Effects of ascorbic acid on physiological and biochemical responses of Zinnia elegans L. to different levels of light intensity

The aim of this study was to investigate the effect of different light intensities and ascorbic acid on some physiological and biochemical characteristics of Zinnia elegans L. The experiment was designed as a completely randomized design in a form of split-plot with three replications. The treatments were consisted of three light intensity levels (600, 1200 and 1800 μmol m-2 s-1) as the main factor using shade net and spraying three ascorbic acid concentrations weekly (0, 1, 2 mM) as sub-plots. Analysis of variance showed that light intensity had a significant effect on all studied traits, except for the guard cell width. As light intensity increased, proline content, catalase, and ascorbate peroxidase activity increased. The lower light intensity increased chlorophyll a and b, carotenoids, total chlorophyll, and peroxidase enzyme activity. Further, with increasing light intensity, stomatal density and index, and epidermal cells density increased, so that stomatal density of plants grown under 1800 μmol m-2 s-1 light intensity was twice of that under 600 μmol m-2 s-1 light intensity. Moreover, application of ascorbic acid increased ascorbate peroxidase enzyme activity, stomatal density, guard cell length, while, it reduced proline content, catalase and peroxidase enzyme activities. Overall, the results showed that increasing light intensity induced stress in Zinnia and weekly application of ascorbic acid alleviated the stress effects.