Accumulation of Storage Materials,Precocious Germination and Development of Desiccation Tolerance During Seed Maturation in Mustard (Sinapis alba L.)

Under defined environmental conditions (20°C, continuous light of 15 klx) development of mustard seeds from artificial pollination to maturity takes about 60 d. After surpassing the period of embryo cell division and histodifferentiation (12–14d after pollination = dap), the seed enters into a maturation period. The time courses of various physiological, biochemical, and structural changes of embryo and testa during seed maturation were analyzed in detail (dry and fresh mass changes, osmotic and water potential changes, respiration, DNA amplification by endomitosis, total ribosome and polysome formation, storage protein synthesis and accumulation, storage lipid accumulation). In addition to the final storage products protein and lipid, embryo and testa accumulate transiently large amounts of starch within the chloroplasts during early maturation. Concomitantly with the subsequent total breakdown of the starch, the plastids lose most of their internal structure and chlorophyll and shrink into proplastids, typical for the mature seed. At about 30 dap the seeds shift from a desiccation-sensitive to a desiccation-tolerant state and are able then to germinate rapidly upon drying and reimbibition. If isolated from the immature fruit and sown directly on water, the seeds demonstrate precocious germination from about 13 dap onwards. Young seeds (isolated ≦ 38 dap) germinate only after surpassing a lag-phase of several days (after-ripening) during which the embryo continues to accumulate storage protein and lipid at the expense of the surrounding seed tissues. We conclude from these results that the maturing seed represents a rather closed developmental system which is able to continue its development up to successful germination without any specific regulatory influence from the mother plant. Immature seeds are able to germinate without a preceding dehydration treatment, which means that partial or full desiccation does not serve as an environmental signal for reprogramming seed development from maturation to germination. Instead, it is argued that the water relations of the seed are a critical element in the control of maturation and germination: during maturation on the mother plant the embryo is subject to a considerable turgor pressure (of the order of 12 bar) accompanied by a low water potential (of the order of ?12 bar). This turgor permits maturation growth but is subcritical for germination growth. However, upon imbibition in water, the low water potential provides a driving force for a burst of water uptake overcoming the critical turgor threshold and thereby inducing germination.     

Conservation between higher plants and the moss <Emphasis Type="Italic">Physcomitrella patens</Emphasis>in response to the phytohormone abscisic acid: a proteomics analysis

Background  

The plant hormone abscisic acid (ABA) is ubiquitous among land plants where it plays an important role in plant growth and development. In seeds, ABA induces embryogenesis and seed maturation as well as seed dormancy and germination. In vegetative tissues, ABA is a necessary mediator in the triggering of many of the physiological and molecular adaptive responses of the plant to adverse environmental conditions, such as desiccation, salt and cold.     

Proteomic analysis of rice (Oryza sativa) seeds during germination

Although seed germination is a major subject in plant physiological research, there is still a long way to go to elucidate the mechanism of seed germination. Recently, functional genomic strategies have been applied to study the germination of plant seeds. Here, we conducted a proteomic analysis of seed germination in rice (Oryza sativa indica cv. 9311) - a model monocot. Comparison of 2-DE maps showed that there were 148 proteins displayed differently in the germination process of rice seeds. Among the changed proteins, 63 were down-regulated, 69 were up-regulated (including 20 induced proteins). The down-regulated proteins were mainly storage proteins, such as globulin and glutelin, and proteins associated with seed maturation, such as "early embryogenesis protein" and "late embryogenesis abundant protein", and proteins related to desiccation, such as "abscisic acid-induced protein" and "cold-regulated protein". The degradation of storage proteins mainly happened at the late stage of germination phase II (48 h imbibition), while that of seed maturation and desiccation associated proteins occurred at the early stage of phase II (24 h imbibition). In addition to alpha-amylase, the up-regulated proteins were mainly those involved in glycolysis such as UDP-glucose dehydrogenase, fructokinase, phosphoglucomutase, and pyruvate decarboxylase. The results reflected the possible biochemical and physiological processes of germination of rice seeds.     

