Search

Colonization of the rhizosphere by micro-organisms results in modifications in plant growth and development. This review examines the mechanisms involved in growth promotion by plant growth-promoting rhizobacteria which are divided into indirect and direct effects. Direct effects include enhanced provision of nutrients and the production of phytohormones. Indirect effects involve aspects of biological control: the production of antibiotics and ironchelating siderophores and the induction of plant resistance mechanisms. The study of the molecular basis of growth promotion demonstrated the important role of bacterial traits (motility, adhesion and growth rate) for colonization. New research areas emerge from the discovery that molecular signalling occurs through plant perception of eubacterial flagellins. Recent perspectives in the molecular genetics of cross-talking mechanisms governing plant-rhizobacteria interactions are also discussed. [ABSTRACT FROM AUTHOR]

Abstract: Phosphate (Pi) is an essential element for plant development and metabolism. Due to its low availability and mobility in soils, it is often a limiting nutrient for their growth. This phenomenon is reinforced by the formation of insoluble complexes in the environment with many cations, affecting the solubility of both phosphate and associated ions. This interaction is investigated here for iron, a strong phosphate chelator. Depleting the medium in phosphate clearly resulted in an increase of iron content in Arabidopsis. These modifications triggered molecular responses linked with iron status (transport, homeostasis and accumulation). Interestingly, physiological modifications affecting iron storage were also observed. The accumulation of phosphate/iron complexes in the vacuoles of plants grown in Pi-rich medium disappeared in Pi-depleted medium in favor of accumulation of iron inside the chloroplasts, likely associated with ferritin. [Copyright &y& Elsevier]