Effects of exogenous phytohormones and kinetin on the hydrolytic activity of proton pumps in the tonoplast of red beet at different stages of plant development

The effects of plant growth regulators (IAA, ABA, GA, and kinetin) applied at concentrations from 10(-10) to 10(-4) M on the hydrolytic activity of va cuolar H+-ATPase and H+-pyrophosphatase were investigated on vacuoles isola ted from red beet (Beta vulgaris L.) taproots at different stages of plant development. All growth regulators activated both H+-translocating enzymes, although maximum stimulation was exerted by different phytohormones at dif ferent stages of plant development. H+-ATPase was highly sensitive to the a ction of the hormones. The maximum increase in its activity (to a level of 300%) was found in the presence of kinetin during the second growing season . H+-pyrophosphatase was less sensitive to hormone action, and IAA was the most effective stimulator of this enzyme. The strongest effects of phytohor mones on the activity of this enzyme were exerted by the lowest concentrati ons tested (10(-10) M). Based on these results, it was concluded that phyto hormones are able to regulate the hydrolytic activity of the proton pumps o f the tonoplast.