A comparative study of four Malayan ferns, Christensenia aesculifolia (Bl.) Maxon, Tectaria singaporeana (Wall.) Ching, Abacopteris multilineata (Wall.) Ching and Hymenophyllum polyanthos Sw. from shady habitats and another four, Dicranopteris linearis (Burm.) Und., Lygodium scandens (L.) Sw., Blechnum orientate Linn, and Stenochlaena palustris (Burm.) Bedd. from sunlit habitats showed that the total chlorophyll content expressed on a gram fresh weight basis was greater in the shade ferns. There was little difference in the chlorophyll content between the sun and shade ferns when it was expressed on a per unit leaf area basis. The protein and protohaem content was greater in the sun ferns. Measurements of the in vitro photochemical activities of the photosystems I and II in isolated chloroplasts by means of an oxygen electrode showed higher rates in the sun ferns. As determined by spectrophotometric analysis, the photosynthetic cytochrome content from isolated chloroplasts was greater in the sun ferns. The results indicate that the sun ferns have physiological characteristics favouring greater capacity for photosynthesis. Mitochondria isolated from the sun ferns showed faster rates of electron transport using exogenous NADH as substrate.
Leaf respiration in the dark (Rdark ) is often measured at a single time during the day, with hot-acclimation lowering Rdark at a common measuring temperature. However, it is unclear whether the diel cycle influences the extent of thermal acclimation of Rdark , or how temperature and time of day interact to influence respiratory metabolites. To examine these issues, we grew rice under 25°C : 20°C, 30°C : 25°C and 40°C : 35°C day : night cycles, measuring Rdark and changes in metabolites at five time points spanning a single 24-h period. Rdark differed among the treatments and with time of day. However, there was no significant interaction between time and growth temperature, indicating that the diel cycle does not alter thermal acclimation of Rdark . Amino acids were highly responsive to the diel cycle and growth temperature, and many were negatively correlated with carbohydrates and with organic acids of the tricarboxylic acid (TCA) cycle. Organic TCA intermediates were significantly altered by the diel cycle irrespective of growth temperature, which we attributed to light-dependent regulatory control of TCA enzyme activities. Collectively, our study shows that environmental disruption of the balance between respiratory substrate supply and demand is corrected for by shifts in TCA-dependent metabolites.
Chilling restrains the distribution of mangroves. We tested whether foliar phosphorus (P) fractions and gene expression are associated with cold tolerance in mangrove species. We exposed seedlings of six mangrove populations from different latitudes to favorable, chilling and recovery treatments, and measured their foliar P concentrations and fractions, photochemistry, nighttime respiration, and gene expression. A Kandelia obovata (KO; 26.45°N) population completely and a Bruguiera gymnorhiza (Guangxi) (BGG; 21.50°N) population partially (30%) survived chilling. Avicennia marina (24.29°N), and other B. gymnorhiza (26.66°N, 24.40°N, and 19.62°N) populations died after chilling. Photosystems of KO and photosystem I of BGG were least injured. During chilling, leaf P fractions, except nucleic acid P in three populations, declined and photoinhibition and nighttime respiration increased in all populations, with the greatest impact in B. gymnorhiza. Leaf nucleic acid P was positively correlated with photochemical efficiency during recovery and nighttime respiration across populations for each treatment. Relatively high concentrations of nucleic acid P and metabolite P were associated with stronger chilling tolerance in KO. Bruguiera gymnorhiza exhibited relatively low concentrations of organic P in favorable and chilling conditions, but its partially survived population showed stronger compensation in nucleic acid P and Pi concentrations and gene expression during recovery.
