Table I.
Intracellular distribution of folate in green and etiolated pea leaves
| Folate Content | Protein Content | Folate Distribution | |
|---|---|---|---|
| pmol mg−1 protein | % | pmol mg−1 leaf soluble protein | |
| Green leaves | |||
| Whole leaf | 240 ± 25 | 100 | 240 ± 25 |
| Mitochondria | 1,800 ± 300 | 4 ± 2 | 72 ± 6 |
| Chloroplasts | 35 ± 4 | 70 ± 8 | 24 ± 3 |
| Cytosolic fraction | 550 | 26 | 144 |
| Etiolated leaves | |||
| Whole leaf | 125 ± 25 | 100 | 125 ± 25 |
| Mitochondria | 900 ± 200 | 6 ± 2 | 54 ± 4 |
| Etioplasts | 45 ± 4 | 24 ± 5 | 11 ± 2 |
| Cytosolic fraction | 110 | 72 | 60 |
Mitochondria and plastids were purified from pea leaves after 9 d of growth in the light (12-h photoperiod) or in darkness. Folate was determined after osmotic lysis of organelles, and values are expressed on the basis of soluble proteins. The contribution of organelles proteins to whole cell soluble proteins was estimated through fumarase activity measurements for mitochondria (Hill and Bradshaw, 1969) and chlorophyll/carotenoids determinations for chloroplasts/etioplasts (Lichtenthaler, 1987). Values are an average of four different determinations ± se. To estimate the proteins/folate contents in the cytosolic fraction (which comprised cytosol, nucleus, and vacuole), the average values obtained for the organelles were subtracted from the values obtained for the whole-leaf organ. For each subcellular compartment, folate distribution is expressed as picomoles per milligram of protein with reference to total soluble proteins measured in the green/etiolated leaves.