TITLE	Regulation of sucrose phosphate synthase of the sweet potato callus is related to illumination and osmotic stress
AUTHOR	Mu-Ho Lee Graduate Institute of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan 106 Chien-Chi Yang Graduate Institute of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan 106 Heng-Long Wang Department of Life Science, National University of Kaoshiung, Kaohsiung University Rd., Kaohsiung, Taiwan 811 Ping-Du Lee Graduate Institute of Agricultural Chemistry, National Taiwan University, Taipei, Taiwan 106
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ABSTRACT	Sucrose phosphate synthase (SPS) was purified from sweet potato callus grown under different conditions, including illumination, darkness, and osmotic stress. The properties of the enzymes purified from the different conditions were compared. Since sucrose synthase (SS) could also be purified using the purification process, the expression patterns and properties of the two enzymes were also compared. The SPS purified from the calli tissue medium under illumination had an optimum pH of 7.5. The enzyme had an optimum reaction temperature of 37°C, and maintained stable activity at pH 6 to 8. It was allosterically regulated using either Glc 6-P or Pi. However, the enzyme purified from the tissues grown under osmotic stress conditions was not allosterically regulated using Glc 6-P or Pi. The maximal activity of SPS and maximal protein content of the illumination grown calli appeared on the 14th day after the culture was transferred into a new medium. This was compared with the peak value on the 7th day for the samples under osmotic stress. The maximum activity for SS was observed on the 14th day. The dark grown cells had very low SPS, but normal SS activities. A histological study revealed an abundance of starch granules in the osmotic stressed cells. The in situ hybridization technique showed that the illumination and osmotic stress conditions induced the accumulation of SPS mRNA. The PAGE and enzyme activity assay data showed that, in addition to enhancing SPS gene expression, the activation of SS gene expression isozymes may be achieved under the illumination and osmotic stress conditions.
KEYWORD	Dark; Illumination; Osmotic stress; Sucrose phosphate synthase; Sucrose synthase; Sweet potato callus;
ARTICLE INFO	Botanical Bulletin of Academia Sinica, Volume 44 Number 4 October 2003, page 257-265, 9 pages
PUBLISHER	Institute of Plant and Microbial Biology, Academia Sinica, Taipei, Taiwan, Republic of China