明适应条件下鲤属鱼L-型外水平细胞反应的给光-瞬变成分

在明适应条件下鲤属鱼 L-型外水平细胞的反应显示明显的给光-瞬变成分(on-transient)、它与刺激波长有关——对蓝、绿光的反应比对红光的反应有更明显的瞬变成分,其光谱特性提示它与绿敏锥细胞的输入信号有关。与已报道的其它动物 L 型水平细胞的给光-瞬变成分不同,它的出现在一定范围内与网膜受照射的面积无关。绿色(502nm)和红色(706nm)闪光同时照射所引起反应的给光-瞬变成分比各自单独刺激时要显著得多,提示它也与绿敏锥细胞和红敏锥细胞输入的相互作用有关。     

A new pollen type,C-banded and fluorochrome counterstained chromosomes,and evolution inGuatteria and related genera (Annonaceae)

Guatteria, Guatteriopsis, Guatteriella andHeteropetalum share the same conspicuous pollen type which is new for theSpermatophyta. It is zonoaperturate with a folded aperture region and an extremely reduced exine. First chromosome counts and karyotype analyses forGuatteriopsis (4 species investigated) andGuatteriella (1 species) are identical with those ofGuatteria (19 species seen): 2n = 28. The genome is characterized by diploidization and partly telocentric chromosomes. Sequentially Giemsa C- and fluorochrome banded chromosomes and interphase nuclei are described. The cuticular folding pattern is distinct forHeteropetalum only. Growth forms and ecology are reported for many species. The evolutionary pattern of theGuatteria group is discussed and compared with other genera and families.     

Purification and properties of indole 2,3-dioxygenase from maize leaves

An indole 2,3-dioxygenase was purified ca 38-fold from maize leaves. The enzyme had an MW of about 98000, an optimum pH of 5.0 and the energy of activation was 9.1 kcal/mol. The K_max for indole was 1.4 × 10^?4 M. The enzyme was inhibited by diethyldithiocarbamate, salicylaldoxime and sodium dithionite. The inhibition by diethyldithiocarbamate was specifically reversed by Cu²⁺. The dialysed enzyme was stimulated by Cu²⁺. Four atoms of oxygen were utilized in the disappearance of 1 mole of indole. Inhibition of the enzyme by -SH compounds and -SH group inhibitors, and their partial removal by Cu²⁺ only, suggested the involvement of -SH groups in binding of Cu²⁺ at the catalytic site.     

Occurrence of esterified triterpenoid alcohols in the leaves of Pilosella officinarum

The mature winter leaves of Pilosella officinarum coll. Schultz and Schultz contained 29 mg esterified triterpenoid alcohols (g dry weight)⁻¹, of which over 80% was esterified with long-chain (C16-C18) fatty acids. The major fatty acids were 16:0, 18:2ω6 and 18:3ω3 and their amounts varied according to the season and stage of leaf development. In mature leaves the amount of triterpenoid alcohols esterified with long-chain fatty acids varied only slightly with the season. The changes in the fatty acid proportions in late winter-early spring, however, indicated a turnover in the esterified triterpenoid alcohol pool. In late winter after the snow had melted a 50% decrease occurred in the amount of triterpenoid alcohols esterified with short-chain fatty acids. The amount of esterified triterpenoid alcohols in immature leaves was relatively low [4 mg (g dry weight)⁻¹].
In the mature leaves esterified triterpenoid alcohols were found in globules whose appearance varied greatly according to the season. The globules were partly dissolved in late winter, and this together with the activation of respiration, suggests that the globules function as short-term energy reservoirs. Relationships between the appearance of lipid globules and the amount of esterified triterpenoid alcohols are discussed.     

水稻叶片衰老过程中氨肽酶活性的变化

水稻叶片中存在着氨肽酶,其最适反应pH和最适反应温度分别为8.2℃和40℃,酶促反应的产物量在最初30min内与时间呈直线相关。 水稻叶片衰老过程中叶绿素和蛋白质含量下降,而氨肽酶比活上升;用植物激素延缓或促进叶片衰老蛋白质降解的同时也抑制或促进了氨肽酶比活的上升,说明氨肽酶在水稻叶片衰老蛋白质降解过程中起一定的作用。根据水稻叶片衰老过程中大分子化合物和叶片外部形态的变化,可将叶片衰老过程划分为缓衰期、急衰期和竭衰期。     

Specialized formations of endoplasmic reticulum in parenchyma cells ofMimosa pudica L.

