title: Buffering growth variations against water deficits through timely carbon usage.
abstract: Water stresses reduce plant growth but there is no consensus on whether carbon metabolism has any role in this reduction. Sugar starvation resulting from stomatal closure is often proposed as a cause of growth impairment under long-term or severe water deficits. However, growth decreases faster than photosynthesis in response to drought, leading to increased carbohydrate stores under short-term or moderate water deficits. Here, we addressed the question of the role of carbon availability on growth under moderate water deficits using two different systems. Firstly, we monitored the day/night pattern of leaf growth in Arabidopsis plants. We show that a moderate soil water deficit promotes leaf growth at night in mutants severely disrupted in their nighttime carbohydrate availability. This suggests that soil water deficit promotes carbon satiation. Secondly, we monitored the sub-hourly growth variations of clementine fruits in response to daily, natural fluctuations in air water deficit, and at contrasting source-sink balances obtained by defoliation. We show that high carbohydrate levels prevent excessive, hydraulic shrinkage of the fruit during days with high evaporative demand, most probably through osmotic adjustment. Together, our results contribute to the view that growing organs under moderate soil or air water deficit are not carbon starved, but use soluble carbohydrate in excess to partly release a hydromechanical limitation of growth.
authors.affiliation: UMR 759, Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, Institut de Biologie Intégrative des Plantes, Institut National de la Recherche Agronomique Montpellier, France.
authors.forename: Florent
authors.initials: F
authors.lastname: Pantin
authors.affiliation: UMR 759, Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, Institut de Biologie Intégrative des Plantes, Institut National de la Recherche Agronomique Montpellier, France ; UR 1103, Génétique et Ecophysiologie de la Qualité des Agrumes, Institut National de la Recherche Agronomique San Giuliano, France ; UR 1115, Plantes et Systèmes de Culture Horticoles, Institut National de la Recherche Agronomique Avignon, France.
authors.forename: Anne-Laure
authors.initials: AL
authors.lastname: Fanciullino
authors.affiliation: UMR 759, Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, Institut de Biologie Intégrative des Plantes, Institut National de la Recherche Agronomique Montpellier, France.
authors.forename: Catherine
authors.initials: C
authors.lastname: Massonnet
authors.affiliation: UMR 759, Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, Institut de Biologie Intégrative des Plantes, Institut National de la Recherche Agronomique Montpellier, France.
authors.forename: Myriam
authors.initials: M
authors.lastname: Dauzat
authors.affiliation: UMR 759, Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, Institut de Biologie Intégrative des Plantes, Institut National de la Recherche Agronomique Montpellier, France.
authors.forename: Thierry
authors.initials: T
authors.lastname: Simonneau
authors.affiliation: UMR 759, Laboratoire d'Ecophysiologie des Plantes sous Stress Environnementaux, Institut de Biologie Intégrative des Plantes, Institut National de la Recherche Agronomique Montpellier, France.
authors.forename: Bertrand
authors.initials: B
authors.lastname: Muller
keywords: VPD; carbon satiation; carbon starvation; fruit growth; leaf growth; starch metabolism; water deficit