Envolvimento da peroxidase e polifenoloxidase no bloqueio xilemático de hastes de ave-do-paraíso (Strelitzia reginae)

• Autor(a) principal: Karsten, Juliane
• Data de Publicação: 2009
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/4309
• topic: POD; PPO; Oclusão vascular; Inibidores enzimáticos; POD; PPO; Vascular occlusion; Enzymatic inhibitors; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOTECNIA::FISIOLOGIA DE PLANTAS CULTIVADAS

The goals of this work were to determine the time in which occurs the vascular occlusion and the contribution of the peroxidase (POD) and polyphenoloxidase (PPO) in this process; partially purify and characterize these enzymes and verify the effect of the use of enzymatic inhibitors combined or not with sucrose in the pulsing solution on the postharvest life of the bird-of-paradise. To determine the time of occlusion, the stalks were dry stored for different periods of time (0, 8, 16, 24, 32, 40 and 48 hours), and after being placed in water. The variation of fresh mass and the relative water content (RWC) of the sepals were evaluated within the first 24 hours, and the POD and PPO activity were determined after 100 hours. Harvested flowers were immediately placed in water and had their fresh mass variation, and POD and PPO activity daily evaluated up to 8th day, when the first floret was complete wilted. Flowers maintained for 16 hours under dry storage recuperated the initial fresh mass index and RWC after being placed in water, suggesting that the vascular occlusion occured after 16 hours of dry storage. The POD activity was higher in control stalks and the PPO was higher in stalks which suffered moderated water stress (16, 24, 32 and 40 hours). Throughout the vase life, the POD activity reached the highest level in the 8th day of vase life, and the PPO was kept constant. The POD activity was higher than the PPO in all the analyses, suggesting a higher influence of the POD in the xylematic occlusion of this specie. In the process of enzymatic characterization, the ideal pH and the optimum temperature for both enzymes were determined, as well as the optimum substrate for the PPO. The stability in different pHs, thermal stability and the effect of different inhibitors were also observed. The highest activity of POD was found in pH 5.0 and 60ºC, and the prexi incubation for 120 minutes in pH 2.5 and 25ºC lead to the inhibition of 93.1% of the initial activity, 120 minutes in 70ºC to 98.7% of inhibition and 80ºC for 10 minutes or 90ºC for 1 minute lead to complete inactivation. A complete inhibition of this enzyme was also achieved in the presence of different inhibitors, like ascorbic acid, L-cysteine, sodium metabissulfite, sodium azide, β-mercaptoethanol and DTT. The PPO presented the highest activity with 4-methylcatecol as substrate, in pH 6.0 and 40ºC. Complete inactivation of this enzyme was obtaining by incubating for 10 minutes at 80ºC or using 1 mM of DTT, L-cisteyne, sodium metabissulfite and β-mercaptoethanol. Finally, different pulsing solutions containing enzymatic inhibitors, combined or not with sucrose 40% were applied for 24 hours. The fresh mass variation, RWC and number of open florets were daily determined, and the longevity was determined until the wilting of the last opened floret. From the inhibitors applied alone, the sodium azide was able to provide the highest values of fresh mass, longest longevity and highest number of open florets. Combined with sucrose, the ascorbic acid and the sodium azide were able to provide the best results, with the highest number of open florets and longer longevity. The occlusion of xylematic vessels of this specie is related to the POD and PPO activity and the use of pulsing solutions containing enzymatic inhibitors is a viable technique to extend the vase life of bird-of-paradise of flowers.