Ameliorating effect of foliar applied proline on morphological and nutritional characteristics of UCB1 pistachio rootstock under drought stress conditions

Water deficit is the most important stresses that limit the production of many crops and fruits worldwide (Fattahi et al., 2021) and severely impairs plants growth and development through alterations in the physiological, morphological, biochemical, and molecular attributes. As well as, Proline is one of the active amino acids in the osmotic regulation phenomenon and it has an effective role in reducing cell damage and improving drought tolerance. Different plants use different strategies to deal with drought stress which one of them is the use of osmotic substances such as proline. Through foliar application, which reducing significantly the destructive effects of stress on plants. Among these, the use of proline exogenous has been an effective way to reduce the adverse effects of stress (Soroori et al., 2020). The aim of this study was influence of exogenous application of proline on growth and root and leaf nutrient content of drought-stressed UCB1 plants.

The experiment was carried out in factorial format based on completely randomized design in greenhouse conditions of Shahrekord university (in 2019) with 3 replications and 3 samples. The first factor was drought stress in three levels (100% as the control, 70% and 40 % of field capacity as the treatments) for 60 days and second factor was proline application in three levels (0 as the control, 75 and 150 mg. l-1 as the treatments). To measure the dry weight of the aerial and root organs, the samples were kept in an oven at 70 °C and the weight was measured by a digital scale with 0.01 g accuracy. Proline was determined following Bates et al. (1973). The absorbance of the organic phase was recorded at 520 nm. The phosphorus amount was determined by measuring the absorbance at 470 nm using a spectrophotometer (Olsen et al., 1954).

Water limitation reduced the leaf area, leaf and root DW, also under drought stress conditions, the mineral content (P, K, Ca, Mg, Fe and Zn) of the UCB1 rootstock markedly decreased. The accumulation of minerals in the leaves and roots of sprayed plants was significantly higher than in the non-sprayed plants with proline. Proline foliar application (150 mg. l-1) improved the nutritional status (K, Ca, Fe, Zn in the leaves and roots of the pistachio rootstocks) of the UCB1 under stress conditions (Table 1&2). The significant (p < 0.05) decrease in leaves area, leaf and root dry weights of UCB1plants (Table 1) under drought stress conditions could be due to the reduction of water absorption from the soil and consequently to decreased cell division and elongation as well as plant growth. On the other hand, reducing the stomatal conductance, reducing carbon stabilization, limiting water absorption and nutrients. Increased growth by proline in drought stress is likely due to increased proline accumulation, which not only protects the enzymes and structures of proteins and organ membranes, but also provides a source of energy for growth and helps plants survive through resistance to stress.

Foliar application of proline increased the dry weight of leaf and root organs, leaf area, as well as improved the nutritional status (P, K, Mg, Ca, Fe and Zn) of the UCB1under stress conditions. drought stress also reduced all traits except proline. In general, it can be suggested that foliar application of proline (150 mg L-1) can be used as a defense factor in plants under drought stress.