Effects of lead stress on rice (Oryza sativa L.) growth and metabolism in the rhizosphere microenvironment: the role of eicosanoid compounds

As agricultural environments deteriorate, proper management of crop growth and regulation requires an understanding of tolerance strategies to heavy metal stress. Rice (Oryza sativa L.) growth and reproduction processes are influenced through lipid peroxidation and altered eicosanoid metabolism, both of which are induced by lead (Pb) poisoning. This study aimed to explore the relationship between rice growth and flowering processes and the metabolism of eicosanoid compounds in the rhizosphere microenvironment under Pb stress. Pot cultivation was conducted by using paddy soil and exogenously applied Pb. The following parameters were determined: soil physicochemical properties; rice biomass of stem, leaf, panicle, grain; flowering time and anther numbers; and metabonomics in the rhizosphere microenvironment. Compared with that of the low-Pb treatment (30 mg kg−1) and control groups (without exogenous Pb), the rice flowering stage of the high-Pb treatment groups (1000 mg kg−1) occurred approximately 2 days earlier, whereas in high-Pb treatment groups, biomass and yield decreased significantly, resulting in a 42.39% reduction in dry biomass per plant and a 23.64% reduction in thousand-kernel weight (TKW), compared with the low-Pb treatment groups. The addition of Pb to the soil further altered metabolic processes within the rhizosphere, among which arachidonic acid (AA) metabolism was the most significant pathway with the greatest rich factor in all Pb level comparisons. The high-Pb treatment induced downregulation of lecithin but upregulation of prostaglandins (PGs) A2, B2, and J2. Eicosanoid-related metabolism was significantly affected in the rhizosphere microenvironment under Pb stress, which resulted in the hydrolysis of cell membrane phospholipids (mainly AA) and an upregulation in PGs and LTs, which ultimately led to plant impairment but resulted in early flowering. Sexual reproduction may be stimulated and advanced by increased eicosanoid metabolism, revealing an active heavy metal tolerance strategy for rice survival.