Phospholipase D��1 Acts as a Negative Regulator of High Mg2+-Induced Leaf Senescence in Arabidopsis.. A knockout mutant of PLD��1 (pld��1-1), exhibits premature leaf senescence under high-Mg2+ conditions. In pld��1-1 plants, higher accumulation of abscisic and jasmonic acid (JA) and impaired magnesium, potassium and phosphate homeostasis were observed under high-Mg2+ conditions.