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Plant Science Today (PST)

Research Articles

Vol. 13 No. 3 (2026)

Zinc-induced modulation of growth and stress biochemistry in mandarin orange (Citrus reticulata Blanco): A comprehensive study for delineating deficiency and toxicity threshold

DOI
https://doi.org/10.14719/pst.12354
Submitted
19 October 2025
Published
02-07-2026 — Updated on 09-07-2026
Versions

Abstract

While existing studies have primarily emphasised zinc (Zn) supplementation strategies, limited efforts have been made to identify critical biochemical and morphological markers that reflect leaf Zn status during early plant development. This study addressed the gap by evaluating the effects of zinc sulphate heptahydrate (ZnSO₄.7H₂O) at five concentrations (5.0, 7.5, 10.0, 12.5 and 15.0 mM) on mandarin seedlings grown in washed sand under greenhouse conditions. Zinc application significantly improved plant health up to an optimal concentration of 10.0 mM, beyond which toxicity symptoms became evident. Control plants exhibited classic deficiency symptoms such as chlorosis and stunted growth, coupled with reduced levels of superoxide dismutase (SOD), proline, phenol, free amino acids (FAA) and relative water content (RWC). Seedlings treated with 7.5–10.0 mM ZnSO₄ demonstrated robust growth, optimal biochemical profiles and no visual stress symptoms, with leaf Zn levels reaching up to 0.45 mM. In contrast, concentrations above 10.0 mM led to phytotoxicity, including leaf mottling, wrinkling, scorching and elevated tissue Zn accumulation (0.98–1.00 mM). These findings define clear physiological and biochemical thresholds of Zn nutrition in mandarin seedlings, offering critical insights for nursery-stage nutrient management. Further validation under diverse field conditions may refine these thresholds for wider agronomic application.

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