Abstract
Gravity is a crucial environmental factor regulating plant growth and development. Plants have the ability to sense a change in the direction of gravity, which leads to the re-orientation of their growth direction, so-called gravitropism. In general, plant stems grow upward (negative gravitropism), whereas roots grow downward (positive gravitropism). Models describing the gravitropic response following the tilting of plants are presented and highlight that gravitropic curvature involves both gravisensing and mechanosensing, thus allowing to revisit experimental data. We also discuss the challenge to set up experimental designs for discriminating between gravisensing and mechanosensing. We then present the cellular events and the molecular actors known to be specifically involved in gravity sensing.
Highlights
Among the factors that influence the growth orientation in plants, gravity represents one of the most important environmental signals. This biological process known as gravitropism, starts from seed germination through the upright growth of shoots, ensuring the photosynthesis and the reproduction as well as the dispersion of seeds, and the downright growth of roots, supplying the plant in water and nutrients
In trees and perennial plants, the active cambium initiated in organs undergoing secondary growth contributes to the reorientation of the shoot through the differentiation and shrinkage of reaction wood (RW – i.e., tension wood or compression wood in eudicotyledonous and conifers respectively; IAWA, 1964; Archer, 1986)
Gravitropism is essential in the control of the posture and the form of land plants (Coutand et al, 2007; Moulia et al, 2011)
Summary
Among the factors that influence the growth orientation in plants (e.g., light, gravity, water availability, and touch), gravity represents one of the most important environmental signals. Even if this sine law has been confirmed in several species both in stems and roots, it is valid only in a limited range of inclination angles, ranging from 0 to 90◦ (see introduction in Göttig and Galland, 2014) and it does not characterize gravitropic movements of the whole organ over-time (reviewed in Moulia and Fournier, 2009).
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