A modified fluorometric method to quantify the concentration effect (pI50) of photosystem II-inhibiting herbicides

Chlorophyll fluorescence induction curves of isolated thylakoids were measured in the absence and in the presence of various concentrations of photosystem II-inhibiting herbicides. A mathematical program was applied to simulate the curves. Based on these simulated curves a new method is developed to determine the concentration effect (pI₅₀) of the herbicides. The results of the new method correspond well with reported values in the literature. The method is very convenient and time-saving.     

Manganese modulates the responses of nitrogen-supplied and Rhizobium-nodulated Phaseolus vulgaris L. to inoculation with arbuscular mycorrhizal fungi

In Venezuela, low yields of black bean crops are attributed, in part, to the low manganese (Mn) and phosphorus (P) contents in the Quartzipsamment soils where this crop is usually sown. To test this hypothesis, black bean plants were grown in sterilized sand to simulate soil physical properties, were fertilized with increasing Mn concentrations (0.1-20 μM) and inoculated with a commercial mixture of Rhizobium leguminosarum bv phaseoli strains 127K44, 127K89, 127K105 (+Rh), in combination with arbuscular mycorrhizal fungi Scutellospora heterogama and Entrophospora colombiana (+AMF). Non-inoculated plants fertilized with 6 mM NO₃ and 2 mM P served as controls. Plants were harvested at 18, 25, 33, and 40 days after emergence. At all harvests, the greatest growth and highest P and iron (Fe) leaf concentrations occurred in control plants grown in 5 μM Mn. The growth of +AMF plants was promoted at 0.1 μM Mn and inhibited at higher than 1 μM Mn. Whereas, concentrations of 5-10 μM Mn enhanced the growth and the Mn concentrations in leaves of +Rh plants 40 days after emergence. The tripartite symbiosis (+Rh+AMF) decreased growth, nodulation and leaf ureide and chlorophyll concentrations in plants grown in less than 20 μM Mn, imputed to severe ultrastructural alterations in the leaf and nodule tissues. Only +Rh+AMF plants grown in 20 μM Mn were effectively nodulated, AMF colonized and reached the flowering stage, although with diminished growth and low chlorophyll concentrations. Results confirm the high Mn requirement of +Rh plants for growth and nodulation and question the implementation of the tripartite symbiosis to improve yields in early flowering black bean varieties planted in soils deficient in Mn and P.     

低温胁迫下棉叶叶绿体、液胞超微结构的变化

实验通过棉花幼苗期进行低温胁迫试验 ,用透射电镜观察其叶肉细胞超微结构的变化 ,结果表明 :在低温锻炼过程中 ,叶肉细胞内的叶绿体显著变形 ,液泡内出现大量的膜性结构物质 ,而线粒体等其它细胞器则表现较为稳定。     

低温胁迫下植物光合作用的研究进展

低温是影响植物正常生长的主要非生物胁迫因子之一,严重威胁农作物的产量形成。植物的光合作用对低温十分敏感,就低温胁迫对植物光合作用的影响进行综述,包括细胞器叶绿体、光合色素、净光合效率(A)、气孔导度(Gs)、光化学反应、光合产物的运转与分配,以及植物光合作用的防御机制,为解决低温对植物光合作用的伤害问题提供理论依据。     

Role of water stress in differential aluminum tolerance of six sunflower cultivars grown in an acid soil

