| Symplocos paniculata,a group of morphologically similar plants within the Symplocos genus of the Symplocaceae family,possesses fruits with a high oil content,rendering them suitable for cultivation as edible oilseed trees.Nonetheless,flowering patterns and low fruit set rate vary among different species of Symplocos paniculata.To address this,we conducted a comparative analysis between Symplocos chinensis and Symplocos hunanensis,both widely distributed in Hunan and exhibiting desirable characteristics such as high fruit oil content and economic viability.Our investigation encompassed the floral bud differentiation process,endogenous hormones,endogenous polyamines,and nutrient composition,employing a multidisciplinary approach encompassing morphology,anatomy,physiology,biochemistry,and transcriptomics.We also screened the key genes in the phytohormone signal transduction pathway in the bud dormancy of Symplocos paniculata,with the aim of providing scientific basis for the selection and cultivation management of Symplocos paniculata.The main findings of this paper are as follows:1.Different Symplocos paniculata floral bud differentiation processes.According to the morphological and anatomical studies,it was found that the bud scales of Symplocos chinensis flower buds had longer and more villi covered,while the outer villi of the bud scales of Symplocos hunanensis flower buds were short and less;the flower buds of Symplocos chinensis were light in color and the bud scales were softer,while the flower buds of Sympolocos The flower buds of Symplocos chinensis were light in color and had soft bud scales,while those of Symplocos hunanensis were dark in color and had hard bud scales.The morphological differentiation of flower buds was initiated in mid-September in Symplocos chinensis and in late September in Symplocos hunanensis by field observation and combined with the anatomical results,and both finished flower bud differentiation in mid-late March of the following year;anatomical observation of the process of bud differentiation revealed no significant differences in the internal microstructure of the two species.2.Different Symplocos paniculate Variation in nutrient content of flower bud differentiation.At the stage of physiological differentiation of flower buds,the contents of soluble sugars,starch and protein in the flower buds of Symplocos chinensis and Symplocos hunanensis increased,which contributed to the transition from physiological to morphological differentiation of flower buds of both species;in the morphological differentiation stage of flower buds,the soluble sugar content increased,the protein content decreased,and the starch content decreased and then increased in Symplocos chinensis and Symplocos hunanensis flower buds,indicating that the soluble sugar content promoted the morphological differentiation process of flower buds of both species;during bud dormancy,the starch content of Symplocos chinensis and Symplocos hunanensis decreased and the soluble sugar content increased,indicating that bud dormancy requires a large amount of energy for maintenance.The accumulation of soluble sugars helps to release dormancy of flower buds in the following year.3.Different Symplocos paniculata Variation in endogenous hormone content of flower bud differentiation.In Symplocos chinensis and Symplocos hunanensis,the contents of IAA,GA3,ABA,and ZR increased significantly at the stage of physiological differentiation of flower buds,indicating that the accumulation of IAA,GA3,ABA,and ZR contents in flower buds contributed to the transition from physiological differentiation to morphological differentiation of flower buds of the two Symplocos paniculata species;in the morphological differentiation stage of flower buds,the contents of IAA,GA3 and ZR in Symplocos chinensis and Symplocos hunanensis were significantly higher than those in the previous physiological differentiation stage,indicating that the increase of IAA,GA3 and ZR contents helped the morphological differentiation of flower buds of two species of Symplocos paniculata differentiation;when the flower buds entered dormancy,the IAA and ZR contents of Symplocos chinensis and Symplocos hunanensis decreased significantly,and when dormancy was lifted,the IAA and ZR contents started to increase,and the ABA and GA3 contents of the two Symplocos paniculata species were basically the same at this stage,indicating that the IAA and ZR contents the decrease of IAA and ZR contents and the increase of ABA and GA3 contents helped the flower buds to enter dormancy to adapt to the external environment,while the increase of I AA and ZR contents and the decrease of ABA and GA3 contents helped to release the flower buds from dormancy.4.Changes in endogenous polyamine content in flower bud differentiation in different Symplocos paniculata.At the stage of physiological differentiation of flower buds of Symplocos chinensis and Symplocos hunanensis,Spd and Spm contents increased and Put contents decreased,which helped the transition from physiological differentiation to morphological differentiation of flower buds;at the stage of morphological differentiation of flower buds,Spd and Put contents increased significantly,which helped the morphological differentiation of the two Symplocos paniculata flower buds;when flower buds entered dormancy,Spd and Spm contents increased,and when dormancy was lifted,Spd and Spm contents decreased,and Put continued to decrease throughout the dormancy process,indicating that the increase of Spd and Spm contents and the decrease of Put helped flower buds enter dormancy to resist low temperature,and the decrease of Spd,Spm and Put contents helped flower buds lift dormancy.5.Comparative transcriptomic analysis of different Symplocos paniculata flower buds.A total of 65 differential genes were screened in the phytohormone signaling pathway,and TIR1,AUX1/LAX,ARF,and ABF differential genes were selected by screening.Transcriptome analysis showed that the down-regulation of AUX1/LAX expression in Symplocos chinensis and Symplocos hunanensis might be The downregulation of TIR1 and ABF expression in Symplocos chinensis and Symplocos hunanensis was the main reason for the increase of IAA content and the decrease of ABA content when the flower buds of these two species entered dormancy.Symplocos chinensis and Symplocos hunanensis flower buds entered dormancy,and the increase of IAA content and decrease of ABA content helped the two Symplocos paniculata flower buds to release from dormancy. |
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