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Abstract
For photosynthesizing plants, studies on the effect of different levels of Nitrogen on chlorophyll could let us know about the overall physiological status of the plant under different environmental conditions. Objective of our study was to understand if there was any difference among the ten recombinant inbred lines (RILs) of IBM population and their parents B73 and Mo17 for chlorophyll content and dry matter accumulation in their response to the N stress. Five IBM genotypes that carry predominantly B73 alleles and five IBM genotypes that carry Mo17 alleles at 5 quantitative trait loci (QTL) regions associated with root traits and N use efficiency from the published Maize Genome Database were evaluated in this study along with their parents. Plants were grown in the Guterman Green House (Cornell University, USA). Two nitrogen treatments (solution with high N contained 65.79 g Ca (NO3)2 4H2O in 100L of 1X solution making 5.0mM NO3 and solution with low N contained 2.63 g Ca (NO3)2 4H2O in 100L of 1X solution making 0.2 mM NO3) were given. Plant traits like leaf dry weight, stalk dry weight and root dry weight were observed. Chlorophyll content was estimated to measure the effect of different N levels on photosynthetic activity. Genotype with high in B73 composition had relative advantage over Mo17 in chlorophyll content, and dry weight of roots under low N condition. The highest root-shoot ratio under low and high N was observed in IBM056 and IBM153 respectively. Except for IBM153 and IBM337, all other genotypes showed reduced LFS at high N. The result showing lower root-shoot ratio and leaf fraction of shoot (LFS) under the high N treatment suggests that shoot growth increases more than root growth in response to increased N application and that within the shoot, stem growth increases more than leaf growth. Results support the conclusion that under low N condition, shoot growth is retarded than root growth. Keywords: Nitrogen, Maize, Chlorophyll, Dry matter accumulation, Photosynthesis.
Highlights
Nitrogen supply has substantial effects on plant growth and development, as it is one of the main constituents of leaf cell components, those associated with the photosynthetic apparatus, including carboxylating enzymes and membranes proteins (Pandey et al, 2000)
Five IBM genotypes that carry predominantly B73 alleles and five IBM genotypes that carry Mo17 alleles at 5 quantitative trait loci (QTL) regions associated with root traits and N use efficiency from the published Maize Genome Database were evaluated in this study along with their parents
Under low N conditions, IBM recombinant inbred lines (RILs) with high Mo17 at the target QTL regions had higher root-shoot ratio and leaf fraction of shoot (LFS) than the high-B73 RILs (Table 5)
Summary
Nitrogen supply has substantial effects on plant growth and development, as it is one of the main constituents of leaf cell components, those associated with the photosynthetic apparatus, including carboxylating enzymes and membranes proteins (Pandey et al, 2000). Research is carried out to identify some of the components responsible for the physiological control of the „stay-green‟ phenotype in relation to NUE In both sorghum and maize, delayed leaf senescence allowed photosynthetic activity to be prolonged, which had a positive effect on the N uptake capacity of the plant. In sorghum this enabled the plant to assimilate more carbon and use more N for biomass production (Borrel et al, 2001), whilst in maize yields were higher (Ma and Dwyer, 1998; Rajcan and Tollenaar, 1999 a, b). Further investigation is required to characterize better the physiological and molecular basis of the stay-green phenotype (Verma et al, 2004) in relation to N supply, root N uptake capacity, root architecture, and leaf structure, and to determine whether such a phenotype can be beneficial when N fertilization is reduced (Borrell et al, 2000)
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