Salt-induced expression of the vacuolar H+-ATPase in the common ice plant is developmentally controlled and tissue specific

For salinity stress tolerance in plants, the vacuolar type Ht-ATPase (V-ATP ase) is of prime importance in energizing sodium sequestration into the cen tral vacuole and it is known to respond to salt stress with increased expre ssion and enzyme activity. In this work we provide information that the exp ressional response to salinity of the V-ATPase is regulated tissue and cell specifically under developmental control in the facultative halophyte comm on ice plant (Mesembryanthemum crystallinum). By transcript analysis of sub unit E of the V-ATPase, amounts did not change in response to salinity stre ss in juvenile plants that are not salt-tolerant. In a converse manner, in halotolerant mature plants the transcript levels increased in leaves, but n ot in roots when salt stressed for 72 h. By in situ hybridizations and immu nocytological protein analysis, subunit E was shown to be synthesized in al l cell types. During salt stress, signal intensity declined in root cortex cells and in the cells of the root vascular cylinder. In salt-stressed leav es of mature plants, the strongest signals were localized surrounding the v asculature. Within control cells and with highest abundance in mesophyll ce lls of salt-treated leaves, accumulation of subunit E protein was observed in the cytoplasm, indicating its presence not only in the tonoplast, but al so in other endoplasmic compartments.