Relationships Between Anther Browning and Plantlet Formation in Anther Culture of Nicotiana tabacum L.

Abstract

Summary Anthers of Nicotiana tabacum cv. Wisconsin 38 contammg pollen grains in various developmental stages were cultured for 55 days at 23°C to investigate the relationship between the formation of plantlets from pollen and browning of the anther. Browning took place in anthers containing binucleate pollen grains during the first 10 days after inoculation onto Nitsch's basal medium (1969) , whereas it was continuously observed for as long as a month in anthers containing micros pores in the uninucleate stage and in those undergoing pollen mitosis. Plantlet formation in the first instance was observed during the first 3 to 5 weeks of culture and was never detected thereafter. There was no positive correlation between anther browning and plantlet formation. Plantlet induction was delayed for one week, but it was observed to be continuously effective until the cultures were 50 days old in the anthers containing uninucleate and mitotic microspores. The protraction of senescence in anthers appears to be of great importance for the induction of embryogenesis in microspores at this stage of development. There was a positive correlation between the duration of anther browning and the time required for plantlet production. That is, the percentage of plantlet formation in anthers having browned during the first 2 weeks was low, whereas the frequency of plantlet formation was high in long-lived anthers. These results suggest that there is a critical period for the induction of pollen embryogenesis in the early binucleate stage. Most microspores not yet having undergone pollen mitosis can attain to this stage with the nutritional or hormonal aid of living anther tissue; the embryogenesis can never proceed if anther browning has occurred before this stage has been attained. In a more advanced stage the duration of such a situation seems to be shorter.