BioelectriCity, gravity and plants

Abstract

This brief review summarizes gravity-induced changes in bioelectric parameters and evaluates their contribution to our understanding of the sensing of gravity, and the transduction and transmission of the gravity stimulus in plants. During the last few decades, information has accumulated demonstrating gravity-induced changes in surface potentials, membrane voltages, endogenous electric currents and ion fluxes. These changes point to the plasma membrane as the site of perception and transduction of the gravity signal. To date, it is reasonable to assume that gravity affects the state of ion channels (in particular, Ca2+ channels) and the activity of ion pumps (in particular, the electrogenic H(+)-ATPase) in the plasma membrane leading to intracellular and apoplasmic changes in ion activities and in membrane voltages. The flow of H+ and Ca2+ currents is probably the means by which information about gravity is amplified and transmitted from sensing to responding cells. No data are available so far about the effect of microgravity on bioelectric parameters. However, it would be interesting to learn if plants become hypersensitive to gravity during a prolonged stay in microgravity. If so, such plants might fire action potentials after return to earth, because more Ca2+ channels than usual may be activated by 1 g in microgravity-adapted plants.

Transcription Profiling of the Early Gravitropic Response in Arabidopsis Using High-Density Oligonucleotide Probe Microarrays,

“…The relatively low number of genes regulated by gravity may be attributable to a masking effect, because the total RNA samples were extracted from heterogeneous tissues from whole seedlings. Among the identified genes were those whose gene products were previously implicated to be involved in gravitropism, such as calcium-binding/calmodulin/ calmodulin-like proteins (Feldman and Gildow, 1984;Bjö rkman and Leopold, 1987;Hasenstein and Evans, 1988;Lu and Feldman, 1997), Na ϩ /H ϩ -exchanging protein (for review, see Wiesenseel and Meyer, 1997;Scott andAllen, 1999) expansin (Caderas et al, 2000) and putative auxin-induced protein IAA12 (there , and sequence logos of potential cis-regulatory motifs identified in upstream sequences of these genes (B-G). Increase in transcript abundance is shown in red, decrease in green.…”

Gravireception in <i>Phycomyces</i>: Threshold Determination on the Sounding Rocket TEXUS 50

“…The responses cited above are faster than the electrical signals that are triggered in plants after gravistimulation. The shortest latencies of such gravi-elicited electrical signals are 8 s [17]; typically they are, however, longer amounting to some 30 s [18] or even several minutes [19]- [22]. Using a sounding rocket allows to eliminate vibrational impact present in parabolic flights [23] and thus allows to determining the threshold of gravitropism.…”

Optospectroscopic Detection of Primary Reactions Associated with the Graviperception of Phycomyces. Effects of Micro- and Hypergravity

“…The GIACs found in sporangiophores of P. blakesleeanus are thus even faster than the change of the swimming velocity of Paramecium when it is subjected to microgravity; the latency for this reaction (gravikinesis) is in the order of 250 ms (Bräucker et al, 1998). The GIACs of P. blakesleeanus are also faster than electrical responses that have been measured upon gravistimulation in plant roots (Weisenseel and Meyer, 1997;Monshausen and Sievers, 2002). The fastest electrophysiological signals that are associated with graviperception were observed in roots of Lepidium after 8 (Behrens et al, 1985) and 30 s (Behrens et al, 1982), respectively.…”