Mechanism and application of germanium in plant growth

Germanium (Ge), a semiconductor element belonging to group IV of the periodic table which is a series of carbon (C), silicon (Si), getin (Sn) and lead (Pb), can scavenge reactive oxygen species (ROS) and is widely used in electrons and medicine. Although studies have shown that Ge exists in animals, plants and biomaterials, limited studies have analyzed the effect of Ge on plant physiology. Recent studies on plant Ge have mainly focused on improving plant growth and quality, and on plant damage toxicity. Thus in order to comprehensively understand Ge and its bioactivities, a detailed review of physiochemical properties, origin and distribution of Ge was conducted in this paper. The mechanisms of plant physiological and biochemical response to Ge as well as the application of Ge in plant growth were also comprehensively discussed. Ge could directly scavenge ROS due to its electron configuration 4S²4P². Ge played pivotal role in key enzyme activities and microbes related to nutrient transformation and cycling in soil. In plants, Ge changed nutrient absorption and utilization at a high efficiency. Ge also influenced plant photosynthesis by varying photosynthetic pigments. Ge enhanced the activities of endogenous antioxidant enzymes and non-enzymatic substances by chelating reaction in some vegetable and cereal plants. It increased the accumulation of polysaccharides, sugars, soluble proteins and amino acid in several plants. However, with excessive accumulation of Ge, normal metabolism of roots and shoots was interrupted in plants. Studies on the absorption, transport and distribution of Ge in plants as well as the corresponding mechanisms were very few. In future, there was need for further studies on the interactions of other elements with Ge. Until now, the application of Ge in agricultural production included seed germination, seedling growth and plant quality. Ge had also been applied to control algae growth. This paper provided the basis for Ge regulation of plant growth and the responding physiological and ecological mechanisms. It also provided a useful guide for Ge uptake by plants.