Melatonin has different functions in plant growth and development, especially in the protection of plants suffering from various forms of abiotic stress. We explored the effect of melatonin priming on photosynthetic activity of tomato (Lycopersicon esculentum L.) leaves. Our results showed that 100 µM is the optimal concentration used for alleviation of the damage to photosynthetic apparatus. Melatonin priming both in the form of leaf spray and direct root application was found to reduce the damage to photosynthetic apparatus, and increase the electron transfer rate and quantum yield of PSI and PSII photochemistry, to protect the thylakoid membrane from damage caused by low-temperature stress. Our study provides fundamental information for further research on the molecular mechanism of melatonin function in regulating photosynthesis., X. L. Yang, H. Xu, D. Li, X. Gao, T. L. Li, R. Wang., and Obsahuje bibliografii
This study compared the effects of salt (NaCl) stress on growth, photosynthesis and solute accumulation in seedlings of the three poplar (Populus bonatii) cultivars Populus × BaiLin-2 (BL-2), Populus × BaiLin-3 (BL-3), and Populus × Xjiajiali (XJJL). The results showed that BL-2 and BL-3 could not survive at a salinity level of 200 mM but XJJL grew well. The effect of moderate salt stress on leaf extension of the three cultivars was only slight. At a high level of salinity, however, NaCl clearly inhibited leaf extension of BL-2 and BL-3, whereas it did not affect that of XJJL, and the net photosynthetic rate (PN) in XJJL was much higher than those of BL-2 and BL-3. The lower PN of BL-2 and BL-3 might be associated with the high concentration of Na+ and/or Cl- accumulated in the leaves, which could be toxic in photosynthesis system. In summary, the greater salt-tolerance of XJJL compared with that of BL-2 and BL-3 might be explained by the higher PN and photosynthetic area, the lower Na+/K- ratio and Cl- in the leaf, and the greater accumulation of soluble sugars and SO4 2-. and W. Chen ... [et al.].
a1_Attention should be paid to ozone (O3) sensitivity of greening plant since ground-level O3 concentrations are increasing especially in urban and suburban area. We studied the ecophysiological responses to elevated O3 of four shrub species [Euonymus bungeanus Maxim. (EB), Photinia × fraseri (PF), Chionanthus retusus Lindl. & Paxt. (CR) and Cornus alba L. (CA)], which are often used for garden greening in China. Saplings of those species were exposed to high O3 concentration (70 nmol mol-1, 7 h d-1 for 65 d) in open-top growth chambers. Responses to O3 were assessed by gas exchanges, chlorophyll (Chl) fluorescence and dry mass. We found that elevated O3 significantly decreased lightsaturated net photosynthetic rate (PNsat), transpiration rate (E) and stomatal conductance (gs). The ratio of intercellular CO2 to ambient CO2 concentration (Ci/Ca) did not reduce under O3 fumigation which suggested that the O3-induced depressions of P Nsat under O3 fumigation were probably due to limitation of mesophyll processes rather than stomatal limitation. High O3 exposure also significantly depressed the maximum efficiency of photosystem II (PSII) photochemistry in the dark-adapted state (Fv/Fm) which meant the O3-induced photoinhibition. Both root dry mass and root/shoot ratios were significantly decreased under ozone fumigation, but the total mass was unchanged. The responses of gas exchange such as PNsat in these four shrubs to O3 exposure were species-specific. Highest loss of PNsat was observed in EB (-49.6%), while the CR had the lowest loss (-36.5%). Moreover, the O3-exposed CR showed similar gs as CF, reflecting that its O3 flux might be unchanged under elevated O3 environment. Ozone drastically decreased actual quantum yield of PSII (ΦPSII) and electron transport rate (ETR) in EB while increased ΦPSII and ETR in CR., a2_Furthermore, the relative losses in P Nsat positively correlated with the relative decreases in ΦPSII and ETR which indicated that the impairment of photosynthesis was probably affected by the light reaction process. The light reaction of EB was impaired most seriously but that of CR was not damaged. All results indicated that EB was probably the most sensitive shrub species to O3 while CR the most tolerant one. Therefore, CR might be an ideal choice for greening in ozone-polluted areas., L. Zhang ... [et al.]., and Obsahuje bibliografii
