| Abstract: | The magnesium dependence of NADP-reduction, oxygen evolutionand concomitant ATP-formation was studied as a function of theage of the Cucurbita cotyledons from which the chloroplastswere isolated. Whereas NADP-reduction under alkaline assay conditionsalways exhibits a stimulation upon addition of Mg++, measurementsin an acidic medium show an age-dependent reversal to inhibition.The data for oxygen evolution are more complex in nature, dueto participation of consecutive reactions. The Mg++ concentrationfor optimal ATP formation decreases with the age of the cotyledonarymaterial. The results are discussed from the viewpoint of apossible control of essential photosynthetic functions in vivoby magnesium. |
