Table II.

Biosynthesis of ascorbate in potato leaves at different stages of development

Leaf Age	Total Ascorbate Content		Indirect GLDH Activity		GLDH Activity
	nmol disc−1	nmol mg−1 fresh wt	nmol ascorbate disc−1	nmol ascorbate mg−1 fresh wt	nmol min−1 mg−1 protein
Young	88 ± 1 (10%)	4.51 ± 0.05	77.5 ± 6.5	4.0 ± 0.3	62.7 ± 5
Mature	53.2 ± 4 (21%)	3.15 ± 0.2	55.6 ± 3	3.3 ± 0.2	29.2 ± 1.4
Senescent	8.9 ± 0.7 (68%)	0.62 ± 0.05	10.2 ± 3	0.7 ± 0.2	15.2 ± 1.3

Indirect GLDH activity is measured as the difference in ascorbate content in whole leaves after incubation in 50 mm GL for 3 h. Values in parentheses indicate the percentage of DHA. Values represent the mean of three different experiments ± sd.