Do the higher oxidation states of the photosynthetic O2-evolving system contain bound H2O?

A modified mass spectrometer was used to determine whether the higher oxidation states of the photosynthetic O2-evolving system contain substrate water that is not freely exchangeable with the external medium. Our data indicated that the higher oxidation states contain no appreciable bound, non-exchangeable H2O. This suggests that H2O oxidation takes place via a rapid, concerted, all-or-none mechanism rather than by a mechanism involving stable, partially oxidized, H2O-derived intermediates. These findings set definite constraints on possible mechanisms of O2 evolution.     

阿尔金山地区奥陶纪头足类

阿尔金山地区的奥陶系分布于索尔库里和色什考贡的断块中,首先为新疆区调队发现。1979年,该队在索尔库里以北金鸿山西北乱石山东南7km处(东经90°59′;北纬39°)测制了奥陶系剖面,自上而下,划分出环形山组、乱石山组和亚普恰萨依组,顶部出露不全,底部平行不整合覆于震旦纪大理岩之上。两个地点的腕足类化石经刘第墉等(1984,156页)研究,认为其时代应主要归于Llandeilian。索尔库里的环形山组厚约414m,上部为深灰色薄层灰岩,下部是深灰色薄层灰岩夹少量细砂岩,产腕足类、笔石和三叶虫化石。从所产三叶虫化石(790H_2-XV-26)Xinjianjia tari     

Translucent Tissue Defects in Solanum tuberosum L. : II. Alterations in Lipolytic Acyl Hydrolase, Lipoxygenase, and Morphology of Mitochondria and Amyloplasts

We analyzed a physiological defect that involved translucent-like tissue which occurred randomly in potato tubers (Solanum tuberosum L., cv Kennebec) after 8 months of storage. The translucent areas had reduced lipoxygenase (0.73-fold) and lipolytic acyl hydrolase (0.27-fold) activities. The effect(s) of these reduced enzyme activities in vivo is uncertain, but they may have influenced composition, turnover and permeability of membranes because potato lipid is primarily membranous in nature. Electron micrographs of the translucent tissue revealed a discernible decrease in the number of starch granules compared to normal/healthy tissue. A few remaining amyloplasts, which still contained starch granules, possessed large electrondense areas (stroma) within the organelle. Mitochondria in translucent tissue appeared to be present in increased numbers, were aggregated, had fewer but swollen cristae, and, morphologically, were of irregular size and shape suggestive of division. The result of this tuber defect appeared, in part, to be an exaggerated or accelerated form of senescence.     

Photocontrol of Dark Circadian Rhythms in Stomata of Phaseolus vulgaris L

Stomatal diffusion resistance in primary leaves of Phaseolus vulgaris L. which had been grown in light:dark cycles followed a marked circadian rhythm when the plants were transferred to continuous darkness. Reentrainment of the rhythm required more than one inductive change in photoperiod. The phasing of the rhythm of dark stomatal opening was contolled primarily by the light-on (dawn) signal, whereas the rhythm of dark closure was related to the light-off (dusk) signal. The evidence points to a dual control of the circadian clock in which a product of photosynthesis plays a major role. No evidence for phytochrome involvement in the phasing of the rhythm was found. An influence of phytochrome on the amplitude of the stomatal rhythm was observed in which removal of phytochrome-far-red absorbing form caused rapid damping.     

Differential Proteolysis of Glycinin and beta-Conglycinin Polypeptides during Soybean Germination and Seedling Growth

The degradation of the major seed storage globulins of the soybean (Glycine max [L.] Merrill) was examined during the first 12 days of germination and seedling growth. The appearance of glycinin and β-conglycinin degradation products was detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis of cotyledon extracts followed by electroblotting to nitrocellulose and immunostaining using glycinin and β-conglycinin specific antibodies. The three subunits of β-conglycinin were preferentially metabolized. Of the three subunits of β-conglycinin, the larger α and α′ subunits are rapidly degraded, generating new β-conglycinin cross-reactive polypeptides of 51,200 molecular weight soon after imbibition of the seed. After 6 days of growth the β-subunit is also hydrolyzed. At least six polypeptides, ranging from 33,100 to 24,000 molecular weight, appear as apparent degradation products of β-conglycinin. The metabolism of the glycinin acidic chains begins early in growth. The glycinin acidic chains present at day 3 have already been altered from the native form in the ungerminated seed, as evidenced by their higher mobility in an alkaline-urea polyacrylamide gel electrophoresis system. However, no change in the molecular weight of these chains is detectable by sodium dodecyl sulfate-polyarylamide gel electrophoresis. Examination of the glycinin polypeptide amino-termini by dansylation suggests that this initial modification of the acidic chains involves limited proteolysis at the carboxyl-termini, deamidation, or both. After 3 days of growth the acidic chains are rapidly hydrolyzed to a smaller (21,900 molecular weight) form. The basic polypeptides of glycinin appear to be unaltered during the first 8 days of growth, but are rapidly degraded thereafter to unidentified products. All of the original glycinin basic chains have been destroyed by day 10 of growth.     

蜜蜂毒溶血活性肽(melittin)的研究进展

蜜蜂毒(下称蜂毒)是很早以来人们就十分关注的毒性物质。在动物毒液中,它是研究得较早的。但对它的组成和作用模式的研究仅有二、三十年。就其组成成分的药理作用和治疗价值,无论在理论上还是在实践上都还很有限。蜂毒中含多种蛋白质和多肽,其多肽成分具较强的药理学和生物学活性,有抗炎镇痛等作用,临床上用于风湿、类风湿和牛皮癣等胶原性疾病的治疗,也可用于高血压及动脉粥样硬化、神经痛等的治疗,总有效率达80％。据报道在蜂毒中至少含有14个生物活性肽:melittin,melittin F,apamine,secapin,     

化学杀雄剂在组织培养过程中对黄瓜的杀雄作用的初步研究

选取黄瓜小孢子单核期的花药以组织培养方法检验铁氰化钾的杀雄效应,并初步探讨该试剂的杀雄机理。实验表明,该试剂在组织培养条件下,使用的浓度范围为0.1—10ppm 时,均显示有杀雄效应。表现为:处理的花药发育缓慢,小孢子变形或外粉壁不能形成。同时处理雌花则作用不明显。通过细胞形态观察,过氧化物酶、核酸、蛋白质及多糖组化定位及花粉壁的扫描电镜观察,初步认为:该试剂的杀雄效应与绒毡层、小孢子的过氧化物酶活性受抑制有关,故为生理性不育。