[Phytochrome dependent variation of grouth and ion uptake of leaves and internodes of etiolated pea (pisum sativum) seedlings].

Inhibition of internodial growth of pea seedlings by light is compensated for by increased growth of leaves. At a given time the sum of fresh weight of internodes plus the product of fresh weight of leaves times a certain factor is constant in darkness or with different periods of light. This correlation may reflect a competition of internodes and leaves for materials delivered at a lightindependent rate from the cotyledons. This hypothesis was tested by immersing roots of pea seedlings into (86)Rb labelled K-solutions for one day in darkness, removing the plants from the solutions, exposing the seedlings to near or far red light and measuring the radioactivity and fresh weights of leaves and internodes separately. Radioactivity and fresh-weight were both dependent on phytochrome; i.e. inhibition of ion uptake and of growth in internodes and promotion of both processes in leaves by near red light as compared to dark or far red controls are mediated by phytochrome.Short time experiments of ion uptake by the roots show that K transport into the shoot organs is promoted by light after a lag phase of somewhat more than one hour. This interval corresponds well to the lag phase of the light induced growth inhibition of internodes.Seedlings deprived of cotyledons and roots grow well in water but exhibit no difference in growth rate of leaves and internodes in light and darkness. Light dependence is restored if the seedlings are submersed in approximately 3% sucrose solutions. This result seems to indicate that the influence of light on growth rates of leaves and internodes is dependent on the uptake of material by the cell. It seems possible that in the etiolated pea seedling light promotes growth of leaves by promoting uptake and hampers growth of internodes by inhibiting uptake of essential growth material delivered from the cotyledons.