| High temperature toghther with high light are important environmental factorsaffecting wheat grain development during grain filling stage. To illustrate the performanceof the wheat photosynthetic characteristics in hybrids, we chose Xiaoyan54(XY54), Jing411(J411) and their stabilized hybrid offspring lines1-12as materials to study theirphotosynthetic characteristics and antioxidant mechanisms during flowering to grain fillingstage, the main results are as follows.(1). Net photosynthetic rate (Pn) in flag leaves of different wheat genotypes of theparents and their offspring after anthesis kept rising to a peak till15days after anthesis,photosynthetic rate reached its maximum, and then began to decline. Parental J411had ahigher photosynthetic rate before15days after anthesis, but later, the photosynthetic ratedecreased significantly. Offspring1-12performanced a relatively photosynthetic betweenits parents before15days after anthesis, however during the late grain filling stage,1-12hada higher photosynthetic rate compared to their parents. Photosynthetic rate of paternal J411decreased significantly, showed serious photoinhibition at noon. The maximumphotochemical efficiency of PSII (Fv/Fm) in the three genotypes maintained around0.83within15days after anthesis, late on the Fv/Fm in J411decreased obviously than1-12andXY54, whereas1-12maintained a certain Fv/Fm. Wheat flag leaves in flowering stage weresuffered to midday depression of photosynthesis and photoinhibition phenomenon, which1-12and XY54showed less midday depression of photosynthesis and photoinhibition.Theseresults illustrated that1-12lines inherited some parental advantage not only the highphotosynthetic efficiency from J411but also antioxidant activity from XY54.(2) After anthesis, the chlorophyll content of different varieties wheats were firstmaintained a certain level, then decreased, and the chlorophyll content in J411declinedsignificantly.1-12line performanced relative a lesser extent compared to its parents. Theultrastructure of chloroplasts showed that before15days after anthesis. chloroplastultrastructure of three species were relatively intact, and there were no obvious difference,but24days after anthesis, J411and XY54showed adventitial significant dissolution phenomenon, also a large number of osmiophilic granules, indicated ealier senescencecharacteristics than its hybrid1-12.(3)19days after anthesis, MDA content in J411was significantly increased than1-12and XY54, indicating higher level membrane lipid peroxidation in J411. Antioxidantenzymes such as CAT, POD and APX were first increased and then decreased after anthesis,CAT and APX activities reached the maximum in10days after anthesis, while POD was15days after anthesis. The activities of CAT, POD and APX in1-12were higher than that ofXY54and J411, and J411had lowest antioxidant enzyme activities.(4) Through the determination of two key enzymes of the Calvin cycle, Rubisco andGAPDH, and sucrose synthesis two related enzymes cFBPase and SPS, we found that theiractivities all reached to a peak in15days after anthesis, and then began to significantlydecline, while the1-12maintained a relatively higher activities of these enzymies.(5) The heat shock protein assay showed that before the15days after anthesis, HSP70content maintained a high level, and there were no difference among two parents and theirhybrid. In the15th day after anthesis, HSP70showed significant increasing trend at noon,especially in1-12.(6) In the15th day after anthesis, flag leaves in midday under high temperature andstrong light in different parents and offspring were choosed to do the chip hybridizationexperiments and found that1522differentially expressed genes performanced in offspring1-12compared to its parents, in which817downregulated and705upregulated genes.Subsquently blast results showed that many small molecular weight heat shock proteinsynthesis genes are up-regulated expression and other genes needs to be further verified. |
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