Effects of Salt Stress on the Activity and the Amount of Tonoplast H+-ATPase from Pea Roots

To study the function and adaptive mechanism of tonoplast H+ATPase under salt stress, pea ( Pisum sativum L.) seedlings were treated with different concentrations of salt （100-250 mmol/L NaCl） and with 100 mmol/L NaCl for different days (1-3 d). The ATP hydrolytic activity and the proton transport activity and the changes of the amount of tonoplast H+ ATPase (subunit A) were measured. ATP hydrolytic activity of H+ATPase prepared from plants treated with 250 mmol/L NaCl was reduced by about 25% compared to that of control plants, but that of stressed plants treated with 100 mmol/L and 200 mmol/L NaCl was unchanged. The activity from plants treated with 100 mmol/L NaCl for up to 3 d was lower than that of control plants by 20%. But the proton transport activity was increased under the same salt stresses as above. These results showed that the changes of the hydrolytic activity and the proton transport activity were not in proportion and salt stress may cause the change of the coupling ratio of H+ transport activity to ATP hydrolysis. The protein amount kept unchanged and reduced a little only when pea was treated with 100 mmol/L NaCl for 3 d. These results indicated that salinity stimulated the increase of the pump efficiency of the V-ATPase from pea roots, which was due to the change of the coupling ratio, but not due to the increase of ATP hydrolysis and the amount of V-ATPase.     

蚕豆保卫细胞质膜水通道蛋白的鉴定及其在气孔运动中的作用

水通道或水通道蛋白是水分运动的主要通道.以RD28 cDNA和RD28抗体为探针证明了蚕豆(Vicia fabaL.)保卫细胞中存在水通道蛋白,并以气孔运动为指标,结合抗体和抑制剂处理证明水通道蛋白是水分运动的主要通道.研究表明编码质膜水通道蛋白的RD28转录体在叶片保卫细胞、叶肉细胞和维管束中高表达,尤以保卫细胞中最多;荧光免疫染色和Confocal显微镜观察表明,RD28抗体反应主要位于保卫细胞质膜.进一步采用RD28抗体和水通道蛋白抑制剂--HgCl2 (25μmol/L)处理可抑制壳梭孢素(FC)、光照诱导的气孔开放和原生质体体积膨胀以及ABA诱导的气孔关闭,但这种抑制作用可以被水通道抑制剂的逆转剂β-巯基乙醇(ME)逆转.表明蚕豆保卫细胞中存在水通道蛋白并参与蚕豆保卫细胞的运动过程.     

An Arabidopsis glutathione peroxidase functions as both a redox transducer and a scavenger in abscisic acid and drought stress responses

We isolated two T-DNA insertion mutants of Arabidopsis thaliana GLUTATHIONE PEROXIDASE3 (ATGPX3) that exhibited a higher rate of water loss under drought stress, higher sensitivity to H(2)O(2) treatment during seed germination and seedling development, and enhanced production of H(2)O(2) in guard cells. By contrast, lines engineered to overexpress ATGPX3 were less sensitive to drought stress than the wild type and displayed less transpirational water loss, which resulted in higher leaf surface temperature. The atgpx3 mutation also disrupted abscisic acid (ABA) activation of calcium channels and the expression of ABA- and stress-responsive genes. ATGPX3 physically interacted with the 2C-type protein phosphatase ABA INSENSITIVE2 (ABI2) and, to a lesser extent, with ABI1. In addition, the redox states of both ATGPX3 and ABI2 were found to be regulated by H(2)O(2). The phosphatase activity of ABI2, measured in vitro, was reduced approximately fivefold by the addition of oxidized ATGPX3. The reduced form of ABI2 was converted to the oxidized form by the addition of oxidized ATGPX3 in vitro, which might mediate ABA and oxidative signaling. These results suggest that ATGPX3 might play dual and distinctive roles in H(2)O(2) homeostasis, acting as a general scavenger and specifically relaying the H(2)O(2) signal as an oxidative signal transducer in ABA and drought stress signaling.     

Induction characteristics and response of photosynthetic quantum conversion to changes in irradiance in mulberry plants

A study was conducted, using rapid time course of chlorophyll (Chl) fluorescence parameters, and light-response curves of Chl fluorescence parameters, to determine the induction requirements and response of photosystem II (PSII) photochemistry and non-photochemical reactions after changes in irradiance in greenhouse mulberry plants. The induction of PSII photochemistry rapidly approached to steady state after leaves were treated from darkness to low irradiance (LI). When irradiance of leaves changed from darkness to high irradiance (HI), a biphasic induction was observed. A slight photoinhibition occurred in the leaves exposed to sunlight coming to the greenhouse, whereas a chronic photoinhibition occurred in the leaves fully exposed to sunlight outside the greenhouse. The chronic photoinhibition was demonstrated by sustained reduction of maximal quantum yield of PSII photochemistry (Fv/Fm). Moreover, the leaves of mulberry plants in greenhouse were sensitive to abrupt changes in irradiance and the sensitivity of leaves suffered in a short-term (1h) high light treatment was reduced, based on the changes in photosynthetic quantum conversion. These results demonstrated an inducible response of photosynthetic quantum conversion to changes in irradiance in mulberry.     

蚕豆水孔蛋白可能参与微丝骨架对气孔运动的调节

水孔蛋白的抑制剂HgCl2可明显抑制壳梭孢菌素（FC）和微丝骨架的解聚剂细胞松弛素D（CD）对蚕豆保卫细胞原生质体膨胀的诱导作用,而对微丝骨架的稳定剂鬼笔环肽（phalloidin）的抑制作用影响不明显。这表明水孔蛋白可能介导了FC和微丝骨架对气孔运动的调节。     

Revealing the F_actin Networks in Interphase Nuclei of Garlic Clove Cells by Confocal Fluorescence Microscopy

The interphase nuclei of parenchyma cells and epidermal cells of garlic (Allium sativum L.) clove were labelled with rabbit anti-actin antibody and FITC-conjugated goat anti-rabbit IgG antibody. The authors observed results with fluorescence microscopy and confocal laser scanning microscopy. The nuclei showed prominent green-yellow fluorescence, indicating the presence of actin in the nuclei. Fluorescence examination with TRITC-phalloidin showed distinctive red fluorescence in the nuclei, indicating that F-actin is present in the nuclei. Confocal laser scanning microscopy indicated the presence of F-actin containing network structures in the nuclei, but the network structures were absent and the nuclei still showed red fluorescence when the cells were treated with cytochalasin D before fixation; the red fluorescence in the nuclei was hard to be observed when the cells were treated with unlabelled phalloidin before the cells were stained with TRITC-phalloidin. These results indicate that F-actin is in the nuclei and forms network structures in the nuclei of garlic cells.     

植物水通道蛋白及其活性调节

水通道蛋白是对水专一的通道蛋白,普遍存在于动、植物及微生物中。研究表明高等植物的质膜和液泡膜上存在着丰富的水通道蛋白,其种类繁多,分布广泛,并具有一定的组织特异性。植物水通道蛋白的活性受到严格的调控,其调节方式主要有两种,分别为基因水平的表达调控和翻译后的修饰作用。