Actual Quantum Yield Research Articles

Influence of Paclobutrazol on the Growth and Photosynthesis of Sequoia sempervirens Seedlings

Abstract Paclobutrazol (PAC), as a commonly used plant regulator, has the important function of improving the plant’s stress resistance. Sequoia sempervirens Endl. is a large caliber, fast-growing timber species and one of the world’s five major landscaping tree species. This study researched the effects of spraying PAC on the growth and photosynthetic activity of S. sempervirens seedlings. The results showed the plant height and the plant crown diameter were decreased significantly with the increase in PAC concentration (500 – 3,000 mg·dm−3). However, the ground shoot diameter, net photosynthetic rate, stomatal conductance, inter-cellular CO2 concentration, transpiration rate, actual photochemical quantum yield, and photosynthetic electron transport rate all showed the trend of increasing first reaching the maximum at 2,000 mg·dm−3 and then decreased. Water use efficiency showed the opposite trend. Spraying 2 times was better than once. The conclusion suggests that PAC can protect the photosynthetic activity and improve the resistance of S. sempervirens seedlings under natural cooling and draught in autumn and winter.

Phosphorus-fertilisation has differential effects on leaf growth and photosynthetic capacity of Arachis hypogaea L.

The objectives of this study were to assess how Arachis hypogaea L. (peanut or groundnut) responds to different P supplies in terms of growth and photosynthesis, and to determine the optimum P supply and differential P stress thresholds. We investigated biomass production, leaf expansion, photosynthetic parameters, relative chlorophyll concentration, P700 parameters and chlorophyll fluorescence in a climate-controlled chamber at different P supplies (0.1, 0.5, 1, 1.5, 2 mM). Both deficient and excessive exogenous P supplies significantly reduced leaf growth, relative chlorophyll concentration and dry matter production in two high-yielding peanut cultivars. The optimum P range was 0.8–1.1 mM for peanut seedlings. Through principal component analysis (PCA) and data fitting, we found that the trade-off of the normalised actual quantum yield [Y(II)] and non-regulatory quantum yield [Y(NO)] in photosystem II (PSII) under light is one of the best proxies to determine the suboptimal, supraoptimal, deficient and toxic P supplies, because they are the two key factors with major positive and negative effects of PC1, accounting for 75.5% of the variability. The suboptimal P range was 0.41–0.8 mM and the supraoptimal P range was 1.1–1.72 mM. The suboptimal P supplies corresponded with a leaf P concentration range of 4.8–8.1 mg P g−1 DW, while the supraoptimal P supplies corresponded with a leaf P concentration range of 9.9–12.2 mg P g−1 DW. Both deficient and toxic P levels severely inhibited leaf growth and photosynthesis of peanut, and these unfavourable conditions were associated with significant reduction of biomass and photosynthesis, and photodamage extending beyond PSII. The trade-off of the normalised Y(II) and Y(NO) is a useful benchmark to demarcate deficient, suboptimal, supraoptimal and toxic P-fertilisations levels in A. hypogaea.

Effects of bensulfuron-methyl residue on photosynthesis and chlorophyll fluorescence in leaves of cucumber seedlings.

A potted soil experiment was conducted to investigate the effects of bensulfuron-methyl (BSM) residue on the growth and photosynthesis of seedlings of a local cucumber variety (Xia Feng No.1). When the residue of bensulfuron-methyl in soil exceeded 50μg kg-1, it significantly inhibited the growth of cucumber, chlorophyll content and photosynthetic capacity of cucumber. BSM treatment caused significant decreases in the biomass, chlorophyll content, net photosynthesis rate, stomatal conductance, and transpiration rate, photosystem II (PSII) maximum quantum yield, actual quantum yield, photochemical quenching coefficient, and electron transport rate in cucumber seedlings, but increased the minimal fluorescence yield and dark respiration rate. Moreover, comparisons of the patterns of absorbed light energy partitioning revealed that the fractions of excess and thermally dissipated energy increased with rising concentrations of the BSM residue, but the fraction of PSII photochemistry declined. The BSM residues caused reversible destruction in the PSII reaction centers and decreased the proportion of available excitation energy used in PSII photochemistry. The results suggested that rice or wheat fields sprayed with BSM will not be suitable for planting cucumbers in succession or rotation.

