Gravistimulated asymmetries in the outer epidermal cell walls of graviresponding coleoptiles

Abstract

Gravitropic plant growth is due to gravistimulated asymmetric extension rates of the affected flanks of the graviresponding organ. Differential growth of the upper and lower flanks (UFs, LFs) of graviresponding plant organs may in principle be achieved by various biochemical and/or biophysical asymmetries. The gravistimulated mechanism(s) by which the different growth rates are determined is still unresolved, as is the mechanism of IAA-regulated growth. The purpose of this brief review is to summarize and critically evaluate data concerning gravistimulated asymmetries, especially with respect to the interface of the plasma membranes and of the extension-restricting, load-bearing epidermal cell walls (Masuda and Yamamoto 1972 Physiol Plant 27:109-115). In addition, recent results obtained by the author in experiments with rye coleoptiles will be presented and discussed in the context of a tentative model of gravistimulated wall asymmetries temporarily causing differential growth.

Lateral redistribution of auxin is not the means for gravitropic differential growth of coleoptiles: A new model

“…As earlier suggested (Edelmann 1997), temporary inhibition of growth of the upper organ flank might therefore be achieved by a calcium-mediated inhibition of the infiltration of secreted wall-loosening factors into the walls, temporarily preventing wall loosening. Concerning the effect on growth, such a mechanism would not only be compatible but identical with an apparent decrease of IAA sensitivity as reported earlier for a number of systems (Salisbury et al 1988, Rorabaugh and Salisbury 1989, Stinemetz 1996.…”

“…1 and Table 1 in Edelmann and Sievers 1995). In fact, within the growth-inhibited flank the number of OPs between the plasma membrane and the outermost epidermal cell walls was increased two to 3-fold compared with the periplasmic space of the lower flank, which showed no significant difference to vertical, non-stimulated controls (Edelmann andSievers 1995, Edelmann and. However, within the peripheral cytoplasm along their presumptive secretory path, the numbers of OPs were similar in epidermal cells of both the lower and upper flanks, indicating that their secretion is unaffected but that their infiltration into the walls is affected by gravistimulation.…”

“…caused lateral redistribution of the occurrence of OPs in negatively graviresponding coleoptiles (Edelmann andSievers 1995, Edelmann and. However, in contrast to what would be expected from the Cholodny-Went hypothesis (CWH), namely a relative increase in the number of periplasmic OPs in the fast-growing epidermal cells of the lower flank and a decrease on the growth-inhibited upper organ flank due to the lateral redistribution of IAA from the upper to the lower flank, a distribution pattern opposite to this was detected (also see Fig.…”

Characterization of the asymmetric growth of gravistimulated snapdragon spikes by stem and cell dimension analyses

“…Recently, the mechanism of bending of inflorescence shoots has become more of a focus, and it is being extensively investigated (Weise et al, 2000;Morita et al, 2002;Friedman et al, 2003). In hypocotyls, coleoptiles, and grass pulvini, the upward bending resulted from differential growth of the upper and lower flanks (Digby and Firn, 1979;Firn and Digby, 1980;Dayanandan and Kaufman, 1984;Salisbury, 1993;Cosgrove, 1997;Edelmann, 1997). However, the growth pattern was rarely characterized in detail in gravistimulated mature stems and flowering shoots (Clifford and Oxlade, 1989;Meicenheimer and Nackid, 1994).…”

The role of auxin and ethylene for gravitropic differential growth of coleoptiles and roots of rye- and maize seedlings

“…Yet, in the same study in which redistribution of IAA was detected in coleoptiles, no IAA gradient could be detected between the upper and lower flanks of graviresponding maize roots or sunflower hypocotyls (Mertens and Weiler, 1983). Therefore, redistribution of IAA in gravistimulated organs may occur in addition to the processes that induce differential growth (Feldman, 1985;Edelmann, 1997). Thus, IAA would permit rather than regulate gravitropism.…”