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).