Change of thiamin-binding protein and thiamin levels during seed maturation and germination in sesame

Thiamin-binding proteins (TBPs) occur in many types of plant seeds. The biochemical and structural properties such as subunit structure and affinity for thiamin of the proteins have been characterized. However, the change of TBP and thiamin during seed maturation and germination is little known. Sesame (Sesamum indicum L.) seeds have unique albumin TBPs, because the other TBPs from plant seeds are generally globulins. In this study, we studied the change of the TBP and thiamin levels in sesame seeds. The protein content and thiamin-binding activity of the seeds increased with seed development after flowering. Immunological analysis using an antibody against the TBP of sesame seeds showed that the protein was accumulated in seeds during maturation. The thiamin content of the seeds increased with seed development after flowering. On the other hand, the thiamin-binding activity decreased during seed germination when TBP was degraded. The thiamin content of the seeds decreased during the germination. However, the amount of thiamin phosphate in the seeds during germination was little changed. These results suggested that thiamin was accumulated and stored as a complex with TBP in sesame seeds.     

Hormonal and temperature regulation of seed dormancy and germination in <Emphasis Type="Italic">Leymus chinensis</Emphasis>

Fluctuating temperature plays a critical role in determining the timing of seed germination in many plant species. However, the physiological and biochemical mechanisms underlying such a response have been paid little attention. The present study investigated the effect of plant growth regulators and cold stratification in regulating Leymus chinensis seed germination and dormancy response to temperature. Results showed that seed germination was less than 2 % at all constant temperatures while fluctuating temperature significantly increased germination percentage. The highest germination was 71 % at 20/30 °C. Removal of the embryo enclosing material of L. chinensis seed germinated to 74 %, and replaced the requirement for fluctuating temperature to germinate, by increasing embryo growth potential. Applications of GA₄₊₇ significantly increased seed germination at constant temperature. Also, inhibition of GA biosynthesis significantly decreased seed germination at fluctuating temperatures depending upon paclobutrazol concentration. This implied GA was necessary for non-dormant seed germination and played an important role in regulating seed germination response to temperature. Inhibition of ABA biosynthesis during imbibition completely released seed dormancy at 20/30 °C, but showed no effect on seed germination at constant temperature, suggesting ABA biosynthesis was important for seed dormancy maintenance but may not involve in seed germination response to temperature. Cold stratification with water or GA₃ induced seed into secondary dormancy, but this effect was reversed by exogenous FL, suggesting ABA biosynthesis during cold stratification was involved in secondary dormancy. Also, cold stratification with FL entirely replaced the requirement of fluctuating temperature for germination with seeds having 73 % germination at constant temperature. This appears to be attributed to inhibition of ABA biosynthesis and an increase of GA biosynthesis during cold stratification, leading to an increased embryo growth potential. We suggest that fluctuating temperature promotes seed germination by increasing embryo growth potential, mainly attributed to GA biosynthesis during imbibitions. ABA is important for seed dormancy maintenance and induction but showed less effect on non-dormant seed germination response to temperature.     

Does seed ingestion by bats enhance germination? A new meta‐analysis 15 years later

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野生鸭儿芹种子休眠特性及破除方法

鸭儿芹种子具有休眠特性,且休眠期长,不经任何处理的种子很难萌发,影响其人工种植。研究了鸭儿芹种子的休眠特性和解除休眠的最佳方法,为我国人工种植野生鸭儿芹提供理论依据。结果表明:TTC法对种子活力的测定表明有活力的种子为(55.33±3.71)%;切破种皮种子与完整种子吸水率在前12 h相差较大,但最终吸水率相差不大,分别达到(70.00±1)%和(68.32±0.32)%,表明种皮并不阻碍种子吸水;种子中存在内源抑制物,其粗提液在较低浓度下即可抑制芹菜种子的萌发;鸭儿芹种子成熟时胚未分化完全,胚率为(28.65±2.488)%,经过低温处理后完成后熟,胚率达到(65.93±3.86)%,萌发率达到100%,因此鸭儿芹种子具有形态生理休眠特性。清水浸种和低温冷藏共同处理可有效解除其休眠,浸种和低温冷藏具有交互效应,浸种36 h、5℃冷藏30d即可解除其休眠,萌发率达到100%,发芽势达到(91.11±0.91)%。已破除休眠的种子适宜其萌发的温度范围扩大(15.0—27.5℃),而且在土壤中也可较好地萌发,萌发率达到(96.67±3.33)%,发芽势达到(71.11±1.93)%。     

