Tsukuba, Japan
Tsukuba, Japan
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Tesfamariam T.,Crop | Yoshinaga H.,Crop | Deshpande S.P.,Indian International Crops Research Institute for the Semi Arid Tropics | Srinivasa Rao P.,Indian International Crops Research Institute for the Semi Arid Tropics | And 5 more authors.
Plant and Soil | Year: 2014

Background and aims: Nitrification and denitrification are the two most important processes that contribute to greenhouse gas emission and inefficient use of nitrogen. Suppressing soil nitrification through the release of nitrification inhibitors from roots is a plant function, and termed "Biological Nitrification Inhibition (BNI)". We report here the role and contribution of sorgoleone release to sorghum-BNI function. Methods: Three sorghum genotypes (Hybridsorgo, IS41245 and GDLP 34-5-5-3) were evaluated for their capacity to release sorgoleone, which has BNI-activity, in hydroponic and soil culture. Sorgoleone released was measured using HPLC; BNI-activity was determined using a luminescent recombinant Nitrosomonas europaea assay. Results: Sorgoleone production and BNI-activity release by roots are closely associated (1 μg of sorgoleone is equivalent to 1 ATU activity in assay). Purified sorgoleone inhibited Nitrosomonas activity and suppressed soil nitrification. Sorghum genotypes release varying quantity of sorgoleone; GDLP 34-5-5-3 and Hybridsorgo showed higher capacity for both sorgoleone release and BNI-activity than did IS41245. In soil culture, GDLP 34-5-5-3 released higher quantity of sorgoleone into the rhizosphere, which had higher BNI-activity, and suppressed soil nitrification to a greater extent than did by IS41245. Conclusions: These results demonstrate genetic differences for sorgoleone release and its functional link with BNI-capacity; there is potential for genetic improvement of sorghum BNI-capacity and deployment of this in low-nitrifying sorghum production systems. © 2014 Springer International Publishing Switzerland.

Zeng H.,Crop | Zeng H.,Hangzhou Normal University | Di T.,Crop | Zhu Y.,Nanjing Agricultural University | Subbarao G.V.,Crop
Plant and Soil | Year: 2015

Aims: Sorghum (Sorghum bicolor) roots release biological nitrification inhibitors (BNIs) to suppress soil nitrification. Presence of NH4+ in the rhizosphere stimulates BNIs release and it is hypothesized to be functionally associated with plasma membrane (PM) H+-ATPase activity. However, whether the H+-ATPase is regulated at the transcriptional level, and if so, which isoforms of the H+-ATPases are involved in BNIs release are not known. Also, it is not clear whether the stimulation on BNIs release from roots is due to NH4+ uptake or its assimilation, which are addressed in this study. Methods: Root exudates from intact sorghum plants were collected using aerated solutions of NH4+ or methyl-ammonium (MeA); and the BNI-activity release was determined. PM vesicles were isolated from fresh roots using a two-phase partitioning system; and the hydrolytic H+-ATPase activity was determined. All genes encoding PM H+-ATPases were searched in sorghum genome, and their expression in response to NH4+ or MeA were analyzed by quantitative RT-PCR in sorghum roots. Results: BNIs release and PM H+-ATPase activity increased with NH4+ concentration (≤1.0 mM) in the root-exudate collection solutions, but at higher concentrations, it did not respond further or declined in case of the PM H+-ATPase activity. Twelve PM H+-ATPase genes were identified in sorghum genome; and these isoforms were designated SbA1 to SbA12. Five H+-ATPase genes were stimulated by NH4+ in the rhizosphere, and have similar expression pattern, which is consistent with the variation in H+-ATPase activity. MeA, a non-metabolizable analogue of NH4+, had no significant effects on BNIs release, H+-ATPase activity, or expression of the H+-ATPase genes. Conclusions: Our results suggest that the functional link between PM H+-ATPase activity and BNIs release is evident only at NH4+ levels of ≤1.0 mM in the rhizosphere. The variation in PM H+-ATPase activity by NH4+ is due to transcriptional regulation of five isoforms of the H+-ATPases. The stimulatory effect of NH4+ on BNIs release is functionally associated with NH4+ assimilation and not just with NH4+ uptake alone. © 2015 Springer International Publishing Switzerland

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