Gravity perception in plants: a multiplicity of systems derived by evolution?

Abstract

The origin and subsequent evolution of life on Earth have taken place within an environment where a 1g gravitational field is omnipresent. Living organisms, at whatever stage in their evolution, have accommodated this variable in both their structure and their function. Systems have also evolved whereby gravitational accelerations are perceived by gravisensors and these, in turn, have led to responses that give particular spatial orientations to living processes. It is proposed that, the higher the evolutionary status of an organism, the more likely it is that it will possess multiple systems for gravisensing because evolution discards little that assists fitness and hence supplements with new gravisensing systems those which already existed within evolutionarily older, less complex organisms. Moreover, in comparison with a single gravisensing system, a multiplicity of systems permits gravity to participate in a wider range of developmental programmes, such as taxes, morphisms and tropisms, through the action of different sensory mechanisms coupled to distinct signalling and response pathways. Whatever the precise mechanism of graviperception in any given set of conditions, all may transduce the g-force by means of a membrane system. Transduction may involve the endoplasmic reticulum and thence the plasma membrane.

LAZY Genes Mediate the Effects of Gravity on Auxin Gradients and Plant Architecture

“…over evolutionary time as roots and shoots became specialized for the competitive capture of water, minerals, and light on land (Barlow, 1995). Accordingly, the LAZY-dependent mechanism may have been superimposed on an ancestral LAZY-independent mechanism that now plays a modulatory role by acting in weaker opposition.…”

Phototropism and Gravitropism in Lateral Roots of Arabidopsis

“…Thus, while amyloplasts and a full complement of starch are necessary for full gravisensing, starch is not required for gravitropism (MacCleery and Kiss 1999). Although it is possible that even starchless plastids have sufficient mass to function in graviperception, an alternate hypothesis is that plants have multiple types of gravisensing mechanisms (Barlow 1995, Sack 1997, Kiss 2000. According to this latter view, since gravity is a sustained and pervasive presence for life on earth, a "multiplicity of systems" for gravity perception is likely to have arisen throughout evolutionary history (Barlow 1995).…”

“…Although it is possible that even starchless plastids have sufficient mass to function in graviperception, an alternate hypothesis is that plants have multiple types of gravisensing mechanisms (Barlow 1995, Sack 1997, Kiss 2000. According to this latter view, since gravity is a sustained and pervasive presence for life on earth, a "multiplicity of systems" for gravity perception is likely to have arisen throughout evolutionary history (Barlow 1995). Therefore, in addition to plastid-based gravisensing in the root cap, other types of sensing remain to be discovered and characterized.…”

Effet de la dur�e d'application d'un stimulus gravitationnel sur la formation de bois de tension et de bois oppos� dans de jeunes pousses de peuplier (Populus euramericana cv `Ghoy')

“…Il est très largement admis que le gravitropisme, réaction d'un végétal à l'effet de la pesanteur terrestre, constitue le mécanisme par lequel les plantes se repèrent dans l'espace [3,9,15,28,34,46]. La tige principale des arbres fait preuve d'un orthogravitropisme négatif, c'est-à-dire que la croissance est orientée verticalement dans une direction opposée à la force de 32 B. Jourez et Th.…”