Phosphorus solubilizing bacteria (PSB) can promote the level of plant-absorbable phosphorus (P) in agro-ecosystems. However, little attention has been paid to PSB harboring abilities in utilizing multiple phosphorus sources and their potentials for heavy metal immobilization. In this study, we applied the strategy of stepwise acclimation by using Ca 3 (PO 4) 2 , phytate, FePO 4 , and AlPO 4 as sole P source. We gained 18 PSB possessing abilities of multiple P sources utilization, and these bacteria belonged to eight genera (Acinetobacter, Pseudomonas, Massilia, Bacillus, Arthrobacter, Stenotrophomonas, Ochrobactrum, and Cupriavidus), and clustered to two apparent parts: Gram-positive bacteria and Gram-negative bacteria. The isolate of Acinetobacter pittii gp-1 presented good performance for utilizing Ca 3 (PO 4) 2 , FePO 4 , AlPO 4 , and phytate, with corresponding P solubilizing levels were 250.77, 46.10, 81.99, and 7.91 mg/L PO 4 3−-P, respectively. The PSB A. pittii gp-1 exhibited good performance for solubilizing tricalcium phosphate in soil incubation experiments, with the highest values of water soluble P and available P were 0.80 and 1.64 mg/L, respectively. Additionally, the addition of A. pittii gp-1 could promote the immobilization of lead (Pb), and the highest Pb immobilization efficiency reached 23%. Simultaneously, we found the increases in abundances of both alkaline phosphatase gene (phoD) and β-propeller phytase gene (bpp) in strain gp-1 added soils. Besides, we observed the expression up-regulation of both pyrroloquinoline quinone gene (pqq) and polyphosphate kinases gene (ppk), with the highest relative expression levels of 18.18 and 5.23, respectively. We also found the polyphosphate particles using granule staining. To our knowledge, our findings first suggest that the solubilizing of tricalcium phosphate by phosphorus solubilizing bacterium belonging to Acinetobacter is coupled with the synthesis of polyphosphate. Taken together, A. pittii gp-1 could be a good candidate in improving soil fertility and quality.

No abstract

No abstract

N-Acetylchitoheptaose strongly induces a set of defense reactions in suspension-cultured rice cells including cytoplasmic acidification (K. Kuchitsu, Y. Yazaki, K. Sakano, and N. Shibuya, Plant Cell Physiol. 38:1012-1018, 1997) and the accumulation of mRNAs for two rapidly activated genes, EL2 and EL3 (E. Minami, K. Kuchitsu, D.-Y. He, H. Kouchi, N. Midoh, Y. Ohtsuki, and N. Shibuya, Plant Cell Physiol. 37:563-567, 1996), as well as phenylalanine ammonia-lyase (PAL), chitinase and β-1,3-glucanase. Treatment of cells with propionic acid resulted in the accumulation of the mRNAs for EL2, EL3, and PAL in a manner similar to the accumulation induced by N-acetylchitoheptaose. Concomitantly, there was a rapid decrease in the cytoplasmic pH as detected with in vivo 31P-nuclear magnetic resonance (NMR) spectroscopy. Interestingly, K-252a, a potent inhibitor of Ser/Thr protein kinases, strongly inhibited gene induction by N-acetylchitoheptaose, but showed much less inhibition of gene induction caused by propionic acid. Calyculin A, a protein phosphatase inhibitor, induced mRNA accumulations for EL2, EL3 and PAL, with concomitant acidification of the cytoplasm. On the other hand, chitinase and β-glucanase mRNA levels did not change after addition of propionic acid or calyculin A. Treatment of the cells with propionic acid did not induce the production of reactive oxygen species. These results strongly suggest that cytoplasmic acidification at the early stage of elicitor action could be a key step in the signal transduction events leading to the expression of elicitor-responsive genes. A hypothetical model of elicitor signal pathway is proposed based on these results.

By using subtracted probes, two cDNA clones of rice, EL2 and EL3, were isolated as genes responsive within 6 min to N-acetylchitoheptaose, a potent biotic elicitor for phytoalexin biosynthesis. Analyses of the sequence of the cDNAs showed that both of EL2 and EL3 encoded basic proteins with no significant similarities to those of known genes.

No abstract

No abstract

Plants respond to biotic and abiotic stresses through the activation and coordination of various signalling pathways. The activation often requires the phosphorylation of proteins. In this study, we have identified the wheat TaFLRS MAP kinase (Fusarium and Leaf Rust Sensitive) gene that was upregulated in a wheat EST (expressed sequence tag) array analysis following a wheat-leaf rust interactive challenge. Our results demonstrate that TaFLRS is transcriptionally upregulated in incompatible interactions involving wheat and leaf rust and Fusarium graminearum, suggesting that this MAPK maybe involved in defence responses to these wheat pathogens. RT-PCR revealed that TaFLRS transcript levels are not altered by salicylic acid (SA) treatment. However, immunoprecipitation and western blotting analysis show that phosphorylation of TaFLRS at the TEY motif was enhanced by SA in the Fusarium head blight (FHB) resistant cultivar Frontana following challenge with the FHB pathogen. The role of TaFLRS MAP kinase in defence responses in wheat is discussed.