Differential sensitivities of photosynthetic component processes govern oxidative stress levels and net assimilation rates in virus-infected cotton

Cotton ( Gossypium hirsutum L.) leafroll dwarf virus disease (CLRDD) is a yield-limiting threat to cotton production and can substantially limit net photosynthetic rates (A N ). Previous research showed that A N was more sensitive to CLRDD-induced reductions in stomatal conductance than electron transport rate (ETR) through photosystem II (PSII). This observation coupled with leaf reddening symptomology led to the hypothesis that differential sensitivities of photosynthetic component processes to CLRDD would contribute to declines in A N and increases in oxidative stress, stimulating anthocyanin production. Thus, an experiment was conducted to define the relative sensitivity of photosynthetic component processes to CLRDD and to quantify oxidative stress and anthocyanin production in field-grown cotton. Among diffusional limitations to A N , reductions in mesophyll conductance and CO 2 concentration in the chloroplast were the greatest constraints to A N under CLRDD. Multiple metabolic processes were also adversely impacted by CLRDD. ETR, RuBP regeneration, and carboxylation were important metabolic (non-diffusional) limitations to A N in symptomatic plants. Photorespiration and dark respiration were less sensitive than photosynthetic processes, contributing to declines in A N in symptomatic plants. Among thylakoid processes, reduction of PSI end electron acceptors was the most sensitive to CLRDD. Oxidative stress indicators (H 2 O 2 production and membrane peroxidation) and anthocyanin contents were substantially higher in symptomatic plants, concomitant with reductions in carotenoid content and no change in energy dissipation by PSII. We conclude that differential sensitivities of photosynthetic processes to CLRDD and limited potential for energy dissipation at PSII increases oxidative stress, stimulating anthocyanin production as an antioxidative mechanism.