|Paliyath, Gopinadhan - UNIV GUELPH, ONT, CANADA|
|Tiwari, Krishnaraj - UNIV GUELPH, ONT, CANADA|
|Yuan, Haiying - XINJIANG AG UNIV, CHINA|
Submitted to: Postharvest Biology and Technology
Publication Type: Book / Chapter
Publication Acceptance Date: August 14, 2008
Publication Date: December 20, 2008
Citation: Paliyath, G., Tiwari, K., Yuan, H., Whitaker, B.D. 2008. Structural deterioration in produce: Phospholipase D, membrane deterioration and senescence. In: Postharvest Biology and Technology of Fruits, Vegetables, and Flowers, Paliyath, G., Murr, D.P., Handa, A.K., Lurie, S., editors. Postharvest Biology and Technology. p. 195-239. Technical Abstract: Following cloning of the first phospholipase D (PLD) gene from castor bean, there has been good progress in determining physiological roles of members of the plant PLD gene family, now known to comprise six classes: alpha, beta, gamma, delta, epsilon and zeta. Most notably, phosphatidic acid derived from PLD hydrolysis of phosphatidylcholine and other phospholipids is an important signaling molecule that mediates responses to various types of biotic and abiotic stress. Despite this progress, however, one of the earliest roles ascribed to PLD, i.e., initiator of the cascade of phospholipid catabolism in senescing plant tissues, has received relatively little attention. PLDs of the alpha class, typically the most abundantly expressed and accounting for most of the total activity, are the best candidates to perform this function. Although antisense knockout of AtPLDa1 did not alter natural senescence in Arabidopsis, it did delay ethylene- and abscisic acid-induced senescence of detached leaves. This finding indicates a likely role of PLD in postharvest senescence of fresh fruits and vegetables, particularly in climacteric fruits such as tomato and melon, which produce moderate to high levels of ethylene. Three isogenes encoding PLD alphas in tomato, referred to here as LePLDa1, LePLDa2 and LePLDa3, have been cloned and further studied. In addition, two PLD alpha isogenes from honeydew melon (CmPLDa1 and CmPLDa2), one gene from strawberry fruit (FaPLDa1), and one gene from cucumber fruit (CsPLDa1) have been cloned and characterized. This chapter summarizes what is currently known about the expression of these PLD alpha genes, and the activity and localization of their encoded enzymes, in relation to ripening and senescence of fruit tissues. On the whole, research results support the hypothesis that membrane association and activation of PLD alpha induced by increasing cytosolic calcium levels and acidity, as well as increased PLD alpha gene expression, play a substantial part in membrane degradation that hastens loss of fruit quality after harvest.