POLYAMINES, FLORAL INDUCTION AND FLORAL DEVELOPMENT OF STRAWBERRY (FRAGARIA ANANASSA-DUCH)

In the short-day plant, strawberry (Fragaria ananassa Duch.), polyamines (putrescine, spermidine and spermine), conjugated spermidine (water-insoluble compounds) and bound amines (putrescine, spermidine, phenylethylamine, 3-hydroxy, 4-methoxyphenylethylamine) accumulated in the shoot tips during floral induction and before floral emergence. Different associations of free amines and conjugated amines were observed during floral induction, as compared with the reproductive phase. During the whole period of floral development, phenylethylamine (an aromatic amine) was the predominant amine, representing 80 to 90% of the total free amine pool. Phenylethylamine conjugates (water-insoluble compounds) were the predominant amides observed prior to fertilization. These substances decreased drastically after fertilization. In vegetative shoot tips from plants grown continously under long days, free polyamines (putrescine, spermidine) and bound polyamines (putrescine, spermidine) were low and no change was observed. Free amines (spermine and phenylethylamine), bound aromatic amines (phenylethylamine, 3-hydroxy, 4-methoxyphenylethylamine), conjugated spermidine and phenylethylamine did not appear. Male-sterile flowers were distinguished by their lack of conjugated spermidine and phenylethyalamine and by a decrease in free phenylethylamine. In normal and sterile strawberry plants alpha-DL-difluoromethylomithine (DFMO), a specific irreversible inhibitor of ornithine decarboxylase (ODC), caused inhibition of flowering and free and polyamine conjugates. When putrescine was added, polyamine titers and flowering were restored. A similar treatment with alpha-DL-difluoromethylarginine (DFMA), a specific, irreversible inhibitor of arginine decarboxylase (ADC), did not affect flowering and polyamine titers. These results suggest that omthine decarboxylase (ODC) and polyamines are involved in regulating floral initiation in strawberry. The relationship between polyamines, aromatic amines, conjugates, floral initiation and male sterility is discussed.