Fig. 5. Activity of ascorbate peroxidase (units gfw^–1) in cotton tissues from early planting (DOY 113) in 2003 and late plantings (DOY 133) in 2003 and 2004 at Lubbock, TX. A unit of ascorbate peroxidase is defined as the amount necessary to oxidize 1 µmole of ascorbate per minute at 25°C (290-nm extinction coeffcient = 2.8 mM^–1 cm^–1). Each data point represents a minimum of three samples. Error bars indicate standard error of the mean.