A structural study on the mode of action of CHA^TM Chemical Hybridizing Agent in wheat

Summary

This study has compared mature pollen grains while still in the anther, as well as post-pollination responses, from untreated and CHA^TM Chemical Hybridizing Agent-treated wheat plants using light (bright-field, phase-contrast, and fluorescence), scanning, and transmission electron microscopy. The chemical, azetidine-3-carboxylic acid (A3C), was applied at three treatment levels of 0.75, 1.0 and 1.5 kg/ha for the mature pollen investigations. It was found that the major effect of A3C on mature pollen is an alteration of the wall precursor vesicles (wp-vesicles), which form a high proportion of the contents of the mature grass pollen grain. The degree of deformation of the wp-vesicles is dose dependent. There is some evidence that increased aggregations of ribosomes are formed in treated pollen cytoplasm. Pollination studies (all at a treatment level of 1.0 kg/ha) show that, in most cases, the treated pollen does not germinate, and a high percentage of the pollen grains burst (60% burst grains in treated material compared to 28% in controls). In about 20% of the cases from treated plants, a short pollen tube forms, but no tubes were seen to grow far enough to enter the stigma hairs of the pistil. Thus, A3C does not act by preventing pollen formation, but by the prevention of normal pollen tube growth. There appears to be a specific targeting of the wp-vesicles such that, even in cases where the ultra-structure of the vesicles is not altered, the normal course of events leading to the incorporation of their contents into the extending tube wall is arrested. Further studies must be undertaken to determine the significance of the effect of CHA^TM Chemical Hybridizing Agent on wp-vesicle composition.