Effect of N-nutrition in apple on the response of its secondary metabolism to prohexadione-Ca treatment

The response of in vitro grown apple plantlets onto the treatment with the growth retardant prohexadione-Ca is demonstrated with regards to their secondary metabolism and under the influence of N nutrition. Reported prohexadione-Ca induced changes of the flavonoid composition were the formation of the uncommon 3-deoxycatechin luteoliflavan, a decrease of catechins, procyanidins and flavonols, which was also observed in our experiments on 'Royal Gala' and 'Golden Delicious'. The extent of effects, however, was markedly modified by N-nutrition of the plantlets. In general, high N-nutrition reduces the amount of total phenolic compounds in apple leaves whereas low N supply favours the accumulation of flavonoids and the formation of resistance related compounds after prohexadione-Ca treatment.