Abstract:

Objective: This study investigates the physiological and biochemical mechanisms by which spermosphere fungi promote the germination of Ormosia henryi seeds, aiming to provide a theoretical foundation and microbial resources for breaking dormancy of seeds with hard seed coats in tree species. Method: Three fungal strains with germination-promoting activity, isolated from the spermosphere soil of O. henryi, were used to evaluate their capacity to secrete seed coat-degrading enzymes and produce endogenous hormones. Three fungal strains were used to initiate germination experiments on O. henryi seeds, and the physiological and biochemical indicators in the seeds were measured at various stages of germination. Seeds treated with conventional methods served as controls to verify the priming germination effects by the fungi. A systematic assessment was carried out to elucidate the physiological regulatory effects of the three spermosphere fungi on germination of O. henryi seeds. Result: 1) The strains SS-1-14, SS-2-3, and SS-2-22 all secreted seed coat-degrading enzymes within 7 days of cultivation. SS-1-14 preferentially degraded the pectin layer, SS-2-3 consistently released highly active pectinase and lipase, and SS-2-22 efficiently disrupted the seed coat barrier at the initial stage by rapidly producing both cellulase and pectinase. 2) All strains produced auxin and cytokinin precursors, thereby promoting embryonic cell differentiation. SS-1-14 generated high levels of indoleacetic acid, salicylic acid, and salicylic acid glucoside, which both promote growth and activate systemic resistance. SS-2-3 produced higher quantities of indole-3-acetonitrile, tryptamine, and zeatin, which directly influence cell division and plumule differentiation. SS-2-22 primarily synthesized auxin and cytokinin precursors of N6-isopentenyladenosine and isopentenyladenine, which were converted into active hormones to reduce metabolic burden. 3) The priming effect of spermosphere fungi effectively promoted seed germination by dynamically regulating antioxidant enzymes and storage material metabolism in O. henryi seeds. The three strains enhanced antioxidant capacity by regulating CAT and PPO throughout germination, and POD and SOD during the last stage. SS-1-14 exhibited the most pronounced regulatory effect, significantly increasing SOD activity in the last stage of germination by 19.10%, and CAT activity in the early and last stages of germination by 127.13% and 41.20%, respectively. The three strains promoted storage material mobilization by regulating protease and lipase activities throughout germination, as well as amylase and acid phosphatase activities in the last stage of germination. SS-1-14 exhibited the most pronounced effect, increasing protease and lipase activities by 67.31% and 58.61% in the early stage of germination, and by 77.16% and 59.32% in the last stage of germination, respectively. All three strains were able to accelerate macromolecule degradation and micromolecule generation throughout germination, among which SS-1-14 had the best comprehensive effect, increasing triglyceride degradation by 32.20% in the early stage of germination and starch degradation by 60.51% in the last stage of germination, and accelerating ATP production by 188.83% in the early stage of germination and soluble sugar accumulation by 65.24% in the last stage of germination. 4) Compared with traditional physical and chemical treatments such as scarification, acid etching, and hot water soaking, fungal induction reduced seed electrical conductivity and MDA content, alleviated oxidative damage during germination, and preserved cell membrane integrity. Conclusion: Spermosphere fungi promote the germination of O. henryi seeds through a multidimensional “physical-chemical-biological” priming mechanism. This mechanism involves secreting enzymes that degrade the seed coat to overcome mechanical barriers, synthesizing phytohormones to activate seed physiological activity, and enhancing antioxidant and material-converting enzyme systems to reduce germination-induced damage and facilitate storage material mobilization.

Key words: spermosphere fungi, Ormosia henryi, hard seed, bio-priming, physical dormancy