Different peroxidase activities and expression of abiotic stress-related peroxidases in apical root segments of wheat genotypes with different drought stress tolerance under osmotic stress

One-week-old seedlings of Triticum aestivum L. cv. Plainsman V, a drought tolerant; and Cappelle Desprez, a drought sensitive wheat cultivar were subjected gradually to osmotic stress using polyethylene glycol (PEG 6000) reaching 400 mOsm on the 11th day. Compared to controls cv. Plainsman V maintained the root growth and relative water content of root tissues, while these parameters were decreased in the drought sensitive cv. Cappelle Desprez under PEG-mediated osmotic stress. Simultaneously, H2O2 content in 1-cm-long apical segment of roots comprising the proliferation and elongation zone, showed a transient increase in cv. Plainsman V and a permanent raise in cv. Cappelle Desprez. Measurements of the transcript levels of selected class III peroxidase (TaPrx) coding sequences revealed significant differences between the two cultivars on the 9th day, two days after applying 100 mOsm PEG. The abundance of TaPrx04 transcript was enhanced transitionally in the root apex of cv. Plainsman V but decreased in cv. Cappelle Desprez under osmotic stress while the expression of TaPrx01, TaPrx03, TaPrx19, TaPrx68, TaPrx107 and TaPrx109-C decreased to different extents in both cultivars. After a transient decrease, activities of soluble peroxidase fractions of crude protein extracts rose in both cultivars on day 11, but the activities of cell wall-bound fractions increased only in cv. Cappelle Desprez under osmotic stress. Parallel with high H2O2 content of the tissues, certain isoenzymes of covalently bound fraction in cv. Cappelle Desprez showed increased activity suggesting that they may limit the extension of root cell walls in this cultivar.