Stimulation of isoprene emissions and electron transport rates as key mechanisms of thermal tolerance in the tropical species Vismia guianensis

Interactions between leaf phenological type and functional traits drive variation in isoprene emissions in central Amazon forest trees

The Amazon forest is the largest source of isoprene emissions, and the seasonal pattern of leaf-out phenology in this forest has been indicated as an important driver of seasonal variation in emissions. Still, it is unclear how emissions vary between different leaf phenological types in this forest. To evaluate the influence of leaf phenological type over isoprene emissions, we measured leaf-level isoprene emission capacity and leaf functional traits for 175 trees from 124 species of angiosperms distributed among brevideciduous and evergreen trees in a central Amazon forest. Evergreen isoprene emitters were less likely to store monoterpenes and had tougher and less photosynthetically active leaves with higher carbon-to-nitrogen ratios compared to non-emitters. Isoprene emission rates in brevideciduous trees were higher with a higher diversity of stored sesquiterpenes and total phenolics content. Our results suggest that the way isoprene emissions relate to growth and defense traits in central Amazon trees might be influenced by leaf phenological type, and that isoprene may participate in co-regulating a chemical-mechanical defense trade-off between brevideciduous and evergreen trees. Such knowledge can be used to improve emission estimates based on leaf phenological type since, as a highly-emitted biogenic volatile organic compound (BVOC), isoprene affects atmospheric processes with implications for the Earth's radiative balance.

Concurrent Measurement of O2 Production and Isoprene Emission During Photosynthesis: Pros, Cons and Metabolic Implications of Responses to Light, CO2 and Temperature

Traditional leaf gas exchange experiments have focused on net CO2 exchange (Anet). Here, using California poplar (Populus trichocarpa), we coupled measurements of net oxygen production (NOP), isoprene emissions and δ18O in O2 to traditional CO2/H2O gas exchange with chlorophyll fluorescence, and measured light, CO2 and temperature response curves. This allowed us to obtain a comprehensive picture of the photosynthetic redox budget including electron transport rate (ETR) and estimates of the mean assimilatory quotient (AQ = Anet/NOP). We found that Anet and NOP were linearly correlated across environmental gradients with similar observed AQ values during light (1.25 ± 0.05) and CO2 responses (1.23 ± 0.07). In contrast, AQ was suppressed during leaf temperature responses in the light (0.87 ± 0.28), potentially due to the acceleration of alternative ETR sinks like lipid synthesis. Anet and NOP had an optimum temperature (Topt) of 31°C, while ETR and δ18O in O2 (35°C) and isoprene emissions (39°C) had distinctly higher Topt. The results confirm a tight connection between water oxidation and ETR and support a view of light-dependent lipid synthesis primarily driven by photosynthetic ATP/NADPH not consumed by the Calvin-Benson cycle, as an important thermotolerance mechanism linked with high rates of (photo)respiration and CO2/O2 recycling.

Water deficit and storm disturbances co-regulate Amazon rainforest seasonality

Canopy leaf abundance of Amazon rainforests increases in the dry season but decreases in the wet season, contrary to earlier expectations of water stress adversely affecting plant functions. Drivers of this seasonality, particularly the role of water availability, remain debated. We introduce satellite-based ecophysiological indicators to demonstrate that Amazon rainforests are constrained by water during dry seasons despite light-driven canopy greening. Evidence includes a shifted partitioning of photosynthetically active radiation toward more isoprene emissions and synchronized declines in leaf and xylem water potentials. In addition, we find that convective storms attenuate light-driven ecosystem greening in the late dry season and then reverse to net leaf loss in the wet season, improving rainforest leaf area predictability by 24 to 31%. These findings highlight the susceptibility of Amazon rainforests to increasing risks of drought and windthrow disturbances under warming.

The isoprene-responsive phosphoproteome provides new insights into the putative signalling pathways and novel roles of isoprene

Many plants, especially trees, emit isoprene in a highly light- and temperature-dependent manner. The advantages for plants that emit, if any, have been difficult to determine. Direct effects on membranes have been disproven. New insights have been obtained by RNA sequencing, proteomic and metabolomic studies. We determined the responses of the phosphoproteome to exposure of Arabidopsis leaves to isoprene in the gas phase for either 1 or 5 h. Isoprene effects that were not apparent from RNA sequencing and other methods but were apparent in the phosphoproteome include effects on chloroplast movement proteins and membrane remodelling proteins. Several receptor kinases were found to have altered phosphorylation levels. To test whether potential isoprene receptors could be identified, we used molecular dynamics simulations to test for proteins that might have strong binding to isoprene and, therefore might act as receptors. Although many Arabidopsis proteins were found to have slightly higher binding affinities than a reference set of Homo sapiens proteins, no specific receptor kinase was found to have a very high binding affinity. The changes in chloroplast movement, photosynthesis capacity and so forth, found in this work, are consistent with isoprene responses being especially useful in the upper canopy of trees.

