g., Sellers et al. 1997; Hubbard et al. 2001; Tardieu 2003; Buckley 2005). Even mild water deficits, when relative water content remains above 70%, primarily cause limitation to carbon dioxide uptake because of stomatal closure. With greater water deficits, direct inhibition BGB324 ic50 of photosynthesis occurs (Gupta and Berkowitz 1988; Smirnoff 1993). Phloem is responsible for the transport of photosynthates such as

sucrose from leaves to the rest of the plant. If unloading is inhibited photosynthesis will be decreased. Therefore, there is a strong interrelationship between photosynthesis activity/CO2 assimilation, plant water status, and xylem and phloem transport/hydraulic conductance (Daudet et al. 2002). Although these principles are now well known, the dynamics of the interrelationship and integration between these processes on plant level is still lacking. What we need is to be able to measure in intact plants phloem and xylem flow in relation to water content in the surrounding tissues (the storage pools), under normal

and under water limiting or even stress conditions see more (e.g., drought or as a function of phloem loading/unloading mechanisms due to e.g., anoxia), in relation to photosynthesis activity. MRI methods and dedicated hardware have been presented to measure xylem and phloem water transport in relation to water content in different storage tissues (bark, cambial zone, xylem, and parenchyma) non-invasively in the stem of intact plants

(Van As 2007; Van As and Windt 2008). In addition, portable NMR (non-spatially resolved) is becoming available for RVX-208 water content measurements in leaves (Capitani et al. 2009). These NMR and MRI methods can be combined with measurements of photosynthesis activity, e.g., monitoring by PAM techniques. In this review, we introduce these NMR and MRI methods and discuss them in relation to spatial and temporal resolution and (sub)cellular water content. Imaging principles and partial volume effects In a homogeneous main magnetic field B 0, equal spins (e.g., protons of the water molecules) have identical Larmor precession frequency, and a single resonance line in the frequency spectrum is observed at $$ \nu_0 = (\gamma/2\pi )B_0 $$ (1) γ is the gyromagnetic ratio that is a characteristic property for each type of spin bearing nuclei. For mobile (liquid) molecules the resonance line is Lorenzian shaped with a width at half maximum inversely proportional to the T 2, the spin–spin or transverse relaxation time.