acid-phosphatase and indoleacetic-acid

Rhizobia may possess other plant growth-promoting mechanisms besides nitrogen fixation. These mechanisms and the tolerance to different environmental factors, such as metals, may contribute to the use of rhizobia inocula to establish a successful legume-rhizobia symbiosis. Our goal was to characterize a collection of native Portuguese chickpea Mesorhizobium isolates in terms of plant growth-promoting (PGP) traits and tolerance to different metals as well as to investigate whether these characteristics are related to the biogeography of the isolates. The occurrence of six PGP mechanisms and tolerance to five metals were evaluated in 61 chickpea Mesorhizobium isolates previously obtained from distinct provinces in Portugal and assigned to different species clusters. Chickpea microsymbionts show high diversity in terms of PGP traits as well as in their ability to tolerate different metals. All isolates synthesized indoleacetic acid, 50 isolates produced siderophores, 19 isolates solubilized phosphate, 12 isolates displayed acid phosphatase activity, and 22 exhibited cytokinin activity. Most isolates tolerated Zn or Pb but not Ni, Co, or Cu. Several associations between specific PGP mechanisms and the province of origin and species clusters of the isolates were found. Our data suggests that the isolate's tolerance to metals and ability to solubilize inorganic phosphate and to produce IAA may be responsible for the persistence and distribution of the native Portuguese chickpea Mesorhizobium species. Furthermore, this study revealed several chickpea microsymbionts with potential as PGP rhizobacteria as well as for utilization in phytoremediation strategies.

Topics: Acid Phosphatase; Biodegradation, Environmental; Biodiversity; Cicer; Cytokinins; DNA, Bacterial; Geography; Indoleacetic Acids; Mesorhizobium; Metals, Heavy; Nitrogen Fixation; Phosphates; Phylogeny; Plant Development; Portugal; Rhizobium; RNA, Ribosomal, 16S; Sequence Analysis, DNA; Siderophores; Soil Microbiology; Symbiosis; Tryptophan

The phytohormone ethylene plays important roles in regulating plant responses to phosphate (Pi) starvation. To date, however, no molecular components have been identified that interact with ethylene signalling in regulating such responses. In this work, an Arabidopsis mutant, hps4, was characterized that exhibits enhanced responses to Pi starvation, including increased inhibition of primary root growth, enhanced expression of Pi starvation-induced genes, and overproduction of root-associated acid phosphatases. Molecular cloning indicated that hps4 is a new allele of SABRE, which was previously identified as an important regulator of cell expansion in Arabidopsis. HPS4/SABRE antagonistically interacts with ethylene signalling to regulate plant responses to Pi starvation. Furthermore, it is shown that Pi-starved hps4 mutants accumulate more auxin in their root tips than the wild type, which may explain the increased inhibition of their primary root growth when grown under Pi deficiency.

Topics: Acid Phosphatase; Alleles; Anthocyanins; Arabidopsis; Arabidopsis Proteins; Chromosome Mapping; Ethylenes; Gene Expression Regulation, Plant; Indoleacetic Acids; Intracellular Signaling Peptides and Proteins; Meristem; Mutation; Organ Specificity; Phosphates; Plant Growth Regulators; Plant Leaves; Plant Roots; Signal Transduction; Stress, Physiological

Topics: Acid Phosphatase; Gibberellins; Indoleacetic Acids; Plant Development; Plants; Plants, Toxic; Ricinus communis