Leaf structure plays an important role in photosynthesis. However, the causal relationship and the quantitative importance of any single structural parameter to the overall photosynthetic performance of a leaf remains open to debate. In this paper, we report on a mechanistic model, eLeaf, which successfully captures rice leaf photosynthetic performance under varying environmental conditions of light and CO2 . We developed a 3D reaction-diffusion model for leaf photosynthesis parameterised using a range of imaging data and biochemical measurements from plants grown under ambient and elevated CO2 and then interrogated the model to quantify the importance of these elements. The model successfully captured leaf-level photosynthetic performance in rice. Photosynthetic metabolism underpinned the majority of the increased carbon assimilation rate observed under elevated CO2 levels, with a range of structural elements making positive and negative contributions. Mesophyll porosity could be varied without any major outcome on photosynthetic performance, providing a theoretical underpinning for experimental data. eLeaf allows quantitative analysis of the influence of morphological and biochemical properties on leaf photosynthesis. The analysis highlights a degree of leaf structural plasticity with respect to photosynthesis of significance in the context of attempts to improve crop photosynthesis.
Graphitic carbon nitride (g-C3 N4 ) is a kind of ideal metal-free photocatalysts for artificial photosynthesis. At present, pristine g-C3 N4 suffers from small specific surface area, poor light absorption at longer wavelengths, low charge migration rate, and a high recombination rate of photogenerated electron-hole pairs, which significantly limit its performance. Among a myriad of modification strategies, point-defect engineering, namely tunable vacancies and dopant introduction, is capable of harnessing the superb structural, textural, optical, and electronic properties of g-C3 N4 to acquire an ameliorated photocatalytic activity. In view of the burgeoning development in this pacey field, a timely review on the state-of-the-art advancement of point-defect engineering of g-C3 N4 is of vital significance to advance the solar energy conversion. Particularly, insights into the intriguing roles of point defects, the synthesis, characterizations, and the systematic control of point defects, as well as the versatile application of defective g-C3 N4 -based nanomaterials toward photocatalytic water splitting, carbon dioxide reduction and nitrogen fixation will be presented in detail. Lastly, this review will conclude with a balanced perspective on the technical and scientific hindrances and future prospects. Overall, it is envisioned that this review will open a new frontier to uncover novel functionalities of defective g-C3 N4 -based nanostructures in energy catalysis.
Carnivorous pitcher plants produce specialised pitcher organs containing secretory glands, which secrete acidic fluids with hydrolytic enzymes for prey digestion and nutrient absorption. The content of pitcher fluids has been the focus of many fluid protein profiling studies. These studies suggest an evolutionary convergence of a conserved group of similar enzymes in diverse families of pitcher plants. A recent study showed that endogenous proteins were replenished in the pitcher fluid, which indicates a feedback mechanism in protein secretion. This poses an interesting question on the physiological effect of plant protein loss. However, there is no study to date that describes the pitcher response to endogenous protein depletion. To address this gap of knowledge, we previously performed a comparative RNA-sequencing experiment of newly opened pitchers (D0) against pitchers after 3 days of opening (D3C) and pitchers with filtered endogenous proteins (>10 kDa) upon pitcher opening (D3L). Nepenthes ampullaria was chosen as a model study species due to their abundance and unique feeding behaviour on leaf litters. The analysis of unigenes with top 1% abundance found protein translation and stress response to be overrepresented in D0, compared to cell wall related, transport, and signalling for D3L. Differentially expressed gene (DEG) analysis identified DEGs with functional enrichment in protein regulation, secondary metabolism, intracellular trafficking, secretion, and vesicular transport. The transcriptomic landscape of the pitcher dramatically shifted towards intracellular transport and defence response at the expense of energy metabolism and photosynthesis upon endogenous protein depletion. This is supported by secretome, transportome, and transcription factor analysis with RT-qPCR validation based on independent samples. This study provides the first glimpse into the molecular responses of pitchers to protein loss with implications to future cost/benefit analysis of carnivorous pitcher plant energetics and resource allocation for adaptation in stochastic environments.
