Shoot organogenesis from roots of seabuckthorn (Hippophaë rhamnoides L.): structure, initiation and effects of phosphorus and auxin

Abstract

Shoots from roots formed on seedlings in vitro in the groove of lateral roots as on plants growing in a natural habitat. The finding has ecological and applied relevance. Shoot organogenesis from roots (root suckers, shoots from roots, SfRs) allows vegetative propagation of the small tree seabuckthorn (Hippophae rhamnoides L.) in addition to sexual propagation and is an important trait associated with the root system. Using an in vitro system, we studied initiation, localization and development of SfRs and interacting roles of phosphorus (P) and indole-3-acetic acid (IAA). After transfer of seedlings to the W4 medium (WPM medium with added IAA, benzyl adenine and giberellic acid), SfRs protruded after 2 weeks from the primary root initially at the groove of lateral roots (LR) as seen by scanning electron microscopy and light microscopy. This is also the location of SfRs on plants growing in natural conditions, which suggests a similar developmental pathway. To localize SfR initiation, staining by the DNA-binding fluorochrome 4′,6-diamidino-2-phenylindole in root cross sections revealed a high density of small cells as in meristems in the pericycle area between endodermis and vascular tissue. During 8–10 weeks, SfRs emerged also in other positions on the primary root, concomitantly with senescence of existing LRs and suppression of new LR formation. Since SfR formed in relation to LRs, we hypothesized that P and IAA play a role in SfR formation. Highest production of SfRs occurred in W4 medium after pre-treatment with high P in the presence of IAA while LR production in WPM was stimulated by IAA in low and middle P. SfRs developed in vitro on seedlings originating from three subspecies of H. rhamnoides showing this trait to be common. This experimental system allowed studies of organogenesis of SfRs and LRs in response to plant growth regulators, P and IAA and may be further implemented in basic studies and in applied clonal propagation of seabuckthorn.