Daidzein and genistein are plant-to-bacterium signal compounds involved in soybean nodule formation. They can induce nod gens expression in Bradyrhizobium japonicum. The objective of this study was to determine whether the production of signal molecules was affected by low root zone temperatures (RZTs) in a manner that varied among soybean cultivars. Daidzein and genistein concentrations of soybean seedling roots were measured at three RZTs by high performance liquid chromatography (HPLC). The results indicated that daidzein content and concentration per plant were higher at 15 and 17.5°C than those at 25°C. AC Bravor had higher daidzein contents and concentrations than did Maple Glen and KG20. At 17.5°C. KG20 had higher genistein content and concentration levels than Maple Glen, and no difference existed for the two cultivars at 15 and 25 C. Daidzein contents and concentrations of Maple Glen and AC Bravor increased with harvest time. However, for cultivar KG20, the content and concentration decreased at 19 days after inoculation. Genistein contents and concentrations of the three cultivars increased under each RZT up to the last harvest. There was an interaction between soybean cultivar and RZT for root genistein and daidzein contents and concentrations. The content and concentration of daidzein in soybean seedling roots were much higher (more than five times) than those of genistein.
"High temperature (39 8C) increases the release of the isoflavonoid signals from soybean seeds during the first 24 h, but the compounds released have decreased nod gene-inducing activities (Hungria and Stacey, 1997). The addition of genistein to the inoculant or the rhizosphere could at least partially alleviate the deleterious effects of these environmental factors (Zhang and Smith, 1995, 1996b, 1997; Smith and Zhang, 1996; Hungria and Stacey, 1997; Pan et al., 1998). Besides inhibiting the synthesis and excretion of isoflavonoids by soybean roots, low RZTs also suppress bacterial nod gene expression, and this also could be partially overcome by genistein application (Zhang et al., 1996a). "
[Show abstract][Hide abstract] ABSTRACT: Serratia proteamaculans 1-102 (1-102) promotes soybean-bradyrhizobia nodulation and growth, but the mechanism is unknown. After adding isoflavonoid inducers to 1-102 culture, an active peak with a retention time of about 105 min in the HPLC fractionation was isolated using a bioassay based on the stimulation of soybean seed germination. The plant growth-promoting activity of this material was compared with 1-102 culture (cells) and supernatant under greenhouse conditions. The activator was applied to roots in 83, 830 and 8300 HPLC microvolts (microV) per seedling when plants were inoculated with bradyrhizobia or sprayed onto the leaves in same concentrations at 20 d after inoculation. The root-applied activator, especially at 1 ml of 830 microV per seedling, enhanced soybean nodulation and growth at the same level as 1-102 culture under both optimal and sub-optimal root zone temperatures. Thus, this activator stimulating soybean seed germination is also responsible for the plant growth-promoting activity of 1-102 culture. However, when sprayed onto the leaves, the activator did not increase growth and in higher concentrations decreased average single leaf area. The results suggest that this inducible activator might be a lipo-chitooligosaccharide (LCO) analogue. LCOs act as rhizobia-to-legume signals stimulating root nodule formation. The activator could provide additional 'signal', increasing in the signal quality (the signal-to-noise ratio, SNR) of the plant-rhizobia signal exchange process.
Journal of Experimental Botany 07/2002; 53(373):1495-502. · 5.53 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Isoflavonoids, as plant-to-bacteria signal molecules, play an important role in the establishment of the soybean (Glycine max (L.) Merr.)-Bradyrhizobium japonicum nitrogen (N) fixing symbiosis. They are essential to the development of effective root nodules and responsible for inducing the nod genes of B. japonicum. Because N affects a broad range of infection events, especially the symbiotic events occurring within 18 h of inoculation, it is reasonable to hypothesize that mineral N disrupts the inter-organismal signal exchange between soybean host plants and B. japonicum. High performance liquid chromatographic (HPLC) analysis of root extracts of soybean, inoculated with B.japonicum or not, grown with various levels of mineral N in the rooting medium were performed to test this hypothesis. The results of these studies indicated that: (1) at early plant growth stages (before the onset of N fixation), a strong negative relationship between N application and soybean root isoflavonoid (genistein and daidzein) concentrations existed; (2) although isoflavonoid (genistein and daidzein) concentrations in both inoculated and non-inoculated soybean root systems were generally decreased by N application, at very low N levels (10 mg N 1 -1) genistein in the non-inoculated plant roots was not decreased relative to the 0 N plants; (3) averaged over all mineral N treatment levels and sampling times, inoculation of soybean with B. japonicum increased root daidzein concentrations (P > 0.05), but did not affect genistein. Overall, N application reduced the isoflavonoid concentration of soybean root systems, which probably plays a part in the regulation of soybean nodule formation by available N.
Journal of Agronomy and Crop Science 04/2000; 184(3):197 - 204. DOI:10.1046/j.1439-037x.2000.00372.x · 2.44 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Lipo-chitooligosaccharides (LCOs), also known as nod factors, are the bacteria-to-plant signal molecules synthesized in response to the plant-to-bacteria signals, usually ¯avonoids. In Canada, low soil temperature is potentially a major factor limiting soybean growth and symbiotic nitrogen ®xation. Low temperatures cause reductions in the amount of ¯avonoids, especially genistein, in soybean roots and also inhibit the expression of nod genes resulting in a delay in the onset of nodulation. The addition of genistein can overcome the earlier negative effects of low temperature. However, genistein is expensive and more cost-effective approaches to this problem may exist. We used UV mutagenesis to generate 10 mutants from Bradyrhizobium japonicum strain USDA 110, that expressed nod genes in the absence of plant-to-bacteria signal molecules (e.g. genistein) and they were further screened for their ability to synthesize LCO at three different temperatures (15, 17 and 25 8C). No detectable LCO was produced by these strains and mutants at 0 and 0.01 mM genistein. However, at higher genistein levels (0.1 and 1 mM) all mutants produced more LCO, at the three temperatures tested, than the wild type USDA 110 and 532C. Mutants Bj30054, Bj30056 and Bj30057 were most promising, producing the maximum concentration of LCO at low incubation temperatures (15 and 17 8C). Therefore, we envisage that under short season conditions that are characterized by low spring soil-temperatures these mutants (Bj30054, Bj30056 and Bj30057) would produce more LCO than USDA 110 or 532C, possibly leading to better nodulation and N 2 ®xation and eventually soybean yield. q 2002 Published by Elsevier Science Ltd.
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