Physiological And Biochemical Mechanisms Of Shade Avoidance Response And Its Regulation In Maize Plants Under Different Group Structures

One way of increasing production in maize is through adoption of high planting densities. However, high planting densities are associated with intra-specific competition between plants for resources, especially for sunlight, which is severely attentioned through plant canopies and regareded as a significant limitation in maize production in high densities. Shade avoidance response is an adopting machanism for plant reacting to high densities, thus plays an important role in plant growth and productivity. This study was conducted to investigate the light signals under maize canopies and plant shade avoidance response in maize in different cannopy structures. Besides, the role of ethyelen, gibberellin and light quality in shade avoidance response was evaluated. Cv. Zhengdan958and Nongda4967were used in the study. The main results were as follows:(1) In a certern range, high densities improved the enlongation of low and middle group of leaf and internode, but reduced the leaf width and internode maximum diameter. The leaf area, biomass accumulation and grian yield per plant was decreased. Under the experiment densities, yield of Nongda4967increased with the elevation of planting density, while Zhengdan958exihibited a maximum yield in density of67,500plants ha-1.(2) With the increase of plant density, light radiation espcially PAR under maize cannopies significantly decreased. Light attenuation in wavelengths of400-500nm and600-700nm was strickingly, while that in700-800nm was gentle, which resulted a reduced ratio of light in400-500nm and600-700nm to total light radiation (400-800nm) and an elevated proportion of light in700-800nm wavelength. Besides, R/FR under cannopies of miaze in high densities was highly reduced.(3) High density significantly improved the biosynthesis of GAs, ethyelen, IAA, ZR and iPA. The elevation of GA4level in high densities was attributed to the expression of ZmCPSl and ZmKSl, while the increase of ethyelen biosynthesis was accrodding to the enhanced accumulation of ACC and activity of ACO. Meanwhile, high density induced the expression of genes related in ethylene signal pathway.(4) The application of ETH significantly inhibited the elongation of internode and attenuated the shade avoidance response. Similar to ETH, plants treated with AOA exibitted a shortend internode too, but the shade avoidance response was enhanced. Application of GA3induced a typical phenotype of shade avoidance response, and elevated the differences in basal internode elongation among densities. PAC, in contrast, highly inhibited the growth of plants in low density. The harvest index was increased treated by PAC, and grain yield of PAC treatment under high densities was higher than CK.(5) Similar to dense vegetation, Slalso induced a typical phenotype of shade avoidance response, while effect of S2on internode elongation was mostly inhibition.(6) Sowing orientation significantly affected the morphogenesis and grian yield in maize. The results showed that, compared to N-S, the E-W row orientation could promote the growth of leaf and internode and elevate the biomass accumulation and harvest index, and led to a higher grain yield in maize.