Osmanthus fragrans （Thunb.） Lour. is one of the ten traditional flowers in China and is well known for its fragrance. This study focused on the dynamic characteristics of the aromatic components and anatomical observation of the perianth in three cultivars of O. fragrans. The results could lay the foundation for further the development and utilization of O. fragrans.
Three cultivars of O. fragrans (‘Rixiang Gui’, ‘Yucheng Dan’ and‘Boye Yin’) were sampled at four flowering stages：the Xiangyan stage, initial flowering stage, full flowering stage, and final flowering stage. Then, the aromatic components in the three cultivarswere detected and analyzed by headspace solid-phase microextraction and gas chromatography-mass spectrometry (GC-MS). Further, the differences in the aromatic components among the three cultivars were evaluated using the multivariate statistical analysis. In addition, the perianth microstructure was observed by scanning electron microscopy and transmission electron microscopy.
The GC-MS analysis detected a total of 51 volatile aromatic components, most of which were terpenes. Among the three cultivars of O. fragrans, 29, 27 and 33 aromatic components were identified in the petals of ‘Rixiang Gui’, ‘Yucheng Dan’ and ‘Boye Yin’, respectively. According to the relative content of aromatic components, the main components in the three cultivars of O. fragrans included linalool, cis-linalool oxide, trans-linalool oxide, α-ionone, β-ionone, and 2H-β-ionone; in addition, some common aromatic substances, such as trans-β-ocimene, cis-β-ocimene, and γ?decalactone were identified. The differences in the relative content of aromatic components and the interaction of all aromatic components together resulted in the unique aroma of the different cultivars. For example, β?ionone was the main aromatic component in the petals of ‘Boye Yin’, but its relative content was lower in ‘Yucheng Dan’. Linalool and its oxides were the main aromatic components in the petals of ‘Rixiang Gui’ and ‘Yucheng Dan’, but not in the petals of ‘Boye Yin’. The results from the partial least squares-discriminate analysis showed different aromatic components in the three cultivars of O. fragrans. Moreover, 10 critical differential compounds were screened using variable importance in projection, namely, ethyl butanoate, cis-linaloloxide, trans-β-ocimene, 4-(2,6,6-trimethyl-cyclohex-1-enyl)-butan-2-ol, γ?decalactone, 3-hydroxy-2-butanone, (E)-2-hexenal, megastigma-4,6(E),8(Z)-triene, cis-β-ocimene, and β-ionone. The cluster analysis based on the relative content of the 10 key differential compounds showed that three flowering stages (the Xiangyan stage, initial flowering stage, and full flowering stage) of ‘Rixiang Gui’ (A1, A2, A3), ‘Yucheng Dan’ (B1, B2, B3), and ‘Boye Yin’ (C1, C2, C3) could be clustered together, respectively, implying that the three cultivars could be distinguished by the amounts of the 10 key aromatic substances that they possessed during these three stages. However, the final flowering stage of the three cultivars could be clustered together. This may have been because of the decreased content of volatile aromatic substances during the final flowering stage; the weakened ability of the flower to release aroma may have led to the lack of major differences in the fragrance of the cultivars. The results of the scanning electron microscopy and transmission electron microscopy revealed abundant fold structures on the cell surface of the petals. The fold structures in the petals of ‘Boye Yin’ and ‘Yucheng Dan’ were more regular than that in the petals of ‘Rixiang Gui’. The density of the structures differed among different cultivars; for example, it was higher in the petals of ‘Boye Yin’ than that in the petals of ‘Rixiang Gui’ and ‘Yucheng Dan’. In addition, we observed a large number of granular substances (osmiophilic matrix granules) attached inside the cells and on the cell surface in the petals of O. fragrans.These granules were highly volatile aggregates of aromatic substances. The density and quantity of granules in the petals of ‘Boye Yin’ and ‘Rixiang Gui’ were higher than those in the petals of ‘Yucheng Dan’. We speculated that there were no secretory structures on the surface of O. fragrans petals; instead, most cells in the petals had aromatic glands involved in the synthesis and secretion of aromatic substances. The whole petal was like a large aromatic gland where the aggregates of aromatic substances (osmiophilic matrix granules) formed in the cytoplasts, then overflowed from the cell walls, spilled out through the abundant fold structures in the epidermal cells, and quickly evaporated. We surmised that this was why O. fragrans was highly fragrant.
There were similar and differential aromatic substances among the three cultivars of O. fragrans, and the differing proportions of these aromatic substances led to the unique aroma of the three cultivars. Overall, the floral fragrance of O. fragrans mainly differed according to the cultivar but was also affected bythe flowering stages. In addition, the differences in the density of fold structures and the amount of aromatic substance (osmiophilic matrix granules) aggregated on the epidermal cells of the perianth in the three cultivars of O. fragrans may be reasons for the differences in fragrance.
