HORMONAL-REGULATION OF CA-2+-STIMULATED K+ INFLUX AND CA-2+, K+-ATPASE IN RICE ROOTS - INVIVO AND INVITRO EFFECTS OF AUXINS AND RECONSTITUTION OF THE ATPASE

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 Shali). In vivo treatment of seedlings with 2,4-D at 2 .times. 10-6 M for a short period enhanced subsequent Ca2+-stimulated K+ influx and Ca2+, K+-ATPase activity; a longer treatment diminished K+ influx and ATPase activity. IAA at 10-10-10-8 M induced ATPase activity. In in vitro experiments both 2,4-D and IAA (10-10-10-8 M) stimulated Ca2+, K+-ATPase activity of a plasmalemma-rich microsomal 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 the necessity of the lipid 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 subunit.