Volume 1 Numbers 1 & 2 2007

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CONTENTS AND ABSTRACTS

Number 1

Haim Nerson (Israel) Seed Production and Germinability of Cucurbit Crops (pp 1-10)

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Invited Mini-Review: Cucurbit crops are mostly produced for their immature or mature fruits. However, a relatively high proportion of cucurbit fields are destined for seed production, either for seed consumption or for propagation material. Production of cucurbits for seed consumption (as a snack food) is very popular in some parts of the globe and almost unknown in others. Open-pollinated cultivars (inexpensive seeds) are used in almost all crops for seed consumption. In the last decades the proportion of hybrids has dramatically increased because of the advantages of heterosis, improved technology and utilization of controlled environments. Cucurbit crops are insect-pollinated, and the introduction of honey-bee colonies into cucurbit seed production fields is an essential step for success. However, isolation is required to prevent outcrossing, both for open-pollinated cultivars and hybrid cucurbit seeds. Understanding the role of phytohormones and growth regulators in sex expression of cucurbits has greatly facilitated hybrid seed production. The germination ability of cucurbit seeds is related both to external and internal factors. Variability in germination ability of any seed population harvested at a particular site during a given season is based on inter- and within-plant variations. The failure of cucurbit seeds to germinate may at times have no relation to seed quality but may also be due to the lack of specific requirements. This is probably the case in conditional dormancy which is typical for some cucurbits. Appropriate temperature is probably the most important factor, but gas exchange, water potential and hormones are also involved in regulating germination. Seed quality can be affected by the maternal environment, seed maturity at harvest, extraction procedure, and storage conditions. Priming treatments can improve germination, especially when applied to poor quality seeds, or under stressful environments.

Xiaonan Yu, Rong Zhao, Fangyun Cheng (China) Seed Germination of Tree and Herbaceous Peonies: A Mini-Review (pp 11-14)

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Invited Mini-Review: Tree and herbaceous peonies are beautiful and vigorously-growing plants commonly employed in the ornamental industry in China and around the world. Germinating peony seeds is a pre-requisite for peony breeding. Much attention has recently been attracted by researchers to the seed germination of peonies for most of them have the habit of double dormancy in hypocotyls and epicotyls. This paper provides a short review of this field. The review covers several themes :1) the effect of seed collecting time on germination; 2) the effect of different storage conditions on seed germination; 3) physical and chemical pretreatments on seed germination; 4) changes in metabolite content during seed germination; 5) embryo culture of peony seed.

Number 2

Emilio Cervantes, Juana G. de Diego (Spain) Seeds and Stress: Integration of Endogenous and Environmental Signals in Multiple Adaptive Response Pathways (pp 15-17)

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Research Note: The term “stress” is widely used in relationship with plants, but there is no evidence at all of plants suffering any stress. The application of the term to the plant sciences is metaphorical, but nevertheless it helps to reveal new aspects of plant physiology, especially concerning environmental adaptation and responses during seed germination. New DNA sequences, not previously reported for Arabidopsis, or in plants, and even not similar to any sequences reported in databases, were identified as being expressed during germination of the model plant Arabidopsis thaliana, suggesting that complex genome dynamics operate in this process. The mRNA encoding prohibitin was identified as up-regulated during germination. It contains features suggesting that it may be involved in translational control. Seeds are fascinating systems to study genome dynamics and translational control.

Raquel Iglesias-Fernández, Angel J. Matilla, Iñigo Pulgar, Francisco de la Torre (Spain) Ripe Fruits of Sisymbrium officinale L. Contain Heterogeneous Endospermic Seeds with Different Germination Rates (pp 18-24)

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Original Research Paper: The seeds of Sisymbrium officinale are largely heterogeneous in mass and colour within the ripe fruit. In order to initiate the characterization of the germinative process from these heterogeneous seeds, we have used two different seed lots (i.e. brown and light-brown), and studied several physical and physiological properties and their possible influence on the germination rate. The most notable features from this work were: (i) the mass of the brown seeds was higher than the light-brown ones, which imbibed more quickly; (ii) light seeds contain much less mucilage (myxospermy) than do the brown; (iii) under optimal germination conditions for the brown seeds, the light-brown ones germinated 6-fold less; and (iv) very similar profiles of germination stimulation was found in the presence of gibberellins (i.e. GA ₄₊₇) and ET in brown seeds, but both hormones were not capable of stimulating the germination in light-brown ones. As a general conclusion, we have demonstrated the coexistence in ripe fruits of S. officinale of two seed lots with remarkable physiological and physical heterogeneity that could be used as a tool to increase our knowledge about the germination process.

Eugeniya F. Markovskaya, Elena G. Sherudilo, Marina I. Sysoeva (Russia) Cucumber Seed Germination: Effect and After-effect of Temperature Treatments (pp 25-31)

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Invited Mini-Review: In this review an attempt has been made to analyze the results of the studies on the problem of cucumber seed germination under different temperature treatments published since the 1950s, including papers that have been available in Russian only. The effects of daily alternating temperatures on cucumber seed germination have been studied for decades. There are different types of temperature pre-germination seed treatments, i.e. by constant low temperature and daily alternating temperatures (daily temperature gradients and temperature drop). This review shows that temperature treatments affect cucumber seed germination and have long after-effects on subsequent plant growth and development. Temperature pre-germination treatments of cucumber seeds can enhance plant development, increase plant productivity and resistance. The level of plant response depends on the type of treatment.