Photosynthetic responses and tolerance to root-zone hypoxia stress of five bean cultivars (Phaseolus vulgaris L.)

Common bean (Phaseolus vulgaris L.) is very sensitive to waterlogging, which is considered a limiting factor for its production. The objective of this study was to evaluate photosynthetic responses and tolerance to root-zone hypoxia stress of five bean cultivars (Cerinza, Bachue, Bianca, Bacatá and NUA35). Bean seedlings of the five cultivars were grown in hydroponics and subjected for 14 days to two treatments (i) high oxygen availability in the root zone or (2) low oxygen availability or hypoxia stress. Results showed that all cultivars under hypoxia stress exhibited reductions in photosynthesis rate (62%–82%), stomatal conductance (73%–97%), transpiration rate (51%–92%), actual quantum yield, non-photochemical quenching, electron transport rate and in the content of chlorophylls and carotenoids. An increase in leaf electrolyte leakage was also observed, which suggests a loss in the stability of cell membranes because of hypoxia stress. The cultivars Bachue, Bianca, Cerinza and NUA35 showed an increase in proline content (300%–750%) compared to plants grown with high oxygen. The cultivar with the highest water use efficiency and the lowest loss of dry mass was Cerinza, followed by NUA35. These cultivars, Cerinza and NUA35, showed a higher tolerance to hypoxia (0.36 and 0.38) according to the waterlogging tolerance coefficient compared with the other cultivars grown with low oxygen availability. The performance of these cultivars could be attributed to the greater reduction in stomatal conductance, maintaining low rates of transpiration but without a high reduction in the CO2 intake. In this way, the tolerance in these cultivars could be associated with the greater water use efficiency during the conditions of hypoxia, compared with the other cultivars.

Exogenous 1-Aminocyclopropane-1-carboxylic acid Controls Photosynthetic Activity, Accumulation of Reactive Oxygen or Nitrogen Species and Macroelement Content in Tomato in Long-term Experiments

Exogenous ethylene (ET) or its precursor, 1-aminocyclopropane-1-carboxylic acid (ACC) may increase stress tolerance of plants in long-term experiments. ACC applied in hydroponic culture of tomato (Solanum lycopersicum L. cv. Rio Fuego) brought about concentration-dependent differences in plant responses. ACC at 0.01 µM changed K+ distribution between shoots and roots but at higher concentrations K+/86Rb+ uptake was inhibited. Surprisingly, excess Na+ and reduced K+ accumulation could be measured in root and leaf tissues, respectively, which at 100 µM ACC led to a decreased K+/Na+ ratio and to a weak ionic stress in these plant organs. ACC at low concentrations increased the net CO2 fixation rate (AN), however, at 100 µM, it triggered a parallel decline in stomatal conductance, AN and in the actual quantum yield of photosystem II. Photosystem I (PSI) was less sensitive to ACC, lower concentrations caused an increasing tendency in the effective quantum yield and changed the non-photochemical quenching profile of PSI from donor-side dominant to acceptor-side-dominant limitation. Photoinhibition was avoided via the dissipation of light energy by regulated non-photochemical quenching and by transiently enhanced cyclic electron flow (CEF) around PSI. The decrease in CEF at 100 µM ACC correlated well with the accumulation of O2•− and H2O2 in the leaf tissues suggesting that molecular oxygen may function as an electron acceptor when natural acceptors of the linear electron transport were over-reduced. Concentration-dependent changes in soluble sugars and sorbitol as osmoprotectants may also contribute to the stress resistance of plants elicited by ET/ACC.