ABA调控种子发育的研究进展

种子发育是一个复杂的生物学过程，受各种遗传和外界因素的调节，显著影响农作物特别是禾谷类作物的种子活力和产量与质量。脱落酸(ABA)是调控种子发育和萌发最重要的植物激素之一，其活性水平、信号转导及其LAFL网络在种子发育包括胚胎发生和成熟过程的调控中起关键作用。该文主要综述了近年来ABA调控种子发育的研究取得的重要进展，包括ABA代谢和信号转导对种子发育的调控，ABA与种子成熟转录因子(AFL-B3、FUS3、ABI3、LEC2等)的作用，以及ABA在种子发育中的作用机制，并提出了需要进一步研究的科学问题，为深入理解种子发育的分子机制提供参考，从而提高种子的活力、产量和质量。     

Seed enhancement: getting seeds restoration‐ready

Seed enhancement technologies such as seed priming and seed coating, developed by the agricultural seed industry, are standard procedures for the majority of crop and horticultural seeds. However, such technologies are only just being evaluated for native plant seeds despite the potential benefits of such treatments for improving restoration effectiveness. Key approaches applicable to native seed include: (1) seed priming, where seeds are hydrated under controlled conditions, and (2) seed coating, in which external materials and compounds are applied onto seeds through a diversity of treatments. These technologies are commonly employed to accelerate and synchronize germination and to improve seed vigor, seedling emergence, establishment, and to facilitate mechanized seed delivery to site, through standardizing seed size and shape. Seed enhancement technologies have now been tested on native seeds to overcome logistical and ecological barriers in restoration. However, further research is needed to extend the application of seed enhancements to a broader array of species, ecosystems, and regions as well as to evaluate new and innovative approaches such as the incorporation of beneficial soil microorganisms and plant growth regulators in the coatings. As techniques in native seed enhancement develop, these approaches need to be capable of being scaled‐up to provide the tonnages of seed required for global restoration.     

Phytochromes differentially regulate seed germination responses to light quality and temperature cues during seed maturation

The ratio of red to far-red light (R : FR) experienced by seeds during maturation affects germination, but the genetic regulation of this effect is poorly understood. In Arabidopsis thaliana , responses to R : FR are governed by five phytochrome photoreceptors, PHYA–PHYE . PHYA , PHYB and PHYE mediate germination, but their roles in germination response to the seed maturation environment are largely unknown. Seeds of A. thaliana phytochrome mutants and natural accessions were matured in a factorial combination of cold (16 °C) and warm (24 °C) temperatures and high (R : FR = 1) and low (R : FR = 0.6) R : FR environments, resembling sunlight and foliar shade, respectively. Germination was observed in resulting seeds. All five phytochromes mediated germination responses to seed maturation temperature and/or R : FR environment. PHYA suppressed germination in seeds matured under cold temperature, and PHYB promoted germination under the same conditions. PHYD and PHYE promoted germination of seeds matured under warm temperature, but this effect diminished when seeds matured under reduced R : FR. The A. thaliana natural accessions exhibited interesting variation in germination responses to the experimental conditions. Our results suggest that the role of individual PHY loci in regulating plant responses to R : FR varies depending on temperature and provide novel insights into the genetic basis of maternal effects.     

Occurrence of Free Ceramide in Acetobacter xylinum

Oryzacystatin, a proteinaceous cysteine proteinase inhibitor (cystatin) from rice seeds and probably the first well-defined cystatin superfamily member of plant origin, was immunologically investigated for its occurrence in rice seeds during maturation and germination. The enzyme-linked immunosorbent assay (ELISA) using anti-oryzacystatin Immunoglobulin G showed that all the investigated 23 cultivars of rice, Oryza sativa L. japónica, contained oryzacystatin at 1 ~ 4 mg % in their seeds. Particularly, oryzacystatin levels were high in precocious cultivars and low in sticky rice cultivars. The use of the ELISA method for the representative rice cultivar, Nipponbare, gave the result that in the seed maturation process, oryzacystatin was synthesized in precedence to total seed protein. In the germination process, oryzacystatin tended to decrease in accordance with degradation of total seed protein.     

