniques for separating specific cells in the micro-system.

Kotamballi N. Chidambara Murthy, Chandrappa Dayananda, Gokare Aswathanarayana Ravishankar (India) Blocking of Sterol Biosynthesis by Statin Enhances Carotenoid Production in Dunaliella (pp 361-365)

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Original Research Paper: In order to meet the demand for b-carotene, which is gaining commercial significance due to its health attributes, the algae Dunaliella is being commercially exploited. The current study was aimed at finding methods for enhanced production of b-carotene and also to understand the relationship between other pathways which were interlinked. The unicellular marine micro algal strains of Dunaliella species namely Dunaliella salina and Dunaliella bardawil were studied to understand the effect of atorvastatin, a well-known drug and HMG-CoA reductase inhibitor which inhibits cholesterol biosynthesis. Different concentrations of atorvastatin (5.0, 10.0 and 25.0 mg L^-1) were employed at different time intervals of growth (added on 3^rd, 6^th and 9^th day). The algae were harvested and analyzed for yield of fresh biomass, and contents of b-carotene and squalene. Squalene content of the treated groups was analyzed and no traces were found whereas the control cultures of D. bardawil and D. salina contained 0.6 µg g^-1 and 0.53 µg g^-1 of squalene, respectively. Subsequently SDS-PAGE analysis showed an increase in the contents of lycopene cyclase (43.0 KD) in the treated cultures which was also further confirmed by analysis of lycopene cyclase activity. The total carotenoids content was found to be enhanced by 1.9- and 1.4-fold after 16 days in D. bardawil treated with 10 mg L^-1 and 25.0 mg L^-1 of statin, respectively while in D. salina this content was enhanced 1.8- and 2-fold, respectively in the same time period. D. salina accumulated 3.15 mg L^-1 of carotenoids in the 10 mg L^-1 atorvastatin treatment. Correspondingly, D. bardawil accumulated 5.6 mg L^-1 of carotenoids in the 10 mg L^-1 atorvastatin treatment. This is the first report on the effect of atorvastatin on the microalgae Dunaliella.

Maurizio Sajeva, Elisabetta Oddo (Italy) Water Potential Gradients between Old and Developing Leaves in Lithops (Aizoaceae) (pp 366-368)

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Original Research Paper: Lithops plants consist of a pair of opposite succulent leaves inserted on a short stem. The apical meristem produces a new pair of leaves within the old one every growing season, recycling water from the old leaves. Since there are no data on water relations between the two pairs of leaves, we measured leaf water potential at different stages of development with a pressure chamber. Osmotic potential of cell sap was measured with a cryoscopic osmometer and turgor pressure was calculated indirectly. Leaf water potentials were never very low even though plants were not irrigated. In old leaves water potential ranged between -0.5 and -0.28 MPa. In young leaves water potential increased with size from -1.05 to -0.5 MPa and was always lower than in the corresponding old leaves. The water potential gradient between old and new leaves was steeper in the early stages of development (0.6 MPa) and gradually decreased (0.15 MPa) when young leaves had almost completed their expansion. Our data show that in Lithops water movement from old to young leaves occurs according to a water potential gradient. The maintenance of this gradient may be ascribed to differences in turgor pressure, due to the more elastic and plastic walls of cells of young leaves. The possibility to perform a complete life cycle without external water supply is an extreme adaptation to the arid environment where Lithops grows.