Effect of cold storage treatment for forcing bulbs on the C and N metabolism of tulip plants

Abstract

Abstract The changes in the carbohydrate and N constituents in tulip bulb scales were investigated in relation to the physiological role of cold treatment for forcing cultivation, by comparing the plants subjected or not subjected to the conventional cold storage treatment. When the bulbs subjected to cold storage were cultivated in a greenhouse, they grew rapidly and flowering occurred normally in early December, whereas without cold storage the growth of the shoots was markedly depressed, they exhibited a rosette form, and flowering occurred in the middle of January. Regarding the changes in the carbohydrate content in the scales of bulbs subjected to the cold treatment, starch degradation occurred rapidly after the onset of the treatment. Based on the morphological observations, small starch granules with a spherical shape disappeared initially, and subsequently the amount of the large granules with a lenticular shape decreased. Along with the starch degradation, there was a considerable accumulation of sucrose and fructosyl sucroses with a low degree of polymerization. On the other hand in the case of the scales of bulbs which were not subjected to the cold treatment, the conversion of starch to mobile sugars did not occur until planting. As for the N constituents in the bulb, cold temperature treatment was essential for the mobilization of the storage protein-N. The concentration of Gln and 4-MeGln in the scales increased markedly with the decrease in the protein-N content, while Arg concentration was not significantly affected by the temperature treatments. Based on these results and compared with those obtained in tulips cultivated under natural conditions, it was suggested that the changes in the carbohydrate and N constituents in forced bulbs subjected to the cold storage treatment proceeded in the same way as in the plants grown under natural conditions. On the contrary, in the untreated bulbs the solubilization of storage C and N was insufficient to support the normal development of the shoots.