Elementos fisiológicos, bioquímicos e moleculares da aplicação exógena de prolina em plantas de sorgo submetidas à salinidade

Abstract

The aim of this present work was to evaluate the effects of foliar proline spray on biochemistry, physiology and molecular biology of sorghum plants (Soghum bicolor), CSF 20 cultivar, under saline stress conditions. For this, in a first experiment, proline solutions were sprayed to indicate the most suitable concentration to be sprayed onto the leaves in order to promote improvement in plant growth under stress with 75 mM NaCl. At 14 days after the treatments (DAT), analysis of growth parameters showed that the proline concentration that presented the best result was 30 mM. In a second experiment, performed under the same sowing and growing conditions as the previous one, plants were submitted to the following treatments: 1. control/water – without NaCl and spraying with deionized water; 2. control/proline – without NaCl and proline at 30 mM; 3. saline/water – 75 mM NaCl and spraying with deionized water; and 4. saline/proline – 75 mM NaCl and proline at 30 mM. The plants were collected with 7 and 14 DAT. As a result, it was observed that the saline/proline treatment reduced deleterious effects caused by salinity, mainly at 14 DAT, being smaller the reductions in leaves and roots fresh and dry masses and in leaf area. This was related, in part, to lower reductions in membrane damage, relative leaf water content, and net photosynthesis and transpiration rates caused by saline stress. Also, in the saline/proline treatment, at 14 DAT, there was complete recovery in reduction of stomatal conductance caused by saline stress and lower reduction in b and total chlorophyll contents. In saline/proline treatment, Na+ and Cl- contents decreased and K+, Ca2+ and K+/Na+ increased, resulting in a more favorable ionic relationship. Also in leaves, N-compounds and Carbohydrate levels was increased during proline saline treatment at 14 DAT and, regardless of sampling time, glutamine, glutamate, aspartate and asparagine contents were generally higher in saline/proline treatment. In leaves, at 7 DAT, the large increase in proline levels in saline/proline treatment, compared to saline/water treatment, was accompanied by a reduction in activity of synthesis enzyme (P5CS) and increase in activity of degradation enzyme (ProDH), such that at 14 DAT the proline levels were the same in these two treatments. In a third experiment, conducted under similar conditions described, gene expression of p5cs1, p5cs2, oat and prodh genes involved in proline metabolism was studied. Of these genes, p5cs1 expression (in leaf and root) and prodh (in leaves) genes was modulated over time, and this was related to the variation in P5CS and ProDH activity in leaves of saline/proline treatment. Therefore, the results obtained demonstrate that exogenous proline minimizes deleterious effects of salinity.