Two seasons’ study on nifH gene expression and nitrogen fixation by diazotrophic endophytes in sugarcane (Saccharum spp. hybrids): expression of nifH genes similar to those of rhizobia

Abstract

To explore the presence and expression of the nifH gene of diazotrophic endophytes in sugarcane (Saccharum spp. hybrids) cv. NiF8, we conducted pot experiments for two seasons in a glasshouse from 10 June to 17 September (high temperature and long days) in 2005 and 1 September to 9 December (low temperature and short days) in 2006. The expression of nifH genes in the stems and roots of sugarcane plants at 50 (or 59) and 100 days after transplanting was investigated by reverse transcription (RT)-PCR and by examining the nifH nucleotide sequence diversity. N 2 fixation was assessed by the 15 N-dilution method. The nifH RNA sequences in the stems and roots of the first experiment were similar to those of Bradyrhizobium sp. and Azorhizobium caulinodans. In the second experiment, nifH expression from these bacteria was not detected in the stems. nifH gene expression in the stems was in accordance with 18-24% N derived from air in the high-temperature season and negligible in the low-temperature season. Both the proliferation of N 2 fixers and expression of the nifH gene indicated that bacteria similar to rhizobia may contribute to N 2 fixation in sugarcane under our experimental conditions.

Diversity of Nitrogen-Fixing Bacteria Associated with Switchgrass in the Native Tallgrass Prairie of Northern Oklahoma

“…strain BTAi 1, affiliated with phylotype 1, is a photosynthetic rhizobium that also can fix nitrogen under free-living conditions (8,48). Bradyrhizobium species have been found as endophytes in rice (49) and sugarcane (15,50). Despite the abundance of Bradyrhizobium bacteria associated with switchgrass, however, the paucity of Bradyrhizobium-like nifH sequences derived from root RNA suggests that these bacteria fix little or no nitrogen in association with native switchgrass.…”

Ecosystem Fertility: A new paradigm for nutrient availability to plants in the humid tropics

“…Nutrient cycling among neighboring plants via roots to roots is also an effective manner of quick nutrient capture by nutrient-deficient plants, such as N transfer from legumes to non-legumes (Chalk et al 1996). N fixation by Symbionts and endophytes (Thaweenut et al 2011) Figure 2 The Ecosystem Fertility scheme for humid tropical ecosystems. may contribute significantly as direct N sources of fixed N (amino acids) to plants.…”

Challenges, Opportunities and Recent Advances in Sugarcane Breeding

“…Sustainable production systems necessarily involve low demands of inorganic nitrogen. Interestingly, sugarcane is able to establish a mutualistic symbiosis with diazotrophic endophytes that reside in xylem cells (especially the bacteria Glucoacetobacter diazotrophicus; Cavalcante & Dobereiner, 1988) and in the rhizosphere (such as bacteria of the genera Azotobacter, Azospirillum, Beijerinckia, Derxia, Enterobacter, and Erwinia) (Thaweenut et al, 2011), which partially supply the plant's requirement of nitrogen, and contributes to minimize nitrogen fertilizer applications, at least under Brazilian conditions (Giller, 2001). Recently, G. diazotrophicus had its complete genome sequenced (Bertalan et al, 2009), which will help to understand the symbiotic interaction between this prokaryote and sugarcane at the genetic and molecular levels with perspectives of increasing symbiotic nitrogen supply to sugarcane plants.…”