Biological Characteristics Research On Dormancy And Flower Bud Differentiation Of Crocus Sativus L.

Crocus sativus L.,commonly called saffron,is not only a valuable traditional Chinese medicine,but also the world’s most expensive spice and dye.This plant can’t reproduce sexually because of the triploidy of its chromosomes,so it produces asexually mainly via corm nutrition.In recent years,due to the lack of intensive research on its dormancy and flowering characteristics,compared with the original place,the saffron in China still exists many problems,such as corm degeneration,flowering shortened,low yield stigma.Which seriously restricts the cultivation and promotion of Crocus sativus and affects the healthy development of saffron industry in China.Therefore,this subject systematically studied the changes of morphological structure,physiological and biochemical and differential gene expression in saffron corms during indoor dormancy and flower bud differentiation,in order to explore the dormancy releasing and flower bud differentiation process of Crocus sativus from the microscopic structure,and to discuss the mechanism of releasing dormancy and flowering from the aspects of physiology,biochemistry and molecular regulation.This study provided a theoretical basis for the development of new techniques such as artificial dormancy breaking,flowering regulation and yield expansion of Crocus sativus.The main research results are as follows:1.Morphological structure research of Crocus sativus during the dormancy and flower bud differentiation processThe saffron corms do degenerate in actual planting and production,especially in diameter and fresh weight.There was no significant change in the external morphology of the saffron corms during the dormancy and flower bud differentiation,but significant structural changes occurred inside the apical bud.From late June to early July,the apical buds of the saffron were still in the vegetative growth stage,and no organ differentiation occurred during this period.In the middle of July,the apical buds began to differentiate into leaf primordia,suggesting that the saffron corms have completely broken dormancy.From early August to middle of September,the floral organs of saffron were differentiated in the order of floral primordium,perianth primordium,stamen primordium and pistil primordium.The whole flower bud differentiation process took about 45 days,which was faster in the early stage of differentiation and slower in the later stage.2.physiological and biochemical research of Crocus sativus during the dormancy and flower bud differentiation processThe physiological and biochemical indexes of saffron in the process of dormancyand flower bud differentiation showed a regular change:the starch content in the apical bud tissues decreased during the whole dormancy maintenance and release process,the soluble sugar content first increased and then decreased,and the soluble protein showed a dynamic change trend of decrease-increase-decrease.The activities of antioxidant enzymes including CAT,POD and SOD decreased to some extent before dormancy breaking.ABA content increased first and then decreased,the contents of GA₃,IAA and the ratios of GA₃/ABA and IAA/ABA continued to increase with the release of dormancy.The ZT content was relatively stable and did not increase or decrease significantly.Which indicated that the inhibition of ABA may be one of the factors that induced dormancy of saffron corms,and the high levels of soluble sugar,protein,GA₃,IAA and low activity antioxidant enzymes contributed saffron corms to breaking dormancy.During the whole process of flower bud differentiation（12-18 weeks）,the starch content continued to decrease,the soluble sugar increased sharply in the early stage of differentiation,and the protein content was at a higher level,but decreased slightly at the end of differentiation.The activities of CAT,POD and SOD increased as a whole,and POD and SOD peaked at the pistil primordium and stamen primordium differentiation stages,respectively.The content of ABA decreased continuously,IAA increased first and then decreased,ZT content continued to increase,GA₃ showed no obvious change,but its ratio with ABA showed a significant upward trend.Which indicated that higher levels of soluble sugar and IAA contribute to the initiation of flower bud differentiation of saffron,while low levels of ABA,high content of protein,ZT,high ratio of GA₃/ABA,ZT/ABA and high activity antioxidant enzymes facilitate the morphological development of flower organs.Among which highly active POD was more conducive to the differentiation of pistil primordium,high activity SOD was more favorable to the differentiation of stamen primordium.3.Transcriptomic research of Crocus sativus during the dormancy and flower bud differentiation processThe saffron transcriptomic database was constructed with the apical bud tissues at dormancy,dormancy breaking and flower bud differentiation stage.A total of 60,203Unigene sequences were obtained by Illumina sequencing,of which 34,265 Unigenes were annotated in the Nr,Swiss-Prot,KOG,KEGG databases.Using FDR<0.05 and|log2FC|>1 as the standard,a total of 19,490 differentially expressed Unigene sequences were obtained.These differential genes were widely involved in the regulation of various substances metabolism,cell division,proliferation,differentiation,and catalytic activity.And mainly involved in amino acid synthesis,protein processing,ribosome,starch sucrose metabolism,hormone signal transduction,carbon metabolism and other biochemical metabolic pathways.Focusing on the analysis of expression patterns of 208 differential gene associated with dormancy and flowering regulation pathways,including sugar metabolism,hormone signal transduction,cell cycle regulation,reactive oxygen metabolism,photoperiod and autonomous pathways,we found that most of the gene expression was significantly up-regulated.Combining the research results of morphological structure,physiological and biochemical and other related studies,a molecular regulation model of saffron breaking dormancy and flowering transition was proposed:the dormancy state of saffron corms was gradually broken under the regulation of sugar metabolism,hormone signal transduction,cell cycle regulation and reactive oxygen metabolism pathways,afterwards the saffron corms under the regulation of sugar signal,hormone signal transduction,photoperiod and autonomous pathway succeeded in achieving the transition from vegetative growth to reproductive growth,namely floral transition.