Abstract
Sugar concentrations in plants often increase during the day (Photosynthesis) and decrease during the night. Herbivores often show a preference for the extra sugars. Green-leafy vegetables are an important component of human diets. But little is known about these diurnal changes in greens or the effect that they may have on shelf-life or human preference. We grew three lettuce varieties (Black Simpson, Green Salad, and Speckled Trout) in two gardens near Kimberly, ID. These were sampled at sundown (PM) and the next morning at sunup (AM) during the week of June 2-7, 2001. Tissue was frozen, freeze dried, ground, and analyzed for sugars. There was about 20% more sugar in the PM than AM harvested tissue. Afternoon harvest favors higher sugar and dry matter concentrations which may be opposing factors for ideal transport, marketing, and overall human preference.
Methods:Black Simpson, Green Salad, and Speckled Trout leaf lettuce varieties were grown in two gardens near Kimberly, Idaho. Leaf bunches were harvested during the week of June 2-7 2001 at sundown and again the next morning at sunup. Tissue was frozen, freeze-dried and ground through an abrasion mill. Total non structural carbohydrates (TNC) were analyzed following the procedure of Fisher and Burns (Agron. J. 79:236-242).