Effect of promoter and inhibitors of phenylalanine ammonia-lyase enzyme on stem bending of cut Gerbera flowers

The main postharvest disorder of cut gerbera flowers is the stem bending and break. The cause of stem bending is not completely clear. Although the genetic background seems to play the major role, some plant hormones such as ethylene and cytokinins may enhance or reduce the incidence of stem break during postharvest life. The choice of withstand genotypes seems to be a good strategy. In fact, stem bending incidence strongly varies among cultivars. The aim of this work was to evaluate the role of PAL activity and tissue lignifications on stem bending. Cut gerbera flowers were obtained from local growers and immediately transferred to postharvest evaluation room. Cut flowers were screened and selected in order to have homogenous samples. Chemicals were applied as pulse treatments for 24 h using 2 mM amino-oxyacetic acid (AOA), 1 mM α-aminooxi-β-phenylpropionic acid (AOPP) or 100 μl L-1 ethylene. During postharvest life the stem elongation, stem bending, PAL activity and vase life were measured. Results showed a strong variation of stem bending incidence among cultivars. Pulse treatments with PAL inhibitors such as AOA and AOPP strongly increased stem bending even after 1-2 days after treatments. Ethylene reduced the stem bending incidence increasing the PAL activity.