Transcriptomic and Metabolic Analysis Reveal Potential Mechanism of Starch Accumulation in Spirodela polyrhiza Under Nutrient Stress

Compared with traditional grain starch sources, duckweed (<i>Spirodela polyrhiza</i>, <i>S. polyrhiza</i> for simple) does not require soil to produce starch, and the process is less affected by the external environment. Moreover, it produces high levels of starch under certain conditions. This study investigated the patterns and mechanisms of starch accumulation in <i>S. polyrhiza ZH0196</i> under nutrient stress by determining the changes in starch content, photosynthesis, and amylase activity at different stress induction times. Under nutrient stress, the culture solution was replaced with deionized water. The starch content increased from 1.95% to 41.71% (dry weight) after 2 days of nutrient stress induction. Short-term nutrient-stress treatment had little effect on frond photosynthesis, enhanced the activity of starch synthesis-related enzyme, and weakened the activity of degradation-related enzymes. The transcriptome results further indicated that the key genes and metabolic patterns of starch synthesis promoted starch accumulation in <i>S. polyrhiza ZH0196</i> fronds by accelerating the response to CO₂ fixation via the Calvin cycle, promoting straight-chain starch synthesis, and decreasing starch degradation after short-term oligotrophic treatment. This study suggests that nutrient stress is a green and efficient method of increasing the starch yield of duckweed, which represents an important insight for developing duckweed starch resources.