Effects of graphene oxide on cadmium uptake and photosynthesis performance in wheat seedlings

Graphene oxide (GO) is extensively used in various fields because of its versatility. The presence of GO in the environment enhances the toxicity of toxicants or pollutants. Cadmium (Cd) and GO pollution is a problem in aquatic environment, which should be solved. We investigated the toxic effects of Cd on photosynthesis and oxidative stress in wheat seedlings in the presence of GO, by measuring seedling biomass, Cd content, photosynthesis, reactive oxygen species (ROS) level, antioxidant enzyme activities, and malondialdehyde (MDA) content. At low concentrations, GO alone had limited effects, but at concentrations > 20 mg L−1, seedlings were negatively affected. Under combined Cd–GO treatment, GO was significantly toxic at only 5 mg L−1 concentration, and increasing concentration significantly increased Cd accumulation and decreased biomass. The net photosynthetic rate, stomatal conductance, transpiration rate, primary maximum photochemical efficiency of photosystem II, actual quantum yield, photosynthetic electron transport rate, chlorophyll content, and ribulose-1,5-bisphosphate carboxylase/oxygenase concentration decreased significantly, whereas intercellular CO2 concentration increased significantly. These changes can be attributed to impairment of ROS level, antioxidant enzyme activities, and MDA level, and toxicity mechanisms are suggested to be due to oxidative stress. The resulting damage to the photosynthetic systems and structures likely contributed to the overall decrease in biomass.

Waterlogging tolerance of Bidens pilosa translates to increased competitiveness compared to native Bidens biternata

Waterlogging is a common natural disturbance that has negative impacts on dry-land plant species. However, few studies have focused on how waterlogging influences the invasiveness of non-native plant species on dry lands. Bidens pilosa is an invasive dry-land plant of the Asteraceae family that causes serious damage to biodiversity and agricultural production in southern China. To date, it remains unclear how waterlogging affects the competitiveness and growth of B. pilosa. The goal of this study is to determine whether waterlogging promotes the competitiveness of invasive B. pilosa. The growth and physiological responses of invasive B. pilosa and native B. biternata and the competition effects between them were studied after 0 (control), 5, 10, 15, and 20 days of waterlogging stress (wherein the water level was maintained at the soil surface level). After short-term waterlogging stress, the competitive balance index of invasive B. pilosa significantly increased, indicating that short-term waterlogging on dry lands could significantly improve the competitiveness of invasive B. pilosa. Invasive B. pilosa maintained more rapid adventitious root generating capacity and higher root dehydrogenase activity under waterlogging conditions than native B. biternata, which allowed B. pilosa to adapt to the anoxic conditions much more rapidly. The smaller reductions in net photosynthetic rate, actual quantum yield of photosystem II and relative growth rate in B. pilosa than in B. biternata showed that invasive B. pilosa had stronger tolerance to waterlogging than native B. biternata. Our results indicate that invasive B. pilosa has stronger tolerance to waterlogging than native B. biternata and that short-term waterlogging on dry lands can significantly improve the competitiveness of invasive B. pilosa. Short-term waterlogging on dry lands caused by extreme precipitation during the rainy season is expected to promote the invasive potential of exotic B. pilosa.

Effects of vertically heterogeneous soil salinity on tomato photosynthesis and related physiological parameters

Soil salinity is rarely uniform, but the understanding of the physiological responses of plants to vertically heterogeneous salinity in the root zone is still limited. In the present study, pot experiments were conducted in a greenhouse from April to July in 2014 and 2015. In both experiments, four treatments, T1:1, T1:5, T2:4 and T3:3, differing in their vertical soil salt distributions, were established, with salt contents of 1‰, 1‰, 2‰ and 3‰ in the upper soil layer and 1‰, 5‰, 4‰ and 3‰ in the lower soil layer, respectively. Straw layer was buried to isolate the upper soil layer from the lower soil layer. The objectives of this research were to evaluate the effects of vertically heterogeneous salinity on the changes in the plant biomass, shoot Na+ and K+ contents, photosynthesis rate (Pn), stomatal conductance (gs), chlorophyll fluorescence and chlorophyll contents (Chl) of tomato plants (Solanum lycopersicum L.var. Yazhoufenwang). Under the similar average soil salt content, the heterogeneous salt distribution in the root zone (T1:5) prevented Na+ accumulation and promoted K+ absorption compared with the homogeneous salt distribution (T3:3) treatment, leading to an increase in the K+/Na+ ratio. The vertically heterogeneous soil salinity in both experiments was proved to benefit photosynthesis and the related physiological parameters in tomatoes, such as stomatal conductance (gs), maximum electron transport rate (ETRmax), maximal efficiency of PSII photo-chemistry (Fv/Fm), actual quantum yield of PSII (ΦPSⅡ) and chlorophyll content (Chl). Significant increase was observed in these parameters in T1:5 compared with T3:3 during the fruiting and harvesting stages (P < 0.05). Chlorophyll fluorescence (ETRmax, Fv/Fm and ΦPSⅡ) was found to be most closely related to the water-weighted mean soil salinity (P < 0.01) rather than to the lowest, highest or mean soil salinity in the root zone. The overall results suggested that vertically heterogeneous soil salinity could relieve salt stress and benefit photosynthesis and the related physiological parameters of tomato plants.

