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| The
role of phosphoinositides in the gravitropic response of cereal grass
pulvini Imara Perera and Ingo Heilmann Gravitropic upward curvature of maize and oat stems is conferred by differential elongation growth of specialized tissues, the pulvini, which are located immediately above each node. The pulvini contain starch granules which are thought to be involved in the initial perception of gravistimulation. When plants are placed horizontal, rapid fluctuations in InsP3 between the upper and the lower half of the stimulated pulvinus can be observed after as little as 10s of stimulation. A long-term increase in InsP3 which is confined to the lower half of the pulvinus precedes the onset of gravitropic bending. Synthesis of PtdInsP2, the lipid-precursor of InsP3, is up-regulated in the lower pulvinus half during the period of the long-term InsP3-increase. Application of pharmacological inhibitors of phospholipase C prevents the long-term increase in InsP3 and greatly reduces the bending response. Although the bending response is attenuated in the cold, gravity-induced changes in InsP3 are not affected by low temperature. References: Perera et al., 1999; Perera et al., 2001 |