Dm. Hunter et Jta. Proctor, PACLOBUTRAZOL REDUCES PHOTOSYNTHETIC CARBON-DIOXIDE UPTAKE RATE IN GRAPEVINES, Journal of the American Society for Horticultural Science, 119(3), 1994, pp. 486-491
Paclobutrazol applied as a soil drench at 0, 1, 10, 100, or 1000 mug a
.i./g soil reduced photosynthetic CO2 uptake rate of leaves formed bef
ore paclobutrazol treatment within 3 to 5 days of treatment and the re
ductions were maintained for 15 days after treatment. The percentage o
f recently assimilated C-14 exported from the source leaf was reduced
only at the highest paclobutrazol dose, and there was little effect of
treatment on the partitioning of exported C-14 between the various si
nks. In response to increasing doses of paclobutrazol, particularly at
the higher doses, an increasing proportion of recent photoassimilates
was maintained in a soluble form in all plant components. Reduced dem
and for photoassimilates as a result of the inhibition of vegetative g
rowth may have contributed to a reduction in photosynthetic CO2 uptake
rate, but this reduction in photosynthesis rate could not be attribut
ed to a feedback inhibition caused by a buildup of starch in the leave
s. Paclobutrazol had only a minor effect, if any, on photosynthetic el
ectron transport. Chemical name used: beta-[(4-chlorophenyl) ha-(1,1-d
imethylethyl)-1H-1,2,4-triazole-1-ethanol (paclobutrazol).