Impacts of salicylic acid on the morpho-physiological and biochemical characteristics of Ceratonia siliqua L. vitroseedlings under salt stress

Salinity has emerged as a significant global challenge, severely limiting the productivity of agricultural crops. This problem has been further exacerbated by climate change, which amplifies its impact. Unfortunately, the carob tree (Ceratonia siliqua), despite its importance in the Mediterranean region, its often cultivated on saline soils, which can negatively affect its productivity. Currently, various approaches are being explored to mitigate the detrimental effects of salinity on plants. Among the most recommended solutions is the use of phytohormones such as salicylic acid. Salicylic acid is an endogenous growth hormone known for its ability to enhance plant resistance to various types of abiotic stress. Furthermore, its effect has already been tested on several species. The aim of this study is to evaluate the response of Ceratonia siliqua vitroplants, derived from seedlings, to salt stress (80 mM, 240 mM) in the presence of salicylic acid (0.5 mM). The results indicated that salt stress led to an increased latency period, a 50% reduction in germination rate, and diminished growth and leaf area incarob vitroseedlings. Additionally, it caused disruption of photosynthesis. Salt stress also affected the levels of osmoprotectants by increasing their synthesis, such as proline, soluble sugars, and glycine-betaine. It also affected the content of polyphenols and the antioxidant activity of the plant. The introduction of salicylic acid in the presence of high stress (240 mM) led to a decrease in the latency period of vitroseedlings by 1 day. Furthermore, it increased the germination rate from 50 to 66.67%. As for other morphological parameters, a slight decrease in aerial part and root length, internode spacing, and leaf area was observed. Concerning the biochemical parameters, the application of salicylic acid under high-stress conditions resulted in a reduction of glycine-betaine and soluble sugar content, decreasing from 0.28 to 0.22 mg·g-1 DM and from 1.89 to 1.35 mg/g MF, respectively. Nevertheless, the results have indicated an increase in both proline and total polyphenol contents. However, by subjecting the vitroplants to salicylic acid in the presence of moderate salt stress (80 mM), a significant increase was recorded in soluble sugars, proline, and total polyphenols.