Metabolic interconnectivity among alternative respiration,residual respiration,carbohydrates and phenolics in leaves of Salvinia minima exposed to Cr(VI)

Floating and submerged leaves of the aquatic fern Salvinia minima were used to analyze a metabolic interconnectivity among mitochondrial alternative respiration, residual respiration (R_resp), carbohydrate metabolism and soluble phenolics (SP) accumulation occurring under Cr(VI) stress. Treatment with Cr enhanced alternative pathway capacity (AP_cap) and (R_resp) in both leaf types. AP_cap/T_resp ratio revealed an increasing relative contribution of the alternative respiration to total respiration rate under Cr(VI) treatment. Sucrose content increased in Cr-treated leaves, but glucose and starch decreased. Enzyme profile showed that sucrose synthase (SS) rather than soluble acid invertase (AI) seems to be involved in sucrose metabolism of Cr-treated plants. Accumulation of SP showed a positive correlation with both AP_cap and R_resp in floating leaves. Decreases of SP in submerged leaves can be explained by an increased synthesis of polymerized phenolics. Results provide important new insights about influence of alternative and residual respirations on the synthesis of phenylpropanoid-derivative compounds. This work could also represent the first communication about involvement of the R_resp in defence mechanism of S. minima against Cr(VI) toxicity.