Root segment development

Fig. (24). Shoot formation of cultured root segment a Shoot formation in the dark. Segment was cultured on HF B5 solid medium in the dark for 1 month, b Development of shoots cultured in the dark for 2 months, c Plantlet was further cultured under 16 hr/day light for 1 month, d 17-month old regenerated plant cultivated in a greenhouse. Bars represent I cm (a, b, c) or 5 cm (d).

The cultured root segments were divided into proximal, distal and newly developed lateral root parts and their endogenous lAA levels were periodically analyzed using enzyme-linked immunosorbent assay (ELISA) kits for lAA (PHYTODETEK iAA, Idetek Inc., USA) according to the procedure of Weiler et al. [39]. The lAA levels in the root segments are indicated in Fig. (26). The lAA levels in the roots cultured on HF B5 medium that initiated shoot formation increased once at day 9 and consequently decreased in both proximal and distal parts. On the other hand, lAA levels in proximal part of the roots cultured in the presence of 0.5 mg/1 TIBA increased along with the culture period. The roots cultured on the MS medium containing 0.5 mg/1 NAA (source for the experiments) accumulated low amounts of lAA and the lateral roots did not accumulate detectable amounts of lAA in all the cases. 

The Duboisia myoporoides - D. leichhardtii hybrid (M-II-8-6), which was used for explants, is cultivated at the Research Center for Medicinal Plant Resources, Tsukuba, Japan. Leaves were dipped in 75% ethanol for 10 seconds, rinsed in sterilized water, surface-sterilized for 10 minutes in 2% sodium hypochlorite containing Tween 20 (1 drop per 40 ml) and then washed three times with sterilized water. Leaf segments (ca. 5x5 mm) were incubated on MS solid medium containing 1 mg/1 lAA and 3% sucrose in the dark at 25 "C. Within 3 weeks, adventitious roots developed. 

Evans ML, Schmitt MR (1975) The nature of spontaneous changes in growth rate in isolated coleoptile segments. Plant Physiol 55 757-762 Evans ML, Simon M, Vesper MJ (1977) Further characterization of the spontaneous growth response in Zea coleoptile segments. Plant Cell Physiol 18 441-452 Feldman LJ (1975) Cytokinins and quiescent center activity in roots of Zea. In Torrey JG, Clarkson DT (eds) The development and function of roots. Academic Press, London New York, pp 55-72... 

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