Summary Parenchyma cells ofMimosa pudica display close associations between two or more cisternae of the endoplasmic reticulum. These associations form simplified types of lamellar bodies in which inner paired lamellae have lost their ribonucleoprotein granules and are separated by a dense layer.     

Photosynthetic electron transport and establishment of an associated trans-thylakoid proton electrochemical gradient during development of the wheat leaf

Abstract Photosynthetic electron transport activities and the ability to generate and maintain a trans-thylakoid proton electrochemical gradient were examined during chloroplast development in 4-day-old wheat leaves grown under a diurnal light regime. Polarographic and spectropholometric studies on leaf tissue demonstrated that poorly developed chloroplasls at the leaf base could photo-oxidize water and transfer electrons from photosystem 2 to photosystem 1. The capacity for non-cyclic whole-chain electron transport increased during chloroplast development. Thylakoids isolated from the leaf base, although capable of pumping protons into the inlrathylakoid space, could not maintain a trans-membrane proton electrochemical gradient; this ability developed at later stages of chloroplast biogenesis in the leaf. The implications of these results for the energetics of the developing leaf are discussed.     

The senescence retarding ability and metabolism of trihydroxy-zeatin in Avena leaf segments

6-(2,3,4-Trihydroxy-3-methylbutylamino) purine, trivial name trihydroxy-zeatin (THZ), an oxidation product of zeatin was applied via the epidermis or cut end of Avena leaf segments. THZ did not retard senescence of the segments in either case. With epidermal application THZ remained unmetabolised while the cut end method of application resulted in its metabolism to more polar THZ metabolites of unknown identity. The Avena leaf tissue did not apparently cleave the isoprenoid side chain of the THZ molecule.     

Leaf senescence in a non-yellowing mutant of Festuca pratensis: Photosynthesis and photosynthetic electron transport

The photosynthetic capacity of detached leaves of a non-yellowing mutant of Festuca pratensis Huds. declined during senescence at a similar rate to that in a normal cultivar. Respiratory oxygen uptake in the dark continued at similar rates in both genotypes during several days of senescence. In chloroplasts isolated from leaves at intervals after excision, the rate of photosystem I (PS I)-mediated methyl viologen reduction using reduced N,N,N,N-tetramethyl-p-phenylene diamine as electron donor also declined in both genotypes, possibly due to loss of integrity of the photosynthetic apparatus in the cytochrome f-plastocyanin region. There was a similar fall in PS II electron transport using water as electron donor and measured at the rate of reduction of 2,6-dichlorophenolindophenol. Partial restoration of this activity by the addition of diphenyl carbazide was evidence for lability of the oxygen-evolving complex during senescence. An accentuated difference between mutant and normal material in this case indicated that the mutant retains a greater number of functional PS II centres. Changes in the light-saturation characteristics of the two photosystems have been discussed in relation to the organization of the photosynthetic membranes during senescence.Abbreviations and symbols DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - DCPIP 2,6-dichlorophenolindophenol - DMSO dimethyl sulphoxide - DPC diphenyl carbazide - MV methyl viologen - PS I, PS II photosystem I, II - TMPD N,N,N,N-tetramethyl-p-phenylene diamine     

The effect of oxygen on nitrate and nitrite assimilation in leaves of Zea mays L. under dark conditions

The assimilation of nitrate under dark-N₂ and dark-O₂ conditions in Zea mays leaf tissue was investigated using colourimetric and ¹⁵N techniques for the determination of organic and inorganic nitrogen. Studies using ¹⁵N indicated that nitrate was assimilated under dark conditions. However, the rate of nitrate assimilation in the dark was only 28% of the rate under non-saturating light conditions. No nitrite accumulated under dark aerobiosis, even though nitrate reduction occurred under these conditions. The pattern of nitrite accumulation in leaf tissue in response to dark-N₂ conditions consisted of three phases: an initial lag phase, followed by a period of rapid nitrite accumulation and finally a phase during which the rate of nitrite accumulation declined. After a 1-h period of dark-anaerobiosis, both nitrate reduction and nitrite accumulation declined considerably. However, when O₂ was supplied, nitrate reduction was stimulated and the accumulated nitrite was rapidly reduced. Anaerobic conditions stimulated nitrate reduction in leaf tissue after a period of dark-aerobic pretreatment.