Callogenesis and rhizogenesis in date palm leaf segments: are there similarities between the two auxin-induced pathways?
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In date palm (Phoenix dactylifera L. cv. Ahmar, Arecaceae), as for many monocotyledons, callogenesis is a prerequisite for the initiation of somatic embryogenesis, and requires the presence of auxin in the medium. Immature leaf explants were cultivated in medium supplemented with either 1 or 54 μM 1-naphtaleneacetic acid in order to induce either rhizogenesis or callogenesis. Histological studies performed throughout the culture period established that precocious cell reactivation is similar in both morphogenetic pathways. Early cytological modifications are associated with cell reactivation and are observed in the pluripotent cells of perivascular sheaths. Divergence between the callogenesis and rhizogenesis pathways is observed later, during the subsequent determination and morphological differentiation phases. We established that in date palm, the rhizogenesis and callogenesis pathways are initiated from the same cell type, the ultimate developmental fate depending upon auxin concentration.
KeywordsAuxin Cell competence Developmental patterns NAA Phoenix dactylifera Pluripotency
Callus induction medium
Periodic acid Schiff
Root induction medium
H. Saïd-Ahmed gratefully acknowledges grant from EGIDE-Ministère des affaires étrangères (France) for his Master’s degree. B. Gueye and D. Sané were supported by grants from the department for capacity-building support to scientific communities in the South (DSF, Institut de Recherche pour le Développement-IRD). Histological sections of nodular callus and root/root-like structure at d63 were kindly provided by Mrs M. Collin (IRD). F. Aberlenc-Bertossi (IRD) is also thanked for her comments on oil and date palms histology. The authors are indebted to Prof S. Hawkins (UMR 1281, USTL) for his critical reading of the manuscript, valuable discussion and checking English language.
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