濒危植物百山祖冷杉种子发育特征及其胚培养

百山祖冷杉(Abies beshanzuensis)种子萌发率低,发育特性尚不明确,极大地限制了种群在原生境的自然更新。该研究以百山祖冷杉不同发育时期的雌球果为材料,通过研究球果中种子的胚与胚乳数量、重量和显微结构特性,及测定种子发育关键时期胚乳的初生代谢物,探究种子发育特征及影响种子发育的主要因素。结果表明,7月是百...     

Seed coats: Structure,development, composition,and biotechnology

Summary Although seeds have been the subject of extensive studies for many years, their seed coats are just beginning to be examined from the perspective of molecular genetics and control of development. The seed coat, plays a vital role in the life cycle of plants by controlling the development of the embryo and determining seed dormancy and germination. Within the seed coat are a number of unique tissues that undergo differentiation to serve specific functions in the seed. A large number of genes are known to be specifically expressed within the seed coat tissues; however, very few of them are understood functionally. The seed coat synthesizes a wide range of novel compounds that may serve the plant in diverse ways, including defense and control of development. Many of the compounds are sources of industrial products and are components of food and feeds. The use of seed coat biotechnology to enhance seed quality and yield, or to generate novel components has not been exploited, largely because of lack of knowledge of the genetic systems that govern seed coat development and composition. In this review, we will examine the recent advances in seed coat, biology from the perspective of structure, composition and molecular genetics. We will consider the diverse avenues that are possible for seed coat biotechnology in the future. This review will focus principally on the seed coats of the Brassicaceae and Fabaceae as they allow us to merge the areas of molecular biology, physiology and structure to gain a perspective on the possibilities for seed coat modifications in the future. The authors have contributed equally and are considered first authors.     

Fruit and seed development inCucurbita foetidissima

Cucurbita foetidissimaHBK., a wild perennial xerophytic species indigenous to semi-arid lands of North America is reproduced primarily vegetatively, but is a prolific producer of fruit and seed. The seed contains an acceptable edible oil. Fruit development reaches its maximum weight 10 days after pollination, but seed development continues until 32 to 34 days after pollination. Physiological development of the seed as measured by germination is not coincidental with physical development.     

Concentration and localization of zinc during seed development and germination in wheat

In a field experiment, the effect of foliar Zn applications on the concentration of Zn in seeds of a bread wheat cultivar ( Triticum aestivum L. cv. Balatilla) was studied during different stages of seed development. In addition, a staining method using dithizone (DTZ: diphenyl thiocarbazone) was applied to (1) study the localization of Zn in seeds, (2) follow the remobilization of Zn during germination, and (3) develop a rapid visual Zn screening method for seed and flour samples. In all seed development stages, foliar Zn treatments were effective in increasing seed Zn concentration. The highest Zn concentration in the seeds was found in the first stage of seed development (around the early milk stage); after this, seed Zn concentration gradually decreased until maturity. When reacting with Zn, DTZ forms a redcolored complex. The DTZ staining of seed samples revealed that Zn is predominantly located in the embryo and aleurone parts of the seeds. After 36 h of germination, the coleoptile and roots that emerged from seeds showed very intensive red color formation and had Zn concentrations up to 200 mg kg⁻¹, indicating a substantial remobilization of Zn from seed pools into the developing roots (radicle) and coleoptile. The DTZ staining method seems to be useful in ranking flour samples for their Zn concentrations. There was a close relationship between the seed Zn concentrations and spectral absorbance of the methanol extracts of the flour samples stained with DTZ. The results suggest that (1) accumulation of Zn in seeds is particularly high during early seed development, (2) Zn is concentrated in the embryo and aleurone parts, and (3) the DTZ staining method can be used as a rapid, semiquantitative method to estimate Zn concentrations of flour and seed samples and to screen genotypes for their Zn concentrations in seeds.     