Microbial fuel cells operating with autotrophic microorganisms are known as biophotovoltaic devices. It represents a great opportunity for environmentally-friendly power generation using the energy of the sunlight. The efficiency of electricity generation in this novel system is however low. This is partially reflected by the poor understanding of the bioelectrochemical mechanisms behind the electron transfer from these microorganisms to the electrode surface. In this work, we propose a combination of electrochemical and fluorescence techniques, giving emphasis to the pulse amplitude modulation fluorescence. The combination of these two techniques allow us to obtain information that can assist in understanding the electrical response obtained from the generation of electricity through the intrinsic properties related to the photosynthetic efficiency that can be obtained from the fluorescence emitted. These were achieved quantitatively by means of observed changes in four photosynthetic parameters with the bioanode generating electricity. These are the maximum quantum yield (Fv/Fm), alpha (α), light saturation coefficient (Ek) and maximum rate of electron transfer (rETRm). The relationship between the increases in the current density collected by the bioanode to the decrease of the rETRm values in the photosynthetic pathway for the two microorganisms was also discussed.
Lignosulfonate (LS) is a by-product obtained during sulfite pulping process and is commonly used as a growth enhancer in plant growth. However, the underlying growth promoting mechanism of LS on shoot growth remains largely unknown. Hence, this study was undertaken to determine the potential application of eco-friendly ion-chelated LS complex [sodium LS (NaLS) and calcium LS (CaLS)] to enhance recalcitrant indica rice MR 219 shoot growth and to elucidate its underlying growth promoting mechanisms. In this study, the shoot apex of MR 219 rice was grown on Murashige and Skoog medium supplemented with different ion chelated LS complex (NaLS and CaLS) at 100, 200, 300 and 400 mg/L The NaLS was shown to be a better shoot growth enhancer as compared to CaLS, with optimum concentration of 300 mg/L. Subsequent comparative proteomic analysis revealed an increase of photosynthesis-related proteins [photosystem II (PSII) CP43 reaction center protein, photosystem I (PSI) iron-sulfur center, PSII CP47 reaction center protein, PSII protein D1], ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco), carbohydrate metabolism-related proteins (glyceraldehyde-3-phosphate dehydrogenase 3, fructose-bisphosphate aldolase) and stress regulator proteins (peptide methionine sulfoxide reductase A4, delta-1-pyrroline-5-carboxylate synthase 1) abundance in NaLS-treated rice as compared to the control (MSO). Consistent with proteins detected, a significant increase in biochemical analyses involved in photosynthetic activities, carbohydrate metabolism and protein biosynthesis such as total chlorophyll, rubisco activity, total sugar and total protein contents were observed in NaLS-treated rice. This implies that NaLS plays a role in empowering photosynthesis activities that led to plant growth enhancement. In addition, the increased in abundance of stress regulator proteins were consistent with low levels of peroxidase activity, malondialdehyde content and phenylalanine ammonia lyase activity observed in NaLS-treated rice. These results suggest that NaLS plays a role in modulating cellular homeostasis to provide a conducive cellular environment for plant growth. Taken together, NaLS improved shoot growth of recalcitrant MR 219 rice by upregulation of photosynthetic activities and reduction of ROS accumulation leading to better plant growth.
WeedLock is a broad-spectrum plant-based bioherbicide that is currently on the market as a ready-to-use formulation. In this study, we investigated the physiological and biochemical effects of WeedLock (672.75 L ha-1) on Ageratum conyzoides L., Eleusine indica (L.) Gaertn, Zea mays L., and Amaranthus gangeticus L. at four different time points. WeedLock caused significant reductions in chlorophyll pigment content and disrupted photosynthetic processes in all test plants. The greatest inhibition in photosynthesis was recorded in A. conyzoides at 24 h post-treatment with a 74.88% inhibition. Plants treated with WeedLock showed increased malondialdehyde (MDA) and proline production, which is indicative of phytotoxic stress. Remarkably, MDA contents of all treated plants increased by more than 100% in comparison to untreated. The activity of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) was elevated following treatment with WeedLock. Significant increases were observed in the SOD activity of A. conyzoides ranging from 69.66 to 118.24% from 6 to 72 h post-treatment. Our findings confirm that WeedLock disrupts the normal physiological and biochemical processes in plants following exposure and that its mode of action is associated with ROS (reactive oxygen species) production, similar to that of PPO (protoporphyrinogen oxidase) inhibitors, although specific site-of-action of this novel bioherbicide warrants further investigation.
