Abstract
Perception of inclination in the gravity field and perception of light direction are two important environmental signals implicated in the control of plant shape and habit. However, their quantitative study in light-grown plants remains a challenge. We present a novel method here to determine the sensitivities to gravitropism and phototropism. The method combines: (i) an original experimental device of isotropic light to disentangle gravitropic and phototropic plant responses; and (ii) model-assisted phenotyping using recent models of tropism perception—the AC model for gravitropism alone and the ArC model for gravitropism combined with phototropism. We first assessed the validity of the AC and ArC models on poplar, the classical species model for woody plants. We then tested the method on three woody species contrasted by their habit and tolerance to shade: poplar (Populus tremula*alba), oak (Quercus petraea) and beech (Fagus sylvatica). The method was found to be effective to quantitatively discriminate the tested species by their ratio of tropistic sensitivities. The method thus appears as an interesting tool to quantitatively determine tropistic sensitivities, a prerequisite for assessing the role of tropisms in the control of the variability of the habit and/or tolerance to shade of woody species in the future.
Highlights
Gravitropism and phototropism, the orientation of growth as a function of gravity and light, respectively, are two major processes implicated in the regulation of plant shape [1,2]
The AC and ArC models have been partially experimentally validated for seedlings and young stems of woody species
In these plants, the main stem is sufficiently slender for the motor aspects not to be a limiting factor of tropistic movements, and gravi- and photogravitropic equilibrium can be reached in a few weeks
Summary
Gravitropism and phototropism, the orientation of growth as a function of gravity and light, respectively, are two major processes implicated in the regulation of plant shape [1,2] Their combination allows aerial organs to forage for light without losing mechanical stability [3]. Even if several molecular cross-talks between the gravitropic and phototropic pathways have been identified [5], very few quantitative studies have been conducted on the interaction between photo- and gravitropism and none provides numerical values of sensitivities to gravi- and phototropism for trees This lack of data does not make it possible to compare the contribution of gravi- and phototropism between different tree species and prevents further advances in quantifying the contribution of gravi- and phototropism in the control of tree shape (habit) variability
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