scholarly journals Discrepancy in photosynthetic responses of the red alga Pyropia yezoensis to dehydration stresses under exposure to desiccation, high salinity, and high mannitol concentration

2021 ◽  
Author(s):  
Guoying Du ◽  
Xiaojiao Li ◽  
Junhao Wang ◽  
Shuai Che ◽  
Xuefeng Zhong ◽  
...  
Keyword(s):  
Chlorophyll Fluorescence ◽  
High Salinity ◽  
Pyropia Yezoensis ◽  
Photochemical Quenching ◽  
Northwestern Pacific ◽  
Heterogeneous Effects ◽  
Relative Electron ◽  
Photosynthetic Responses ◽  
Photosynthetic Activities ◽  
Mannitol Concentration

AbstractMacroalgae that inhabit intertidal zones are exposed to the air for several hours during low tide and must endure desiccation and high variations in temperature, light intensity, and salinity. Pyropia yezoensis (Rhodophyta, Bangiales), a typical intertidal red macroalga that is commercially cultivated in the northwestern Pacific Ocean, was investigated under different dehydration stresses of desiccation, high salinity, and high mannitol concentration. Using chlorophyll fluorescence imaging, photosynthetic activities of P. yezoensis thalli were analyzed using six parameters derived from quenching curves and rapid light curves. A distinct discrepancy was revealed in photosynthetic responses to different dehydration stresses. Dehydration caused by exposure to air resulted in rapid decreases in photosynthetic activities, which were always lower than two other stresses at the same water loss (WL) level. High salinity only reduced photosynthesis significantly at its maximum WL of 40% but maintained a relatively stable maximum quantum yield of photosystem II (PSII) (Fv/Fm). High mannitol concentration induced maximum WL of 20% for a longer time (60 min) than the other two treatments and caused no adverse influences on the six parameters at different WL except for a significant decrease in non-photochemical quenching (NPQ) at 20% WL. Illustrated by chlorophyll fluorescence images, severe spatial heterogeneities were induced by desiccation with lower values in the upper parts than the middle or basal parts of the thalli. The NPQ and rETRmax (maximum relative electron transport rate) demonstrated clear distinctions for evaluating photosynthetic responses, indicating their sensitivity and applicability. The findings of this study indicated that the natural dehydration of exposure to air results in stronger and more heterogeneous effects than those of high salinity or high mannitol concentration.

scholarly journals Performance of Hydroponically Cultivated Geranium and Common Verbena under Salinity and High Electrical Conductivity Levels

Agronomy ◽  
2021 ◽  
Vol 11 (6) ◽  
pp. 1237
Author(s):  
Antonios Chrysargyris ◽  
Spyridon A. Petropoulos ◽  
Dejan Prvulovic ◽  
Nikolaos Tzortzakis
Keyword(s):  
Electrical Conductivity ◽  
Chlorophyll Fluorescence ◽  
Nutrient Solution ◽  
High Salinity ◽  
Stomatal Resistance ◽  
Water Sources ◽  
Total Flavonoid ◽  
Control Treatment ◽  
Total Phenolic ◽  
High Electrical Conductivity

Abiotic factors in nutrient solutions (NSs), such as salinity and high electrical conductivity (EC), may adversely alter plant growth and crop performance. However, there are medicinal/aromatic plants which can not only withstand these adverse conditions, but which can also increase their productivity or even enhance their quality in such conditions. As fresh water sources suitable for irrigation are becoming more and more limited, the use of low-quality water sources and hydroponic growing systems have been suggested as the main alternatives. Towards that direction, this study aims to evaluate the effect of high EC levels in NSs on geranium (Pelargonium graveolens L’Hér.) and common verbena (Verbena officinallis L.) plants cultivated in a soilless (perlite) hydroponics system. Plants were irrigated with a full nutrient solution of EC 2.1 dS m−1 and pH 5.8 until they reached a uniform size. Then, three treatments were applied, namely: (a) a control treatment with an EC of 2.1 dS m−1 in the NS, (b) a high-salinity NS created by adding 75 mM of NaCl (EC under 8.5 dS m−1) and (c) a concentrated NS with an EC of 8.5 dS m−1. In pelargonium, high salinity decreased the total phenolic and total flavonoid contents; antioxidant capacity; N, K, Mg and P content; as well as chlorophyll fluorescence, compared to the control treatment. On the other hand, increased salinity levels increased the Na and Ca content and stomatal resistance. In common verbena, salinity decreased total phenolic content and chlorophyll fluorescence but increased total flavonoid content; antioxidants; leaf K, P, Na, Cu and Zn content; and stomatal resistance, compared to the control. In both species, high EC did not affect polyphenols, flavonoids or antioxidants, whereas it increased stomatal resistance and nutrient accumulation in the leaves, and decreased chlorophyll fluorescence compared to the control treatment. Damage indices, indicated by lipid peroxidation, hydrogen peroxide production and the elevation of enzymes’ antioxidant activities, were evidenced in both saline- and high-EC-treated plants. In conclusion, despite having the same EC levels in the nutrient solution, it seems that ionic stress caused by high mineral concentrations in the nutrient solution had less severe effects on the tested plants than the relevant osmotic stress caused by high salinity due to the addition of NaCl in the nutrient solution.