Adjusting function of camphor on primary metabolism in Cinnamomum camphora stressed by high temperature

Cinnamomum camphora has great economic value for its wide utilization in traditional medicine and furniture material, and releases lots of monoterpenes to tolerate high temperature. To uncover the adjusting function of monoterpenes on primary metabolism and promoting their utilization as anti-high temperature agents, the photosynthetic capacities, primary metabolite levels, cell ultrastructure and associated gene expression were surveyed in C. camphora when it was blocked monoterpene biosynthesis with fosmidomycin (Fos) and fumigated with camphor (a typical monoterpene in the plant) under high temperature (Fos+38 °C+camphor). Compared with the control (28 °C), high temperature at 38 °C decreased the starch content and starch grain size, and increased the fructose, glucose, sucrose and soluble sugar content. Meanwhile, high temperature also raised the lipid content, with the increase of lipid droplet size and numbers. These variations were further intensified in Fos+ 38 °C treatment. Compared with Fos+ 38 °C treatment, Fos+ 38 °C+camphor treatment improved the starch accumulation by promoting 4 gene expression in starch biosynthesis, and lowered the sugar content by suppressing 3 gene expression in pentose phosphate pathway and promoting 15 gene expression in glycolysis and tricarboxylic acid cycle. Meanwhile, Fos+ 38 °C+camphor treatment also lowered the lipid content, which may be caused by the down-regulation of 2 genes in fatty acid formation and up-regulation of 4 genes in fatty acid decomposition. Although Fos+ 38 °C+camphor treatment improved the photosynthetic capacities in contrast to Fos+ 38 °C treatment, it cannot explain the variations of these primary metabolite levels. Therefore, camphor should adjust related gene expression to maintain the primary metabolism in C. camphora tolerating high temperature.

Symbiont Identity Impacts the Microbiome and Volatilome of a Model Cnidarian-Dinoflagellate Symbiosis

The symbiosis between cnidarians and dinoflagellates underpins the success of reef-building corals in otherwise nutrient-poor habitats. Alterations to symbiotic state can perturb metabolic homeostasis and thus alter the release of biogenic volatile organic compounds (BVOCs). While BVOCs can play important roles in metabolic regulation and signalling, how the symbiotic state affects BVOC output remains unexplored. We therefore characterised the suite of BVOCs that comprise the volatilome of the sea anemone Exaiptasia diaphana ('Aiptasia') when aposymbiotic and in symbiosis with either its native dinoflagellate symbiont Breviolum minutum or the non-native symbiont Durusdinium trenchii. In parallel, the bacterial community structure in these different symbiotic states was fully characterised to resolve the holobiont microbiome. Based on rRNA analyses, 147 unique amplicon sequence variants (ASVs) were observed across symbiotic states. Furthermore, the microbiomes were distinct across the different symbiotic states: bacteria in the family Vibrionaceae were the most abundant in aposymbiotic anemones; those in the family Crocinitomicaceae were the most abundant in anemones symbiotic with D. trenchii; and anemones symbiotic with B. minutum had the highest proportion of low-abundance ASVs. Across these different holobionts, 142 BVOCs were detected and classified into 17 groups based on their chemical structure, with BVOCs containing multiple functional groups being the most abundant. Isoprene was detected in higher abundance when anemones hosted their native symbiont, and dimethyl sulphide was detected in higher abundance in the volatilome of both Aiptasia-Symbiodiniaceae combinations relative to aposymbiotic anemones. The volatilomes of aposymbiotic anemones and anemones symbiotic with B. minutum were distinct, while the volatilome of anemones symbiotic with D. trenchii overlapped both of the others. Collectively, our results are consistent with previous reports that D. trenchii produces a metabolically sub-optimal symbiosis with Aiptasia, and add to our understanding of how symbiotic cnidarians, including corals, may respond to climate change should they acquire novel dinoflagellate partners.

Functional annotation of rhizospheric phageome of the wild plant species Moringa oleifera

Introduction

The study aims to describe phageome of soil rhizosphere of M.oleifera in terms of the genes encoding CAZymes and other KEGG enzymes.