Parasitic plants are known to discard photosynthesis thus leading to the deletion or loss of the plastid genes. Despite plastid genome reduction in non-photosynthetic plants, some nucleus-encoded proteins are transported back to the plastid to carry out specific functions. In this work, we study such proteins in Rafflesia cantleyi, a member of the holoparasitic genus well-known for producing the largest single flower in the world. Our analyses of three transcriptome datasets, two holoparasites (R. cantleyi and Phelipanche aegyptiaca) and one photosynthetic plant (Arabidopsis thaliana), suggest that holoparasites, such as R. cantleyi, retain some common plastid associated processes such as biosynthesis of amino acids and lipids, but are missing photosynthesis components that can be extensions of these pathways. The reconstruction of two selected biosynthetic pathways involving plastids correlates the trend of plastid retention to pathway complexity - transcriptome evidence for R. cantleyi suggests alternate mechanisms in regulating the plastidial heme and terpenoid backbone biosynthesis pathways. The evolution to holoparasitism from autotrophy trends towards devolving the plastid genes to the nuclear genome despite the functional sites remaining in the plastid, or maintaining non-photosynthetic processes in the plastid, before the eventual loss of the plastid and any site dependent functions.
The FLUXNET2015 dataset provides ecosystem-scale data on CO2, water, and energy exchange between the biosphere and the atmosphere, and other meteorological and biological measurements, from 212 sites around the globe (over 1500 site-years, up to and including year 2014). These sites, independently managed and operated, voluntarily contributed their data to create global datasets. Data were quality controlled and processed using uniform methods, to improve consistency and intercomparability across sites. The dataset is already being used in a number of applications, including ecophysiology studies, remote sensing studies, and development of ecosystem and Earth system models. FLUXNET2015 includes derived-data products, such as gap-filled time series, ecosystem respiration and photosynthetic uptake estimates, estimation of uncertainties, and metadata about the measurements, presented for the first time in this paper. In addition, 206 of these sites are for the first time distributed under a Creative Commons (CC-BY 4.0) license. This paper details this enhanced dataset and the processing methods, now made available as open-source codes, making the dataset more accessible, transparent, and reproducible.
The presence of abundant oil palm residues in Malaysia prompted the need to utilize this waste to avoid environmental
pollution. This waste was abundant at the oil palm mill and accounted for almost 50% of production. The study was
conducted to determine the morphological effect of Palm Oil Mill Effluent (POME) sludge on the maize growth performance
and gas exchange. Physicochemical, growth morphology and gas exchange was measured after treated with POME sludge
from different treatment pond systems: Mixing, anaerobic, facultative, algae and dumping. The results indicated the
pH, C, and CEC of mixing the < anaerobic < facultative < algae < dumping ponds. There was a significant presence of
macronutrient (N, Mg, Ca, Fe, S) in the treated POME sludge, contrary to the presence of heavy metal (Cd, Cu, Ni and
Pb) elements which were not significantly different in all the treatments and lower than WHO/FAO standard. Root Shoot
Ratio (RSR) and Specific Leaf Area (SLA) indicated significant difference in biomass accumulation and yield compared to
the control. The gas exchange variable was a significant difference on stomata conductivity (Gs) and transpiration rate
(E). However, the POME sludge from the facultative, algae and dumping ponds showed positive correlations between net
photosynthesis, stomata conductivity and transpiration rate. Indeed, the increased transpiration rate (E) was correlated
with stomata conductance (Gs) after treatment with anaerobic, facultative, algae and dumping ponds. In conclusion, the
POME sludge amendment was able to increase the maize biomass and yield.
