V. Haake et al., A MODERATE DECREASE OF PLASTID ALDOLASE ACTIVITY INHIBITS PHOTOSYNTHESIS, ALTERS THE LEVELS OF SUGARS AND STARCH, AND INHIBITS GROWTH OF POTATO PLANTS, Plant journal, 14(2), 1998, pp. 147-157
Antisense expression of a full length cDNA encoding plastid aldolase l
ed to decreased expression of aldolase at the transcript and protein l
evel in several 'antisense' potato transformants. To quantify the inhi
bition, activity was compared in corresponding leaves down a plant and
in plants of different ages. Aldolase activity was decreased by 32-43
%, 56-71%, 79-83% and 91-97% in A-70, A-3, A-51 and A-2. Separation on
a Q-Sepharose-FF column showed the decrease was due to inhibition of
plastid aldolase. The transformants showed a small increase of Rubisco
activity, a small decrease of phosphoribulokinase activity, and large
r but subproportional decreases of sedoheptulose-1,7-biphosphatase and
plastid fructose-1,6-bisphosphatase activity. Ambient photosynthesis
was inhibited by 10%, 40%, 66% and 85% in A-70, A-3, A-51 and A-2. The
transformants contained increased triose phosphates, and very low rib
ulose-1,5-bisphosphate and glycerate-3-phosphate. Chlorophyll fluoresc
ence indicated that photosystem II was more reduced and thylakoid ener
gization was increased. Starch synthesis was decreased by 16% and 36%
in A-70 and A-3, whereas sucrose synthesis was less strongly inhibited
. Plant growth was not significantly altered in A-70, was decreased by
41% in A-3, and was severely inhibited in plants with under 20% of wi
ld-type aldolase activity. Although plastid aldolase catalyses a readi
ly reversible reaction, possesses no known regulatory properties, and
would appear irrelevant for the control of metabolism and growth, smal
l changes in its activity have marked consequences for photosynthesis,
carbon partitioning and growth.