Tomato plant responses induced by sparingly available inorganic and organic phosphorus forms are modulated by strigolactones

Background and aims Phosphorus (P) is an essential nutrient for plant growth, but is also one of the least accessible in soil. Plants have evolved several strategies to cope with P deficiency and recently the role of the phytohormones strigolactones (SLs) in modulating tomato plants acclimation to P shortage has been described. How SLs regulate the use of P from sparingly accessible P sources, such as organic P or precipitated metal-P systems, is however still unknown in tomato. Methods In this study, we compared P acquisition strategies of wild-type (WT) and SL-depleted tomato plants grown hydroponically in the presence of dissolved inorganic phosphate (Pi), dissolved myo-inositol hexaphosphate (myoInsP6), or their coprecipitated form following Fe(II) oxidative precipitation. Results Irrespective of the P treatment, SL-depleted plants accumulated more P in their tissues than the WT, possibly due to the constitutively higher expression of high-affinity P transporters and activity of P-hydrolyzing enzymes. Wild-type plants were conversely more effective at acidifying their growth medium and exuding more organic compounds in the presence of dissolved myoInsP6 or coprecipitated forms of P, but this behaviour did not translate into a higher P acquisition. Conclusions The two genotypes activated different subsets of responses to bypass low P bioavailability, although the P acquisition efficiency (PAE) was not effectively increased. Strigolactone-depleted plants achieved higher PAE values than WT plants regardless of the applied P form, highlighting a central role of SLs in controlling P uptake and optimizing the cost/benefit ratio of P acquisition.