Volume 1 Number 2 2007

CONTENTS AND ABSTRACTS

Anja Geitmann (Canada), Ravishankar Palanivelu (USA) Fertilization Requires Communication: Signal Generation and Perception During Pollen Tube Guidance (pp 77-89)

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Invited Review: The generation of novel hybrid lines is critically limited by the compatibility between pollen and pistil and their ability to achieve successful seed formation. Fertilization in flowering plants requires the successful transfer of the male gametes from the pollen grain to the egg contained within an ovule. This occurs via the formation of a tubular protrusion from the pollen grain - the pollen tube. This specialized structure grows extremely fast and has the complex task to invade the stigmatic and stylar tissues of the receptive flower, to find the ovary and an ovule, and to subsequently release the male gametes to the egg and central cell to achieve double fertilization. Failure of the pollen tube to penetrate the pistil or find its target results in the absence of fertilization and sterility. Understanding the signals that regulate the compatible interaction between a pollen tube and all the female cells in its path is therefore critical to generate tools for breeders in their quest to break species barriers and produce novel hybrids. In this review, we will discuss the signals and cues that guide pollen tubes to their targets, the mechanism of pollen tube growth and how the pollen tube readjusts its growth direction in response to these signals. In addition, we will present in vitro experimental strategies to study the pollen tube’s ability to find its target and/or the ovule’s capacity to attract or repulse a growing pollen tube.

Adalberto Di Benedetto (Argentina) Alternative Substrates for Potted Ornamental Plants Based on Argentinean Peat and Argentinean River Waste: A Review (pp 90-101)

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Invited Review: Choosing the right media to grow quality pot plants is a key factor in crop production. Horticultural container media may be formulated from a variety of materials, with the goal to optimize physical and nutritional characteristics. However, suitable organic amendments are becoming expensive and increasingly difficult to obtain. Although Argentinean peat does not seem to be a fully acceptable substitute for Sphagnum Canadian peat, it would be an alternative pot plant growing media when combined with river waste. Alternative substrates, which are well characterized and corrected by suitable mixtures, make it possible to produce better quality plants, more rapidly and avoid the over-exploitation of natural Sphagnum peatlands. Chemical and physical characteristics of Argentinean peat and river waste-based alternative substrates for different ornamental perennials and bedding pot plants are also discussed.

P.K. Nagar, M. Sharma, P.K. Pati, P.S. Ahuja (India) Rose: Some Important Findings with Special Reference to Physiology of Flowering (pp 102-114)

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Invited Review: Rose, a commercial crop, is distributed worldwide. Due to several natural and artificial changes over time the Rosa species have become very difficult to determine. However, successful attempts have been made to classify the genus Rosa with the aid of cytological and phenotypic studies. The crop also encounters serious problems of biotic stress and issues related to flower production and enhancement of their shelf-life. These problems are addressed with difficulty through conventional breeding and biotechnological approaches are currently playing a vital role in the rose improvement programme. On the other hand, biochemical and physiological studies are powerful approaches toward understanding organ differentiation and their growth and development. However, relatively little is known about the physiology of flowering in rose. The whole natural period of growth and development is much shorter for petals than leaves and hence petals seem to be an excellent model system for the study of fundamental physiological processes. The present chapter extensively summarizes the studies conducted on various physiological and biochemical aspects of flowering with special reference to two species of scented rose i.e. Rosa damascena and R. bourboniana. Such a review will be helpful to expand our insight of the flowering behaviour and in finding out suitable indicators of various physiological processes which may help in enhancing essential oil production of both the diverse species of rose.

Ling Zhang, Jin Chen, De-Zhu Li, Qing-Jun Li (China) Reproductive Biology, Mating System, and Population Genetics of Devil Flower: An Autonomous Selfing Plant with Showy Floral Display (pp 115-124)

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Invited Review: Tacca, a genus of tropical herbs, possesses near black flowers, conspicuous involucral bracts and whisker-like filiform bracteoles. These unusual floral features puzzle every botanist and beg the question whether their large involucral bracts and long whisker-like filiform bracteoles play a role in pollinator attraction, or function in defense from herbivores. Recent studies of pollination, mating system and population genetics of Tacca chantrieri revealed that it is a highly self-pollinating species, and their showy floral structures play a limited role in pollinator attraction. This mating pattern leads to significant spatial genetic variation among populations. The population genetic structure is also determined by the population history and environmental circumstances. Significant genetic differences between two distinct geographic regions of T. chantrieri have been documented and might be attributable to vicariance along the Tanaka Line, as gene flow was blocked. T. integrifolia also possesses the same population genetic pattern. Moreover, because of their ornamental floral structure, Tacca plants have become increasingly popular in the horticultural trade; and some relevant studies about their seed biology and horticultural techniques have been done. Future studies about Tacca should focus on the origin and evolution of their bizarre floral structures and the function of natural selection on reproductive traits in natural populations.

