Table II.
The subcellular location of AGPase activity
| Enzyme | Activity
|
Activity Recovered in Pellet | ||
|---|---|---|---|---|
| Homogenate | Supernatant | Pellet | ||
| μmol min−1 endosperm−1 | % homogenate | |||
| Bomi | ||||
| Plastid marker enzymes | ||||
| Soluble starch synthase | 7.43 ± 0.30 | 5.61 ± 0.26 | 1.29 ± 0.13 | 17.4 ± 1.9 |
| Alkaline pyrophosphatase | 636 ± 77 | 513 ± 48 | 98.9 ± 6.0 | 15.9 ± 1.9 |
| Cytosolic marker enzymes | ||||
| Alcohol dehydrogenase | 179 ± 23 | 176 ± 18 | 1.26 ± 0.26 | 0.71 ± 0.1 |
| UDP-Glc pyrophosphorylase | 6,280 ± 408 | 6,300 ± 398 | 36.6 ± 2.1 | 0.59 ± 0.04 |
| AGPase | 686 ± 108 | 612 ± 107 | 22.9 ± 1.8 | 3.42 ± 0.27 |
| Risø 16 | ||||
| Plastid marker enzymes | ||||
| Soluble starch synthase | 7.03 ± 0.61 | 3.19 ± 0.52 | 3.60 ± 0.39 | 51.0 ± 2.3 |
| Alkaline pyrophosphatase | 662 ± 64 | 281 ± 23 | 324 ± 27 | 49.1 ± 0.6 |
| Cytosolic marker enzymes | ||||
| Alcohol dehydrogenase | 205 ± 26 | 195 ± 27 | 1.83 ± 0.19 | 0.89 ± 0.03 |
| UDP-Glc pyrophosphorylase | 6,760 ± 609 | 6,670 ± 728 | 42.9 ± 2.0 | 0.64 ± 0.03 |
| AGPase | 73.1 ± 8.3 | 34.8 ± 4.8 | 37.2 ± 4.0 | 51.0 ± 1.3 |
Plastid-enriched pellet and cytosol-enriched supernatant fractions were prepared from homogenates of developing endosperms of Bomi and Risø 16 as described for wheat by Burton et al. (2002b). The activities in these fractions of AGPase and marker enzymes for the plastids and the cytosol were determined. From these values, the percentage of AGPase activity in the plastids was calculated according to Denyer and Smith (1988). Mean values ± se for measurements made on three individual samples of endosperm were, for wild-type barley endosperms, 14.9% ± 2.4%, and for Risø 16, 96.4% ± 2.7%.