Carbohydrate Partitioning and Compartmental Analysis for a Highly Productive CAM Plant, Opuntia jicus-indica

(, Carbon partitioning patterns of Opuntiaficus-indica, a widely cultivated crassulacean acid metabolism species, were analysed to estimate carbon fluxes. After labelling a cladode with 14CO2, activities of 14C in various organs were measured for 6 weeks; the observed 14C time-courses for 14C in the labelled cladode and for transfer into other organs were simulated with a compartment model. Within the first week, half of the newly synthesized carbohydrate in the labelled cladode was either converted into structural material in that cladode, lost by respiration of that cladode, or moved to other organs. In the non-labelled cladode and the roots, such newly synthesized carbohydrate initially increased, reached maxima, and then declined. The basal cladode and the daughter cladode used 65 and 96%, respectively, of their own assimilate. Roots imported 12 and 2% of carbohydrate from the basal cladode and the daughter cladode, respectively. When the whole plant was shaded, the daughter cladode incorporated nearly threefold more carbohydrate from the basal cladode into structural material compared with the control. When plants were droughted, roots incorporated 23% more and the daughter cladode incorporated 68% less carbohydrate from the basal cladode into their structural material than for the control. The basal cladodes of the 18-month-old plants exported 60% more carbon than those of the 6-month-old plants. Carbon flux rates derived from compartmental analysis can be used as parameter values in plant production models. ~