Inhibition of the Gravitropic Response of Snapdragon Spikes by the Calcium-Channel Blocker Lanthanum Chloride

Abstract

The putative Ca 2؉ -channel blocker LaCl 3 prevented the gravitropic bending of cut snapdragon (Antirrhinum majus L.) spikes (S. Philosoph-Hadas, S. Meir, I. Rosenberger, A.H. Halevy [1996] Plant Physiol 110: 301-310) and inhibited stem curvature to a greater extent than vertical and horizontal stem elongation at the bending zone. This might indicate that LaCl 3 , which modulates cytosolic Ca 2؉ , does not influence general stem-growth processes but may specifically affect other gravity-associated processes occurring at the stem-bending zone. Two such specific gravity-dependent events were found to occur in the bending zone of snapdragon spikes: sedimentation of starch-containing chloroplasts at the bottom of stem cortex cells, as seen in cross-sections, and establishment of an ethylene gradient across the stem. Our results show that the lateral sedimentation of chloroplasts associated with gravity sensing was prevented in cross-sections taken from the bending zone of LaCl 3 -treated and subsequently gravistimulated spikes and that LaCl 3 completely prevented the gravity-induced, asymmetric ethylene production established across the stem-bending zone. These data indicate that LaCl 3 inhibits stem curvature of snapdragon spikes by preventing several gravity-dependent processes. Therefore, we propose that the gravitropic response of shoots could be mediated through a Ca 2؉ -dependent pathway involving modulation of cytosolic Ca 2؉ at various stages.Various aboveground plant parts, such as coleoptiles, hypocotyls, seedlings, grass-shoot pulvini, and flowering stems, respond to a change in a gravity vector by differential growth that leads to upward bending. Most of the work on negative gravitropism has been performed with seedlings and specific graviresponsive organs such as coleoptiles, epycotyls and grass-shoot pulvini (Kaufman et al., 1985; Migliaccio and Galston, 1987; Gehring et al., 1990; Brock et al., 1992; Kim and Kaufman, 1995). However, there have been several reports of gravitropism of stem-like organs (Rorabaugh and Salisbury, 1989; Kiss et al., 1997; Strudwick et al., 1997), vegetative stems (Meicenheimer and Nackid, 1994), and flowering shoots (Kohji et al., 1979; Halevy and Mayak, 1981;Woltering, 1991; PhilosophHadas et al., 1995 PhilosophHadas et al., , 1996 Fukaki et al., 1996). In this respect, the graviresponding spikes of snapdragon (Antirrhinum majus L.; Philosoph-Hadas et al., 1996) provide an excellent model system for investigating the gravitropic phenomenon in mature inflorescence stems.The common underlying mechanisms of negative gravitropism involve perception of the stimulus and its transduction into physiological processes that lead to a differential growth response (Salisbury, 1993). Gravity perception is considered to be accomplished by a mass pressure on the lower cell membrane following changes in organ orientation. This mass is believed to be either that of specific plastids, usually amyloplasts or chloroplasts, which sediment only in cells of a specific developmental stage...

An auxin-responsive 1-aminocyclopropane-1-carboxylate synthase is responsible for differential ethylene production in gravistimulated Antirrhinum majus L. flower stems

“…The absence of a normal endodermis in A. thaliana mutants lacking a gravitropic response in shoots and inflorescence stems confirmed these earlier observations, and shows that indeed this layer is important for gravisensing (Tasaka et al 1999). In A. majus flowering stems, gravity-induced sedimentation of starch-containing chloroplasts in the inner cortex and around the vascular system in the stele was observed (Friedman et al 1998(Friedman et al , 2003, which shows that a similar process is involved in gravisensing in A. majus. Recently, an A. thaliana auxin efflux regulator (PIN3), involved in asymmetric auxin Bending angle was measured after 6 h of gravistimulation.…”

“…Only a few reports have been published on the gravitropic response of flower stalks (e.g. Halevy and Mayak 1981;Clifford and Oxlade 1989;Woltering 1991;Fukaki et al 1996;Philosoph-Hadas et al 1996;Friedman et al 1998;Weise and Kiss 1999).…”

The Calcium-Binding Activity of a Vacuole-Associated, Dehydrin-Like Protein Is Regulated by Phosphorylation

“…The concentration at which the other cations were tested is unlikely to be achieved in living plants. Lanthanum (a trivalent cation), an often-used nonphysiological inhibitor for calcium-binding sites and in particular calcium channels (Friedman et al, 1998;Dennison and Spalding, 2000), was strongly inhibitory to calcium binding by VCaB45.…”

Hypocotyl Directional Growth in Arabidopsis: A Complex Trait

“…This mechanical signal is consequently transduced via many secondary messengers and several hormones including auxin and ethylene (Wheeler and Salisbury, 1980;Estelle, 1996;Sinclair and Trewavas, 1997;Friedman et al, 1998;Fasano et al, 2001;Kato et al, 2002;Perera et al, 2006). These secondary messengers orchestrate changes in lateral auxin transport, which in turn leads to asymmetric auxin distribution across the organ Friml and Palme, 2002;Paciorek et al, 2005).…”