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Opuntia ficus indica roots grown hydroponically at 20 or 30-degrees-C were subjected to a range of heat-shock temperatures as high as 50-degrees-C for 2 h. Roots grown at 30-degrees-C sustained a greater level of total protein synthesis than did 20-degrees-C-grown roots following heat-shock treatments greater-than-or-equal-to 45-degrees-C. The 30-degrees-C-grown roots synthesized 31 families of heat-shock proteins between 38 and 47-degrees-C in comparison with 20-degrees-C-grown roots, which synthesized 19 families of heat-shock proteins at 45-degrees-C. In both groups of roots, the heat-shock response was dominated equally by the 71-75 and a 62 kDa heat-shock protein families. In addition, the 20-degrees-C-grown roots expressed 11 families of cold-shock proteins following 2 h at 4-degrees-C, five of which had similar relative molecular masses to heat-shock protein families. There were numerous qualitative differences in the heat shock protein profiles between the roots grown at 20 and 30-degrees-C; the 30-degrees-C-grown roots expressed several unique heat shock protein families.