Bryan J. King

Glutamine synthetase genes are regulated by ammonia provided externally or by symbiotic nitrogen fixation.

Glutamine synthetase is the key enzyme in the assimilation by plants of reduced nitrogen provided from either the soil or fixed symbiotically in association with Rhizobium. We have isolated a number of cDNA clones for soybean glutamine synthetase (GS) from a nodule‐cDNA library, using RNA from polysomes immunoprecipitated by GS antibodies. Transcripts corresponding to two clones differing in their 3′ non‐translated sequences were present in both root and nodule tissue; however, the concentration in the nodules was several times higher. The relative concentrations of these sequences in both tissues is about 9:1. Availability of ammonium ions [provided as NH4NO3 or (NH4)2SO4] enhanced the expression of both sequences in root tissue within 2 h, reaching a level similar to that in nodules by 8 h, while KNO3 had no effect during this period. When nitrogen fixation was prevented by replacing nitrogen with argon in the root environment or when the nodules were formed by a Fix‐ mutant of Bradyrhizobium japonicum, the amounts of GS mRNA did not increase over that in roots. These experiments, together with the time course of increase in GS mRNA transcripts, suggest that the genes encoding cytosolic GS are directly induced by the available ammonia.

A Multichannel System for Steady–State and Continuous Measurements of Gas Exchanges from Legume Roots and Nodules

Detailed studies of the exchanges of gases between plant tissues and their environment have provided invaluable information in investigations of plant function. Measurement of gas exchange is one of the few methods available to plant scientists which permits an assessment of biological activity in undisturbed, intact plant tissue. In this review we describe a multichannel, computer–controlled gas exchange system which has been designed for studies of steady–state and nonsteady–state rates of respiration, photosynthesis and nitrogenase activity in nodulated legumes. Methods are also discussed for the use of this system and a brief review is presented of results which have been obtained to date in studies of both assimilate partitioning in plants (Walsh and Layzell 1986, Vessey and Layzell 1987) and the regulation of N2 fixation and O2 diffusion into legume nodules (Layzell et al. 1984a; Pankhurst and Layzell, 1984, Hunt et al. 1987; Walsh et al. 1987; Lin et al. 1988; Vessey et al. 1988a, b).

Inexpensive, Computer-Automated HPLC for Ion Exchange Separation and Quantification of Amino Acids in Physiological Fluids

Abstract An inexpensive, computer-automated HPLC for separation and quantification of amino acids in physiological fluids is described. The system offers fully automated equipment control, data collection, processing and storage capabilities. The component nature of the system and the software flexibility permit extensive system modification, accomodating a wide variety of different separatory procedures which are not possible with many dedicated amino acid analysers. The system uses a lithium-based ion exchange column with post-column o-phthalaldehyde derivatization. A time of 128 minutes, including column regeneration, is required for separation of all amino acids through to arginine. The advantages of post-column derivatization over pre-column derivatization methods for post-separatory amino acid techniques are discussed. Accurate quantification of radiolabel in amino acids is demonstrated.