Submitted to: Advanced Plant Biochemistry
Publication Type: Book / Chapter
Publication Acceptance Date: June 27, 1996
Publication Date: N/A
Technical Abstract: Striking progress has been made in the isolation and characterization of the genes involved in primary assimilation of N in plants. Antibodies have been prepared and both cDNAs and genomic clones have been isolated for NR, NiR, GS, AS, AAT, GOGAT, and PEPC. The expression of many of the genes involved in the primary assimilation of N is closely associated with C metabolism. In fact NiR, GS, AAT, and GOGAT have plastid forms that are essential for N metabolism. Light is also integrally involved in regulating the expression of many genes of N assimilation as evidenced by its positive effect on NR and NiR and its negative effect on AS. Because there is little information on the signal transduction pathway in activation of the genes involved in primary N assimilation, this field will be a central target for future research. Additionally, direct genetic manipulation of N assimilation by over and/or under expression of enzyme activity through sense and antisense technology will show whether plant N metabolism and quality can be improved. Fundamental progress has also been made in the molecular genetics of N2 fixation for both free living and symbiotic systems. The signal transduction mechanisms involved in symbiotic N2 fixation have been identified and offer a model paradigm for plant microbe interactions. Future research will focus on whether similar signals are involved in other systems and whether these signals can be used to improve root nodulation. Many plant mutants altered in N2 fixation and nodulation have been identified and characterized at the structural and biochemical levels. However, no plant genes controlling these processes have been identified; future studies will pursue this exciting field.