Methods

Genes of the rhizospheric virome of the wild plant species Moringa oleifera were investigated for their ability to encode useful CAZymes and other KEGG (Kyoto Encyclopedia of Genes and Genomes) enzymes and to resist antibiotic resistance genes (ARGs) in the soil.

Results

Abundance of these genes was higher in the rhizospheric microbiome than in the bulk soil. Detected viral families include the plant viral family Potyviridae as well as the tailed bacteriophages of class Caudoviricetes that are mainly associated with bacterial genera Pseudomonas, Streptomyces and Mycobacterium. Viral CAZymes in this soil mainly belong to glycoside hydrolase (GH) families GH43 and GH23. Some of these CAZymes participate in a KEGG pathway with actions included debranching and degradation of hemicellulose. Other actions include biosynthesizing biopolymer of the bacterial cell wall and the layered cell wall structure of peptidoglycan. Other CAZymes promote plant physiological activities such as cell-cell recognition, embryogenesis and programmed cell death (PCD). Enzymes of other pathways help reduce the level of soil H₂O₂ and participate in the biosynthesis of glycine, malate, isoprenoids, as well as isoprene that protects plant from heat stress. Other enzymes act in promoting both the permeability of bacterial peroxisome membrane and carbon fixation in plants. Some enzymes participate in a balanced supply of dNTPs, successful DNA replication and mismatch repair during bacterial cell division. They also catalyze the release of signal peptides from bacterial membrane prolipoproteins. Phages with the most highly abundant antibiotic resistance genes (ARGs) transduce species of bacterial genera Pseudomonas, Streptomyces, and Mycobacterium. Abundant mechanisms of antibiotic resistance in the rhizosphere include "antibiotic efflux pump" for ARGs soxR, OleC, and MuxB, "antibiotic target alteration" for parY mutant, and "antibiotic inactivation" for arr-1.

Discussion

These ARGs can act synergistically to inhibit several antibiotics including tetracycline, penam, cephalosporin, rifamycins, aminocoumarin, and oleandomycin. The study highlighted the issue of horizontal transfer of ARGs to clinical isolates and human gut microbiome.

Halotolerant plant growth-promoting bacteria, Bacillus pumilus, modulates water status, chlorophyll fluorescence kinetics and antioxidant balance in salt and/or arsenic-exposed wheat

Seed priming is an effective and novel technique and the use of eco-friendly biological agents improves the physiological functioning in the vegetative stage of plants. This procedure ensures productivity and acquired stress resilience in plants against adverse conditions without contaminating the environment. Though the mechanisms of bio-priming-triggered alterations have been widely explained under induvial stress conditions, the interaction of combined stress conditions on the defense system and the functionality of photosynthetic apparatus in the vegetative stage after the inoculation to seeds has not been fully elucidated. After Bacillus pumilus inoculation to wheat seeds (Triticum aestivum), three-week-old plants were hydroponically exposed to the alone and combination of salt (100 mM NaCl) and 200 μM sodium arsenate (Na₂HAsO₄·7H₂O, As) for 72 h. Salinity and As pollutant resulted in a decline in growth, water content, gas exchange parameters, fluorescence kinetics and performance of photosystem II (PSII). On the other hand, the seed inoculation against stress provided the alleviation of relative growth rate (RGR), relative water content (RWC) and chlorophyll fluorescence. These negative impacts were reversed by B. pumilus inoculation. Since there was no effective antioxidant capacity, As and/or salinity caused induction of H₂O₂ accumulation and thiobarbituric acid reactive substances content (TBARS) in wheat leaves. The inoculated leaves had high activity of superoxide dismutase (SOD) under stress. B. pumilis decreased the NaCl-induced toxic H₂O₂ levels by increasing peroxidase (POX) and enzymes/non-enzymes related to ascorbate-glutathione (AsA-GSH) cycle. In the presence of As exposure, the inoculated plants exhibited an induction in CAT activity. On the other hand, for H₂O₂ scavenging, the improvement in the AsA-GSH cycle was observed in bacterium priming plants plus the combined stress treatment. Since B. pumilus inoculation reduced H₂O₂ levels against all stress treatments, lipid peroxidation subsequently decreased in wheat leaves. The findings obtained from our study explained that the seed inoculation with B. pumilus provided an activation in the defense system and protection in growth, water status, and gas exchange regulation in wheat leaves against the combination of salt and As.

