MCB 9416016 Spalding Blue light induces a large, transient membrane depolarization a few seconds before a large reduction in the rate of stem elongation in etiolated seedlings. The molecular mechanism that mediates this depolarization is unknown although there is evidence that the plasma membrane H+-ATPase is inhibited and anion channels are activated. The proposed work is an electrophysiological investigation of the changes in ion transport at the plasma membrane that participate in the transduction of blue light into growth inhibition. The growing cells of etiolated Arabidopsis hypocotyls will be studied with the patch clamp technique to characterize the ion channels that undergo a change in activity after a pulse of blue light. The participation of anion-selective channels will be given particular attention. The effect of blue light on the activity of the H+-ATPase will be determined both electrophysiologically and biochemically. Mutants in Arabidopsis that do not display blue-light inhibited growth will be studied in addition to the wild-type. Well defined energies and wavelengths of blue light will be used to construct fluence rate response curves for the magnitudes and kinetics of the electrical responses of the different genotypes. At least one double mutant, blu1 hy4, will be constructed and similarly studied. The results will demonstrate if and how the genetic lesions affect these early blue-light induced changes in membrane transport. This combination of electrophysiology, biochemistry and genetics is expected to reveal some important features of a transduction chain that links blue- light receptors to a growth control mechanism. %%% Seedlings grown in the dark undergo a suite of developmental changes upon illumination, resulting in a green plant that is competent to perform photosynthesis. One aspects of this important developmental process is the inhibition of stem elongation by bright blue light . A pulse of blue light inhibits stem growth after a few seconds. This means a receptor that absorbs blue light is closely connected to a mechanism that controls the growth rate of the stem. The events that occur between the activation of the blue light receptor and the beginning of the growth response are said to transduce the blue light into growth inhibition. Collectively these events are called a transduction chain. All that is currently known about this transduction chain is that the transport across the cells outer membrane of ions is altered just before the growth rate slows. The proposed work is focused on elucidating at the molecular level the details of how blue light alters the activities of ion pumps and channels in the membrane and how this then affects the seedlings growth rate . The electrophysiological technique of patch clamping will be used for many of the experiments, all of which will be performed on the Arabidopsis plant In addition, genetic techniques to take advantage of the existence of mutants in Arabidopsis which do not display blue light inhibited growth will be sued, as will some biochemical techniques. Taken together, these experiments will reveal certain aspects of how light controls plant growth and development and how ion channels and pumps participate in the transduction of environmental signals. ***
