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This video is adapted from 10.3390/microorganisms9051041
In the rhizophagy cycle, bacteria alternate between a free-living phase in soils, where bacteria acquire soil nutrients, and an endophytic phase in root cells, where nutrients are extracted from bacteria. Reactive oxygen (superoxide) produced by root cells is used to extract nutrients from bacterial cells in the endophytic phase within root cells. It is thought that plants acquire a significant amount of nutrients from soil bacteria in the rhizophagy cycle, nutrients acquired may include nitrogen, phosphorus, potassium, etc. Some of the microbes internalized into roots are also spread to developing leaves of plants where they enter non-photosynthetic epidermal cells, particularly leaf hairs (called trichomes). Within the hairs on roots and leaves a sustained nutrient interaction between plant cells and endophytic nitrogen-fixing bacteria occurs where sugars are provided to microbes by plants and microbes provide nitrogen to plant cells. The mechanism of exchange in this symbiosis has been called the ‘nutrient exchange trap’, because once a microbe is engaged with the plant in nutrient exchange, it cannot exit the interaction under penalty of degradation by superoxide produced by the plant. The nutrient exchange trap is characterized by two chemical interactions as follows. The first chemical interaction between endophyte and plant is initiated by microbe-produced ethylene that triggers plant cells to grow, release nutrients and produce superoxide. The superoxide combines with ethylene to form products hydrogen peroxide and carbon dioxide. In the second interaction between microbe and plant the microbe responds to plant-produced superoxide by secretion of nitric oxide to neutralize superoxide. Nitric oxide and superoxide combine to form peroxynitrite that is catalyzed by carbon dioxide to form nitrate. The two chemical interactions underlie hypothesized nutrient exchanges in which plant cells provide intracellular bacteria with fixed carbon, and bacteria provide plant cells with fixed nitrogen. As a consequence of these two interactions between endophytes and plants, plants grow and acquire nutrients from endophytes, and plants acquire enhanced oxidative stress tolerance, becoming more tolerant to abiotic and biotic stresses.