J. D. Goeschl

An integrated tracer kinetics system for studying carbon uptake and allocation in plants using continuously produced11CO2

SummaryAn integrated approach to study the effects of environmental factors on plants is described. The central theme of the system is the use of CO2 labelled with11C supplied continuously to the plant and following the emitted radiation in vivo in the leaf, the phloem and the various sinks. The system consists of six components and with minor changes can be used for other tracers such as13N for nitrogen fixation studies. Because of the short half life of the isotope, several experiments can be carried out on the same plant under the same environmental conditions without disturbing the plant. A host of ecologically, agriculturally and genetically important questions can be answered using this technique.

Continuously produced, high specific activity 11C for studies of photosynthesis, transport and metabolism

Abstract A continuous supply of high specific activity 11CO2 was produced for studies of photosynthesis, transport, metabolic utilization, and storage in plants. The reaction 12C(p,d) 11C from a 35 MeV proton beam on a 300 cm3 gaseous 12CO2 target yielded 7.7 × 105 atoms/μA/sec in a flow of 1 cm3/sec, and yielded 2.1 × 10911C atoms/μA/sec from a dry ice target. The resultant 11CO was purified (in air), then oxidized to 11CO2, and 12CO2 was added in known amounts to produce the mixture air/12CO2/11CO2 of known concentration and specific activity. By analyzing pulse-fronts and steady-state labelling levels in an individual plant it is possible to extract considerably more information about uptake rates, product pool sizes and turnover rates, transport velocities and concentrations, metabolic sink strengths, and other parameters, than would be attainable by pulse methods alone. The high yields of 11C and potentially of 13N by these and related methods would also be of use in radiopharmaceuticals and biomedical tracers.

A time-dependent mathematical expression of the münch hypothesis of phloem transport

Abstract A time-dependent mathematical expression of the Munch, osmotically driven mass flow hypothesis of phloem transport is presented. The dependent variables include concentration of solutes, pressure, velocity of phloem sap, osmotic flux of water, and concentration dependent unloading of solutes. The model meets conservation requirements during all iterations, and responds realistically to changes in independent variables. Given the same set of independent variables the time-dependent model converges to the same values as the closed-form steady-state model of Goeschl et al. (1976) regardless of the initial conditions.

Short-lived isotope kinetics: a window to the inside

An integrated approach to studying the effects of environmental factors on plants is described. The central theme of the system is the use of CO2 labelled with 11C supplied continuously to the plant and following the emitted radiation in vivo in the leaf, the phloem, and the various sinks. The system consists of six components and with minor changes can be used with other tracers such as 13N for nitrogen fixation studies. Because of the short half-life of the isotope, several experiments can be carried out on the same plant under the same environmental conditions without disturbing the plant. When this system is coupled with mathematical models of phloem transport and carbon allocation a host of ecologically, agriculturally, and genetically important questions can be answered (redundent). Carbon assimilation and allocation patterns in plant leaves were measured using this system. The concepts and analytical techniques of tracer kinetics of extended square wave (ESW) input of 11CO2 were used in calculating the parameters of carbon allocation dynamics in plant systems under different physiological conditions. Examples of the latter include (1) recovery from mechanical agitation, (2) diurnal patterns, and (3) effects of drought stress.

Measurement of carbon fixation and allocation using (super 11) C-labeled carbon dioxide.

This paper describes the use of continuously produced and applied /sup 11/C in measurements of carbon dioxide assimilation and C movement in plant research. This technique differs from the pulsing type /sup 11/C research underway in other laboratories by being continuous and on-line with computer analysis making steady-state measurements of carbon fixation and movement possible. The studies to be described here make clear the advantages of using continuously produced and applied short half-lived isotopes.

USE OF SHORT-LIVED ISOTOPES IN THE STUDY OF XENOBIOTIC TRANSPORT

Abstract The application of short-lived isotopes (11C) in studying the dynamics of carbon allocation in plants using an integrated tracer kinetics system is described. The analogy of the transolcation of xenobiotics (herbicides) labelled with 32P in vivo , to that of assimilates, is illustrated in a preliminary experiment. The information obtained concerning the dynamics of herbicide translocation could be immense, when the general transport patterns of the plant are known from the 11C studies.

A System for Dynamic Analysis in Biological Systems with Carbon-11

An integrated approach to the study of effects of environmental factors on plants is described The system relies on the continuous labelling and measurement of naturally occurring tracer activity as it courses through the plant These features allow the investigation of the magnitude of the photosynthate distribution, the transport times of photosynthates, and the dynamic response of the distribution to environmental factors A host of ecologically, agriculturally and genetically important questions can be answered with this technique, including the consequences of increased CO2 concentration in the atmosphere, and other environmental effects.