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Title: Water Uptake along the Length of Grapevine Fine Roots: Developmental anatomy, tissue specific aquaporin expression, and pathways of water transport

Author
item Gambetta, Greg - University Of California
item Fei, Jiong - University Of California
item Rost, Thomas - University Of California
item Knipfer, Thorsten - University Of California
item Matthews, Mark - University Of California
item Walker, Andrew - University Of California
item Mcelrone, Andrew

Submitted to: Plant Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/15/2013
Publication Date: 11/10/2013
Publication URL: http://www.plantphysiol.org/content/163/3/1254.abstract
Citation: Gambetta, G., Fei, J., Rost, T., Knipfer, T., Matthews, M., Walker, A., Mcelrone, A.J. 2013. Water Uptake along the Length of Grapevine Fine Roots: Developmental anatomy, tissue specific aquaporin expression, and pathways of water transport. Plant Physiology. 163:1254-1265.

Interpretive Summary: To date, we still lack a thorough understanding of physiological controls of water uptake in perennial woody crop roots. Aquaporins are water permeable protein channels embedded in cellular membranes of plant cells, including roots. Here we describe the role of aquaporins in influencing water uptake along grapevine roots and how these changes are linked with structural changes associated with anatomical changes as well.

Technical Abstract: To better understand water uptake patterns in root systems of woody perennial crops, we detailed the developmental anatomy and hydraulic physiology along the length of grapevine fine roots- from the tip to secondary growth zones. Our characterization included localization of suberized structures and aquaporin gene expression and determination of hydraulic conductivity (Lpr) and aquaporin protein activity (via chemical inhibition) in different root zones under both osmotic and hydrostatic pressure gradients. Tissue specific mRNA levels of the plasma membrane aquaporin isogenes (VvPIPs) were quantified using laser capture micro-dissection and quantitative PCR. Our results highlight dramatic changes in structure and function along the length of grapevine fine roots. While the root tip lacked suberization altogether, a suberized exo- and endodermis developed in the maturation zone, which gave way to the secondary growth zone containing a multilayer suberized periderm. Longitudinally, VvPIP isogenes exhibited strong peaks of expression in the root tip that decreased precipitously along the root length in a pattern similar to Arabidopsis roots. In the radial orientation, expression was always greatest in interior tissues (i.e. stele, endodermis, and/or vascular tissues) for all root zones. High Lpr and aquaporin protein activity were associated with peak VvPIP expression levels in the root tip. This suggests that aquaporins play a limited role in controlling water uptake in secondary growth zones, which contradicts existing theoretical predictions. Despite having significantly lower Lpr, woody roots can comprise the vast majority of the root system surface area in mature vines and thus provide for significant water uptake potential.