Polyethylene glycol (PEG) improved macro- and micro-morphological traits of in vitro shoots of Hedyotis biflora (L.) Lam.

Abstract

Key message

The incorporation of optimal concentration of polyethylene glycol with the optimized growth regulators in the nutrient medium promoted shoot growth and improved foliar micro-morpho-anatomical traits of Hedyotis biflora which improved the survival success of the plantlets during ex vitro hardening and field trials.

Polyethylene glycol (PEG) is widely recognized as an effective agent for stimulating osmotic stress in plant tissue cultures. In this study, the micropropagated shoots of Hedyotis biflora (L.) Lam was subjected to varied concentrations of polyethylene glycol (PEG-6000) under in vitro conditions to evaluate the effect of PEG on the morpho-anatomical development of shoots. The cultures were established by culturing nodal shoots on Murashige and Skoog (MS) medium supplemented with 2.0 mg L⁻¹ 6-benzylaminopurine (BAP), and the shoots were proliferated on the optimized plant growth regulators (1.0 mg L⁻¹ BAP + 0.5 mg L⁻¹ Kinetin (Kn) + 0.1 mg L⁻¹ Indole-3-acetic acid (IAA). Among the varied concentrations of PEG used in the MS medium, 60 mg L⁻¹ PEG with optimized growth regulators in the medium increased the rate of proliferation and elongation of shoots (14.0 shoots with 7.0 cm length) and leaf area (1.6 cm length × 1.0 cm width) than the control (medium without PEG). The foliar micro-morpho-anatomical elucidations revealed that the control leaves showed a thin cuticle, non-functional stomata, mesophyll with isobilateral tissues, and poorly developed mechanical, dermal, and vascular tissues. The incorporation of 60 mg L⁻¹ PEG (optimal) in the medium increased cuticle thickness, palisade and spongy mesophyll differentiation, functional stomata, dense vascular tissues, and well-developed ground tissues. The PEG-treated shoots showed better rhizogenesis on half-strength MS medium containing 2.0 mg L⁻¹ Indole-3-butyric acid (IBA) (21.0 roots with 4.0 cm average length). These morphometric and structural improvements were sequentially reflected in the increased survival of plantlets (96%) during acclimatization and field transplantation of H. biflora.