Physiological And Molecular Studies Of Stay Green Caused By Pod Removed And Seed Injury In Soybean

In recent years, “Zhengqing” occurred in Huanghuaihai region in China and severely decreases the yield of soybean. Zhengqing is accompanied by the staygreen of leaves that don’t abscise untill plant withered. The feedback regulation of pod and seed on leaf development remains unclear. we investigated the effects of pod/seed status on the leaf senescence by conducting the pod removal and seed injury treatments, in order to know the physiological and molecular mechanism of seed-leaf relationship during the reproductive development of soybean. The pod removal(0, 10, 20, all pod(intact) remained each plant respectively) and seed injury(punctured) treatments were conducted since the full pod(R4) stage. The leaf senescence process was observed, the contents of chlorophyll, soluble protein, soluble sugar and endogenous hormones(IAA, ABA and GA3) in leaves were measured, and the expression of four genes of GmSARK(senescence-related), GmSGR1, GmCYN1(key genes in the chlorophyll degradation pathway) and GmNAC(gene encoding transcriptional factor in ABA biosynthetic pathway) were detected after the pod removal and seed injury treatments.1.The results showed that the pod removal and seed injury delayed the leaf senescence and resulted in stay green of leaves in soybean. There was dosage effects of pod number on the degree of stay green. The less the pods remained each plant, the severer the stay green happened in the leaves.2.Along with the the seed filling and maturation, the relative contents of chlorophyll(SPAD value), soluble protein, soluble sugar decreased in leaves of the intact plants, but the that in depoded and seed-injured plants were stable(SPAD), decreased less(soluble protein) or even increased(soluble sugar).3.During the seed development, the content of IAA decreased, that of ABA increased, but the change trend was more apparent in the intact plant. And the ratio of GA3/ABA decreased gradually in all treatment, The content of GA3 was relatively stable and that in the intact plants was somehow higher than in the depoded plants.4.GmSARK was the marker gene in soybean leaf senescence, regulate the leaf senescence through chlorophyll and hormone changing, GmNAC was the transcription factor in ABA pathway, GmCYN1 and GmSGR1 were the gene in degradation chlorophyll. The expression levels of the four genes declined in the depoded or seed-injured treatments, and the expression levels were dependent on the number of leaves remained on the plants.5.GmFT2 a is a major flowering promoting gene and one of the integrators in the flowering pathway. E1 inhibit plant flowering. The transcription level of GmFT2 a increase and E1 decrease in the depoded treatment.Considering the results above, it was postulated that seed can regulate the developmental process of soybean leaf. The changes of phenological traits, physiological indices and gene expression in the 0-pod(totally depoded) plants were similar with that of the seed-injured ones, indicating that the stay green was caused by the halt of the seed development. Seed can produce some signals to regulate leaf senescence with a dosage effect during the late reproductive development of soybean.