Expression of ACC synthase and ACC oxidase genes in different tissues of immature and mature cucumber fruits

Ethylene biosynthesis and expression of 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS) and ACC oxidase (ACO) genes were investigated in immature [harvested at 10 days after anthesis (DAA)] and mature (harvested at 35 DAA) cucumber fruits. During storage or in response to exogenous ethylene, ACS activity in fruit harvested at 35 DAA remained at low levels resulting in very little ethylene production, although ACO activity was markedly enhanced by the treatment. Northern blot analysis revealed that transcripts for CS-ACS1, a cucumber ACS gene highly homologous to CMe-ACS1 which is expressed during melon fruit ripening, did not accumulate in any mature cucumber tissues. Exogenous ethylene did not induce accumulation of CS-ACS1 transcripts but suppressed CS-ACS2 mRNA accumulation in the peel and mesocarp tissues. CS-ACO1 transcripts were increased by exogenously applied ethylene, but CS-ACO2 was constitutively expressed regardless of the treatment. The results confirm that cucumber belongs to non-climacteric fruits because CS-ACS1 expression was not induced during fruit ripening or in response to exogenous ethylene.