DIURNAL CHANGES AND GROWTH RATES AS ASSOCIATED WITH ASCORBIC ACID, TITRATABLE ACIDITY, CARBOHYDRATE AND NITROGENOUS FRACTIONS IN THE LEAVES OF ANANAS COMOSUS (L.) MERR

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Abstract
Diurnal changes affected greatly the chemical composition of the chlorophyllous tissues of the leaves of pineapple. The concs. of ascorbic acid in the chlorophyllous tissues at different diurnal intervals varied slightly. Such variations were related possibly more to the carbohydrate supplies in the leaves than to diurnal intervals. Titratable acidity of the tissues, composed mostly of malic and citric acids, increased in darkness, at night, but decreased in light during the day; being highest at 6 a.m. and lowest at 6 p.m. About 75% of malic acid and 37% of citric acid disappeared in the tissues from 6 a.m. to 6 p.m. Total sugars decreased in darkness, at night, but increased in light, at day, being lowest at 6 a.m. and highest at 6 p.m. Also, more sugars were found in the chlorophyllous tissues of the leaves of plants with low than high growth rates, indicating less utilization by the former than by the latter plants. Titratable acidity was inversely related to total sugars, suggesting possible generation of acidity after oxidation of sugars by processes allied to respiration. Plant growth, as measured by leaf or plant wts., correlated positively with titratable acidity and negatively with total sugars, suggesting that the rate of metabolic activity and, in turn, of respiration, being greater in plants growing more than less rapidly, caused the generation of more acidity at the expense of sugars in the large than small plants. Residual N, i.e., the insoluble fraction in macerated tissues after extraction of the water-soluble fraction, was greater from tissues collected at intervals in darkness than in light, but extractable N, in the water-soluble fraction, was reversed. The increase in extractable N was attributed to a greater hydration and dispersion in the cells of the proteinaceous residual-N fraction in light than in darkness by changes in the acidity of the tissues which presumably modified the sizes of protein particles by swelling or contraction and either facilitated or retarded the extraction of residual N from the cells at different diurnal intervals. The data are discussed and interpreted as well as possible in the light of recent advances in enzymology.