The effects of plant growth regulators, amino acids and minerals on ethylene biosynthesis and evolution in 'Tsugaru' and 'Akane' apple fruit

The internal ethylene concentration (IEC), 1- aminocyclopropane- 1-carboxyl ate (ACC) contents, N-malonyl-ACC (MACC) contents, ACC synthase activities, and ACC oxidase activities were determined on intact (early-maturing) and detached 'Tsugaru' and 'Akane' Apples to study the mechanism of ethylene bi osynthesis. The effects of plant growth regulators, amino acids, and minera ls on ethylene evolution by sliced and whole fruits were also examined. The IEC in 'Tsugaru' fruit rapidly increased from late August to September, reaching 300 mu l . l(-1) and 800 mu l l(-1) in intact and detached fruit, respectively. In contrast, the attached fruit of 'Akane', IEC was only 5.6 mu l . l(-1) at its climacteric peak, whereas in detached fruits, it was l ess than 10 mu l . l(-1) during storage. ACC content and ACC synthase activ ity were both higher in 'Tsugaru' than they were in 'Akane' fruit. These re sults indicate that ethylene biosynthesis in both cultivars is regulated by ACC synthase activity, as reported previously for other cultivars, such as 'Fuji' and 'Senshu' (Suzuki, et al., 1997). Flesh slices dipped in 10 and 100 ppm GA(3) had slightly reduced ethylene e volution. In whole fruit similarly treated with GA(3), the ethylene evoluti on significantly decreased 2 weeks after treatment in comparison with the c ontrol; the decrease continued throughout the treatment period. Treatment w ith 10 mM or 100 mM aspartic acid and 100 mM glutamine significantly reduce d the ethylene evolution in sliced tissue, whereas 100 ppm Ca and NH4 -N te nded to reduce ethylene evolution; contrarily, the same treatments at 300 p pm stimulated it.