Cell wall biosynthesis and the molecular mechanism of plant enlargement

Abstract

Abstract.Recently discovered reactions allow the green alga Chara corallina (Klien ex. Willd., em. R.D.W.) to grow well without the benefit of xyloglucan or rhamnogalactan II in its cell wall. Growth rates are controlled by polygalacturonic acid (pectate) bound with calcium in the primary wall, and the reactions remove calcium from these bonds when new pectate is supplied. The removal appears to occur preferentially in bonds distorted by wall tension produced by the turgor pressure (P). The loss of calcium accelerates irreversible wall extension if P is above a critical level. The new pectate (now calcium pectate) then binds to the wall and decelerates wall extension, depositing new wall material on and within the old wall. Together, these reactions create a non-enzymatic but stoichiometric link between wall growth and wall deposition. In green plants, pectate is one of the most conserved components of the primary wall, and it is therefore proposed that the acceleration-deceleration-wall deposition reactions are of wide occurrence likely to underlie growth in virtually all green plants. C. corallina is one of the closest relatives of the progenitors of terrestrial plants, and this review focuses on the pectate reactions and how they may fit existing theories of plant growth.

Exocytosis Precedes and Predicts the Increase in Growth in Oscillating Pollen Tubes

“…Of further interest, the addition of pectins, one of the components of the cell wall, allows these isolated Chara cells to achieve normal rates of elongation Boyer, 2006a, 2006c). Within this scenario it appears that the role of pectin is twofold: (1) insertion of new pectin molecules into the wall matrix would weaken existing linkages (intussusception), and (2) pectins already acted upon by PME would locally chelate Ca 2+ and modulate the stiffening effect of this ion on cell wall structure (Boyer, 2009).…”

“…In proposing the above model, we do not exclude a role for wall-loosening factors, such as expansin or degrading enzymes. However, applying Occam's razor, it is our view that specifically localized cell wall loosening and expansion in the pollen tube can be explained through the combined processes of intussusception, PME activity, and local Ca 2+ regulation (Boyer, 2009).…”

A finite strain fibre-reinforced viscoelasto-viscoplastic model of plant cell wall growth

“…The differences are not just a matter of scale. The cell wall growth of terrestrial plants is believed to be governed by the breaking and reforming of hemicelluloses crosslinks, whereas in Chara it appears that a similar role is performed by calcium pectate, controlled by the concentration of calcium ions [77]. The presence of calcium ions inhibits bond loosening, while depletion of calcium ions causes bond loosening and permits growth to occur.…”

“…The presence of calcium ions inhibits bond loosening, while depletion of calcium ions causes bond loosening and permits growth to occur. Although the biochemical details are different from those for terrestrial plant cells, the underlying mechanisms are sufficiently similar that Chara has been studied in order to gain an understanding of plant cell behaviour [77]. For this reason, published data on the response of Chara to pressure loading [16] [66] are used here, and in an earlier study [51], as the basis of a series of case studies.…”

Cell wall integrity

“…107 Similarly, remodeling of cell walls in response to abiotic stresses such as drought and cold is also believed to be a source of oligosaccharins released during these processes, thus mediating transduction of signals between cell wall and cytoplasm. 108,109 Changes in cell wall mechanical properties can also be involved in stress responses; this was strongly evidenced by demonstration of the relationship between cytoskeleton orientation and cellulose deposition. 110 During water stress, microtubules are eliminated by proteolytic degradation (Wang et al, 2011) followed by cellulose microfibril re-organization and activation of phospholipase-D dependent signaling during osmotic adaptation.…”