Thermal protection function of camphor on Cinnamomum camphora cell membrane by acting as a signaling molecule

Isoprenoids serve important functions in protecting plant membranes against high temperature. Cinnamomum camphora is an excellent economic tree species, and releases plenty of monoterpenes. To uncover the protective mechanism of monoterpenes on the membrane system for promoting their development and utilization as anti-high temperature agents, the membrane permeability, cell ultrastructure, membrane lipid variations and related gene expression were investigated in C. camphora fumigated with camphor, one of the main monoterpenes in the plant, after fosmidomycin (Fos) blocking the monoterpene biosynthesis under high temperature (Fos+38 °C + C). High temperature at 38 °C caused the rupture of plasma as well as chloroplast and mitochondrion membranes, deformation of chloroplasts and mitochondria, and electrolyte leakage in C. camphora. High temperature with Fos treatment (Fos+38 °C) aggravated the damage, while camphor fumigation (Fos+38 °C + C) showed alleviating effects. High temperature at 38 °C disturbed the membrane lipid equilibrium by reducing the levels of 14 phosphatidylcholine, 8 phosphatidylglycerol and 6 phosphatidylethanolamine molecules, and increasing the levels of 8 phosphatidic acid, 4 diacylglycerol, 5 phosphatidylinositol, 16 sphingomyelin and 5 ceramide phosphoethanolamine molecules. Fos+38 °C treatment primarily exhibited intensifying effects on the disturbance, while these membrane lipid levels in Fos+38 °C + C5 (5 μM camphor) treatment exhibited variation tendencies to the control at 28 °C. This should result from the expression alterations of the genes related with phospholipid biosynthesis, fatty acid metabolism, and sphingolipid metabolism. It can be speculated that camphor can maintain membrane lipid stabilization in C. camphora under high temperature by acting as a signaling molecule.

Age effects of Moso bamboo on leaf isoprene emission characteristics

Isoprene is a highly reactive volatile organic compound that significantly affects atmospheric oxidant capacity, regional air quality, and climate change. Moso bamboo (Phyllostachys edulis), a species widely distributed in tropical and subtropical regions, particularly in China, is a strong isoprene emitter with great potential for carbon sequestration. Carbon sequestration is negatively correlated with culm age; however, the effect of this correlation on isoprene emissions remains unknown. In this study, we investigated the photosynthetic and isoprene emission characteristics of Moso bamboo at different culm ages. The results showed that the age effect on isoprene emission was different from that on photosynthesis; the net photosynthesis rate (Pn) was the highest in young, followed by mature, and then old bamboo, whereas the isoprene emission rate (Iso) was the highest in young, followed by old, and then mature bamboo. Moreover, the percentage of carbon loss as isoprene emission (C-loss) during photosynthesis of old bamboo was 35% higher than that of mature bamboo under standard conditions (leaf temperature: 30°C; light intensity: 1000 µmol m-2 s-1). Therefore, we strongly recommend considering the culm age when establishing an isoprene emission model of Moso bamboo. Additionally, because the Iso and C-loss of old bamboo were higher than those of mature bamboo, we suggest that attention should be paid to the management of bamboo age structure and timely felling of aged bamboo to reduce environmental risk.

The uppermost monoterpenes improving Cinnamomum camphora thermotolerance by serving signaling functions

Terpenes serve important functions in enhancing plant thermotolerance. Cinnamomum camphora mainly has eucalyptol (EuL), camphor (CmR), linalool (LnL) and borneol (BeL) chemotypes basing on the uppermost monoterpenes. To reveal the thermotolerance mechanisms of these uppermost monoterpenes (eucalyptol, camphor, linalool, and borneol) in C. camphora, we surveyed the ROS metabolism and photosynthesis in the 4 chemotypes fumigated with the corresponding uppermost monoterpene after fosmidomycin (Fos) inhibiting monoterpene synthesis under high temperature at 38°C (Fos+38°C+monoterpene), and investigated the related gene expression in EuL and CmR. Meanwhile, the thermotolerance differences among the 4 uppermost monoterpenes were analyzed. In contrast to normal temperature (28°C), ROS levels and antioxidant enzyme activities in the 4 chemotypes increased under 38°C, and further increased in the treatment with Fos inhibiting monoterpene synthesis at 38°C (Fos+38°C), which may be caused by the alterations in expression of the genes related with non-enzymatic and enzymatic antioxidant formation according to the analyses in EuL and CmR. Compared with Fos+38°C treatment, Fos+38°C+monoterpene treatments lowered ROS levels and antioxidant enzyme activities for the increased non-enzymatic antioxidant gene expression and decreased enzymatic antioxidant gene expression, respectively. High temperature at 38°C reduced the chlorophyll and carotenoid content as well as photosynthetic abilities, which may result from the declined expression of the genes associated with photosynthetic pigment biosynthesis, light reaction, and carbon fixation. Fos+38°C treatment aggravated the reduction. In contrast to Fos+38°C treatment, Fos+38°C+monoterpene treatments increased photosynthetic pigment content and improved photosynthetic abilities by up-regulating related gene expression. Among the 4 uppermost monoterpenes, camphor showed strong abilities in lowering ROS and maintaining photosynthesis, while eucalyptol showed weak abilities. This was consistent with the recovery effects of the gene expression in the treatments with camphor and eucalyptol fumigation. Therefore, the uppermost monoterpenes can enhance C. camphora thermotolerance as signaling molecules, and may have differences in the signaling functions.

