Melatonin Promotes Rice Seed Germination under Drought Stress by Regulating Antioxidant Capacity

Drought stress is a serious threat to the germination of plant seeds and the growth of seedlings. Melatonin has been proven to play an important role in alleviating plant stress. However, its effect on seed germination under drought conditions is still poorly understood. Therefore, we studied the effects of melatonin on rice seed germination and physiological characteristics under drought stress. Rice seeds were treated with different concentrations of melatonin (i.e., 0, 20, 100, and 500 μM) and drought stress was simulated with 5% polyethylene glycol 6000 (PEG6000). The results showed that 100 μM melatonin can effectively improve the germination potential, rate and index; the vigor index of rice seeds; and the length of the shoot and root. In addition, that treatment also increased the activity of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), and reduced the content of malondialdehyde (MDA). The grey relational grade between the shoot MDA content and the melatonin seed-soaking treatment was the highest, which could be useful for evaluating the effect of melatonin on drought tolerance. Two-way analysis of variance showed that the effect of single melatonin treatment on rice seeds was more significant than that of single drought stress and interaction treatment of drought and melatonin (p < 0.05). The subordinate function results showed that 100 μM melatonin significantly improved the germination and physiological indexes of rice seeds and effectively alleviated the adverse effects of drought stress on rice seedlings. The results helped to improve the understanding of the morphological and physiological involvement of melatonin in promoting seed germination and seedling development under drought stress.     

Germination ofRubus palmatus var.coptophyllus andR. microphyllus seeds buried in soil for 7.5 years

Seeds of twoRubus species,R. palmatus var.coptophyllus andR. microphyllus, buried for 7.5 years in soil were subjected to germination tests to investigate their germinability and germination traits. Most of the retrieved seeds were viable, and germinated at the alternating temperatures of 20/30°C in both light and dark. The twoRubus species showed similar responses of germination to temperature and light, although the final percentages of germination were slightly higher inR. palmatus var.coptophyllus. These characteristics of seed dormancy and germination would be involved in the species' utilization of ephemeral habitats created by unpredictable and infrequent disturbances.     

盐磷胁迫对木麻黄和台湾相思种子萌发及幼苗生长的影响

恶劣环境下,人工海防林因面临养分胁迫而经营困难。为探讨盐、磷胁迫对主要海防林树种木麻黄和台湾相思种子萌发及生长的影响,该研究分别用不同浓度的NaCl(盐)和KH₂PO₄(磷)溶液处理种子和浇灌幼苗,测定种子萌发和幼苗生长指标。结果表明：(1)高盐胁迫显著抑制种子萌发,对幼苗生长有一定影响,但两种植物影响程度不同;台湾相思种子萌发耐盐性高于木麻黄,前者相对盐害率最大值为23.03%,后者为89.15%;随着盐浓度增加,木麻黄和台湾相思种子的发芽率、发芽势、发芽指数和活力指数均降低,对应最大值分别为38.70%、34.67%、18.70、0.055和76.67%、62.22%、48.46、6.11。(2)两种植物的株高和根长随盐浓度增加而降低,木麻黄和台湾相思株高分别为12.29～6.01 mm和48.27～17.33 mm,根长分别为8.57～1.45 mm和33.41～5.88 mm;台湾相思根、茎、叶生物量及根冠比均随盐浓度的增加逐渐减小,木麻黄各处理差异较小。(3)台湾相思的种子和幼苗较木麻黄更耐低磷环境,二者最适磷浓度存在差异;木麻黄种...     

珍稀濒危植物蒜头果种子萌发特征与幼苗类型的研究

以去除果皮后阴干的珍稀濒危植物蒜头果种子为材料,在温室大棚沙池内进行层积处理,从层积处理开始至子叶出土的不同萌发阶段,考察蒜头果种子发育形态、贮藏物质积累、酶活性以及幼苗类型等变化特征,初步探讨其种子休眠形成原因。结果显示：(1)蒜头果种子从解除休眠开始至萌发形成幼苗的过程约需195 d,其中幼胚的形态发育后熟约需75 d,随后30 d内是种子集中萌发的时期,其发芽率达到最高(53.33%);依据种胚发育形态的标志特征将此过程划分为7个阶段(S1～S7阶段):S1阶段种子未萌发,S2阶段种胚“露白”,S3阶段胚根突破种皮长超过1 cm, S4阶段下胚轴与胚根连接处形成弯钩结构,S5阶段“S”型胚形成及胚根前端膨大,S6阶段种子不仅具有膨大的胚根且已有侧根的分化,S7阶段子叶脱落,胚芽出土,真叶出现。(2)蒜头果种子在湿沙层积过程中,种胚胚长和胚率从S1阶段的(5.49±1.57)mm和(19.48±5.72)%分别增加至S6阶段的(67.92±2.94)mm和(240.75±15.29)%,胚率平均增加了12.4倍,显示蒜头果种子的胚需要经历后熟过程才能萌发,属于胚后熟型种子。(3)从...     

