VARIATIONS OF THE PATTERNS OF ABSCISIC-ACID AND PROLINE DURING MATURATION OF NICOTIANA-TABACUM POLLEN GRAINS

Abscisic acid (ABA) and proline were evaluated during in situ developm ent of anthers and pollen grains of Nicotiana tabacum. No conjugated f orms of ABA were detected. The maximum accumulation of free ABA in the whole anther occurred at the mid-binucleate stage (MB), almost 95% of the ABA being located in the pollen; this ABA distribution was not ob served in the microspore (Mi) or mature (Ma) stages of the anther, in which the sporophytic tissue provided more ABA than did the pollen. A maximum in proline accumulation was also found at the MB stage of the anther; however, at the Ma pollen stage (when the ABA was scarcely det ectable) the proline accumulation was maximum. The germination of the pollen grain was inhibited by exogenous ABA and stimulated by fluridon e, a compound that inhibits carotenoid biosynthesis. The results of th e present work suggest an important role for ABA in maturation and ger mination, as well as in the elongation of the pollen tube of N. tabacu m.