Free Sugars and Organic Acids in the Leaves of Various Plant Species and their Compartmentation Between the Tissues4

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Abstract
The distribution of free sugars and organic acids between the epidermis and mesophyll of Tulipa gesneriana L., Vicia faba L., and Commelina communis L. leaves was studied using mainly gas-liquid chromatography. Fructose, glucose, sucrose, and myo-inositol were found in the epidermis and mesophyll of all three species. In T. geeneriana leaf tissues arabinose (trace levels), stachyose, tuliposides A and B (mainly in the mesophyll), and xylose (trace levels also in V. faba tissues) were also detected. The acids were more difficult to detect and identify, being at considerably lower concentrations than the sugars in both tissues. Fumaric, citric, malic, ascorbic (trace levels), and an unidentified acid were common to the epidermis and mesophyll of all three species. Of special interest was the detection of large amounts of glyceric acid in the epidermis and mesophyll of V. faba; this acid was not detected in the tissues from the other species. Fumaric acid was also very abundant in the epidermis of V.faba. A special study was made of the compartmentation of acids and sugars between the epidermis and mesophyll of T. geeneriana leaves after light and dark treatments. No changes in free acid or sugar levels were detected in the epidermis or mesophyll after these treatments. Except for suceinic acid (P < 0·05), there were no statistically significant differences in acid levels between the epidermis and mesophyll but for most of the sugars (myo-inositol, arabinose, and xylose being exceptions) differences were highly significant (P < 0·001), highest levels occurring in the mesophyll. The differences in sugar levels and the similarity in acid levels between epidermis and mesophyll of tulip leaves were considered to be essentially due to the different CO2 fixing mechanisms and capacities of the two tissues. The energy source for the essentially non-green epidermal tissue was discussed.