Root Hairs on Chlorotic Tomatoes are an Effect of Chlorosis Rather Than Part of the Adaptive Fe-Stress-Response

Extensive research has been reported from studies of the Fe-deficiency-stress responses of chlorotic-Fe plants, but little has been done to evaluate the more relevant Fe-stress-responses of plants that exhibit no chlorosis. The present work examined the stress responses using a novel, chelator-buffered hydroponic solution able to induce a wide range of Fe-deficiency and stress response even in green plants. The solution contains DTPA (diethylentriamine-pentaacetate), a chelator that limits the availability of Fe2+ (formed at the root by reduction of Fe3+DTPA) to plants by catalyzing Fe2+ oxidation back to the substrate Fe3+DTPA. This produces Fe stress and induces the adaptive Fe-stress-response in tomatoes (Lycopersicon esculentum) and other non-Poaceae. At 1831.6 pM FeDTPA (with 100 pM free DTPA), tomatoes had increased rates of Fe3+-chelate reduction and proton secretion, but remained green because the adaptive Fe-stress-response allowed the roots to obtain adequate Fe. Below 18 pM FeDTPA, the plants become increasingly chlorotic as FeDTPA was decreased.