Differential Expression of 1-Aminocyclopropane-1-carboxylate Synthase and Oxidase Gene Family in Micro-Tom Tomato Leaves and Roots Under Short Daily UV Radiation

Few studies focussed on the effects of UV radiation on ethylene (ET) production, thus little is known about the changes in the expression of the ET biosynthetic genes and there are no data about roots. Based on our previous results showing reduced ET emission by UV-treated leaves of Micro-Tom tomato plants, the effects of short UV treatments (0.132 and 0.015 W m(-2) biologically effective UV-B and UV-A irradiance, respectively, 15 min/day for 11 days) on the gene expression of the ET biosynthetic enzymes, ACC synthase (ACS1-7) and ACC oxidase (ACO1-5), were checked to determine whether UV radiation could cause changes at the transcriptional level and which isoforms were affected. The study regarded also roots to understand whether the invariance of root ET emission might relate to unchanged transcription of the biosynthetic genes or to a balance between up- and down-regulation of different isoforms. Chlorophylls and UV-responsive metabolites were quantified to verify plant healthiness and responsiveness. The general downregulation of ACO isoforms after 8 and 11 days of UV treatment was probably the cause of the reduced foliar ET emission, whilst after 3 days of recovery the similar ET levels agreed with the invariance of ACO transcript levels between control and treated plants. These data strengthen our hypothesis of ACOs as key ET regulators under short mild UV treatments, though, since we focussed on only 50% of the ACS genes, others may be involved in the tomato plant response to UV. Fluctuations of ACS and ACO mRNA were evident in roots, but this did not influence the ET emission of this organ.