Further Characterization of the Red Beet Plasma Membrane Ca-ATPase Using GTP as an Alternative Substrate

The GTP-driven component of Ca²⁺ uptake in red beet (Beta vulgaris L.) plasma membrane vesicles was further characterized to confirm its association with the plasma membrane Ca²⁺-translocating ATPase and assess its utility as a probe for this transport system. Uptake of ⁴⁵Ca²⁺ in the presence of GTP demonstrated similar properties to those previously observed for red beet plasma membrane vesicles utilizing ATP with respect to pH optimum, sensitivity to orthovanadate, dependence on Mg:substrate concentration and dependence on Ca²⁺ concentration. Calcium uptake in the presence of GTP was also strongly inhibited by erythrosin B, a potent inhibitor of the plant plasma membrane Ca²⁺-ATPase. Furthermore, after treatment with EGTA to remove endogenous calmodulin, the stimulation of ⁴⁵Ca²⁺-uptake by exogenous calmodulin was nearly equivalent in the presence of either ATP or GTP. Taken together these results support the proposal that GTP-driven ⁴⁵Ca²⁺ uptake represents the capacity of the plasma membrane Ca²⁺-translocating ATPase to utilize this nucleoside triphosphate as an alternative substrate. When plasma membrane vesicles were phosphorylated with [γ-³²P]-GTP, a rapidly turning over, 100 kilodalton phosphorylated peptide was observed which contained an acyl-phosphate linkage. While it is proposed that this peptide could represent the catalytic subunit of the plasma membrane Ca²⁺-ATPase, it is noted that this molecular weight is considerably lower than the 140 kilodalton size generally observed for plasma membrane Ca²⁺-ATPases present in animal cells.     

Adaptation and growth of tomato cells on the herbicide 2,6-dichlorobenzonitrile leads to production of unique cell walls virtually lacking a cellulose-xyloglucan network

Suspension-cultured cells of tomato (Lycopersicon esculentum VF 36) have been adapted to growth on high concentrations of 2,6-dichlorobenzonitrile, an herbicide which inhibits cellulose biosynthesis. The mechanism of adaptation appears to rest largely on the ability of these cells to divide and expand in the virtual absence of a cellulose-xyloglucan network. Walls of adapted cells growing on 2,6-dichlorobenzonitrile also differ from nonadapted cells by having reduced levels of hydroxyproline in protein, both in bound and salt-elutable form, and in having a much higher proportion of homogalacturonan and rhamnogalacturonan-like polymers. Most of these latter polymers are apparently cross-linked in the wall via phenolic-ester and/or phenolic ether linkages, and these polymers appear to represent the major load-bearing network in these unusual cell walls. The surprising finding that plant cells can survive in the virtual absence of a major load-bearing network in their primary cell walls indicates that plants possess remarkable flexibility for tolerating changes in wall composition.     

龟背竹的快速繁殖

龟背竹(Monstera deliciosa Liebm.)系天南星科(Araceae)龟背竹属(Monstera)的一种多年生木质藤本攀缘性常绿灌木,生于林中,攀缘树上。龟背竹幼苗的叶片呈披针状长圆形,全缘。大苗的老叶叶片大,轮廓心状卵形,宽40—60厘米,厚革质,表面发亮,淡绿色,背面绿白色,边缘羽状分裂,侧脉间有1—2个较大的空洞,靠近中肋者多为横圆形,宽1.5—4厘米,向外的为横椭圆形,宽5—6厘米。各热带     

水分胁迫对小麦叶片光合作用的影响及其与抗旱性的关系

在水分胁迫初期,两个小麦品种叶片光合速率,气孔导度和细胞间隙CO_2浓度降低,气孔限制值增加,光合速率的降低主要是气孔因素的限制。中度到严重水分胁迫使叶片光合速率、气孔导度和气孔限制值降低,细胞间隙CO_2浓度明显增加,且叶圆片放氧能力,叶绿体Hill反应、叶绿素荧光强度和表观量子产额降低,此时光合速率的降低主要是叶肉细胞光合活性的下降引起的。抗旱性弱的郑引一号叶肉细胞光合活性比抗旱性强的丰抗13更容易受到水分胁迫的影响。     

