SALT STRESS INDUCES AN INCREASED EXPRESSION OF V-TYPE H-ATPASE IN MATURE SUGAR-BEET LEAVES()

In the halotolerant sugar beet co-expression of V-ATPase and a vacuola r Na+/H+-antiporter provides a mechanism for vacuolar salt sequestrati on. To analyze salt-induced changes in the expression of the vacuolar H+-ATPase (V-ATPase) a partial cDNA of the proton-channel forming subu nit c was cloned by RT-PCR. Southern blot analysis indicated a small g ene family. In control plants transcript levels were high in roots and young growing leaves but low in fully expanded leaves. In mature leav es salt exposure (400 mM, 48 h) induced a strong increase in subunit c -mRNA. Transcripts for the catalytic subunit A followed a similar deve lopmental and stress-modulated pattern, indicating a coordinate regula tion of transcripts for both V-ATPase subunits. Concomittant with the mRNA increases the amount of V-ATPase protein increased as well.