A Unified Model of Shoot Tropism in Plants: Photo-, Gravi- and Propio-ception

Renaud Bastien, Stéphane Douady, Bruno Moulia, Mark S Alber
2015 PLoS Computational Biology  
Land plants rely mainly on gravitropism and phototropism to control their posture and spatial orientation. In natural conditions, these two major tropisms act concurrently to create a photogravitropic equilibrium in the responsive organ. Recently, a parsimonious model was developed that accurately predicted the complete gravitropic and proprioceptive control over the movement of different organs in different species in response to gravitational stimuli. Here we show that the framework of this
more » ... ifying graviproprioceptive model can be readily extended to include phototropism. The interaction between gravitropism and phototropism results in an alignment of the apical part of the organ toward a photogravitropic setpoint angle. This angle is determined by a combination of the two directional stimuli, gravity and light, weighted by the ratio between the gravi-and photo-sensitivities of the plant organ. In the model, two dimensionless numbers, the graviproprioceptive number B and the photograviceptive number M, control the dynamics and the shapes of the movement. The extended model agrees well with two sets of detailed quantitative data on photogravitropic equilibrium in oat coleoptiles. It is demonstrated that the influence of light intensity I can be included in the model in a power-law-dependent relationship M(I). The numbers B and M and the related photograviceptive number D are all quantitative genetic traits that can be measured in a straightforward manner, opening the way to the phenotyping of molecular and mechanical aspects of shoot tropism. Author Summary Although plants are mostly seen as static, they are constantly moving to adapt to changes in their stature and to their environment. Gravity and light, among others, are major factors that sculpt the shapes of plants. Plants tend to grow in the direction of the light to get access to their energy resource. At the same time, however, they need to maintain their balance and control their posture. In a recent study, we showed that postural control is PLOS Computational Biology |
doi:10.1371/journal.pcbi.1004037 pmid:25692607 pmcid:PMC4332863 fatcat:563us7dqwnfo7pendfqqlpkiby