In Situ Investigation of Leaf Water Status by Portable Unilateral Nuclear Magnetic Resonance        

Abstract

A portable unilateral nuclear magnetic resonance (NMR) instrument was used to detect in field conditions the water status of leaves of herbaceous crops (Zea mays, Phaseolus vulgaris), mesophyllous trees (Populus nigra), and natural Mediterranean vegetation characterized by water-spending shrubs (Cistus incanus) and water-saving sclerophyllous trees (Quercus ilex). A good relationship was observed between NMR signal, leaf relative water content, and leaf transpiration in herbaceous leaves undergoing fast dehydration or slowly developing a drought stress. A relationship was also observed between NMR signal and water potential of Populus leaves during the development of a water stress and when leaves recovered from the stress. In the natural vegetation, the relationship between NMR signal and water status was found in Cistus, the species characterized by high transpiration rates, when measured during a drought stress period and after a rainfall. In the case of the sclerophyllous Quercus, the NMR signal, the relative water content, and the transpiration rate did not change at different leaf water status, possibly because a large amount of water is compartmentalized in cellular structures and macromolecules. The good association between NMR signal and relative water content was lost in leaves exposed for 24 h to dehydration or to an osmotic stress caused by polyethylene glycol feeding. At this time, the transverse relaxation time became longer than in leaves maintained under optimal water conditions, and two indicators of membrane damage, the ion leakage and the emission of products of membrane lipoxygenation [(Z)-3-hexenal, (Z)-3-hexenol, and (E)-2-hexenol], increased. These results taken all together give information on the physiological state of a leaf under a developing stress and show the usefulness of the NMR instrumentation for screening vegetation health and fitness in natural and cultivated conditions. It is concluded that the portable unilateral NMR instrument may be usefully employed in field conditions to monitor nondestructively the water status of plants and to assist agricultural practices, such as irrigation scheduling, to minimize stomatal closure and the consequent limitation to plant production.

Leaf Development Monitoring and Early Detection of Water Deficiency by Low Field Nuclear Magnetic Resonance Relaxation in Nicotiana tabacum Plants

“…Furthermore, a unilateral instrument operating at a low magnetic field enables non-destructive NMR measurements. Using that tool, Capitani et al measured a decrease in the mean T 2 of the leaf with the decrease in leaf relative water content of different species directly in the field [37].…”

“…NMR relaxation is thus a powerful tool to monitor changes in water relations inside the leaf caused by development or different stress as Nitrogen deficiency [35] or thermal stress [36]. Only a few studies have focused on the impact of water stress on the NMR relaxation signal of the leaf [37,38]. Nagarajan et al demonstrated that the mean NMR relaxation time of the leaf was longer in drought tolerant wheat varieties [31].…”

Structural Changes in Senescing Oilseed Rape Leaves at Tissue and Subcellular Levels Monitored by Nuclear Magnetic Resonance Relaxometry through Water Status

“…Finally, in the study of Maheswari et al (1999), the CPMG decay curve was acquired over 250 ms, which was not long enough for reliable fitting of the curve, since the baseline was not reached (last point , 1.4 3 T 2-max ). On the other hand, Capitani et al (2009) investigated the leaves of several species using a portable unilateral NMR apparatus (18.153 MHz) characterized by an inhomogenous magnetic field that did not allow measurement of the FID signal and produced shortening of the T2 values measured. Relaxation decays in the unstressed leaves were described by two or three exponential decays with T2 values of up to 40 ms.…”

“…Qiao et al (2005) attempted to associate NMR signal components with different chive (Allium schoenoprasum) cells using combined transverse relaxation and restricted diffusion measurements. Finally, Capitani et al (2009) recently used a portable unilateral NMR instrument to detect the water status of leaves of herbaceous crops, mesophyllous trees, and natural Mediterranean vegetation under field conditions. Further investigations are necessary to improve leaf characterization by NMR, especially in the attribution of NMR signal components to the tissue and subcellular compartments.…”

Influence of salicylic acid on the growth of lettuce (<i>Lactuca sativa</i> var longifolia) during reduced leaf water potential

“…Exogenous application of SA boosted the relative water content of water stressed plants. SA treatment has been reported to be able to enhance the maintenance of high relative water content of stressed plants compared to the ones without SA (Capitani et al, 2009). In a contrast report by Sanchez-Blanco et al, (2004), the relative water content of Zea mays during water stress was not altered.…”