Ecophysiological approach to study of the role of cell-bound peroxidase forms in wheat leaves of different morphology

Abstract

Extracellular peroxidase enzymes, both ionically - and covalently bound, have been implicated in the biochemical changes of cell wall and furthermore for regulation of leaf and root extension growth. However, the role of cell wall bound peroxidase in changes of mature leaf morphology is poorly understood. The aim of this study was to determine whether ionically and covalently bound peroxidase activities exhibit any relationships with drought-induced leaf rolling of wheat. An activity and thermostability of three wheat genotypes with different leaf rolling degree were studied. The results clearly show that two genotypes with leaf rolling trait exhibited significantly higher activity of both extracellular peroxidase fractions in comparison to non-rolling cv. 'Omskaya 9'. In addition, the significant genotypic differences were found in thermostability of ionically and covalently bound peroxidase. A 35 °C-treatment decreased the activity of ionically bound peroxidase (IBP) in non-rolling leaves of parent cultivar and enhanced the activity of IBP in rolling leaves of 'Alba' genotype. Under 45 and 55 °C-treatment the IBP was more stable in rolling leaves of both genotypes 'Otan' and 'Alba'. Despite to low activity of covalently bound peroxidase it was more stable after heating by 45 °C compare with ionically bound fraction. The heating of covalently bound peroxidase (CBP) extracts by 35 °C and 45 °C also has enhancing effect on its activity by both leaf rolling genotypes (on 16 and 40% by 'Otan' and 'Alba', respectively). At the same time the CBP activity of non-rolling genotype decreased significantly on 40%. Even after 55 °C-treatment the CBP of both rolling genotypes remained very stable, although there were further inhibition of CBP purificated from leaves of non-rolling genotype. Both wheat genotypes with inserted leaf rolling trait exhibited a much higher blue-green fluorescence emission than non-rolling leaves of parent cultivar 'Omskaya 9'. Thus, the molecular mechanism of leaf rolling regulation seems to include an adjustment of cell wall properties and probably involves an activity of cell wall bound peroxidase. Further investigation is expected to reveal the regulatory mechanism for leaf rolling in wheat.