Diurnal and Seasonal Changes in the Ascorbic Acid Content of Some Vegetables.

Introduction As part of a general study concerned with improving the food value of crop plants, a number of experiments have been conducted to determine the factors which control the ascorbic acid content of plants. The most important papers on this subject have been reviewed by REID (6) and more recently by MAYNARD and BEESON (3). In spite of some inconsistencies in their results, these investigations lead to the following general conclusions: 1. Mineral nutrition has little influence on the ascorbic acid content of plants except under conditions where normal growth is seriously disturbed by deficiencies in one or more essential elements. 2. Genetic factors play an important role. Different varieties of the same species frequently show large differences in the quantity of vitamin C they contain. 3. Some data indicate that the growing temperature affects the rate at which ascorbic acid accumulates in the plant. MOLDTMAN (4) and REID (5) observed that at moderate temperatures an inverse relation exists between the ascorbic acid content of plants and the temperature at which they are grown. 4. Light, its intensity and the duration of illumination, are known to have a definite influence on the vitamin C content of plant tissue. REID (6) studied the effect of various light intensities on cowpea seedlings. SUGAWARA (8) exposed etiolated seedlings of several kinds of vegetables to artificial light of different intensities. HAMNER and PARKS (2) determined ascorbic acid in turnip greens grown for seven days at light intensities ranging from 200 to 5000 foot candles. All these studies show that, other conditions remaining unchanged, the ascorbic acid of plant tissue increases with rising intensities of light. The magnitude of the increase depends on the duration of the light treatment, the range of intensity studied, and the type of plant tissue involved. A question of practical importance is whether an appreciable decrease occurs in the ascorbic acid content of crop plants at night. MOLDTMAN (4) observed diurnal fluctuations in the vitamin C content of leaves of deciduous trees which in some instances varied as much as 50 per cent. However, since MOLDTMAN expressed his data as percentages of fresh weight, part of the observed fluctuations were probably caused by corresponding diurnal changes in the water content of the leaves. REID (6) working with seedlings of cowpea plants found a significant rise in the absolute quantity of vitamin Paper no. 264 Department of Vegetable Crops, Cornell University, Ithaca, N. Y. 98