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<p><i>Melia volkensii</i>, a drought-tolerant hardwood of ecological and economic importance in East Africa, remains difficult to propagate due to poor seed performance and limited clonal multiplication systems. Aromatic cytokinins are widely used in woody plant micropropagation, but their effectiveness depends not only on intrinsic activity, but also on their metabolic behavior, tissue distribution, and interaction with auxins. In this study, we compared 6-benzyladenine (BA; 10 µM) and meta-topolin riboside (mTR; 10 µM) over three subculture cycles, in the presence or absence of indole-3-butyric acid (IBA; 0.5&#xa0;mg L⁻¹ ≈ 2.46 µM) using a factorial treatment design. Morphological responses were evaluated alongside quantitative cytokinin profiling using UPLC–MS/MS. mTR significantly improved shoot elongation, multiplication, and leaf expansion compared with BA and hormone-free controls. Cytokinin profiling revealed clear tissue-specific distribution patterns. Callus tissues accumulated higher total cytokinin concentrations and were enriched in conjugated forms, whereas shoots maintained a larger proportion of metabolically accessible cytokinins. BA treatment was associated with greater accumulation of glucosylated derivatives, while mTR maintained a higher proportion of ribosides. Auxin supplementation did not significantly affect shoot morphology but reduced total cytokinin concentrations and shifted the cytokinin profile toward conjugated forms, indicating auxin-mediated modulation of cytokinin homeostasis. Notably, mTR-derived ribosides remained relatively more abundant under auxin treatment than BA-derived ribosides. These results indicate that cytokinin metabolism and tissue-specific distribution, rather than cytokinin identity alone, determine morphogenic performance in <i>M. volkensii</i>. The findings support meta-topolin riboside as a suitable cytokinin for clonal propagation of this species and highlight the importance of considering hormone metabolic behavior in woody plant micropropagation.</p>

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Cytokinin Metabolic Fate and Tissue-Specific Distribution Influence Aromatic Cytokinin–Mediated Responses During Micropropagation of Melia volkensii Gürke

  • 期刊论文

  • 发表日期：

    2026年5月27日

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  • Nandini Bhogar Suresh,
  • Lenka Plačková,
  • Karel Doležal,
  • Stefaan P.O. Werbrouck

摘要

Melia volkensii, a drought-tolerant hardwood of ecological and economic importance in East Africa, remains difficult to propagate due to poor seed performance and limited clonal multiplication systems. Aromatic cytokinins are widely used in woody plant micropropagation, but their effectiveness depends not only on intrinsic activity, but also on their metabolic behavior, tissue distribution, and interaction with auxins. In this study, we compared 6-benzyladenine (BA; 10 µM) and meta-topolin riboside (mTR; 10 µM) over three subculture cycles, in the presence or absence of indole-3-butyric acid (IBA; 0.5 mg L⁻¹ ≈ 2.46 µM) using a factorial treatment design. Morphological responses were evaluated alongside quantitative cytokinin profiling using UPLC–MS/MS. mTR significantly improved shoot elongation, multiplication, and leaf expansion compared with BA and hormone-free controls. Cytokinin profiling revealed clear tissue-specific distribution patterns. Callus tissues accumulated higher total cytokinin concentrations and were enriched in conjugated forms, whereas shoots maintained a larger proportion of metabolically accessible cytokinins. BA treatment was associated with greater accumulation of glucosylated derivatives, while mTR maintained a higher proportion of ribosides. Auxin supplementation did not significantly affect shoot morphology but reduced total cytokinin concentrations and shifted the cytokinin profile toward conjugated forms, indicating auxin-mediated modulation of cytokinin homeostasis. Notably, mTR-derived ribosides remained relatively more abundant under auxin treatment than BA-derived ribosides. These results indicate that cytokinin metabolism and tissue-specific distribution, rather than cytokinin identity alone, determine morphogenic performance in M. volkensii. The findings support meta-topolin riboside as a suitable cytokinin for clonal propagation of this species and highlight the importance of considering hormone metabolic behavior in woody plant micropropagation.