The Capacity of Leaves of Bryophyllum calycinum to Recover from Prolonged Exposure to Darkness or to Light.

Publisher Website
Google Scholar
Abstract
Initially identical samples of excised leaves of Bryophyllum calycinum were subjected to prolonged culture in water in darkness, individual samples being transferred to light at intervals. A second set of samples was subjected to the converse conditions to test capacity of the leaves to resume the normal rhythm of variation in composition with respect to starch and organic acids. Prolonged culture either in darkness or in light set up a condition interpreted as a steadily increasing physiological stress. This condition was characterized by the diminishing speed of major chemical changes in composition subsequent to transfer as the culture period was prolonged. The data refer to synthesis and decomposition of starch and the correlated reciprocal changes in malic and citric acids. Total protein of the leaf slowly diminished in amount. It is tentatively suggested that changes in the rates at which leaves are able to recover from the stressed condition are correlated with loss of protein and specifically with the gradual, although only partial, destruction of essential enzymes. Enzymes concerned with metabolism of malic acid appear to have been especially sensitive to prolonged culture in light. Reciprocal changes in starch and organic acids showed that, in general, approximately the correct quantity of carbon was supplied by the component which diminished in amount to account for the carbon of the component which was synthesized. However, this did not hold for synthesis of organic acids in leaves which had been stressed by prolonged culture in light and were then placed in darkness. In these leaves, there was a marked deficiency in synthesis of organic acids. In contrast to its behavior in Bryophyllum leaves exposed to light under greenhouse conditions, citric acid diminished slowly, if at all, when leaves were exposed to artificial light at a controlled temperature in the vicinity of 20[degree]C.