Ethylene modifies architecture of root system in response to stomatal opening and water allocation changes between root and shoot.

Ethylene plays a key role in the elongation of exploratory and root hair systems in plants, as demonstrated by pharmacological modulation of the activity of ethylene biosynthesis enzymes: ACC synthase (ACS) and ACC oxidase (ACO). Thus, treatments with high concentrations (10 microM) of aminoethoxyvinylglycine (AVG, inhibitor of ACS) and 1-aminocyclopropane carboxylic acid (ACC, ethylene precursor, ACO activator) severely decrease the elongation of the exploratory root system but induce opposite effects on the root hair system: root hair length and numbers were increased in seedlings treated with ACC, whereas they were reduced in seedlings treated with AVG. Until now, such elongation changes of root architecture had not been questioned in terms of nitrate uptake. In the march issue of Plant Physiology we report that N uptake and nitrate transporter BnNrt2.1 transcript level were markedly reduced in ACC treated seedlings, but were increased in AVG treated seedlings compared to the control.1 Because recent studies have revealed that ethylene can also modulate stomatal opening as well as root hair cell elongation, we have examined whether pharmacological modulation of ethylene biosynthesis could affect, in an integrated manner, and at a whole-plant level, the exploratory and root hair systems, through changes of stomatal conductance and water allocation between the root and shoot.