Enhancement of Vacuolar H+-ATPase and H+-pyrophosphatase Expression by Phytohormones in Pear Fruit

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Vacuolar H+-pumps, vacuolar H+-ATPase and vacuolar H+-pyrophosphatase (V-ATPase and V-PPase), have important roles in the accumulation of sugars in vacuoles, in which their expression seems to be associated with changes in phytohormones. We investigated how phytohormones affect the expression of vacuolar H+-pumps by using immature fruit of pear (Pyrus communis L. var. sativa DC, 'La France') that actively accumulates sugars. Abscisic acid (ABA), gibberellic acid (GA), indole acetic acid (IAA) or 6-benzyladenine (BA) treatments increased markedly the levels of V-ATPase subunit proteins (A subunit (65 kDa), B subunit (55 kDa), and c subunit (16 kDa)). The V-ATPase activity increased by 28% over the control in disc tissues incubated with 10 μM ABA, accompanied by an increase in A subunit mRNA level. GA increased the V-ATPase activity by 48% over the control, but not the mRNA level. IAA and BA had no effect on the activity. Treatment with 100 μM GA increased the V-PPase protein level, the V-PPase activity by 20% over the control, and mRNA. IAA and BA also increased V-PPase protein but not the activity. These results show that the expression of vacuolar H+-pumps is complicated; it is controlled at each level of mRNA, protein, or activity, and that the increase in protein does not always lead to an increase in activity.
園芸学会の論文