CHLOROPLAST DEVELOPMENT IN RYE COLEOPTILES

In the parenchyma cells of 1-d-old dark-grown rye coleoptiles (Secale cereale) proplastids occurred which sometimes contained starch grains. During coleoptile growth in darkness starch-filled amyloplasts are fo rmed from the preexisting proplastids. No prolamellar bodies were obse rved in the stroma of the plastids of the etiolated coleoptile. After irradiation of 3-d-old etiolated coleoptiles with continuous white lig ht three different types of plastids occurred. In the epidermal cells proplastids were observed. The parenchyma cells below the stomata of t he outer epidermis (above the two vascular bundles) contained mature, spindle-shaped chloroplasts with a well-developed thylakoid system. In the parenchyma cells that surround the vascular bundles amyloplasts w ith some thylakoid membranes (chloroamyloplasts) occurred. The mesophy ll cells of the primary leaves of dark-grown seedlings contained etiop lasts with large prolamellar bodies. In the primary leaves of irradiat ed plants chloroplasts similar to those of the parenchyma cells of the coleoptile were observed. Our results show that the rye coleoptile, w hich grows underground as a heterotrophic organ, is capable of develop ing mature chloroplasts upon reaching the light above the soil surface . The significance of this expression of photosynthetic capacity for t he carbon economy of the developing seedling is discussed.