Xiaomin Zhou

A novel bacteriocin, thuricin 17, produced by plant growth promoting rhizobacteria strain Bacillus thuringiensis NEB17: isolation and classification.

Aims:  The aim of this study was to identify and characterize a compound produced by the plant growth promoting bacterium, Bacillus thuringiensis non‐Bradyrhizobium Endophytic Bacterium 17.

The class IId bacteriocin thuricin-17 increases plant growth.

The mechanisms by which many plant growth promoting rhizobacteria (PGPR) affect plants are unknown. We recently isolated a rhizosphere bacterium (Bacillus thuringiensis NEB17), that promotes soybean growth and screened the liquid growth medium in which it grew for plant growth stimulating materials. We have also shown that it produces a bacteriocin (named by us as thuricin-17 and a member of the recently described class IId bacteriocins). Here we show that application of this bacteriocin to leaves (spray) or roots (drench) directly stimulates the growth of both a C3 dicot (soybean) and a C4 monocot (corn). This growth stimulation is similar in nature to that previously seen when plants are treated with Nod factors. Strain NEB17 contains three copies of the gene for thuricin 17 that code for identical amino acid sequences. These two lines of evidence suggest that the dual functions of these proteins may have constrained their evolution. This is the first report of direct plant growth enhancement by a bacteriocin.

Seed quality of sweet white lupin (Lupinus albus) and management practice in eastern Canada

White lupin (Lupinus albus) has shown considerable yield potential as a spring-sown grain legume in eastern Canada and the northern USA. However, the effects of agronomic factors on seed protein and oil of white lupin cultivars have not been quantified under such short growing season conditions. The objective of this research was to determine appropriate management practices for production of better quality sweet white lupin. A 2-year study was conducted in eastern Canada to determine the responses of seed protein and oil in two large-seeded white lupin cultivars (Primorski and Ultra) to management factors. The two lupin cultivars were factorially combined on two soil types, with two planting dates and two row spacings. Of the 2 years, 1991 was more or less typical for the region, while 1992 was unusually cool and rainy. Both lupin protein and oil concentrations were not affected by the tested management factors over three of the 4 location years, except that the early planting date decreased the protein concentration of seeds in pods formed on the stem. The protein yield of seeds in pods formed on the branches was more sensitive to management factors in both sites in 1991. Total protein and oil yields of Ultra were higher than those of Primorski in the typical year (1991), but not in the atypically cool year (1992). On average, protein and oil yields were 59 and 93% higher, respectively, under the cooler climate conditions of 1992 than in 1991. The seed protein:lipid ratio in white lupin seeds was :4:1 and 3:1 in 1991 and 1992, respectively. In general, early planting in narrow rows resulted in the highest yields of both protein and oil.

Combined effects of plant growth-promoting rhizobacteria and genistein on nitrogen fixation in soybean at suboptimal root zone temperatures.

Abstract Application of plant growth‐promoting rhizobacteria (PGPR) or the plant to bacteria signal molecule genistein has been shown to increase nodulation and nitrogen (N) fixation by soybean [Glycine max (L.) Merr.] over a range of root zone temperatures (RZTs) and, specifically, off‐sets at least some of the ill‐effects of low RZTs. Two sets of controlled‐environment experiments, one on a growth bench and the other in a greenhouse, were conducted to examine the combined ability of both PGPR and genistein to reduce the negative effects of low RZT on soybean nodulation and N fixation. Each of two the PGPR strains, Serratia proteamaculans 1–102 and Serratia liquefaciens 2–68 were co‐inoculated with Bradyrhizobium japonicum USDA 110 preincubated with 17.5 (somewhat inhibitory), and 15°C (very inhibitory). At RZTs of 25 and 17.5°C PGPR strains and genistein in combination increased the number of nodules and the amount of Nn fixed. The most stimulatory effect was observed at 17.5°C for the combination: S. proteamaculans 1–102 plus B. japonicum USDA 110 pre‐incubated in 15 μM genistein under greenhouse conditions. For most treatment combinations the stimulatory effects of PGPR and genistein were additive at RZTs of 17.5 and 25°C. Surprisingly, the combination of these two factors resulted in antagonism at the very inhibitory RZT of 15°C. The results suggest that the negative effects of certain low RZTs could be more effectively off‐set by combined treatments of PGPR plus geneistin pre‐incubation of rhizobial cultures than by their individual treatment.

