Exudation of an allelopathic substance lepidimoide from seeds during germination

Lepidimoide promotes growth of the cockscomb hypocotyl. It is exuded from germinating seeds of various plant species into their culture environment. The mode of exudation of lepidimoide from seeds into the culture solution, using sunflower and buckwheat seeds, was studied in relation to seed germination. In the dry seeds, about 75% of the lepidimoide was found in the seed coat and about 25% in the kernel. Upon water imbibition it was released into the culture solution. However, the quantity of lepidimoide detected in the seed exudate was more than three times the total amount in dry and imbibed seeds, suggesting that lepidimoide was also produced de novo in the seeds and subsequently released. When seed coats or kernels were imbibed separately, the quantity of lepidimoide released from the seed coats into the culture solution was much the same as that in the dry seeds, but the amount of lepidimoide detected in the exudate of kernels was about 16 times that in the dry kernels. These results suggest that lepidimoide, already present in dry seeds, as well as that newly produced in the kernels following imbibition, was released into the environment.     

一种刺激肉苁蓉种子萌发和吸器发育的方法

以3种肉苁蓉属（Cistanche）植物种子为材料,研究了氟啶酮对肉苁蓉种子萌发和吸器发育的影响。结果表明：氟啶酮处理10天后种子开始萌发,然后,胚根顶端膨大,发育出吸器。管花肉苁蓉种子萌发率最高,达到82％;盐生肉苁蓉吸器诱导率最高,达到52％;对照处理的种子不萌发。这说明氟啶酮是有效刺激肉苁蓉种子萌发和吸器发育的信号物质。     

一种刺激肉苁蓉种子萌发和吸器发育的方法

以3种肉苁蓉属(Cistanche)植物种子为材料, 研究了氟啶酮对肉苁蓉种子萌发和吸器发育的影响。结果表明: 氟啶酮处理10天后种子开始萌发, 然后, 胚根顶端膨大, 发育出吸器。管花肉苁蓉种子萌发率最高, 达到82%; 盐生肉苁蓉吸器诱导率最高, 达到52%; 对照处理的种子不萌发。这说明氟啶酮是有效刺激肉苁蓉种子萌发和吸器发育的信号物质。     

死、活地被物对红松伴生树种天然更新影响的实验研究

1963年在小兴安岭丰林自然保护区红松林及有关的皆伐迹地上设置了61组,325个实验样方,定期观察到1965年,以研究死、活地被物对人工播种的红松林伴生树种种子发芽和幼苗初期存活、生长的影响。实验表明死、活地被物,特别是死地被物的干湿变化剧烈,影响幼苗的成活,甚至使种子或幼根无法接触土壤,因而种粒越小,或轻而带翅,受影响越大。此外本文还指出了桦树种子的强迫休眠和延迟发芽现象。讨论了实验结果在红松林演替和人工促进天然更新中的意义。     

Expression and inhibition of aquaporins in germinating Arabidopsis seeds

Extensive and kinetically well-defined water exchanges occur during germination of seeds. A putative role for aquaporins in this process was investigated in Arabidopsis. Macro-arrays carrying aquaporin gene-specific tags and antibodies raised against aquaporin subclasses revealed two distinct aquaporin expression programs between dry seeds and young seedlings. High expression levels of a restricted number of tonoplast intrinsic protein (TIP) isoforms (TIP3;1 and/or TIP3;2, and TIP5;1) together with a low expression of all 13 plasma membrane aquaporin (PIP) isoforms was observed in dry and germinating materials. In contrast, prevalent expression of aquaporins of the TIP1, TIP2 and PIP subgroups was induced during seedling establishment. Mercury (5 microM HgCl(2)), a general blocker of aquaporins in various organisms, reduced the speed of seed germination and induced a true delay in maternal seed coat (testa) rupture and radicle emergence, by 8-9 and 25-30 h, respectively. Most importantly, mercury did not alter seed lot homogeneity nor the seed germination developmental sequence, and its effects were largely reversed by addition of 2 mM dithiothreitol, suggesting that these effects were primarily due to oxidation of cell components, possibly aquaporins, without irreversible alteration of cell integrity. Measurements of water uptake in control and mercury-treated seeds suggested that aquaporin functions are not involved in early seed imbibition (phase I) but would rather be associated with a delayed initiation of phase III, i.e. water uptake accompanying expansion and growth of the embryo. A possible role for aquaporins in germinating seeds and more generally in plant tissue growth is discussed.     

