The role of maize (Zea mays L.) radicle root hairs in seedling establishment under adverse phosphorus and water seedbed conditions.

Abstract

Background and aims: A vigorous root system is crucial for maize seedling establishment. Its formation and subsequent plant performance are hindered by nutrient- and water deficiency. Upon germination, maize seedlings develop primary, then seminal roots, covered with pubescent root hairs. Functions of root hairs at this developmental stage remain scarcely understood. This study examined their role during phosphorus- (P) and water limitations during early seedling development at the physiological, elemental, and molecular level, comparing a roothairless maize mutant (rth3) and its isogenic wildtype (WT).

Methods: Shoot- and root-system-architecture phenotyping and elemental analysis were performed on 5-day-old rth3 and WT plants experiencing various P- and water-deficient conditions in different growth substrates. Microscopy of root hairs and specific RT-qPCR of various P-nutrition regulators and aquaporins in roots were performed.

Key results: WT seedlings responded with a morphologically typical root hair elongation solely to water-reduced but not P-deficient conditions. In contrast, at the molecular level, WT and rth3 responsively upregulated P transporters in roots upon P deficiency, while water channel transcript abundances did not change upon water limitations. Surprisingly, under these adverse seedbed conditions no differences in shoot biomass, shoot nutrient concentrations, shoot water content were detected between the WT and the roothairless mutant which additionally formed a generally shorter total root length compared to the WT. P deficiency caused the development of thicker primary roots in rth3 and significant increase in expression of P transporters compared to the WT.

Conclusions: Germinating rth3 seedlings showed neither disadvantages in terms of shoot vigor, nor with respect to shoot water- and nutrient levels in suboptimal seedbed conditions compared to the WT, despite possessing shorter roots and no root hairs. An increase of the root diameter and P-transporter expression particularly in rth3 seminal roots may have been sufficient to physiologically compensate for the missing root hairs.