Variability in yield and yield component responses to genistein pre-incubated Bradyrhizobium japonicum by soybean [Glycine max (L.) Merr] cultivars

The sub-tropical legume, soybean [Glycine max (L.) Merr.], has lower grain yields at low temperatures, mainly due to reduced nitrogen fixation. The isoflavone genistein has been identified as one of the major compounds in soybean seed and root extracts responsible for inducing the expression of the B. japonicum nod genes. A 2-year field study was conducted in 1997 and 1998 with 11 soybean cultivars recommended for Québec, and representing a range of yield potentials and maturity groups. The objective of this study was to assess the variability among soybean cultivar maturity groups in terms of response to genistein application under Canadian short season and cool-spring conditions. The experiments were organized in a randomized complete block design with three replications. The two genistein treatments included B. japonicum inoculant pre-incubated with 20 μm genistein and B. japonicum inoculant only. The inoculants were applied into the furrow at the time of planting. The results of this study showed that genistein pre-incubated B. japonicum increased soybean grain yield and protein content over two years. In 1998, pod number per plant−1 and seed number plant−1 were also clearly increased. When 20 μm genistein was applied in 1998, cultivars in the late maturity group had 28 and 70% more shoot and total protein content, respectively, than the early maturity groups with or without genistein, or the late maturity without genistein, in 1998. There was no interaction between genistein application and soybean cultivar in this study, indicating that both early and late maturing cultivars responded similarly to genistein pretreated inocula. Pre-incubation of B. japonicum with genistein can increase N2 fixation potential in short season areas. Key words: Soybean, cultivars, genistein, yield, and yield components

Distribution of 15N‐labeled urea injected into field‐grown corn plants

Abstract Nitrogen (N) assimilate supply to developing corn (Zea mays L.) ears plays a critical role in grain dry weight accumulation. The use of stem‐perfused/ injected 15N labeled compounds to determine the effects of an artificial N source on the subsequent distribution of injected N and grain weight of field‐grown corn plants has not been reported previously. Our objective was to assess the distribution of N added via an artificial source. Three soil N fertilizer levels (0, 180, and 270 kg N ha‐1) and three N solutions (distilled water control and 15N enriched urea at 15 and 30 mM N) were arranged in a split‐plot design. Three N concentrations were injected using a pressurized stem injection technique. The injection started fifteen days after silking and continued until immediately prior to plant physiological maturity. The average uptake volume was 256 mL over the 30‐day injection period. The N supplied via injection represented 1.5 to 3% of the total plant N. Neither soil applied N fertilizer nor inj...

Carbon and nitrogen supplementation to soybean through stem injection and its effect on soybean plant senescence

Abstract Plant senescence studies have indicated that internal competition for nutrients such as carbon (C) and nitrogen (N) can be an important factor in the initiation of senescence. A greenhouse experiment was conducted to determine the effect of increased supplies of C and N on senescence of soybean (Glycine max [L.] Merr) plants. Soybean plants were injected with solutions of sucrose (150gL‐1), N (15 mM N), and distilled water from the onset of flowering until senescence using a modified stem injection technique. The average uptake rate of all solutions was 1.3 mL d‐1 per plant. The plants injected with sucrose accumulated the most biomass, followed by those injected with N and distilled water. Soybean plants injected with sucrose senesced 17 days later than the distilled water control while senescence was not delayed for plants injected with N. Injection of either N or sucrose increased the concentration and content of N in soybean plants. The results indicated that intra‐plant‐competition for reduced C plays an important role in plant senescence. Because the total amount of N injected was only 2% of the total plant N, as compared to 31 % for C, the role of intra‐plant competition for N was less clear.

Effect of Nod factor sprays on soybean growth and productivity under field conditions

Abstract A field experiment was conducted at Ste. Anne de Bellevue, Quebec during the growing seasons of 2002 and 2003, to study the effect of Nod factor treatments, applied at specific growth stages, on photosynthesis and biomass accumulation by soybean grown under two tillage systems (conventional tillage, no-tillage). Spray application of Nod factors increased photosynthesis at the four fully expanded trifoliate leaves and full bloom growth stages under no-tillage and conventional tillage; they increased plant biomass at the beginning seed filling stage. Nod factor treatment did not affect yield in 2002, due to severe drought during the reproductive period. In 2003, Nod factor application increased yield under conventional tillage but not under no-tillage, and this may have been due to the negative effect of no-tillage on plant growth on the clay-loam soil at the experimental site. This study indicated that responses to Nod factors are affected by environmental conditions, and that Nod factors may be useful when applied to soybean grown under conventional tillage.