Gs. Smith et al., CHANGES IN ABSCISIC-ACID CONCENTRATION, SURFACE CONDUCTANCE, AND WATER-CONTENT OF DEVELOPING KIWIFRUIT, Scientia horticulturae, 61(1-2), 1995, pp. 13-27
Seasonal changes in abscisic acid (ABA) concentration, surface conduct
ance to water vapour and water content, were measured in developing fr
uit from the upper and lower canopies of 8 year old kiwifruit vines (A
ctinidia deliciosa var. deliciosa). Three stages were apparent for the
accumulation of ABA by the developing fruit. The first stage was char
acterised by a high initial concentration of ABA in the skin, coupled
with high surface conductance of the fruit, suggesting that ABA accumu
lation during the first 1-2 weeks after anthesis was via the transpira
tion stream. A marked reduction in concentration of ABA during the sec
ond stage of accumulation was consistent with dilution by fruit growth
. The constancy in the concentration of ABA during stage three (from W
eek 12 until harvest) suggested that ABA was, in some way, linked to p
hotosynthate loading into the fruit. The larger quantity of ABA in fru
it from the upper canopy, which had greater dry matter gains, is consi
stent with this conclusion. The positive relationship between ABA conc
entration and rapid fruit growth suggests that ABA may have a role in
the allocation of assimilates to fruit. Changes in water content of ki
wifruit followed closely the stages of fruit growth. A close relations
hip between the water content and shape of the developing fruit and pu
blished data for glucose in kiwifruit, is consistent with fruit enlarg
ement being osmotically driven. The reduction in percent water content
during the latter stages of growth, especially for fruit from the upp
er canopy, could largely be accounted by the large build-up of starch
during that period. The surface conductance of the fruit declined rapi
dly during the first 9 weeks after anthesis. The conductance then rema
ined relatively constant at low levels until harvest. Compared with ap
ple, the surface conductance of kiwifruit (0.1-0.8 mmol H2O m-2s-1) wa
s up to ten times greater during the early stages of growth.