Effects of exogenous melatonin on photosynthesis and physiological characteristics of chry-santhemum seedlings under high temperature stress.

We examined the effects of exogenous melatonin (MT) on the resistance of Chrysanthemum morifolium 'Jinba' to high temperature stress. Chrysanthemum leaves were sprayed with 200 µmol·L-1MT, and then subjected to high temperature stress at 40 ℃ (day)/ 35 ℃ (night). The ultrastructure of chloroplast and thylakoid of chrysanthemum leaves were observed, and the photosynthetic and physiological indices were measured. The results showed that the chloroplast and thyla-koid structures of chrysanthemum were damaged under high temperature stress. The chlorophyll contents and maximum fluorescence (Fm) were significantly reduced, while the OJIP curve changed with the fluorescence of K and J points increased. The net photosynthetic rate (Pn), transpiration rate (Tr) and stomatal conductance (gs) were significantly decreased, while the internal CO2 concentration (Ci) was significantly increased. The relative conductivity (REC), malondialdehyde (MDA), reactive oxygen species (ROS), osmotic adjustment substances content and antioxidant enzyme activity all increased significantly. Spraying exogenous MT onto leaves could maintain the integrity of chloroplast and thylakoid structure under high temperature in chrysanthemum and significantly decrease the increment in the K and J points of OJIP curve. Exogenous application of MT alleviated the inhibition of high temperature stress on photosynthesis and fluorescence of chrysanthemum, as indicated by significantly higher Fm, Pn, gs, Tr and photosynthetic pigment contents and lower Ci. Exogenous MT also significantly reduced the REC, MDA and ROS contents of chrysanthemum under high temperature stress, and enhanced the osmotic adjustment substances content and antioxidant enzyme activity in chrysanthemum leaves. It suggested that exogenous MT could protect the integrity of chloroplast structure of chrysanthemum leaves, enhance photosynthesis, inhibit the excessive production of ROS in the plants under high temperature stress, improve the activity of antioxidant enzyme system, reduce the level of membrane peroxidation and keep the integrity of lipid membrane, and thus improve the ability of chrysanthemum plants to resist high temperature stress.

[Effect of methyl jasmonate on aphid resistance of chrysanthemum.] / èŒ‰èŽ‰é ¸ç”²é ¯å¯¹èŠèŠ±æŠ—èšœæ€§çš„å½±å“.

We examined the effects of methyl jasmonate on aphid resistance of Chrysanthemum 'Hangbai'. Leaves of chrysanthemum cuttings were sprayed by methyl jasmonic with different concentrations (0.01, 0.05, 0.1, 0.5 and 1 mmol·L-1) and then inoculated with the aphids Macrosiphoniella sanborni. The following parameters are measured, including protective enzymes activities, defense enzyme activities, osmotic substances, secondary metabolites, and key genes of the jasmonic signaling pathway. The relationship between aphid resistance and the jasmonic signaling pathway in chrysanthemum was probed. The results showed that, under the treatments of all the five concentrations of methyl jasmonic, the activities of leaf protective enzymes and defense enzymes as well as the contents of secondary metabolite were increased in Chrysanthemum, whereas the contents of malondialdehyde and soluble sugar were reduced. Moreover, exogenous methyl jasmonate treatment induced the expression of CmAOS and CmCOI1, enhanced the content of endogenous jasmonic acid and the aphid resistance of chrysanthemum.

Comprehensive transcriptome analysis of grafting onto Artemisia scoparia W. to affect the aphid resistance of chrysanthemum (Chrysanthemum morifolium T.).

BACKGROUND: Aphid (Macrosiphoniella sanbourni) stress drastically influences the yield and quality of chrysanthemum, and grafting has been widely used to improve tolerance to biotic and abiotic stresses. However, the effect of grafting on the resistance of chrysanthemum to aphids remains unclear. Therefore, we used the RNA-Seq platform to perform a de novo transcriptome assembly to analyze the self-rooted grafted chrysanthemum (Chrysanthemum morifolium T. 'Hangbaiju') and the grafted Artermisia-chrysanthemum (grafted onto Artemisia scoparia W.) transcription response to aphid stress. RESULTS: The results showed that there were 1337 differentially expressed genes (DEGs), among which 680 were upregulated and 667 were downregulated, in the grafted Artemisia-chrysanthemum compared to the self-rooted grafted chrysanthemum. These genes were mainly involved in sucrose metabolism, the biosynthesis of secondary metabolites, the plant hormone signaling pathway and the plant-to-pathogen pathway. KEGG and GO enrichment analyses revealed the coordinated upregulation of these genes from numerous functional categories related to aphid stress responses. In addition, we determined the physiological indicators of chrysanthemum under aphid stress, and the results were consistent with the molecular sequencing results. All evidence indicated that grafting chrysanthemum onto A. scoparia W. upregulated aphid stress responses in chrysanthemum. CONCLUSION: In summary, our study presents a genome-wide transcript profile of the self-rooted grafted chrysanthemum and the grafted Artemisia-chrysanthemum and provides insights into the molecular mechanisms of C. morifolium T. in response to aphid infestation. These data will contribute to further studies of aphid tolerance and the exploration of new candidate genes for chrysanthemum molecular breeding.