Family life at close quarters: communication and constraint in angiosperm seed development

The formation of viable angiosperm seeds involves the co-ordinated growth and development of three genetically distinct organisms, the maternally derived seed coat and the zygotic embryo and endosperm. The physical relationships of these tissues are initially established during the specification and differentiation of the female gametophyte within the tissues of the developing ovule. The molecular programmes implicated in both ovule and seed development involve elements of globally important pathways (such as auxin signalling), as well as ovule- and seed-specific pathways. Recurrent themes, such as the precisely controlled death of specific cell types and the regulation of cell–cell communication and nutrition by the selective establishment of symplastic and apoplastic barriers, appear to play key roles in both pre- and post-fertilization seed development. Much of post-fertilization seed growth occurs during a key developmental window shortly after fertilization and involves the dramatic expansion of the young endosperm, constrained by surrounding maternal tissues. The complex tissue-specific regulation of carbohydrate metabolism in specific seed compartments has been shown to provide a driving force for this early seed expansion. The embryo, which is arguably the most important component of the seed, appears to be only minimally involved in early seed development. Given the evolutionary and agronomic importance of angiosperm seeds, the complex combination of communication pathways which co-ordinate their growth and development remains remarkably poorly understood.     

细胞分裂素调控种子发育、休眠与萌发的研究进展

种子萌发是子代植株建立、生长和繁育的重要阶段,在种子植物生命周期中起重要作用。种子休眠是在发育过程中形成的,在生理成熟期达到峰值。种子休眠与萌发的植物激素调控可能是种子植物中一种高度保守的机制。细胞分裂素(CK)是植物体内的一种重要信号分子,调控植物生长发育的许多方面。生物活性CK的水平由其生物合成、活化、失活、再活化...     

杂交小麦制种研究现状及展望

利用杂种优势对提高小麦单产具有重要作用,杂交小麦制种是小麦种业未来发展的重要方向之一。目前,小麦在强优势杂交组合选配方面取得较大进步。由于缺乏优异高异交结实率的制种亲本资源和高产高效杂交制种体系,导致大面积制种效率低。因此,探究杂交制种技术体系进展、亲本种质资源改良和生产流程标准化等方面的研究现状,将有利于对杂交制种发展瓶颈和未来发展方向等问题的整体把握。综述杂交小麦制种技术的影响因素,并通过商业化大田杂交作物与新型杂交小麦比较,对杂交小麦快速商业化等方面提出建议,对其发展趋势进行展望。     

Seed development in the rare cold desert sand dune shrub Eremosparton songoricum and a comparison with other papilionoid legumes

No study has yet been carried out on seed development in a cold desert sand dune papilionoid legume. Thus, our primary aims were to (i) monitor seed development in the cold desert sand dune species Eremosparton songoricum from the time of pollination to seed maturity, and (ii) compare seed development in this species with that in other species of papilionoid legumes. Fruit and seed size, mass and seed moisture content, and seed imbibition, germination, desiccation tolerance and water retention during development (pollination to seed maturity) were monitored in the papilionaceous shrub E. songoricum in the Gurbantunggut Desert of northwest China. The duration of seed development was 40 days. Seeds reached physiological maturity 28 days after pollination (DAP), at which time 58% of them germinated and they had developed desiccation tolerance. Seeds became impermeable 36–40 DAP, when their moisture content was about 10%. The final stage of maturation drying occurred via loss of water through the hilum. The developmental stages and their timing (DAP) in seeds of E. songoricum are generally similar to those reported for other papilionaceous legumes with a water‐impermeable seed coat (physical dormancy). In general, the developmental features of seeds with water‐impermeable coats at maturity do not appear to be specific to habitat or phylogeny.     

Gibberellins are required for embryo growth and seed development in pea

The gibberellin (GA) biosynthesis mutants lh-1 and lh-2 have been used to examine the physiological role of GAs in pea seed development. The LH protein is required for the three-step oxidation of ent -kaurene to ent -kaurenoic acid early in the GA biosynthesis pathway. The allele-specific interaction of lh-1 and lh-2 with chemical inhibitors of these three steps suggests that LH encodes the multi-functional GA biosynthesis enzyme ent -kaurene oxidase. Unlike the lh-2 mutation which reduces seed weight and decreases seed survival by ∼50% compared with wild-type plants, the lh-1 allele has a transient effect on embryo and seed growth and only slightly increases seed abortion. These seed phenotypes parallel the effects of the two mutant alleles on GA levels in young seeds. Detailed examination of the growth of lh-1 seeds reveals homeostatic regulation of GA-promoted embryo and seed growth. Although GA-deficient seeds grow more slowly than WT seeds, decreased assimilate availability to the developing seeds is not the primary reason for the altered seed development. Instead, GAs act to promote some process(es) required for embryo and seed growth and only indirectly influence the distribution of assimilates. How GA deficiency causes seed abortion is not known but it may simply be a consequence of reduced seed or embryo growth rate. These results demonstrate that even relatively small changes in the levels of GAs in young seeds can alter seed development and suggest that the available GA-related mutants may represent only a subset of all possible mutants with reduced GA levels or GA signalling.     

