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.