Shoot regeneration seedlings from transverse thin cell layer explants excised from cotyledon, petiole, hypocotyl of [{Brassica juncea} L. Czern.] in the presence of CdCl$_2$

The present work describes a novel neoformation process of Brassica juncea (L.) Czern. seedlings from transverse thin cell layers in the presence of CdCl2. In order to investigate the regeneration ability of this crop, the effect of CdCl2 on shoot regeneration (frequency of regeneration and bud number per tTCL) was examined. The tTCL explants were excised from cotyledon, petiole and hypocotyl of 7 day-old B. juncea seedlings and cultivated on a solid basal MS medium supplemented with α-naphtalenacetic acid (NAA : 3.22 μM), 6-benzylamino-purine (BAP : 26.6 μM), sucrose (2 %, w/v), silver nitrate (AgNO3 : 10 μM) and various concentrations of CdCl2 (0 250 μM). A concentration of CdCl2 of 5 μM is enough to reduce significantly the percentage of regenerated tTCL from 95-100 % to 77-86 % for all organs tested. In addition, 5 μM of CdCl2 reduces the bud number from 4.5 to 2.98 and 3.2 to 2.02 of hypocotyl and petiole tTCLs, but not for cotyledon tTCLs. Besides, 250 μM of CdCl2 is lethal for all tTCLs whatever the organ, and 200 μM is lethal only for cotyledon and petiole tTCLs but not for hypocotyl explants which had 3.6 % of frequency of shoot regeneration. Plantlets regenerated from all shoots, whatever the treatment, developed and flowered normally 6 weeks after the transfer to pots. The regenerated plants were fertile and identical to source plants.