Applications of radiotracer in plant biology

Abstract

A radioactive tracer (radiotracer) is generally defined as a radioactive isotope that is used as a tracer, which can be followed or tracked within a system of interest. The use of radiotracers involves the substitution of a radioactive isotope for one of the naturally occurring isotopes of a particular element. Radiotracers have a wide range of application due to two unique features: a high level of detection sensitivity, and an ability to integrate into living systems. These features make the use of radiotracers particularly useful for studying the dynamic processes that comprise metabolic activity. This work focuses on the use of radiotracers to identify and follow specific biological pathways to facilitate our understanding of plant biology. All of the plants used in this work are Arabidopsis thaliana plants (wild type, col-0 and its different mutants). Plants are the most common living organisms on earth and have critical roles for the global environment, including human societies. Plants are able to reduce the problem of pollutions, such as uptake contaminants from soils and waters. Also, plants are the basic food producers for other living organisms, which are not only the ones above ground, but also below ground in the rhizosphere (microorganisms). Therefore, if the plant systems are disturbed, it could affect the ecosystem dramatically. In this dissertation, we are trying to use radiotracers to explore the mechanisms of the basic physiology and metabolisms in plants. In Chapter 2, heavy metal uptake and accumulation in one of the Arabidopsis mutant, opt3-2 mutant, was investigated in order to understand the possible mechanisms of phytoremediation. The results showed that the opt3-2 mutant plants accumulate Pb2+ in both influorescence stems and rosette leaves compared to the wild type (WT). In addition, the results from the radioactive 203Pb uptake assays indicated that the heavy metal accumulation phenotype in the opt3-2 mutant plants is not due to a kinetic rapid uptake, but to a long-term regulation. In Chapter 3, the carbon metabolism and translocation in Arabidopsis plants were investigated using both 12C and 11C methods to explore the dynamics of carbon flux in plants, as well as diurnal effects on carbon flux. Three starch mutants (sex1-1, adg1-1 and pgm-1) and the WT Arabidopsis were used in this study. The results showed that starch regulation is essential not only for plant growth, but also affects sugar metabolism (fructose, glucose and sucrose), carbon allocation to plant roots, and root exudation. In Chapter 4, the relationship between Fe status and carbon metabolism was discussed. Both 12C and 11C methods were used in this study to investigate the carbon metabolism and translocation in Arabidopsis plants. Two iron-transport mutants (opt3-2 and irt1-1 mutants) and the WT Arabidopsis were used for this study. The results showed that the Fe status in plants affects the carbon fixation ability in plant leaves, and also alters carbon partitioning (possibly through the production of more organic acids under Fe deficient stress), carbon allocation, and root exudation in plants. Diurnal effects on carbon metabolism and allocation were observed in this study, as well.