Metabolomics and transcriptomics analysis revealed the response mechanism of alfalfa to combined cold and saline-alkali stress.

Cold and saline-alkali stress are frequently encountered by plants, and they often occur simultaneously in saline-alkali soils at mid to high latitudes, constraining forage crop distribution and production. However, the mechanisms by which forage crops respond to the combination of cold and saline-alkali stress remain unknown. Alfalfa (Medicago sativa L.) is one of the most essential forage grasses in the world. In this study, we analyzed the complex response mechanisms of two alfalfa species (Zhaodong [ZD] and Blue Moon [BM]) to combined cold and saline-alkali stress using multi-omics. The results revealed that ZD had a greater ability to tolerate combined stress than BM. The tricarboxylic acid cycles of the two varieties responded positively to the combined stress, with ZD accumulating more sugars, amino acids, and jasmonic acid. The gene expression and flavonoid content of the flavonoid biosynthesis pathway were significantly different between the two varieties. Weighted gene co-expression network analysis and co-expression network analysis based on RNA-Seq data suggested that the MsMYB12 gene may respond to combined stress by regulating the flavonoid biosynthesis pathway. MsMYB12 can directly bind to the promoter of MsFLS13 and promote its expression. Moreover, MsFLS13 overexpression can enhance flavonol accumulation and antioxidant capacity, which can improve combined stress tolerance. These findings provide new insights into improving alfalfa resistance to combined cold and saline-alkali stress, showing that flavonoids are essential for plant resistance to combined stresses, and provide theoretical guidance for future breeding programs.

Directional emission from ZnO hexagonal disks.

Lots of theories and experiments have so far tried to acquire the directional emission with whispering-gallery modes (WGMs) from micro- and nanostructures, which will enhance the applications of micro- and nanoscaled whispering-gallery resonators in optoelectronic devices. Here for the first time we report a series of directional emission patterns with WGMs from the single ZnO hexagonal micro- and nanodisk. Based on the cathodeluminescence technique, we observed far-field emissions from ZnO hexagonal micro- and nanodisks in four geometries with different deformations. Mechanisms of directional emissions above were suggested. These investigations facilitated the applications of ZnO hexagonal micro- and nanodisks in photonic devices.