Ae. Percy et al., XYLOGLUCAN ENDOTRANSGLYCOSYLASE ACTIVITY DURING FRUIT-DEVELOPMENT ANDRIPENING OF APPLE AND KIWIFRUIT, Physiologia Plantarum, 96(1), 1996, pp. 43-50
Xyloglucan endotransglycosylase (XET) activity was measured in apple (
Malus domestica Borkh. cv. Braeburn) pericarp and kiwifruit (Actinidia
deliciosa [A. Chev.] C. F. Liang et A. R. Ferguson var. deliciosa cv.
Hayward) outer pericarp and core tissues in order to establish whethe
r a correlation exists between the activity of the enzyme anti differe
nt stages of fruit development. Whereas the growth rate of kiwifruit p
aralleled changes in XET activity throughout fruit growth, that of app
le did not. Both fruits showed the highest XET activity, on a fresh we
ight basis, in the first two weeks after anthesis when cell division w
as at its highest. XET activity then decreased sharply, but as the fru
it increased in size (4-8 weeks after anthesis) there was a concomitan
t increase in XET activity in both fruits. In the latter stage of frui
t development (16-26 weeks after anthesis) XET activity increased to p
eak at harvest in apple fruit. During this time there was relatively l
ittle increase in fruit size and presumably therefore minimal cell exp
ansion. XET activity then declined as fruit softened after harvest. In
core tissue from kiwifruit, XET activity increased throughout the lat
er stages of fruit growth to harvest maturity in a similar manner to a
pple, but continued to increase after harvest until fruit were ripe. I
n contrast, XET activity in the outer pericarp of kiwifruit did not in
crease until ripening after harvest. In apple tissue up to 30% of the
XET activity was cell wall bound and could not be solubilised, even in
buffer containing 2 M NaCl. The results implicate XET in cell wall as
sembly during cell division and expansion early in apple and kiwifruit
growth. However, the disparity between apple and kiwifruit with respe
ct to XET activity late in fruit development and ripening and the diff
erent affinities of the enzyme for the cell wall in each fruit, sugges
t that XET has several roles in plant development, not all of which ar
e related to cell wall loosening during periods of accelerated growth.