INFLUENCE OF PHOTOPERIOD ON THIAMINE, RIBOFLAVIN AND NIACIN CONTENT OF GREEN PLANTS

Abstract

IT IS A WELL KNOWN FACT that the climate and the seasons influence the vitamin content of green plants. Many investigators, among them Wolf (1938), Moldtmann (1939), Reid (1941, 1942), Hamner et al. (1944), Rodahl (1944), Aberg (1946), Somers et al. (1948), and Gustafson (1948, 1950), have shown that both light and temperature are factors of great importance in vitamin synthesis. Yet when light intensity and temperature have been accounted for there is still something lacking to account for the high vitamin content of plants during the summer. In 1940 Bonner found that Xanthium pennsylvanicum, Cosmos sulfureus, Lycopersicum esculentum, Brassica nigra and B. alba had a higher concentration of thiamine in the leaves when subjected to a photoperiod of 18-20 hr. than when exposed to a 9-hr. photoperiod. Reid (1942) found that medium to long days were conducive to the production of a high ascorbic acid content in cow peas, whereas short photoperiods produced plants with low ascorbic acid content. Hamner et al. (1944) also found that the tomato produced less ascorbic acid under an 8-hr. photoperiod than when exposed to a 16-hr. photoperiod. In the spring of 1951 the writer had the opportunity of spending several months at the Earhart Plant Research Laboratory at the California Institute of Technology, Pasadena, California, and it was decided to take advantage of the unusual opportunity offered at this laboratory to study the influence of the photoperiod on vitamin content in several different plants. MATERIAL AND METHODS.-The plants used for these studies were Alaska peas, Black Valentine beans and San Jose Canner tomatoes. The plants were grown in natural light at day temperature of 23 or 260C., and a photoperiod of 14-15 hr. until placed under the experimental conditions. The age of the plants varied considerably but within any one experiment the plants used were of the same age and were closely selected for size and stage of development. The plants were grown in plastic boxes in gravel and vermiculite, and were watered with Hoagland's nutrient solution. In the first experiments the plants were transferred directly from the greenhouse to the experimental rooms, but in the Iater experiments they were first placed in the