Phosphate Starvation Alters Root Calcium Signatures

Plant roots foraging in the soil have to sense, transduce, and respond to fluctuations in water and nutrients plus a multitude of stresses to which they may be subjected. Biotic and abiotic stresses (including mechanical, salt, osmotic, and oxidative stress) trigger rapid and transient modulations in cytosolic and organellar free Ca²⁺ in plant cells. Recently, Ca²⁺ has also been implicated in signaling nutrient status and availability. While the involvement of Ca²⁺ as a second messenger in nutrient signaling is now beginning to be explored, few studies have examined the impact of nutrient deficiency on Ca²⁺ signaling per se. Thus, Matthus et al. (10.1104/pp.18.01469) set out to test how P_i starvation of Arabidopsis might influence the root’s use of Ca²⁺ as a signal, employing a range of abiotic stresses known to evoke robust, rapid, and transient [Ca²⁺]_cyt signatures (mechanical, salt, osmotic, and oxidative stress). Additionally, as mechanical stimulation, salt, and osmotic stress increase the accumulation of extracellular ATP (eATP), which in turn transiently increases [Ca²⁺]_cyt, they also tested the root response to extracellular purine nucleotides. By expressing the Ca²⁺-reporting photoprotein aequorin in Arabidopsis, the authors show that inorganic phosphate (P_i) starvation, but not nitrogen starvation, strongly dampens the [Ca²⁺]_cyt increases evoked by mechanical, salt, osmotic, and oxidative stress as well as by extracellular nucleotides. These results indicate that, while P_i availability does not seem to be signaled through [Ca²⁺]_cyt, Pi starvation strongly affects stress-induced [Ca²⁺]_cyt signatures.