Plasticity Of Root Architecture Research Articles

Involvement of polyamines in root development

Root development is under the control of hormonal, metabolic, and environmental cues that can act on genetically-controlled developmental programmes and thus affect the plasticity of root architecture. These processes involve not only the five `classical' plant hormones, but also other growth regulators, such as polyamines. The present review emphasises the importance of polyamines in the different aspects of root development: primary root growth and lateral and adventitious root formation. Free (agmatine, putrescine, spermidine, spermine), conjugated (such as hydroxycinnamate conjugates) and macromolecule-bound polyamines are reported to be present in root systems. Modifications of their endogenous levels by inhibitor treatment, by mutation, by gene manipulation, or by exogenous treatment can have drastic effects on root development and subsequent architecture. These effects may be related to the involvement of polyamines in the control of cell division and differentiation, which plays an important role in the root apex and during lateral and adventitious root formation. The exact mechanisms of action remain to be elucidated, but accumulating evidence in plant and animal cells supports the idea that, besides biophysical effects on membranes and nucleic acids, polyamines interact with protein kinases and transcription factors and are thus involved in signal transduction pathways. The high flexibility of polyamine metabolism in response to environmental stress and the metabolic link between polyamine and ethylene synthesis strongly suggest that polyamines may play a role in environmentally-induced plasticity of root development. Moreover, polyamines may be implicated in the establishment of biotic interactions between roots and rhizospheric micro-organisms.

Involvement of polyamines in root development at low temperature in the subantarctic cruciferous species Pringlea antiscorbutica

Polyamine involvement in root development at low temperature was studied in seedlings of Pringlea antiscorbutica R. Br. This unique endemic cruciferous species from the subantarctic zone is subjected to strong environmental constraints and shows high polyamine contents. In the present study, free polyamine levels were modified by inhibitors of polyamine biosynthesis (D-arginine, difluoromethylornithine, cyclohexylammonium, and methylglyoxal-bis-guanylhydrazone) and variations of the endogenous pools were compared to changes in root growth. The arginine decarboxylase pathway, rather than that of ornithine decarboxylase, seemed to play a major role in polyamine synthesis in Pringlea antiscorbutica seedlings. Root, but not shoot, phenotypes were greatly affected by these treatments, which modified polyamine endogenous levels according to their expected effects. A positive correlation was found between agmatine level and growth rate of the primary root. Spermidine and spermine contents also showed positive correlations with primary root growth whereas the putrescine level showed neutral or negative effects on this trait. Free polyamines were therefore found to be differentially involved in the phenotypic plasticity of root architecture. A comparison of developmental effects and physiological concentrations suggested that agmatine and spermine in particular may play a significant role in the control of root development.