The acquisition of desiccation tolerance in maize seed: Effects of genotype, developmental stage and drying environment

Abstract

The effects of genotype, developmental stage, and drying environment on the acquisition of desiccation tolerance were characterized in two maize {Zea mays L.) inbreds differing in sensitivity to high temperature (HT) desiccation, A632, tolerant, and B73, sensitive. Ears harvested periodically were dried: at room temperature (Rm); in thin-layer dryers (TL) at 25°C (TL25), 35°C (TL35) or 45°C (TL45); or in high relative humidity (HRH). In all treatments, axis moisture content (mc) decreased more slowly than that of whole seed and equilibrated to a higher final mc. Increasing warm and cold germination percentages and seedling dry weights (SDW), decreasing shoot to root ratios (S:R) and conductivity measures and respiration indicated tolerance acquired in Rm material at 15 days after pollination (DAP) but not to HT imtil 30DAP in A632 and 40DAP in 373. Sucrose and raffinose content increased differentially in A632 relative to B73 during development and drying. Concentration of non-heat-denatured protein was greater in A632 and increased in response to drying earlier in development than in B73. In vivo incorporation of p^S]-methionine/cysteine into soluble, non-heat-denatured embryo protein was greatest at 20DAP and in response to TL drying. Bands at 24 to 27 kDa were prominent in all treatments except 0 h; HT induced unique bands at 98, 78, 60, 45 and 40 kDa in A632 and 91, 68 and 43 kDa in B73. The effects of sample geometry and air velocity on drying rate and subsequent seed quality were investigated using a susceptible genotype, B73X(H99xH95). Ears were harvested periodically, dried or hand-shelled and individual seed dried at TL25, TL35, TL45, Rm, or HRH, or (seed only) in a fluidized bed (FB) at 25° or 35°C. Drying times varied from ~4 h in FB to ~70 h in TL to ~300 h at RM. Germination