Data/hora: 05/06/2024 02:11:15

Biblioteca(s): 	Embrapa Milho e Sorgo.	
Data corrente: 	02/09/1998	
Data da última atualização: 	13/07/2018	
Autoria: 	PURCINO, A. A. C.; ARELLANO, C.; ATHWAL, G. S.; HUBER, S. C.	
Afiliação: 	ANTONIO ALVARO CORSETTI PURCINO, CNPMS.	
Título: 	Nitrate effect on carbon and nitrogen assimilating enzymes of maize hybrids representing seven eras of breeding.	
Ano de publicação: 	1998	
Fonte/Imprenta: 	Maydica, Bergamo, v. 43, n. 2, p. 83-94, 1998.	
Idioma: 	Inglês	
Conteúdo: 	The objective of this study was to determine possible differences in the carbon and nitrogen metabolism of 14 maize era hybrids released since 1930. Plants fed 1.6 mM N03- had nitrate reductase activity (NRA) comparable to plants fed 16 mM N03- but did not sustain maximum NRA, and had reduced growth. Nitrate reductase (NR) and sucrose phosphate synthase (SPS) activities were not related to year of hybrid release. However, the activation states of NR under low nitrate, and of SPS under high nitrate increased up to 1970 and then leveled off. This suggests a trend towards increased efficiency for both No3- reduction in low nitrate plants, and sucrose synthesis in high nitrate plants. Chloroplastic glutamine synthetase (GS2) protein did not respond to NO3- supply and was not related to year of hybrid release. However, cytosolic glutamine synthetase (GS1) protein was higher in low nitrate plants compared to high nitrate plants. Furthermore, in low nitrate plants, GS1 protein correlated negatively to NRA indicating that its role was to remobilize N compounds Phosphoenophyruvate carboxylase (PEPC) activity responded to increased No3- supply and increased up to 1970's declining thereafter. In most hybrids, PEPC specific activity (activity mg-1 protein .s-1) was higher in the high nitrate plants. The specific activities of NR, SPS and glutamate dehydrogenase (GDH) tended to be lower in high nitrate plants, although SPS and GDH activities, expressed on a g fresh weight basis, responded to increased nitrate supply. These observations support the hypothesis that PEPC protein is preferentially increased during the estabhishment of the C4 syndrome GDH activity declined over the last 70 years in the low nitrate plants. A negative correlation was found between GDH specific activity and GS2 protein in the high nitrate plants. When trends in enzyme activity were examined over time, it was observed that from the 1930's to the 1970's breeding for increased grain yield indirectly selected plants with increased PEPC activity and more activated NR and SPS. This trend was not observed in hybrids released during the 1930's and 1990's, indicating thar increments in grain yield observed during these last two decades were not due to additional enhancements in nitrate reduction, primary carbon fixation and sucrose metabolism.	
Palavras-Chave: 	Maize; Nitrate.	
Thesagro: 	Carbono; Melhoramento; Milho; Nitrato; Nitrogênio; Zea Mays.	
Thesaurus Nal: 	breeding; carbon; metabolism; nitrogen.	
Categoria do assunto: 	S Ciências Biológicas	
Registro original: 	Embrapa Milho e Sorgo (CNPMS)	
Exemplares: 	CNPMS - (9099-1) - UPC - AP - DD -  -  -  - DIS