| Summary: | The aim of this study was to determine the influence of meta-topolin (mT) and 6-benzyl-aminopurine (BAP) on the hydrogen peroxide (H2O2) level and antioxidant enzymes activities in relation to the shoot formation and senescence process in Pelargonium hortorum cultivars, which differ in their susceptibility to leaf yellowing under in vitro conditions.
In an early senescing cultivar ‘Grand Prix’, the addition of an aromatic cytokinin mT to abscisic acid (ABA)-enriched Murashige and Skoog (MS) basal medium more efficiently inhibited leaf yellowing than BAP. In both genotypes, meta-topolin was also the most effective in shoot formation. It was found that Pelargonium species varying in their susceptibility to senescence differ in H2O2 production and antioxidant enzymes activities. Generally, meta-topolin more effectively enhanced H2O2 production and POD activity than BAP and control medium, but its effect depended on genotype. The highest H2O2 production stimulated by mT was observed on day 5 of subculture in late senescing cv. ‘Bergpalais’. In both geranium genotypes, superoxide dismutase (SOD) and catalase (CAT) levels were highest at the beginning of the subculture period, during the initiation of shoot formation. SOD showed the highest activity on day 5 of subculture on the medium without cytokinin and generally being higher in cv. ‘Bergpalais’ than in cv. ‘Grand Prix’. CAT activity was positively regulated by both cytokinins. POD activity was most effectively enhanced by mT, but on different days of subculture - on the 2nd day of subculture in cv. ‘Bergpalais’ and on the 22nd day of subculture in cv. ‘Grand Prix’. The enhanced activity of POD in the presence of mT, 4-fold higher than on control medium, at the end of subculture in P. hortorum ‘Grand Prix’ coincided with the inhibition of leaf senescence.
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