Lipid Profiling Demonstrates That Suppressing Arabidopsis Phospholipase Dδ Retards ABA-Promoted Leaf Senescence by Attenuating Lipid Degradation

Senescence is the last phase of the plant life cycle and has an important role in plant development. Degradation of membrane lipids is an essential process during leaf senescence. Several studies have reported fundamental changes in membrane lipids and phospholipase D (PLD) activity as leaves senesce. Suppression of phospholipase D alpha 1 (PLD alpha 1) retards abscisic acid (ABA)-promoted senescence. However, given the absence of studies that have profiled changes in the compositions of membrane lipid molecules during leaf senescence, there is no direct evidence that PLD affects lipid composition during the process. Here, we show that application of n-butanol, an inhibitor of PLD, and N-Acylethanolamine (NAE) 12:0, a specific inhibitor of PLD alpha 1, retarded ABA-promoted senescence to different extents. Furthermore, phospholipase D delta (PLD delta) was induced in leaves treated with ABA, and suppression of PLD delta retarded ABA-promoted senescence in Arabidopsis. Lipid profiling revealed that detachment-induced senescence had different effects on plastidic and extraplastidic lipids. The accelerated degradation of plastidic lipids during ABA-induced senescence in wild-type plants was attenuated in PLD delta-knockout (PLD delta-KO) plants. Dramatic increases in phosphatidic acid (PA) and decreases in phosphatidylcholine (PC) during ABA-induced senescence were also suppressed in PLD delta-KO plants. Our results suggest that PLD delta-mediated hydrolysis of PC to PA plays a positive role in ABA-promoted senescence. The attenuation of PA formation resulting from suppression of PLD delta blocks the degradation of membrane lipids, which retards ABA-promoted senescence.