Boron deficiency responses in maize (Zea mays L.) roots

Background: Boron (B) is an essential micronutrient for plants. Dicot plants respond to insufficient B supply by altering root architecture and root hair growth. How root systems of rather low-B demanding monocot species such as maize (Zea mays L.) respond to B deficiency in terra has not been experimentally resolved, yet. Aims: The study aims to investigate root responses and their physiological consequences under B deficiency during the vegetative growth of maize. Methods: B73 wild-type (WT) maize and its root hairless rth3 mutant were grown under varying B supply conditions in soil columns and in an automated root phenotyping facility. Biomass data, root system architecture traits, the mineral elemental composition and molecular B-deficiency responses were quantified. Results: Though having very low leaf B concentrations, no major growth deficit, apart from chlorotic stripes on leaves, was recorded on maize root and shoot development, with or without root hairs, on B-deficient conditions. Although leaf B concentration of the rth3 mutant is significantly lower under B-deficient and under B-surplus conditions compared to the WT, the rth3 mutant neither developed a larger total root length, more fine roots nor displayed a higher expression of B uptake transporters as compensatory adaptations. Conclusions: Strikingly, maize plants did neither react with an inhibited root growth nor by a compensatory root foraging behaviour to severe B-deficient in terra growth conditions. This is rather atypical for plants. The performance and altered leaf B concentrations of rth3 mutants may be biased by secondary effects, such as an overall reduced root growth.