An investigation of photosynthetic sucrose production in bean leaves

Abstract

First trifoliate leaves of wax beans. Phaseolus vulgaris, were exposed to 14CO2 in light for periods of 15 to 75 s. Leaves were frozen in liquid N2 and a chloroplast fraction was isolated nonaqueously. The chloroplast fraction contained a small amount of contaminating cytoplasm that could not be removed. Labelled photosynthetic compounds were separated from the whole leaves and from the corresponding chloroplast fractions and their radioactivity was measured.The compounds fell into two groups in their behaviour. Glyceric acid and ribulose, derived from photosynthetic 3-phosphoglyceric acid and ribulose diphosphate respectively, remained largely or exclusively in the chloroplast fraction. Labelled sucrose and serine and glycine, on the other hand, were located in the chloroplast fraction only during the first 15–30 s of 14CO2 supply, and appeared in the cytoplasmic fraction in increasing amounts thereafter. The results suggest that serine and glycine are produced in organelles in the layer of cytoplasm that closely surrounds the chloroplasts and is isolated with them in the non aqueous technique. Sucrose may also be synthesized from photosynthetic intermediates in this layer of cytoplasm. Sucrose was not formed from intermediates of the glycolate pathway in detached leaves.