Kinetics of Stress Relaxation Properties of Oat Coleoptile Cell Wall after Geotropic Stimulation

Abstract

This study describes the stress relaxation of the cell wall of oat (Avena sativa) coleoptiles after different periods of geotropic stimulation. The upper and lower tissues (with respect to gravity) of geotrophically stimulated coleoptiles exhibit different wall properties. The lower tissues are less resistant to deformation than the upper. The ratio of stress to strain is significatly less in the lower than in the upper tissue. Similarly, the relaxation time and the minimum relaxation time, derived from the Maxwell model which describes the physical characteristics of polymers, are also shorter in the lower tissue. However, the maximum relaxation time shows no difference between the upper and lower tissues of a geotropically stimulated coleoptile. The differences between the tissues begin at about 8 minutes after the commencement of stimulation, similar to the time for the initiation of dictyosome redistribution, and precede the onset of geotropism. The above responses of the cell wail of the lower tissue are similar to those induced by indoleacetic acid. The parameters of wall properties of the coleoptiles of both the control and the geostimulated fluctuate rhythmically with time. The periodic changes in wall properties of the coleoptile are compared to other cyclic physiological phenomena.The congregation of dictyosomes (individual stacks of cisternae of the Golgi apparatus) in the bottom of a cell upon geotropic stimulation, and the increased activity (vesicle production) of this organelle in the same part of the cell, have prompted us to suggest that the Golgi apparatus participates in geotropism (11). Furthermore, the change in dictyosome distribution and activation occur before the onset of the tropistic curvature (11). Cell wall loosening is a prerequisite to cell elongation (17), and dictyosomes are closely related to wall deposition (3,8). We now ask, when do the changes in the stress relaxation properties of the coleoptile wall occur, with particular reference to the changes in the dictyosome after different periods of stimulation by gravity?Introductory Considerations. Cell walls of living tissue exhibit viscoelastic characteristics (see discussion by Lockhart [7] Maxwell model of a viscoelastic material, consisting of a spring connected in series with a dashpot, has been used in describing the stress relaxation properties of a polymer. A "generalized" Maxwell model consists of an infinite number of Maxwell models in parallel (4) showing a continuous spectrum of relaxation times. When the Maxwell assembly (Fig. 1) is subjected to a sudden extension (strain), which is then maintained at a fixed level, the initial extension is only in the spring. As time proceeds the springs contract and the dashpots extend. When this happens, the force (stress) required to maintain the strain relaxes. Hence, relaxation time, T, is MATERIALS AND METHODS Victory I oats (Avena sativa) were soaked in warm water (about 50 C) for 2.5 hr. They were stored at 2 to 6 C for 20 hr before planting on lucite bars covered wi...

Apoplast as the site of response to environmental signals

“…1995b. Similarly, the extensibility of the cell wall of the convex side was higher than that of the concave side in gravi-stimulated stems (Shen-MiUer and Masuda 1973, Iwami and Masuda 1974, Cosgrove 1990, Bagshaw and Cleland 1990 and corresponding differential modifications of the cell wall metabolism have been reported in gravitropism (Gibeaut et a/. 1990, Talbott and Pickard 1994, Montague 1995, Edelmann and Sievers 1995.…”

Rhythmicity in the Basipetal Transport of Indoleacetic Acid through Coleoptiles

“…That the control coleoptiles also exhibit a similar cyclic variation in cell-wall relaxation suggests that this rhythm was not initiated by the geotropic stimulus. It is possible that the periodic processes observed in this study and elsewhere (25)(26)(27)29) …”

“…The periods of these organelle fluctuations are tabulated in Table IV and average about 20 mmn. In a study of cell wall properties of control and geostimulated oat coleoptiles (29), we find the wall properties also change with time. The stress-relaxation times of the coleoptile wall have a mean periodicity of 24 min for the geostimulated and the control coleoptiles (29).…”

“…In a study of cell wall properties of control and geostimulated oat coleoptiles (29), we find the wall properties also change with time. The stress-relaxation times of the coleoptile wall have a mean periodicity of 24 min for the geostimulated and the control coleoptiles (29). That the control coleoptiles also exhibit a similar cyclic variation in cell-wall relaxation suggests that this rhythm was not initiated by the geotropic stimulus.…”

Rhythmic Differences in the Basipetal Movement of Indoleacetic Acid between Separated Upper and Lower Halves of Geotropically Stimulated Corn Coleoptiles

“…The velocities for the tip, mid, and base region of the coleoptile are tabulated in (Fig. 4) were also observed in intact coleoptiles of corn and oats (29), in the wall relaxation of oat coleoptiles (31), in growth and geotropic response of corn and oats (32), and in the number of dictyosomes and of mitochondria (29). The periods tabulated for these various responses are by no means precise.…”