Influence of plant growth regulators on polygalacturonase expression in strawberry fruit

VILLARREAL NM; MARTÍNEZ GA; CIVELLO PM

PLANT SCIENCE

Elsevier Scientific Publishers Ireland Ltd.

Lugar: Irlanda; Año: 2009 vol. 176 p. 749 - 757

0168-9452

Strawberry (Fragaria ananassa Duch.) fruit undergoes extensive softening during ripening due to cell wall disassembly, caused by a coordinated action of cell wall proteins and enzymes including polygalacturonases (PGs). The influence of plant growth regulators on PG activity and expression of the corresponding genes has been scarcely analyzed. In this work, the immuno-detection of PG protein (FaPG1) during ripening of strawberry cultivars with contrasting firmness is reported. Two proteins were recognized with molecular mass of 45–50 kDa, which accumulate from 25% red stage in the firmer cultivar (Camarosa) and from white stage in the softer (Toyonoka). The presence of two immunoreactive bands is apparently the product of the differential glycosylation of the same polypeptide. In addition, the effect of different plant growth regulators on the expression of polygalacturonase gene, accumulation of FaPG1, and PG activity was analyzed. The treatment with naphthalene acetic acid (NAA) delayed ripening and anthocyanin accumulation, reduced the expression of FaPG1 and T-PG, the accumulation ofFaPG1 protein, and decreased PG activity. The application of ABA increased slightly the expression of PG transcripts, but did not modify significantly the enzyme activity. The treatment with GA3 reduced anthocyanin accumulation and PG activity, though did not produce remarkable effects on the expression of FaPG1 and T-PG. Anthocyanins increased after treatment with ethephon (ethylene releasing reagent) or sodium nitroprusside (NO providing reagent). The expression of FaPG1 and T-PG increased considerably in response to ethylene and NO. Western-blot data confirmed the trends observed in the expression analysis in response to ethephon and NO, but PG activity was not modified by any of these treatments. However, the application of 1-MCP reduced PG activity, suggesting that ethylene could play a role in the regulation of polygalacturonase expression during strawberry fruit ripening.