Lawrence Berkeley National Laboratory

Boron (B) plays a crucial role in plant physiological processes, and imbalances in its supply can markedly affect plant morphophysiology. This study evaluated the effects of a B concentration gradient on the growth and morphophysiological responses of Alternanthera tenella under in vitro conditions. Stem segments were cultured on media supplemented with different B concentrations (0, 125, 250, 500, 750, 1000, and 2000 µM) for 30 days. Growth traits, anatomical features, nutrient accumulation, photosynthetic pigment content, and photosystem II (PSII) performance were assessed. Increasing B availability enhanced Mg and S accumulation, while the thickness of root vessel elements increased progressively up to 750 µM B. Tissues associated with nutrient transport exhibited improved functionality, indicating more efficient translocation from roots to shoots under adequate B supply. Photosynthetic pigment content and PSII parameters were also highest at 750 µM B. The tolerance index remained above 68% across all treatments, demonstrating that A. tenella is tolerant to elevated B levels. However, excessive B concentrations (≥ 1000 µM) induced physiological disturbances and PSII structural damage, likely associated with pigment reduction. Anatomical adjustments observed in plants exposed to high B concentrations may represent adaptive mechanisms limiting further B uptake. In addition, the study suggests that 750 µM B is recommended to enhance its morphophysiological performance under in vitro culture.