The Study Of Cross Resistance To Salt Stress And Heat Stress In Atriplex Centralasiatica

Nowadays the researches on cross resistance of the multiple stresses receive more and more attention. The plants living in the saline or alkaline lands not only suffer the harm of salt stress, but also high temperature especially on a hot summer day. In this experiment, we chose Atriplex centralasiatica as the experimental material and studied the cross adaptation mechanism of Atriplex centralasiatica under salt stress and heat stress. The main results were as follows:1. The critical temperature of heat stress in Atriplex centralasiatica and the influence of NaCl treatment on it The net photosynthetic rate of Atriplex centralasiatica decreased with temperature.Above 42?, the net photosynthetic rate of the control group decreased significantly.But the net photosynthetic rate of 300 mmol·L-1 NaCl treatment group was less affected. Above 45?, the net photosynthetic rate of NaCl treatment group began to decrease significantly. At 51?, the net photosynthetic rate of the two groups was negative. Analysis of the diagrams of Gs, Ci and Ls showed that the decline of the net photosynthetic rate was mainly due to the stomatal limitation factors when the temperature was below the critical high temperature of heat stress. However, when the temperature was above the critical high temperature of heat stress, the damage to photosynthetic apparatus was serious and the main reason was non-stomatal limitation factors. The changes of ?PSII were similar to Pn.The chl a fluorescence curve of Atriplex centralasiatica showed that the curves of the control group showed typical K-phase above 42 ?. For NaCl treatment group,typical K-phase appeared at 45?. According to the analysis of the parameters of chlorophyll fluorescence, we found that the parameters of the control group sharply changed when the temperature was 42?. For NaCl treatment group, on the contrary,it was 45 ?. According to Arrhenius plot of the parameters of chlorophyll fluorescence, the above conclusion was confirmed. In conclusion, we speculated thecritical temperature of heat stress in Atriplex centralasiatica was 42? and the critical temperature of 300 mmol·L-1 NaCl treatment group was 45?.2. Effects of NaCl treatment on heat resistance of Atriplex centralasiaticaAt 40?, the net photosynthetic rate of the 300 mmol·L-1NaCl treatment group was higher than that control. ?Po, ?Eo, RC/CSm and PIABS of NaCl treatment group were also higher than those of control, but ?Do was lower than that of control. That shows even at 40?, NaCl treatment group still had a number of the active reaction centers,which was beneficial to maintain critical functions of photosynthetic apparatus and the dissipated energy was decreased. Proline content, soluble sugar content and SOD activities in the leaves of NaCl treatment group were also higher than that of control.Furthermore, the osmotic potential was lower in salt-treated group, which suggested that water retention ability and antioxidant capacity of NaCl treatment group were stronger. At 40 ?, DGDG content and PG content in the leaves of NaCl treatment group were higher than in those of control The ratio of DGDG content to MGDG content and saturated fatty acid contents of PG of NaCl treatment group was also higher. The increase of the ratio of DGDG content to MGDG content can help to protect photosynthetic apparatus to get the photosynthesis done well. The increasing of saturated fatty acid contents of PG contributed to increase phase-transition temperature and increase the heat resistance. Therefore, NaCl treatment in certain extent can improve the heat resistance of Atriplex centralasiatica.3. Effects of heat treatment on salt tolerance of Atriplex centralasiaticaThe net photosynthetic rate of Atriplex centralasiatica which were treated by 40?was higher than that of control, when they suffered from salt shock. ?Po, ?Eo, ?Do and PIABS of heat treatment group were also higher than those of control, but there was little difference between them. That showed salt shock made serious damage to the two groups. Proline content in the leaves of heat treatment group was higher,while MDA content and relative electrical conductivity were significantly less than the control. It suggested heat treatment group suffered less damage by salt stress relatively. Therefore heat treatment alleviated the salt damage to Atriplex centralasiatica to some extent, yet not significantly.