Effect of Rapid Dehydration on the Activity of Rubisco 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. RUBISCO activity was measured through the incorporation of 14CO2. The maximal RUBISCO activity increased 50% with the decrease of RWC from full-saturation to 60%, both when expressed on dry weight and soluble protein bases. On the contrary, initial activity decreased to half in severely stressed leaves. Accordingly, a sharp decrease of the % of activation was observed under stress. Lower initial activities suggest a lower carbamylation status of the enzyme of stressed leaves. Possible mechanisms will be discussed. The increase of maximal activity points to de novo synthesis of the enzyme. This hypothesis will be checked by RUBISCO protein quantification.