scholarly journals Photosynthetic responses of <i>Emiliania huxleyi</i> to UV radiation and elevated temperature: roles of calcified coccoliths

2011 ◽  
Vol 8 (6) ◽  
pp. 1441-1452 ◽  
Author(s):  
K. Xu ◽  
K. Gao ◽  
V. E. Villafañe ◽  
E. W. Helbling
Keyword(s):  
Elevated Temperature ◽  
Carbon Fixation ◽  
Emiliania Huxleyi ◽  
Photochemical Quenching ◽  
Photosynthetic Carbon Fixation ◽  
Level 3 ◽  
Two Temperatures ◽  
Photosynthetic Responses ◽  
Radiation Treatments ◽  
Non Photochemical Quenching

Abstract. Changes in calcification of coccolithophores may affect their photosynthetic responses to both, ultraviolet radiation (UVR, 280–400 nm) and temperature. We operated semi-continuous cultures of Emiliania huxleyi (strain CS-369) at reduced (0.1 mM, LCa) and ambient (10 mM, HCa) Ca2+ concentrations and, after 148 generations, we exposed cells to six radiation treatments (>280, >295, >305, >320, >350 and >395 nm by using Schott filters) and two temperatures (20 and 25 °C) to examine photosynthesis and calcification responses. Overall, our study demonstrated that: (1) decreased calcification resulted in a down regulation of photoprotective mechanisms (i.e., as estimated via non-photochemical quenching, NPQ), pigments contents and photosynthetic carbon fixation; (2) calcification (C) and photosynthesis (P) (as well as their ratio) have different responses related to UVR with cells grown under the high Ca2+ concentration being more resistant to UVR than those grown under the low Ca2+ level; (3) elevated temperature increased photosynthesis and calcification of E. huxleyi grown at high Ca2+ concentrations whereas decreased both processes in low Ca2+ grown cells. Therefore, a decrease in calcification rates in E. huxleyi is expected to decrease photosynthesis rates, resulting in a negative feedback that further reduces calcification.

scholarly journals The role of coccoliths in protecting <i>Emiliania huxleyi</i> against stressful light and UV radiation

2016 ◽  
Vol 13 (16) ◽  
pp. 4637-4643 ◽  
Author(s):  
Juntian Xu ◽  
Lennart T. Bach ◽  
Kai G. Schulz ◽  
Wenyan Zhao ◽  
Kunshan Gao ◽  
...  
Keyword(s):  
Solar Radiation ◽  
Uv Radiation ◽  
Growth Rates ◽  
Emiliania Huxleyi ◽  
Photochemical Quenching ◽  
Visible Radiation ◽  
Light Levels ◽  
Relative Electron ◽  
Non Photochemical Quenching

Abstract. Coccolithophores are a group of phytoplankton species which cover themselves with small scales (coccoliths) made of calcium carbonate (CaCO3). The reason why coccolithophores form these calcite platelets has been a matter of debate for decades but has remained elusive so far. One hypothesis is that they play a role in light or UV protection, especially in surface dwelling species like Emiliania huxleyi, which can tolerate exceptionally high levels of solar radiation. In this study, we tested this hypothesis by culturing a calcified and a naked strain under different light conditions with and without UV radiation. The coccoliths of E. huxleyi reduced the transmission of visible radiation (400–700 nm) by 7.5 %, that of UV-A (315–400 nm) by 14.1 % and that of UV-B (280–315 nm) by 18.4 %. Growth rates of the calcified strain (PML B92/11) were about 2 times higher than those of the naked strain (CCMP 2090) under indoor constant light levels in the absence of UV radiation. When exposed to outdoor conditions (fluctuating sunlight with UV radiation), growth rates of calcified cells were almost 3.5 times higher compared to naked cells. Furthermore, the relative electron transport rate was 114 % higher and non-photochemical quenching (NPQ) was 281 % higher in the calcified compared to the naked strain, implying higher energy transfer associated with higher NPQ in the presence of calcification. When exposed to natural solar radiation including UV radiation, the maximal quantum yield of photosystem II was only slightly reduced in the calcified strain but strongly reduced in the naked strain. Our results reveal an important role of coccoliths in mitigating light and UV stress in E. huxleyi.

