Plasticity of wheat seedling responses to K+ deficiency highlighted by integrated phenotyping of roots and root hairs over the whole root system.

The availability in the soil of potassium (K⁺), a poorly mobile macronutrient required in large quantities for plant growth, is generally suboptimal for crop production in the absence of fertilization, making improvement of the ability of crops to adapt to K⁺ deficiency stress a major issue. Increasing the uptake capacity of the root system is among the main strategies to achieve this goal. Here, we report an integrative approach to examine the effect of K⁺ deficiency on the development of young plant entire root system, including root hairs which are known to provide a significant contribution to the uptake of poorly mobile nutrients such as K⁺, in two genetically distant wheat varieties. A rhizobox-type methodology was developed to obtain highly-resolved images of root and root hairs, allowing to describe global root and root hair traits over the whole root system via image analysis procedures. The two wheat varieties responded differently to the K⁺ shortage: Escandia, a wheat ancestor, reduced shoot biomass in condition of K⁺ shortage and substantially increased the surface area of its root system, specifically by increasing the total root hair area. Oued Zenati, a landrace, conversely appeared unresponsive to the K⁺ shortage but was shown to constitutively express, independently of the external K⁺ availability, favorable traits to cope with reduced K⁺ availability, among which a high total root hair area. Thus, valuable information on root system adaptation to K⁺ deficiency was provided by global analyses including root hairs, which should also be relevant for other nutrient stresses.