The carbohydrate metabolism and the drought tolerance in citrus

Abstract

The use of rootstocks with tolerance to drought is an effective strategy to reduce the impact of water shortage on citriculture. The Rangpur lime rootstock is able to change the scion sensitivity to water deficit, maintaining the overall carbohydrate availability and root growth under unfavorable conditions. These responses induced by the Rangpur lime rootstock suggest its ability in coordinating the source-sink relationship towards an equilibrium between the synthesis and consumption of resources through changes on photosynthesis, respiration and carbohydrate partitioning. In such context, the hypothesis of this proposal is that the carbohydrate metabolism is more active in roots of drought-tolerant rootstocks, which would lead to higher root growth and increase sink demand. As consequence, increase in photoassimilate transport to roots and stimulus of leaf carbohydrate exportation would occur under water deficit. The three most important rootstocks in Brazilian citriculture, Swingle citrumelo, Sunki mandarin and Rangpur lime will be evaluated in two experiments to test the above hypothesis. In growth chamber, one group of plants grafted on a given rootstock will be subjected to water deficit for 18 days and afterwards re-hydrated. Another group will be maintained under well-watered conditions. We will evaluate leaf gas exchange, leaf water potential, plant biometry, carbohydrate concentrations on leaves, stem and roots, the activity of key enzymes of sucrose metabolism and ATP concentration. In the second experiment, plants will be subjected to a gaseous mixture containing 13C before water withholding. Besides leaf gas exchange and leaf water potential, we will evaluate the concentration and partitioning of 13C in plants, as well as the sap sucrose concentration. Both experiments will be arranged in random blocks, following a factorial scheme in which the factors are rootstock species, water regime and evaluation time. Data normality will be checked and then the analysis of variance will be carried out, with mean values being compared through the Tukey test (p<0.05). (AU)