Ionic Signaling in Plant Responses to Gravity and Touch

Abstract

Touch and gravity are two of the many stimuli that plants must integrate to generate an appropriate growth response. Due to the mechanical nature of both of these signals, shared signal transduction elements could well form the basis of the cross-talk between these two sensory systems. However, touch stimulation must elicit signaling events across the plasma membrane whereas gravity sensing is thought to represent transformation of an internal force, amyloplast sedimentation, to signal transduction events. In addition, factors such as turgor pressure and presence of the cell wall may also place unique constraints on these plant mechanosensory systems. Even so, the candidate signal transduction elements in both plant touch and gravity sensing, changes in Ca2+, pH and membrane potential, do mirror the known ionic basis of signaling in animal mechanosensory cells. Distinct spatial and temporal signatures of Ca2+ ions may encode information about the different mechanosignaling stimuli. Signals such as Ca2+ waves or action potentials may also rapidly transfer information perceived in one cell throughout a tissue or organ leading to the systemic reactions characteristic of plant touch and gravity responses. Longer-term growth responses are likely sustained via changes in gene expression and asymmetries in compounds such as inositol-1,4,5-triphosphate (IP3) and calmodulin. Thus, it seems likely that plant mechanoperception involves both spatial and temporal encoding of information at all levels, from the cell to the whole plant. Defining this patterning will be a critical step towards understanding how plants integrate information from multiple mechanical stimuli to an appropriate growth response.

The Fast and Transient Transcriptional Network of Gravity and Mechanical Stimulation in the Arabidopsis Root Apex

“…Mechanical stimuli such as wind, rain, and obstacles in the soil trigger changes in growth patterns (Braam and Davis, 1990;. Gravitropic and mechanical stimulation in the root are interactive processes, mutually influencing differential growth (Mullen et al, 2000;Fasano et al, 2002;. The mechanisms of sensing and signal transduction for either stimulus are not well understood, but it has been shown that the transcript levels of specific genes are regulated early during signal transduction after either stimulus Braam and Davis, 1990).…”

Ways of signal transmission and physiological role of electrical potentials in plants

“…Chemical stimuli induce changes of electrical potential, which in turn stimulate growth of etiolated seedlings and affect nutation and phototropic movements (Spalding and Cosgrove 1993). Touch and gravitation are stimuli, which affect growth of Arabidopsis seedlings, and APs, besides other candidates, are recognized as factors mediating between stimulus and reaction (Fasano 2002).…”

Plant tropisms: providing the power of movement to a sessile organism

“…Unfortunately, it is not trivial to monitor changes in intracellular calcium between different stores. Investigators have had to resort to very indirect methods to gauge the impact of Ca 2+ on gravitropism such as application of Ca 2+ channel blockers or Ca 2+ chelators or by removing/altering the function of certain calcium regulatory proteins such as calmodilin-like proteins (for review see Fasano et al, 2002). Recently, however, Plieth and Trewavas (2002) used a luminescent Ca 2+ reporter aequorin to look at transient increases in [Ca 2+ ] cyt .…”

“…Interestingly, other mechanical stimulations don't have the same effect on [Ca 2+ ] cyt spiking (Plieth and Trewavas, 2002). Future experiments should include using this biosensor for calcium in conjunction with amyloplast mutants to see whether a link can truly be drawn between the sedimentation of starch molecules and the transient changes in [Ca 2+ ] cyt (Plieth and Trewavas, 2002;Fasano et al, 2002). Inositol-1,4,5-triphosphate (IP3) is another potential second messenger.…”