Changes in plant anthocyanin levels in response to abiotic stresses: a meta-analysis

Anthocyanins are small molecule antioxidants that play important roles in plant response and resistance to abiotic stresses. Their levels increase when plants are exposed to abiotic stress. However, the general response patterns and magnitude of anthocyanin increase, and how they confer resistance to abiotic stresses, are difficult to evaluate because of the influence of experimental variables. In this study, changes in plant anthocyanin content under different abiotic stresses and the effect of anthocyanin overproduction on various physiological indicators were investigated through meta-analysis derived from 1039 datasets of 102 studies. Results showed that among the different stress types, heavy metals, especially copper (Cu) and mercury (Hg), induced the most significant synthesis of anthocyanins. Among the different types of drought treatments, mannitol caused anthocyanin content in plants to increase by 2.4-fold, which was more significant than that of polyethylene glycol and natural drought. Furthermore, UV stress led plant anthocyanins to increase 1.3-fold in C4 plants, which was higher than that in C3 plants. In addition, anthocyanins increased the most when the applied stresses were low and moderate, and of short duration. Moreover, plants overexpressing genes encoding MYB transcription factors increased anthocyanin content by 5.8-fold and significantly improved plant stress tolerance. Among the 21 physiological indicators, glutathione and proline levels increased the most in transgenic plants overproducing anthocyanins when exposed to abiotic stress. Taken together, this meta-analysis indicates that anthocyanins enhance stress tolerance by improving the antioxidant, metal-chelating, and osmoregulatory abilities of the plant. The results presented here can help guide future applications of anthocyanins as plant growth regulators in dryland agriculture and breeding for plant stress tolerance.