Suppression of sucrose synthase gene expression represses cotton fiber cell initiation,elongation, and seed development

Cotton is the most important textile crop as a result of its long cellulose-enriched mature fibers. These single-celled hairs initiate at anthesis from the ovule epidermis. To date, genes proven to be critical for fiber development have not been identified. Here, we examined the role of the sucrose synthase gene (Sus) in cotton fiber and seed by transforming cotton with Sus suppression constructs. We focused our analysis on 0 to 3 days after anthesis (DAA) for early fiber development and 25 DAA, when the fiber and seed are maximal in size. Suppression of Sus activity by 70% or more in the ovule epidermis led to a fiberless phenotype. The fiber initials in those ovules were fewer and shrunken or collapsed. The level of Sus suppression correlated strongly with the degree of inhibition of fiber initiation and elongation, probably as a result of the reduction of hexoses. By 25 DAA, a portion of the seeds in the fruit showed Sus suppression only in the seed coat fibers and transfer cells but not in the endosperm and embryo. These transgenic seeds were identical to wild-type seeds except for much reduced fiber growth. However, the remaining seeds in the fruit showed Sus suppression both in the seed coat and in the endosperm and embryo. These seeds were shrunken with loss of the transfer cells and were <5% of wild-type seed weight. These results demonstrate that Sus plays a rate-limiting role in the initiation and elongation of the single-celled fibers. These analyses also show that suppression of Sus only in the maternal seed tissue represses fiber development without affecting embryo development and seed size. Additional suppression in the endosperm and embryo inhibits their own development, which blocks the formation of adjacent seed coat transfer cells and arrests seed development entirely.     

Seed coat development in Leucospermum cordifolium (Knight) Fourcade (Proteaceae) and a clarification of the seed covering structures in Proteaceae

MANNING, J. C. & BRITS, G. J., 1993. Seed coat development in Leucospermum cordifolium (Knight) Fourcade (Proteaceae) and a clarification of the seed covering structures in Proteaceae . The development of the seed coat and pericarp is studied in Leucospermum cordifolium from ovule to mature seed. The ovule and seed are characterized by a tegmic pachychalaza. The pericarp is adnate to the integuments from anthesis and remains unthickened to maturity. The outer integument forms the seed coat and the seed is endotestal: the outer epidermis becomes tanniniferous and the inner epidermis develops into a crystalliferous palisade. The inner integument degenerates at an early stage. Examination of the literature reveals that the crystal palisade layer of the outer integument has been erroneously assumed to constitute an endocarp. This finding indicates that a re-interpretation of all published information on the seed coat in indehiscent Proteaceae is necessary before any speculations on the phylogenetic significance of the seed coat can be entertained.     

Changes in lipid status and glass properties in cotyledons of developing sunflower seeds

Biochemical events involved in the acquisition of germinability and storability during orthodox seed development are well documented; however, the roles played by the physical organization of lipids and water are poorly characterized. The aim of this work was to determine, using a thermodynamic approach, whether changes in thermal properties of lipid reserves, and intracellular glasses might play a role in sunflower (Helianthus annuus L.) seed development. Triacyglycerols (TAGs) accumulated in cotyledons until the end of seed filling, which occurred 42 days after anthesis (DAA). Further seed development, leading to mature seed at 58 DAA, was mainly associated with an enlargement of lipid bodies without significant changes either in the lipid content or in their composition. When cooled to -100 degrees C, lipid reserves from cotyledons of mature seeds displayed alpha and beta' polymorphic crystalline structures; however, the ability to form alpha crystals, which was an indicator of lipid purity, progressively appeared during seed development. Characteristics of lipid melting confirmed that seed maturation drying was associated with changes in TAG physical organization. Cotyledon development was associated with an increase in the temperature of glass to rubber transition (Tg), thus suggesting a decrease in molecular mobility during maturation drying. This phenomenon was concomitant with an increase in raffinose content. Our results demonstrate that physical characteristics of lipid reserves and glasses of sunflower cotyledons are developmentally regulated and might play a role in acquisition of seed germinability and storability.     

