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Abstract
Salicylic acid (SA) is involved in the regulation of metabolic activity and acts as a defense mechanism in plants under various stress conditions. This study was conducted to determine the effects of SA (10–500 µM) on seedling growth, development, and nitrogen use efficiency (NUE) in cucumber (Cucumis sativus L.) plants with and without nitrogen nutrient. SA increased the contents of chlorophyll, total non-structural carbohydrate, and total nitrogen, as well as nitrate assimilation through the induction of nitrate reductase (EC 1.6.6.1) activity in isolated cucumber cotyledons. Accumulation of SA was twice as high in cotyledons without nitrate supply as in those with nitrate supply. The germination percentage, root length, shoot length, and dry mass of cucumbers increased significantly in response to 50 µM SA. Higher concentrations of SA were, however, found to inhibit these physiological activities. The present results show that optimal physiological concentrations of SA (50 µM) are required to increase NUE in field applications, particularly during germination and seedling growth.