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Influence of Shading upon Changes in the Ascorbic Acid and Carotene Content of Turnip Greens as Compared with Changes in Fresh Weight, Dry Weight and Nitrogen Fractions

U. S. Plant, Soil and Nutrition Laboratory, Agricultural Research Service, Ithaca, New York

1. Turnip plants were grown in sand culture outdoors two summers. The variety Shogoin was grown one year and Seven Top the other. When the plants were a few weeks old some of them were moved into a shade house which reduced the illumination to about 25 to 30% of full sunlight. Subsequently some plants were moved from shade into full sunshine once more and at the same time additional plants were moved into the shade. Frequent samples were analyzed over periods of 7 to 11 days for ascorbic acid (reduced), carotene, total N, soluble N and insoluble N.

2. The results show that the fresh weight of the plants and the number of leaves per plant were greater for those plants which had been grown in full sunshine previous to the sampling period. Illumination during the sampling period had no effect on these two variables. On the other hand, the dry weight of the plants was influenced principally by the illumination during the sampling period. Plants in full sunshine contained more dry matter than those in the shade.

3. While the amount of soluble or insoluble N in the leaf blades on a per plant basis was influenced by the illumination treatments, the total N per plant was not influenced by these treatments.

4. On all bases used for comparison (fresh weight, dry weight, per plant and per gram total N) plants in full sunshine contained more ascorbic acid than those in the shade, although on a dry weight basis significant differences between treatment were not observed in all experiments. Illumination treatments both during and previous to the sampling period evoked significant responses.

5. On all bases used for comparison plants in full sunshine contained less carotene than those in the shade.

6. The responses of both carotene and ascorbic acid to changes in illumination were reversible.

7. Partial correlations between the composition of the plants, their fresh weight, their dry weight and their age showed a consistent positive correlation between ascorbic acid and dry weight. Carotene showed a consistent negative correlation with dry weight and a consistent positive correlation with fresh weight. The nitrogen fractions also showed a consistent positive correlation with fresh weight.

² Present address: Department of Vegetable Crops, Cornell University, Ithaca, New York.

Manuscript received 2 November 1956.