Table I.
Comparison of antifreeze activity of individual native proteins with the activity of crude apoplastic extracts from cold-acclimated and nonacclimated plants
| Sample | Protein Concentration | Antifreeze Activity Rating |
|---|---|---|
| mg mL−1 | ||
| Apoplastic extract | ||
| Cold-acclimated | 0.45 ± 0.12 | 5 |
| Nonacclimated | 0.56 ± 0.07 | 0 |
| NP1 | 0.40 ± 0.09 | 0 |
| NP2 | 0.50 ± 0.14 | 3 |
| NP3 | 0.45 ± 0.10 | 3 |
| NP4 | 0.52 ± 0.08 | 4 |
| NP5 | 0.42 ± 0.08 | 3 |
| NP6 | 0.48 ± 0.09 | 2 |
| NP7 | 0.50 ± 0.10 | 2 |
| NP8 | 0.45 ± 0.08 | 0 |
| NP9 | 0.52 ± 0.15 | 0 |
The individual proteins were separated by native-PAGE (Fig. 1), eluted, and assayed for antifreeze activity. Antifreeze activity of each sample was rated from 0 to 5 based on the shape of ice crystals grown in solution (see Methods), with 5 representing the highest activity and 0 representing no activity. The protein concentration of each sample was determined using the Bradford (1976) method, as modified by Bio-Rad, and is presented as the mean ± se (n = 3).