| Abstract: | Carboanhydrase activity and extractable zinc as indicator of the zinc supply of plants 1. Maize, millet, tobacco, sugar-beet and vine were grown under controlled environmental conditions with different zinc concentrations in the substrate. Plant growth, zinc and phosphorus content of the dry matter, extractable zinc and carbonic anhydrase activity in the leaves were measured. 2. Increasing supply of zinc to strongly zinc deficient plants resulted in a marked increase of growth, whereas total zinc content of the leaf dry matter was only slightly and carbonic anhydrase activity was strongly affected. In extremely zinc deficient plants carbonic anhydrase activity was close to zero even though the zinc content of the dry matter was higher than 10 μg/g. Therefore carbonic anhydrase activity appears to reflect the amount of physiologically active zinc in the leaf tissue. It seems to be useful to decide critical cases even at latent zinc deficiency. 3. The P/Zn ratio is also an indicator of zinc supply when plants are extremely zinc deficient, but not under latent deficiency. Moreover the P/Zn ratio can vary in a wide range when plants are well supplied with zinc. 4. The zinc concentration of aqueous leaf extracts increased with increasing level of zinc. 2-3 μg Zn/ml extract were found to be sufficient for all plant species used and all conditions of growth applied. Apparently, the Zn-concentration of the aqueous leaf extract is a better parameter of zinc supply than total zinc or carbonic anhydrase activity which, in addition, is much more difficult to determine. |