Jackrit Anantasaran (Thailand), Max B. Schröder, Klaus Eimert (Germany), Kamnoon Kanchanapoom (Thailand) Cytogenetic Characterization of Zinnia Species and Cultivars (pp 125-130)

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Original Research Paper: Zinnia is a tropical ornamental plant, and its cultivar classification is complicated. The typical characters such as height, flower size and leaf shape are of a quantitative nature, and under strong environmental control. In some cases, unequivocal determination of cultivars may be difficult using morphological features only. So in this study, cytological, cytogenetical and molecular biological characteristics of Zinnia have been analyzed. The DNA content of Zinnia angustifolia (cv. ‘Starbright’), Zinnia elegans (cv. ‘Short Stuff’, ‘Dreamland’, ‘Jupiter’, ‘Border Beauty’, ‘Jungle’, ‘Piccolo’, ‘Sinnita’), Zinnia haageana (cv. ‘Chippendale Daisy’, ‘Persian Carpet’) and the F₁ hybrid cv. ‘Profusion’ (Z. elegans x Z. angustifolia) has been analyzed by flow cytometry, and compared to morphological features (guard cell size, number of chloroplasts per guard cell, number of chromosomes). The three analyzed species Z. angustifolia, Z. haageana and Z. elegans could be clearly distinguished by their DNA content. The nuclear DNA content ranged from 1 pg (2C) in Z. angustifolia cv. ‘Starbright’ up to 5 pg in the tetraploid Z. elegans cv. ‘Jungle’. Genetic diversity among and between Zinnia varieties was accessed by RAPD, confirming a higher genetic identity in Z. elegans cv. ‘Dreamland’ when compared to Z. haageana cv. ‘Persian Carpet’.

Ru-Fang Tan, Jun Tao, Ling Li (China) Genetic Transformation of Ipomoea purpurea Mediated by Agrobacterium rhizogenes (pp 131-135)

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Original Research Paper: The transformation of Ipomoea purpurea mediated by Agrobacterium rhizogenes was studied. Almost all roots induced by four bacterial strains, R1000, A4, R1601 and R1025 were putative hairy roots. Hairy roots were formed on wounds in cotyledons or hypocotyls infected for 10-15 days by A. rhizogenes. The frequency of hairy root formation in hypocotyls infected by A4, R1025, R1000 and R1601 was 7.6%, 16.5%, 20.0 and 28.7%, respectively while that for cotyledons infected by R1000, R1601 and R1025 ranged between 30.5%, 44.6% and 19.80%, so that R1000 was the optimal bacterial strain to infect cotyledons. Almost all roots which could survive on selection medium (MS containing 500 mg L^-1 carbenicillin and 200 mg L^-1 kanamycin) were putative hairy roots. The effects of silver nitrate, infection time, aeration and light treatment on the transformation were also described in subsequent experiments used with R1000. The transformation frequency increased to 42.6% when the infection time was increased to 10 minutes as previously described, or to 34.61% when 2 mg L^-1 silver nitrate was used for selection of transformed I. purpurea plants. The experiments also showed that aerating cultures were better than airproof cultures, and that light was better than darkness. After selecting on 200 mg L^-1 kanamycin in solid medium, the results of PCR and Southern blot analysis of the rolB gene for the hairy roots indicated that the Ri plasmid had integrated into the genome of I. purpurea.

S. Mukundan, B.N. Sathyanarayana (India), Luke Simon (UK/India), Suresh N. Sondur (India) Comparative Analysis and Phylogenetic Relationships between Populations of Commercially Important Jasminum sp. by Using RAPD Markers (pp 136-141)

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Original Research Paper: In the present paper, genetic relationships of 32 varieties of jasmine belonging to four species, [Jasminum sambac (Linn.) Ait., J. grandiflorum Linn., J. auriculatum Vahl., and J. multiflorum (Burm.f.) Andr.] obtained from different locations in southern India are described on the basis of RAPD (Randomly Amplified Polymorphic DNA) markers. PCR-amplifiable DNA was isolated using the CTAB method and 169 amplified fragments were obtained using 8 random primers. The genetic dissimilarity matrix was calculated based on Squared Euclidian Distances, which revealed a maximum genetic distance of 56% between varieties, ‘Bale Japani’ and ‘Manamadhurai Mullai’, while the minimum genetic distance (8%) was between the varieties ‘Rameswaram Mallige’ and ‘Nilakottai Mallige’, belonging to the species (J. sambac). The Ward’s method of cluster analysis grouped all the individuals on the dendrogram into two major clusters ‘A’ and ‘B’ at 52 linkage distances. Cluster ‘A’ consisted of two varieties belonging to species J. multiflorum, clustered at 18 linkage distances. Cluster ‘B’ was segregated into two sub-clusters at 44 linkage distances with varieties of J. auriculatum in sub-cluster ‘B₁’, and varieties of J. sambac and J. grandiflorum in sub-cluster ‘B₂’ at 39 linkage distances. The present study showed low to moderate genetic diversity among the Jasminum sp. Thus RAPD has the potential for use in species identification and genetic relationships between taxa and species of jasmine for breeding programs.

