DEVELOPMENT AND CHARACTERIZATION OF GENETIC RESOURCES FOR AGRONOMIC AND QUALITY TRAITS USING GENOMIC TOOLS
Location: Dale Bumpers National Rice Research Center
Title: Associating rice root morphology and physiological traits with grain mineral concentrations of 24 varieties with extreme mineral compositions
Submitted to: Botanical Society of America Proceedings
Publication Type: Proceedings
Publication Acceptance Date: April 3, 2012
Publication Date: July 7, 2012
Citation: Ratnaprabha, Pinson, S.R., Tarpley, L. 2012. Associating rice root morphology and physiological traits with grain mineral concentrations of 24 varieties with extreme mineral compositions. Botanical Society of America Proceedings. 1.
The first step towards mineral accumulation in plant seeds is the absorption/uptake of minerals from the soil by roots. Root physiological activities, such as root respiration and metabolism, modify physical (soil temperature), chemical (soil pH, redox potential, root exudates, allelochemicals, and soil nutrient concentrations) and biological (microbial associations) properties of the rhizosphere, which greatly impact the availability, solubility and mobility of minerals in the soil. Root morphology, including length, area, and exploited volume, influences mineral absorption/uptake from soil into the roots. The main goal of the research was to evaluate root physiological processes and morphological differences and their bases for identifying genes that control mineral accumulation patterns of rice grains. In 2007 and 2008, preliminary field trials in both flooded and unflooded conditions identified varieties with widely varying levels of minerals in rice grains. Our hypothesis was that, with respect to some minerals, these varieties exhibit different root morphology and physiology attributes that in turn result in different rice grain mineral concentrations. The objectives of this study were to 1) quantify and compare root morphology and physiology characteristics of 24 varieties selected for extreme grain mineral concentrations including US standard variety Lemont, and 2) identify distinct root traits and investigate their relations to concentrations of specific minerals in grains. Six replications of 24 varieties were grown in hydroponic medium in a growth chamber until 4 weeks. At harvest, roots were thoroughly washed, scanned and the root morphological traits calculated using WinRhizo Pro software (Regent Instruments, Canada). Root respiration was measured spectrophotometrically by treating roots with naphthylamine and quantifying naphthylamine oxidation. Across the 24 varieties, distinct relationships of individual root morphological and physiological traits with pre-determined grain mineral concentrations were not found, suggesting that the root control of concentrations of some minerals might be due to active uptake mechanisms. Principal component analysis was then performed for variable reduction. Shoot traits such as shoot height, leaf area and shoot biomass were large contributors to the first component, whereas soil solution traits such as pH and redox largely defined the second component, and average diameter of the individual roots the third component. Future study will be conducted on F2 progenies for segregation of ionomic characteristics and for association of root traits and their components with ionomic characteristics as bases to identify DNA markers and genes.