Circulation of water within wheat grain revealed by nuclear magnetic resonance micro-imaging

Abstract

Observation of water movement in situ is difficult and very few methods are available for measuring directly the motion of water. Movement of solutes or suspended particles is not a reliable guide and the use of radioactive or heavy water is limited to a few applications. Thus, although much has been inferred about the mechanism of water movement through comparatively lengthy pathways¹, less is known for the shorter and more tortuous pathways within and between cells. Still more challenging is the investigation of water motion within structurally complex organs of small dimensions such as the fruits and seeds of plants, some of which behave (for water) as practically closed systems. We have observed longitudinally oriented bulk flow of water in developing grains of wheat using a pulsed gradient spin echo nuclear magnetic resonance technique combined with microscale imaging. Movement of water is associated with import of nutrients by the grain but is on too large a scale to be due to phloem transport alone. The flow observed could be associated with unloading and/or transport of nutrients in the vicinity of the vascular system. This is the first report of the observation in vivo of water movement on a sub-millimetre scale by non-invasive methods in any biological system.