No abstract

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 a-DL-difluoromethylomithine (DFMO), a specific irreversible inhibitor of omithine 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 cr-DL-difluoromethylarginine (DFMA), a specific, irreversible inhibitor of arginine decarboxylase (ADC), did not affect flowering and polyamine titers. These results suggest that omithine 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.Abbreviations: ADC = arginine decarboxylase; ODC = omithine decarboxylase; DFMA = o-DLdifluoromethylarginine; DFMO = o+DL-difluoromethylomithine; Put = putrescine; Spd = spermidine; Spm = spermine; Phen = phenylethylamine; 3H4M Phen = 3-hydroxy, 4-methoxyphenylethylamine.

The primary free polyamines identified during growth and development of strawberry (Fragaria x ananassa Duch.) microcuttings cultivated in vitro were putrescine, spermidine and spermine. Polyamine composition differed according to tissue and stages of development; putrescine was predominant in aerial green tissues and roots, a-DL-difluoromethylarginine (DFMA), a specific and irreversible inhibitor of the putrescine-synthesizing enzyme, arginine decarboxylase (ADC), strongly inhibited growth and development. Application of agmatine or putrescine to the inhibited system resulted in a reversal of inhibition, indicating that polyamines are involved in regulating the growth and development of strawberry microcuttings, a-DL-difluoromethylornithine (DFMO), a specific and irreversible inhibitor of putrescine biosynthesis by ornithine decarboxylase, promoted growth and development. We propose that ADC regulates putrescine biosynthesis during microcutting development. The application of exogenous polyamines (agmatine, putrescine, spermidine) stimulated development and growth of microcuttings, suggesting that the endogenous concentrations of these polyamines can be growth limiting.Abbreviations: ADC -arginine decarboxylase, ODC -omithine decarboxylase, DFMA -adifluoromethylarginine, DFMO -a-difluoromethylornithine, Put -putrescine, Spd -spermidine, Sp -spermine, DW -dry weight, PA -polyamine, PPF -photosynthetic photon flux

In Petunia hybrida, a major gene called Rm1 is able to induce a considerable increase in the meiotic recombination rates. To monitor the effect of Rm1 on meiotic synapsis, synaptonemal complex (SC) formation was investigated in pollen mother cells of Rm1 Rm1 and rm1 rm1 plants. Three-dimensional serial-section reconstruction showed no morphological difference in their SC structure. In two-dimensional spreading nuclei, although extensive SC formation was observed in the absence of Rm1, our observations strongly suggest that SC formation is more regular and more efficient in the presence of Rm1. SC analysis showed that the reduced chiasma frequency observed in rm1 rm1 plants corresponds to a partial failure of synapsis involving chromosome ends, pericentric regions, and may also extend to the whole length of short chromosome arms. It is proposed that Rm1 probably corresponds to a regulatory system with multiple effects, including the course of synapsis and the extent and quality of SC formation.Key words: synaptonemal complex, synapsis, chiasma, recombination modulator gene, petunia.