The Regulation of ROSs and Antioxidant Enzymes under Partial Shade
Plants possess a strong antioxidant system that regulates membrane oxidation by scavenging reactive oxygen species (ROS) (Gill & Tuteja, 2010). An increase in oxidative processes in plants leads to the production of ROS. This oxidative damage subsequently causes physiological changes and cell membrane damage in plants (Mutlu et al., 2016). However, the upregulation of antioxidant enzymes directly compensates for or decreases the effect of the ROS in plants, which is consistent with the present study. Here, NL increased the activities of ROS than partial shading, suggesting that cell membrane performance was reduced in NL (Fig. 2). In partial shade treatment, ZmPHYA1b gene expression was significantly increased in PS but decreased in PF. However, ZmPHYB1c expression was opposite to ZmPHYA1b(Fig. 7). The increased expression of ZmphyA1b in PS negatively regulated FHY3 and FAR1 and reduced ROS accumulation. It is reported that the disruption of phytochrome A (PHYA) the crucial components far-red elongated hypocotyls 3 (FHY3) and far-red-impaired response 1 (FAR1) caused light-induced precocious leaf senescence and increased sensitivity to oxidative stress (Ma et al., 2016; Wang & Wang, 2015). Recent research reported that PHYB regulated systemic stomatal aperture closure responses and high ROS accumulation in excess light (Devireddy et al., 2020). ZmPHYB1cdownregulation in PS also inhibited the ROS level. Increased antioxidant activities were observed in partial shading than NL (Fig. 2). These results agreed with previous studies where partial shading increased the activity of antioxidant enzymes, which subsequently reduced the lipid peroxidation, which delayed the senescence process in winter wheat (Xu et al., 2016). However, our results presented a new insight into maize leaves behavior and mutual interaction under heterogenous shading conditions. Interestingly, within PL, partial shading significantly boosted the antioxidative response of maize leaves that protected the leaves on both sides and encountered the initial rise in oxidative stress and membrane damage effectively. Recently, a study reported drought tolerance and improved growth parameters of pre-shaded leaves due to the upregulation of antioxidative response and osmoregulation (Asghar et al., 2020). Similarly, the results in our study suggested that partial light-induced moderate oxidative stress triggered the antioxidative response and, as a result, improved the growth of maize plants which resulted in delayed leaf senescence.