A molecular framework for the embryo growth in germinating seeds of Solanum lycocarpum A. St.‐Hil., a nurse plant species

We are clarifying how the functional embryo growth occurs in germinating seeds of Solanum lycocarpum A. St.‐Hil., a nurse plant with a central role in forest dynamics in the Cerrado (a biodiversity hotspot). For that, we used classical seed germination measurements (germinability, mean germination time, mean germination rate, coefficient of variation of the germination time, synchronisation index and germination time range) and gene expression of mRNA codifying key proteins/enzymes for the success in the seed–seedling transition (Cyclin, Actin, Small Heat Shock Protein, Glutathione S‐transferase, Malate Dehydrogenase, Alcohol Dehydrogenase). Our findings demonstrate: (a) Although germination kinetics in S. lycocarpum seeds is slower than that in tomato seeds, the fold change of genes codifying key enzymes for the embryo development is similar in germinating seeds of both species. (b) The genes used here are useful, from a technical point of view, for classifying commercial seed samples of the species in relation to physiological quality. More notably, cyclin and malate dehydrogenase genes have a greater expression, both in germination sensu stricto and in immediate post‐germination. (c) A molecular framework for the embryo growth in germinating seeds of S. lycocarpum can be a functional explication for the species to be a nurse plant. Thus, the overlapping of classical and contemporary measurements is especially interesting to those species playing a central role in the environment, such as nurse plants, and may represent a new conservationist paradigm.     

Effects of the pericarp on imbibition,seed germination,and seedling establishment in seeds of <Emphasis Type="Italic">Hedysarum scoparium</Emphasis> Fisch. et Mey

Four independent experiments were designed to investigate the effects of the pericarp on seed imbibition, dehydration, germination, seedling establishment, and seed longevity in the field in seeds of Hedysarum scoparium Fisch. et Mey. The results showed that the presence of the pericarp decreased seed imbibition rates in the first 6 h, but the seeds attained significantly higher final water content after 24 h of soaking. The pericarp caused seed dormancy, and removal of the pericarp improved the germination percentage to 90 from 44%. In the pot experiment, where the level of moisture was maintained at field capacity (control), seeds with the pericarp removed had significantly improved seedling establishment. However, no statistical differences were observed in seedling establishment when the experiment was repeated under dry conditions at 40% of the field water capacity. The seedling biomass derived from seeds without the pericarp was much higher in the control but the trend was reversed under dry conditions. For seed longevity, 2 months burial in the field killed almost all seeds without the pericarp, while more than 70% of the seeds with the pericarp intact remained viable. These results indicated that the pericarp was beneficial for seedling establishment and seed longevity in arid environments. The results of this study may have practical application in grassland restoration in dry areas, especially for aerial seeding, which has been extensively used in the northern part of China.     

Phytotoxic effects of fumonisin B1 on maize seedling growth

Fumonisin B₁ toxin is produced by the fungusFusarium moniliforme Sheldon, which is systemic to maize (Zea mays L.) and maize seeds. The effects of zero to 100 parts per million fumonisin B₁ on the germination process of maize seeds was determined. The presence of fumonisin had no effect on percent seed germination, but fumonisin inhibited radicle elongation by up to 75% after 48 hours of imbibition. An analysis of amylase secretion in the maize endosperm indicated that fumonisins inhibited amylase production in the germinating seed. Isoelectric focusing of endosperm extracts indicated that secretion of the low pI class of amylases was affected more that other amylase isozymes. The results suggested that the presence of high levels of fumonisin in maize seed may have deleterious effects on seedling emergence.     

