Plant Hormones and Nutrient Deficiency Responses

Abstract

Terrestrial plants, differently from animals, cannot move in search of nutrients they need. Instead, they have to continuously change their physiology and morphology to adapt to the availability of different nutrients in the soil. When plants suffer from a nutrient deficiency, they develop several deficiency responses aimed to adapt their growth to the limiting conditions. Some of these responses are rather unspecific and help plants to efficiently manage the nutrients they already have. Other more specific responses are aimed at acquiring the deficient nutrient(s) from the medium. These include both physiological and morphological responses and are mainly located in roots. Physiological responses include acidification of the rhizosphere, enhanced expression of transporters, release of chelating agents into the medium, and other physiological changes; and morphological responses include changes in root system architecture, development of root hairs, and other morphological changes. The ways plants perceive the different nutrient deficiencies and transmit this perception into the activation of the physiological and morphological responses is not totally known but many experimental results suggest that plant hormones, like auxin and ethylene, play an important role in the process. Besides hormones, oxidative stress and other signaling molecules, like nitric oxide, glutathione, sucrose, peptides and microRNAs, have also been related to most nutrient deficiency responses. Some of these hormones and signals originate in the roots themselves while others move from shoots to roots through the phloem. Once plants acquire enough of the limiting nutrient, the responses are switched off and hormones, like cytokinins and jasmonic acid, have also been involved in such a process. This review summarizes the progress in understanding the interactions of different hormones with other signaling molecules in the regulation of the main nutrient deficiency responses.