Peroxidase Activity In Fruit Research Articles

Effects of fruit thinning on ascorbate–glutathione cycle metabolism in black currants (Ribes nigrum L.)

To elucidate mechanisms regulating ascorbic acid (AsA) biosynthesis and accumulation in the fruit and leaves of black currants, AsA and the activities of key enzymes in the ascorbate–glutathione (AsA–GSH) cycle were measured from fruit set to fruit ripening during fruit thinning treatments of three common commercial black currant cultivars that differed in their AsA levels: ‘Risager’ (low), ‘Brodtrop’ (medium) and ‘Adelinia’ (high). Treatments were 50% fruit reduction (50% of total fruit set) by hand, control was no thinning. Fruit thinning treatment significantly increased AsA content in fruit of all three cultivars from weeks 2 to 8, significantly decreased AsA content in leaves from weeks 3 to 8. Dehydroascorbate reductase and monodehydroascorbate reductase activities in fruit and leaves had a similar pattern, increasing during week 2, rose until they peaked in week 4. Ascorbate peroxidase activity in fruit in the thinning treatment was slightly lower than in the control. Fruit thinning was shown to be a good model to test AsA biosynthesis regulation and accumulation in black currants. The results from our study provided strong evidence that AsA–GSH cycle involved in AsA synthesis and accumulation in fruit.

Role of Ca2+ and calmodulin in on-tree oleocellosis tolerance of Newhall navel orange

Previous studies have shown that spraying calcium on the canopy can significantly reduce the incidence of on-tree oleocellosis (OTO). However, the OTO regulation with calcium spraying has not been reported clearly. Therefore, the physiologic mechanism of spraying Ca(NO3)2 and calmodulin (CaM) inhibitors (trifluoperazine-TFP) on the canopy of 8-year-old Newhall navel orange on Lichi16-6 trifoliata (P. trifoliate) including the ratio (RO) and degree of OTO (DO) have been studied under high summer temperature. The results showed that exogenous Ca(NO3)2 treatment significantly decreased DO value by increase in CaM content of leaves, peroxidase (POD) activity in leaves, and fruit peels. However, TFP treatment significantly decreased CaM content in leaves, SOD and CAT activity in fruit peels, while the POD activity in fruit peels significantly increased, and the formation of Ca(NO3)2-induced DO tolerance in citrus fruits was weakened by TFP treatment. Exogenous Ca(NO3)2 treatment increased stomatal conductance (Gs) and transpiration rate (Tr), and decreased the daily range of rind oil release pressure (△RORP) significantly. However, TFP treatment had no significant influence on transpiration rate (Tr) and △RORP. The results were consistent with the RO of different treatments. These results confirm that Ca2+ and CaM regulate DO value, and the RO of OTO was mainly related to the regulation of △RORP through water metabolism.

Redução da severidade da podridão-amarga de maçã em pós-colheita pela imersão de frutos em quitosana

O objetivo deste trabalho foi avaliar a aplicação de quitosana no controle da podridão-amarga da maçã em pós-colheita e seus efeitos sobre Colletotrichum acutatum e a atividade da peroxidase nos frutos. Frutos previamente infectados com o patógeno foram imersos em suspensões de quitosana com diferentes concentrações e pHs. Para estudar possíveis mecanismos de ação envolvidos no controle da doença, foram realizados testes in vitro, para avaliar o efeito da quitosana sobre a germinação de conídios de C. acutatum e sobre o crescimento micelial. Foi avaliada a capacidade da quitosana de induzir a síntese de enzimas relacionadas à defesa da planta (peroxidases), por meio de ensaio espectrofotométrico. Houve efeito de doses e de pH da quitosana sobre a redução da severidade da podridão-amarga em maçã. A suspensão de quitosana a 10 g L-1 e pH 4 foi a mais apropriada tecnicamente para o controle da doença, pois reduziu a severidade em 26%. O polissacarídeo não elevou a atividade de peroxidases nos frutos, mas reduziu a germinação de conídios e o crescimento micelial do patógeno. A quitosana aplicada em pós-colheita é uma medida alternativa aos fungicidas para o manejo da podridão-amarga.

カボス果実の脱緑に伴うクロロフィルの分解

Changes in concentrations of chlorophylls (Chls) a and b and their derivatives and peroxidase and chlorophyllase activities were determined to elucidate the pathway of Chl degradation in developing and stored kabosu (Citrus sphaerocarpa Hort. ex Tanaka) fruits.Surface color of kabosu fruits gradually turned from green to yellow with fruit development. The level of phenolic compounds involving in Chl degradation and peroxidase activity increased concurrently.The Chl contents sharply decreased concurrent with the degreening of stored kabosu fruits. The patterns of HPLC tracings derived from extracts of fresh kabosu fruit revealed the presence of pheophytin a, 10-hydroxychlorophylls a and b, and chlorophyllides a and b, as Chl derivatives. These Chl derivatives in rind extracts gradually disappeared as degreening progressed during storage at 20°C; some were barely detectable on day 50. Peroxidase activity in fruits held at 20°C increased appreciably during the first 20 days of storage and then decreased. Chlorophyllase activity in the rind of fruits stored at 20°and 4°C increased slightly on day 20 but subsequently decreased.It is inferred from these results that most Chls in kabosu fruits are degraded into a colorless product through a peroxidase pathway.

Peroxidase activity in avocado fruit stored at chilling temperatures

No increase in peroxidase activity was observed in ‘Fuerte’ avocado fruits which showed chilling injury symptoms as a result of storage at 0 or 2°C. Peroxidase activity in the fruit declined along with fruit softening during the ripening process. It is suggested that peroxidase acitivity in avocado fruit mesocarp has no role in the development of the chilling injury disorder appearing as dark patches on the skin of the fruit.