Evaluating soil seed banks of phosphate mining restoration in the hyper-arid Negev desert

Ecological systems are severely damaged by the anthropogenic disturbance of mining. Phosphate open-pit mining fields cover over 200 km² of the Negev desert, Israel. However, the effects of the ongoing mine site restoration efforts on the plant community have not been studied. Plants and their seed banks have a major role in ecosystem processes and restoration. In this study, we focused on three mining sites, restored in different years, along Zin River valley. We compared the plant community of restored mining plots within these areas to adjacent natural plots. We asked whether plant community germination potential from the soil seed bank differs between the restored plots and the adjacent natural plots within a mining site. We hypothesized that: (1) there is a lack of seed bank in the restored plots; (2) the altered soil composition at the restored plots inhibits germination. We used soil samples collected from the different mining sites and set up greenhouse experiments. One experiment compared natural and restored areas with different soil treatments. In another experiment, we added native seeds to test their germination potential on restored soil. Our results indicate that lack of seed bank is the major limiting factor hindering germination and not the composition of the soil after restoration. Our findings shed light on the constraints of seed bank establishment in post-mining areas of hyper-arid regions. We suggest considering active restoration practices to facilitate natural dispersal and improve seed bank establishment.     

Seed dormancy and the control of germination

Seed dormancy is an innate seed property that defines the environmental conditions in which the seed is able to germinate. It is determined by genetics with a substantial environmental influence which is mediated, at least in part, by the plant hormones abscisic acid and gibberellins. Not only is the dormancy status influenced by the seed maturation environment, it is also continuously changing with time following shedding in a manner determined by the ambient environment. As dormancy is present throughout the higher plants in all major climatic regions, adaptation has resulted in divergent responses to the environment. Through this adaptation, germination is timed to avoid unfavourable weather for subsequent plant establishment and reproductive growth. In this review, we present an integrated view of the evolution, molecular genetics, physiology, biochemistry, ecology and modelling of seed dormancy mechanisms and their control of germination. We argue that adaptation has taken place on a theme rather than via fundamentally different paths and identify similarities underlying the extensive diversity in the dormancy response to the environment that controls 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     

Environmental and genetic influences on the germination of Arabidopsis thaliana in the field

Seasonal germination timing strongly influences lifetime fitness and can affect the ability of plant populations to colonize and persist in new environments. To quantify the influence of seasonal environmental factors on germination and to test whether pleiotropy or close linkage are significant constraints on the evolution of germination in different seasonal conditions, we dispersed novel recombinant genotypes of Arabidopsis thaliana into two geographic locations. To decouple the photoperiod during seed maturation from the postdispersal season that maternal photoperiod predicts, replicates of recombinant inbred lines were grown under short days and long days under controlled conditions, and their seeds were dispersed during June in Kentucky (KY) and during June and November in Rhode Island (RI). We found that postdispersal seasonal conditions influenced germination more strongly than did the photoperiod during seed maturation. Genetic variation was detected for germination responses to all environmental factors. Transgressive segregation created novel germination phenotypes, revealing a potential contribution of hybridization of ecotypes to the evolution of germination. A genetic trade-off in germination percentage across sites indicated that determinants of fitness at or before the germination stage may constrain the geographic range that a given genotype can inhabit. However, germination timing exhibited only weak pleiotropy across treatments, suggesting that different sets of genes contribute to variation in germination behavior in different seasonal conditions and geographic locations. Thus, the genetic potential exists for rapid evolution of appropriate germination responses in novel environments, facilitating colonization across a broad geographic range.     

Cloning capacity helps seeds of Garcinia xanthochymus counter animal predation

Seed predators have the potential to act as agents of natural selection that influence seed traits and seed fates, which in turn affect the whole plant population dynamic. Accordingly, plants deploy a variety of mechanisms (e.g., resistance and tolerance strategies) to lessen the impact of predation on seed crop or on an individual seed. In this study, we described a novel mechanism, seed cloning strategy, in a tropical plant species in countering animal predation. By conducting field‐ and laboratory‐based germination experiments, we found that both rodent damaged and artificially damaged seed fragments of a large‐seeded tree Garcinia xanthochymus (Clusiaceae) could successfully germinate and establish as seedlings. Tissue culture experiments revealed that G. xanthochymus has no endosperm in seeds, and its seed fragments own strong capacity of differentiation and cloning. Seed damage negatively affected seedling growth and germination, but the seed germination rate was remarkably high. Our study suggests that, seed cloning capacity, adopted by the large‐seeded tree G. xanthochymus may act as a novel strategy counteract for seed predation and would play a significant role in stabilizing the mutualism between plant and animals.