K. Padmalatha, M.N.V. Prasad (India) Seed Germination Studies in Pterocarpus santalinus L.f. - an Endangered and Endemic Medicinal Plant, and Relevance to Conservation (pp 32-34)

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Short Communication: Pterocarpus santalinus L.f (Fabaceae), an endangered tree, is commercially and medicinally the most valuable endemic to the Deccan ecoregion of India. It is a highly recalcitrant leguminous species and the seeds show a dormancy period of approximately one year. Studies on seed germination from various locations were carried out with the aim of producing appropriate germination protocols for use in ex situ conservation. In field conditions 60% germination was observed from seeds collected from Balpally. In vitro studies revealed 100% germination with 3% sucrose solution i.e., in water and in different combinations of Murashige and Skoog (MS) medium, which is highly cost effective. Among all the locations of collection, seeds from Balpally and Papireddypally showed the highest percentage of seed germination.

Queila Souza Garcia, Patrícia Gonçalves Oliveira (Brazil) Germination Patterns and Seed Longevity of Monocotyledons from the Brazilian Campos Rupestres (pp 35-41)

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Invited Mini-Review: The Brazilian campos rupestres vegetation is associated with the Espinha?o Mountain chain, a region recently declared a Biosphere Reserve by UNESCO, in recognition of its high diversity and large numbers of endemic species. The campos rupestres vegetation typically occupies exposed rocky areas, sandy plains, and swamps, at above 900 meters, and is generally composed of a mix of herbaceous plants and sparse shrubs and subshrubs. The proposal of this study was to present a revision of the biometry, germination behavior, and longevity of the seeds of four families of monocotyledons occurring in the campos rupestres. The family Bromeliaceae is widely distributed in Brazil, while Eriocaulaceae, Xyridaceae, and Velloziaceae are quite abundant in the campos rupestres of the Espinhaço Mountains. The seeds of all the species analyzed were small, with average lengths of 0.6-2.6 mm and average dry weights of 0.0019-0.49 mg. The seeds of the Bromeliaceae are generally aphotoblastic, while those of Eriocaulaceae, Xyridaceae, and Velloziaceae are positive photoblastic. In general, the seeds demonstrate high germination rates over a wide range of temperatures (most will germinate between 15-35°C). The analysis of seed longevity in the soil indicated that, except for the Bromeliaceae, all of the species examined maintained their viability in the soil for more than a year and thus had the potential to form persistent soil seed banks. The persistence of these seeds in the soil is related to their small size and to light requirements for germination - characteristics that contribute to successful recruitment in open environments like the campos rupestres, with high solar radiation levels and wide temperature fluctuations.

Dang-Quan Zhang, Xiao-Feng Tan, Hong-Peng Chen (China) Characteristics and Molecular Genetics of Lipid Biosynthesis in Tea-oil Tree Seed (pp 42-47)

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Invited Mini-Review: Tea-oil tree (Camellia oleifera), whose seed has an oil-yield rate of about 55%, is an edible oil tree growing specifically in China. Recent research has suggested that the oiliness of tea-oil is far better than that of palm, rape, bean and peanut oil, and could even exceed that of olive oil. More than 90% of tea-oil consists of unsaturated fatty acids including 82% oleic acid, and 8.6% of both linoleic acid and linolenic acid. They are very healthy for humans. Moreover, tea-oil is abundant in vitamins A and E, and lacks the unhealthy compounds sinapic acid and falvacin. Tea-oil exists in the form of oil bodies in seed, and the oleosins and their number determine the quantity and characteristics of the oil product. The biosynthesis process of tea-oil is very complicated and involved many proteins and enzymes. The dynamic of synthesis and the concentration of malonyl coenzyme A decide how soon the saturated fatty acids are made in C. oleifera seed. The key enzymes in the monounsaturated fatty acid formation pathway are stearoyl-ACP desaturase (SAD), which controls the quantity of unsaturated fatty acids, while the fatty acid desaturases (FADs) are important for the synthesis of polyunsaturated fatty acids in C. oleifera seeds. ESTs of many genes relative to the biosynthesis of fatty acids in C. oleifera seed have been identified. However, the acquirement of the complete genetic information of all genes in the fatty acid pathway is essential for gene functional studies with approaches such as prokaryotic overexpression, transgenic plants or RNA interference (RNAi). These will eventually lead to an understanding of the molecular genetics of lipid biosynthesis in C. oleifera.

Cüneyt Çirak, Ali Kemal Ayan, Mehmet Serhat Odabas, Ömer Çaliskan (Turkey) Nature of Seed Dormancy in Stinging Nettle (Urtica dioica L.) (pp 48-50)

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Short Communication: The present study was conducted to determine the germination requirements of stinging nettle seeds. For this purpose, before placing the seeds in Petri dishes, they were soaked for 30 min in 50, 100 and 150 mg/L GA solution, 40, 50 and 60°C hot water, or 0.5, 1 and 1.5 % H₂SO₄ solutions. To evaluate the effect of light on germination, the study was performed in growth chambers under both continuous illumination [1200 lux (14.4 µmol/m²/s) white light] and darkness. Light was found to be the most effective factor in promoting germination. Untreated control seeds under light produced the highest germination rate observed in the present study (83.33%) followed by light-mediated 30 and 40°C hot water treatments (44 and 38%, respectively). In contrast, all other treatments significantly deteriorated germination and this negative effect was more pronounced in H₂SO₄ treatments. The results indicated that European nettle seeds may have endogenous dormancy concerning their light requirement for germination.