Effect of rigidity of gel medium on benzyladenine‐induced adventitious bud formation and vitrification in vitro in <i>Picea abies</i>

Observations on the effects of different degrees of rigidity of both an agar (Tayio) and a non‐agar (Gelrite) gel on the uptake of radiolabelled N 6 ‐benzyladenine ( 14 C‐BA) were also extended to mode of application and positioning of the explant. Regression analysis showed a highly significant inverse correlation between 14 C‐BA accumulation and degree of gel stiffness. Significantly greater numbers of adventitious buds per explant were induced at low to medium levels of rigidity (2.5–10 g Tayio 1 −1 , 1–5 g Gelrite 1 −1 ); this advantage was almost completely nullified at the lower levels (2.5 and 5.0 g Tayio 1 −1 , 1 and 1.5 g Gelrite 1 −1 ) as a result of the high incidence of vitrification. In addition to turgor distension, vitrified buds displayed cellular damage. Explants with their cotyledons flattened onto the agar surface accumulated less 14 C‐BA after 96 h than upright explants, but produced greater numbers of adventitious buds, pseudobuds and phylloids. It was suggested that BA was taken up only by “target” cells, presumably the differentiating subsidiary cells of those stomatal complexes in surface contact with the medium. Pulse treatments of relatively short durations (2 h) with optimal concentrations of BA (ca 125 μ M ), followed by subculturing on hormone‐free media gelled with 10 g agar 1 −1 , produced a satisfactory balance between yield and competence of adventitiously‐induced buds.