Labavitch Lab

Cell wall metabolism in ripening fruits.
  When fruits ripen, they become softer. However once they begin to soften they are easily damaged during shipping and storage and become more susceptible to pathogens.  An understanding of the factors that contribute to this ripening-associated softening should the biochemical factors that lead to softening should be useful in designing strategies for maintaining fruit quality.  Changes in fruit cell turgor pressure influence softening rates, but much of the softening is a consequence of the metabolism of fruit cell wall polysaccharides and the integrity of polysaccharide networks. We have published descriptions of wall metabolism in many kinds of fruits, however most of our work has focused on tomatoes because of the relative ease in genetically engineering changes in the expression of fruit cell wall digesting proteins (CWDPs).  Much of this work (and the additional studies described below) has been done in collaboration with our Plant Sciences Department colleagues, Alan Bennett and Ann Powell.  Fruit CWDPs that are particularly important in the ripening-related wall changes in tomatoes and other fruits are polygalacturonase (PG, a pectin polymer digesting enzyme) and expansin (Exp, a protein thought to loosen associations between cellulose microfibrils and hemicelluloses).  A recent report (Cantu et al., 2008a) describes our study of wall changes in ripening tomatoes in which PG and Exp expression has been suppressed.  The ripened -PG-Exp tomatoes are significantly firmer than ripened, unmodified fruits.

The firmness of ‘Ailsa Craig’ (AC, control) tomatoes and AC fruit with suppressed expression of polygalacturonase (PG), expansin (Exp), and both PG and Exp was measured at the mature green (MG), breaker (BR), light-red (LR) & red-ripe (RR) stages of ripeness.

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