Exploring The Dynamic Distribution Of Water And Water Soluble Carbohydrates During Grain Filling In Wheat By Nuclear Magnetic Resonance

Both the wheat canopy temperature characteristics that was revealed in 30 years and the phenomenon of Inverse Leaf Aging Sequence(ILAS)that was reported recently are found in relation with wheat yield.It highlights the importance of the activity of water long-distance transport and water soluble carbohydrates(WSCs)translocation for grain filling.This thesis employed multiple nuclear magnetic resonance(NMR)schemes to estimate water content,leaf physiology and stem WSCs in wheat by a non-invasive and non-destructive way.The synergistic development of leaves and stem in living plants with different canopy temperature traits at grain-filling stage were presented.The role change as photo-assimilate source center from flag leaf to penultimate leaf and corresponding activation of stem WSCs storage pool were also investigated.These findings broaden the wheat grain filling theory and give a theoretic basis for wheat breeding.The main results include:1.NMR T2 relaxivity can be used to analyze the water status of wheat in a quick,precise,non-invasive and non-destructive way.The amplitude of T2 relaxation spectrum in wheat leaves,stems and kernels is very significantly correlated with water content.It appears multiple compoents in the T2 relaxation spectrum of each kind of wheat organ.Wheat stem presents clearly-seperated peaks in T2 relaxation spectrum.The two main components can be denoted by T2,s and T2,1 component,respectively.It was suggested that these two components is related to parenchyma and vascular tissues.While the T2,s component derives from parenchyma,the T2,1 component originated from both parenchyma and vascular water.2.The T2 relaxation spectrum of wheat leaf is related to its physiology.The degree of leaf senescence can be evaluated by NMR T2 relaxivity,T1 weighted imaging or T2 weighted imaging.From the beginning of senescence to the degradation stage,the average T2 relaxation time(T2,mean)gradually increases.When leaf approaches the death stage,both the amplitude and the average T2 relaxation time reaches its minimum value.The two magnetic resonance imaging(MRI)methods directly present the physiological status of leaf.At the beginning of senescence,the signal intensity of leaf T1 weighted image decreases.But the signal intemsity of leaf in T2 weighted image increases on the contrary.During the degradation stage,both T1 weighted image and T2 weighted image lose its intensity.At the death stage,leaf does not give any signal in T2 weighted imaging.3.It is difficult to precisely quantify WSCs content in wheat stem by using T2,mean since WSCs content varies significantly between different wheat cultivars.However,dynamics in WSCs content in a specific wheat cultivar can be shown qualitatively since the relative WSCs content is negatively correlated with T2,mean.Therefore,T2 relaxivity can be used in monitoring the variation of stem WSCs content in a living wheat seedling.4.Membrane permeability of the roots of hydroponically cultured plant can be quantified by integrating several NMR methods.By using two dimensional D-T2 correlation spectrum,Plasma membrane permeability can be estimated according to diffusion model.In addition,T2 relaxivity or T2 mapping can obtain T2 relaxation time of vacuolar water in root cells,which is related to tonoplast membrane permeability.5.The temperature of wheat canopy is an indirect criterion for transpiration activity and is related to yield and drought tolerance.Relationship of water transport,leaf functional period and stem WSCs storage were explored by NMR methods.The wheat cultivar with low canopy temperature,namely the cold-type wheat,is characterized by high transpiration rate,comparatively long leaf period and large WSCs storage.These traits ensure the cold-type wheat a high photosynthesis activity and a high rate in photoassimilate unloading in leaves and a large quantity of WSCs in stem for remobilizing to kernels.6.ILAS phenotype appears in a certain proportion in some wheat cultivars with low canopy temperature.ILAS wheat was reported with high yield comparing to traditional cold-type wheat.Water status and WSCs content in flag leaf,penultimate leaf,peduncle and penultimate internode were analyzed by NMR methods and physiological measurements.ILAS wheat was found with high photo-assimilates content in leaves and stem.In addition,activation of stem WSCs storage for translocation in ILAS wheat was comparatively late.It can be concluded that the integral functional period of top two leaves in ILAS wheat is much longer,even though the flag leaf appeared an early senescing.These discoveries verify the hypothesis that ILAS wheat develops in a unique grain-filling style,namely ’relay’ grain filling,which is specified by a high flux rate in a long period.