REGULATION OF ROOT PLASMA-MEMBRANE H+-ATPASE IN SUNFLOWER SEEDLINGS

We have developed specific assays for the levels of mRNA, antigenic protein and catalytic activity under standard conditions of the root plasma membrane H+-ATPase of sunflower (Helianthus annuus L. var. HSE) seedlings. During the first 6 days of root development there is a parallel increase in the levels of mRNA, antigenic protein and activity. No significant changes were induced by alkaline pH or NaCl. Acetic acid at pH 4 reduces the level of mRNA more than the levels of antigenic protein and activity (to 30% and 50-60% of controls. respectively). Illumination of the aerial part of the seedlings reduces the antigenic protein and activity in the roots to 50-60% of controls without affecting the level of mRNA. These results suggest that there is regulation of the expression of root plasma membrane H+-ATPase by development and environmental conditions.