Zinc Deficiency, Carbonic Anhydrase, and Photosynthesis in Leaves of Spinach

Abstract

A shortage in the zinc supply to spinach (Spinacia oleracea L.) drastically reduced carbonic anhydrase levels with little effect on net C02 uptake per unit leaf area, except with the most severe zinc stresses. Under these conditions, carbonic anhydrase was below 10% and photosynthesis 60 to 70% of the control levels. When photosynthesis was measured at a range of CO2 supply levels, zinc-deficient leaves were less efficient at 300 to 350 microliters per liter CO2 and above, but the same as controls at lower CO levels. This suggests that carbonic anhydrase does not affect the diffusion of C02, and that the effect of zinc deficiency was on the photosynthetic process itself. Our evidence does not support the hypothesis that carbonic anhydrase has some role in facilitating the supply of C02 to the sites of carboxylation within the chloroplast.Carbonic anhydrase is widespread in plants, but its exact physiological role is still uncertain. It may be directly involved in photosynthesis, facilitating the diffusion of CO2 through the liquid phase of the cell to the chloroplast (9,13,20). In algae grown at high CO2, carbonic anhydrase is absent. After transfer to low CO2, photosynthesis is at first negligible, but later increases in step with increasing carbonic anhydrase levels (8). In higher plants, acetazolamide, an inhibitor of carbonic anhydrase, has been shown to reduce photosynthesis by intact chloroplasts. The inhibition can be overcome by raising the bicarbonate level (4). Acetazolamide also inhibits the photosynthesis of detached leaves of spinach and maize (5). Wood and Sibly (19) found that zinc-deficient plants contained low levels of carbonic anhydrase. In the experiments reported in this paper, we have studied the relationship between carbonic anhydrase and photosynthesis by manipulating the zinc supply to the plant. By this means, we have obtained large changes in carbonic anhydrase. However, these were accompanied by small effects on photosynthesis. The results reported do not support the hypothesis that carbonic anhydrase is directly involved in photosynthesis. MATERIALS AND METHODS

Subcellular volumes and metabolite concentrations in barley leaves

“…Barley (Hordeum vulgare L. cv. Apex, Kleinwanzlebener Saatzucht, Einbeck, FRG) was grown hydroponically in 5-L vessels containing fire-clay particles in a glasshouse (15 h light of 400-600 ~tmol photons.m 2. s 1, 22oc; 9 h darkness, 17~ The nutrient medium contained 4 mM Ca(NO~)2, 4 mM MgC12, 6 mM KNO3, 2 mM MgSO4, 1 mM KH2PO4 and Na2-Fe-EDTA, and trace elements according to Randall and Bouma (1973). Only the middle parts of fully expanded primary leaves of 21-d-old plants, harvested after 5 h of darkness or after 9 h of illumination within the same day, were used for nonaqueous fractionation.…”

Iron Deficiency Tolerance at Leaf Level in <i>Medicago ciliaris</i> Plants

“…It has been previously suggested that a limitation in the concentration of a micronutrient can depress its corresponding isoform enzyme activity but apparently there is a compensatory mechanism involving the induction of other isoforms, in order to keep an adequate level of SOD for the cell protection against deleterious effects of superoxide radicals. So far, this compensatory mechanism between Mn-SOD and CuZn-SOD has been well described in pea leaves [36] and in tobacco plants grown under limiting Mn conditions [37] [38], between Mn-SOD and Fe-SOD in Fe deficient pea leaves [39] and between CuZn-SOD and Fe-SOD in pea leaves conducted under Cu-limiting conditions [40]. Peroxidase enzymes are importantly involved in reducing H 2 O 2 to H 2 O.…”

SEQUESTRATION OF CYTOPLASMIC ORTHOPHOSPHATE BY MANNOSE AND ITS DIFFERENTIAL EFFECT ON PHOTOSYNTHETIC STARCH SYNTHESIS IN C3 AND C4 SPECIES

“…Spinach beet was grown in nutrient medium as described by Randall and Bouma (1973). For phosphate-deficient solution, potassium dihydrogen phosphate was omitted from the standard medium and, as the potassium nitrate present provided an adequate source of potassium, no further addition was made.…”