Effect of Cycocel derivatives and gibberellin on choline kinase and choline metabolism

Cycocel stimulated the activity of partial purified choline kinase from spinach or squash leaves, but it inhibited the activity of yeast choline kinase. The activity of different Cycocel analogs on plant growth corresponded to their stimulatory effect on the isolated choline kinase. Cycocel had no effect upon the activity of a plant phosphatase which hydrolyzed phosphorylcholine nor upon adenosine triphosphatase from wheat roots or leaves. Gibberellin A(3) inhibited choline kinase activity and reversed the stimulatory effect of Cycocel on the kinase. Total choline kinase activity per squash plant was not greatly increased by Cycocel treatment. However, on the basis of fresh weight, total kinase activity was increased by Cycocel treatment. Gibberellin A(3) partially reversed these increases. Treatment with Cycocel plus indoleacetic acid resulted in a large increase in choline kinase activity. The same distribution of tracer among phosphorylcholine, choline and betaine was observed when either phosphorylcholine-C(14) or choline-C(14) was fed to barley or wheat roots. Cycocel stimulated the incorporation of choline-C(14) into the insoluble fraction and into lipids. Cycocel inhibited phosphorylcholine uptake by roots. Thus Cycocel stimulated choline kinase activity and the utilization of choline-C(14). The effect of Cycocel upon kinase activity in vivo and in vitro was reversed by gibberellin A(3).

Choline kinase and phosphorylcholine phosphatase in plants

Choline kinase was present in barley and wheat roots and leaves of barley, wheat, tobacco, spinach and squash plants. The kinase was purified 25-fold from spinach leaves. The enzyme had a broad pH optimum between 7.5 and 10.0. Mg(++) was required for activity and in the presence of Mg(++) the enzyme was relatively stable. Maximum enzyme activity was obtained when the Mg(++): ATP ratio was 1:1. The K(m) was 1 x 10(-4)m. The kinase from leaves was similar to that from rapeseed or from yeast, except that the leaf and seed enzymes were not inhibited by compounds which attach sulfhydryl groups. Only a very slow hydrolysis of phosphorylcholine by similar plant extracts was observed. This phosphatase activity was purified 200- or 300-fold and appeared to be caused by a nonspecific acid phosphatase. The activity of both the kinase and the phosphatase did not seem sufficient to account for the rapid equilibration of the large phosphorylcholine reservoir of plants with exogenous P(32)-labeled orthophosphate.