Effect of Rapid Dehydration on the Activity of PEPC from the C4 Grass Paspalum dilatatum

Abstract

Plants of Paspalum dilatatum were grown hydroponically in a phytotron under a PPFD of 600 m mol m-2s-1 and 25/18 oC (day/night) temperature. The first fully expanded leaf was excised and allowed to be rapidly dehydrated by exposure to the phytotron atmosphere. Relative water content (RWC) was monitored in a parallel sample and leaves at different RWC were frozen in liquid nitrogen. Leaf samples were later ground for enzyme extraction. PEPC activity was measured spectrophotometrically. The maximal PEPC activity increased 45% with severe stress when expressed on a dry weight basis but no correlation was found on a soluble protein basis. Physiological activity increased twice both when expressed on dry weight and soluble protein bases. The % of activation increased 40% under severe stress. Higher physiological activities obtained under these conditions suggest that the enzyme is more phosphorylated. Possible mechanisms will be discussed.