Response of water deficit-stressed Vigna unguiculata performances to silicon, proline or methionine foliar application

- Foliar application of Si, proline or methionine mitigated the adverse effects of drought stress on cowpea plants.
- Growth and productivity, enzymatic and non-enzymatic antioxidants were improved by Si, proline or methionine application to plants.
- Si, proline or methionine application maintained RWC, increased WUE, and restored nutrients in plants under deficit irrigation.
- Foliar application of Si, proline or methionine protected the antioxidative defense system in cowpea plants under drought stress.
- Si had the highest, while methionine had the lowest ameliorative actions.

Environmental stresses are increasing over time adversely affecting crop productivity. To face these stresses, plants adopt endogenous mechanisms, but they are not enough in most cases. Therefore, the effect of exogenous application of proline, silicon (Si) or methionine on growth and yield criteria, leaf physio-biochemical properties and leaf anatomical structure of cowpea plants grown under three levels of water deficit (W0; 60, W1; 40 and W2; 20% of soil water holding capacity) was investigated. The water level W0 was adequate to optimum cowpea plant growth and specified as a control. Results obtained indicated that growth criteria (i.e., shoot dry weight, plant height, leaf area and number of branches per plant), yield characteristics (i.e., dry seed weight and biological yield per plant, and 100-seed weight), contents of leaf chlorophylls a and b, total carotenoids, shoot and seed nutrients (i.e., N, P and K), and leaf relative water content and membrane stability index were significantly decreased, while activity of leaf antioxidant enzymes such as peroxidase (POX), superoxide dismutase (SOD) and catalase (CAT), content of leaf proline and electrolyte leakage, and shoot Si were significantly increased under water deficit stress (W1 and W2) conditions compared to the control (W0). However under water deficit stress, foliar application of proline, Si or methionine seemed to overcome the harmful effects of water deficit stress, at varying degrees, on the abovementioned cowpea plants characters, which were improved, compared to the corresponding controls. The Si was the most helpful one, where it increased growth criteria (i.e., shoot dry weight, plant height, leaf area and number of branches per plant), yield characteristics (i.e., dry seed weight and biological yield per plant, and 100-seed weight), contents of leaf chlorophylls a and b, total carotenoids, shoot and seed nutrients (i.e., N, P and K), and leaf relative water content and membrane stability index, and further increased shoot Si content and leaf antioxidant enzyme activities of cowpea plants compared to those of either proline or methionine application. For leaf anatomical features, the width of midvein and xylem, and the thickness of midvein, phloem and xylem tissues, and palisade and spongy tissues of leaf blade were decreased with increasing the water deficit stress; however, foliar spray of Si improved all histological features compared to those of untreated plants.