Investigations into the heat-shock response and HSP22 expression as they relate to mitochondrial integrity, seed vigor and viability maintenance in primed and non-primed seeds of Zea maize

In seeds of Zea maize, priming increased seed germination percentage and growth rate of derived seedlings. However, grow-out assays on controlled deteriorated maize seeds indicated that vigor and viability maintenance (VVM) in primed seeds was inferior to that in non-primed seeds. Heat-shock (HS) treatments improved primed maize seed VVM. In seeds of genotypes identified as 166 (Mo17 type) and 171 (B73 type), HS increased germination percentage by 28.9% and 10.0%, normal seedling percentage by 91.7% and 35.4%, and total dry weight by 87.3% and 38.7%, respectively in controlled deteriorated, primed seeds. HS influenced integrity of mitochondria from germinating non-aged and CD-conditioned primed seed embryos and etiolated seedlings. In embryo mitochondria from non-aged, HS-primed 166 and 171 seeds, ADP/Os were improved by 19.8% in 171 at 26°C and 229.8% in 166 at 42°C and respiratory control ratios (RC) were improved by 13.3% in 171 at 26°C and 17.9% in 166 at 42°C. In embryo mitochondria from CDconditioned HS-primed seeds, ADP/Os were improved by 5.3 and 22.6% at 26 and 42°C, respectively, in 166 and 21.3% in 171 at 26°C. In mitochondrial fractions from heat-shocked etiolated 166 and 171 seedlings, ADP/Os at 42°C were improved by 81.2 and 27.3%, respectively. Low base levels of acidic and basic 22-kD proteins (HSP22) were increased in primed seed embryo mitochondria through HS, and in non-primed and primed seeds through CD conditioning. Increased levels of HSP22 persisted through germination in a non-stress growth temperature regime. Elevated levels of HSP22 in embryo mitochondria from primed, heat-shocked seeds prior to CD-conditioning correlated with VVM improvements in primed maize seeds. Overall, HS appeared to promote VVM in primed maize seeds. This effect was associated with mitochondrial integrity and HSP22 expression