Kinetin alleviates the influence of waterlogging and salinity on growth and affects the production of plant growth regulators in Vigna sinensis and Zea mays

Growth criteria ( shoot height, root length and dry weight) of 14-d-old Vigna sinensis and Zea mays were mostly suppressed by waterlogging or salinization using artificial seawater mixture during the subsequent 3 weeks; the water level in pots was, respectively, kept at 120% or 60% of water field capacity. The suppression in growth induced by salinization was greater than that obtained by waterlogging. The pattern of changes in growth appeared similar to chlorophyll a and b as well as activity of delta-aminolevulinic acid dehydratase (ALA-D). On the other hand, waterlogging significantly increased indole-acetic acid (IAA) in shoots of both species but salinity had a decreasing effect. Both treatments decreased gibberellic acid (GA(3)) levels in shoots of Vigna sinensis and Zea mays as well as zeatin in shoots of Zea mays. Meanwhile, abscisic acid (ABA) was greatly accumulated in shoots of the stressed plants. Foliar application of 50 ppm kinetin counteracted the resulting reduction in growth and in chlorophylls of both species but partially lowered the inhibition in ALA-D activity. Moreover, kinetin increased IAA, GA(3) and zeatin in the stressed plants to mostly reach control levels, but markedly reduced ABA. These findings indicate that relief of the damage and restoration of normal conditions was maintained either partially or completely by application of kinetin. This recovery may be a consequence of several roles played by such hormones, which can cause triggering of the internal cellular metabolism and also induce alterations in the ratios of growth regulators.