Xylem transport and Physiology
A novel technique for measuring the xylem composition of transpiring plants: Development and validationavailable
Despite the undisputed importance of xylem in transporting water and solutes around the plant, the negative pressures in this tissue prevents sap collection from transpiring plants. This difficulty has restricted progress in many areas of plant physiology. This project will overcome this barrier by developing and rigorously testing a technique exploiting the xylem feeding insect Philaenus spumaris. We will use a recently developed xylem perfusion system to test the hypothesis that insect excreta composition and xylem sap composition are directly correlated by quantifying the effect of insect metabolism on extracted sap. We will then demonstrate the validity of the technique in in vivo by testing the hypothesis that concentration of xylem solutes are not regulated independently but are a passive consequence of water flux.
available
Fruits, such as tomato, have low transpiration rates and therefore solute and water influx is domianted by phloem transport. The low influx of material from the xylem can cause problems since some solutes (such as calcium, the cause of blosom end rot) are largely excluded from the phloem. The ongoing development in Birmingham of techniques to tap the major plant transport routes of phloem (using aphid styletomy) and transpiring xylem (via Philaneus spumaris) make it possible to monitor the supply and regulation of solutes and water to developing fruits In vivo.
Tomato plants will be grown in the greenhouse under a variety of nutritional (e.g. high and low Ca, K and NO3) and environmental (e.g. drought) conditions. The rate of fruit growth will be measured and correlated with changes in solute and water relations at both cell and tissue/organ level. Sampling phloem sap usign aphid stylectomy allows measurement of the inorganic (EDAX, HPLC-Dionex) and organic (HPLC, osmotic pressure) composition of the phloem. Xylem samples obtained from transpiring plants using the new Philaenus technique will be similarly analysed to provide a complete and unique picture of solute budget during fruit development.
A comprehensive knowledge of the nutrient budget of developing fruits, paticularly from transpiring plants will allow prediction to be made about nutritional and environmental manipulation of fruit quality. These will be tested by following the fate of tracers of solute transport (eg 14C, sucrose, Rb etc). The project will provide information about both the regulation of phloem and xylem composition under different environmental conditions and the mechanisms underlying regulation of fruit composition.