3.2. Effects of different types and concentrations of auxin in combinations
with optimal cytokinin concentration on shoot proliferation
The presence of auxin at all the concentrations tested gave an
increase in shoot proliferation (Table 2). In most cases, the number of
adventitious shoots produced, number of adventitious shoots greater
than 10 mm in length and the length of the longest shoot increased
significantly with the presence of auxin when compared to cultures
without any auxin. The highest shoot production (18 shoots per explant)
was recorded in cultures supplemented with 5 μM mT and
2 μM IBA (Fig. 1d). Furthermore, an increase in the number of shoots
greater than 10 mm in length and the length of the longest shoot
were observed with an increase in auxin concentration. Depending on
the plant species and tissue type, auxins can interact with cytokinins
in a synergistic, additive or antagonistic manner at different levels to
produce a physiological response (Coenen and Lomax, 1997). The findings
in the present study indicate an additive or perhaps a synergistic effect
of auxins with meta-topolin on shoot proliferation in this species.
Are mu et al. (2012) observed that there is a dearth of information on
the interaction of topolins with auxins. Therefore, studies involving
the interaction or combination of auxins with topolins are undoubtedly
helpful in further elucidating and maximising the activities of topolins
in plant tissue culture (Amoo and Van Staden, 2013). Such studies are
important considering the fact that many developmental processes in
plants such as cell growth, cell division and differentiation as well as organogenesis
in tissue and organ cultures are controlled by an interaction
between cytokinins and auxins (Gaspar et al., 1996).