Individuation in Sorghum bicolor: A self-organized process involved in physiological adaptation to salinity

Abstract

In Sorghum bicolor, salt-adaptation was defined as the capacity of plants to grow at 300 mM NaCl (a lethal concentration) following a 3-week pre-treatment with 150 mM NaCl (a sublethal concentration). Large populations induced for salt-adaptation were analysed. Two modes of osmotic regulation (Na-includer and Na-excluder) were differentiated during induction of salt-adaptation, in spite of the genetic and environmental homogeneity. This variability was not related to any incapacity of the Na-includers to control accumulation of Na+ ions in the shoot, because most of the pre-treated plants displayed a similar capacity of growth and control of Na+ uptake after transfer to 300 mM NaCl. This unsuspected complexity of initially homogeneous populations points on the inadequacy of physiological studies focused on the 'average individual'. Further analyses showed that variability was not directly related to micro-environmental variations. It is concluded that a process of individuation is caused by a third source of variability, which is the expression of a self-organizing process normally occurring during the transition phases in development. In constraining environments, this phenomenon of individuation includes adaptive modifications.