Plant age and the effects of substrate and root hair formation on maize resource allocation, elemental composition and gene expression

Aim: Laboratory studies have identified fundamental processes and genetic determinants affecting the growth and stress tolerance of maize, but oversimplify complex field conditions where soil and climate variables interact. In this study, we assess the importance of plant development stage, substrate, and root hair formation on field-grown maize in terms of root gene expression, leaf element status and resource allocation patterns.Methods: Wild type and root hairless rth3 mutant maize were grown on two substrates, sand and loam and sampled during the 4-leaf, 9-leaf and tassel emergence stages. Leaf elemental composition was assessed by ionome analysis, root gene expression by RNA sequencing and qRT-PCR, and root resource allocation of recently assimilated carbon and nitrogen by stable isotope labeling.Results: Growth stage accounted for the main differences, followed by substrate and root hair formation in all analyses. During tassel emergence, the concentrations of several elements in maize leaves decreased, but nutrient transporter expression in roots increased; whereas cell wall formation-related root gene expression and carbon allocation to roots decreased. Substrate-related changes were pronounced during tassel emergence. Root nutrient transporter and plant immunity-related genes showed differential expression between two depths of soil. The effect of root hairs was negligible concerning mostly cell developmental gene expression. The extent of unexplained variation - presumably by the environment - was particularly high for gene expression levels.Conclusion: Our results demonstrate strong effects and interactions between the growth stage and substrate on maize, and suggest a negligible importance of root hairs for maize nutrition and gene expression in the field.