The Behavior of Isocitric Acid in Excised Leaves of Bryophyllum Calycinum During Culture in Alternating Light and Darkness

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Abstract
The behavior of isocitric acid in excised leaves of B. calycinum subjected to culture in water under greenhouse conditions of illumination was reexamined with improved technical methods. The observation that this substance does not change significantly in quantity in the normal course of the phenomena of diurnal variation of acidity is confirmed. Although the relative quantities of starch and of malic acid which undergo diurnal fluctuations in response to light conditions are such as to indicate that mutual interconversion occurs, these substances being respective end-products of what is doubtless a complex series of enzymatically controlled chemical reactions, the simple hypothesis that diurnal variation of acidity is to be accounted for in terms of a reversible equilibrium between starch and malic acid is inadequate to account for all of the observations. Although this may be an expression of the most important reaction from the point of view of quantity, it furnishes an incomplete picture of the metabolic events. Notable among the complicating factors are the evidences of assimilation of carbon both in light and in darkness, and the behavior of citric acid and of the soluble carbohydrates. The chemical details of all of these reactions remain to be explained.