Journal of Experimental Botany vol:64 issue:6 pages:1497-1507
In contrast to the well documented roles of its mono- and bisphosphate esters, the occurrence of free sedoheptulose in plant tissues remains a matter of conjecture. The present work sought to determine the origin of sedoheptulose formation in planta as well as its physiological importance. Elevated CO2 and sucrose induction experiments were used to study sedoheptulose metabolism in the CAM plants Kalanchoë pinnata and Sedum spectabile. Experimental evidence suggests that sedoheptulose is produced from the oxidative pentose phosphate pathway intermediate sedoheptulose-7-phosphate, by a sedoheptulose-7-phosphate phosphatase. Carbon flux through this pathway is stimulated by increased triose-P levels (elevated CO2, compromised sink availability, sucrose incubation of source leaves) and attenuated by ADP and Pi.
The accumulation of free sedoheptulose is proposed to act as a mechanism contributing to both C and P homeostasis by serving as an alternative carbon store under elevated CO2 or compromised sink capacity to avoid sucrose accumulation, depletion of inorganic phosphate and suppression of photosynthesis. It remains to be established whether this acclimation avoiding mechanism is confined to CAM plants, which might be especially vulnerable to Pi imbalances, or whether some C3 and C4 plants also dispose of the genetic capacity to induce and accelerate sedoheptulose synthesis upon CO2 elevation.