In vitro propagation and biochemical changes in Aloe pruinosa

Abstract

Aloe pruinosa is a vulnerable traditional medicinal plant extensively used in South Africa. Efficient in vitro mass propagation and analysis of biochemical changes of the species was established to counter extinction threats, for commercial cultivation and to understand the effect of oxidative enzymes and phenolic metabolism on oxidative browning in vitro from shoot-tip and leaf explants using various concentrations and combinations of plant growth regulators (PGRs), sucrose and phloroglucinol (PG). The highest number of regenerated shoots per shoot-tip explant (15.4±0.9) was obtained on solid Murashige and Skoog (MSS) medium supplemented with a combination of 5μM benzyladenine (BA) and 4μM indole-3-acetic acid (IAA). Shoots developed significantly more roots (8.6±0.7 per shoot) on ½-MSS medium containing 2μM indole-3-butyric acid (IBA) and 40μM PG. The plantlets were successfully acclimatized (100%) ex vitro in a vermiculite-soil mixture (1:1 v/v) in the greenhouse. Somatic embryogenesis with all developmental stages of somatic embryos (SEs: 38–26) were obtained from friable embryogenic callus (FEC) of leaf explants in liquid MS (MSL) containing 0.5μM picloram (Pic), 2μM BA or 1μM thidiazuron (TDZ) and 10μM PG. However, germination and conversion of plantlets from SEs were inhibited as a result of oxidative browning. Polyphenolic enzymes (polyphenol oxidase (PPO) and peroxidase (POD)) activity and total phenolics of different in vitro growth phases (adventitious shoots, regenerated plantlets and calli) with different PGR treatments were determined. The application of PGRs and PG resulted in the control of morphogenic properties, oxidative exudates and browning in A. pruinosa. The study highlights the role of natural PGR (meta-topolin riboside) and PG in reducing the impact of polyphenolic exudation and can be used to improve future in vitro programmes. In addition, micropropagation protocols facilitate commercial and rapid propagation of A. pruinosa for conservation and could satisfy pharmaceutical, cosmetic and food industry demands.