Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress

Giardini Naxos, Italy - 18/21 September, 2002

ISBN 88-900622-3-1

Poster Abstract - 5.23

POLYAMINE APPLICATION DELAYS PEACH (PRUNUS PERSICA L.) FRUIT RIPENING INDEPENDENTLY OF INHIBITION OF ETHYLENE BIOSYNTHESIS

ZIOSI V.*, SCARAMAGLI S.*, BREGOLI A.M.**, RASORI A.***, BIONDI S.*, COSTA G.**, TORRIGIANI P.*

*) Dip. Biologia evoluzionistica sperimentale

**) Dip. Colture Arboree, Università di Bologna

***) Dip. Agronomia Ambientale e Produzioni Vegetali, Agripolis, Università di Padova

polyamines, ACC synthase, ACC oxidase, ethylene biosynthesis, peach fruit ripening

Polyamines (PAs) are ubiquitous plant growth regulators, e.g. tobacco mutants overproducing PAs display vegetative and floral abnormalities; moreover, which can affect molecular events in signal transduction. The interaction between PAs and ethylene is much studied since they share the common precursor SAM, a possible metabolic switch, depending upon the physiological conditions (Biondi et al. 1998 Protoplasma 202, 134-144). During fruit development a relationship between increases in PA content and cell division has been demonstrated (Biasi et al. 1991 Plant Physiol Biochem 29, 497-506). In fact, PA titres generally decline during peach fruit development and ripening (stages S1–S4) (Kushad 1988 J Am Soc Hort Sci 123, 950-955). Previous results show that exogenous PAs affected ethylene synthesis and flesh firmness in ripening Redhaven peaches modestly altering the endogenous levels (Bregoli et al. 2002 Physiol Plant 114, 472-481).

In the present work, several PAs and aminoethoxyvinylglycine (AVG), the ACS activity inhibitor, concentrations were applied on peach trees (Prunus persica L. Batch cv. Stark Red Gold) in middle S3 (87 dAFB) and in S4 (107 dAFB) fruit growth stages. Control and treated nectarines were selected for uniform size and sampled at weekly intervals while (commercial) harvest was performed at 115 dAFB. The double sigmoidal fruit growth curve was established, quality traits analysed and ethylene measured. PA titresjj were evaluated by HPLC; a peach SAMDC gene fragment was obtained by PCR; expression studies were performed by northern analysis on SAMDC transcript levels as well as on those of the ethylene biosynthetic genes ACS and ACO.

Results show that PA treatment delays flesh softening and affects other parameters earlier than inhibition of ethylene emission while reduction of fruit drop was achieved by earlier PA applications. Moreover, no residual polyamines were detected in addition to the endogenous complement in the epicarp or mesocarp one month following treatment. Transcript levels of ethylene biosynthetic enzymes were repressed or not affected. Equally, expression of polyamine biosynthetic genes was repressed or not affected depending upon concentration. AVG application led to similar effects. These results lend support to the contention that PAs delay ripening independently of ethylene.