Photosynthetic activity of Prorocentrum donghaiense Lu acclimated to phosphorus limitation and its photosynthetic responses to nutrient depletion

Prorocentrum donghaiense blooms periodically occur in late spring and early summer in the phosphorus (P)-limited East China Sea; however, few studies have been conducted in nutrient conditions that resembled those in the East China Sea. To study the actual photosynthetic status of P. donghaiense in P-limited conditions, we established stable P-limited conditions using semi-continuous culture at two dilution rates (0.1 and 0.3 day−1). When the external nutrient concentrations remained steady after 26 days, time did not affect the maximum quantum yield (Fv/Fm), normalized Stern-Volmer quenching (NPQNSV), maximum light use efficiency (α), maximum relative electron transport rate (rETRmax), and light saturation intensity (Ik). Prorocentrum donghaiense acclimated to P limitation, and the high actual quantum yield of photosystem II (ΦPSII) and rETRmax, low NPQNSV at 0.3 day−1, and increased ΦPSII with time at 0.3 day−1 indicated the photosynthetic advantages of P. donghaiense at a high growth rate. To test the responses of P-limitation-acclimated P. donghaiense to nutrient inputs, nutrient-addition experiments were conducted. Nitrate and phosphate addition thoroughly depleted P or nitrogen (N). Greater decreases in Fv/Fm, ΦPSII, α and rETRmax, and higher NPQNSV derived from rapid light curves (RLCs) were found under the P-depletion condition than under the N depletion condition. These results showed that the P-limitation-acclimated P. donghaiense had a weaker photosynthetic tolerance to P depletion. Given the differences in the photosynthetic tolerance of P. donghaiense to nutrient depletion, our results suggested that reduced P inputs should be considered during the management of P. donghaiense blooms.

Growth of Ormosia henryi seedlings and photosynthetic and physiological characteristics with rhizobia inoculation.

To screen the growth-promoting strains of rhizobia for Ormosia henryi and to establish a good symbiotic nitrogen-fixing system, root nodules of O. henryi collected from Guizhou, Zhejiang, Anhui, Fujian, and Jiangxi Provinces were isolated and identified. Using randomized block design, 20 strains of rhizobia that passed reinoculation and 16SrDNA sequence analysis were inoculated into one-year-old aseptic potted O. henryi seedlings followed by measurement of the photosynthetic rate, transpiration rate, chlorophyll fluorescence parameters, growth indexes, and nodulation indexes. Results showed that the nodulation rates of the 20 strains were above 90.0%, the nodule number and nodule weight of strain No. 7 was the highest. Compared to the control which was not been inoculated, inoculation rhizobium significantly (P < 0.05) increased photosynthetic rate, transpiration rate and chlorophyll fluorescence parameters of O. henryi seedlings. Rhizobium also promoted the growth of above ground and underground parts as well as accumulation of total biomass. Seedlings with different rhizobium strains increased the photosynthetic rate (41.6%-197.4%), transpiration rate (3.2%-512.9%), actual photosynthetic quantum yield (4.8%-95.2%), total root surface area (3.4%-866.1%), average root diameter (6.7%-193.3%), root number (0.5%-92.1%), seedling height growth (6.3%-273.8%), diameter growth (10.7%-185.7%), and biomass (37.9%-310.3%). The comprehensive evaluation showed that the best five strains for promoting growth of O. henryi seedlings were No. 15, 16, 7, 18, and 17, and these could be used as excellent strains for inoculation of O. henryi seedlings.