[Effects of low temperature- and weak light stress and its recovery on the photosynthesis and chlorophyll fluorescence parameters of cut flower chrysanthemum].

The cut flower chrysanthemum 'Jinba' was respectively treated with lower temperature and weaker light (16 degrees C/ 12 degrees C, PFD 100 micromol x m(-2) x s(-1)) and critical low temperature and weak light (12 degrees C/8 degrees C, PFD 60 micromol x m(-2) x s(-1)) for 11 days, and then transferred to normal condition (22 degrees C/18 degrees C, PFD 450 micromol x m(-2) x s(-1)) for 11 days, aimed to study the low temperature- and weak light stress and its recovery on the photosynthesis and chlorophyll fluorescence of chrysanthemum leaves. Under the stress of lower temperature and weaker light, the net photosynthetic rate (P(n)) and stomatal limitation (L(s)) of chrysanthemum leaves decreased while the intercellular CO2 concentration (C(i)) increased, the maximal photochemical efficiency of PS II (F(v)/F(m)) in dark and the initial fluorescence (F(o)) had no obvious change, but the maximal photochemical efficiency of PS II (F(v)'/F(m)') in light increased after an initial decrease. Contrarily, under the stress of critical low temperature and weak light, the F(o) increased, and the F(v)/F(m) and F(v)'/F(m)' decreased significantly. The quantum yield of PS II electron transport (phi(PS II)), photochemical quenching (q(p)), and apparent photosynthetic electron transfer rate (ETR) of chrysanthemum leaves decreased with increasing stress and time, and recovered quickly after the release of lower temperature- and weaker light stress but more slowly after the release of critical low temperature- and weak light stress. At the same time, the photochemistry react rate (Prate) decreased, but the hot dissipation of antenna (Drate) and the energy dissipation of PS II (Ex) increased under the stress conditions. Drate was the main pathway of superfluous light allocation.

[Effects of exogenous Ca2+ on leaf photosynthetic apparatus and active oxygen scavenging enzyme system of chrysanthemum under high temperature stress].

Taking cut flower chrysanthemum 'Jinba' as test material, the effects of exogenous Ca2+ on its photosynthetic system and antioxidant enzyme activities under high temperature stress were investigated, with the possible action mechanisms of Ca2+ discussed. The results showed that under high temperature stress, Ca2+ addition greatly inhibited the net photosynthesis rate (P(n)) and quantum yield of PS II electron transport (phi(PS II)). After 24 h treatment, the P(n) and psi(PS II) were increased by 31.11% and 21.88% , respectively, and the initial fluorescence (F(o)) decreased by 13.19%, compare with the control. Ca2+ addition also greatly enhanced the activities of SOD, POD and CAT, and thus, the active oxygen was scavenged timely. After 24 h treatment, the MDA accumulation and REC were 29.20% and 35.81% lower than the control, respectively. In conclusion, Ca2+ addition could efficiently protect chrysanthemum leaves from the damage in photosynthetic apparatus under short-term high temperature stress.

[Effects of high temperature stress on photosynthesis and chlorophyll fluorescence of cut flower chrysanthemum (Dendranthema grandiflora 'Jinba')].

Cut flower chrysanthemum (Dendranthema grandflora 'Jinba') plants were treated with 40 degrees C/35 degrees C or 33 degrees C/28 degrees C (day/night) for 11 days and then transferred to 23 degrees C/18 degrees C for 5 days to study the changes in their photosynthesis and fluorescence parameters under high temperature stress and normal temperature recovery. The results showed that on the 5th day of 33 degrees C/28 degrees C treatment, net photosynthesis (P(n)) decreased gradually and stomatal conductance (G(s)) decreased evidently; while after recovery for 5 days, both P(n) and G(s) resumed to 80% of the control. At 40 degrees C/35 degrees C, P(n) and G(s) decreased dramatically. The increase of intercellular CO2 concentration (C(i)) at the early stage under given high temperatures showed that the photosynthesis inhibition by high temperature stress was resulted from non-stomatal limitations. However, 9 days later, stomatal limitation became the mainly cause of photosynthesis inhibition. The intrinsic photochemical efficiency (F(v)/F(m)), quantum yield of PS II (phi(PS II), and the efficiency of excitation energy capture by open PS II reaction center (F(v)'/F(m)') at 33 degrees C/28 degrees C and 40 degrees C/35 degrees C all decreased, with antenna heat dissipation increased, indicating that reaction center was protected by decreased light capture and efficiency of electron transfer through PS II. The photochemical quenching (q(p)) at 33 degrees C/28 degrees C descended first and turned to rise then, suggesting that the electron transfer was firstly restrained by the stress. Contrastively, q(p) rose continuously at 40 degrees C/35 degrees C, indicating that oxygen-evolving complex (OEC) was the location in chrysanthemum photosynthesis apparatus most sensitive to extreme high temperature.