Abstract
This Thesis describes the application of a nondestructive pulsed proton NMR method mainly to measure water transport in the xylem vessels of plant stems and in some model systems. The results are equally well applicable to liquid flow in other biological objects than plants, e.g. flow of blood and other body fluids in human and animals (Chapter 8). The method is based on a pulse sequence of equidistant πpulses in combination with a linear magnetic field gradient G.Following a general introduction and a survey of the properties of water in plants (Chapters 1 and 2), the basic NMR theory as well as reviews on the application of pulsed NMR to the determination of flow, diffusion and water content are presented in chapter 3.A mathematical treatment has produced analytical expressions for the shape of the signal S(t), based on a model in which the flowing fluid is thought to receive a ½πτ(πτ) _{n} pulse train: a ½πpulse upon entering the r.f. coil followed by a sequence of equidistant πpulses until the fluid leaves the coil; simultaneously, this movement. of the fluid along a magnetic field gradient applied in the direction of flow produces a phase shift of the nuclear magnetization with respect to the rotating frame of reference (Chapter 4). Although this model does not lead to perfect agreement between the experimental and theoretical signal shape S(t), it correctly predicts the effects of experimental parameters on S(t) via analytical expressions. The main results from this theoretical treatment in combination with computer simulations, which have been experimentally verified in glass capillary systems, are:
 as long as T _{2≥} ½T _{1} , the mean linear flow velocity v can be found from the time t _{max} at which a maximum appears in the signal shape: v=C/t _{max} , where C is a calibration constant, depending on G, τand the flow profile. If T _{2} <½T _{1} v can only be reliably determined when both T _{1} and T _{2} of the flowing fluid are known.
 T _{2} and the amount of flowing water in the coil V, and consequently the volume flowrate Q, can be determined from the height of the maximum S(t _{max} ) and t _{max} . Depending on the value of T _{2} and the value of the ratio T _{1} /T _{2} , T _{2} and V are found from a semilog plot of either S(t _{max} ) vs. t _{max} (T _{1} >>T _{2} ) or ∂[S(t _{max} ) . t _{max} ]/∂t _{max} vs. t _{max} (T _{1≈} T _{2} ).Based on flow measurements in plant stem segments (Chapter 5) it has been suggested that T _{2} strongly depends on the vessel diameter for the narrow xylem capillaries. This behaviour of T _{2} can explain negative results in plant stems with small vessel diameter. Under the present experimental conditions the method has been successfully applied to Cucurbitaceae (cucumber, gherkin, pumpkin) and tomato plants.T _{2} measurements in wheat leaves have been shown to be insensitive to the presence of cellbound paramagnetic ions (Chapter 7). The magnitude of T _{2} of two separate water fractions (covering 90% of the total water content) has been found to be inversely proportional to water content. Measurements of flow and water content have been combined for an intact gherkin plant (Chapter 5), demonstrating that the combination of both NMR methods results in a powerful noninvasive method to study important parts of the plant water balance simultaneously. The results strongly suggest that the method can be used as an early warning for development of stress phenomena in plants, due to drought and other factors. From the flow measurements it has been shown how in a plant system the values of T _{2} and T _{1} of the water in the xylem vessels can be determined and estimated, respectively.A comparison between the results obtained with NMR, heat pulse and weight balance flow measurements is presented in Chapter 6. A linear relationship between the linear flow velocity obtained by NMR and the volume flowrate determined by the balance method yields an effective crosssectional area available for flow of ~50% of the crosssectional area of the xylem vessels measured by using a microscope. NMR measurements alone yield a slightly lower value of the effective crosssectional area. Compared with the NMR method, the heat pulse method monitors only relative changes in the flow velocity. A plot of the flow velocity obtained by the heat pulse method versus the volume flowrate obtained by the balance method exhibits some unwanted experimental scatter.Chapter 8 suggests some applications of the pulsed NMR flow method, also to other systems than plants, and defines important instrumental requirements for these applications.
 as long as T _{2≥} ½T _{1} , the mean linear flow velocity v can be found from the time t _{max} at which a maximum appears in the signal shape: v=C/t _{max} , where C is a calibration constant, depending on G, τand the flow profile. If T _{2} <½T _{1} v can only be reliably determined when both T _{1} and T _{2} of the flowing fluid are known.
 T _{2} and the amount of flowing water in the coil V, and consequently the volume flowrate Q, can be determined from the height of the maximum S(t _{max} ) and t _{max} . Depending on the value of T _{2} and the value of the ratio T _{1} /T _{2} , T _{2} and V are found from a semilog plot of either S(t _{max} ) vs. t _{max} (T _{1} >>T _{2} ) or ∂[S(t _{max} ) . t _{max} ]/∂t _{max} vs. t _{max} (T _{1≈} T _{2} ).Based on flow measurements in plant stem segments (Chapter 5) it has been suggested that T _{2} strongly depends on the vessel diameter for the narrow xylem capillaries. This behaviour of T _{2} can explain negative results in plant stems with small vessel diameter. Under the present experimental conditions the method has been successfully applied to Cucurbitaceae (cucumber, gherkin, pumpkin) and tomato plants.T _{2} measurements in wheat leaves have been shown to be insensitive to the presence of cellbound paramagnetic ions (Chapter 7). The magnitude of T _{2} of two separate water fractions (covering 90% of the total water content) has been found to be inversely proportional to water content. Measurements of flow and water content have been combined for an intact gherkin plant (Chapter 5), demonstrating that the combination of both NMR methods results in a powerful noninvasive method to study important parts of the plant water balance simultaneously. The results strongly suggest that the method can be used as an early warning for development of stress phenomena in plants, due to drought and other factors. From the flow measurements it has been shown how in a plant system the values of T _{2} and T _{1} of the water in the xylem vessels can be determined and estimated, respectively.A comparison between the results obtained with NMR, heat pulse and weight balance flow measurements is presented in Chapter 6. A linear relationship between the linear flow velocity obtained by NMR and the volume flowrate determined by the balance method yields an effective crosssectional area available for flow of ~50% of the crosssectional area of the xylem vessels measured by using a microscope. NMR measurements alone yield a slightly lower value of the effective crosssectional area. Compared with the NMR method, the heat pulse method monitors only relative changes in the flow velocity. A plot of the flow velocity obtained by the heat pulse method versus the volume flowrate obtained by the balance method exhibits some unwanted experimental scatter.Chapter 8 suggests some applications of the pulsed NMR flow method, also to other systems than plants, and defines important instrumental requirements for these applications.
Original language  English 

Qualification  Doctor of Philosophy 
Awarding Institution  
Supervisors/Advisors 

Award date  31 Mar 1982 
Place of Publication  Wageningen 
Publisher  
Publication status  Published  31 Mar 1982 
Keywords
 liquids
 circulation
 sap flow
 absorption
 emission
 nuclear magnetic resonance
 measurement
 estimation
 recording
 data collection
 hydrodynamics
 fluids