Engineering the CO2
-fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) to improve photosynthesis
has long been sought. Rubisco large subunits (RbcL) are highly-conserved but because of certain undefined sequence
differences, plant Rubisco research cannot fully utilise the robust heterologous Escherichia coli expression system and its
GroEL folding machinery. Previously, a series of chimeric cyanobacteria Synechococcus elongatus Rubisco, incorporated
with sequences from the green alga Chlamydomonas reinhardtii, were expressed in E. coli; differences in RbcL sections
essential for holoenzyme formation were pinpointed. In this study, the remaining sections, presumably not crucial for
holoenzyme formation and also the small subunit (RbcS), are substituted to further ascertain the possible destabilising
effects of multiple section mutations. To that end, combinations of Synechococcus RbcL Sections 1 (residues 1-47), 2
(residues 48-97), 5 (residues 198-247) and 10 (residues 448-472), and RbcS, were swapped with collinear Chlamydomonas
sections and expressed in E. coli. Interestingly, only the chimera with Sections 1 and 2 together produces holoenzyme and
an interaction network of complementing amino acid changes is delineated by crystal structure analysis. Furthermore,
sequence-based analysis also highlighted possible GroEL binding site differences between the two RbcLs.
Drought is one of the commonly occurring environmental stresses, limiting crop production in many countries. Selection
of cultivar is the most effective and economical means for alleviating the adverse effects of drought stress on crops. The
present study aimed to investigate the growth, some physiological processes, yield and quality of some newly-developed
wheat cultivars (AARI-2011, AAS-2011, Faisalabad-2008, Millat-2011 and Punjab-2011) under field drought stress
conditions. The cultivars were sown in a field under normal irrigation and drought-induced conditions. Maximum net
photosynthetic rate was recorded in cv. AAS-2011 at growth stage of 67 days after wheat emergence under normal irrigation
and cv. Faisalabad-2008 at 67 days after wheat emergence under drought condition. Leaf stomatal conductance and
transpiration rate were maximum in cv. Faisalabad-2008 under drought conditions. The adverse effects of drought stress
were observed more on cv. Millat-2011 than Faisalabad-2008, with respect to net photosynthetic rate and transpiration.
Drought exerted a significant adverse effect on leaf stomatal conductance at 74 days after wheat emergence which was
recorded as 230 mmol m-2 s-1. Among the cultivars, AAS-2011 recorded maximum yield traits and grain yield under normal
irrigation condition and Faisalabad-2008 under drought condition. Cultivar Millat-2011 was the most susceptible to
drought and Faisalabad-2008 the most resistant to drought. Faisalabad-2008 maintained the quality at the most under
drought stress conditions. It is concluded that Fasialabad-2008 should be grown under field drought conditions to achieve
maximal yield and quality of wheat.
The relationship between heavy metal and trophic properties in polymictic lake at Sembrong Lake, Peninsular Malaysia was assessed. Sixteen parameters, including heavy metals and trophic parameters were monitored. pH, temperature, dissolved oxygen and heavy metals level changes significantly influenced by the dynamic of polymictic mixing pattern. The mean concentrations of heavy metals in the reservoir decreased in the following order: Fe > Mn > Zn > Cu > As > Pb. The result showed that this polymictic lake is being threatened by cultural eutrophication with TSI value range from 72.40 to 80.41 and classified as a hypereutrophic lake. The levels of heavy metal pollution in the reservoir range from slightly polluted to polluted. Factor analysis was performed to determine the relationship between heavy metals and trophic parameters. Five factors were responsible for data structure and explained the 83% of total variance. These factors differentiate each group of parameters according to their common characteristics. Photosynthesis, respiration and redox processes were main factors contributing to the variability of both properties.
