Role of the Cell Wall-Sustaining System in Gravity Resistance in Plants

Abstract

Gravity resistance is one of two principal gravit y re sponse s in plants , comparable to gravitropism. In the final step of gravity resistance, plants increase the rigidity of their cell walls via modifications to the metabolism. Various constituents of the plasma membrane and the cytoskeleton play an important role in sustaining functions of the cell wall in gravity resistance. Mechanoreceptors located on the plasma membrane are involved in the perception of gravity signal. The perceived signal may be, at least partly, transformed and transduced via membrane sterol rafts, d e p e n d i n g o n i t s m a g n i t u d e . C e l l u l o s e synthases and proton pumps are responsible for modifications to the cell wall metabolism and the apoplastic environment, respectively. On the other hand, the reorientation of cortical microtubules contributes to modification of growth anisotropy, which is related to gravity resistance. Also, microtubule -associate d proteins are important in maintenance of the structure and induction of the reorientation of cortical microtubules. Gravity resistance in plants is thus mediated by the structural continuum or physiological continuit y of cortical microtubules-plasma membranecell wall.

Cortical microtubules are responsible for gravity resistance in plants

“…12 These results suggest that cortical microtubules are involved in gravity resistance. 2,13 To confirm this point, we investigated the changes in cell morphology and orientation of cortical microtubule arrays in hypocotyls of Arabidopsis tubulin mutants grown under hypergravity conditions. 14 We used three mutants, tua3(D205N), tua4(S178∆) and tua6(A281T) 15,16 in the study.…”

Role of the plant cell wall in gravity resistance

“…Studies on cell wall changes under true microgravity in space have been limited to fragmental analyses of the levels and organization of cellulose and lignin, without any report on the effects of microgravity on the mechanical properties Hoson et al, 2005;Hoson et al, 2009). We have analyzed both the mechanical and chemical properties of the cell wall of space-grown seedlings under conditions where environmental factors other than gravity, such as temperature, light, water, and gas composition, were strictly regulated (Hoson et al, 2002;Soga et al, 2002).…”

“…We have termed this response 'gravity resistance' and examined its nature and mechanism mainly by ground-based experiments using hypergravity conditions, produced by centrifugation, and by space experiments Hoson et al, 2005;Hoson et al, 2009). As a result, we have clarified the outline of the sequence of events in gravity resistance, and shown that gravity resistance is surely the major graviresponse in plants, distinct from gravitropism.…”

The Utilization of Plant Facilities on the International Space Station—The Composition, Growth, and Development of Plant Cell Walls under Microgravity Conditions

“…The mechanism of gravity resistance consists of signal perception, transformation and transduction of the perceived signal, and response to the transduced signal, as is seen in other environmental responses as well. The outline of the sequence of events in gravity resistance has already been described [ 5 , 15 ]. The gravity signal may be perceived by mechanoreceptors (mechanosensitive ion channels) on the plasma membrane, and it appears that amyloplast sedimentation in statocytes is not directly involved.…”