Floret Degradation And Its Response To Nitrogen In Wheat

The number of grains per spike of wheat(Triticum aestivum L.)is determined by the number of spikelets,the number of florets per spike and floret setting percentage,while floret setting percentage was determined by floret degradation.The degradation of florets during spike development greatly reduces the probability of florets to continue to develop,and ultimately reduces the number of grains per spike.the number of grains per spike.Nitrogen is one of the three nutrition elements of wheat.Nitrogen application can promote the photosynthesis of wheat,and is an important cultivation measure to improve the yield and quality of wheat.Nitrogen application in the degenerated stage of floret could not only stabilize the number of effective spikes,but also increase the number of grains per spike.However,the morphological and structural characteristics of floret degradation in wheat and the pathways of nitrogen regulation remain unclear.In this study,spring wheat ’Young Mai 15’ and winter wheat ’Zhong You 16’ were used as experimental materials.After stripping the protective and inner glume of young spikes of wheat,stereomicroscopes and cameras were used to record the development process of young spikes of wheat,and analyzed the difference of gene expression in different stages of floret development(prophase of anther connective stage and prophase of pollen development)by transcriptome sequencing.After that wheat were treated with 0,120 and 240 kg/hm2 nitrogen in the early stage of floret degeneration(anther connective stage),and the characteristics of floret degeneration in each stage were recorded.The main research results are as follows:(1)During the pollen development period of the florets,the pistil and stamens were found to be shrunken through the observation of morphology and microstructure,and the cells that promote pollen development in the anther sac appeared vacant.The vascular system of spikelet rachis narrowed from the base to the top of the spikelet,and the vascular bundle of spikelets in sterile florets was thin and the number decreased continuously.The appearance of the above morphological characteristics is not conducive to the development of florets,leading to the degeneration of the distal floret primordia into degenerated florets.The research on the change of endogenous hormone content during floret development found that the content of auxin increased with the progress of flower development,while the content of abscisic acid first increased and then decreased,reaching the highest peak in the period of pistil feather elongation.(2)Transcriptome sequencing results showed that there were 10798 differentially expressed vs genes in floret degeneration,5774 of which were up-regulated and 5024 of which were down-regulated.GO functional enrichment and KEGG pathway analysis showed that the above differentially expressed genes were related to programmed cell death,floral organ aging and pollen development,including abscisic acid activation signal pathway,plant hormone signal transduction and auxin biosynthesis.In the above results,77 genes were screened.The up-regulated genes EAT1 and PTC1 are related to floret development and programmed cell death.These two genes may participate in floret degeneration by regulating the programmed death,degeneration and abortion of tapetal cells in anthers;the up-regulated gene TAA1 mediates auxin biosynthesis;the down-regulated gene TIFY 11b is involved in the jasmonic acid-mediated signaling pathway.(3)When the apical spikelets were not differentiated,nitrogen treatment could effectively delay the differentiation of top spikelets in Yangmai 15,and the number of side spikelets increased.After nitrogen treatment at anther connective stage,the growth rate of wheat spike length was significantly accelerated,but the floret development process was slowed down,and the pollen development cells in the anthers of F4 florets were intact under N240 nitrogen application.Nitrogen application had a greater effect on the F3 and F4 florets at the apical and basal spikelet of the two cultivars.For Yangmai 15,nitrogen application can tap the development potential of F4 florets in the middle spikelet,while the F5 florets in the middle spikelet of Zhongyou 16 have a greater potential to develop into grains.N240 nitrogen application significantly increased the dry weight of wheat caryopsis and cob,promoted the transfer of dry matter from the cob to each spikelet,increased the distribution ratio of dry matter in the spikes,and provided the nutrients needed for the development of F4 and F5 florets.N240 nitrogen application could significantly increase the number of grains per spike,the number of spikelets,the length of panicle and the weight of grains per spike.The above research results indicated that the floret degeneration event occurred in the early stage of pollen development,and the degenerated florets were white and shrunken,with intact anther epidermis but no pollen development cells.Transcriptome sequencing analysis during floret degeneration and before floret degeneration showed that EAT1,PTC1,TAA1,TIFY 11b and other genes may be involved in the floret degeneration process.Nitrogen fertilization at intervals before floret degeneration is beneficial to delay floret development,promote the distribution of dry matter,and make distal florets develop into grains.N240 nitrogen application significantly improves the spike traits of wheat.This study expounded the basic characteristics of floret degeneration from multiple perspectives such as morphology,physiology,and molecular level.The results of the study have important theoretical significance for finding more agronomic measures to delay floret degeneration and increase the number of grains per spike in wheat production.The breeding of new wheat varieties with large spikes and low grains per spike and the improvement of wheat yield also have certain practical significance.