Abstract
Drought is a multifaceted environmental stress condition that limits crop productivity worldwide. Spermidine (Spd), one of the types of polyamines (PAs), is involved in plant stress tolerance. However, the molecular mechanism underlying the changes in the abundance of metabolites induced by Spd in drought stress tolerance is poorly understood. We aimed to examine the effects of Spd on the endogenous PA content, growth, photosynthesis, antioxidant system, and metabolite profiles as well as the expression of stress-responsive genes (NtP5CS, NtHsp18 and NtLEA5) in N. tabacum under drought stress and to investigate the underlying mechanisms with which Spd is involved. The results revealed that Spd application significantly increased the Spd, putrescine (Put), and spermine (Spm) contents and plant biomass under drought stress. Biochemical assays indicated that, under water-deficit conditions, plants treated with Spd presented increased chlorophyll contents, photosynthesis rate, and activities of antioxidant enzymes (SOD, POD, CAT and APX), but reduced O2•− production speed, H2O2 content, MDA content and electrolyte leakage. Furthermore, metabolite profiles revealed that Spd significantly promoted the contents of carbohydrates, unsaturated fatty acids, IAA and ABA phytohormone, but decreased most amino acid levels compared to those in drought-exposed plants. This study provides a comprehensive understanding of Spd-mediated drought stress tolerance from physiological, biochemical and metabolic perspectives.
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