Effects of Iron Deficiency Stress on the Growth and Chlorophyll Fluorescence Characteristics of Gypsophila paniculata L. Tissue-cultured Seedlings

Purpose To investigate the physiological response mechanisms of Gypsophila paniculata L. tissue-cultured seedlings under iron deficiency stress conditions, providing a theoretical basis for iron nutrition regulation and culture medium optimization of G. paniculata tissue-cultured seedlings .

Methods Using G. paniculata tissue-cultured seedlings as experimental material, iron deficiency treatments with different concentrations (0, 10, 50 µmol/L Fe²⁺) were applied. Phenotypic and growth index changes under different treatments were observed, and chlorophyll fluorescence kinetics curves and 820 nm light reflectance curves were measured.

Results Short-term (14 d) iron deficiency (10 µmol/L Fe²⁺) treatment promoted plant height growth, whereas long-term (35 d) iron deficiency (0-10 µmol/L Fe²⁺) induced chlorosis and whitening in young leaves of the seedlings, accompanied by a significant reduction in chlorophyll content (P<0.05). Chlorophyll fluorescence analysis revealed that iron deficiency (0-10 µmol/L Fe²⁺) disrupted electron transport on both the donor side and acceptor side (Q_A→Q_B) of PSⅡ, reduced the number of active reaction centers per cross-section (RC/CS_O), increased energy capture (TR_O/RC) and dissipation (DI_O/RC), decreased the reducing capacity of terminal electron acceptors in PSⅠ, and diminished the plastoquinone pool capacity. Concurrently, the maximum photochemical efficiency (φ_Po), performance index (PI_abs), and total performance index (PI_total) of PSⅡ were reduced. Parameters such as TR_O/RC and DI_O/RC were identified as key indicators for iron deficiency stress. The 50 µmol/L Fe²⁺ treatment maintained normal seedling development and photosynthetic electron transport.

Conclusion Iron (Fe²⁺) concentrations below 10 µmol/L in the culture medium inhibit PSⅠ/PSⅡ activity and electron transport, thereby impairing the growth of G. paniculata tissue-cultured seedlings. The 50 µmol/L Fe²⁺ treatment meets the requirements for normal growth and photosynthetic function in tissue-cultured seedlings, and can serve as the standardized benchmark for iron nutrition supply in tissue culture production. These findings provide critical threshold parameters and theoretical basis for optimizing the culture medium and managing iron nutrition in G. paniculata tissue culture.