A novel fluorescence imaging approach to monitor salt stress-induced modulation of ouabain-sensitive ATPase activity in sunflower seedling roots.

Seedlings exposed to salt stress are expected to show modulation of intracellular accumulation of sodium ions through a variety of mechanisms. Using a new methodology, this work demonstrates ouabain (OU)-sensitive ATPase activity in the roots of sunflower seedlings subjected to salt stress (120 mM NaCl). 9-Anthroylouabain (a derivative of ouabain known to inhibit Na(+), K(+) -ATPase activity in animal systems, EC 3.6.3.9) has been used as a probe to analyze OU-sensitive ATPase activity in sunflower (Helianthus annuus) seedling roots by spectrofluorometric estimation and localization of its spatial distribution using confocal laser scanning microscopy. Salt stress for 48 h leads to a significant induction of OU-sensitive ATPase activity in the meristematic region of the seedling roots. Calcium ions (10 mM) significantly inhibit enzyme activity and a parallel accumulation of sodium ions in the cytosol of the columella cells, epidermis and in the cells of the meristematic region of the roots is evident. As a rapid response to NaCl stress, the activity of OU-sensitive ATPase gets localized in the nuclear membrane of root protoplasts and it gets inhibited after treatment with calcium ions. Nuclear membrane localization of the OU-sensitive ATPase activity highlights a possible mechanism to efflux sodium ions from the nucleus. Thus, a correlation between OU-sensitive ATPase activity, its modulation by calcium ions and accumulation of sodium ions in various regions of the seedling roots, has been demonstrated using a novel approach in a plant system.