Abstract
Reduced availability or absence of light is a major debacle for plant growth and yield. Exogenous application of plant growth regulators (PGRs) partially replaces light requirement(s) during seed germination, but studies are scarce on the interactive role of light and the PGRs in etiolated plants. In this research, non-etiolated, etiolated and de-etiolated maize (Zea mays L.) hybrid P-1543 seedlings were sprayed with optimized levels of ascorbic acid (AsA; 0.5 mM), thiourea (TU; 10 mM), cycocel (CCC; 1.2 mM) and kinetin (KIN; 3.0 mu M) and gmwn for six days. Etiolation caused seedling elongation, reduced dry weight but increased elongation-to-dry weight ratio, which decreased strongly in de-etiolated seedlings. Reductions in chlorophyll (Chl) a and b, carotenoids (Car), net photosynthesis (Pn), transpiration rate (E) and stomatal conductance (gs) under etiolation (27-48%) were lowly improved with the PGRs under no-etiolation (5-15%), but were greatly improved (18-76%) in de-etiolated seedlings. Etiolation exacerbated the hydrogen peroxide (H2O2) and malondialdehyde (MDA) contents, which were marginally lowered with the PGRs spray (18 and 12%, respectively). Nonetheless in de-etiolated seedlings, the PGRs spray declined H2O2 (32%) and MDA (40%) contents apropos improving soluble phenolics (PHE), flavonoids (FLA), anthocyanins (ANT), ascothate (AsA), niacin (NIA) and riboflavin (RIB) contents (20-37%). Although not correlated in etiolated seedlings, the seedling dry weight was positively associated with pigments, leaf gas exchange, the PHE and ANT, but negatively with substomatal CO2 concentration (Ci) of de-etiolated seedlings. The applied PGRs alleviated oxidative damage, improved ANT, FLA, pigment contents and leaf gas exchange in aptly producing stout seedlings during de-etiolation. In conclusion, the hypothesis that light was quite effective in augmenting the effects of PGRs in seedling growth, which were principally due to alleviation of oxidative damage and improved photosynthesis was accepted. (C) 2020 Friends Science Publishers