Two japonica rice cultivars with different panicle trait index (PTI), HP917 (a high-PTI cultivar) and DP128 (a low-PTI cultivar) were used to investigate the effects of the nitrogen (N) rate and plant density on the grain distribution of secondary branches on the panicle axis, leaf photosynthetic characteristics, and grain yield by a split plot design. The main plots were assigned to four N rates (0, 140, 200, and 260 kg ha-1), and the subplots were assigned to two plant densities: (D20, 15 plants m-2; D10, 30 plants m-2). Results showed that the grain yield was increased by increasing N rate and plant density, reaching a peak at N200 with D10. Compared with N0 treatment, the PTIs of HP917 and DP128 increased with an increase in the N rate, respectively. The PTIs of HP917 and DP128 increased by 4% with increasing plant density from D20 to D10. The leaf capacity was significantly affected by N rate and plant density. The grain distribution characteristics of secondary branches on the panicle axis was closely related to yield. Correlation analysis showed the PTI was positively correlated with grain yield and net photosynthetic rate. These results suggested the improvement in PTI from 0.15 to 0.52 was beneficial to increase the grain yield, which might contribute to the increased grain number of secondary branches of the middle and bottom panicle.
Ozone (O3) is important air pollutant inducing severe losses of horticultural production. Cultivars of the same species, but with different leaf colors, may differ in their ozone sensitivity. However, it has not been clarified yet if different leaf coloration influences such a sensitivity. In this study, two purple-leafed and two green-leafed cultivars of Pakchoi were selected for ozone fumigation (240 ± 20 nmol mol-1, 09:00-16:00 h). Elevated O₃ decreased chlorophyll content, increased anthocyanin (Ant) content, damaged cell membrane integrity, enhanced antioxidative enzyme activities, depressed photosynthetic rate (PN) and stomatal conductance (gs), inhibited maximal quantum yield (Fv/Fm) and effective quantum yield [YII] of PSII photochemistry, and caused visible injury. Purple-leafed cultivars with higher Ant contents were more tolerant than green-leafed cultivars as indicated by lower relative enhancement in malondialdehyde content and lower relative losses in PN, gs, Fv/Fm, and YII. The higher ability to synthesize Ant in the purple-leafed cultivars contributed to their higher photoprotective ability., L. Zhang, S. Xiao, Y. J. Chen, H. Xu, Y. G. Li, Y. W. Zhang, F. S. Luan., and Obsahuje bibliografii
Winter wheat (Triticum aestivum L. cv. Jingdong 8) was exposed to short-term high ozone treatment after anthesis and then was either well irrigated with soil water content (SWC) of 80-85 % (O3+W) or drought treated (SWC 35-40 %, O3+D). Short-term ozone exposure significantly decreased irradiance-saturated net photosynthetic rate (PN) of winter wheat. Under good SWC, PN of the O3-treated plant was similar to that of control on 2 d after O3-exposure (6 DAA), but decreased significantly after 13 DAA, indicating that O3 exposure accelerated leaf senescence. Meanwhile, green flag leaf area was reduced faster than that of control. As a result, grain yield of O3+W was significantly decreased. PN of O3+D was further notably decreased and green flag leaf area was reduced more than that in O3+W. Consequently, substantial yield loss of O3+D was observed compared to that of O3+W. Although PN was significantly positively correlated with stomatal conductance, it also had notable positive correlation with the maximum photochemical efficiency in the dark adapted leaves (Fv/Fm), electron transport rate (ETR), photochemical quenching (qP), as well as content of chlorophyll, suggesting that the depression of PN was mainly caused by non-stomatal limitation. Hence optimal soil water condition should be considered in order to reduce the yield loss caused by O3 pollution. and H. Xu ... [et al.].