Coupling physiological analysis with proteomic profile to understand the photosynthetic responses of young Euterpe oleracea palms to drought.

This study examined whether drought sensitivity in açaí (Euterpe oleracea Mart.) is associated with reductions in photosynthesis and increasing oxidative stress in response to down-regulation of proteins related to photosynthetic reactions, photorespiration, and antioxidant system. Well-watered (Control) and drought-stressed plants were compared when leaf water potential in stressed plants reached around - 1.5 and - 3.0MPa, representing moderate and severe drought. Drought caused 84 and 96% decreases in net photosynthetic rate (Pn) and stomatal conductance. Stress-mediated changes in maximum quantum efficiency of photosystem II (PSII) photochemistry were unobserved, but drought decreased photochemical quenching, actual quantum yield of PSII electron transport, and apparent electron transport rate (ETR). Moderate and severe drought induced, respectively, decreases and increases in non-photochemical quenching (NPQ) and 74 and 273% increases in ETR/Pn. Moderate drought down-regulated PSII protein D2, chlorophyll a-b binding protein 8, photosystem I reaction center subunit N, sedoheptulose-1,7-bisphosphatase, and transketolase; while severe drought down-regulated LHC II proteins, ferredoxin-NADP reductase, ATP synthase subunits ε and ß, and carbonic anhydrase isoform X2. The glutamate-glyoxylate aminotransferase 2 and glycine dehydrogenase were down-regulated upon moderate drought, while catalase 2 and glycine cleavage system H protein 3 were up-regulated. Severe drought up-regulated glycolate oxidase, glycine cleavage system H protein 3, and aminomethyl transferase, but most of photorespiration-related proteins were only found in control plants. Down-regulation of chaperones and antioxidant enzymes and increased lipid peroxidation in stressed plants were observed upon both stress severities. Therefore, the decreases in Pn and failure in preventing oxidative damages through adjustments in NPQ and photorespiration- and antioxidant-related proteins accounted for drought sensitivity in açaí.

Assessing stomatal and non-stomatal limitations to carbon assimilation under progressive drought in peanut (Arachis hypogaea L.)

Drought is known to limit carbon assimilation in plants. However, it has been debated whether photosynthesis is primarily inhibited by stomatal or non-stomatal factors. This research assessed the underlying limitations to photosynthesis in peanuts (Arachis hypogaea L.) grown under progressive drought. Specifically, field-grown peanut plants were exposed to either well-watered or drought-stressed conditions during flowering. Measurements included survey measurements of gas exchange, chlorophyll fluorescence, PSII thermotolerance, pigment content, and rapid A-Ci response (RACiR) assessments. Drought significantly decreased stomatal conductance with consequent declines in photosynthesis (AN), actual quantum yield of PSII, and electron transport rate (ETR). Pigment contents were variable and depended on stress severity. Stomatal closure on stressed plants resulted in higher leaf temperatures, but Fv/Fm and PSII thermotolerance were only slightly affected by drought. A strong, hyperbolic relationship was observed between stomatal conductance, AN, and ETR. However, when RACiR analysis was conducted, drought significantly decreased AN at Ci values comparable to drought-stressed plants, indicating non-stomatal limitations to AN. The maximum rate of carboxylation and maximum electron transport rate were severely limited by drought, and chloroplast CO2 concentration (CC) declined substantially under drought along with a comparable increase in partitioning of electron flow to photorespiration. Thus, while stomatal conductance may be a viable reference indicator of water deficit stress in peanut, we conclude that declines in AN were largely due to non-stomatal (diffusional and metabolic) limitations. Additionally, this is the first study to apply the rapid A-Ci response method to peanut, with comparable results to traditional A-Ci methods.