Seed demography of three co-occurring Acer species in a Japanese temperate deciduous forest

Abstract. Seed demography of three co-occurring Acer species in an old-growth mixed deciduous forest in Japan was studied. Almost all of the seeds of A. mono germinated in the first spring, while those of A. palmatum var. amoenum showed a delay in germination of almost one year. A. rufinerve showed a rather opportunistic germination habit. Both A. palmatum var. amoenum and A. rufinerve form short-term persistent seed banks, but without input of newly dispersed seeds they may become extinct in about one year. The seed bank for these two species is not as significant as for a typical pioneer species, and the seedling bank is important for all three species. Only a small proportion of the dispersed propagules contained viable embryos, mainly due to pollination failure or abortion (A. mono and A. palmatum var. amoenum), and invertebrate predation (A. rufinerve). For all three species, larger seed crops had a higher percentage of viable seeds. Even for these relatively small, wind-dispersed seeds, the predation pressure was very high. A large part of the dispersed seeds was eaten by wood mice during the first winter (30–80 %). Estimation from the 5-yr average of seed dispersal and seedling emergence showed that only 7–16 % of the dispersed viable seeds succeeded in germinating.     

Amino Acids Content in Germinating Seeds and Seedlings from Castanea sativa L

During germination the chestnut (Castanea sativa L.) var ecotype 33 accumulates a large amount of asparagine in the cotyledons. This compound also accumulates in the growing axis:shoots and roots. In the cotyledons, γ-aminobutyrate (GABA) represents a major amino compound during germination and early seedling growth. In young seedlings, 35 days old, arginine predominates over the other soluble amino acids, particularly in roots. Five enzymic activities involved in arginine and GABA have been measured in the storage organ of the seed: arginase and ornithine carbamyltransferase decrease during germination indicating the slowing down of the urea cycle. In contrast, ornithine aminotransferase increases. Glutamate decarboxylase is particularly active about 21 days after imbibition and GABA aminotransferase activity decreases during germination. These two activities are in good agreement with the likely transport of GABA from cotyledons to growing axis. Asparagine, arginine, and GABA are the three amino compounds obviously involved in the mobilization of nitrogen reserves in the germinating chestnut seeds Castanea sativa.     

Expression of a GALACTINOL SYNTHASE gene in tomato seeds is up-regulated before maturation desiccation and again after imbibition whenever radicle protrusion is prevented

Raffinose family oligosaccharides (RFOs) have been implicated in mitigating the effects of environmental stresses on plants. In seeds, proposed roles for RFOs include protecting cellular integrity during desiccation and/or imbibition, extending longevity in the dehydrated state, and providing substrates for energy generation during germination. A gene encoding galactinol synthase (GOLS), the first committed enzyme in the biosynthesis of RFOs, was cloned from tomato (Lycopersicon esculentum Mill. cv Moneymaker) seeds, and its expression was characterized in tomato seeds and seedlings. GOLS (LeGOLS-1) mRNA accumulated in developing tomato seeds concomitant with maximum dry weight deposition and the acquisition of desiccation tolerance. LeGOLS-1 mRNA was present in mature, desiccated seeds but declined within 8 h of imbibition in wild-type seeds. However, LeGOLS-1 mRNA accumulated again in imbibed seeds prevented from completing germination by dormancy or water deficit. Gibberellin-deficient (gib-1) seeds maintained LeGOLS-1 mRNA amounts after imbibition unless supplied with gibberellin, whereas abscisic acid (ABA) did not prevent the loss of LeGOLS-1 mRNA from wild-type seeds. The presence of LeGOLS-1 mRNA in ABA-deficient (sitiens) tomato seeds indicated that wild-type amounts of ABA are not necessary for its accumulation during seed development. In all cases, LeGOLS-1 mRNA was most prevalent in the radicle tip. LeGOLS-1 mRNA accumulation was induced by dehydration but not by cold in germinating seeds, whereas both stresses induced LeGOLS-1 mRNA accumulation in seedling leaves. The physiological implications of LeGOLS-1 expression patterns in seeds and leaves are discussed in light of the hypothesized role of RFOs in plant stress tolerance.     

