Table I.
Activity and latency of AGPase and marker enzymes in fractions from plastid preparations
| Enzyme | Columella and Placenta (Activity as a Percentage of That in the Homogenate)
|
Latency | Pericarp (Activity as a Percentage of That in the Homogenate)
|
Latency | ||
|---|---|---|---|---|---|---|
| Pellet | Pellet + supernatant | Pellet | Pellet + supernatant | |||
| % | % | |||||
| AGPase | 9.5 ± 0.7 | 102 ± 3 (9) | 77 ± 3 | 19.8 ± 2.5 | 113 ± 32 (5) | 61 ± 20 |
| Plastidial marker enzymes | ||||||
| Alkaline pyrophosphatase | 9.8 ± 0.6 | 100 ± 6 (7) | 79 ± 6 | 17.5 ± 2.4 | 93 ± 12 (5) | 64 ± 9 |
| Soluble starch synthase | 8.2 ± 1.2 | 97 ± 5 (5) | NDa | 15.6 ± 1.4 | 110 ± 3 (5) | ND |
| Cytosolic marker enzymes | ||||||
| Alcohol dehydrogenase | 0.23 ± 0.12 | 91 ± 3 (9) | 9 ± 3 | 0.46 ± 0.15 | 110 ± 3 (5) | 7 ± 0.01 |
| PPi: fructose 6-P 1-phosphotransferase | 0.16 ± 0.13 | 96 ± 5 (7) | ND | 0.22 ± 0.11 | 102 ± 6 (5) | ND |
In each experiment, about 15 g of pericarp or 5 g of columella from fruit of 8 to 11 DPP was chopped to produce a homogenate. Pellet and supernatant fractions were derived from homogenates by centrifugation. The activities of AGPase and marker enzymes in the pellet fraction were expressed as percentages of the activities in the original homogenates. For each enzyme, the recovery during the fractionation is estimated as the percentage of the activity in the original homogenate that was recovered in the pellet and supernatant fractions. Values in these columns are means ± se of estimates from the no. of separate plastid preparations shown in parentheses. Values of latency were derived by assaying duplicate samples of unfractionated homogenate in the presence of 0.6 m sorbitol (AGPase and alcohol dehydrogenase) or 0.6 m Suc (alkaline pyrophosphatase). The organelles in one sample were kept intact, whereas in the other sample they were lysed by the addition of detergent. The activity in the lysed sample minus that in the intact sample is expressed as a percentage of that in the lysed sample to give the latency value. In each experiment, each enzyme was assayed three times in intact and in lysed samples. Values are means ± se of estimates from three separate experiments.
ND, Not determined.