Role of hydrogen peroxide and the redox state of ascorbate in the induction of antioxidant enzymes in pea leaves under excess light stress

In this work we used two different pea cultivars, JI281 is a semidomesticated land race of pea from Ethiopia whereas JI399 is a typical domesticated pea variety. Exposure of pea leaves to excess light (EL) for 1 h caused a reversible photoinhibition of photosynthesis as showed by changes in F-v/F-m. Although little difference existed between the two pea genotypes with respect to photoinhibition, after 60 min of EL the decline in F-v/F-m was higher in JI281 than in JI399 leaves. As a consequence of EL, H2O2 increased in both pea cultivars, whereas lipid peroxidation and protein oxidation slightly increased, although differences between cultivars were minimal. The redox state of ascorbate shifted towards its oxidised form under EL stress in both cultivars. Transcript levels of genes coding antioxidant enzymes varied with EL in both cultivars, but the response was more pronounced in JI399. The induction observed during EL was maintained or increased after the stress period, as occurred for cytGR and chlMDHAR. GR protein accumulation and activity correlated with the transcript accumulation in JI399, but not in JI288. In this work, a possible role for H2O2 and redox status of ascorbate in the photoxidative stress signalling is discussed.