Cold, salinity and drought stresses: an overview.

Publisher Summary The chapter presents a discussion on plant growth-regulating (PGR) substances in the rhizosphere, with emphasis on microbial production and functions. The chapter discusses the rhizosphere as a site of plant-microbe interactions; plant growth-regulating substances and their sources; biochemistry of microbial production of PGRs; production of PGRs by rhizosphere microorganisms; metabolism of PGRs in soil; and ecological significance of PGRs produced in the rhizosphere. The chapter provides a better understanding of the mechanisms of actions of microbially derived PGRs and their interactions with plants. Moreover, development of hormone-deficient plant mutants can provide opportunities to clearly define the role of microbially produced PGRs in plan-microbe interactions. An understanding of these aspects can aid in the utilization of microbial PGRs for the betterment and benefit of sustainable agriculture.

Plant growth-regulating substances in the rhizosphere: microbial production and functions

Gibberellin research has its origins in Japan in the 19th century, when a disease of rice was shown to be due to a fungal infection. The symptoms of the disease including overgrowth of the seedling and sterility were later shown to be due to secretions of the fungus Gibberella fujikuroi (now reclassified as Fusarium fujikuroi), from which the name gibberellin was derived for the active component. The profound effect of gibberellins on plant growth and development, particularly growth recovery in dwarf mutants and induction of bolting and flowering in some rosette species, prompted speculation that these fungal metabolites were endogenous plant growth regulators and this was confirmed by chemical characterisation in the late 1950s. Gibberellins are now known to be present in vascular plants, and some fungal and bacterial species. The biosynthesis of gibberellins in plants and the fungus has been largely resolved in terms of the pathways, enzymes, genes and their regulation. The proposal that gibberellins act in plants by removing growth limitation was confirmed by the demonstration that they induce the degradation of the growth-inhibiting DELLA proteins. The mechanism by which this is achieved was clarified by the identification of the gibberellin receptor from rice in 2005. Current research on gibberellin action is focussed particularly on the function of DELLA proteins as regulators of gene expression. This review traces the history of gibberellin research with emphasis on the early discoveries that enabled the more recent advances in this field.

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A century of gibberellin research

Recent advances in stereoselective c-glycoside synthesis

The influence of the Na and Le genes in peas on gibberellin (GA) levels and metabolism were examined by gas chromatographic-mass spectrometric analysis of extracts from a range of stem-length genotypes fed with [13C, 3H]GA20. The substrate was metabolised to [13C, 3H]GA1, [13C, 3H]GA8 and [13C, 3H]GA29 in the immature, expanding apical tissue of all genotypes carrying Le. In contrast, [13C, 3H]GA29 and, in one line, [13C, 3H]GA29-catabolite, were the only products detected in plants homozygous for the le gene. These results confirm that the Le gene in peas controls the 3β-hydroxylation of GA20 to GA1. Qualitatively the same results were obtained irrespective of the genotype at the Na locus. In all Na lines the [13C, 3H]GA20 metabolites were considerably diluted by endogenous [12C]GAs, implying that the metabolism of [13C, 3H]GA20 mirrored that of endogenous [12C]GA20. In contrast, the [13C, 3H]GA20 metabolites in na lines showed no dilution with [12C]GAs, confirming that the na mutation prevents the production of C19-GAs. Estimates of the levels of endogenous GAs in the apical tissues of Na lines, made from the 12C:13C isotope ratios and the radioactivity recovered in respective metabolites, varied between 7 and 40 ng of each GA per plant in the tissue expanded during the 5 d between treatment with [13C, 3H]GA20 and extraction. No [12C]GA1 and only traces of [12C]GA8 (in one line) were detected in the two Na le lines examined. These results are discussed in relation to recent observations on dwarfism in rice and maize.

Internode length in Pisum

The metabolism of substrates normally produced by wild-type strains of Gibberella fujikuroi has been determined in resuspended cultures of the mutant B1-41a at pH 3·5 and 7·0. The metabolites were identified by g.l.c.–mass spectrometry and g.l.c.–radio-counting. From the results at pH 3·5 the metabolic steps from ent-kaurenoic acid to the fungal gibberellins have been deduced. The oxidation level at which C-20 is lost in the formation of the C19-gibberellins could not be determined. ent-7-Oxokaurenoic acid does not serve as a precursor of gibberellin A12 aldehyde. At pH 7·0 the pathway from gibberellin A12 is diverted completely to 3-deoxygibberellins such as gibberellin A9.

Fungal products. Part XIV. Metabolic pathways from ent-kaurenoic acid to the fungal gibberellins in mutant B1-41a of Gibberella fujikuroi

Position of the metabolic block for gibberellin biosynthesis in mutant B1-41a of Gibberella fujikuroi.

The metabolism of steviol to 13-hydroxylated ent-Gibberellanes and ent-kauranes ☆

The biosynthesis of kaurenolide diterpenoids by gibberella fujikuroi

http://harp.lib.hiroshima-u.ac.jp/hbg/file/4325/20140328150823/%E6%9D%BE%E5%B0%BE094.pdf

John R. Bearder

Papers

Fungal products. Part XIV. Metabolic pathways from ent-kaurenoic acid to the fungal gibberellins in mutant B1-41a of Gibberella fujikuroi

Position of the metabolic block for gibberellin biosynthesis in mutant B1-41a of Gibberella fujikuroi.

The metabolism of steviol to 13-hydroxylated ent-Gibberellanes and ent-kauranes ☆

The biosynthesis of kaurenolide diterpenoids by gibberella fujikuroi

Diterpene acids from Helianthus species and their microbiological conversion by Gibberella fujikuroi, mutant B1-41a