Figure 3.

Altered apyrase transcript and activity under the control of the tuber-specific B33 promoter affects tuber phenotype and starch content. A, Combined transcript levels of StApy1 and StApy3 in tubers of 8-week-old plants were determined from cDNA by real-time PCR and expressed as percentages of the wild type. B, Apyrase activity was analyzed using an assay containing 1 mm ATP as substrate and displayed in units per gram fresh weight (FW). C and D, Tuber number (C) and starch content (D) in two independent trials were determined in tubers from 13-week-old plants. There were characteristic changes in tuber morphology (see E), which were similar to those observed in lines in which apyrase was decreased using the constitutive 35S promoter (see Fig. 2D). Results are means ± se, n = 8 (A and B) and 12 to 15 (C and D). Significant differences from the wild type according to Student's t test are indicated with asterisks (P < 0.05). E shows typical examples.