Abstract
Main conclusionThe regulation of source-to-sink sucrose transport is associated withAtSUC andAtSWEET sucrose transporters’ gene expression changes in plants grown hydroponically under different physiological conditions.Source-to-sink transport of sucrose is one of the major determinants of plant growth. Whole-plant carbohydrates’ partitioning requires the specific activity of membrane sugar transporters. In Arabidopsis thaliana plants, two families of transporters are involved in sucrose transport: AtSUCs and AtSWEETs. This study is focused on the comparison of sucrose transporter gene expression, soluble sugar and starch levels and long distance sucrose transport, in leaves and sink organs (mainly roots) in different physiological conditions (along the plant life cycle, during a diel cycle, and during an osmotic stress) in plants grown hydroponically. In leaves, the AtSUC2, AtSWEET11, and 12 genes known to be involved in phloem loading were highly expressed when sucrose export was high and reduced during osmotic stress. In roots, AtSUC1 was highly expressed and its expression profile in the different conditions tested suggests that it may play a role in sucrose unloading in roots and in root growth. The SWEET transporter genes AtSWEET12, 13, and 15 were found expressed in all organs at all stages studied, while differential expression was noticed for AtSWEET14 in roots, stems, and siliques and AtSWEET9, 10 expressions were only detected in stems and siliques. A role for these transporters in carbohydrate partitioning in different source–sink status is proposed, with a specific attention on carbon demand in roots. During development, despite trophic competition with others sinks, roots remained a significant sink, but during osmotic stress, the amount of translocated [U-14C]-sucrose decreased for rosettes and roots. Altogether, these results suggest that source–sink relationship may be linked with the regulation of sucrose transporter gene expression.
Highlights
Plants grow autotrophically and perform photosynthesis by assimilating CO2 and using light and water to produce carbohydrates
RT-qPCR using At5g12240 (Czechowski et al 2005) gene as reference and represent the mean of measures obtained from a pool of five plants The expression of specific genes as osmotic stress markers are followed in the leaf: AtRD29 (b) and in the root: AtTIP1.2 (d) or as senescence-associated gene: AtSAG12 (b) during osmotic stress and during rewatering phase in many others studies, hydroponically grown plants show the same morphological and physiological traits (Fig. 1a) as plants cultivated in soil (Gibeaut et al 1997; Norén et al 2004), as e.g. demonstrated for the inflorescences development during the reproductive phase (Arteca and Arteca 2000)
In our results (Fig. 10 and Table S2), we have found AtSWEET11-15 genes expressed in root as we already observed during water deficit in soil (Durand et al 2016), AtSWEET13 gene being the most expressed and its expression increased during the night as AtSUC1
Summary
Plants grow autotrophically and perform photosynthesis by assimilating CO2 and using light and water to produce carbohydrates. Photosynthates make carbon (C) available for growth and maintenance of non-photosynthetic organs. At the end of development it can be assumed that two sinks, roots and seeds, enter in competition for carbon resources and fluxes will be determined by their respective “sink strength” (Ho 1988). At this point, roots are still consuming energy to provide enough water and mineral nutrients to complete whole-plant development, seeds filling
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