Relationship between pollen degeneration and amino acids, especially proline, in male-sterile Japanese radish ( Raphanus sativus L. var. longipinnatus Bailey)

Abstract

Proline has been found to occur in only small quantities in sterile anthers, whereas it is abundant in fertile ones. However, the cause-and-effect relationship between proline and pollen degeneration was not clear. The present study was undertaken to solve this problem, using male-sterile and male-fertile plants of Japanese radish. The content of free amino acids in anthers of both plants was analyzed at the pollen mother cell (PMC) stage and at the mature (or degenerated) pollen stage. At the PMC stage there was little difference in proline content between sterile and fertile anthers, suggesting that proline is not involved in the condition of the anthers which leads to either sterility or fertility. At the mature (or degenerated) pollen stage, every amino acid occurred more abundantly in fertile anthers than in sterile ones. Fertile anthers at this stage contained much more proline than at the PMC stage. On the other hand, the quantities of amino acids in sterile anthers were small, and the decrease of proline was dramatic. These small amounts of amino acids, including proline, may be a result of pollen degeneration, because at this stage the collapse of pollen is so complete that only dried anther walls are anatomically observed. Filaments of sterile stamens contained much proline, suggesting its accumulation in situ due to the prevention of transfer to the destroyed anther.