Adaptive nature of the transition phases in development: the case of Sorghum bicolor

An increase in tolerance to salinity is induced in Sorghum bicolor by exposure to a sublethal concentration of NaCI during early vegetative development. The phase of competence for induction of this response, termed salt adaptation, is well defined in time and it coincides with the emergence of the first adventitious roots. The link between these events was investigated. Competence for salt adaptation varies among genotypes. It is shown that competence is especially high for genotypes in which the link between the seminal root and the shoot is reduced during emergence of the adventitious root. These data relate the capacity for salt adaptation with development in the absence of NaCl, suggesting that: (i) functional integration of the adventitious roots within the whole plant has an adaptive nature in normal development; (ii) salt adaptation results from an integration of the environmental constraint (NaCl) during this developmental readjustment. It is concluded that perturbations generated by emergence of a new organ are the cause of rapid variations in sensitivity required to open a competence window.