Growth and physiological impairments in Fe-starved alfalfa are associated with the downregulation of Fe and S transporters along with redox imbalance

Abstract

Background Iron (Fe) is an essential plant nutrient. Its deficiency is a major constraint in crop production systems, affecting crop yield and quality. It is therefore important to elucidate the responses and adaptive mechanisms underlying Fe-deficiency symptoms in alfalfa. Materials and methods The experiment was carried out on 12-day-old alfalfa plants grown in hydroponics under Fe-sufficient and Fe-deficient conditions. Results The Fe-starved alfalfa showed decreased plant biomass, chlorophyll score, PSII efficiency, and photosynthesis performance index in young leaves under low Fe. Further, Fe shortage reduced the Fe, Zn, S and Ca concentration in root and shoot of alfalfa accompanied by the marked decrease of MsIRT1, MsZIP, MsSULTR1;1, MsSULTR1;2 and MsSULTR1;3 transcripts in root and shoot. It indicates that retardation caused by Fe-deficiency was also associated with the status of other elements, especially the reduced Fe and S may be coordinately attributed to the photosynthetic damages in Fe-deficient alfalfa. The ferric chelate reductase activity accompanied by the expression of MsFRO1 in roots showed no substantial changes, indicating the possible involvement of this Strategy I response in Fe-deficient alfalfa. However, the proton extrusion and expression of MsHAI1 were significantly induced following Fe-deficiency. In silico analysis further suggested their subcellular localization in the plasma membrane. Also, the interactome map suggested the partnership of MsFRO1 with plasma membrane H+-ATPase, transcription factor bHLH47, and nitrate reductase genes, while MsHAI1 partners include ferric reductase-like transmembrane component, plasma membrane ATPase, vacuolar-type H-pyrophosphatase, and general regulatory factor 2. In this study, SOD and APX enzymes showed a substantial increase in roots but unable to restore the oxidative damages in Fe-starved alfalfa. Conclusion These findings promote further studies for the improvement of Fe-starved alfalfa or legumes through breeding or transgenic approaches. Graphic Abstract