Expression profiles of PtHsp90 genes. A. Heat map showing 10 PtHsp90 genes under heat stress. Expression is indicated as the fold-change in photosynthetic optimum (31.75°C, temperature producing the maximum net CO2 assimilation rate), 20% inhibition of optimum (38.4°C) and 30% inhibition of optimum (40.5°C) relative to baseline (22°C, the growth temperature), and was visualized using heat maps (see Methods). Microarray data were obtained from GEO (GSE26199). B. Heat map showing 10 PtHsp90 genes across various tissues and genotypes (GEO: GSE16786). The genotypes analyzed were P. fremontii × P. angustifolia clones 1979, 3200, and RM5; P. tremuloides clones 271 and L4; and P. deltoids clones Soligo and Carpaccio. The tissues analyzed were young leaves (YL), expanding leaves (EL), mature leaves (L), root tips (RT), and suspension cell cultures (C). Stress treatments were nitrogen limitation (low N), methyl jasmonate elicitation (MeJ), and wounding, with sampling either 1 week or 90 h after wounding. C. Heat map showing 10 PtHsp90 genes under conditions of short- and long-term water deficit (GEO: GSE17230). EAR, early response to water deficit (by 36 h), LMI, long-term (10-day) response to mild stress with a soil relative extractable water (REW) level of 20–35%, LMO, long-term (10-day) response to moderate stress with a soil REW level of 10–20%.