Promotive effect of exogenously applied thiourea on key physiological parametersand oxidative defense mechanism in salt-stressed Zea mays L. plants

A greenhouse experiment was conducted to examine the alleviating role of thiourea (TU) on antioxidants and some vital physiological attributes in salt-stressed plants of two maize cultivars. The maize cv. DK 5783 performed better than cv. Apex 836 in an initial experiment. Of the six TU levels used in the initial experiment, 400 and 500 mg L-1 were chosen for subsequent studies. The two cultivars were subjected to saline stress (100 mM NaCl) and two levels of TU were applied presowing or as foliage spray. Salt stress suppressed total biomass, maximum fluorescence yield (Fv/Fm), chlorophyll, and leaf water potential ($\Psi$w), but it increased proline, hydrogen peroxide (H2O2), malondialdehyde (MDA), leaf osmolality (LO), membrane permeability (MP), and antioxidant enzymes. Exogenous TU application resulted in considerable increases in the dry weight of salt sensitive and tolerant cultivars (38% and 35%, respectively). TU partially improved the salt tolerance of maize plants; it reduced Na+ but increased N, K+, Ca2+, and P in the maize plants under saline regimes. TU regulated the growth of maize plants under stress conditions by reducing MP, MDA, and H2O2 levels, and altering activities of antioxidant enzymes as well as increasing photosynthetic pigments under a saline regime.