Mechanical signalling, calcium and plant form

Abstract

Calcium is a dynamic signalling molecule which acts to transduce numerous signals in plant tissues. The basis of calcium signalling is outlined and the necessity for measuring and imaging of calcium indicated. Using plants genetically transformed with a cDNA for the calcium-sensitive luminescent protein, aequorin, we have shown touch and wind signals to immediately increase cytosol calcium. Touch and wind signal plant cells mechanically, through tension and compression of appropriate cells. Many plant tissues and cells are very sensitive to mechanical stimulation and the obvious examples of climbing plants, insectivorous species as well as other less well-known examples are described. Touch sensing in these plants may be a simple evolutionary modification of sensitive mechanosensing system present in every plant. The possibility that gravitropism may be a specific adaptation of touch sensing is discussed. There is a growing appreciation that plant form may have a mechanical basis. A simple mechanical mechanism specifying spherical, cylindrical and flat-bladed structures is suggested. The limited morphological variety of plant tissues may also reflect mechanical specification. The article concludes with a discussion of the mechanisms of mechanical sensing, identifying integrin-like molecules as one important component, and considers the specific role of calcium.

Molecular Cloning and Functional Analysis of Polyphosphoinositide-dependent Phospholipase D, PLDβ, from Arabidopsis

“…This observation is particularly relevant considering that 100 nM and 1 M are the respective resting and stimulated intracellular calcium concentrations of plants and animals (33,34). It remains to be elucidated how Ca 2ϩ is involved in the PLDmediated hydrolysis of phospholipids.…”

Evidence for a Mechanically Induced Oxidative Burst

“…In plants, mechanically triggered pathways are also believed to contribute to osmoregulation (Schroeder and Hedrich, 19891, but they may be further involved in thigmotropism, geotropism, ethylene generation, and callose biosynthesis (Jaffe, 1973;Jaffe et al, 1985;Pickard and Ding, 1992). As was the case with animal systems, stretch-activated ion channels are again hypothesized to help inaugurate these responses via sites of contact between the cytoskeleton and the cell wall (Trewavas and Knight, 1994). In fact, stretchactivated channels have already been identified in the plasma membranes of onion epidermal cells (Ding and Pickard, 1993), Vicia fuba guard cells (Schroeder and Hedrich, 1989), and cultured tobacco cells (Falke et al, 1988).…”

Calmodulins and Calcineurin B–like Proteins

“…Many extracellular signals, including light, biotic, and abiotic stress factors, elicit changes in cellular Ca 2 ϩ concentration in plants (Trewavas and Knight, 1994;Bush, 1995;Braam et al, 1997;McAinsh et al, 1997;Sanders et al, 1999;Rudd and Franklin-Tong, 2001). In addition, many intrinsic growth and developmental processes, such as elongation of root hairs and pollen tube formation, are controlled by Ca 2 ϩ transients (Felle and Hepler, 1997;Holdaway-Clarke et al, 1997;Wymer et al, 1997).…”