Lagerstroemia is an economically important ornamental shrub that is distributed from tropical to northern temperate zones. It commonly blooms from summer until fall， and it has a significant value in city landscaping and environmental protection. However， classification of Lagerstroemia plants at the species level is currently challenging. To provide a theoretical support for crape myrtle breeding and identification， 85 Lagerstroemia germplasms were collected and the genetic diversity of Lagerstroemia germplasm resources was studied using single nucleotide polymorphisms （SNP） markers.
85 Lagerstroemia germplasms at home and abroad were used to study genetic diversity. The high-quality SNP markers were selected depending on the mini-sequencing result. The polymorphism information content （PIC）， expected heterozygosity （He）， gene diversity， and genetic similarity （GS） were calculated using PowerMarker V3.25 software. The genetic distance between the 85 germplasms was calculated based on Nei’s 1972 method. A dendrogram of 85 Lagerstroemia germplasms was constructed using MEGA 6.0 software according to the genetic similarity based on neighbor-joining method. Additionally， 85 samples were classified based on four different flower colors （46 purple-flowered， 26 red-flowered， 5 white-flowered， and 5 compound-flowered individuals）. Next， the genetic differentiation parameters with the cluster and color groups were computed using GenAIEx 6.5 software， and the genetic diversity and genetic relationship were analyzed among the cluster and color groups.
The 21 high quality SNP markers were selected from MassARRAY sequencing results. The polymorphic information content of Lagerstroemia germplasm resources ranged from 0.04 to 0.37 and the mean was 0.33. The expected heterozygosity ranged from 0.12 to 0.49 and the mean value was 0.33. The genetic similarity ranged from 0.24 to 0.95. The 85 Lagerstroemia germplasms were divided into seven major groups using the unweighted pair group method with the arithmetic mean （UPGMA） method cluster analysis. The cluster group Ⅵ had the highest number of alleles with the 2.00， and the cluster group Ⅶ had the lowest number of alleles with 1.33. In contrast to the expected heterozygosity and observed heterozygosity， cluster group Ⅰ had the highest value and cluster group Ⅱ had the lowest. Meanwhile， the 85 Lagerstroemia germplasms were classified into four major groups based on four different flower colors， including the purple-flowered， red-flowered， white-flowered， and compound-flowered group. The purple-flowered group had the highest number of alleles at 2.00， while the compound-flowered group was the lowest at 1.33.
Lagerstroemia possessed abundant genetic diversity and high levels of gene flow between groups. The purple-flowered and white-flowered groups had the highest genetic diversities. In addition， the SNP markers were useful for analyzing the genetic diversity of Lagerstroemia.
To illustrate the response mechanism to salt stress, effects of different concentrations of salt stress on biomass partitioning, photosynthetic characteristics and chloroplast ultrastructure in seedlings of Cornus hongkongensis subsp. elegans were analyzed.
The seedlings were cultured in the 1/2 Hogland nutrients solution with five salt gradient concentrations［0(CK), 0. 20% , 0. 30% , 0. 40% , 0. 45%)］. During culture, salt injury symptoms in seedlings were recorded, photosynthetic parameters(including gas exchange parameters, chlorophyll fluorescence parameters, chlorophyll content)were measured, and changes of chloroplast ultrastructure were observed. Also, the responses of biomass partitioning to salt stress were assessed at the end of experiment.
Salt-damage symptoms such as yellowing, purplish and anthracnose-like gradually appeared in the leaves of seedlings from bottom to top under salt stress. With the increment of salt concentration and the elongation of stress, leaves and new shoots withered, until the whole plant wilted and died. Periods of 50% survival for treatments with >0. 20% salt concentrations were lower than 20 days. Although gradual increments were monitored in biomass of root /shoot with strength of salt stress, the effects of salt stress on biomass partitioning was still not significant. With the increase of salt concentrations and the lasting duration of culture, net photosynthetic rate(Pn), stomatal conductance(Gs), intercellular CO2 concentration(Ci)and transpiration rate(Tr) were decreased, but leaf water use efficiency(EWUE)was improved. Of all salt treatments, photosynthetic parameters in seedlings suffering from 0. 20% salt stress were affected slightly. Compared with a little effect of salt stress on maximum optical quantum yield(Fv/Fm), the potential photochemical activities of PSⅡ(Fv/F0)were significantly affected by salt stress. Significantly, treatments with >0.20% salt concentrations decreased the contents of chlorophyll a(Chl a), chlorophyll b(Chl b), total chlorophyll(Chl a+b) and carotenoid(Car). Meanwhile, salt stress obviously changed chloroplast ultrastructure, showing that number of starch grains, lipid droplets and osmiophilic globules in chloroplast were increased, and stromal lamellae structure was loose and getting swell with strengthen of salt stress.
Salt stress exerted significantly inhibitions on photosynthetic characteristics and chloroplast ultrastructure, resulting in various salt-damage symptoms on leaves of seedlings and different survival rates corresponding to salt concentrations. Considering the responses of all measured indexes to salt stress, growth, photosynthetic characteristics and chloroplast ultrastructure in seedlings of Cornus hongkongensis subsp. elegans treated with 0.20 % salt concentration were similar to that of CK, which is in accord with the results of field trial.
