Abstract
Understanding the mechanisms by which nutritional signals impact upon root system architecture is a key facet in the drive for greater nutrient application efficiency in agricultural systems. Cereal plants reduce their rate of lateral root emergence under inorganic phosphate (Pi) shortage; this study uses molecular and pharmacological techniques to dissect this Pi response in Triticum aestivum. Plants were grown in coarse sand washed in high- or low-Pi nutrient solution before being assessed for their root branching density and expression of AUX/IAA and PIN genes. Seedlings were also grown on media containing [(14)C]indole acetic acid to measure basipetal auxin transport. Seedlings grown in low-Pi environments displayed less capacity to transport auxin basipetally from the seminal root apex, a reduction in root expression of PIN auxin transporter genes, and perturbed expression of a range of AUX/IAA auxin response genes. Given the known importance of basipetally transported auxin in stimulating lateral root initiation, it is proposed here that, in T. aestivum, Pi availability directly influences lateral root production through modulation of PIN expression. Understanding such processes is important in the drive for greater efficiency in crop use of Pi fertilizers in agricultural settings.
Highlights
The plasticity of root system architecture in response to environmental cues is a crucial component of a plant’s nutrient foraging capacity
Seedlings grown in low-Pi media supplemented with 1 μM 2,4-D demonstrated a significant recovery in root branching frequency, demonstrating that they retained the capacity to respond to exogenous auxin (Fig. 1C, D)
The inclusion of 100 μM triiodobenzoic acid (TIBA) in the growth media showed that inhibition of auxin transport could severely reduce lateral root outgrowth (Fig. 1E), a similar response to that found in other plant species (KarabaghliDegron et al, 1998)
Summary
The plasticity of root system architecture in response to environmental cues is a crucial component of a plant’s nutrient foraging capacity. The production of lateral root branches is genetically controlled and may increase root surface area in nutrient-rich soil (Drew, 1975; Linkohr et al, 2002), or enable the exploration of a greater soil volume by lateral growth through the topsoil in nutrient-poor soil (Linkohr et al, 2002; Zhu and Lynch, 2004) An example of this process is the acquisition of inorganic phosphate (Pi), in which the production of lateral roots is crucial for Pi accumulation in some plants (Lynch, 2011). The concentrations of Pi in soil solution are, typically very low, due to Pi’s propensity to bind strongly to soil surfaces or form insoluble complexes with cations (Norman and Hemwall, 1957) This means that Pi is often a limiting factor in plant growth and development.
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