| The young grape plants (Vitis viniferaXV.labrussa L. cv. Jingxiu)were used as materials to study on the mechanisms of thermotolerance induced by heat acclimation or exogenous salicylic acid(SA), and probe the way of SA signal transduction. The results obtained were as following:Ultrastructural changes of the mesophyll cells under heat stress were observed via transmission electron microscope. Under heat stress at 45±0.5℃ for 3h or 6h, the ultrastructure of normal mesophyll cells was damaged remarkably. There was a little change of ultrastructure after the leaves pretreated with heat acclimation, but heat acclimation pretreatment delayed the ultrastructural damage induced by heat stress, principally showing in plasmolemma, vacuole membrane, nucleus and chloroplasts. No ultrastructural change showed after SA pretreatment, but the degree of ultrastructional damage after SA pretreatment was less than that of H2O pretreatment while the leaves under heat stress.The activity of H+-ATPase or Ca2+-ATPase of plasmolemma was studied with biochemistry assay in which the method of two-phase partition was used to purify plasmolemma and electromicroscopic-cytochemical location in which cerium trichloride precipitation method was adopted. At last, the results were almost same. After the young plants were treated with heat acclimation or SA, H+-ATPase or Ca2+-ATPase activity of plasmolemma was higher than that of control or H2O pretreatment, and enhanced the stability of H+-ATPase or Ca2+-ATPase activity under the following heat stress. If the young plants were stressed at 45 ± 0.5℃ for 6h, the H+-ATPase activity of plasmolemma of heat acclimation or SA pretreatment was 7.1 or 3.7 times than that of control or H2O pretreatment, however, the Ca2+-ATPase activitiy of plasmolemma of heat acclimationor SA pretreatment was 4.4 or 4.6 times than that of control or H2O pretreatment. Through observation of electromicroscope, the H+-ATPase or Ca2+-ATPase activity of plasmolemma of heat acclimation or SA pretreatment remained active after heat stress at 45±0.5℃ for 6h, but the activity of control or H2O pretreatment was completely inactive. These results showed that the young plantings thermotolerance induced by heat acclimation or SA pretreatment was related with the H+-ATPase or Ca2+-ATPase activity of plasmolemma, heat acclimation and SA almost had the same regulating mechanism. In addition, the Fe (CN) 63- reduction of plasmolemma in leaf cells of heat-acclimated young plants was enhanced and kept higher level under the following heat stress, but SA pretreatment had no effect on the Fe (CN)63- reduction of plasmolemma.Effect of Ca2+ on the young plants thermotolerance induced by SA was studied with pretreatment of Ca2+ and antagonists of Ca2+ or CaM. The results showed that Ca2+ enhanced the SA-induced thermotolerance. In contrast, pretreatment with the Ca2+ chelator EGTA, the plasmolemma Ca2+ channel blockers La3+, which was expected to inhibit the influx of extracellular Ca2+ into cells, and the CaM antagonist W7 weakened the SA-induced thermotolerance. Pretreatmentwith SA or Ca2+( SA+Ca2+) increased CaM content of leaves, but EGTA(SA+ EGTA ), La3+(SA+ La3+) or W7(SA+ W7) decreased the CaM content of leaves under heat stress at 45±0.5# for 3h. SA pretreatment enabled young plants to maintain higher activity of SOD or CAT and a lower level of MDA to weaken oxidative stress induced by heat stress. However, Ca2+ pretreatment enhanced the activity of SOD or CAT SA-induced, but EGTA, La3+ and W7 had a contrary effect. POD or APX activity of each treatment had little change before and after heat stress. In addition, pretreatment of SA or Ca2+ (SA+Ca2+) enhanced the content of proline and kept higher level under heat stress. These results showed that SA-induced thermotolerance was medicated by Ca2+ and required the entry of extracellular Ca2+ into cells through plasmolemma, and was related with antioxidant enzymes and proline.The midst leaf of young planting was fed with 14C-SA, and the other side leaf above... |
PDF Full Text Request