Viability of onion (Allium cega) seed as influenced by temperature during seed growth

The yield and performance of seeds from crops of winter-hardy, bolting-resistant onion grown at temperatures of 15–16, 18–19 and 22–23°C in 1979, 1980 and 1982 were compared. Yields of seed from crops grown at 22–23°C were lower than those from crops grown at lower temperatures but the seeds ripened between 11 and 32 days earlier. Seeds from crops grown at mean temperatures of above 18°C gave higher percentage germination when imbibed at 30°C than 20°C and they also gave higher percentage seedling emergence than those from crops grown at lower temperatures. Seedlings from seeds produced at mean temperatures above 18°C were heavier than those from seeds of a similar weight but produced at lower temperatures. None of these differences were associated with differences in seed weight, embryo weight or seed dormancy but were positively correlated with differences in seed N-concentration. The differences were also associated with the rate of imbibition of water as high germination, high N-content seeds had a slower rate of imbibition than low germination, low N-content seeds of the same weight.     

Protein mobilization in germinating mung bean seeds involves vacuolar sorting receptors and multivesicular bodies

Plants accumulate and store proteins in protein storage vacuoles (PSVs) during seed development and maturation. Upon seed germination, these storage proteins are mobilized to provide nutrients for seedling growth. However, little is known about the molecular mechanisms of protein degradation during seed germination. Here we test the hypothesis that vacuolar sorting receptor (VSR) proteins play a role in mediating protein degradation in germinating seeds. We demonstrate that both VSR proteins and hydrolytic enzymes are synthesized de novo during mung bean (Vigna radiata) seed germination. Immunogold electron microscopy with VSR antibodies demonstrate that VSRs mainly locate to the peripheral membrane of multivesicular bodies (MVBs), presumably as recycling receptors in day 1 germinating seeds, but become internalized to the MVB lumen, presumably for degradation at day 3 germination. Chemical cross-linking and immunoprecipitation with VSR antibodies have identified the cysteine protease aleurain as a specific VSR-interacting protein in germinating seeds. Further confocal immunofluorescence and immunogold electron microscopy studies demonstrate that VSR and aleurain colocalize to MVBs as well as PSVs in germinating seeds. Thus, MVBs in germinating seeds exercise dual functions: as a storage compartment for proteases that are physically separated from PSVs in the mature seed and as an intermediate compartment for VSR-mediated delivery of proteases from the Golgi apparatus to the PSV for protein degradation during seed germination.     

Protein Synthesis During Rehydration, Germination and Seedling Growth of Naturally and Precociously Matured Soybean Seeds (Glycine max)

Soybean seeds [Glycine max (L.) Merr.] synthesize de novo andaccumulate several non-storage, soluble polypeptides duringnatural and precocious seed maturation. These polypeptides havepreviously been coined ‘maturation polypeptides’.The objective of this study was to determine the fate of maturationpolypeptides in naturally and precociously matured soybean seedsduring rehydration, germination, and seedling growth. Developingsoybean seeds harvested 35 d after flowering (mid-development)were precociously matured through controlled dehydration, whereasnaturally matured soybean seeds were harvested directly fromthe plant. Seeds were rehydrated with water for various timesbetween 5 and 120 h. Total soluble proteins and proteins radio-labelledin vivo were extracted from the cotyledons and embryonic axesof precociously and naturally matured and rehydrated seed tissuesand analyzed by one-dimensional PAGE and fluorography. The resultsindicated that three of the maturation polypeptides (21, 31and 128 kDa) that had accumulated in the maturing seeds (maturationpolypeptides) continued to be synthesized during early stagesof seed rehydration and germination (5–30 h after imbibition).However, the progression from seed germination into seedlinggrowth (between 30 and 72 h after imbibition) was marked bythe cessation of synthesis of the maturation polypeptides followedby the hydrolysis of storage polypeptides that had been synthesizedand accumulated during seed development. This implied a drasticredirection in seed metabolism for the precociously maturedseeds as these seeds, if not matured early, would have continuedto synthesize storage protein reserves. Glycine max (L.) Merr, soybean, cotyledons, maturation, germination/seedling growth     

Diversity of epicotyl dormancy among tropical montane forest species in Sri Lanka

