Specialized metabolites present in Camellia reticulata nectar inhibit the growth of nectar-inhabiting microorganisms

Lijie Xun ^1,2 Rong Huang ¹ Qiongyan Li ² Qingxin Meng ¹ Rui Su ² Xiaoman Wu ¹ Renbin Zhang ³ Linshu Li ⁴ Xueyang Gong ¹ Kun Dong ^1*

• ¹ Yunnan Agricultural University, Kunming, Yunnan, China
• ² Institute of Sericulture and Apiculture, Yunnan Academy of Agricultural Sciences, Mengzi, Yunnan, China
• ³ Shaba State-owned Forest Farm of Tengchong, Tengchong, China
• ⁴ Animal Husbandry Workstation of Tengchong, Tengchong, China

Plant specialized metabolites are species-specific compounds that help plants adapt and survive in constantly changing ecological environments. Nectar contains various specialized metabolites, essential for maintaining nectar homeostasis. The results of this study revealed that some Camellia reticulata nectar can spoilage and deteriorate, disrupting its nectar homeostasis, and significantly reducing the pollination efficiency of C. reticulata by pollinators. Compared to natural nectar, the spoilage nectar exhibited significant changes in color, odor, sugar composition, pH, and hydrogen peroxide (H2O2) content. Additionally, the number of species as well as the quantity of microorganisms in the spoilage nectar were considerably higher than those in natural nectar.Quantitative testing revealed that the H2O2 content in natural nectar could reach (55.5 ± 1.80) μM, whereas it was undetectable in spoilage nectar. Furthermore, 364 differential metabolites were identified between spoilage nectar and natural nectar using Liquid Chromatography-Tandem Mass Spectrometry (LC-MS/MS) analysis, including various secondary metabolites, lipids, organic acids, and antibiotics. Fifteen different microbial strains were isolated and identified from the nectar of C. reticulata. In vitro experiments had verified the effects of metabolites screened from C. reticulata nectar on its isolated strains, demonstrated that H2O2 can inhibit all the bacteria in C. reticulata nectar with the exception of Serratia liquefaciens. 12-Methyltetradecanoic Acid inhibited Bacillus subtilis, Curtobacterium flaccumfaciens, and Rothia terrae, while Myristic Acid only inhibited Rothia terrae. However, the nectar metabolites screened in this study did not affect the nectar specialist yeast Metschnikowia reukaufii. In summary, the findings of this study revealed that C. reticulata nectar regulates the growth of microorganisms through its metabolites to maintain nectar homeostasis and prevent spoilage. The study enhances the understanding of the physiological mechanisms employed by C. reticulata to preserve nectar homeostasis and offers theoretical support for controlling nectar diseases and sustaining reproductive fitness in C. reticulata.