Dr. Geiger et al., PHOTOSYNTHETIC CARBON METABOLISM AND TRANSLOCATION IN WILD-TYPE AND STARCH-DEFICIENT MUTANT NICOTIANA-SYLVESTRIS L, Plant physiology, 107(2), 1995, pp. 507-514
A high rate of daytime export of assimilated carbon from leaves of a s
tarch-deficient mutant tobacco (Nicotiana sylvestris L.) was found to
be a key factor that enabled shoots to grow at rates comparable to tho
se in wild-type plants under a 14-h light period. Much of the newly fi
xed carbon that would be used for starch synthesis in leaves of wild-t
ype plants was used instead for sucrose synthesis in the mutant. As a
result, export doubled and accumulation of sucrose and hexoses increas
ed markedly during the day in leaves of the mutant plants. The increas
ed rate of export to sink leaves appeared to be responsible for the in
crease in the proportion of their growth that occurred during the day
compared to wild-type plants. Daytime growth of source leaves also inc
reased, presumably as a result of the increased accumulation of recent
ly assimilated soluble carbon in the leaves. Even though starch accumu
lation did not occur in the leaves of mutant plants, nearly all the su
gar that accumulated during the day was exported in the period of decr
easing irradiance at the end of the diurnal light period. Changes in c
arbon allocation that occurred in leaves of wild-type and mutant plant
s near the end of the light period appeared to result from endogenous
diurnal regulation associated with the day-night transition.