Acta Horticulturae 991 (2013) 115-122. Using portable NMR to measure sap flow and water in the intact plant Carel W. Windt Forschungszentrum Jülich IBG-2: Plant Sciences Germany Peter Blümler Institute of Physics University of Mainz Germany Keywords: transport, water status, growth, portable NMR, MRI Nuclear Magnetic Resonance (NMR) and NMR imaging (MRI) offer the possibility to quantitatively and non-invasively measure the presence and movement of water. Unfortunately, NMR hardware historically is expensive, poorly suited for plants, and, because of its bulk and complexity, not suitable for use in the field. But does it need to be? We here illustrate how novel, small scale portable NMR devices can be used in a sensor-like fashion to assess sap flow towards terminal organs such as the bean pod (Phaseolus vulgaris), and to directly measure xylem sap flow by means of NMR velocimetry in a poplar tree (Populus nigra). INTRODUCTION Ever since NMR (Nuclear Magnetic Resonance) was discovered, more than half a century ago, researchers have recognized its potential to non-invasively study plants and fruit. The most important feature of NMR for the plant sciences is that it makes it possible to measure the presence and behaviour of protons (i.e. the nucleus of the hydrogen isotope 1 H) in normal water, oil and fat, without any need for tracers. This property is successfully exploited in a wide variety of applications. Typical examples are imaging of anatomy, or the effects of illnesses in growing plants and fruit (Clark et al., 1997), water content and cavitation events in stems (Choat et al., 2010, Scheenen et al., 2007), growth of roots in soils (Hillnhütter et al., 2012), and xylem- and phloem sap flow imaging in stems, roots and fruits (Scheenen et al., 2002, Windt et al., 2009). For a more comprehensive overview see Borisjuk et al (Borisjuk et al., 2012). In the plant sciences an important challenge is to measure sap flow without damaging or affecting the plant. Xylem- and phloem sap flows are forbiddingly difficult – ––to study because of their extreme sensitivity to invasive experimentation (Knoblauch et al., 2001, Wei et al., 1999). Consequently, only little is known about the dynamics of sap flow in the intact plant. This is surprising as well as problematic, considering the pivotal role that both the xylem and phloem play in the plants’ water and carbohydrate household (Tyree et al., 1991, van Bel, 2003). NMR has become a well proven method to fill this methodological gap, yet is still far away from becoming a standard research tool in botany. The most important factors preventing this are the costs, size and complexity of the machinery. Much of that is due to the magnet that is at the heart of every scanner. Most current magnets that could be suitable for plants are of the superconducting, tube shaped type. To be able to handle an intact plant the bore of the magnet then needs to be wider than the shoot or crown, and if the plant is not long enough, wider than the pot as well. Large superconducting magnets are not only expensive to buy, but also to run and 1