Proline ——Improve plant resistance to osmotic stress and pollen viability

Proline is one of the components of plant proteins and can exist widely in plants in free state. Under drought, salinity and other stress conditions, proline accumulated in many plants. In addition to being a osmotic regulator in plant cytoplasm, proline also plays an important role in stabilizing biological macromolecular structure, reducing cell acidity, relieving ammonia toxicity and regulating cell redox as an energy bank. Under stress conditions (drought, saline alkali, heat, cold and freezing), the content of proline in plants increased significantly. The content of proline in plants reflects the stress resistance of plants to a certain extent. Varieties with strong drought resistance often accumulate more proline. Therefore, the determination of proline content can be used as a physiological index of drought resistance breeding. In addition, due to its strong hydrophilicity, proline can stabilize the protoplast colloid and the metabolic process in the tissue, so it can reduce the freezing point and prevent cell dehydration. At low temperature, the increase of proline in plant tissue can improve the cold resistance of plants. Therefore, it can also be used as a physiological index of cold resistance breeding. In organisms, proline is not only an ideal osmotic regulator, but also a protective substance for membranes and enzymes and a free radical scavenger, so as to protect the growth of plants under osmotic stress. For the accumulation of another important osmotic regulator in vacuoles in potassium ion organisms, Proline can also regulate the osmotic balance of cytoplasm.

The role of proline accumulation in environmental stress has always been the focus of plant stress molecular biology. At the same time, accumulating evidence shows that proline also plays an important role in plant growth and development. Studies have shown that proline, as a signal molecule, can promote plant flowering. It can also induce the production of reactive oxygen species, cause programmed cell death, and inhibit the growth of plant seedlings. Indeed, proline can induce the expression of many genes. This effect of proline is mediated by signal transduction pathway. As a storage of nitrogen and energy, proline may provide energy for some energy consuming physiological processes, especially in stress recovery. Despite its importance, the molecular mechanism of this effect of proline needs to be further studied.