Submitted to: National Plant Lipid Cooperative Meeting
Publication Type: Abstract Only
Publication Acceptance Date: May 2, 2005
Publication Date: June 12, 2005
Citation: Whitaker, B.D., Lester, G.E. 2005. Pld-alpha and lox genes and enzyme activities associated with development and senescence of honeydew melon (cucumis melo l.) mesocarp tissues.. [abstract]. National Plant Lipid Cooperative Meeting. Paper No. 15. p. 38. Technical Abstract: Phospholipase D (PLD) and lipoxygenase (LOX) have been implicated to play a role in both normal and stress-induced senescence in mesocarp tissues of melons. Senescence of ripe cantaloupe and honeydew melons, characterized by excessive tissue softening and water loss, was delayed by treatment with polyamines or chelated calcium, and this was correlated with reduced membrane leakage, maintenance of plasma membrane H+-ATPase activity, and reduced PLD and LOX activities in hypodermal mesocarp tissue. We have initiated efforts to clone PLD and LOX genes from Cucumis melo cv. Honey Brew, and to characterize their expression and the activities of their encoded enzymes in relation to development, ripening, and senescence of honeydew melon. Cloning has thus far yielded one complete cDNA encoding a PLD-alpha and one partial LOX cDNA (3’ half). The CmPLDa1 is apparently the first PLD reported for the Cucurbitaceae. It has 77% and 83% identity, respectively, with the nucleotide and encoded AA sequences of castor bean PLDa1. The partial LOX cDNA is very closely similar (95% nucleotide identity) to a cucumber 9-LOX cDNA. An initial study showed expression of both the PLD-alpha and LOX genes to be highest in young, developing fruit (20-30 days post-anthesis); LOX transcript levels as well as 9-LOX activity were particularly high in hypodermal mesocarp from 20-day fruit. PLD-alpha activity was highest in 20-day fruit, declined over 20 to 40 days post-anthesis, then rose again with full ripening of the fruit (ca. 55 days). Activity of PLD-alpha was generally higher in mid-mesocarp than in hypodermal mesocarp tissue. Efforts to clone additional melon PLD and LOX genes will continue, with a focus on isogenes expressed at relatively high levels in fruit tissues during ripening or in response to stress.