Response of carboxylate metabolism to zinc deficiency in Lactuca sativa and Brassica oleracea plants

Species or genotypes differ in their zinc use efficiency (ZnUE) under low Zn availability in the soil. Organic acids (OAs) synthetized by plant carboxylate metabolism may play a role in Zn‐deficiency tolerance. The main objective of the present work was to assess the response of two species of great agronomic interest such as Lactuca sativa and Brassica oleracea to Zn deficiency focusing on OAs and carboxylate metabolism. For this, L. sativa and B. oleracea plants were grown in hydroponic culture with two different Zn‐application rates: 10 µM Zn as control and 0.1 µM Zn as deficiency treatment. ZnUE parameters, concentrations of OAs and enzymes of carboxylate metabolism were analyzed. L. sativa showed better Zn uptake efficiency (ZnUpE), while B. oleracea demonstrated better Zn utilization efficiency (ZnUtE). In L. sativa, citrate and oxaloacetate concentrations and phosphoenolpyruvate carboxylase and citrate synthase activities increased, while fumarase and malate dehydrogenase activities declined. In B. oleracea no significant response was found in concentrations of carboxylate metabolism or enzyme activity except for a decrease in fumarase activity. These results suggest that a possible factor that induces the tricarboxylic acid cycle could be the low ZnUtE rather than the low Zn concentration under Zn‐deficiency conditions. In L. sativa citrate, oxaloacetate, phosphoenolpyruvate carboxylase, and citrate synthase may play a key role to face Zn deficiency, while in B. oleracea the higher ZnUtE cannot be explained in terms of a rise in OAs synthesis.