PHOTOSYNTHESIS AND CARBON PARTITIONING IN SAMANTHA ROSES

In Rosa hybrida ’Samantha’ roses, all leaves on the flowering shoot had similar photosynthetic capacities at a stage of shoot development when the flower bud first showed red color. Whole plant net CO2 exchange rate (NCER) was 45% lower than that of individual leaves at saturating light levels due to respiration of nonphotosynthetic organs and mutual shading of the leaves in the plant canopy. Decreasing the oxygen concentration to 2% increased the NCER of both individual leaves and whole plants by approximately 15%. Studies with 11CO2 labelling indicated that the translocation speed from the source leaves was approximately 0.27 cm min−1, typical of woody plants. Nearly 60% of the newly fixed 14CO2 was in the sugar fraction predominantly in sucrose. Four hours after labelling only 21–24% of the total 14C-assimilates had been exported from the source leaves. Of the exported 14C, 98% from the first trifoliate leaf and 87% from the fourth leaf were translocated towards the developing flower bud indicating its role as the major sink. Taken together, the data for NCER of leaves and whole plants suggest that a rooted single shoot plant of Samantha roses represents a good model system for both studying flower development and predicting the growth and development of roses in commercial greenhouse canopies.Key words: Rosa hybrida ’Samantha’, photosynthesis, carbon partitioning