Changing concepts in plant hormone action

in In Vitro Cellular & Developmental Biology-Plant (2003), 39(2, MAR-APR), 85-106

A plant hormone is not, in the classic animal sense, a chemical synthesized in one organ, transported to a second organ to exert a chemical action to control a physiological event. Any phytohormone can be ... [more ▼]

A plant hormone is not, in the classic animal sense, a chemical synthesized in one organ, transported to a second organ to exert a chemical action to control a physiological event. Any phytohormone can be synthesized everywhere and can influence different growth and development processes at different places. The concept of physiological activity under hormonal control cannot be dissociated from changes in concentrations at the site of action, from spatial differences and changes in the tissue's sensitivity to the compound, from its transport and its metabolism, from balances and interactions with the other phytohormones, or in their metabolic relationships, and in their signaling pathways as well. Secondary messengers are also involved. Hormonal involvement in physiological processes can appear through several distinct manifestations (as environmental sensors, homeostatic regulators and spatio-temporal synchronizers, resource allocators, biotime adjusters, etc.), dependent on or integrated with the primary biochemical pathways. The time has also passed for the hypothesized 'specific' developmental hormones, rhizocaline, caulocaline, and florigen: root, stem, and flower formation result from a sequential control of specific events at the right places through a coordinated control by electrical signals, the known phytohormones and nonspecific molecules of primary and secondary metabolism, and involve both cytoplasmic and apoplastic compartments. These contemporary views are examined in this review. [less ▲]

Integrating phytohormone metabolism and action with primary biochemical pathways. II. Interrelationships between disturbed nitrogen and carbon metabolism and changes in hormonal concentrations and sensitivities in tissue cultures

in Greppin, Hubert; Penel, Claude; Broughton, Walter (Eds.) et al Integrated Plant Systems (2000)

The paper begins with a review of the concept of neoplastic progressions in plant tissue cultures, with the progressive acquisition of (a relative) independence to the hormones auxins and cytokinins. It ... [more ▼]

The paper begins with a review of the concept of neoplastic progressions in plant tissue cultures, with the progressive acquisition of (a relative) independence to the hormones auxins and cytokinins. It takes advantage of the deviations of carbon and nitrogen metabolisms shown in these particular cases, to illustrate the interdependence with the metabolisms of the hormones (and increased sensitivities to) polyamines and ethylene. These results provide additional examples of the changing concepts in hormonology. [less ▲]

Shemin Pathway and Peroxidase Deficiency in a Fully Habituated and Fully Heterotrophic Non-Organogenic Sugarbeet Callus: An Adaptative Strategy or the Consequence of Modified Hormonal Balances and Sensitivities in These Cancerous Cells? A Review an

in Cell Proliferation (1999), 32(5), 249-70

There are many arguments for considering a specific fully habituated (auxin and cytokinin-independent) and fully heterotrophic non-organogenic (HNO) sugarbeet callus cell line as terminating a neoplastic ... [more ▼]

There are many arguments for considering a specific fully habituated (auxin and cytokinin-independent) and fully heterotrophic non-organogenic (HNO) sugarbeet callus cell line as terminating a neoplastic progression, and thus to be made of cancerous cells. The similarities with animal tumour and cancer cells are recalled. All types of habituated tissues examined in the literature share at least three common biochemical characteristics: low apparent peroxidase activity, high content of polyamines (PAs) and low production of ethylene. However, results concerning their auxin and cytokinin levels are not consistent. Peroxidase synthesis in the achlorophyllous HNO callus appears to arise from aminolevulinic acid (ALA) synthesis through the Shemin pathway, commonly used by animals and fungi. This pathway is limited by disturbed nitrogen metabolism that diverts glutamate (directly used for ALA synthesis in green higher plants) from the Kreb's cycle into PA synthesis. There is no argument to suggest that the low ethylene production is caused by a competition with PAs for their common precursor, S-adenosylmethionine. The results we report here indicate modified anabolic and catabolic pathways of auxins and cytokinins but also the possibilities of unusual compounds playing similar roles (dehydrodiconiferyl alcohol glucosides, for instance). A higher turnover of PAs is shown in the HNO callus, which could suggest a role for H2O2 and gamma-aminobutyric acid, products or intermediates in the PA catabolic pathway, as secondary messengers. The habituated cells retain some sensitivity towards exogenous auxins and cytokinins. Their increased sensitivity to PAs and ethylene suggests modified hormonal balances for the control of these actively dividing cells. [less ▲]

Atypical metabolisms and biochemical cycles imposing the cancerous state on plant cells

in Plant Growth Regulation (1998), 24(2), 135-144

The biological, morphological and biochemical characteristics which define plant cancer cells at the end of a neoplasic progression in the absence of pathogens and which distinguish them from tumorous ... [more ▼]

The biological, morphological and biochemical characteristics which define plant cancer cells at the end of a neoplasic progression in the absence of pathogens and which distinguish them from tumorous cells are summarized. Such plant cancer cells have in common with animal cancer cells many metabolic disturbances. The present paper reviews the biochemical changes in nitrogen, carbon, sugar and heme metabolisms which contribute to polyamine (PAs) accumulation. It indicates how these changes are interconnected and even form between each other biochemical cycles which likely maintain these cells in their irreversible state. The role of these cycles in the maintenance of such cells under a probable permanent oxidative stress is debated. [less ▲]