Table I.
Effect of cations and freeze-thaw cycles on the structure of apoplastic proteins from winter rye leaves as determined by Trp fluorescence
| Salt | No. of Freeze-Thaw Cycles | λmax |
|---|---|---|
| nm | ||
| EDTA | 0 | 327.7 ± 0.3, 360.3 ± 0.3 |
| EDTA | 3 | 355.2 ± 0.2 |
| CaCl2 | 0 | 336.5 ± 0.2 |
| CaCl2 | 3 | 335.5 ± 0.0 |
| MgCl2 | 0 | 336.3 ± 0.2 |
| MgCl2 | 3 | 334.8 ± 0.4 |
Proteins were dialyzed in 5 mm EDTA, 20 mm CaCl2, or 20 mm MgCl2. Half the samples were stored at 4°C until analysis as unfrozen controls, and the remaining samples were subjected to three freeze-thaw cycles in which they were frozen at −20°C for 2 h and thawed at 20°C for 5 min. Trp residues were excited at 280 nm, and the wavelengths of maximum fluorescence emission (λmax) were recorded. Data are presented as means ±se, n = 3.