Heat Stress during Grain Filling Modifies Kernel Protein Composition in Field‐Grown Maize

Episodes of extremely high temperatures (>35°C) may cause a premature cessation of maize kernel growth (i.e., heat stress), depressing crop grain yield. However, little is known about the influence of this constraint on chemical composition of maize kernels, a key trait for end‐use related attributes. Four maize genotypes (flint, popcorn, temperate semi‐dent, and temperate × tropical semi‐dent) with distinctive endosperm types were grown at heated and non‐heated temperature regimes during the early or late stages of the effective grain‐filling period. Heat stress during early stages decreased both protein and starch contents of kernels, but the impact on the former was lower (up to −42%) than on the latter (up to −50%), resulting in increases of kernel protein concentration (up to +14%). The flint and popcorn hybrids, with hard endosperm type, tended to be less vulnerable to such effects due to an enhanced capacity to sustain kernel growth. For all hybrids, heat stress during late stages of kernel growth, reduced similarly protein and starch contents (up to −38%), without affecting kernel protein concentration. Heat stress always altered endosperm protein composition by increasing the relative abundance of glutelins, and β‐ plus γ‐zeins, at the expense of that of α‐zeins. The significant environment × endosperm‐type interaction for kernel chemical compounds should be linked to quality parameters for different maize end‐uses.