The Physiology of Flowering Plants - KHAM PHA MOI

HIGH-TEMPERATURE STRESS 365homology between a number of HSP from unrelated organisms, e.g.flowering plants and Drosophila. But there are several families of HSPand these vary in importance in different organisms. The small HSPfamily (masses 17–30 kDa) is particularly abundant in flowering plants;these HSP form granules which are believed to provide surfaces onwhich partially heat-denatured proteins are held and protected fromirreversible denaturing and aggregation. The HSP100 family (massesabout 100 kDa) is also common in flowering plants; HSP100 are thoughtto act by solubilizing proteins which have aggregated. At least onemember of this family, HSP101 from Arabidopsis,isofmajorimportance.Heat-shock survival of plants engineered with lowered HSP levels isreduced in proportion to the amount of decrease in HSP101, and plantsconstructed to make HSP101 constitutively show increased thermotolerancewithout heat hardening (Gurley 2000). Other types of HSPMWkDa11697664536292420A B C D EMWkDa1049794878385767472643425242321181716Fig: 13:12 Detection of heatshockprotein synthesis by SDS-PAGE separation (see Box 13.2).Seedlings of sorghum (Sorghumbicolor) were grown at 35 8C(optimal temperature for this cerealof warm climates), and sampleswere incubated for 2 h attemperatures of up to 47 8C in thepresence of the amino acidmethionine, radioactively labelled.The proteins synthesized duringthat period are detectable asradioactive bands on the gels.Temperatures of incubation were:(A) = 35 8C; (B) = 40 8C; (C) =43 8C; (D) = 45 8C and (E) = 47 8C.With increasing temperature,synthesis of many proteins ceases,but new HSP appear. Molecularmass values of standards (runparallel to the extracts) are shownto the left of the gels; arrowednumbers on the right indicatemolecular masses of recognizableHSP bands. From Howarth &Ougham (1993).14