Pattern of ROS generation and interconversion on wet stigmas in basal and divergent angiosperms

Abstract

The active participation of ROS in the reproductive physiology of flowering plants is well-documented in model species, mainly plants with dry stigmas. Here we studied the release of ROS into stigma exudate – a fluid involved in pollen acceptance on a wet stigma. The study involved plants from different systematic groups: Paeonia suffruticosa, Nicotiana tabacum, Lilium hybr., Aristolochia manshuriensis and Berberis vulgaris; in most cases, exudate was collected from intact flowers on the whole plant to minimize the effect of experimental intervention on the sensitive redox balance system. The dynamics of total oxidizing capacity of stigma exudate was assessed by EPR spectroscopy and different stigma staining. The level of hydrogen peroxide and the activity of superoxide dismutase, which catalyzes H2O2 formation, was also evaluated. In all the plants studied, total ROS level increased with stigma maturation, however, H2O2 concentration decreased in studied representatives of eudicots, except for peony. In lily it increased, while in birthwort it remained low, which was apparently due to the absence of SOD activity. In all divergent plants studied, the enzyme was active on stigmas with two isoenzymes. During the fertile period, activity was higher than at an earlier stage. Based on the obtained data, we speculate on primitive and progressive patterns of ROS generation and transformation on stigma and its possible evolution.