Six cultivars of sunflower (Helianthus annuus L.), were screened under controlled environmental conditions for tolerance to Al stress and water stress imposed separately and in combination with one another. Plants were grown for 4 weeks in waxed cartons containing 1 kg of acid, Al‐toxic Tatum, subsoil (clayey, mixed, thermic, Typic Hapludult) at high (pH 4.3) or low (pH 6.3) Al stress. During the final 2 weeks they were also subjected to low (‐20 to ‐40 kPa) or high (‐60 to ‐80 kPa) water stress. Plant growth responses and symptoms of Al toxicity suggested that a wide range of cultivar sensitivity existed. ‘Manchurian’, ‘S‐212’, ‘S‐254’, and ‘S‐265’ were relatively tolerant to Al toxicity while cultlvars ‘Romania HS‐52’ and ‘RM‐52’ were extremely sensitive. Under high Al stress and high water stress, chloroplasts in cells from the Al‐sensitive cultivar ‘Romania HS‐52’ were smaller and contained less starch than chloroplasts from the Al‐tolerant cultivar ‘Manchurian’. Furthermore, the smaller chloroplasts tended to have fewer grana stacks per unit area than did the chloroplasts from tolerant plants. These differences were not apparent when the Al‐sensitive cultivar was grown either in the absence of Al or water stress. In general, Al‐sensitive cultivars of sunflower were more tolerant to water stress than were Al‐tolerant cultivars. Increasing the soil moisture level reduced Al toxicity in Al‐sensitive cultivars. Similarly, decreasing Al stress partially overcame the detrimental effects of high water stress. Hence, Al stress and water stress are interrelated factors which must be considered in the characterization and breeding of plants for better adaptation to acid soils.     

黄化西瓜叶片叶绿体结构与光合作用特性

对黄化西瓜的黄化性状表现及叶绿素含量、光合速率等指标的测定和叶绿体超显微结构进行了观察,结果表明,黄化西瓜叶绿素含量低,相当于绿叶西瓜中育1号(CK)的55%;叶绿体的发育明显差于对照品种,表现为基粒窄、片层数少、基粒在叶绿体中分布稀疏;黄化西瓜光合速率较低,仅为CK的73.5%～75.8%,地上部全生物量为CK的76%,对光合作用测定相关参数的分析认为黄化西瓜叶绿素含量低是光合速率低的惟一原因;黄化西瓜的光补偿点高达157μmol/m2·s,表明尽管其单位叶面积光合速率较低,但消耗仍然维持了相当的水平。     

甘蓝型油菜黄化(苗)突变体的叶绿素含量及超微结构

用氮离子处理双低高含油量甘蓝型油菜新品系 HDY-8种子 ,M1 出现了一株失绿黄化而后复绿的突变体 ,其 M2 仍有三分之一的植株出现黄化反应。叶绿素含量测定和叶绿体超微结构观察发现 :黄叶、黄绿叶的叶绿素含量明显低于绿叶 ,而叶绿素 a与叶绿素 b的比值又大于绿叶。黄叶细胞内叶绿体数量少 ,形状不规则 ,膜结构已解体 ,无类囊体 ,叶绿体内无淀粉粒 ,嗜锇颗粒较多 ;黄绿叶细胞内叶绿体数目较多 ,形状规则 ,基粒片层清晰可见 ,内有淀粉粒 ;绿叶细胞内叶绿体较多 ,形状规则 ,基粒片层清晰 ,其内淀粉粒多而大 ,嗜锇颗粒较少     

Changes in pigments and plastid ultrastructure during ripening of green-fleshed and yellow-fleshed kiwifruit

Fruit of Actinidia deliciosa have green flesh when ripe, whereas fruit of Actinidia chinensis often have yellow flesh when ripe. The outer and inner pericarps of A. deliciosa fruit retain their chlorophyll during ripening. In those fruit of A. chinensis that become yellow on ripening, the colour change is caused by the disappearance of chlorophylls unmasking the yellow carotenoids already present, rather than by increased synthesis of carotenoids. In fruit of A. deliciosa and those fruit of A. chinensis that remain green, the chloroplasts retain their typical morphology during ripening, whereas in fruit of A. chinensis that become yellow during ripening the chloroplasts of the immature green fruit are transformed into fully developed chromoplasts.     

Some factors controlling carotene destruction by chloroplasts in vitro

Loss of carotene from moist leaf protein stored with a preservative, is closely simulated by the destruction of carotene by acetone extracted chloroplasts (stroma) suspended in acetone containing 30% water. During this exposure, stroma lose destructive ability, but it is restored by mercaptoacetate and other reducing agents. Stroma can therefore be used repeatedly. This catalytic process is activated by removing intrinsic inhibitors, predominantly calcium, by extraction at pHs less than 4, or by alum. The objective is to find inhibitors which would be acceptable in a food. That restricts choice. Citrate, tartarate and phosphate are among the more attractive possibilities.