Sk. Kang et al., SUPERCOOLING CHARACTERISTICS OF SOME DECIDUOUS FRUIT-TREES AS RELATEDTO WATER-MOVEMENT WITHIN THE BUD, Journal of horticultural science & biotechnology, 73(2), 1998, pp. 165-172
To characterize and identify the freezing resistance mechanism of some
deciduous fruit trees, woody stem and dormant buds of apple (Malus do
mestica 'Tsugaru'), grape (Vitis labruscana 'Muscat Bailey A'), peach
(Prunus persica 'Shimizu Hakuto'), Japanese pear (Pyrus pyrifolia 'Nij
isseiki'), and persimmon (Diospyros kaki 'Hiratanenashi') were used in
the following experiments. On thermal analysis (TA), the woody stem t
issues or the buds with woody stem tissue of all fruit trees used show
ed two exotherms, the high temperature exotherm (HTE) and the low temp
erature exotherm (LTE). The flower buds without woody stem tissue of p
each and pear also had two exotherms, the HTE and LTE, and the LTE tem
peratures coincided with the LT(50)s of flower buds although the detec
tion frequency of LTE in pear was considerably lower (<10%). Furthermo
re, in peach and pear, the LTE of buds without woody stem tissue and t
he LT50 of flower buds on woody stem were cooling-rate dependent, and
those temperatures fell with a decrease in cooling rate. Water migrati
on from the flower primordia of both buds to the surrounding tissues w
as also observed during freezing. In apple, although the LTE of bud wi
thout woody stem tissue was not detected in our experiment, the LT50 o
f the bud was cooling-rate dependent, and water migration from the pri
mordia to the other tissues in bud was observed during freezing. These
facts indicate that the mechanisms of freezing tolerance in apple flo
wer buds are the same as in peach and pear flower buds. Contrarily, in
persimmon and grape, flower buds without woody stem tissue showed onl
y one exotherm whose temperature was closely associated with the LT50
of the bud. Also, both the exotherm temperature of bud without woody s
tem tissue and the LT50 of buds on woody stem were independent of cool
ing rate. Persimmon buds showed no changes in the water content of eit
her the primordium or the surrounding tissue during freezing, indicati
ng no water migration from the primordia to the surrounding tissues. I
n addition, provascular strands were found between the bud axis and fl
ower primordia in apple, peach, and pear buds, but not in persimmon an
d grape buds. From these results, the buds of apple, peach and pear ma
y acquire freezing resistance by extra-organ freezing, but grape and p
ersimmon buds are likely to supercool by themselves.