In vitro regeneration and micro-morpho-anatomical characterization of leaves towards epiphytic adaptation in Aechmea bracteata (Sw.) Griseb.
Aechmea bracteata (Sw.) Griseb. is an important bromeliad and is considered for ex situ conservation. Epiphytism and Crassulacean acid metabolism (CAM) make this species resilient to ecological stresses. This study aimed to illustrate the periodic development of epiphytic structural traits in micropropagated plantlets of A. bracteata through in vitro, ex vitro, and in vivo transitions. Freshly collected seeds of A. bracteata were subjected to Murashige and Skoog (MS) medium augmented with 0.5 mg L−1 6-benzylaminopurine (BAP) for in vitro germination (97.2% of seeds responded). The resulting shoots proliferated better (14.0 shoots with 8.2-cm length) on the combination of 0.25 mg L−1 BAP and 0.15 mg L−1 α-naphthaleneacetic acetic acid (NAA). The in vitro-raised shoots were rooted with 100% response (7.0 roots with 3.2-cm average length) when pulse treated with 75.0 mg L−1 NAA solution under ex vitro conditions. The acclimated plantlets were shifted to the natural conditions. The morpho-anatomical assessments were conducted on leaves at different stages of their development and found that the specific micro-climatic conditions prevailing during in vitro development hindered the ideal development of the cuticle, epidermis, mechanical hypodermis, aquiferous parenchyma, chlorenchyma (characterized by fibrous clusters and air channels), and vascular bundles enveloped by a parenchymatic sheath and a cap of fibers. The mixotrophic ex vitro environment imposed the development of dermal, ground, and vascular tissues by cell expansion which led to the beginning of epiphytism. Well-developed air channels, sunken stomata, and well-organized dermal tissues suggested developing epiphytic adaptational traits under field conditions. The current research has the potential to enhance our comprehension of the mechanisms involved in the epiphytic adaptation of Bromeliads.
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