Acid rain-induced oxidative stress regulated metabolic interventions and their amelioration mechanisms in plants

Increased anthropogenic environmental pollution, one of the serious threats associated with rapid industrial/ economic development leads to enhanced release of SO X and NO X in the troposphere which later combined with moisture and results in acid rain (AR). Recurrence of AR leads an array of alterations in plants that includes inhibited seed germination, growth and productivity, biomass accumulation, photosynthesis, enzyme activities, protein synthesis, gene expression patterns, and over production of active oxygen species (AOS). This over produced AOS damages/ oxidizes to lipids, proteins and nucleic acids, and releases a number of cytotoxic intermediate/ end products thereby alterations in metabolic pathways and inactivation of key enzymes. Additionally, AR upsets the balance between AOS generation and elimination by altering the antioxidant defense system, and consequently oxidative stress in plants. However, in the recent past, few attempts have been made, to ameliorate the adverse impacts of AR in plants. Modulation in the levels of antioxidants for prevention against AOS-induced injuries has been recognized as one of the effective approaches towards AR tolerance. Accumulation of ascorbic acid, carotenoids, phenols and proline, and exogenous addition of calcium, polyamines, growth tonic, salicylic acid and β -aminobutyric acid were shown to be the effective strategies to cope low-pH stress in plants. The present review summarizes information on mechanisms of AR formation, uptake of H + , SO − 4 and NO − 3 by plants, AR-induced physiological, biochemical, and molecular changes and their amelioration using potential compounds. Gaps in the existing knowledge on AR-stress in plants, and future research directions are discussed.