The Mechanical Behavior of Isolated Avena Coleoptile Walls Subjected to Constant Stress

Abstract

In order to assess the role of the mechanical properties of the wail in auxin-induced cell elongation, a study has been made of the ability of isolated Arena coleoptile walls to extend (creep) when subjected to a constant applied stress. Creep occurs as a viscoelastic extension which has the following characteristics: the extension is proportional to log time and is partly reversible, and the extension rate has a Qio of about 1.05 and is markedly greater in auxin-pretreated walls. In nonconditioned walls the extension rate is proportional to applied stress, but pre-extension causes the appearance of an apparent yield strain. The similarity of creep and instantaneous plastic deformation in response to temperature or to pretreatment with auxin or KCN suggests that the instantaneous deformation is simply the viscoelastic extension which occurs at very short times. A comparison of these viscoelastic properties with the properties of auxin-induced cell elongation indicates that cell elongation requires more than just a physical extension of the wall. It is suggested that elongation occurs as a series of extension steps, each of which involves a viscoelastic extension preceded or accompanied by an auxin-dependent biochemical change in the wall properties.The increase in cell wall area which accompanies cell elongation involves a stretching of the wall already present (3,25,33) as well as synthesis of new wall (2, 23). There is considerable evidence that auxin controls the rate of cell elongation, at least in part, by altering the ability of walls to be physically extended (5, 12, 18), but the manner in which this is accomplished is still in doubt. One block to our understanding is our lack of knowledge concerning the nature of the wallstretching process.Viscous flow (17, 21), plastic deformation (5, 12, 18), and chemical stress relaxation (24) have all been proposed as mechanisms of wall stretching, but little direct evidence to support any of these is available. The necessary measurements of the ability of the wall to undergo physical extension under constant stress (creep) have been carried out on Nitella (22) but not on

Extensibility and rheology of collenchyma I. Creep relaxation and viscoelasticity of young and senescent cells

“…Collenchyma cell walls have no linear components. A similar result was obtained and reported by Cleland with Avena coleoptiles (6). Therefore, the elongation of the collenchyma cells is not only due to exogenous stresses, but also requires a wall loosening as in the case of the epidermis (21).…”

Water Relations of Seagrasses

“…When a constant stress is applied to a wall segment, initially, an almost instantaneous deformation occurs. This is then followed by further slower deformation or creep which can be reversible on removal of the stress (6,17). The same phenomenon occurs when strain is kept constant and stress relaxation is observed (15).…”

“…The instantaneous Young's modulus is therefore larger than the final equilibrium or stationary Young's modulus. It should be noted however that the value of the initial instantaneous Young's modulus can depend on how rapidly the strain or stress is applied (6,15). Haughton and Sellen (15) suggest that the instantaneous modulus could only be observed at times of I ms or less.…”

Lipid Transfer Proteins Enhance Cell Wall Extension in Tobacco

“…To this end, empirical relations describing the experimental data can be a valuable alternative. In this way, Cleland (1971) observed that the extension of isolated Avena sativa walls behaves logarithmically in time. Others have used logarithmic functions to describe wall creep, the long-term and continuous deformation of cell walls (Bü ntemeyer et al, 1998;Thompson, 2001).…”

“…There are many examples of linear extension after expansin addition (McQueen-Mason et al, 1992;Li and Cosgrove, 2001), but the effect of expansin on A. xylinum material extension is not linear and seems logarithmic (Whitney et al, 2000). Interestingly, when only the effect of endogenous, untreated (e.g., not boiled) cell wall-loosening proteins was measured in the extensometer, by not treating (e.g., boiling) plant material, the extension application appeared logarithmic (Cleland, 1971;McQueen-Mason et al, 1992). It would be interesting to compare the activity of LTP and expansin directly.…”