The production of wheat crop is below average in many regions of the world which is ascribed to adverse environmental
conditions including drought stress. The present study was conducted to appraise the beneficial role of exogenouslyapplied
5-aminolevulinic acid (ALA) on growth, yield and some key physio-biochemical characteristics of two commercially
important wheat cultivars (Shafaq-06 and Uqab-2000) under well watered [100% field capacity (FC)] and water-deficit
(60 and 80% FC) conditions. Imposition of varying water regimes significantly decreased fresh and dry weights of shoots,
photosynthetic pigments (a and b), non-photochemical quenching of chlorophyll fluorescence (NPQ), quenching coefficient
for non-photochemical (N) of chlorophyll fluorescence (qN), K+ (potassium ion), Ca2+ (calcium ion) and P (phosphorus)
accumulation in shoot and root and yield-related attributes. In contrast, water deficit regimes caused improvement in
Fv/Fm (chlorophyll fluorescence measurement), coefficient of photochemical quenching (qP), proline, glycinebetaine
(GB) and hydrogen peroxide (H2O2) contents. Foliar spray of ALA at the rate of 50, 100 and 150 mg/Lalong with control
(no spray (NS) and/or water spray (WS)) significantly enhanced chlorophyll a and b pigments, qN, NPQ, qP, K+, Ca2+
and P accumulation in both roots and shoots, proline, GB, total phenolics and malondialdehyde (MDA) contents and
yield. The wheat Shafaq-06 was better in shoot dry weight, qN, NPQ and Fv/Fm, shoot and root K+, root Ca2+, proline,
GB accumulation and yield attributes, while Uqab-2000 was better in chlorophyll a contents, root P and MDA contents.
Overall, better growth and yield of Shafaq-06 than Uqab-2000 under water deficit regimes was found to be associated
with ALA improved leaf fluorescence (qN, NPQ and Fv/Fm), shoot and root K+, root Ca2+, proline and GB accumulation.
Coral spawning times have been linked to multiple environmental factors; however, to what extent these factors act as generalized cues across multiple species and large spatial scales is unknown. We used a unique dataset of coral spawning from 34 reefs in the Indian and Pacific Oceans to test if month of spawning and peak spawning month in assemblages of Acropora spp. can be predicted by sea surface temperature (SST), photosynthetically available radiation, wind speed, current speed, rainfall or sunset time. Contrary to the classic view that high mean SST initiates coral spawning, we found rapid increases in SST to be the best predictor in both cases (month of spawning: R(2) = 0.73, peak: R(2) = 0.62). Our findings suggest that a rapid increase in SST provides the dominant proximate cue for coral mass spawning over large geographical scales. We hypothesize that coral spawning is ultimately timed to ensure optimal fertilization success.
The photosynthetic cyanobacterium, Synechocystis sp. strain 6803, is a potential platform for the production of various chemicals and biofuels. In this study, direct photosynthetic production of a biopolymer, polyhydroxyalkanoate (PHA), in genetically engineered Synechocystis sp. achieved as high as 14 wt%. This is the highest production reported in Synechocystis sp. under photoautotrophic cultivation conditions without the addition of a carbon source. The addition of acetate increased PHA accumulation to 41 wt%, and this value is comparable to the highest production obtained with cyanobacteria. Transcriptome analysis by RNA-seq coupled with real-time PCR was performed to understand the global changes in transcript levels of cells subjected to conditions suitable for photoautotrophic PHA biosynthesis. There was lower expression of most PHA synthesis-related genes in recombinant Synechocystis sp. with higher PHA accumulation suggesting that the concentration of these enzymes is not the limiting factor to achieving high PHA accumulation. In order to cope with the higher PHA production, cells may utilize enhanced photosynthesis to drive the product formation. Results from this study suggest that the total flux of carbon is the possible driving force for the biosynthesis of PHA and the polymerizing enzyme, PHA synthase, is not the only critical factor affecting PHA-synthesis. Knowledge of the regulation or control points of the biopolymer production pathways will facilitate the further use of cyanobacteria for biotechnological applications.