Potential of Photochemical Reflectance Index for Indicating Photochemistry and Light Use Efficiency in Leaves of European Beech and Norway Spruce Trees

Hyperspectral reflectance is becoming more frequently used for measuring the functions and productivity of ecosystems. The purpose of this study was to re-evaluate the potential of the photochemical reflectance index (PRI) for evaluating physiological status of plants. This is needed because the reasons for variation in PRI and its relationships to physiological traits remain poorly understood. We examined the relationships between PRI and photosynthetic parameters in evergreen Norway spruce and deciduous European beech grown in controlled conditions during several consecutive periods of 10–12 days between which the irradiance and air temperature were changed stepwise. These regime changes induced significant changes in foliar biochemistry and physiology. The responses of PRI corresponded particularly to alterations in the actual quantum yield of photosystem II photochemistry (ΦPSII). Acclimation responses of both species led to loss of PRI sensitivity to light use efficiency (LUE). The procedure of measuring PRI at multiple irradiance-temperature conditions has been designed also for testing accuracy of ΔPRI in estimating LUE. A correction mechanism of subtracting daily measured PRI from early morning PRI has been performed to account for differences in photosynthetic pigments between irradiance-temperature regimes. Introducing ΔPRI, which provided a better estimate of non-photochemical quenching (NPQ) compared to PRI, also improved the accuracy of LUE estimation. Furthermore, ΔPRI was able to detect the effect of drought, which is poorly observable from PRI.

Nutrient allocation and photochemical responses of Populus × canadensis ‘Neva’ to nitrogen fertilization and exogenous Rhizophagus irregularis inoculation

Arbuscular mycorrhizal fungi (AMF) can promote plant growth performance, but their effectiveness varies depending on soil nitrogen (N) availability. To clarify the effectiveness of exogenous AMF along an N-fertilization gradient (0, 2, 10, 20, and 30 mM), the impacts of exogenous Rhizophagus irregularis and N on the growth, photochemical activity, and nutritional status of Populus × canadensis ‘Neva’ in natural soil were evaluated in a pot experiment. The results showed that the 10 mM N level was the optimal fertilization regime with the highest promotion effect on plant growth and the maximum quantum yield of photosystem II (PSII) (Fv/Fm). Excess N (20 and 30 mM) fertilization reduced the actual quantum yield of PSII (ФPSII) and the Fv/Fm of the plants. Regardless of the N availability, inoculated plants exhibited greater Fv/Fm values than did non-inoculated plants. The biomass of inoculated plants was significantly higher compared with the control under low N levels (0 and 2 mM). Under high N levels, inoculated plants showed significant increases in ФPSII. Moreover, the nutrient imbalance of plants inoculated with exogenous R. irregularis was eased by increasing P, Fe, Mn and Cu uptake in roots and higher P, Ca, Mg, Fe, Mn and Zn concentrations in leaves. Moreover, the Fv/Fm and ФPSII exhibited positive correlations with P, Ca, Mg and Zn concentrations in leaves. In conclusion, inoculation with exogenous R. irregularis can benefit plant fitness by improving the photochemical capacity and nutrient composition of poplar under different N levels.

"Over Expression of Jatropha’s Dehydrin Jcdhn-2 Enhances Tolerance to Water Stress in Rice Plants"

<i>Jatropha curcas’s</i>dehydrin (JC-DHN_S) has been previously shown to play a role during natural dehydration process associated with maturation of <i>Jatropha curcasseed</i>. In this study, we generated transformed rice plant (tp) over expressing JC-DHN_Sgene and examined the role of over expressed gene in improving the drought tolerance. The tp plants showed a stronger growth under water stress condition induced by addition 20% of PEG 6000. It also showed an enhanced water stress tolerance as indicated by growth parameters included, fresh and dry weight, chlorophyll content, maximum quantum yield, actual quantum yield of photosystem II and non-photochemical quenching. Also, tp plants showed higher membrane stability under drought comparing with non-transformed plant (wt) as indicated through determination of membrane electrolyte leakage, the values of malondialdehyde and, hydrogen peroxide content as indicator for oxidation level. The tp plant had higher content of osmoregulators substances such as proline, free amino acids and total soluble sugar. The tp plant showed higher content of enzyme activity such as and superoxide dismutase catalase and ascorbate peroxidase compared with wt. Our results clearly showed that tp rice plant with JC-DHNS better coped with drought stress due increasing photosynthetic efficiency and antioxidant enzymes activity.

