Lime-induced iron deficiency stimulates a stronger response in tolerant grapevine rootstocks compared to low iron availability

Iron (Fe) is abundant in soil, but its bioavailability can be limited by environmental factors, negatively impacting plant growth and productivity. While root mechanisms for enhancing Fe uptake are well-studied in some model plants, the responses of tolerant and susceptible grapevine rootstocks to low Fe availability remain poorly understood. This study examined the responses of two grapevine rootstocks, Fercal (tolerant) and 3309C (susceptible), to three Fe conditions: direct Fe deficiency (−Fe), induced Fe deficiency through the addition of bicarbonate (+Fe+BIC), and control (+Fe). Our main findings include: 1) more severe leaf symptoms in 3309C than in Fercal independent of the type of stress, 2) overall growth reduction due to direct Fe deficiency (−Fe), while under induced Fe deficiency (+Fe+BIC) Fercal strongly increased root biomass. This observation is supported by the increased expression of root-development related genes VviSAUR66 and VviZAT6, 3) enhanced organic acid contents under induced Fe deficiency (+Fe+BIC) and different organic acids profiles depending on applied stress and genotype, and 4) stronger modulation of gene expression in Fercal root tips, including enhanced expression of Fe mobilization and transport genes (VviOPT3, VviIREG3, VviZIF1). Overall, bicarbonate-induced Fe deficiency (+Fe+BIC) had greater negative effects than direct Fe deficiency (−Fe), with Fercal showing a higher adaptive capability to maintain Fe homeostasis.