Global warming and ozone depletion, and the resulting increase of ultraviolet radiation (UVR), have far-reaching impacts on biota, especially affecting the algae that form the basis of the food webs in aquatic ecosystems. The aim of the present study was to investigate the interactive effects of temperature and UVR by comparing the photosynthetic responses of similar taxa of Chlorella from Antarctic (Chlorella UMACC 237), temperate (Chlorella vulgaris UMACC 248) and tropical (Chlorella vulgaris UMACC 001) environments. The cultures were exposed to three different treatments: photosynthetically active radiation (PAR; 400-700 nm), PAR plus ultraviolet-A (320-400 nm) radiation (PAR + UV-A) and PAR plus UV-A and ultraviolet-B (280-320 nm) radiation (PAR + UV-A + UV-B) for one hour in incubators set at different temperatures. The Antarctic Chlorella was exposed to 4, 14 and 20°C. The temperate Chlorella was exposed to 11, 18 and 25°C while the tropical Chlorella was exposed to 24, 28 and 30°C. A pulse-amplitude modulated (PAM) fluorometer was used to assess the photosynthetic response of microalgae. Parameters such as the photoadaptive index (Ek) and light harvesting efficiency (α) were determined from rapid light curves. The damage (k) and repair (r) rates were calculated from the decrease in ΦPSIIeff over time during exposure response curves where cells were exposed to the various combinations of PAR and UVR, and fitting the data to the Kok model. The results showed that UV-A caused much lower inhibition than UV-B in photosynthesis in all Chlorella isolates. The three isolates of Chlorella from different regions showed different trends in their photosynthesis responses under the combined effects of UVR (PAR + UV-A + UV-B) and temperature. In accordance with the noted strain-specific characteristics, we can conclude that the repair (r) mechanisms at higher temperatures were not sufficient to overcome damage caused by UVR in the Antarctic Chlorella strain, suggesting negative effects of global climate change on microalgae inhabiting (circum-) polar regions. For temperate and tropical strains of Chlorella, damage from UVR was independent of temperature but the repair constant increased with increasing temperature, implying an improved ability of these strains to recover from UVR stress under global warming.
The eucheumatoids Kappaphycus and Eucheuma are cultivated in tropical or subtropical regions for the production of carrageenan, a hydrocolloid widely used in the food and cosmetic industries. Kappaphycus alvarezii is a highly valued economic crop in the Coral Triangle, with the Philippines, Indonesia and Malaysia ranked among the largest producers. In the absence of measures to mitigate climate change, extreme events including heatwaves, typhoons, severe El Niño and La Niña, are expected to increase in frequency and magnitude. This inadvertently brings adverse effects to the seaweed cultivation industry, especially in the tropics. Temperatures are rapidly reaching the upper limit of biologically tolerable levels and an increase in reports of ice-ice and pest outbreaks is attributable to these shifts of environmental parameters. Nevertheless, few reports on the response of eucheumatoids to a changing environment, in particular global warming, are available. Understanding the responses and possible mechanisms for acclimation to warming is crucial for a sustainable seaweed cultivation industry. Here, the physiological and biochemical responses of K. alvarezii to acute warming indicated that the strain used in the current study is unlikely to survive sudden increases in temperature above 36°C. As temperature increased, the growth rates, photosynthetic performance, phycocolloid quality (carrageenan yield, gel strength and gel viscosity) and pigment content (chlorophyll-a, carotenoid and phycobiliproteins) were reduced while the production of reactive oxygen species increased indicating the occurrence of stress in the seaweeds. This study provides a basis for future work on long term acclimation to elevated temperature and mesocosm-based multivariate studies to identify heat-tolerant strains for sustainable cultivation.