Mechanism of Action of Gametocides As Agents Disturbing the Normal Development of the Male Gametophyte

Abstract

We studied the mechanism of action of gametocides on the male reproductive tissue of plants. Gametocides are known to disturb the normal development of pollen. They are morphogenetic poisons used for treating plants at the stage of initiation of generative organs. Our earlier analysis of a databank on the relationship between the chemical structure and activity of gametocides showed that the gametocidal activity was not correlated with definite types of reactivity or spatial structure of the molecules of these compounds [1]. The results obtained allowed us to assume that the effect of gametocides is determined by a nonspecific response of generative tissues of plants to chemical stress, which is expressed as the induction of apoptosis in these tissues.Mizelle et al. [2] performed an electron microscopic study of the pollen of wheat plants treated with the gametocide phenridazone (I).Changes in mitochondrion ultrastructure were described in the pollen grains of experimental plants. At present, these changes are identified as signs of relatively late stages of apoptosis. We considered it important to demonstrate that a gametocide with a qualitatively different chemical structure and reactivity caused similar structural changes in the cells of the main game-tophyte of experimental plants. In this study, we analyzed the effect of dibuthyl phthalate (DBP, II), a potent gametocide substantially different from compound I in chemical structure. Compound I readily enters oneelectron reduction reactions and, hence, can catalyze the production of the radical. Compound II does not enter redox reactions under mild conditions; however, our data indicate that DBP blocks the initial step of the mitochondrial respiratory chain, which leads to the generation of hydrogen peroxide and, as a result, activation of apoptosis [3]. Therefore, we could expect that, despite the fundamentally different chemical properties, these compounds would exert similar biological effects, including similar changes in the structure of the male gametophyte related to the induction of apoptosis. Here, we report the results of the study on wheat plants treated with DBP at the booting stage.Wheat ( Triticum aestivum L.) cultivar Priokskaya was frown in open ground on small separate plots under the same conditions. At the booting stage, some plants were sprayed with a 1% DBP solution containing also a detergent (dimethyl sulfoxide, 15 g per 100 ml). The treatment was repeated three days later.For electron microscopic study, wheat anthers were fixed with a 4% solution of glutaraldehyde in 0.1 M phosphate buffer solution (pH 7.4) containing sucrose and formalin. Then, postfixation with 1% osmium tetroxide and dehydration with ethanol solutions with increasing concentrations (70% ethanol was saturated with uranyl acetate) were performed. The material was immersed into epoxide resin Epon-812. Ultrathin sections were made with the use of an LKB-III ultramicrotome (Sweden), stained according to Reynolds [4], and examined using HU-11B and HU-12 electron microscope...