Regulating the regulators: responses of four plant growth regulators during clonal propagation of Lachenalia montana

Lachenalia species are endemic southern African plants with narrow geographical distribution, and are well-traded as ornamental plants in the international floriculture industry. In an attempt to have a better understanding of their growth and hormonal physiology, we evaluated the effects of different plant growth regulators (PGRs) during the clonal regeneration of Lachenalia montana. An auxin (α-naphthaleneacetic acid = NAA) and three cytokinin (CK) types (benzyladenine = BA, meta-topolin riboside = mTR and isopentenyladenine = iP), each at three concentrations (1, 5 and 10 µM), were tested and the effect of these PGRs on the accumulation of endogenous CK metabolites was evaluated to provide clues on the observed morphological responses. As the most efficient PGR, 10 µM mTR treatment produced the highest number of shoots (approximately five shoots per explant) while 1 µM BA-treated plants had more bulbs (approximately three bulbs per plantlet). Rooting was generally lower with increasing concentration of PGRs especially with the aromatic-type CKs. Based on the concentrations of endogenous CKs, 10 µM mTR regenerants also had the highest CKs (40 142.5 pmol g−1 DW) which were mainly of the aromatic-type (98%). In terms of the functional role of the CKs, O-glucosides (which are reversible CK storage forms) were the most dominant CK-type in the regenerants from 10 µM mTR treatment. On the other hand, the poor rooting, mostly prominent in regenerants from BA treatments was closely related to the high accumulation of N 9-glucosides (well-known CK metabolites directly involved in rooting inhibition) when compared to regenerants from other treatments. Overall, the current findings provide evidence on the interrelationship existing among the exogenous PGRs, phenotypic responses and the endogenous CKs in the in vitro regenerants.