Activity Of Photosynthesis Enzymes, Carbon Assimilate Transportation In Wheat Spike Under Water Deficit

Drought is one of the main factors that restrict the high and stable yield of wheat in ChinaNorth areas. In recent years, studies have shown that spike bracts have significantphysiological and biochemical advantage under drought stress. It is the important theoreticaland practical significance of crop production to give full excavate to physiological andbiochemical basis of photosynthetic capacity and carbon assimilate transport capacity in spike.In this study, hydroponic experiment is carried out to study the response to drought stress ofwheat seedling leaves C4pathway enzymes by selecting the rainfed variety Xinong1043andplain variety Shaan253, and measuring C3and C4pathway key enzymes activity of leaves intrefoil stage. Pot experiment was carried out to study the contribution of wheat earphotosynthetic characteristics to grain form under water deficit by selecting the rainfedvariety Pubing143and plain variety Zhengyin1, and measuring spike net photosynthetic rate(Pn), chlorophyll content, flag leaves and spike bracts of C3and C4key enzymes activity,using14CO2-photosynthetic label technique, transport of photoassimilate in themid-grain filling was investigated. The main results were listed as follow:1. In hydroponic experiment, leaves Rubisco (C3pathway key enzyme) activity declinewith the increase of PEG stress time, two varieties drop significantly after6h in stress(P<0.05). Compared with plain variety, osmotic stress have a smaller effect on the Rubiscoactivity of rainfed variety in wheat seedling leaves. Activity of C4pathway enzymes in theleaves rise with the increase of stress time and then drop, especially at6h, PEPC (C4pathwaykey enzyme) activity increase by34.7%(P<0.05) in Xinong1043leaves, while no obviousrise in Shaan253, which suggests that PEPC enzyme activity increase more significantlyunder osmotic stress in rainfed variety leaves, may play an important role in thephotosynthetic carbon sequestration.2. In pot experiment, Flag leaf Pndecline with grouting process. At24DAA, flag leaves Pnfell by44.6%(P<0.05) in Pubing143under water deficit, while Zhengyin1have fallen by63.1%(P<0.01), which show that the effect of water deficit on flag leaf net photosynthetic oftwo varieties occur in the whole filling stage, and the plain variety is more sensitive to waterdeficit. The ear Pnof two tested varieties increase with the growth of spike bracts organ andthen drop. In flowering period (0DAA), Pubing143ear Pnincrease by10.6%under waterdeficit (P>0.05), while reduce by16.9%(P>0.05) in Zhengyin l. At12,18,24DAA, ear Pn decline significantly (P<0.05) in Pubing143, while drop highly significantly (P<0.01) inZhengyin l. Spike bracts (glume, lemma and palea) chlorophyll content and relative watercontent decreased slightly (P＞0.05) in rainfed variety Pubing143during the grain fillingstage under water deficit, while plain variety Zhengyin1decreased significantly (P<0.05).Results show that two varieties ear Pndifferences mainly occur in the early grain filling stageunder water deficit, and plain variety spike Pnwas more sensitive to water deficit.3. Under deficit, ear organs and flag leaves Rubisco activity decrease significantly, enzymeactivity of flag leaves fall less than ear organs, and Zhengyin l fall more than1Pubing143,particularly in glume, Zhengyin l drop to45.6%, while Pubing143drop to37.8%. C4pathway enzymes activity of ear organs are significantly higher than of flag leaves. Flagleaves C4pathway enzymes activity decrease under deficit, while ear organs rise. Theamplification of C4pathway enzymes activity is significantly higher in Pubing143thanZhengyin l, especially in lemma, PEPC activity increase by37.9%(P<0.01),84.3%(P<0.01)and83.8%(P<0.05) in Pubing143on12,18and24DAA respectively under drought stress,while rise not significantly in Zhengyin1. Results show that drought stress can induce highenzymes activity of C4pathway, which may be an important reason that spike organs holdrelatively stable photosynthetic rate and yield under water deficit.4. On harvest(30DAA), the14C-photosynthate distribution rate increase by37.8%(P<0.01)in glume of Pubing143under deficit, whereas a reduction of12.3%(P<0.05) is observed inZhengyin1. The distribution rate increase by17.0%(P>0.05) in the lemma (including owns)of Pubing143under water deficit, and decrease by15.3%in Zhengyin1(P<0.05). Thedistribution rate change is not obvious in palea and rachis of two varieties. Grain14C-photosynthate accumulation is significantly higher in Pubing143than in Zhengyin1,grain’s distribution rate of14C-photosynthate reduce by3.8%(P<0.05) in Pubing143underwater deficit, while increase by3.9%(P<0.05) in Zhengyin1. This result may be due to thepromotion of photoassimilate transport from the glume, lemma and palea to the grain in plainvariety under water deficit. By contrast, the influence of water deficit on rainfed variety wasnot obvious.5. Under deficit, the1000-kernel weight decline by11.0%and13.4%(P<0.01) in Pubing143and Zhengyin1, respectively. Yield and HI significantly decrease by25.1%and17.5%(P<0.05), respectively in Zhengyin1, and no obvious change in Pubing143. A (final1000-kernel weight fitted by logistic equation) fall by12.6%and17.3%(P<0.05) in Pubing143and Zhengyin1respectively. The decline of WUE is not obvious in Pubing143, andZhengyin1fall by18.7%(P<0.05), which indicate that less effect on rainfed wheat todrought is associated with its strong drought resistance mechanism.