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Flux management of water and carbon dioxide in inner leaf tissues. Role of aquaporins and consequences for whole plant hydraulics – LeafFlux

Submission summary

The trade-off between water loss by transpiration and assimilation of atmospheric carbon dioxide (CO2) is a critical factor for plant productivity. For this reason, leaf stomata which mediate the exchange of water and CO2 between the plant and the atmosphere have been extensively studied. Parallel fluxes of water and CO2 also occur in inner leaf tissues. Yet, the molecular bases and regulation of these fluxes are poorly understood. They will be the object of the present LeafFlux project. In the leaf, water and CO2 move in gas and liquid phases along specific paths and anatomical structures. A transfer across the plasma membrane of leaf cells is required for both CO2 transport and transcellular water transport. Aquaporins are ubiquitous channel proteins that facilitate the transport across plant cell membranes of water, small neutral solutes, and gas. Recent work suggests that aquaporins play a role in the transport of water and CO2 in leaves. The LeafFlux project is designed along three well identified work packages (WP) and assembles two research teams of complementary expertise. Partner 1 is recognized for its molecular and physiological work on the function and regulation of aquaporins. Partner 2 has a longstanding experience in the biophysics of gas exchange and leaf photosynthesis. The first aim of the project will be to investigate the respective pathways for water (WP1) and CO2 (WP2) transport in inner tissues of Arabidopsis leaves and the contribution of aquaporins in each of these two processes. The role of specific isoforms will be determined and an integrated modelling of water and CO2 cotransport in inner leaf tissues will be attempted. This work will include the development of new methods for measuring the conductance of leaf tissues to water and CO2. In particular, we will introduce non invasive tracing of liquid water flux in the leaf which has not yet been achieved in the community. It is assumed that the different methods will yield different conductivity values, with distinct spatial significance. The role of aquaporins in water and CO2 transport will be dissected by a combination of pharmacological and reverse genetic approaches. The former approach will rely on general aquaporin blockers (mercury, acid loads). The latter will be focused on four isoforms of the Plasma membrane Intrinsic Protein (PIP) subfamily: PIP1;1, PIP1;2, PIP2;1, and PIP2;6 which are the most abundantly expressed aquaporins in the leaf plasma membrane. The transport properties of each aquaporin will be related to its tissue specific expression pattern and to the water and/or CO2 transport phenotype of corresponding knock-out mutant plants. The other main line of research will be to investigate the regulation of water and CO2 transport in response to environmental stimuli. This research will be based on an extensive search for co-regulations. The use of non-invasive flux measurements and original genetic resources may uncover unexpected regulations. We will in particular attempt to uncouple regulation of water and CO2 transport in inner leaf tissue from stomatal regulation using mutants with disrupted stomatal regulations (WP2). A molecular and cellular dissection of the mechanisms involved in the regulation leaf water transport will performed. Proteomic and cell biological tools will be used to characterize the regulation of aquaporins in Arabidopsis leaves (WP3). Here, we will focus on the effects of irradiance, which we know already, acts on water transport at the leaf and whole plant levels. Finally, the LeafFlux project will investigate the consequences for whole plant hydraulics of water transport regulation in leaves (WP3). Emphasis will be made on the effects of light and on how leaves may initiate long-distance signalling to modulate the hydraulic properties of roots. The significance of a coordinated regulation of leaf and root hydraulic properties will be investigated. In conclusion, the study of aquaporin function in leaves offers an unprecedented opportunity for addressing novel aspects in leaf and whole plant physiology. Because of its innovative character, the present project should reach frontiers in plant integrative biology and allow to address general issues about the control by leaves of transpiration and plant growth and the role of leaves in long-distance signalling.

Project coordination

Christophe MAUREL (Organisme de recherche)

The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.

Partner

Help of the ANR 405,000 euros
Beginning and duration of the scientific project: - 36 Months

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