The Cross Adaptation Of Sorghum Bicolor To Salt And High Temperature Stress

Sorghum bicolor is mainly grown in the tropical and subtropical regions.During its lifetime it often meets with salt and high temperature successively,or simultaneously.This study mainly deal with the effects of salt and high temperature stress on Sorghum bicolor and its responsible mechanisms for cross adaptation.The paper mainly includes four parts: the critical high temperature of Sorghum bicolor.The effect of salt stress on the high temperature resistance of Sorghum bicolor.The effect of high temperature stress on the salt tolerance of Sorghum bicolor.And at last,the effect of high temperature and salt interaction on Sorghum bicolor.The results are as follows:1.Effects of salt treatment on the critical high temperature of Sorghum bicolor.Seedlings of Sorghum bicolor were cultivated with 0 or 100 mM NaCl.After 15 days the seedlings were then treated at 30?,33?,36?,39?,42?,45?,48? and 51? respectively followed by determination of transit chlorophyll fluorescence analysis.Results indicated that when Sorghum bicolor cultivated with 0 mM NaCl was treated at 45?,the minimum fluorescence?F₀?and the ratio of variable fluorescence Fk to the amplitude Fj-F₀?Wk?began to increase significantly,and continued to increase gradually with the temperature.However,F₀ and Wk of Sorghum bicolor treated with 100 mM NaCl increased significantly at 48?,which went on increasing with the temperature after that.When seedlings of Sorghum bicolor cultivated with 0 mM NaCl were treated at 45?,the maximum photochemical efficiency of PSII?Fv/Fm?decreased significantly,and gradually decreased with the increase of temperature.On the contrary,Fv/Fm of Sorghum bicolor cultivated at 100 mM NaCl began to decrease significantly at 48?,and continued to decrease gradually with the increase of temperature.The trend of the performance index based on the absorption of light energy(PI_ABS)showed the same trend as the Fv/Fm.After Arrenius plot and analysis,the critical high temperature of Sorghum bicolor treated with 0 mM NaCl is about 45?,while the critical temperature of the Sorghum bicolor treated with 100 mM NaCl is about 47?,indicating that salt treatment increased the critical temperature of Sorghum bicolor for hot stress.2.Effects of salt treatment on high temperature resistance of Sorghum bicolor.Seedlings of Sorghum bicolor were cultivated with Hoagland solution containing 0,75 or 150 mM NaCl for 15 days at room temperature and then transfered to 25? or 43? light incubator for 24 h followed by determination of physiological indices.The results showed that under room temperature,the net photosynthetic rate?Pn?,Fv / Fm and PI_ABS significantly decreased with the increase of salt concentration.High temperature alone?43??also lowered Pn,Fv/Fm and PI_ABS significantly.However,under 43?,the changes of Pn,Fv/Fm and PI_ABS of the Sorghum bicolor treated with 75 mM NaCl was not significant compared with the control group?25??,while those treated with 150 mM NaCl still showed significant increase compared with control.The results indicated that appropriate salt treatment can improve heat resistance in Sorghum bicolor.After high temperature treatment,seedlings of Sorghum bicolor pre-treated with 75 mM NaCl showed no significant change.It was mainly due to the fact that 75 mM NaCl increased SOD activity,the content of soluble sugar,proline as well as betaine in the sorghum leaves,especially in the chloroplasts,which were the main organelles of photosynthesis.After 75 mM NaCl treatment,the compatible solutes such as proline and betain in the chloroplast increased,the SOD activity increased,the unsaturated fatty acid index decreased,accompanied by the decrease of membrane peroxidation and the content of MDA.All these factors improved high temperature resistance in Sorghum bicolor in the following high temperature treatment.3.Effects of high temperature treat on the salt resistance of Sorghum bicolor.Seedlings of Sorghum bicolor were cultivated in the light incubator at 30?,40?or 43? for 7 days,then the plants were removed from the incubator and treated with 0 or 100 mM NaCl respectively.With the increase of temperature,F₀ in 0 mM and 100 mM NaCl-treated Sorghum bicolor leaves gradually increased,indicating the dissociation of oxygen evolving complex?OEC?from PSII.As for the group of 40? treatment,the control group and salt treatment group have no significant change,indicating that 40? pre-treatment of Sorghum bicolor followed by salt treatment had no further significant damage to OEC.With the increase of treatment temperature,the Fv / Fm and PI_ABS of the Sorghum bicolor leaves treated with 0 mM NaCl decreased gradually.The Fv / Fm and PI_ABS of the Sorghum bicolor leaves treated with 100 mM NaCl showed the same trend.However,for the seedlings pre-cultivated at 40?,the salt treatment group and the control group did not change significantly.It suggested that appropriate high temperature hardening can improve salt tolerance in Sorghum bicolor.4.Effects of high temperature and salt interaction on Sorghum bicolor.While high temperature and salt stress were applied to Sorghum bicolor simultaneously,We found that Pn,stomatal conductance?Gs?and intercellular CO2 concentration?Ci?as well as transpiration rate?E?of the Sorghum bicolor leaves in the control?0 mM NaCl?and salt treatment group?100 mM NaCl?were not significantly different at 40?.F₀ was lower in the salt treatment group compared with the control group,while Fv/Fm and PI_ABS were increased.The results were similar to those in the previous part,demonstrating that salt and high temperature co-treatment of Sorghum bicolor can improve its heat resistance to some extent,yet the beneficial effect was lower compared to treating the sweet sorghum with salt and high temperature succesively.