Hormonal Regulation of Ca2+ Stimulated K+ Influx and Ca2+, K+‐ ATPase in Rice Roots: in vivo and in vitro Effects of Auxins and Reconstitution of the ATPase

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Abstract
The role of natural and synthetic auxins in regulation of ion transport and ATPase activity was studied in rice roots (Oryza sativa L. cv. Dunghan Shah). In vivo treatment of seedlings with 2,4‐dichlorophenoxyacetic acid at 2 × 10−6M for a short period enhanced subsequent Ca2+ stimulated K+ influx and ATPase activity, while a longer treatment diminished both K+ influx and ATPase activity. Indoleacetic acid at 10−10–10−8M induced ATPase activity. In in vitro experiments both 2,4‐dichloro phenoxyacetic acid and indoleacetic acid (10−10–10−8M) stimulated Ca2+, K+‐ATPase activity of a plasmalemma rich micro somal fraction from the roots.Acetone extracted ATPase preparations lost their activity. The enzyme regained its activity and its sensitivity towards ions (Ca2++ K+) when reconstituted with phosphatidyl choline. Addition of auxins also indicated that the presence of the lipid was necessary in the interaction between the ATPase and auxins. Auxins and ions probably interact with the intact ATPase lipoprotein complex, which may possess a receptor site for the auxins, possibly as a sub unit.