In order to study the responses of winter wheat cultivars released in different years to short-term high O3 exposure, an old cultivar ('Nongda 311', released in 1960s) and a modern one ('Yannong 19', released in 1990s) were treated with an O3 exposure (145 ± 12 mm3 m-3, 4 h d-1 for 3 d) shortly after anthesis stage (> 50 % main stems blossomed). During the O3 exposure, light-saturated photosynthetic rate (PN) and stomatal conductance (gs) of both cultivars decreased considerably. Elevated O3 did not decrease dark-adapted maximum photochemical efficiency, but induced significant reduction in actual photochemical efficiency and thereby considerably increase in non-photochemical quenching. PN, gs of the modern cultivar 'Yannong 19' decreased more than the older one 'Nongda 311', indicating the former exhibited higher sensitivity to O3 than the latter. After O3 exposure, PN, gs and chlorophyll (Chl) content in flag leaf decreased more quickly than control, indicating induction of faster premature leaf senescence. As a result, the short-term O3 exposure caused substantial yield loss, with larger reduction in 'Yannong 19' (-19.2 %) than in 'Nongda 311' (-8.4 %). Our results indicated that high O3 exposure at grain filling stage would have greater negative impacts on the high yielding modern cultivar relative to the old one with lower yield. and H. Xu ... [et al.].
In order to investigate the effect of chromosome doubling on ozone tolerance, we compared the physiological responses of a diploid honeysuckle (Lonicera japonica Thunb.) and its autotetraploid cultivar to elevated ozone (O3) exposure (70 ng g-1, 7 h d-1 for 31 d). Net photosynthetic rate (PN) of both cultivars were drastically (P<0.01) impaired by O3. Although there were significantly positive correlation between PN and stomatal conductance (gs) in both cultivars under each treatment, the decreased gs in O3 might be the result rather than the cause of decreased P N as indicated by stable or increasing the ratio of intercellular to ambient CO2 concentration(Ci/Ca). PN under saturating CO2 concentration
(PNsat) and carboxylation efficiency (CE) significantly decreased under O3 fumigation, which indicated the Calvin cycle was impaired. O3 also inhibited the maximum efficiency of photosystem II (PSII) photochemistry in the dark-adapted state (Fv/Fm), actual quantum yield of PSII photochemistry (ΦPSII), electron transport rate (ETR), photochemical quenching coefficient (qP), non-photochemical quenching (NPQ), the maximum in vivo rate of Rubisco carboxylation (Vcmax) and the maximal photosynthetic electron transport rate (Jmax) which demonstrated that the decrease in PN of the honeysuckle exposed to elevated O3 was probably not only due to impairment of Calvin cycle but also with respect to the light-harvesting and electron transport processes. Compared to the diploid, the tetraploid had higher relative loss in transpiration rate (E), (gs), (PNsat), Vcmax and Jmax. This result indicated that the Calvin cycle and electron transport in tetraploid was damaged more seriously than in diploid. A barely nonsignificant (P=0.086) interaction between O3 and cultivar on PN suggested a higher photosynthetic sensitivity of the tetraploid cultivar. and L. Zhang ... [et al.].
A sand-culture experiment was conducted in open-top chambers which were constructed in a greenhouse to investigate the responses of salt-stressed wheat (Triticum aestivum L.) to O3. Plant seeding of JN17 (a popular winter wheat cultivar) was grown in saltless (-S) and saline (+S, 100 mM NaCl) conditions combined with charcoal-filtered air (CF, < 5 ppb O3) and elevated O3 (+O3,
80 ± 5 ppb, 8 h day-1) for 30 d. O3 significantly reduced net photosynthetic rate (PN), stomatal conductance, chlorophyll contents and plant biomass in -S treatment, but no considerable differences were noted in those parameters between +O3+S and CF+S treatments. O3-induced loss in cellular membrane integrity was significant in -S plants, but not in +S plants evidenced by significant elevations being measured in electrolyte leakage (EL) and malondialdehyde (MDA) content in -S plants, but not in +S plants. Both O3 and salinity increased proline content and stimulated antioxidant enzymes activities. Soluble protein increased by salinity but decreased by O3. Abscisic acid (ABA) was significantly elevated by O3 in -S plants but not in +S plants. The results of this study suggested that the specificity of different agricultural environments should be considered in order to develop reliable prediction models on O3 damage to wheat plants. and Y. H. Zheng ... [et al.].