Accumulation and degradation of thiamin-binding protein and level of thiamin in wheat seeds during seed maturation and germination

Changes in the levels of thiamin-binding globulin and thiamin in wheat seeds during maturation and germination were studied. The thiamin-binding activity of the seed proteins increased with seed development after flowering. The thiamin content of the seeds also increased with development. Thiamin-binding activity decreased during seed germination. On the other hand, immunological analysis using an antibody directed against the thiamin-binding protein isolated from wheat seeds showed that the thiamin-binding globulin accumulated in the aleurone layer of the seeds during maturation, and then the protein was degraded and disappeared during seed germination. These results suggested that the thiamin-binding globulin of wheat seeds was synthesized and accumulated in the aleurone layer of the seeds with seed development, similar to the thiamin-binding albumin in sesame seeds, and that thiamin bound to the thiamin-binding globulin in the dormant wheat seeds for germ growth during germination.     

D-type cyclins control cell division and developmental rate during Arabidopsis seed development

Seed development in Arabidopsis is characterized by stereotypical division patterns, suggesting that coordinated control of cell cycle may be required for correct patterning and growth of the embryo and endosperm. D-type cyclins (CYCD) are key cell cycle regulators with roles in developmental processes, but knowledge regarding their involvement in seed development remains limited. Here, a family-wide gene expression, and loss- and gain-of-function approach was adopted to reveal additional functions for CYCDs in the development of seed tissues. CYCD genes have both discrete and overlapping tissue-specific expression patterns in the seed as revealed by GUS reporter gene expression. Analysis of different mutant combinations revealed that correct CYCD levels are required in seed development. The CYCD3 subgroup is specifically required as its loss caused delayed development, whereas overexpression in the embryo and endosperm of CYCD3;1 or a previously uncharacterized gene, CYCD7;1, variously leads to induced proliferation, abnormal phenotypes, and elevated seed abortion. CYCD3;1 overexpression provoked a delay in embryonic developmental progression and abnormalities including additional divisions of the hypophysis and suspensor, regions where CYCD3 genes are normally expressed, but did not affect endosperm development. Overexpression of CYCD7;1, not normally expressed in seed development, promoted overgrowth of both embryo and endosperm through increased division and cell enlargement. In contrast to post-germination growth, where pattern and organ size is not generally related to division, results suggest that a close control of cell division through regulation of CYCD activity is important during seed development in conferring both developmental rate and correct patterning.     

Adenylate and nicotinamide nucleotides in developing soybean seeds during seed-fill

Profiles of adenylate and nicotinamide nucleotides in soybean seeds were determined during seed-fill. The ATP content per seed increased during the early seed-filling stages to a level of 10 to 12 micrograms per seed. Seed ATP decreased after 40 days of development and reached its lowest level of less than 1 microgram at maturity. The ATP:ADP ratios were relatively constant at all seed development stages. Sharp increases in AMP levels during the late seed-fill stages were paralleled with a disappearance of ATP and ADP pools resulting in a reduced seed energy charge. Energy charge varied from the highest value of 0.78 at mid-seed-fill to less than 0.10 at maturity.     

Yield and composition of soybean seed as a function of potassium supply

Summary A reduction in K supply to soybean plants to deficiency levels during both vegetative and reproductive development resulted in reductions not only in yield, but also in oil and K concentrations in the seed and a concomittant increase in seed protein concentration. Correlations between mean fruit yield and oil, protein and K concentrations, over a wide range of K regimes, were 0.97, −0.94 and 0.98, respectively. When K supply was increased well above the level necessary to produce maximum yields,i.e. luxury consumption, there was no significant change in K concentration in the seed, indicating a high degree of control in the movement of K to the developing seed under high K regimes. When the K supply to the plant was limiting, the rate of accumulation of oil and carbohydrate fractions, but not of seed protein, declined during the latter part of podfilling. This resulted in a fall in the C/N ratio in the non-structural seed components during this part of seed development. Depriving plants of K only during seed development had no effect on seed composition or yield, whereas resupplying K to deficient plants after anthesis resulted in almost the same seed composition and yield as that which occurred with control plants. Possible mechanisms whereby K deficiency influences soybean seed composition and yield are discussed in terms of movement of carbohydrate and nitrogen to the seed. We suggest that potassium-deficient soils are likely to produce crops with low yields and low seed oil levels; the crop may respond to K fertilizers as late as anthesis.