J. Samaj et al., Bundle sheath cells are responsible for direct root regeneration from leafexplants of Helianthus occidentalis L., J PLANT PHY, 154(1), 1999, pp. 89-94
Direct root organogenesis from isolated leaf explants of Helianthus occiden
talis L. was induced using MS culture media supplemented with alpha-naphtha
lene acetic acid (NAA) and benzyladenine (BA). The highest numbers of roots
were formed de novo from bundle sheath cells located around leaf veins whe
n explants were cultured on induction medium supplemented with 2.7 mu mol/L
NAA and 0.44 mu mol/L BA. The structural events accompanying reactivation
and division of competent bundle sheath cells and cells derived from them w
ere investigated employing light, transmission and scanning electron micros
copy in time course experiments. Vein parenchyma and bundle sheath cells lo
cated around leaf veins started to divide first after 2 days of culture. Ve
in parenchyma cells, however, ceased their divisions by day 5, while reacti
vated bundle sheath cells produced cambium-like cells. These later cells ga
ve origin to circular meristematic tissue, and subsequently to root primord
ia. Root primordia appeared after 7 days and regenerated roots emerged from
leaf explants after 15 days of culture. Ultrastructure of reactivated rege
neration competent cells is described and is compared with other examples o
f regeneration in vitro.