scholarly journals Effects of Different Shading Rates on the Photosynthesis and Corm Weight of Konjac Plant

2019 ◽  
Vol 47 (3) ◽  
Author(s):  
Yaoguo QIN ◽  
Zesheng YAN ◽  
Honghui GU ◽  
Zhengxiang WANG ◽  
Xiong JIANG ◽  
...  
Keyword(s):  
Photosynthetic Efficiency ◽  
Daily Variation ◽  
Photochemical Efficiency ◽  
High Yield ◽  
Photochemical Quenching ◽  
Digital Object Identifier ◽  
Chlorophyll Fluorescence Parameters ◽  
Relative Electron ◽  
Comprehensive Comparison ◽  
Non Photochemical Quenching

To study the effects of shading level on the photosynthesis and corm weight of konjac plant, the chlorophyll fluorescence parameters, daily variation of relative electron transport rate (rETR), net photosynthetic rate (Pn), and corm weight of konjac plants under different treatments were measured and comparatively analyzed through covered cultivation of biennial seed corms with shade nets at different shading rates (0%, 50%, 70%, and 90%). The results showed that with the increase in shading rate, the maximum photochemical efficiency, potential activity, and non-photochemical quenching of photosystem Ⅱ (PSⅡ) of konjac leaves constantly increased, whereas the actual photosynthetic efficiency, rETR, and photochemical quenching of PSⅡ initially increased and then decreased. This result indicated that moderate shading could enhance the photosynthetic efficiency of konjac leaves. The daily variation of rETR in konjac plants under unshaded treatment showed a bimodal curve, whereas that under shaded treatment displayed a unimodal curve. The rETR of plants with 50% treatment and 70% treatment was gradually higher than that under unshaded treatment around noon. The moderate shading could increase the Pn of konjac leaves. The stomatal conductance and transpiration rate of the leaves under shaded treatment were significantly higher than those of the leaves under unshaded treatment. Shading could promote the growth of plants and increase corm weight. The comprehensive comparison shows that the konjac plants had strong photosynthetic capacity and high yield when the shading rate was 50%-70% for the area.   ********* In press - Online First. Article has been peer reviewed, accepted for publication and published online without pagination. It will receive pagination when the issue will be ready for publishing as a complete number (Volume 47, Issue 3, 2019). The article is searchable and citable by Digital Object Identifier (DOI). DOI link will become active after the article will be included in the complete issue. *********

Kinetic response of photosystem II photochemistry in the cyanobacterium Spirulina platensis to high salinity is characterized by two distinct phases

1999 ◽  
Vol 26 (3) ◽  
pp. 283 ◽  
Author(s):  
Congming Lu ◽  
Giuseppe Torzillo ◽  
Avigad Vonshak
Keyword(s):  
Electron Transport ◽  
Quantum Yield ◽  
Photosystem Ii ◽  
Spirulina Platensis ◽  
High Salinity ◽  
Photochemical Quenching ◽  
Second Phase ◽  
Ps Ii ◽  
Reaction Centres ◽  
Two Phases

The kinetic response of photosystem II (PS II) photochemistry in Spirulina platensis(Norstedt M2 ) to high salinity (0.75 M NaCl) was found to consist of two phases. The first phase, which was independent of light, was characterized by a rapid decrease (15–50%) in the maximal efficiency of PS II photochemistry (Fv /Fm), the efficiency of excitation energy capture by open PS II reaction centres (Fv′/Fm′), photochemical quenching (qp) and the quantum yield of PS II electron transport (Φ PS II) in the first 15 min, followed by a recovery up to about 80–92% of their initial levels within the next 2 h. The second phase took place after 4 h, in which further decline in above parameters occurred. Such a decline occurred only when the cells were incubated in the light, reaching levels as low as 45–70% of their initial levels after 12 h. At the same time, non-photochemical quenching (qN) and Q B -non-reducing PS II reaction centres increased significantly in the first 15 min and then recovered to the initial level during the first phase but increased again in the light in the second phase. The changes in the probability of electron transfer beyond QA (ψo) and the yield of electron transport beyond QA (φ Eo), the absorption flux (ABS/RC) and the trapping flux (TRo /RC) per PS II reaction centre also displayed two different phases. The causes responsible for the decreased quantum yield of PS II electron transport during the two phases are discussed.

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