PLANTLET REGENERATION FROM MESOPHYLL PROTOPLASTS OF BETULA-PLATYPHYLLA VAR JAPONICA

In Betula platyphylla var. japonica, colonies were induced efficiently from mesophyll protoplasts cultured in half strength MS (1/2MS) liqui d medium containing 0.6 M mannitol, 0.09 M sucrose and 1 mu M 4-PU and 1 mu M NAA at a cell density of 5 x 10(4)/ml. The colonies grew activ ely and developed into callus after 3 months of culture. Roots differe ntiated from the protoplast-derived white calluses cultured on the 1/2 MS solid media supplemented with 0.1-1 mu M 4-PU and 1 mu M NAA, and 1 0 mu M zeatin with no supplementation of NAA. Furthermore, the protopl ast-derived green callus differentiated shoots with 1/2MS solid medium containing 1 mu M 4-PU or 10 mu M zeatin with no supplementation of N AA. When shoots obtained were cultured on the cytokinin-free MS solid medium with 2.5 mu M IBA and 0.1 mu M NAA, they rooted and developed i nto plantlets after one month of culture. The phenylurea-type cytokini n, 4-PU, was effective for plantlet regeneration from the mesophyll pr otoplasts of B. platyphylla var. japonica. This suggests that there is potential for the use of 4-PU in the culture of protoplasts in many f orest tree species.