Photochemical reflectance index and solar-induced fluorescence for assessing cotton photosynthesis under water-deficit stress

Rapid and non-destructive assessment of water status is essential to enhance crop performance. This study aimed to evaluate photosynthetic performance and to monitor water status in cotton under field conditions. A two-year experiment was conducted with three irrigation regimes to measure the following parameters: photochemical reflectance index (PRI), structural independent pigment index (SIPI), water index (WI), solar-induced fluorescence (SIF; retrieved from reflectance by using Fraunhofer line-depth method), gas exchange, and chlorophyll fluorescence (CF). The results showed that PRI decreased > 30 % in moderate drought (MD) and >50 % in severe drought (SD), compared with control. PRI was found to be positively correlated with net photosynthetic rate (PN), stomatal conductance, transpiration rate, actual quantum yield of photosystem II photochemistry (ΦPSII), but a negatively correlated with nonphotochemical quenching (NPQ). Solar-induced fluorescence around 761 nm (SIF761) had significant correlations with PN, ΦPSII, and NPQ, but not with maximal quantum yield of PS II photochemistry (Fv/Fm). The relationship between PRI and PN was stronger at the beginning of water stress (R2 = 0.86) than for the all stress stages (R2 = 0.54), indicating that PRI could be more effective for assessing PN of cotton at early water stress. PRI was better correlated with relative water content and photosynthetic parameters than SIPI and WI and so it could also be a good indicator to evaluate cotton water status.

Photosynthetic, photochemical and osmotic regulation changes in tobacco resistant and susceptible to Alternaria alternata

Alternaria alternata is a necrotrophic fungus that may cause severe losses. To further elucidate the resistance mechanisms, we investigated the impacts of increasing biotic stress, or severity levels (5%, 25% and 50%), due to A. alternata infection on two tobacco cultivars with varying resistance levels. Under severe stress, the photosynthetic pigment, net photosynthetic rate (Pn), stomatal conductance (Gs) and stomatal limitation value (Ls) all decreased in both cultivars, whereas the intercellular CO2 concentration (Ci) exhibited an upward trend. Moreover, A. alternata caused adverse effects on PSII electron transport rate and chlorophyll a fluorescence parameters, including the maximal quantum yield of fluorescence (Fv/Fm), PSII potential efficiency (Fv/F0), PSII actual quantum yield (ΦPSII), photochemical quenching (qP) and non-photochemical quenching (NPQ), and ultimately decreased PSII photochemical activity. In addition, the contents of MDA, proline and total soluble sugar increased under stress. The adverse effect of A. alternata on the resistant cultivar was less harmful than the susceptible cultivar. We conclude that the reduction of photosynthesis is a result of non-stomatal limitations. However, the resistant cultivar has better self-protection of its photosynthetic system, improved light energy utilization ability and greater accumulation of osmotic regulation substances for mitigating the damage on cellular membranes. These attributes may account for the resistance to A. alternata.

Exposure to lower red to far-red light ratios improve tomato tolerance to salt stress

