顽拗性黄皮种子税水过程中活性氧清除酶活性的变化

以正常性种子花生为对照,研究了顽拗性黄皮种子脱水过程中活性氧清除酶、膜脂过氧化作用以及电解质渗漏率的变化。随着含水量的下降,黄皮胚的电解质渗漏率和膜脂过氧化产物丙二醛（MDA）含量均显著增加;当黄皮胚含水量下降致40％后,SOD活性开始急剧下降,而POD和CAT活性在胚含水量下降过程中呈现出缓慢下降的趋势。花生胚在含水量从45％降至145的过程中,电解质渗漏率没有明显增加,MDA含量只有少量增加;当含水量降至14％后,电解质渗漏率出现少量增加,花生胚脱水初期,活性氧清除酶活怀明显增加,并在整个脱水过程中维持较高的水平。以上结果表明：顽拗性处子黄皮的脱水敏感性与活性氧清除酶相对活性变化有关。脱水引起黄皮胚活性氧清除酶活性降低,活性氧清除能力下降,膜脂过氧化作用加强,膜透性增大。黄皮胚的膜系统可能是脱水伤害的靶位之一。     

脱水速率对黄皮胚轴脱水敏感性及膜膜过氧化的影响

以黄皮种子离体胚轴为材料,研究了不同于燥速率对胚轴脱水反应和膜脂过氧化的影响。在脱水过程中,胚轴的萌发率,活力指数,电解质渗漏速率,超氧化物歧化酶（SOD）,过氧化物酶（POD）和过氧化氢酶（CAT）活性逐渐降低,膜脂过氧化产物MDA的含量不断增加,脱水速率愈快,胚轴的半致死含水量就愈低。快速干燥的胚轴能在较低的含水量存活是因为顾中间含量下发生的膜脂过氧化作用的时间,以及保持较高的SOD,POD和CAT活性,缓慢干燥的胚轴当与周围环境达到水分平衡后,生活力的丧失将与保持在水分平衡后的时间有关,。因此,脱水速率是一种影响顽拗性种子或者胚轴脱水敏感性的重要因子。     

脱水速率对黄皮胚轴脱水敏感性及膜脂过氧化的影响

以黄皮种子离体胚轴为材料,研究了不同干燥速率对胚轴脱水反应和膜脂过氧化的影响.在脱水过程中,胚轴的萌发率、活力指数、电解质渗漏速率,超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)活性逐渐降低,膜脂过氧化产物MDA的含量不断增加.脱水速率愈快,胚轴的半致死含水量就愈低.快速干燥的胚轴能在较低的含水量下存活是因为缩短了在中间含水量下发生的膜脂过氧化作用的时间,以及保持较高的SOD、POD和CAT活性;缓慢干燥的胚轴当与周围环境达到水分平衡后,生活力的丧失将与保持在水分平衡后的时间有关.因此,脱水速率是一种影响顽拗性种子或者胚轴脱水敏感性的重要因子.     

黄皮种子线粒体呼吸速率和活性氧清除酶活性对脱水的响应及其生态学意义

顽拗性种子脱落时具有较高的含水量和代谢活性, 对脱水高度敏感; 但顽拗性种子脱水敏感性的机理至今仍然不清楚。该文以顽拗性黄皮(Clausena lansium)种子为材料, 研究了种子和胚轴对水分丧失的响应, 在脱水过程中胚轴和子叶的呼吸速率, 胚轴和子叶线粒体的细胞色素c氧化酶(CCO)活性、外膜完整性、CCO和交替氧化酶(AOX)途径以及线粒体活性氧清除酶活性的变化。结果表明, 随着水分的丧失, 种子和胚轴的存活率逐渐下降, 种子的脱水敏感性大于胚轴; 胚轴和子叶的呼吸速率以及线粒体外膜的完整性降低。胚轴和子叶线粒体的CCO途径以及胚轴AOX途径的呼吸速率在脱水初期增加, 随着继续脱水下降, 胚轴线粒体AOX途径的呼吸速率则随着脱水显著下降。胚轴线粒体的超氧化物歧化酶(SOD)、抗坏血酸过氧化物酶(APX)和谷胱甘肽还原酶(GR)活性和子叶线粒体的APX活性随着脱水迅速下降; 胚轴线粒体的脱氢抗坏血酸还原酶(DHAR)活性和子叶线粒体的SOD、DHAR和GR活性在脱水初期增加, 然后下降。这些数据表明黄皮种子的脱水敏感性与线粒体的呼吸速率和活性氧清除酶的活性降低密切相关, 也与长期适应热带/亚热带的生境有关。     

