Expression of PpHsp16.4 . (A) Total RNA was extracted from untreated control wild type plants (Ctrl), plants treated for 24 hours with 50 μM ABA, 1 mM SA, 500 mM Mannitol (Mtl), 300 mM NaCl, 10 mM DTT, 100 μM methyl viologen (MV) and 100 μM H2O2. Samples were also obtained after 24 hours exposure to high temperature (37°C), UVB, and after 2 hours of exposure to strong light (SL). Ten μg of RNA were analyzed by Northern blot using a 32P-labeled hybridization probe corresponding to the full-length cDNA sequence of PpHsp16.4. (B) Northern blot analysis of PpHsp16.4 and PpDHNA transcripts in wild type (WT) or abi3 mutant genotypes. Total RNA was extracted from untreated control plants (Ctrl), plants exposed to 37°C or incubated in medium supplemented with 900 mM mannitol (Mtl). Samples were collected after two days of stress, and 6 hours of recovery. Full -length cDNA sequences of PpHsp16.4 and PpDHNA were 32P-labeled and used as hybridization probes. In all experiments, ethidium bromide staining of ribosomal RNA (rRNA) was used to ensure equal loading of RNA samples.