The effects of novel synthetic cytokinin derivatives and endogenous cytokinins on the in vitro growth responses of hemp (Cannabis sativa L.) explants

The biotechnological utilization (genetic transformation, gene editing) of industrial hemp (Cannabis sativa L.) has been hampered by a lack of robust regeneration/in vitro multiplication protocols. In order to break this barrier we propose an approach combining standard application of exogenous growth regulators (auxins, cytokinins) with the knowledge of (1) endogenous cytokinin concentrations in primary explants based on latest analytical techniques and (2) the exogenous application of novel synthetic cytokinins or the regulators of their activity/function. We have tested eight explant types isolated from aseptically germinated seedlings in order to induce shoot regeneration/multiple shoot formation. The main problems appeared were callus formation and strong apical dominance. The latter phenomenon was suppressed using the auxin antagonist α-(2-oxo-2-phenylethyl)-1H-indole-3-acetic acid (PEO-IAA), and multiple shoot cultures were established from isolated apical meristems using media containing the novel synthetic cytokinin derivative 6-benzylamino-9-(tetrahydroxypyranyl)purin (BAP9THP). Endogenous cytokinin concentrations were measured in primary explants and explants cultured under diverse conditions to clarify the interactions between endogenous and exogenously applied cytokinins and their synthetic derivatives. These measurements were subsequently used to optimize the applied concentrations and timing of application of specific cytokinin derivatives to achieve desirable in vitro responses and regeneration including inhibition of callus formation, single shoot formation, and induction of multiple shoots. The well-developed shoots were rooted on media containing auxin (α-naphthaleneacetic acid). The protocol was developed using the variety USO-31 and has been successfully applied to four other industrial hemp varieties: Tygra, Monoica, Bialobrzeskie, Fibrol.