CONCURRENCY OF CARBOHYDRATE FORMATION AND CARBON DIOXIDE ABSORPTION DURING PHOTOSYNTHESIS IN SUNFLOWER LEAVES

Abstract

Sunflower leaves, during photosynthesis, accumulate an amt. of carbohydrate equivalent to the amt. of CO2 absorbed. If other classes of substances are formed, they must accumulate in only very small quantities. Starch and sucrose plus monosaccharides increase in direct proportion to the amt. of CO2 absorbed during photosynthesis. The relationship between the amt. of C recovered as starch and as sucrose plus monosaccharides indicates that starch and sucrose are formed concurrently in side-by-side reactions, and that the sucrose is subsequently inverted to monosaccharides. The possibility exists that sucrose and starch arise irom a common precursor. Other carbohydrate fractions, which are formed in only minor amts., apparently increase also in proportion to the amt. of CO2 absorbed. One fraction, the residue fraction, is increased by treatment of the leaf in the dark with CO2. This increase becomes progressively less as photosynthesis progresses until, in prolonged photosynthesis, an actual decrease in the residue is produced. If the course of the synthesis of the various carbohydrates from a common precursor, as presented here, is confirmed, a new aspect of the sequence of carbohydrate formation will have been gained.