Ph.D Thesis

Ph.D StudentFan Ling
SubjectGrowth Regulation in Plant Roots under Water Deficit
DepartmentDepartment of Agricultural Engineering
Supervisor PROFESSOR EMERITUS Peter Neumann


Plant roots are the organs responsible for water absorption, nutrient uptake and anchorage. These functions ultimately depend on the extension growth of individual cells and roots. The physiological mechanisms that inhibit growth in primary roots of maize (Zea mays L) seedlings under water deficit (WD) were investigated.  Segmental elongation rates and changes in root tip position were recorded using time-lapse photography. Proton efflux was investigated by contacting the 1 cm long root elongation zone for 5 min with a pH indicator gel.  The pH inside growing epidermal cell walls was determined by confocal laser scanning microscopy using a ratiometric method and fluorescent pH indicator dye (DM-NERF). Fourier transform infrared spectroscopy and UV fluorescence microscopy were used to identify segmental changes induced by WD in the chemical composition of root cell walls. These investigations utilized image analysis and customized programs in Matlab. The main findings were: (1) That maintenance of growth 0 to 3 mm behind the tip in maize primary roots under WD and associated inhibition of growth further behind the tip were related to spatially variable changes in proton pumping into expanding cell walls. (2) Accelerated stelar accumulation of phenolic cross linkages between load bearing polysaccharides in the basal elongation zone may cause the localized inhibition by WD of wall extension capacity and root growth. The results were presented at 2 international conferences; one article on the work is in preparation and another was published in Plant Physiology (2004) 135:2291-2300.