Phytohormones and related genes expression in Maize Leaves
Plant hormones regulate various processes, including leaf senescence. Therefore, to estimate the role of phytohormones in delaying leaf senescence under different light conditions, we estimated the contents of IAA, GA3, ABA, and ethylene (Fig. 5). Generally, under all the treatments, the phytohormones ABA, ethylene, and IAA accumulation increased up to 20 days while GA3accumulation decreased, except under PS, in which it significantly increased for the first ten days followed by a sharp decline for the next 10 days and again a subsequent increase in last 20 days. Notably, the initial rise (days from 0 to 20) in IAA, GA, ABA, and ethylene contents in PS was 1.2, 1.4, 1.4, 1.1, 1.3, 1.2, 1.4, 1.2 and 1.3, 1.2, 1.3, 1.1 fold significantly higher than PF, NF, and NS. However, unlike NL treatment, the amount of ABA and ethylene declined under PS and PF in the last 20 days, and treatment PS showed the minimum 0.79 mg g-1 of ABA and 15.9 ng L-1 ethylene at day 40. Furthermore, all the treatments showed the same decreasing trend for IAA after day 20, yet, the treatment PS retained a significantly higher amount of IAA than PF, NF, and NS. Overall, the results revealed that the level of various phytohormones significantly increased under PL conditions for the first 20 days after that they started to decline until day 40. However, the NL conditions did not induce any significant changes between the two sides in the accumulation of studied phytohormones. The transcription levels of ZmABI5.1and ZmEIN3.1 were down-regulated notably under PL than NL treatment, while a slight up-regulation of ZmEIN3.1 was found in PS before day 20 (Fig.6A). However, the minimum expression levels ofZmABI5.1 and ZmEIN3.1 were found in PF leaves, the same results were observed in protein expression of EIN3 (Fig.6B). After thatZmABI5.1 and ZmEIN3.1 under PL started to decline compared to NL treatment, where their expression was significantly increased between days 20 and 30 days, respectively, before declining in the last ten days.