LIGHT-DEPENDENT FIXATION OF POLYAMINES INTO CHLOROPLASTS OF CHINESE CABBAGE

We have been studying the infection of Chinese cabbage by turnip yellow mosaic virus (TYMV), an infection which causes vesiculation of chloroplast membranes, aggregation of chloroplasts and accumulation of virus specifically in pockets between the chloroplasts [ 1,2]. TYMV is rich in spermidine associated with the RNA [3] and the infected plant contains high levels of this triamine [4]. We have observed that a chloroplast fraction isolated from leaf protoplasts can synthesize spermidine from methionine and contains spermidine synthase [S]. The infected plant is also high in putrescine and spermine, and the former increases late in infection, apparently concomitantly with the yellowing and withering of the plant [4]. Since it is known that putrescine accumulates generally in plants in unfavorable soils [6] and is itself toxic to the plant [7], we have asked if the increase of this polyamine in infection is causally related to the developing pathology. Two sets of observations bear on this point: . (1) Putrescine was found to be lethal to a Cyanobacterium, Anacystis nidulans in the light, and to bind covalently to various cellular proteins, including ribosomal subunits [ 81; (2) Protoplasts of the healthy leaves were found to convert methionine to acid-insoluble form by chloroplasts isolated from disrupted protoplasts. It has been found that in the presence of light, chloroplasts do bind polyamines in an acid-insoluble form, of which -l/2 is soluble in 80% acetone or alcohol.