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Plant and Cell Physiology, 1994, Vol. 35, No. 6 869-878
© 1994

Variations of ADPglucose Pyrophosphorylase Activity from Maize Leaf during Day/Night Cycle

Emmanuelle Jeannette and Jean-Louis Prioul

Structure et Métabolisme des Plantes, Institut de Biotechnologie des Plantes, Bât. 630, (CNRS, URA 1128), Université de Paris-Sud 91405 ORSAY Cedex, France

ADPglucose pyrophosphorylase activity (measured in the direction of glucose-IP synthesis) from adult maize leaves was shown to present diurnal variations in activity which were not related to the starch accumulation rate. Extractable ADPG-PPase activity was maximum at the end of the dark period and for the first 8 hours in the light. Subsequently, ADPG-PPase activity progressively declined to half the initial value, by the end of the day. A short 1 hour-dark period during the day may transiently reverse the inhibition. Experiments with excised leaves placed on sucrose or sorbitol solution further showed that the magnitude of ADPG-PPase inhibition was related to high leaf sucrose and starch contents. The differences in activity were not due to changes in the quantity of ADPG-PPase protein as shown by immunodot and immunoprecipitation techniques nor to the differential response of the mesophyll and bundle sheath isoforms nor to a time-dependent susceptibility of the enzyme to proteolysis. Thus, changes in ADPG-PPase specific activity were inferred. A search for in vivo phosphorylation of the protein was proved negative, whatever the light or dark pre-treatment which modified the ADPG-PPase activity. The difference between the 7:00 (morning) and 21:00 (evening) forms was also observed when activity was measured by formation of ADPglucose (the physiological direction) in presence or absence of PGA, as activator. The two forms retained different activity upon gel filtration.

(Received December 27, 1993; Accepted May 25, 1994)
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