Sjr. Underhill et C. Critchley, CELLULAR-LOCALIZATION OF POLYPHENOL OXIDASE AND PEROXIDASE-ACTIVITY IN LITCHI-CHINENSIS SONN PERICARP, Australian journal of plant physiology, 22(4), 1995, pp. 627-632
Cellular localisation of visual browning and oxidative activity studie
s were conducted to determine the relative significance of polyphenol
oxidase (PPO) and peroxidase (POD) activities during pericarp browning
. Pericarp browning was first observed on the protuberance apices and
subsequently extended uniformly over the entire pericarp surface. Anat
omically, browning was highly localised and restricted to the epicarp
and the upper mesocarp. PPO and POD activities were highest in the epi
carp, with progressively less activity in both the mesocarp and endoca
rp. In situ localisation of oxidative activity using tissue blots conf
irmed high epicarp PPO activity. POD activity, although primarily rest
ricted to mesocarp vascular tissue, was also detected in the epicarp.
We believe that litchi pericarp browning is due to highly localised ox
idative activity in the epicarp and upper mesocarp. As PPO and POD act
ivities were significantly higher in this tissue and browning was not
observed when both enzymes were selectively inhibited, it is postulate
d that both PPO and POD activities are associated with litchi pericarp
browning. The current theory that litchi pericarp browning is only ca
used by PPO activity needs to be re-appraised to determine the relativ
e role of POD activity.