Comparative effects of mono and dipotassium phosphates on cell leakiness in corn leaves

The quantity of nutrients which can be sprayed onto the foliage of plants is limited by the onset of burn damage, but the mechanism(s) of burn induction are not defined. Droplets of KH₂PO₄ applied to intact leaf cuticles induced burn damage at concentrations ≥ 0.50 M whereas K₂HPO₄ was damaging at 0.05 M. Different cuticular penetration rates did not account for these differences. We report here on the comparative effects of these two salts on membrane integrity, as expressed by leakage of U.V. absorbing constituents from leaf cells. Infiltration of a hypotonic solution (0.05 to 0.10 M) of either salt into corn leaf segments did not induce selective acceleration of leakage of U.V. absorbing constituents from leaf cells during a 90 min. incubation. However, incubation in 0.10 M K₂HPO₄ lead to a 87% increase in the efflux of cell constituents when followed by a 10 min. osmotic stress treatment in 1M sucrose and subsequent transfer to water.

The induction of damage by K₂HPO₄ applied to intact plants was inhibited by high humidity low stress conditions. The results suggest that K₂HPO₄ has a selective toxic effect on plant cells which is potentiated by environmental water stress.