Modificações da parede celular de frutos do mamoeiro (Carica papaya L.) em diferentes estadios do desenvolvimento / Modifications of the cell wall of fruits of papaya (Carica papaya L.) at various stages of development

AUTOR(ES)
DATA DE PUBLICAÇÃO

2009

RESUMO

The plant cell wall is a unique component of plant tissues and its polysaccharide composition essential to understand food texture and its changes during post-harvestingl especially of climateric fruits, as is the case of papaya. The plant cell wall is composed of three domains: the first is formed by cellulose and hemicelluloses, the second of pectins and the third of proteins. The changes in polymers and their proportions in these domains are a result of enzyme action, which in the case of fleshy fruits lead to the softening of the pulp. Hydrolysis of hemicelluloses such as xyloglucan can play important functions in cell expansion, cell growth and cell wall degradation. Therefore, studying the modifications in xyloglucan by looking at is fine structure (Le. oligosaccharide (OXG) pattern obtained after cellulase action) may be an important way to understand polysaccharide change during fruit development. The present work aimed at understanding the modifications in cell wall during the development of the papaya fruit. Fruits of Carica papaya L. Cv.Sunrise solol were collected directly by the producer (Calimanl SAI Unharesl Espirito Santol Brazil). Samples of fruits were harvested at intervals between 30 and 150 days after anthesis (daa). Our results showed that there were drastic changes in the cell wall of the mesocarp in relation to other compoundsl such as soluble sugars. This is probably an indication that cell expansion process is at least part of the cause of the changes in texture during development. We observed that the main soluble sugar found in fruits is sucrose, this being probably the principal source of energy for development of the organ, as no starch is synthesised in this fruit. In general, the proportion of less branched xyloglucan oligosaccharides decreased at 120 daa, whereas the OXG branched with fucose increased constantly during development up to the same stage. These results suggest that xyloglucans (or part of their molecules) that are poorely brached with fucose are retrieved from the cell wall. This seems to lead to enrichment of fucosylation of xyloglucan. As these OXG turn xyloglucan more interactive with itself and with cellulose, it is possible that these would be the principal effects that the cell walls provoke in the fruit. The changes in the wall were followed by a concomitant increase in activities of beta-galactosidase and betaglucosidase, both thought to be related to xyloglucan hydrolysis in vivo. At the same time, we observed a decrease in the proportion of cellulose in the walls during development. On the basis of these results, we suggest that the cell walls of papaya fruits undertake structural changes untill 120daa after which the wall becomes more accessible to hydrolases denoting the preparation of the papaya fruit for ripening.

ASSUNTO(S)

mamão papaya hydrolases oligossacarideos parede celular vegetal oligosaccharides hidrolases plant cell wall

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