Elevated temperature reduces starch deposition in wheat endosperm by reducing the activity of soluble starch synthase

✍ Scribed by P. L. Keeling; P. J. Bacon; D. C. Holt

• Publisher: Springer-Verlag
• Year: 1993
• Tongue: English
• Weight: 812 KB
• Volume: 191
• Category: Article
• ISSN: 0032-0935
• DOI: 10.1007/bf00195691

✦ Synopsis

Temperatures of more than 25 ~ C adversely affect the activity of soluble starch synthase (SSS), an amyloplastic enzyme, in endosperm of wheat (Triticum aestivum L. cv. Mardler). Enzyme rate was found to have a temperature optimum between 20 and 25~ This effect was apparently reversible after a short period of exposure to elevated temperature. We also found that with a prolonged period of exposure to elevated temperature there was another temperature-related phenomenon which caused a loss of enzyme activity that appeared to be much slower to reverse. We have termed this effect of temperature on SSS activity "knockdown". The knockdown in SSS activity also occurred in-vivo. However, elevated temperature did not affect the activities of several other enzymes in the pathway of starch synthesis (ADP-glucose pyrophosphorylase, UDP-glucose pyrophosphorylase, sucrose synthase, phosphoglucomutase, phosphoglucose isomerase, bound starch synthase or hexokinase). Because the knockdown effect appeared to be specific to the enzyme SSS, we quantified the effect of knockdown on flux of carbon into starch and used these data to calculate the flux-control coefficient for SSS. Using data at 10-20~ the flux-control coefficient was C Starchl(~20C = 0.50, whereas at 20-30 ~ C the flux-control coefficient was C Starch2(~30C= 1.38, and between 30-40~ the flux-control coefficient was C s~"rch3w4~ =0.69. Using data at 10-30~ the flux-control coefficient was cStarch~W3~ = 1.15, and at 10M0~ the flux-control coefficient was cStarchl(~40C=0.82. In conclusion, we suggest that SSS is a major site of regulation of starch synthesis