[Short term changes in soluble sugar and cell-wall carbohydrate content during phytochrome mediated photomorphogenesis in the mustard seedling (Sinapis alba L.)].

Short term changes in the soluble sugar, starch, and cell-wall carbohydrate content of the mustard seedling have been studied in the different organs during phytochrome induced photomorphogenesis in continuous far-red. The program was: imbibition of seeds →36 hrs dark → far-red irradiation. Kinetics have been followed up to 12 hrs after the onset of irradiation.There are no substantial changes in carbohydrate content in the cotyledons and the radicle. In the cotyledons in far-red after a lag-phase of 3 hrs, there is a decrease in oligosaccharide content, and after a lag-phase of 6 hrs, an increase in cell-wall synthesis. The reducing sugar and starch content is not altered upon irradiation. In the radicle immediately after the onset of far-red, there is a temporary rise in the reducing sugar and cell-wall carbohydrate content. However, 6 hrs later the values in far-red again parallel those of the dark control.The important phytochrome dependent changes take place in the hypocotyl. In far-red after a lag-phase of 3 hrs the glucose accumulation is markedly retarded, the sucrose and starch content no longer increased, and the fructose content even decreases below the 3 hrs value. The glucose: fructose ratio, which is constant in dark, is shifted in favour of glucose. The lag-phase of phytochrome controlled hypocotyl elongation is about 1 hr, the lag-phase of the inhibition of cell-wall carbohydrate synthesis is in about the same order of magnitude.There seems to be neither any immediate connection between sugar content and cell-wall carbohydrate synthesis, as shown by the difference in lag-phases, nor does there seem to be any direct relationship between hypocotyl inhibition and overall synthesis of cell-wall material. The relative inhibition of cell-wall synthesis is less than one third of that of hypocotyl elongation (Figs. 5,6). Apparently phytochrome controls hypocotyl elongation by influencing the cell-wall structure.In spite of the fact that fat degradation is higher in far-red than in dark and respiration higher in dark than in far-red (FRIEDERICH, 1968), 6 hrs after the onset of far-red the increase of total carbohydrate content declines compared with that in dark. This finding leads to the conclusion that the efficiency of the fat-carbohydrate-transformation is higher in dark than in far-red.