顽拗性黄皮胚脱水过程中核酸、蛋白质代谢的变化

黄皮种子发育晚期,胚内核酸、蛋白质合成能力增强,而花生胚的核酸、蛋白质合成能力在发育晚期则呈下降趋势。黄皮胚的发育在达到生理成熟后维持着活跃的生理代谢并转入萌发状态;而花生胚的代谢活性逐步降低并转入生理静止状态。脱水处理引起生理成熟期黄皮胚核酸、蛋白质合成能力急剧下降,核酸水解酶活性增强。不同程度脱水的黄皮胚吸胀２４ｈ,核酸、蛋白质的合成能力随脱水程度的加深而降低;生物大分子代谢能力的变化是顽拗性     

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。     

黄皮种子脱水敏感性与萌发事件的研究

黄皮种子对脱水非常敏感,含水量从51％下降至22.4％,种子的发芽率和发芽指数为零,是典型的顽拗性种子。自然脱水时,种子中可溶性糖的含量增加,淀粉的含量下降;磷酸化酶,异柠檬酸裂解酶以及旺轴中α—和β—淀粉酶的活性先增加然后下降;子叶中α—和β—淀粉酶的活性呈下降趋势。这些变化类似于吸水萌发的黄皮和豌豆种子。可以认为黄皮种子脱水敏感性的原因是在脱落时萌发。随着萌发过程的进行,水分成为限制因子,使种子生活力丧失。     

玉米胚发育过程中脱水耐性的变化

对离体玉米胚脱水耐性的变化以及不同脱水速率对其脱水耐性的影响进行了研究。授粉后16d的玉米胚能耐轻微脱水,含水量从1.45降低到0.28gH2Og-1DW时胚的萌发率为100%,但含水量低于0.1gH2Og-1DW时胚死亡。胚的脱水耐性随着发育逐渐加强,表现为电解质渗漏速率逐渐降低,萌发率和幼苗干重逐渐增加。授粉后20d胚内超氧化物歧化酶(SOD)和抗坏血酸过氧化物酶(APX)活性较高,过氧化氢酶(CAT)活性较低;授粉后24d,这些酶的活性与授粉后20d的正好相反。脂质过氧化产物丙二醛(MDA)在种子发育过程中呈下降趋势。不同脱水速率明显地影响胚的脱水耐性:在慢速脱水到含水量0.1~0.18gH2Og-1DW时,胚的萌发率和幼苗干重比快速脱水高,电解质渗漏速率比快速脱水低;在快速脱水条件下胚中的SOD、APX活性和MDA含量也比慢速脱水高;CAT活性的变化不明显。     

黄皮种子脱水敏感性与萌发事件的研究

黄皮种子对脱水非常敏感,含水量从51%下降至22．4%,种子的发芽率和发芽指数为零,是典型的顽拗性种子。自然脱水时,种子中可溶性糖的含量增加,淀粉的含量下降;磷酸化酶,异柠檬酸裂解酶以及胚轴中α-和β-淀粉酶的活性先增加然后下降;子叶中α-和β-淀粉酶的活性呈下降趋势．这些变化类似于吸水萌发的黄皮和豌豆种子。可以认为黄皮种子脱水敏感性的原因是在脱落时萌发。随着萌发过程的进行,水分成为限制因子,使种子生活力丧失。     

豌豆种子吸胀过程中脱水耐性变化的时间模式

研究了豌豆种子吸胀过程中脱水耐性的变化模式。种子在吸胀初期迅速吸收水分,然后缓慢吸收直到平台期。电解质渗漏速率在吸胀初期增加直到11h,然后随着吸胀下降。在吸胀过程中,种子的萌发率逐渐增加,种子和胚轴的脱水耐性逐渐丧失,10％和50％的种子和胚轴被脱水致死的含水量明显增加。赤霉素和脱落酸处理改变豌豆种子的萌发特性,提高胚轴的脱水耐性。研究结果表明,吸胀的豌豆种子脱水耐性的丧失是一种数量性状,正常性种子吸胀后脱水耐性的变化能够作为种子顽拗性研究的模式系统。     

提高黄皮种子活力的途径

黄皮种子经脱水至40％左右或持续贮藏（一年以上）后种子活力迅速下降,PEG对劣变种子直接引发不但不能提高其活力,反而使其活力更为下降,甚至丧失萌发能力而引发加速了代谢物质的消耗和渗漏。在黄皮种子脱水前用ABA、Ca2 、茶多酚（抗氧化剂）预处理,明显降低了黄皮种子的脱水敏感性。结合用PEG引发技术,则能较大幅度提高黄皮种子脱水后的活力,Ca2 短时高温引发也能提高黄皮种子贮藏一年后的活力,说明预处理是提高脱水和贮藏后黄皮种子活力的必要措施。     

黄皮种子脱水敏感性与脂质过氧化作用

黄皮种子自然脱水时,种子的发芽率和发芽指数迅速下降;种子浸泡液的电导率和可溶性物质的量大大增加;线粒体膜和质膜ATPase的活性下降;种子中SOD活性先上升,然后下降;脂质过氧化产物MDA和脂质氢过氧化物的量大大增加。DDC、MDA和Fe2 促进脂质过氧化作用,降低种子生活力;ASA和甘露醇对脂质过氧化有抑制作用,提高种子生活力。     

