Effects And Mechanisms Of BR And Nitrogen On Growth Of Maize Under Low Light And Waterlogging Stress

A pot experiment was adopted in this study with the condition of artificial simulation for low light and waterlogging stress,the regulating effect and its physiological mechanism were studied which is formed under the effects of brassinolide(BR)and nitrogen(N)on the growth and yield of maize.The main results are as follows;1,BR can effectively alleviate the limitation of low light and waterlogging stress on the growth of maize,and the effect of BR ranks NO.1 in all 11 kinds of regulators.Under the condition of low light and waterlogging stress the SPAD value of maize leaves decreased by9.7%,the relative conductivity increased by 52.9%,and the photosynthetic rate and biomass decreased by 31.9% and 29.7%,respectively.With the spraying of phenyl urea,paclobutrazol,ascorbic acid,glycine betaine,abscisic acid and brassinolide on the maize leaves,they each increased the SPAD values by 9.4%,6.3%,3.7%,6.0%,9.1% and 4.7%,respectively,while with the spraying of ascorbic acid,betaine,abscisic acid and BR on the leaves,they each decreased the relative conductivity by 11.5%,14.6%,18.0% and 12.1%,respectively.The maize sprayed with phenylurea,betaine and brassinolide had an increase in photosynthetic rate and biomass by 24.6.%,25.3%,33.2% and 28.6%,33.6%,39.9%respectively,of which the alleviation effect of BR is relatively more obvious.2.The growth and development status of maize under low light and waterlogging stress has been improved by the usage of BR,N and BR+N.Under the condition of low light and waterlogging stress,which made the plant height and height of spike increase by7.8% and 12.4% respectively,while the leaf area index,chlorophyll content and the accumulation of dry matter decreased significantly.The height of the plants applied with BR,N and BR+N increased by 2.9%,1.9% and 3.7% respectively compared to plants applied with CK2,the height of spike increased by 3.9%,4.5% and 4.9% respectively,and the leaf area index increased by 9.5% and 14.4%.19.1% and the accumulation of dry matter increased by 8.4%,11.9%,20.7% respectively,among of which the usage of BR+N has better alleviation effect after stress effect.Under the stress effect it increased the amount of substance distributed to stems and leaves,and reduced the amount of substance distributed to grains.While the application of BR,N and BR+N could significantly change the distribution of dry substance in each part of the plant such as to increase the proportion of substance distributed to seeds,Where BR,N and BR+N were applied in the plants,there is an average increase of seeds by 27.6%,24.7%,and 34.7% compared to plant applied with CK2.The proportion of substance distributed to leaves and stems and sheaths decreased by10.2%,7.3%,17.1%,and 13.6%,11.1%,and 18.3%,respectively.3.The physiological characteristics of maize leaves under low light and waterlogging stress were improved with the application of BR,N and BR+N.Under the compound stress,there was a decrease in the soluble protein content of leaves by 13.8%,while an increase in content of MDA and soluble sugar.Compared with plants applied with CK,The content of soluble sugar in plants applied with BR,N and BR+N decreased by26.0%,15.0% and 27.4%,and the content of MDA decreased by 9.7%,18.4%,16.3%compared to CK2 group.The application of BR,N and BR+N increased the soluble protein of leaves by 6.1%,7.6% and 8.7% respectively,and increased the activity of SOD and POD by 7.6%,2.9%,10.7% and 2.5%,3.6% and 5.4%,respectively.4.The content of endogenous hormones in leaves were changed with the application of BR,N and BR+N.Under low light and waterlogging stress,the contents of endogenous hormones such as ABA,IAA and ZR in leaves increased by 21.6%,10.3% and 14.5%compared with plants applied with CK2,and the content of GA3 decreased by 5.5%.The ratio of(IAA+GA3+ZR)/ABA in maize leaves decreased by 10.2% under the compound stress.With the application of BR,N and BR+N to the plants,there was an average increase in the ratio of(IAA+GA3+ZR)/ABA by.15.9%,11.2%,19.1% compared to plant applied with under compound stress.5.Photosynthetic rate of the leaf were increased by the application of BR,N and BR+N.Under low light and waterlogging stress,there is an average decrease of the photosynthetic rate by 28.8%,and it also cause the activities of photosynthetic enzymes PEP carboxylase and RUBP carboxylase in maize leaves to decrease by 24.1% and 33.4% respectively.Plants processed with BR,N and BR+N resulted in average increase of activities of PEP carboxylase and RUBP carboxylase by 13.2%,18.8%,39.0%,and 14.6%,24.4%,and31.4% respectively.With the process with BR,N and BR+N there is an average increased in the photosynthetic rate by 10.0%,17.1%,and 30.3%,respectively.6.The yield of maize can be significantly increased with the application of BR,N and BR+N under low light and waterlogging stress.Under low light and waterlogging stress,it will cause a reduction of maize yield by 51.5%,leading to kernel number in the spike and weight of 100-kernels drop by 49.8% and 1.3%.Compared with the plants treated with CK2,the plant treated with BR,N and BR+N increased yield by 38.3%,40.0%,and 63.0%,respectively,and all of them reached significant levels.After treatment with BR,N and BR+N there is an increase in the number of kernel per spike by 49.9%,49.6% and 67.9%.There were different when it comes to the effects on grain weight with application of BR,N and BR+N.Before the stress effect if the plant was treated with BR,N and BR+N,it will lead to a decrease in the grain weight by 10.6%,8.8% and 11.5% compared with plant treated with CK2.While the weight of 100-grain decreased with the BR treatment by6.9%compared to that of CK2 after the stress effect and the weight of 100-grain treated with N and BR+N increased by 2.3% and 0.9.% compared to that of CK2.