Heat shock proteins in whiteflies, an insect that accumulates sorbitol in response to heat stress..pdf

Heat shock proteins in whiteˉies, an insect that accumulates sorbitol in response to heat stress Michael E. Salvucci*, Dawn S. Stecher, Thomas J. Henneberry US Department of Agriculture, Agricultural Research Service, Western Cotton Research Laboratory, 4135 E. Broadway Road, Phoenix, AZ, 85040-8830, USA Received 22 July 1999; accepted 15 October 1999 Abstract 1. The heat shock response was examined in the silverleaf whiteˉy. Hsp70 and Hsp90 were the major polypeptides synthesized by whiteˉies in response to heat stress. 2. The amounts of Hsp70 and Hsp60 protein and Hsp70 mRNA were unchanged in response to a diurnal increase in temperature, whereas sorbitol content increased eight-fold. That steady-state levels of Hsps did not increase with higher rates of synthesis suggests that Hsps turn over faster in heat-stressed whiteˉies. 3. Hsp70 transcript levels were highest when nutrient deprivation accompanied heat stress. Thus, Hsps appear to be especially important for heat-stressed whiteˉies when sorbitol synthesis is limited nutritionally. 7 2000 Elsevier Science Ltd. All rights reserved. Keywords: Heat shock proteins; Hsp; Bemisia; Sorbitol; Polyols; Heat stress; Thermotolerance 1. Introduction In the desert southwest of the US, silverleaf white- ˉies, Bemisia argentifolii, Bellows and Perring, increase in population size during the summer (Henneberry et al., 1998) when air temperatures often exceed 428C and relative humidities can be less than 10% (Brown and Russell, 1987). By feeding on the lower surface of leaves, whiteˉies are protected to some extent from the temperature and humidity extremes of the environ- ment. Still, the temperature of a mature leaf of a well- watered cotton plant can exceed 358C (Lu et al., 1997), with even higher temperatures occurring on drought- stressed leaves (Radin et al., 1994). Previous studies from this laboratory have shown that whiteˉies and aphids, two very small phloem-feed- ing insects, accumulate polyhydric alcohols (polyols