黄皮种子发育过程中脱水敏感性与细胞膜透性的关系

黄皮（Ｃｌａｕｓｅｎａ ｌａｎｓｉｕｍ （Ｌｏｕｒ．） Ｓｋｅｅｌｓ）胚轴与完整种子的发育模式以及发育中电解质渗漏率变化有些不同． 种子生理成熟前、后的胚轴对脱水的反应也不同,前者经轻微脱水可提高萌发率和活力指数,后者不耐任何程度的脱水．活力指数的急剧下降伴随着电解质渗漏率的迅速上升．实验表明,黄皮种子在发育过程中没有形成耐脱水性． 细胞膜透性变化可反映脱水对种子的伤害程度     

Cytological and physiological changes in orthodox maize embryos during cryopreservation

Cytological and physiological changes during cryopreservation were studied in maize embryos at 35 days after pollination (DAP). Both dehydration and freezing caused cytological damage, such as plasmolysis, swelled mitochondria, increased heterochromatin, and nuclear shrinkage. Dehydration alone slightly impaired plasma membrane integrity while a drastic increase in electrolyte leakage was observed after freezing of embryos with moisture content above 23%. Damage to cellular ultrastructure and plasmalemma integrity was negatively related to moisture content in unfrozen embryos and positively related in frozen embryos. The pattern of changes in activity of antioxidant enzymes differed from one another during dehydration and/or freezing–thawing treatment. Dehydration increased activity of ascorbate peroxidase (APX) and glutathione reductase (GR) but decreased activity of superoxide dismutase (SOD) and dehydroascorbate reductase (DHAR). Freezing further decreased GR and SOD activity and resulted in extremely low DHAR activity. Embryos at intermediate moisture contents had low catalase (CAT) activity before freezing but highest CAT activity after freeze–thaw. Both dehydration and freezing promoted membrane lipid peroxidation which resulted in an approximately threefold increase at most in the malondialdehyde content in postthaw embryos. Changes in viability of postthaw embryos can be closely related to damage in cellular ultrastructure and plasmalemma integrity but directly related neither to antioxidants nor lipid peroxidation levels.     

Relation Between Desiccation Sensitivity and Membrane Permeability of Developing Clausena lansium Seeds

Desiccation sensitivity and its relation to membrane permeability of the embryonic axes of the developing wampee (Clausena lansium (Lour.) Skeels) seeds were studied by measuring the changes in electrolyte leakage, germination and vigor index after the embryonic axes were rapidly air-dried to various water contents. During development, the fresh and dry weight per seed reached nearly maximum value at 72 d after anthesis, but the dry weight per embryonic axis continuously increased until 85 d after anthesis. The embryonic axes acquired the full capacity for germination at 58 d after anthesis and their vigor index continuously rose up from 51 to 92 d after anthesis. The electrolyte leakage of the developing the embryonic axes linearly declined to the minimum value at 72 d after anthesis and then went up again. The electrolyte leakage of the embryonic axes was higher than that of the whole seeds at the same time. The immature embryonic axes did not germinate completely, while mild desiccation could improve their viability. Any degree of desiccation decreased the vigor index of the embryonic axes which have reached physiological maturation and the decline of vigor index was corresponded to the increase of electrolyte leakage. According to this experiment, the authors concluded that wampee seeds did not gain desiccation-tolerance which was a characteristic of orthodox seeds during development. High water content was essential for maintaining membrane integrity and stabiligy of matured wampee seeds. The injury of seed viability during dehydration could be estimated by using the electro-conductivity method.     

Dehydration effects on imbibitional leakage from desiccation-sensitive seeds

Changes in electrolyte leakage and viability in response to dehydration stress were examined in two species of seeds that do not survive desiccation. Leakage from silver maple (Acer saccharinum L.) seeds increased markedly as seed moisture contents decreased from 45 to 35% (fresh weight basis) and germination decreased from 97 to 5%, coincidentally. Time course curves of imbibitional leakage from areca palm (Chrysalido-carpus lutescens [Bory] Wendl.) embryos showed an increase in both initial leakage and steady-state leakage rates in response to dehydration from an original moisture content of 84 to as low as 53%. Absorbance at 530 nanometers of extracts from triphenyl tetrazolium chloride stained embryos of areca palm was used as a measure of viability. Absorbance decreased significantly in response to dehydration as embryo moisture content decreased from 80 to 30%. Collectively, the data suggest that membranes in the desiccation-sensitive seed tissues studied are damaged by dehydration below a critical moisture content, 40% in silver maple seed and 55% in areca palm embryos, and that the membrane damage contributes to loss of viability.