PHENOLIC OXIDASES IN GALL DISEASE OF MILICIA SPECIES

ABSTRACT

Milicia regia and M . excelsa are inva.lua.iDle plant

species in Ghana for their durable timber. Their

numbers are however dwindling. Efforts by the forestry

department to establish plantations have been

unsuccessful due primarily to attack by Phytolyma

species, resulting in gall formation.

Phenols and phenolic oxidases appear to be important in

the defence mechanisms of some plants as well as in

wound healing and regulation of growth in these plants.

Thus, they may be natural resistance factors of the

Phytolyma-induced gall disease of Milicia species.

The activities of phenolic oxidases, [polyphenol oxidase

(PPO) and peroxidase (PRO)] and the phenolic content in

galls and leaves of Milicia species differing in

susceptibility to Phytolyma attack were determined.

Polyphenol oxidase and peroxidase were also extracted

and partially purified from acetone powders prepared

from the galls and leaves.

The activity of polyphenol oxidase was found to be

higher in the leaves of the resistant plants than in the

x

tolerant and susceptible plants. Galls of the seedlings

also showed higher activity of the enzyme than in the

normal leaves. Similar trends were also observed for

the activity of peroxidase in the samples but the

differences in activity were insignificant. Phenol and

o-dihydroxyphenol contents of galls of seedlings were

slightly lower than in the normal leaves. The resistant

plants also showed slightly higher phenol content than

the tolerant and susceptible plants. The susceptible

plants on the other hand appeared to contain slightly

higher o-dihydroxyphenol than the resistant plants.

Peroxidase and polyphenol oxidase were extracted and

partially purified from acetone powders prepared from

galls and leaves of the samples. The peroxidase and

polyphenol oxidase from the galls were purified 10 and

14-fold, respectively, using gel filtration followed by

ion-exchange chromatography. The peroxidase and

polyphenol oxidase from the leaves were also purified 37

and 17-fold, respectively, using ion-exchange

chromatography followed by gel filtration. The

activities of the two enzymes could not be separated as

they co-eluted in the same fractions. The purified

enzymes from both sources did not oxidize monophenols

and had an estimated molecular weight of 34 kDa.