Time for Metabolic Acclimation to Initial Arsenic Accumulation by Water Lettuce (Pistia stratiotes L.)
摘要
Phytoremediation is a promising approach for remediating arsenic (As)-contaminated sites, a highly toxic metalloid. However, efficient phytoremediation depends on the acclimation of primal metabolism to balance stress tolerance with the maintenance of growth and biomass production, which ultimately is essential for efficient phytoextraction of the contaminant in the plant body. We investigated in this work how the aquatic phytoremediator Water lettuce (Pistia stratiotes L.) acclimates to short-term (24, 48, and 72 h) exposure to As (1.5 mg L−1 of Na2HAsO4.7H2O). The objective was to evaluate which metabolites adjust only to the presence of As in plant tissues and which signal changes in the internal concentration pattern of As in the plant to understand how P. stratiotes initially acclimate to As during phytoremediation. Pistia stratiotes accumulated As, especially in roots, which presented 8.6 times more As content than in leaves in the first 24 h, decreasing this ratio to 4.1 and 4.5 times after exposure to As at 48 and 72 h, respectively. The translocation of As to the leaves decreased the photochemical efficiency of PSII, CO2 quantum yield, carbon assimilation rate, and electron transport rate at all assessment times while increasing the respiration rate by 102% at 48 h. Despite differences in As concentrations between leaves and roots, metabolic parameters, such as sugars (fructose, 3.4 times higher at 48 h), organic acids (fumarate, 9.1 times higher at 48 h), and the activity of tricarboxylic acid cycle enzymes (isocitrate dehydrogenase, 1.5 times higher at 48 h), sustained stable increases between 48 and 72 h, especially in the leaves. Parameters such as glucose, the NAD/NADH, and NADP/NADPH ratios increased in the leaves at 24 h of As treatment by 290, 40, and 83%, respectively. However, these parameters were adjusted to conditions similar to those of the control group throughout experimental time. In summary, acclimation of P. stratiotes to arsenic-contaminated water involves changes in its catabolic pathways, enabling the plant to adjust to a decrease in photosynthetic activity. The increased production of sugars, organic acids, and reduced compounds, such as NAD(P)H, may help supply the plant's defenses with necessary carbon skeletons and reducing power. Conversely, transient changes in key molecules, like glucose, seem to occur in response to fluctuations in the internal arsenic content accumulated by the plant. This response contributes to the plant's acclimation to arsenic stress.