Plant Root Responses to Three Abundant Soil Minerals: Silicon, Aluminum and Iron

Silicon (Si), aluminum (Al), and iron (Fe) are the three most abundant minerals in soil; however, their effects on plants differ because they are beneficial, toxic, and essential to plant growth, respectively. High accumulation of silicon in the shoots helps some plants to overcome a range of biotic and abiotic stresses. However, plants vary in their ability to take up Si from the soil and load it into the xylem and so the accumulation of silicon varies greatly between plant species. Aluminum toxicity is characterized by a rapid inhibition of root elongation but some species and even genotypes within species can tolerate Al toxicity better than others. While the mechanisms controlling this tolerance in most of the more resistant species are poorly understood, some plants are able to detoxify Al externally and/or internally by complexation with ligands or by pH changes in the rhizosphere. Iron is taken up from the soil by two efficient mechanisms called Strategy I and Strategy II, which operate in distinct phylogenic groups. Strategy I plants increase soil Fe solubility by releasing protons and reductants/chelators, such as organic acids and phenolics, into the rhizosphere, while Strategy II plants are characterized by the secretion of ferric chelating substances (phytosiderophores) coupled with a specific Fe³⁺: chelate uptake system. In this review, the molecular mechanisms underlying root response to Si, Al, and Fe are described.

Referee: Professor Zed Rengel, Soil Science & Plant Nutrition, M087, University of Western Australia 35 Stirling Highway, CRAWLEY WA 6009, Australia

Keywords:

• chelation
• nutrient acquisition
• metal detoxification
• transporter

ACKNOWLEDGMENT

Many thanks to Fangjie Zhao, Peter Ryan, Julie Hayes, Jun Furukawa, Daisei Ueno, and Namiki Mitani for their critical reading of this manuscript. The study was partly supported by a Grant-in-Aid for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology of Japan (Nos. 15380053 and 15208008), a grant from the Ministry of Agriculture, Forestry and Fisheries of Japan (Rice Genome Project IP-5003 and QT3006).

Notes

Referee: Professor Zed Rengel, Soil Science & Plant Nutrition, M087, University of Western Australia 35 Stirling Highway, CRAWLEY WA 6009, Australia