Regeneration and maintenance of nodule cultures of Paulownia × taiwaniana.
Nodule cultures of P. taiwaniana were established and maintained for over 1 year by regular subculturing. Vigorous callus clumps were induced from leaf explants cultured on MS medium containing 3 mg IBA and 3 mg BA/litre. To produce nodule cultures, the callus was transferred to half-strength MS liquid medium containing the same IBA and BA concentrations, and shaken at 130 r.p.m. for 6 weeks. Cell growth cycles of 3-month-old and 1-year-old subcultures were determined using settled cell volume and electrical conductivity. The results of the 2 measurements were consistent; after 1 year in subculture the growth patterns obtained were similar to those of 3-month-old subcultures. Cell differentiation and vascular organization were investigated at different growth phases. Nodules maintained organogenic capability in the first few subcultures, but lost it in continued subcultures.