Expression of phospholipase D during castor bean leaf senescence
1995
Ryu, S.B. | Wang, X.
Membrane deterioration in plant senescence is commonly associated with progressive decreases in membrane phospholipid content. This study investigated the expression and regulation of phospholipase D (PLD; EC 3.1.4.4) during senescence in castor bean (Ricinus communis L. cv Hale) leaf discs. The rate of leaf senescence was accelerated by 50 micromolar abscisic acid and was attenuated by 50 micromolar cytokinin during incubation at 23 degrees C for up to 5 d. Leaf senescence was indicated by decreases in the content of total proteins, chlorophyll, and phospholipids. PLD activity in both membrane-associated and cytosolic fractions showed a gradual increase in the absence of phytohormones. Abscisic acid stimulated an increase in membrane-associated PLD and had little effect on the soluble form. On the other hand, cytokinin retarded the increase in membrane-associated PLD. Immunoblotting analysis using PLD-specific antibodies revealed that the changes in PLD activity were correlated with those of PLD protein. Analysis of PLD by nondenaturing PAGE showed the appearance of a PLD structural variant, PLD 3, in abscisic acid-treated leaf discs. Northern blotting analysis using a PLD cDNA probe revealed an increase in PLD mRNA in senescing leaf discs. These data indicate complex mechanisms for the regulation of PLD during senescence, which include increases in membrane-associated PLD, differential expression of PLD isoforms, and changes in amounts of PLD protein and mRNA. Such controlled expression points to a role for PLD in membrane deterioration and plant senescence.
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