三种群生态系统的持续生存

1、引言关于三种群生态系统的持续生存的研究已经有了许多结果,应用动力系统的研究方法,文献对一般三种群捕食-被捕食系统和竞争系统的持续生存进行了研究,得到了几个判别法则;文献对一般抽象动力系统的一致持续生存进行了研究,得到了一个充要的判别法则。但是这些法则对系统在边界上的性质要求较高,特别要求系统在边界     

荧光假单胞菌抗噬菌体菌株的选育

本实验从荧光假单胞菌（Ｐｓｅｕｄｏｍｏｎａｓｆｌｕｏｒｅｓｃｅｎｓ）ＡＳ—３菌株的不正常发酵液中分离到一种噬菌体,将其命名为ＰＦＡＳ。ＡＳ—３菌株能利用葡萄糖发酵产生Ｄ－异维生素Ｃ的前体物质２－酮基－Ｄ－葡萄糖酸。电镜观察表明ＰＦＡＳ噬菌体呈蝌蚪形,具有直径为６６ｎｍ的六角形头部及长１１７ｎｍ的尾部。通过紫外线诱变及自然选育两种途径,配合简便有效的初筛方法,经多次分离、纯化、复筛最终在摇并发酵试验中获得６株产量稳定地高于对照敏感菌的抗噬菌体菌株,可望用于生产。     

Photosystem II Excitation Pressure and Photosynthetic Carbon Metabolism in Chlorella vulgaris

Chlorella vulgaris grown at 5[deg]C/150 [mu]mol m-2 s-1 mimics cells grown under high irradiance (27[deg]C/2200 [mu]mol m-2 s-1). This has been rationalized through the suggestion that both populations of cells were exposed to comparable photosystem II (PSII) excitation pressures measured as the chlorophyll a fluorescence quenching parameter, 1 - qP (D.P. Maxwell, S. Falk, N.P.A. Huner [1995] Plant Physiol 107: 687-694). To assess the possible role(s) of feed-back mechanisms on PSII excitation pressure, stromal and cytosolic carbon metabolism were examined. Sucrose phosphate synthase and fructose-1,6-bisphosphatase activities as well as the ratios of fructose-1,6-bisphosphate/fructose-6-phosphate and sucrose/starch indicated that cells grown at 27[deg]C/2200 [mu]mol m-2 s-1 appeared to exhibit a restriction in starch metabolism. In contrast, cells grown at 5[deg]C/150 [mu]mol m-2 s-1 appeared to exhibit a restriction in the sucrose metabolism based on decreased cytosolic fructose-1,6- bisphosphatase and sucrose phosphate synthase activities as well as a low sucrose/starch ratio. These metabolic restrictions may feed-back on photosynthetic electron transport and, thus, contribute to the observed PSII excitation pressure. We conclude that, although PSII excitation pressure may reflect redox regulation of photosynthetic acclimation to light and temperature in C. vulgaris, it cannot be considered the primary redox signal. Alternative metabolic sensing/signaling mechanisms are discussed.     

Fourier analysis of potential oscillations of a liquid membrane for the discrimination of taste substances

Electrical potential oscillations were obtained across a liquid membrane composed of nitrobenzene/picric acid placed between two aqueous phases in the presence of various taste (i.e. salty, sweet and bitter) substances. The influence of these compounds on electrical oscillations was studied using Fourier analysis to establish a "fingerprint" of the substance that can be correlated with its taste index. Various concentrations of each substance were tested to obtain a Fourier spectrum with discrete peaks which can be further processed. The electrical oscillations consisted of a number of weak damped oscillators, and the Fourier spectra of these signals were found to have a number of discrete peaks of decreasing amplitude at low frequencies (0-0.5 Hz). A correlation of the frequency of the first peak of the Fourier spectrum with the taste index was found for bitter substances, whereas for salty substances the amplitude of the first two peaks of the spectrum was correlated with the taste index.