Silicon-Induced Morphological, Biochemical and Molecular Regulation in Phoenix dactylifera L. under Low-Temperature Stress

Climate changes abruptly affect optimum growth temperatures, leading to a negative influence on plant physiology and productivity. The present study aimed to investigate the extent of low-temperature stress effects on date palm growth and physiological indicators under the exogenous application of silicon (Si). Date palm seedlings were treated with Si (1.0 mM) and exposed to different temperature regimes (5, 15, and 30 °C). It was observed that the application of Si markedly improved fresh and dry biomass, photosynthetic pigments (chlorophyll and carotenoids), plant morphology, and relative water content by ameliorating low-temperature-induced oxidative stress. Low-temperature stress (5 and 15 °C), led to a substantial upregulation of ABA-signaling-related genes (NCED-1 and PyL-4) in non Si treated plants, while Si treated plants revealed an antagonistic trend. However, jasmonic acid and salicylic acid accumulation were markedly elevated in Si treated plants under stress conditions (5 and 15 °C) in comparison with non Si treated plants. Interestingly, the upregulation of low temperature stress related plant plasma membrane ATPase (PPMA3 and PPMA4) and short-chain dehydrogenases/reductases (SDR), responsible for cellular physiology, stomatal conductance and nutrient translocation under silicon applications, was observed in Si plants under stress conditions in comparison with non Si treated plants. Furthermore, a significant expression of LSi-2 was detected in Si plants under stress, leading to the significant accumulation of Si in roots and shoots. In contrast, non Si plants demonstrated a low expression of LSi-2 under stress conditions, and thereby, reduced level of Si accumulation were observed. Less accumulation of oxidative stress was evident from the expression of superoxide dismutase (SOD) and catalase (CAT). Additionally, Si plants revealed a significant exudation of organic acids (succinic acid and citric acid) and nutrient accumulation (K and Mg) in roots and shoots. Furthermore, the application of Si led to substantial upregulation of the low temperature stress related soybean cold regulated gene (SRC-2) and ICE-1 (inducer of CBF expression 1), involved in the expression of CBF/DREB (C-repeat binding factor/dehydration responsive element binding factor) gene family under stress conditions in comparison with non Si plants. The current research findings are crucial for exploring the impact on morpho-physio-biochemical attributes of date palms under low temperature and Si supplementation, which may provide an efficient strategy for growing plants in low-temperature fields.