固定化酶的微环境效应—载体离子基团性质的影响

作者合成了阴离子型和阳离子型葡聚糖,以此为载体,用CNBr活化其剩余羟基,固定化了葡萄糖淀粉酶和葡萄糖异构酶。就离子型载体对固定化酶的蛋白载量、最适pH和热稳定性等的影响做了考察。发现固定化酶的蛋白载量不仅与载体的电性质有关,也与酶分子自身的电性质有关。当载体电性质与酶蛋白电性质相反时,固定化酶的蛋白载量增加,热稳定性提高、载体电性质与酶蛋白电性质相同时,固定化酶的蛋白载量不变或下降,其热稳定性不变。作者还发现当离子型载体孔度和体系缓冲液浓度一定时,酶分子能否进入多孔性载体内部,对其最适pH是否变化影响极大。若酶分子仅被连接在载体的外表层,其最适pH不发生变化,反之亦然。作者还观察到当多糖类载体引入氨基或羧基后,大大增强了其抵抗微生物侵蚀的能力。     

稀土和赤霉素对杨树杂交种子发芽率的影响

本试验采用(银白杨×毛白杨)×唐柳[(Popu-lus alba×P.tomentosa)×P.pseudo-simonii]的室内     

评《光合作用——光子、激子、电子、质子、离子与光合膜之间的相互作用》一书

本书作者葛培根教授系美籍华裔学者,是国际上著名的光合作用专家,并享有很高的声誉。他长期在具有重要影响的光合作用研究中心 Kettering Research Laboratory 主持光合作用研究。光合作用研究的核心问题是光能转化的机理——光合作用的原初反应,即光子、激子、电子、质子、离子与光合膜之间的相互作用。这是光合作用研究中最富于挑战的领域。葛培根教授几十年来在这个研究领域中作出了杰出的贡献,推动了光合作用研究的发展。     

Metabolic bases for differences in sensitivity of two pea cultivars to sulfur dioxide

An oxidative chain reaction of sulfite initiated by the superoxide ion produced in the Mehler reaction has been implicated in the damage of plants exposed to sulfur dioxide. The toxicity of SO₂ may be alleviated by free radical scavenging systems acting to terminate this chain reaction. Hence, the relative sensitivity of plants to SO₂ toxicity could depend on differences in the responses of the levels of antioxidant metabolites and enzymes. The effect of SO₂ exposure on glutathione and ascorbic acid contents, glutathione reductase, and superoxide dismutase activities was assayed in two cultivars (Progress, Nugget) of pea (Pisum sativum L.) in which apparent photosynthesis showed a differential sensitivity to 0.8 microliter per liter SO₂ (R. Alscher, J. L. Bower, W. Zipfel [1987] J Exp Bot 38:99-108). Total and reduced glutathione increased more rapidly and to a greater extent in the insensitive Progress than in the sensitive Nugget, as did glutathione reductase activities. Superoxide dismutase activities increased significantly in Progress, whereas no such change was observed in Nugget as a result of SO₂ exposure. This increase in superoxide dismutase activity was observed at 210 minutes after 0.8 microliter per liter SO₂ concentration had been reached, in marked contrast to the increases in reduced glutathione content and glutathione reductase activity, which were apparent at the 90 minute time point. These data suggest that one basis for the relative insensitivity of the apparent photosynthesis of the pea cultivar Progress to SO₂ is the enhanced response of glutathione reductase, superoxide dismutase activities, and glutathione content.     

Photophosphorylation in Attached Leaves of Helianthus annuus at Low Water Potentials

The in situ response of photophosphorylation and coupling factor activity to low leaf water potential (ψ_L) was investigated using kinetic spectroscopy to measure the flash-induced electrochromic absorption change in attached sunflower (Helianthus annuus L. cv IS894) leaves. The electrochromic change is caused by the formation of an electric potential across the thylakoid membrane associated with proton uptake. Since depolarization of the thylakoid membrane following flash excitation is normally dominated by proton efflux through the coupling factor during ATP formation, this measurement can provide direct information about the catalytic activity of the coupling factor. Under low ψ_L conditions in which a clear nonstomatal limitation of net photosynthesis could be demonstrated, we found a strong inhibition of coupling factor activity in dark-adapted leaves which was probably caused by an increase in the energetic threshold for the activation of the enzyme at low ψ_L. While this result supported earlier in vitro findings, we further discovered that the light-dependent reduction of coupling factor reversed any observable effect of low ψ_L on the energetics of activation or on photophosphorylation competence. Furthermore, coupling factor was reduced, even in severely droughted sunflower, almost immediately upon illumination. Based on these measurements, we conclude that the nonstomatal limitation of photosynthesis observed by us and others in droughted plants cannot be explained by impaired coupling factor activity.     

Comparison of Modeled and Observed Environmental Influences on the Stable Oxygen and Hydrogen Isotope Composition of Leaf Water in Phaseolus vulgaris L

In this paper we describe how a model of stable isotope fractionation processes, originally developed by H. Craig and L. I. Gordon ([1965] in E Tongiorgi, ed, Proceedings of a Conference on Stable Isotopes in Oceanographic Studies and Paleotemperature, Spoleto, Italy, pp 9-130) for evaporation of water from the ocean, can be applied to leaf transpiration. The original model was modified to account for turbulent conditions in the leaf boundary layer. Experiments were conducted to test the factors influencing the stable isotopic composition of leaf water under controlled environment conditions. At steady state, the observed leaf water isotopic composition was enriched above that of stem water with the extent of the enrichment dependent on the leaf-air vapor pressure difference (VPD) and the isotopic composition of atmospheric water vapor (AWV). The higher the VPD, the larger was the observed heavy isotope content of leaf water. At a constant VPD, leaf water was relatively depleted in heavy isotopes when exposed to AWV with a low heavy isotope composition, and leaf water was relatively enriched in heavy isotopes when exposed to AWV with a large heavy isotope composition. However, the observed heavy isotope composition of leaf water was always less than that predicted by the model. The extent of the discrepancy between the modeled and observed leaf water isotopic composition was a strong linear function of the leaf transpiration rate.     

A 150 Kilodalton Cell Surface Protein Is Induced by Salt in the Halotolerant Green Alga Dunaliella salina

Dunaliella salina is an extremely halotolerant, unicellular, green alga lacking a rigid cell wall. Osmotic adaptation to high salinities is based on the accumulation of glycerol. To uncover other functions responsible for halotolerance, protein profiles of algae continuously grown in different salinities were compared. A 150 kilodalton protein (p 150) increased in amount with salt concentration. Furthermore, when the cells were subjected to drastic hyperosmotic shocks, p150 started to rise long after completion of the osmotic response but coincident with reinitiation of cell proliferation. Cells with an initially higher level of p150 resumed growth faster than cells with a lower level of the protein. Addition of cycloheximide early after hyperosmotic shock prevented the rise in p150, indicating this rise was due to de novo synthesis of the protein. These observations suggest that p150 is a saltinduced protein required for proliferation of the cells in saline media. p150 was purified to homogeneity and found to be a detergent-soluble glycoprotein. Polyclonal antibodies against p150 recognized a single protein component in D. salina crude extracts. A high M_r cross-reacting protein was also observed in another Dunaliella strain, D. bardawil. Immunoelectron microscopy localized p150 to the cell surface.