Enzymatic loosening mechanism of endosperm weakening plays a key role in promoting carrot (Daucus carota L.) seed germination by hydro-electro hybrid priming.

• Carrot seeds treated with HEHP showed better germination characteristics. • Mannose metabolism was upregulated by HEHP at both the mRNA and protein levels. • MAN plays a dominant role in the endosperm weakening of carrot seeds. As an innovative physical priming technique, hydro-electro hybrid priming (HEHP) tends to significantly promote the seed germination of carrot. Endosperm weakening at micropylar endosperm is a critical regulatory mechanism for seed germination, but it is unclear whether it plays a role in promoting seed germination through HEHP treatment. In the present work, we conducted association analysis between transcriptome and proteome data of the previous studies and found that HEHP promoted the mannose metabolism in carrot seeds, with key enzymes involved in mannan degradation called β-mannanase (MAN) and the coding genes were both significantly upregulated in HEHP treatment. Based on this, the subcellular structure of micropylar endosperm, the activity of key enzymes in mannan degradation and the expression pattern of MAN coding genes during the germination process were further studied. The results showed that carrot seeds subjected to the priming treatments exhibited more significant endosperm weakening during germination, with significant degradation of the cell wall of micropylar endosperm, and among the three key enzymes involved in mannan degradation, only MAN activity showed significant differences at micropylar endosperm and non-micropylar endosperm. In addition, the priming treatments, especially the HEHP treatment, significantly upregulated the expression of MANs before sowing, and the expression levels of MANs at micropylar endosperm were significantly higher than those at non-micropylar endosperm. Ultimately, it is confirmed that the rapid germination of carrot seeds is closely related to the enzymatic loosening mechanism of endosperm weakening, and that MAN plays a key role in this process. The results ulteriorly deepen the understanding of the rapid germination mechanism of carrot seeds treated with HEHP. [ABSTRACT FROM AUTHOR]