Proceedings Volume 2010 (format .pdf) - SimpBTH

demonstrated direct regeneration from proliferating root epidermal andsubepidermal cells, without a callus phase. However, morphogenic pathways inthese two studies were different, somatic embryogenesis in this study andcaulogenesis in the study of Knoll et al. (1997). Komai et al. (1996) also obtainedSE from seedlings' root sections of cultivar Jiromaru using the same PGRs(10 µM NAA + 0.1 µM GA 3 ), but the process of somatic embryogenesis wasthrough a callus phase. The differences obtained in the three studies may beattributed to different genetic background, since different cultivars were used ineach study, as well as to different explant pretreatment and the stage ofdevelopment. We used roots of 2-3 weeks old seedlings, as was done by Komai etal. (1996), while Knoll et al. (1997) used roots induced from primulae andhypocotyls on NAA-supplemented media.Regeneration success of P-seedlingsOut of 20 randomly chosen seedlings, 16 were capable to regenerate duringthree subcultures, with variable regenerative success (Fig. 2.). The frequencies ofregeneration of the responsive genotypes varied from 0.3% to 64.5% (Fig. 2a), andthe mean SE number per regenerating explant ranged from 1 to 10.8 (Fig. 2b) Themost responsive genotypes were P7, P11, P12, P13 and P18, which formed 94,67, 88, 145 and 136 SE, respectively, for 12-week period (not shown). Thesegenotypes exhibited both high frequency of regeneration and the mean SE numberper explant. EFC indexes, which take into account both of these values, reached1.88 - 4.26 (Fig. 2c). By contrast, some other genotypes formed only a few SEduring this period, exhibiting EFC indexes just a little bit above zero. Dynamics ofthe regeneration process was also variable. During the first subculture onlygenotype P18 regenerated. In the second subculture nine new genotypesregenerated, and the remaining 6 genotypes regenerated until the end of the thirdsubculture (not shown). Four genotypes were irresponsive. Our results are inaccordance with Ishizaki et al. (2001), who demonstrated high individual variationin embryogenic capacity of spinach cultivar Nippon, although Nippon showedhigher regeneration response than Matador, reaching the frequency of up to 90% insome individuals.Fig. 1. - (a, b) Somatic embryo regeneration from spinach seedling's root sectionscultivated on MS medium with 20 µM NAA + 5 µM GA 3 for 8 weeks.49