木波罗种子脱水敏感性与膜脂过氧化的研究

刚采收的木波罗种子含水量为５８．６％。随着含水量下降,种子的发芽率和发芽指数迅速下降,种子对脱水非常敏感,是典型的顽拗性种。自然脱水时,种子胚轴和子叶中超氧物歧化酶的活性先上升,然后下降,丙二醛和脂质氢过氧化物的含量显著增加。其脱水敏感性的原因可能是当种子脱水时,植物酶ＳＯＤ的活性下降,膜脂过氧化作用加强,从而使膜的结构和功能受到破坏,种子生活力丧失。     

鸡冠花种子蛋白质的提纯及分析

鸡冠花种子干燥后用石油醚脱酯,用凯氏定氮法测定蛋白质含量。按Osbern系统分别提取白蛋白、球蛋白、醇溶蛋白、谷蛋白;用Folin一酚试剂法测定各自相对含量,并用单向和双向SDS—PAGE方法分析种子总蛋白和4类不同溶性蛋白质的组成成分及这些组份的热稳定性。实验发现:鸡冠花种子蛋白质含量达26.04％,白蛋白、球蛋白、醇溶蛋白、谷蛋白的相对含量分别为11.5％、72％、4.6％、12％。SDS—PAGE表明;其种子蛋白中20KD球蛋白成份含量最高,其它一些次要组分为63KD、61KD、15KD、13KD白蛋白成份,58KD、37KD、23KD球蛋白成份,39KD、34KD、25KD谷蛋白成份及26KD醇溶蛋白成份,其中58KD由37KD和20KD两亚基经二硫键连接而成,39KD组份由24.5KD和18KD两亚基通过二硫键连接而成,23KD球蛋白组份遇热沉淀。     

Changes in protein synthesis during stratification and dormancy release in embryos of sugar maple (Acer saccharum)

Protein synthesis in dormant embryos of sugar maple ( Acer saccharum ) was investigated in seeds stratified at 4°C or incubated at 15°C. Seeds stratified at 4°C germinated after 27 days; seeds incubated at 15°C failed to germinate. Stratification increased the embryo's capacity for protein synthesis by day 11 as measured by in vivo incorporation of [³⁵S]-methionine into purified protein. At 4°C protein synthesis in the embryonic axis rose in a linear fashion prior to germination, whereas in cotyledons it increased until day 20 and then declined. Analysis of radiolabelled proteins by two-dimensional gel electrophoresis revealed that the levels of specific proteins were altered by temperature, primarily in the cotyledons. Several proteins were expressed in the cotyledons at 15°C but were absent in unstratified embryos and in embryos stratified at 4°C. That is, the expression of these proteins was repressed during stratification and release from dormancy. Levels of other proteins in the cotyledons declined at 4°C during stratification. We suggest that one or more of these proteins may be associated with the inhibition of growth of the embryonic axis imposed by the cotyledons.     

Broad bean wrinkly seed caused by artichoke yellow ringspot nepovirus

Artichoke yellow ringspot nepovirus (AYRV) was isolated from stunted broad bean plants in Crete showing leaf mottling and deformation and wrinkling of seed testas. AYRV identification was based on host range, behaviour during purification, electron microscopy and serology. AYRV-broad bean isolate was seed-transmitted in broad bean, and embryo infection appeared to be a prerequisite for virus transmission to seedlings. Transmission through pollen was not detected in broad bean plants, although pollen grains were externally contaminated by the virus. Ovule infection occurred in a high proportion of seed and was independent of pollination.     

RELATIVE SUCCESS OF SELF AND OUTCROSS POLLEN COMPARING MIXED- AND SINGLE-DONOR POLLINATIONS IN AQUILEGIA CAERULEA

Flowers frequently receive both self (S) and outcross (OC) pollen, but S pollen often sires proportionally fewer seeds. Failure of S pollen can reflect evolved mechanisms that promote outcrossing and/or inbreeding depression expressed during seed development. The relative importance of these two processes was investigated in Aquilegia caerulea, a self-compatible perennial herb. In the field I performed single-donor (S or OC) and mixed-donor (S plus OC) pollinations to compare the relative success of both pollen types at various stages from pollen germination to seed maturity. Single-donor S pollinations produced significantly fewer and lighter seeds (x decrease = 12% and 3%, respectively) than OC pollinations. Abortion rates differed by an average of 38% whereas fertilization rates differed by only 5%, indicating that most differences in seed number arose postzygotically. This suggests that inbreeding depression was responsible for most failure of S pollen. One prezygotic effect measured was that 10% fewer S than OC pollen tubes reached ovaries after 42 hr, suggesting S pollen might fertilize proportionately fewer ovules after mixed pollination. Using allozyme markers, I found mixed-donor pollinations produced significantly more and heavier outcrossed than selfed seeds. However, the proportion of selfed seed, fertilized ovules, and aborted seeds for mixed-donor fruits were each predictable from pollen performance in single-donor fruits, suggesting that differential paternity is best explained by inbreeding depression during seed development. Even given these similarities between mixed- and single-donor fruits in the relative performance of S and OC pollen, both individual seed weight and seed set were significantly higher in multiply-sired fruits.     

3. Genetic conservation in seed banks

The safest and most economical and convenient way of preserving the genetic resources of the majority of crop plants is by long-term seed storage. The technology is well developed, but recent research resulting from a greater understanding of behaviour at very low water potentials is leading to further improvements