Conclusions
In conclusion, the present findings demonstrated that partial light conditions improved communication in maize leaves between light-side (PF) and shade-side (PS). The changes of light signals and phytohormone signals (e. g., light sensor phytochrome A and phytochrome B and phytochrome interaction factor in both light-side and shade-side maize leaves under partial shade regulated IAA and GA biosynthesis which balanced the senescence hormone ABA and ETH. Besides, the enhanced antioxidant enzymes (e.g., POD, SOD, CAT) reduced cell membrane lipid peroxidation and ROS level. The down-regulated ZmPaO gene (pheophorbide an oxygenase) inhibited chlorophyll degradation, and improved maize leaves photosynthetic carbon fixation and sugar biosynthesis in light-side leaves. In the earlier ten days from flowering, more 13C abundance and soluble sugar were observed in shade-side leaves, while starch was degraded through increasing α-amylase, β-amylase, phosphorylase activities indicating compensatory effects between light-side and shade-side leaves. Moreover, the high transcription level of ZmNRT1.1 ,ZmSUT1a, and Zmsweet11.1 and improved net photosynthesis were found in light-side leaves, which strongly and ulteriorly illustrated the above conclusion. Compared to NL, the increase in maize leaf area, greenness, chlorophyll, and decreasing ABA and ETH level, senescence genes, ZmSAG2 and ZmSAG12.1 under PL in the last 20 days showed that the aging process of partial light leaves was delayed. As an adaptive response of carbon fixation, more nitrogen uptake from roots improved leaves totals N content in PL. Finally, the seed’s dry matter peak was also delayed in PL. Still, no significant difference in yield between NL and PL was observed, demonstrating that partial shade improved the utilization of light resources via delaying maize leaf senescence (Fig. 9). This mechanism lays a foundation for a better understanding of using the senescence characteristics of the maize-based intercropping system to improve high yield in areas with more people and less land.
Acknowledgments
This work was supported by the National Natural Science Foundation of China (32071963), a grant from the International S & T Cooperation Projects of Sichuan Province (2020YFH0126), and the Program on Industrial Technology System of National Soybean (CARS-04-PS19).