From Agronomy to Molecular Genetics and Proteomics in an Effort to Improve Nitrogen Use Efficiency in Crops - Crop Improvement: New Approaches and Modern Techniques - page 350

Crop Management Practices and Source-sink
Relationships for Improving NUE
The strategies developed to work in favour of nitrogen utilization efficiency in-
cluded use of variety of fertilizers and their manner of application also avoiding
runoff and limiting the fertilizer loss from soil. Use of slow-release fertilizers and of
organic manures also minimizes N fertilizer use and their loss. The legumes crop-
ping systems have added advantage of correcting the imbalanced use and nutrient
management (Wang et al. 2012a ). Strategies that increase fertilizer N use by crop-
can also be the part of focus by increasing the fertilizer N use during the growing
season since that will decrease the N loss thus, higher NUE (Balasubramanian et al.
2004 ). Other management practices like soybean-corn rotations, forage-only pro-
duction systems, conservation tillage systems have low N losses and improved NUE
(Wen-Yuan et al. 1996 ).When differences were studied by Moll et al. 1982 among
corn hybrids after application of N before anthesis, under low N levels, observed
improved NUE. Machado et al ( 1992 ) observed that NUE status is parallel that off
water use efficiency (WUE) in corn. Another way is to distribute more of N resourc-
es to the organ of interest, such as grains. Since, the efficiency of protein synthesis is
known to be dependent on the light and dark regulation of aspargine synthase (AS)
of leaf that leads to the elevationsasparagine levels that is an important parameter
used to screen for high grain-protein cultivars of maize and rye (Dembinski et al.
1995 ). Also, by controlling the expression of the ASN 1 gene that control the ASN
levels might lead to manipulation of the relationship between Asn and seed N status
and enable another way to enhance nutritional quality which needs to be tested.
Biotechnological Inventions for Improving Nitrogen
Use Efficiency
NUE is governed by multigenes that involve huge number of genes and expand be-
yond the key steps of nitrate metabolism and incorporation. The efforts of creating
transgenic that can targets those genes which participating in N uptake, transport,
assimilation, and carbon metabolism. Manipulation of signalling and metabolic
pathway regulatory elements is emerging as an important target for biotechnologi-
cal advancements. Different transgenic experiments that were attempted in a hope
to improve NUE are summarized below and some of the significant work is listed
in Table 11.2 .
Nitrate reductase enzyme considered being the rate-limiting step of nitrate as-
similation, but its genetic manipulation in Nicotiana spp. indicated its importance
in other steps as well (Ali et al. 2007 ). The constitutive NR expression in tobacco
showed 2-fold increase in its activity while a 20 % decrease in foliar nitrate content
was observed. Also an increase in total amino acids contents, but simultaneously