• Fruiting season of many Sri Lankan tropical montane species is not synchronised and may not occur when conditions are favourable for seedling establishment. We hypothesised that species with different fruiting seasons have different seed dormancy mechanisms to synchronise timing of germination with a favourable season for establishment. Using six species with different fruiting seasons, we tested this hypothesis.
• Germination and imbibition of intact and manually scarified seeds were studied. Effect of GA₃ on germination was examined. Embryo length:seed length (E:S) ratio of freshly matured seeds and of those with a split seed coat was determined. Time taken for radicle and plumule emergence and morphological changes of the embryos were recorded.
• The radicle emerged from Ardisia missionis, Bheza nitidissima and Gaetnera walkeri seeds within 30 days, whereas it took >30 days in other species. Embryos grew in seeds of B. nitidissima and G. walkeri prior to radicle emergence but not in Microtropis wallichiana, Nothapodytes nimmoniana and Symplocos cochinchinensis. A considerable delay was observed between radicle and plumule emergence in all six species. Warm stratification and/or GA₃ promoted germination of all species.
• All the tested species have epicotyl dormancy. Seeds of B. nitidissima and G. walkeri have non‐deep simple morphophysiological epicotyl dormancy, and the other four species have non‐deep physiological epicotyl dormancy. Differences in radicle and epicotyl dormancy promote synchronisation of germination to a favourable time for seedling development. Therefore, information on dormancy‐breaking and germination requirements of both radicle and epicotyl are needed to determine the kind of dormancy of a particular species.

     

华南青刚坚果的萌发和育苗

华南青刚（壳斗科）Ｃｙｃｌｏｂａｌａｎｏｐｓｉｓ ｅｄｉｔｈａｅ（Ｓｋａｎ）Ｓｃｈｏｔｔ的坚果，分别以３种不同的位置（平放、柱座向上及桩座向下）埋进泥土，测试不同位置对种发芽率及幼苗成长的影响。结果显示坚果平放的发芽率最高，幼苗生长亦最快。还就实验结果对苗圃期发育苗的技术作出了讨论。     

The prevention of dehydration injury in celery seeds by polyethylene glycol, abscisic acid, dark and high temperature

Celery seeds ( Apium graveolens L.) given a germination induction period (3 days imbibition at 17°C in the light) could be prevented from germinating by up to 14 days subsequent exposure to high temperature (32°C), polyethylene glycol (PEG), abscisic acid (ABA) or dark (22°C). When the seeds were returned to 17°C in the light, germination occurred and, except for the high temperature treatment, was more rapid compared to seeds given a germination induction period only.
Celery seeds incubated for 3 days at 17°C in the light and then air-dried at 20°C germinated slowly when re-sown at 17°C in the light, and achieved only 19% germination after 21 days. Exposing the seeds to high temperature, PEG, ABA or dark for up to 14 days before drying maintained seed viability and subsequent germination was faster. The longer treatment periods gave increased benefit, and PEG was the most effective treatment. It is suggested that the effectiveness of the treatments in inducing dehydration tolerance relates to their ability to inhibit germination possibly via their prevention of cell expansion.     

Magnetopriming circumvents the effect of salinity stress on germination in chickpea seeds

Chickpea seeds of Pusa 1053 (Mediterranean) and Pusa 256 (native) were magnetoprimed with 100 mT static magnetic field for 1 h to evaluate the effect of magnetopriming on germination of seeds under saline conditions. Enhanced rate of germination and seedling growth parameters (root and shoot length, and vigour indices) under different salinity levels indicated that magnetopriming was more effective in alleviating salinity stress at early seedling stage in Pusa 1053 as compared to Pusa 256. Dynamics of seed water absorption in magnetoprimed seeds showed increased water uptake in Pusa 1053 under non-saline as compared to saline conditions. This could have resulted in faster hydration of enzymes in primed seeds leading to higher rate of germination. Total amylase, protease and dehydrogenase activities were higher in primed seeds as compared to unprimed seeds under both non-saline and saline conditions. Production of superoxide radicals was enhanced in germinating seeds of both the genotypes under salinity irrespective of priming. Increased levels of hydrogen peroxide in germinating magnetoprimed seeds, under both the growing conditions, suggested its role in promotion of germination. Our results showed that magnetopriming of dry seeds of chickpea can be effectively used as a pre-sowing treatment for mitigating adverse effects of salinity at seed germination and early seedling growth.