AUXIN-MODULATED PROTEIN DISULFIDE-THIOL INTERCHANGE ACTIVITY FROM PLASMA-MEMBRANES OF SPINACH LEAVES RESPONDS TO PHOTOPERIOD AND NADH

The renaturation of scrambled (oxidized and inactive) RNase A is catal yzed by plasma membrane vesicles isolated from spinach leaves. The act ivity was assayed using a spectrophotometric assay with cCMP as the RN ase substrate. The protein disulfide-thiol interchange activity requir ed for RNase renaturation was stimulated 1.5- to two-fold by 1 mu M au xin (2,4-D) and up to 1.5-fold by addition of NADH. The activity also was elevated ca. 1.8-fold in plasma membrane vesicles isolated from le aves of plants treated with 1 kg/hectare 2,4-D (1.3 x 10(-2) M if even ly distributed in the treated plants). The activity of the plasma memb rane vesicles isolated from leaves of 2,4-D-treated plants remained au xin-responsive (1.5-fold stimulated by 1 mu M 2,4-D). Also elevated wa s the activity in leaves from short day plants compared with plants in duced to flower by 24 h of continuous light. The activity was reduced ca. two-fold by photoinduction but remained auxin-responsive.