Influence of cytokinins on the methyl jasmonate-promoted senescence in Helianthus annuus cotyledons

Cotyledons of seven-day-old sunflower seedlings were pretreated withcytokinins prior to exposure to methyl jasmonate (MeJA). The rate of senescencewas then followed by measuring chlorophyll loss, electrolyte leakage, ethyleneproduction, and 1-aminocyclopropane-1-carboxylase (ACC) oxidase activity. MeJApromoted all these senescence parameters and the MeJA effects were partiallyblocked by cytokinin pretreatment. 8-azaguanine, which has been reported tohaveanticytokinin activity, blocked the ability of benzyl adenine (BA) to reversethe effect of MeJA on senescence. MeJA also increased SOD and catalaseactivity,decreased protein content. However, while the cytokinin BA more than overcamethe MeJA effect on protein content and SOD activity it did not antagonize theeffect of MeJA on catalase.