SummaryThroughout the life cycle of oat plants carbonic anhydrase activity, which is restricted to the non-chloroplast fraction of leaves, reaches a maximum value and then decreases. After appearance of deficiency symptoms carbonic anhydrase activity is less in zinc-deficient plants than in fully manured controls of the same age and is associated with a lower zinc content of the leaves.An experiment is described wherein uniform tomato plants w'ere grown in zinc-deficient water cultures. The need for using uniform ontogenetic material is discussed. With the onset of zinc deficiency symptoms, which are described, four different concentrations of zinc were added to solutions in which the plants were growing; in order to minimize growth changes plants were harvested at short time intervals after application and carbonic anhydrase activity and zinc and protein-N contents were measured at each harvest.Carbonic anhydrase activity showed highly significant positive linear correlation with both zinc and protein-N contents.Evidence is presented which indicates that in zinc-deficient plants carbonic anhydrase activity is less than in normal plants through blocking of metabolic reactions leading to formation of protein and not by absence of sufficient zinc to activate an apoenzyme.

Three experiments are described in which oat plants (var. Mulga) weregrown in Laffer sand or culture solutions containing varying amounts of addedzinc. In each case, zinc contents of living and dead leaves, stems, roots, inflorescence,and grain were determined at intervals until final harvest.

Carbonic anhydrase activity in leaves of plants is low compared with that in animal tissues.