| The two wheat variety L14 and 935031 with different senescence-types were investigated. After making treatments on field and pot-planted seedlings, we studied both the effects of different high-temperature on leaf photosynthetic apparatus and the function of nitrogen nutrition under high temperature for the purpose of providing theoretical evidence of ultra-high yield cultivation and breeding of wheat. The main results are as follows:1 .The change of relative parameters in wheat varieties with different senescence-type during natural senescenceOur research indicates mat from flowering to harvest stage of wheat, the photosynthetic rate, chlorophyll contents, soluble protein contents and transforming efficiency of light energy in L14 wheat leaves apparently declined more quickly than that in wheat variety 935031, but the beginning time when respectively relevant parameter declined is different. From thirtieth day after blooming, most leaves of 935031 still keep greening at harvest while the leaves of L14 have started withering. This shows wheat variety L14 is leaf pre-senescence variety.2. The effects of heat-stress on photosynthetic characteristics of wheat leafUnder the conditions of moderate heat-stress, photosynthetic rate of wheat leaf at saturate light evidently declined, the activity of key enzyme GO for photorespiration reduced, soluble protein contents decreased, the declining amplitude of L14 noticeably was greater than that of 935031, however, chlorophyll contents changing subtly, two varieties altering with similar regularity. This shows that heat-stress decelerates progress of leaf photosynthetic capacity.Under the conditions of heat-stress, the changes of chloroplast ultramicrostructure of pulp cell in wheat leaves aggravate with the intensification of stress extent, photosynthetic transforming efficiency of light energy keeping accordance with change tendency of ultramicrostructure . Heat-stress causes chloroplast shape round, thylakoid constringine, distance of thylakoid stratum widened, matrix stratum disordering, and finally chloroplast degraded .This further proves the function that heat-stress can accelerate leaf senescence .Heat-stress influences utilization efficiency of light energy in plant leaves, transforming efficiency of light energy of PSII reduced after heat-stress treatment,photo-chemical utilization of absorbed light energy in the leaves decreases, non-photochemical dissipation increases, the change amplitude of above indexes enlarges with the enhancing stress extent, so maybe declining utilization efficiency of light energy under heat-stress conditions leads to excessively absorbed light energy . High temperature stress is one of important reasons of induced pre-senescence in the leaves of wheat with pre-senescent type.3. The effects of heat-stress on active oxygen metabolism in wheat leaves There is close relationship between active oxygen metabolism and leaf senescence in the plant. Moderate high temperature can induce enhancing activity of active oxygen metabolism system, delaying senescence progress of wheat leaves. However, under severe heat-stress conditions, the activity of enzyme system (SOD,CAT,APX) scavenging active oxygen declines, the component contents of non-enzyme system(AsA,GSH) decrease, the harming active oxygen is excessively produced, then ex-oxidation extent of membrane and grease (MDA) aggravates, leaf senescence accelerated. So maybe the disordering of active oxygen metabolism by heat-stress is one of main reasons of photosynthetic apparatus damaged in the leaves.4. The effects of nitrogen nutrition on photosynthetic capacity of wheat leaves under heat-stress conditionsRespectively spraying 0.5mM and 5.0mM KNO3 on the leaves under the pot-planted conditions, and then heat-stress treatment was made on seedlings in the incubation-box. Our study shows nitrogen nutrition can effectively promote photosynthetic rate and apparent quantum yield at saturate light in wheat leaves, enhancing the accumulation of contents of chlorophyll, inc... |
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