M. Ovecka et al., A comparative structural analysis of direct and indirect shoot regeneration of Papaver somniferum L. in vitro, J PLANT PHY, 157(3), 2000, pp. 281-289
Cellular origin of shoot buds, cell morphogenesis and differentiation were
studied during direct and indirect shoot regeneration of Papaver somniferum
L. in vitro. Direct shoot organogenesis was induced in immature somatic em
bryos, where cell division and protomeristem formation started in sub-epide
rmal and epidermal cell layers of hypocotyl. Indirect shoot regeneration wa
s initiated from callus culture using auxins and cytokinins, where compact
globular merisiemoids were produced. The common morphogenetic event of dire
ct and indirect shoot regeneration was an establishment of non-random cell
division and restricted cell expansion within the group of competent cells
during protomeristem formation. However, in contrast to direct regeneration
, where all activated cells became competent, in indirect regeneration, onl
y peripheral cells of meristemoids acquired morphogenetic competence. The s
econd difference occurred in shoot tunica formation: original hypocotyl epi
dermal cells participated in tunica formation during direct organogenesis,
while this layer regenerated de novo in meristemoids. These results indicat
e that cell morphogenesis during shoot regeneration is independent of the d
evelopmental history of the competent cells.