Ib. Ferguson et al., PROTEIN-SYNTHESIS AND BREAKDOWN DURING HEAT-SHOCK OF CULTURED PEAR (PYRUS-COMMUNIS L) CELLS, Plant physiology, 104(4), 1994, pp. 1429-1437
Cultured pear (Pyrus communis L. cv Passe Crassane) cells were subject
ed to temperatures of 39, 42, and 45 degrees C. Heat-shock protein (hs
p) synthesis was greater at 39 degrees C than at temperatures above 40
degrees C and continued for up to 8 h. Both cellular uptake of radiol
abeled methionine and total protein synthesis were progressively lower
as the temperature was increased. Polysome levels decreased immediate
ly when cells were placed at 39 or 42 degrees C, although at 39 degree
s C the levels began to recover after 1 h. In cells from both temperat
ures, reassembly occurred after transfer of cells to 25 degrees C. Fou
r heat-shock-related mRNAs-hsp17, hsp70, and those of two ubiquitin ge
nes-all showed greatest abundance at 39 degrees C and decreased at hig
her temperatures. Protein degradation increased with time at 42 and 45
degrees C, but at 39 degrees C it increased for the first 2 h and the
n decreased. In the presence of cycloheximide, which prevented hsp syn
thesis, protein degradation at 39 degrees C was as great as that at 45
degrees C in the absence of cycloheximide. The data suggest that hsps
may have a role in protecting proteins from degradation at the permis
sive temperature of 39 degrees C. At temperatures high enough to inhib
it hsp synthesis, protein degradation was enhanced. Although ubiquitin
may play a role in specific protein degradation, it does not appear t
o be involved in increased protein degradation occurring above 40 degr
ees C.