BackgroundRed (R) and far-red (FR) light distinctly influence phytochrome-mediated initial tomato growth and development, and more recent evidence indicates that these spectra also modulate responses to a multitude of abiotic and biotic stresses. This research investigated whether different R: FR values affect tomato growth response and salinity tolerance. Tomato seedlings were exposed to different R: FR conditions (7.4, 1.2 and 0.8) under salinity stress (100 mM NaCl), and evaluated for their growth, biochemical changes, active reactive oxygen species (ROS) and ROS scavenging enzymes, pigments, rate of photosynthesis, and chlorophyll fluorescence.ResultsThe results showed that under conditions of salinity, tomato seedlings subjected to a lower R: FR value (0.8) significantly increased both their growth, proline content, chlorophyll content and net photosynthesis rate (Pn), while they decreased malondialdehyde (MDA) compared to the higher R: FR value (7.4). Under conditions of salinity, the lower R: FR value caused a decrease in both the superoxide anion (O2•−) and in hydrogen peroxide (H2O2) generation, an increase in the activities of superoxidase dismutase (SOD, EC 1.15.1.1), peroxidase (POD, EC 1.11.1.7) and catalase (CAT, EC 1.11.1.7). Tomato seedlings grown under the lower R: FR value and conditions of salinity showed a higher actual quantum yield of photosynthesis (ΦPSII), electron transport rate (ETR), and photochemical quenching (qP) than those exposed to a higher R: FR, indicating overall healthier growth. However, the salinity tolerance induced at the lower R: FR condition disappeared in the tomato phyB1 mutant.ConlusionThese results suggest that growing tomato with a lower R: FR value could improve seedlings’ salinity tolerance, and phytochrome B1 play an very important role in this process. Therefore, different qualities of light can be used to efficiently develop abiotic stress tolerance in tomato cultivation.

Effects of GeO&lt;sub&gt;2&lt;/sub&gt; on chlorophyll fluorescence and antioxidant enzymes in apple leaves under strong light

In this study, we chose apple leaf as plant material and studied effects of GeO2 on operation of photosynthetic apparatus and antioxidant enzyme activities under strong light. When exogenous GeO2 concentration was below 5.0 mg L–1, maximum photochemical quantum yield of PSII and actual quantum yield of PSII photochemistry increased significantly compared with the control under irradiances of 800 and 1,600 μmol(photon) m–2 s–1. Photosynthetic electron transport chain capacity between QA–QB, QA–PSI acceptor, and QB–PSI acceptor showed a trend of rising up with 1.0, 2.0, and 5.0 mg(GeO2) L–1 and declining with 10.0 mg(GeO2) L–1. On the other hand, dissipated energy via both ΔpH and xanthophyll cycle decreased remarkably compared with the control when GeO2 concentration was below 5.0 mg L–1. Our results suggested that low concentrations of GeO2 could alleviate photoinhibition and 5.0 mg(GeO2) L–1 was the most effective. In addition, we found, owing to exogenous GeO2 treatment, that the main form of this element in apple leaves was organic germanium, which means chemical conversion of germanium happened. The organic germanium might be helpful to allay photoinhibition due to its function of scavenging free radicals and lowering accumulation of reactive oxygen species, which was proven by higher antioxidant enzyme activities.

Chlorophyll fluorescence characteristics of Phyllostachys edulis during its fast growth period

To explore chlorophyll fluorescence characteristics of a Phyllostachys edulis blade during its fast growth period (early, middle, and late phases), parameters concerning chlorophyll fluorescence of a Ph. edulis blade were measured using PAM-2100 chlorophyll fluorescence spectrometer during its fast growth period of the Bamboo Physiological and Ecological Monitoring Station of Zhejiang A & F University, also comprehensive evaluation of its fluorescence characteristics was then conducted. The results showed that the actual photochemical quantum yield of Photosystem Ⅱ (PS-Ⅱ), the maximal photochemical efficiency of PS-Ⅱ (Fv/Fm), and the potential PS-Ⅱ activity for same-aged Ph. edulis samples had significant differences within different stages of the rapid growth period (P < 0.05) going from a lower level to a higher level for the early phase, the middle phase, and the latter phase. Variation in the Fv/Fm ratio was 0.672-0.773 and in the Fv /Fo ratio was 2.068-3.231. During the fast grwoth period, the value of Non-photochemical Quenching(qNP) in the order: middle phase < late phase < early phase. The qNP value also showed strong daily variation during different phases of the fast growth period. Chlorophyll fluorescence parameters of bamboo blade show significant changes during its fast growth period. Thus, as indicated by the comprehensive comparison, photosynthesis of the Ph. edulis blade showed an increasing tendency during its rapid growth.