Effect of UV-C radiation on gene expression and biochemical and physiological responses in tomato fruit (Solanum lycopersicum Mill.).

A radia????o UV-C ?? utilizada na p??s-colheita de frutos com o objetivo de reduzir o in??culo e a incid??ncia de doen??as. Por??m, ?? poss??vel que atue como estressor abi??tico, ativando mecanismos de defesa dos tecidos vegetais, que ?? qualificado pela indu????o do metabolismo secund??rio, especialmente pela s??ntese de compostos fen??licos e caroten??ides, envolvidos na prote????o ao estresse oxidativo. Nesse contexto, foram avaliadas altera????es moleculares decorrentes da a????o da radia????o UV-C no armazenamento de tomates (20-23??C), e suas rela????es com as respostas bioqu??mico-fisiol??gicas e com os eventos influenciados pelo horm??nio vegetal etileno. Para isso realizaram-se os seguintes tratamentos: UV-C a 3,7 kJ m-2; 1-metilciclopropeno (1-MCP) a 2 ppm; e 1-MCP + UV-C. Desses tratamentos, observou-se que ocorreu redu????o na firmeza dos frutos n??o-tratados e tratados com UV-C ?? medida que a matura????o avan??ou, acompanhado do ac??mulo de transcritos do gene que codifica para a enzima poligalacturonase (PG), indicando que o tratamento UV-C n??o contribui para a preserva????o desse atributo de qualidade. Por outro lado, o 1-MCP participou na preserva????o da firmeza de polpa, mesmo tendo havido ac??mulo de transcritos da PG, sugerindo n??o ser esse gene o respons??vel maior por essa propriedade. A radia????o UV-C promoveu incremento no teor de etileno, e mesmo assim houve retardo no desenvolvimento da colora????o nos frutos submetidos a esse tratamento. Como esperado, frutos tratados com 1-MCP apresentaram retardo no pico da produ????o de etileno, no desenvolvimento de colora????o e na diminui????o da firmeza de polpa. O teor de licopeno foi menor nos frutos submetidos ao tratamento com 1-MCP. No entanto, nos frutos que foram submetidos ao tratamento com 1-MCP + UV-C, o teor de β-caroteno foi significativamente superior no epicarpo dos frutos, o que lhes conferiu uma colora????o alaranjada. O ??cido p-hidroxibenz??ico foi o composto fen??lico predominante encontrado no epicarpo e mesocarpo dos frutos, e a quercetina apresentou maiores teores nos frutos submetidos ao tratamento com 1-MCP + UV-C. δ-tocoferol foi o ??nico tocoferol identificado nos frutos de tomate, o qual apresentou elevados teores no epicarpo dos frutos. Os genes que codificam para as enzimas respons??veis pela s??ntese de caroten??ides fitoeno sintase (PSY) e δ-caroteno desaturase (ZCD); pela s??ntese de fenilpropan??ides, fenilalanina am??nia liase (PAL) e chalcona sintase (CHS); enzimas antioxidantes, catalase (CAT) e super??xido dismutase (SOD) apresentaram alto ac??mulo de transcritos inicialmente no epicarpo e posteriormente no mesocarpo dos frutos submetidos ?? radia????o UV-C. De modo geral, a radia????o UV-C estimulou a produ????o de etileno, e mesmo assim reduziu a velocidade de matura????o, especialmente no que tange ?? altera????o de colora????o. A firmeza de polpa n??o foi afetada pelo tratamento com UV-C. As respostas moleculares ?? aplica????o da radia????o UV-C iniciam no epicarpo e, em seguida, s??o observadas no mesocarpo.UV-C radiation is utilized in postharvest of fruits with the objective of reducing inoculum and disease incidence. However, it is possible that it acts as an abiotic stressor agent, activating defense mechanisms of plant tissues, which is characterized by the induction of secondary metabolism, especially through the synthesis of phenolics compounds and carotenoids, involved in the protection of oxidative stress. In this context, molecular changes derived from the action of UV-C radiation were evaluated in tomato, during storage (20-23??C), and its relationship with biochemical and physiological responses and with events influenced by the plant hormone ethylene. For such, the following treatments were performed: UV-C at 3,7 kJ m-2; 1-methylcyclopropene (1-MCP) at 2 ppm, and 1-MCP + UV-C. From these treatments it was observed that a reduction in fruit firmness occurred in untreated and UV-C treated fruit as maturation advanced, accompanied by the accumulation transcripts of a gene encoding the enzyme polygalacturonase (PG), indicating that UV-C treatment did not contribute for the maintenance of this quality attribute. On the other hand, 1-MCP participated in the maintenance of flesh firmness, even though PG transcript accumulation was found, suggesting this gene is not the primary responsible for this property. UV-C radiation induced an increase in ethylene content, but still, a delay in fruit color development occurred in fruit from this treatment. As expected, 1-MCP treated fruit showed a delayed peak of ethylene production, of the color development, and of decrease in flesh firmness. Lycopene content was lower in fruit subjected to 1-MCP treatment. However, in fruit treated with 1-MCP + UV-C, β-carotene content was significantly higher in the exocarp of the fruit, which conferred them an orange color. p-Hydroxybenzoic acid was the predominant phenolic compound found in exocarp and mesocarp, and quercetin was found in higher content in fruits subjected to 1-MCP + UV-C treatment. δ-tocopherol was the only tocopherol identified in tomato fruit, present in high levels in the exocarp of the fruit. Genes coding for enzymes responsible for synthesis of carotenoids, phytoene synthase (PHS) and δ-carotene desaturase (ZCD) for the synthesis of phenylpropanoids, phenylalanine ammonia lyase (PAL) and chalcone synthase (CHS), antioxidant enzymes, catalase (CAT) and superoxide dismutase (SOD) showed initially high accumulation of transcripts in the exocarp and later in the mesocarp of fruit subjected to UV-C radiation. In general, UV-C radiation induced ethylene production, and yet slowed down maturation, particularly regarding color changes. Flesh firmness was not affected by UV-C treatment. Molecular responses to UV-C radiation application started in the exocarp and were in sequence found in the mesocarp