Characterisation of a Variegated Grapevine Mutant Showing Reduced Polyphenol Oxidase Activity

Abstract

Fruit of the variegated grapevine mutant Bruce's Sport is known to dry to a lighter colour than other seedless varieties. The biochemical basis for this decreased browning capacity was investigated. Bruce's Sport grapes had similar levels of phenolic compounds to Sultana H5. Activity of the enzyme polyphenol oxidase (PPO EC 1.10.3.1) in mature berries of Bruce's Sport was only 20-30% of that in Sultana H5. No evidence of inhibitors or activators of PPO was found when berry extracts were mixed. PPO activity on a fresh weight basis was highest in the grape seed traces, intermediate in the skin, and lowest in the pulp in both varieties. In each tissue type, however, PPO activity in Bruce's Sport was less than 25% of that in Sultana H5. On a fresh weight basis, PPO activity in Sultana H5 berries was high at fruit set then declined as the berry developed. PPO activity per berry increased from fruit set until veraison, then remained constant. PPO activity showed similar changes during development of Bruce's Sport berries but was lower than in Sultana H5 at all stages. The Bruce's Sport grapes were variegated and the green regions of skin had similar PPO activity to Sultana H5 skin while the white regions had very low activity. Only the green regions of skin of Bruce's Sport grapes stained for PPO activity with endogenous or exogenously applied phenolic substrates. The decreased browning in this grapevine mutant apparently results from decreased levels of PPO activity in the white regions of the berry, possibly arising from a disruption in chloroplast development.

Aberrant Processing of Polyphenol Oxidase in a Variegated Grapevine Mutant

“…1). This was consistent with our earlier polarographic measurements of PPO activity in Sultana and Bruce's Sport berries (16).…”

“…This pattern of PPO gene expression correlates well with previous measurements of PPO activity in developing berries of Sultana and Bruce's Sport (16). As Sultana berries developed, PPO activity per berry, which provides an indication of PPO synthesis, increased markedly until the berries reached approximately 11 mm in diameter.…”

“…2, lane 4), which had only small amounts of the 60-kD protein. This suggested that the inactive 60-kD protein was derived from the white tissue, which lacks PPO activity (16), and that there was a direct correlation between the amount of the 40-kD protein and measured PPO activity. The presence of the 60-kD protein in immature, but not mature Sultana berries, and its elevated level in the white regions of Bruce's Sport berries, suggested that this may be an immature protein whose normal processing is interrupted in the mutant.…”

“…Bruce's Sport has an inherently low capacity for browning because it lacks PPO activity in the white regions of berry tissue. The green sections, however, have the same activity as berries of Sultana (16). The aim of this work was to determine the basis for this lack of PPO activity and to investigate the PPO enzyme in Sultana and Bruce's Sport.…”

Caractérisation physicochimique des huiles d’olive produites dans les huileries traditionnelles de la région de la Chaouia-Maroc

“…Les surnageants obtenus après centrifugation sont récupérés et le dosage a été effectué par la méthode au réactif de Folin Ciocalteu à 750 nm, en présence d'une gamme étalon d'acide caféique (Rathjen et al, 1992). renferme les échantillons E4, E7 et E8.…”