A re‐examination of the induction of phloem transfer cell development in pea leaves (Pisum sativum)

Abstract

Abstract The development of phloem transfer cells in expanded dark grown leaflets of pea seedlings (Pisum sativum) has been re‐examined. In agreement with previous observations transfer cells in leaflets maintained in the dark did not form wall ingrowths to the same extent as those placed in the light. A previous report that exposure to light in a carbon dioxide depleted atmosphere inhibited wall ingrowth formation could not be confirmed. It was found that dark grown leaflets could be induced to form wall ingrowths without illumination by immersing them in a glucose solution, demonstrating for the first time that light is not necessary for phloem transfer cell differentiation in leaves.Attempts were made to alter the carbohydrate level in the whole seedling by removing the cotyledons, but this had no recognizable effect on wall ingrowth formation in any of the treatments. Starch grain formation in the plastids was taken as an indication of available soluble carbohydrate level in the leaflets. It is concluded that both light and the presence of soluble carbohydrate can independently induce wall ingrowth formation in phloem transfer cells of pea leaflets.