Cold-stress induced metabolomic and transcriptomic changes in leaves of three mango varieties with different cold tolerance.

BACKGROUND: Mango (Mangifera indica L.) is grown in Hainan, Guangdong, Yunnan, Sichuan, and Fujian provinces and Guanxi autonomous region of China. However, trees growing in these areas suffer severe cold stress during winter, which affects the yield. To this regard, data on global metabolome and transcriptome profiles of leaves are limited. Here, we used combined metabolome and transcriptome analyses of leaves of three mango cultivars with different cold stress tolerance, i.e. Jinhuang (J)-tolerant, Tainung (T) and Guiremang No. 82 (G)-susceptible, after 24 (LF), 48 (MF) and 72 (HF) hours of cold. RESULTS: A total of 1,323 metabolites belonging to 12 compound classes were detected. Of these, amino acids and derivatives, nucleotides and derivatives, and lipids accumulated in higher quantities after cold stress exposure in the three cultivars. Notably, Jinhuang leaves showed increasing accumulation trends of flavonoids, terpenoids, lignans and coumarins, and alkaloids with exposure time. Among the phytohormones, jasmonic acid and abscisic acid levels decreased, while N6-isopentenyladenine increased with cold stress time. Transcriptome analysis led to the identification of 22,526 differentially expressed genes. Many genes enriched in photosynthesis, antenna proteins, flavonoid, terpenoid (di- and sesquiterpenoids) and alkaloid biosynthesis pathways were upregulated in Jihuang leaves. Moreover, expression changes related to phytohormones, MAPK (including calcium and H2O2), and the ICE-CBF-COR signalling cascade indicate involvement of these pathways in cold stress responses. CONCLUSION: Cold stress tolerance in mango leaves is associated with regulation of primary and secondary metabolite biosynthesis pathways. Jasmonic acid, abscisic acid, and cytokinins are potential regulators of cold stress responses in mango leaves.

[Effects of NaCl stress on free polyamines content and reactive oxygen species level in pumpkin roots].

Taking Cucurbita moschata Duch hybrid 360-3 x 112-2 and C. ficifolia Bouche as test materials, the effects of NaCl stress on their plant growth and the O2*- production rate and H2O2 and free polyamines (PAs) contents in their roots were studied with hydroponic culture. The results showed that after 10 d NaCl stress, the plant growth of the two pumpkin varieties was strongly inhibited, compared with the control, and C. ficifolia was more injured than hybrid 360-3 x 112-2. Under NaCl stress, the root O2*- production rate and H2O2 content of the two pumpkin varieties were increased, but their absolute values were lower in hybrid 360-3 x 112-2 than in C. ficifolia. The contents of PAs, putrescine (Put), spermidine (Spd) and spermine (Spm) and Put/PAs ratio in the roots of the two pumpkin varieties were always higher than the control and had a trend of increased first and decreased then; while the (Spd + Spm)/Put ratio was lower than the control and decreased first and increased then. Compared with C. ficifolia Bouche, hybrid 360-3 x 112-2 always had a lower Put/PAs ratio and a lower Put content in its roots, but the (Spd + Spm)/Put ratio and Spd and Spm contents were always higher. It was concluded that under NaCl stress, the increasing PAs content in the roots of test materials played an active role in decreasing or scavenging reactive oxygen species (ROS). The conversion of Put to Spd and Spm was advantageous to the increase of plant salt tolerance. The higher salt tolerance of hybrid 360-3 x 112-2 was closely related to the lower Put/PAs ratio and the higher (Spd + Spm)/Put ratio and PAs content in its roots, and thus, the stronger capacity to scavenge ROS.

[Effects of NaCl stress on polyamine contents in grafted cucumber leaves].

With a Japanese salt-tolerant pumpkin cultivar 'King Shintosa' (Cucurbita maxima x C. moschata) as rootstock and a cucumber (Cucumis sativus) cultivar 'Xintaimici' as cion, this paper studied the temporal dynamics of different form polyamines contents in the leaves of grafted and own-rooted cucumber plants under 100 mmol x L(-1) NaCl stress. The results showed that the free putrescence (Put) content of graftedplant leaves (G2) was significantly higher than that of own-rooted plant leaves (O2), except on the second day of NaCl stress. During the whole period of NaCl stress, the free spermidine (Spd) and spermine (Spm) contents of G2 were significantly higher than those of O2, and the total free polyamine content of G2 peaked on the fourth day of stress. The free Put/PAs value of G2 was significantly lower than that of O2 except on the fourth day of stress, but (Spd + Spm)/Put value was significantly higher than that of O2 during the whole period of stress. In the test period, the contents of conjugated and bound Put, Spd, Spm of G2 were significantly higher than those of O2. The total conjugated and bound polyamine contents of G2 peaked on the sixth day of stress. Both conjugated Put/PAs and conjugated (Spd + Spm)/Put values had a similar changing trend to free polyamine. The bound Put/PAs value of G2 was significantly lower than that of O2 except on the sixth day of stress, while the bound (Spd + Spm)/Put value was significantly higher than that of O2 during the whole period of stress. All of these demonstrated that grafted cucumber plant possessed a stronger salt tolerance.

[Effects of NaCl stress on the growth, antioxidant enzyme activities and reactive oxygen metabolism of grafted eggplant].

By the method of hydroponics and with the salt-tolerant eggplant cultivar 'Torvum Vigor' (Solanum torvum) from Japan as rootstock and the cultivar 'Suqiqie' (Solanum melongena L. ) as scion, this paper studied the differences between grafted and own-root seedlings in their photosynthetic characteristics, antioxidant enzyme activities, and reactive oxygen metabolism under 80 mmol x L(-1) NaCl stress. The results showed that under NaCl stress, the dry mass, chlorophyll content and photosynthetic rate of grafted seedlings were 67.8%, 8. 8% and 31.1% higher than those of own-root seedlings, respectively, and the antioxidant enzyme activities were significantly higher while the O2* producing rate and the hydrogen peroxide (H2O2) and malondiadehyde (MDA) contents were significantly lower in grafted seedlings leaves than in own-root seedlings. For both grafted and own-root seedlings, NaCl stress reduced the chlorophyll content and photosynthetic rate, but increased the O2* producing rate and the H2O2 and MDA contents significantly. However, the growth of grafted seedlings was less affected by NaCl stress. The stronger salt tolerance of grafted eggplant seedlings was related to their higher antioxidant enzyme activities and less oxidative damage.