G-protein-coupled alpha2A-adrenoreceptor agonists differentially alter citrus leaf and fruit abscission by affecting expression of ACC synthase and ACC oxidase.

Temporal and spatial expression patterns of genes encoding 1-aminocyclopropane-1-carboxylate (ACC) synthase (ACS1 and ACS2) and ACC oxidase (ACO), ACC concentration, and ethylene production in leaves and fruit of 'Valencia' orange (Citrus sinensis [L.] Osbeck) were examined in relation to differential abscission after treatment with 2-chloroethylphosphonic acid (ethephon) alone or in combination with guanfacine or clonidine, two G-protein-coupled alpha(2A)-adrenoreceptor selective agonists. Guanfacine and clonidine markedly reduced ethephon-enhanced leaf abscission, but had little effect on ethephon-enhanced fruit loosening.

Phenylalanine ammonia lyase gene expression during abscission in citrus.

Phenylalanine ammonia lyase (PAL) gene expression was examined in fruit and leaf abscission zones of Valencia orange for periods up to 72 h after induction of abscission with Ethrel(R) (CEPA) or the citrus mature fruit-specific abscission material 5-chloro-3-methyl-4-nitro-1H-pyrazole (CMN-P). PAL gene expression was detected in mature fruit abscission zones beginning 6 and 24 h after CEPA and CMN-P application, respectively, and continued up to 72 h. PAL gene expression was detected in leaf abscission zones 6 h after CEPA application and continued throughout the remainder of the study.