Exogenous proline alters the leaf ionomic profiles of transgenic and wild-type tobacco plants under water deficit

Abstract

Water deficit can reduce the absorption, accumulation, partition, and use of nutrients in plants. To mitigate the effects of this stress, plants produce osmolytes, such as proline, which may assist in preventing nutrient deficiencies under water deficiency. Therefore, the objective of this work was to evaluate the effects of exogenous proline application on the ionomic profile of wild-type and genetically modified tobacco (Nicotiana tabacum L.) overproducing proline under water deficit conditions. For this, the exogenous proline application in transgenic tobacco plants with constitutive expression of a mutated heterologous delta-1-pyrroline-5-carboxylate synthase enzyme (VaP5CSF129A) with reduced feedback inhibition and wild-type was studied. Water supply was suspended three days after foliar applications of 10 mM proline and the mineral elements content were determined in leaves nine days after the suspension of irrigation. Hierarchical clustering showed a clear differentiation between groups of plants with or without exogenous proline application, demonstrating that this treatment affected the ionomic profile of tobacco plants more than the water regime. The absorption and translocation mechanisms that were probably affected by the higher amount of proline allowed the separation the mineral elements into five groups by multivariate analysis. Notably, potassium was the nutrient present in the greatest content in tobacco leaves. In general, micronutrients were detected in larger amounts in transgenic plants, with the exception of iron possibly due to the competition with copper. Thus, the data suggest that proline might act, directly, or indirectly as a mitigator of nutritional deficiencies caused by water deficiency in tobacco, if applied prior to the onset of the water deficit conditions.