Root hairs and lateral root proliferation enhance rice seedling rhizosheath development and ABA accumulation under soil water deficit

Rhizosheath development benefits drought resistance in many upland crops. Although water-saving irrigation techniques induce rice rhizosheath formation, how and whether root hairs and different root types influence rice rhizosheath development and shoot water relations at seedling stage in drying soil are unclear. Wild-type (WT) seedlings with root hairs and its root hairless mutant rth2 were watered every 2 or 4 d, with root hair, whole root and shoot traits determined. Less frequent irrigation significantly increased rhizosheath of both genotypes by 14% during the seedling stage. Although root exudates from rth2 adhered 54% more soil than WT, facilitating rhizosheath development, root hairs and 25% greater lateral root proliferation of WT seedlings allowed 48% more rhizosheath especially in older seedlings. Greater root hair length, root hair length density and root hair number/root surface area on lateral than axial roots especially enhanced WT rhizosheath development. Soil water deficit increased root and leaf ABA concentrations especially in WT seedlings, causing stomatal closure that contributed to increased leaf water potential. In 36 d old seedlings, 10% greater shoot biomass of WT plants than rth2 accompanied 15% higher root and 36% higher foliar ABA concentrations and ultimately lower stomatal conductance. Higher ABA concentrations of WT plants at the same soil moisture suggested root hairs may be important in mediating shoot water status of rice seedlings.