Water in plants

Why Do We Need to Know This Material Chapter 9 developed the concepts of chemical equilibria in gaseous systems this chapter extends those ideas to aqueous systems, which are important throughout chemistry and biology. Equilibria between acids, bases, and water in plant and animal cells are vital for the survival of individual organisms. To sustain human societies and protect our ecosystems, we also need these ideas to understand the acidity of rain, natural waters such as lakes and rivers, and municipal water supplies. 

Copper is an essential micronutrient required in the growth of both plants and animals. In humans, it helps in the production of blood haemoglobin. In plants, copper is an important component of proteins found in the enzymes that regulate the rate of many biochemical reactions in plants. Plants would not grow without the presence of these specific enzymes. Research projects show that copper promotes seed production and formation, plays an essential role in chlorophyll formation and is essential for proper enzyme activity, disease resistance and regulation of water in plants (Rehm and Schmitt, 2002). 

Packer and Rees [3] extended the work of Tanner and Stejskal by the development of a theoretical model using a log-normal size distribution function. Measurements made on two water-in-oil emulsions are used to obtain the self-diffusion coefficient, D, of the water in the droplets as well as the parameters a and D0 0. Since then, NMR has been widely used for studying the conformation and dynamics of molecules in a variety of systems, but NMR studies on emulsions are sparse. In first instance pulsed field gradient NMR was used to measure sdf-diffusion coefficients of water in plant cells (e.g. ref. [10]). In 1983 Callaghan... 

The enzyme responsible for the photolysis of water in plants is a multisubunit membrane protein (Fig. 5-22 Klein et al., 1991). Four manganese ions, probably as a tetranuclear cluster, are thought to act as a charge accumulating system and as the active site for water oxidation. Both calcium and chloride ions are also required for activity (Babcock, 1987 Ghantokakis and Yocum, 1990). The water oxidation centre (WOC) contains a total of four Mn atoms and causes the oxidative coupling of two water molecules by a currently unknown mechanism. 

The rise of a liquid in a capillary tube (e.g., rise of oil in the wick of a lamp, rise of underground water to the surface of earth) are well-known phenomenons. These can be explained in terms of surface tension. Capillary-rise phenomenon is partially responsible for the rise of water in plants and soils. 

Although Equation 2.2 refers to the height of capillary rise only in a static sense, it still has important implications concerning the movement of water in plants. To be specific, let us consider a xylem vessel having a lumen radius of 20 pm. From Equation 2.2b, we calculate that water will rise in it to the following height ... 

The role of chlorophyll in the photosynthetic reduction of C02 by water in plants is to provide a source of electrons that may continue to be supplied for a time in the dark. Electron spin resonance studies of light-irradiated chlorophyll show that radicals are formed.33 These are probably of the type (7-IV). The electrons are transmitted through chlorophyll micelles to other intermediates involved in the reduction of C02. 

In an ordinary unassociated liquid such as benzene, the molecules flow by each other by sliding around one another. In water, because of the hydrogen bonds that must be broken before any flow can occur, the motion is rolling rather than sliding. This property gives watCT a relatively low viscosity and makes the pumping of water by BU (for example, the flow of blood in the heart, the flow of water in the hydra, or the movement of water in plants) mnch less energy intensive than it could otherwise be. 

As described in Section 2.1, the xylem conduits communicate not only with each other but also with the tissues around them. A number of lateral transport systems abut against the axially arranged xylem conduits, which will not be described here. However, the possibility of a lateral movement of the xylary sap will be utilized below for the qualitative description of the transport of water in plants. 

Desiccation of plant tissues presents a shift of the water from the liquid to the vapour phase (Sun, 2002). Temperature influences evaporation, as well as the partial water vapour pressure in the air and the energy status of water in plant tissue, both in dry and hydrated plant tissue. An increase in temperature results in a decrease in the equilibrium water content at a given relative humidity (water activity) or an increase in the equilibrium water activity for a given tissue water content (Fig. 1). Water activity can be described as the effective water content, which is thermodynamically available for various physiological processes in cells. The temperature dependence of the isotherm shift is described by the Clausius-Clapeyron Equation ... 

Earlier, the importance of water in plant economics was discussed. Controlling consumption is therefore crucial and the aim is to reduce it to the strict minimum by ... 

M Tomassetti, L Campanella, M Delhni. Determination of water in plant samples A comparative thermogravimetric and NMR study on different species of seeds. Thermochim Acta 705 179-190 (1986). 

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