| In recent years,the worsenesss of ecological environment and the increasing of extreme climate events had a serious effect on the normal production of rice.The stage after rice heading is quite essential for the development of rice and also particularly sensitive to low temperature stress.In this period,if it came to low temperature stress,the yield of rice would decrease largely.However,under the background of yield decreasing,it had not yet been quite clear about functional leaf's photosynthetic physiology,pollen germination and key enzyme activities of starch synthesis under low temperature stress.In this study,The test temperature was controlled by artificial climate boxes,set as low temperature(8:00~18:00,15?,18:00~8:00,10?)and room temperature(8:00~18:00,32?,18:00~8:00,25?).The Indica rice 9311 and Wuyunjing 25 were used to assess physiological characteristics and key enzyme activities of starch synthesis at the flowering and filling stage under low temperature stress;With Fengliangyou 9 as material,it aimed to research the chilling injury on calcium fluorescence characteristics of rice pollen germination and the readjustment of methyl jasmonic acid on floret opening at the flowering stage and the IAA and ABA content of rice leaves and grains at the filling stage.Main experimental results were as follows:1.The leaf chlorophyll content,chlorophyll a/b value,net photosynthetic rate,stomatal conductance,transpiration rate,Fv/Fm,qP,and Y(?)decreased at the flowering stage under low temperature stress compared with room temperature for cultivar Indica rice 9311 and cultivar Wuyunjing 25.However,the parameters of Fo,qN,Y(NPQ),and Y(NO)were significantly higher under low temperature stress than those under room temperature.The results showed that heat dissipation and fluorescence dissipation were increased to protect photosynthetic organs from cold damage.Meanwhile,low temperature significantly decresed the SOD and POD activity,free proline,soluble sugar,and soluble protein content,but MDA content in low temperature increased compared with room temperature.Comprehensive data showed that Wuyunjing 25 had better performance than Indica 9311 under low temperature stress.2.Under low temperature stress,leaf chlorophyll content of Indica 9311 and Wuyunjing 25 at the filling stage dropped;net photosynthetic rate,stomatal conductance and transpiration rate also declined;Fv/Fm and Y(?)declined,while Fo,Y(NPQ)and Y(NO)rose,equal to the changing at the flowering stage.Meanwhile,low temperature stress resulted in the consequence that three key enzyme activities of starch synthesis of both cultivar rice grains including ADPG pyrophosphorylase(ADPGPPase),soluble starch synthase(SSS)and starch branching enzyme(SBE)were lower than those under the room temperature.At the whole filling stage of low temperature treatment,the three enzyme activities were inhibited much larger in the medium term than in the former and late term.Finally,the reduction of 1000-grain weight owed to the cooperate functions of the limiting of leaf photosynthetic capacity and the decreasing of enzyme activities.Under low temperature treatment,Wuyunjing 25 exhibited greater resistance than indica 9311.3.The test was conducted by culturing rice pollens in vitro in a liquid medium,then loading calcium fluorescent probe by the method of low temperature incubation and finally using laser confocal scanning microscope to observe.The results showed that the calcium fluorescence intensity,the ratio of pollen germination,and the length of pollen tube significantly decreased after suffering from low temperature stress.The parameters mentioned above were much lower with the extension of the processing time,indicating that the low temperature stress influenced pollen's normal germination.4.The content of endogenous IAA and ABA in the leaves and grains at the filling stage of rice was tested by enzyme-linked immunosorbent assay(ELISA).The results showed that: the chilling stress gave rise to the drop of the IAA and ABA content in leaves and grains of rice,so that the low temperature resistance ability of rice declined.5.By pre-spraying water and methyl jasonate at the flowering stage,the results were: spraying water can delay floret opening of room temperate treatment,however make it advance under low temperature;the floret opening was delayed and the number of spikelets decreased tremendously by the chilling at the flowering time,however,spraying exogenous methyl jasonate can regulate the flowering of rice,make it more advanced and concentrated whether under the room or the low temperature treatment,and greatly improve the opening number of spikelets under the low temperature,alleviating the chilling injury on the floret opening.The aforesaid results indicated that: low temperature stress had a remarkable influence on all kinds of physiological and biochemical characteristics after rice heading,and the reflection of low temperature stress differed among different cultivars very much.With this study's rice materials as an example,the Wuyunjing 25 exhibits greater resistance than indica 9311.Pre-spraying exogenous methyl jasonate before rice heading can alleviate the damage of low temperature stress on the flowering.This study not only enlarged the theoretical knowledge about how physiological and biochemical features responded on the low temperature stress after heading,but also provided effective technical methods of alleviating the chilling damage after heading. |
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