In vitro micro-morphometric growth modulations induced by N6 cytokinins (Meta-Topolin and 6-benzylaminopurine) in Ceropegia juncea Roxb. – A rare medicinal climber
M. Manokari, K. Jayaprakash, Cokul Raj M, Abhijit Dey, Mohammad Faisal, Abdulrahman A. Alatar, Nirmal Joshee, Monika K Shekhawat
Abstract
Ceropegia juncea Roxb. is a medicinally important, rare, and endemic climber plant species. The present study optimized in vitro regeneration under the influence of different cytokinins and auxins on the morpho-structural changes/disorders during adventitious shoot induction. The highest shoot number (4.2 shoots/node explant with 3.0 cm length) was noted on Murashige and Skoog (MS) basal medium augmented with 1.5 mg L−1 Meta-Topolin (mT) treatment. Nutrient medium fortified with 1.0 mg L−1 mT and 0.5 mg L−1 NAA (α-Naphthalene acetic acid) resulted in the proliferation of a maximum number of shoots (33.0 shoots with an average shoot length of 6.2 cm after 3rd sub-culture). Comparatively, 1.0 mg L−1 BAP (6-benzylaminopurine) and 0.5 mg L−1 NAA treatment resulted in the proliferation of 25.0 shoots with 4.0 cm length after 3rd subculture. Morphometric and microscopic analyses were performed after 3rd sub-culture under in vitro conditions to study the effects of growth regulators. The shoots developed on 1.0 mg L−1 BAP and 0.5 mg L−1 NAA possessed poorly developed anatomical features such as a thin cuticle, unorganized epidermal layer, reduced chlorophylls and tissue density, and low cell wall thickness of xylem vessels and phloem fibers. The leaves and stems produced on 1.0 mg L−1 mT and 0.5 mg L−1 NAA treatment had a larger area of tissue systems, thick cuticle, organized epidermal layer with thick anticlinal walls, and increased cell wall thickenings of xylem and phloem tissues. Further, the shoots generated in treatments including mT and NAA rooted with the highest rooting percentage (98.3%) on half-strength MS medium supplemented with 2.0 mg L−1 NAA (6.2 roots with 4.0 cm length). Hence, the structural developments in the shoots derived from mT and NAA showed greater commitments to cellular differentiation along with the proliferation of shoots and survival (94.0%). Meta-Topolin in the medium moderately alleviated the in vitro-induced structural disorders and supported rooting and hardening procedures for the continuous supply of quality plantlets.