Marian Saniewski (Poland), Hiroshi Okubo, Kensuke Miyamoto, Junichi Ueda (Japan) Susceptibility and/or Responsiveness of Tulip Stem Segments Excised from Cooled or Uncooled Bulbs to Indole-3-Acetic Acid (pp 142-146)

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Original Research Paper: The growth of stem segments excised from cooled and uncooled tulip (Tulipa gesneriana L. ‘Apeldoorn’) bulbs stored for three months after flower bud formation at 5°C and 17°C, respectively, was enhanced by indole-3-acetic acid (IAA) at 0.1% (w/w) in the light and in dark conditions, when it was applied to the place where flower buds were removed. On October 27, the enhanced growth of excised stem segments induced by IAA was very reduced under natural light conditions. On the other hand, the susceptibility and/or responsiveness of tulip stem segments excised from cooled or uncooled bulbs to exogenously applied IAA increased as the age or maturation of tulip bulbs increased until January 15 of the following year. The ability of tulip stem segments to elongate did not depend on low temperature and light conditions. A possible explanation for IAA-induced growth of tulip stem segments is discussed from the aspect of the solutes in the cell sap and on the balance of endogenous plant hormones in the bulbs.

Jinsong Zhou, Guohua Ma (China), Eric Bunn (Australia), Xinhua Zhang (China) In Vitro Shoot Organogenesis from Pelargonium × Citrosum Vanleenii Leaf and Petiole Explants (pp 147-149)

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Original Research Paper: Mosquito plant (Pelargonium × citrosum Vanleenii) is a genetically engineered hybrid possessing the characteristics of geranium coupled with a sweet lemony citronella scent. As such, this hybrid has become much more popular as an ornamental plant with the added benefit of mosquito-repelling capability. We report a novel protocol for shoot organogenesis from young leaf and petiole explants sourced from both pot grown and in vitro plants. Our study shows that 6-benzyladenine, thidiazuron and kinetin are effective in inducing adventitious shoot production, unlike 2-4-dichlorophenoxyacetic acid and α-naphthaleneacetic acid. This suggests that these cytokinins play a key role in inducing adventitious shoots from young P. × citrosum leaf and petiole explants. This study offers a novel and efficient mass shoot propagation and plant regeneration protocol for mosquito plant.

Ronald C. Snijder (The Netherlands), F. Santiago Brown (Ecuador), Jaap M. van Tuyl (The Netherlands) The Role of Plastome-Genome Incompatibility and Biparental Plastid Inheritance in Interspecific Hybridization in the Genus Zantedeschia (Araceae) (pp 150-157)

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Original Research Paper: In most genera combinations of plastomes and genomes function to form normal plants, irrespective of the taxonomical distances between the plastidial genome and the nuclear genome. In some genera plastomes and genomes have co-evolved to such a degree that they can only function within specific combinations. Our aim was to determine plastid inheritance and plastome-genome incompatibility (PGI) among species of Zantedeschia from the section Aestivae. To this end, plastomes and genomes of five taxa (Z. albomaculata subsp. albomaculata, Z. albomaculata subsp. macrocarpa, Z. elliotiana, Z. pentlandii and Z. rehmannii) were combined by interspecific hybridisation. Plastomes were differentiated using plastome specific CAPS-markers. Degrees of plastome-genome incompatibility existed between the hybrid genomes of Z. rehmannii and Z. albomaculata, Z. rehmannii and Z. elliotiana, Z. rehmannii and Z. pentlandii and the plastomes of Z. albomaculata, Z. elliotiana and Z. pentlandii, respectively. The plastome of Z. rehmannii appeared compatible to all tested hybrid genomes in section Aestivae. It was only fully incompatible with the hybrid genome with Z. aethiopica (section Zantedeschia). The plastomes of Z. albomaculata and Z. elliotiana appeared compatible to the hybrid genome of Z. albomaculata and Z. elliotiana. Four plastomes were differentiated among the section Aestivae. Biparental plastid inheritance (3 to 90%) was observed among all crossing combinations, which produced more than 1600 interspecific offspring. Biparental inheritance of plastids thus appeared to be a general phenomenon among interspecific hybrids within the section Aestivae. A literature review shows that biparental plastid inheritance is not uncommon in interspecific hybrids. The genus Zantedeschia shows an unusual wide range of degrees of biparental plastid inheritance that is only recorded in genera that also show plastome-genome incompatibility.