Zinc (Zn) deficiency is an important mineral disorder affecting rice production, and is associated with
the formation of oxidative stress in plant tissue. In this study we investigated processes of oxidative
stress formation as affected by ascorbate (AsA) in two pairs of contrasting rice genotypes: (i) two indica
lines differing in field tolerance to Zn deficiency and AsA metabolism, i.e. RIL46 (tolerant) and IR74
(sensitive); (ii) the japonica wild-type Nipponbare (tolerant) and the AsA deficient TOS17 mutant line
ND6172 (sensitive) having a 20–30% lower AsA level due to the knockout of an AsA biosynthetic gene
(OsGME1). Plants were grown hydroponically under +Zn and
−Zn conditions for 21 days and samples
were investigated after 7, 14, and 21 days of treatment. Tissue Zn concentrations below 20 mg kg−1 in the
−Zn treatment induced the formation of visible symptoms of Zn deficiency from day 14 in all genotypes,
but especially in the sensitive IR74. Significant increases in lipid peroxidation were observed in the leaves
of the sensitive genotypes IR74 and ND6172, and in the roots of IR74, but not in the tolerant genotypes. At
day 21, the tolerant genotypes RIL46 and Nipponbare had significantly higher AsA levels in both shoots
and roots compared to the sensitive lines. Consistently, higher levels of hydrogen peroxide formation in
leaves and roots of the sensitive genotypes were detected using staining methods. Differences in foliar
hydrogen peroxide formation between IR74 and RIL46 became apparent on day 7 and between ND6172
and Nipponbare on day 14. Similarly, genotypic differences in hydrogen peroxide formation in the roots
were seen on day 21. In conclusion, our data demonstrate that Zn deficiency leads to a redox imbalance
in roots and shoots prior to the occurrence of visible symptoms, and that the antioxidant AsA plays an
important role in maintaining the redox homeostasis under Zn deficiency.