Rapid Sampling Protocol of Isoprene Emission Rate of Palm (Arecaceae) Species Using Excised Leaves

The high isoprene emission capacity of palm species can decrease regional air quality and enhance the greenhouse effect when land is converted to palm plantations. Propagation of low-emitting individuals can be a strategy for reducing isoprene emission from palms. However, the identification of low-emitting individuals requires large-scale sampling. Thus, we aimed to develop a rapid method in which the isoprene emission rate of leaf segments is observed. We examined the temperature response and effect of incubation length on the isoprene emission rate of palm leaf and found that leaf temperatures at 25 to 30 °C and an incubation length of 40 min are suitable parameters. To further examine the validity of the method, we applied both the enclosure method and this method to the same sections of leaves. High coefficient of determinations (0.993 and 0.982) between the results of the two methods were detected regardless of seasonal temperature. This result proves that the method is capable of measuring the isoprene emission rate under any growth conditions if the incubation temperature is controlled. By using a water bath tank and a tested light source, we can simply implement a unified environmental control of multiple samples at once, which achieves a higher time efficiency than conventional enclosure measurements.

Handling the heat - photosynthetic thermal stress in tropical trees

Warming climate increases the risk for harmful leaf temperatures in terrestrial plants, causing heat stress and loss of productivity. The heat sensitivity may be particularly high in equatorial tropical tree species adapted to a thermally stable climate. Thermal thresholds of the photosynthetic system of sun-exposed leaves were investigated in three tropical montane tree species native to Rwanda with different growth and water use strategies (Harungana montana, Syzygium guineense and Entandrophragma exselsum). Measurements of chlorophyll fluorescence, leaf gas exchange, morphology, chemistry and temperature were made at three common gardens along an elevation/temperature gradient. Heat tolerance acclimated to maximum leaf temperature (T_leaf ) across the species. At the warmest sites, the thermal threshold for normal function of photosystem II was exceeded in the species with the highest T_leaf despite their higher heat tolerance. This was not the case in the species with the highest transpiration rates and lowest T_leaf . The results point to two differently effective strategies for managing thermal stress: tolerance through physiological adjustment of leaf osmolality and thylakoid membrane lipid composition, or avoidance through morphological adaptation and transpiratory cooling. More severe photosynthetic heat stress in low-transpiring montane climax species may result in a competitive disadvantage compared to high-transpiring pioneer species with more efficient leaf cooling.

Review on plant terpenoid emissions worldwide and in China

Biogenic volatile organic compounds (BVOCs), particularly terpenoids, can significantly drive the formation of ozone (O₃) and secondary organic aerosols (SOA) in the atmosphere, as well as directly or indirectly affect global climate change. Understanding their emission mechanisms and the current progress in emission measurements and estimations are essential for the accurate determination of emission characteristics, as well as for evaluating their roles in atmospheric chemistry and climate change. This review summarizes the mechanisms of terpenoid synthesis and release, biotic and abiotic factors affecting their emissions, development of emission observation techniques, and emission estimations from hundreds of published papers. We provide a review of the main observations and estimations in China, which contributes a significant proportion to the total global BVOC emissions. The review suggests the need for further research on the comprehensive effects of environmental factors on terpenoid emissions, especially soil moisture and nitrogen content, which should be quantified in emission models to improve the accuracy of estimation. In China, it is necessary to conduct more accurate measurements for local plants in different regions using the dynamic enclosure technique to establish an accurate local emission rate database for dominant tree species. This will help improve the accuracy of both national and global emission inventories. This review provides a comprehensive understanding of terpenoid emissions as well as prospects for detailed research to accurately describe terpenoid emission characteristics worldwide and in China.

Are Methanol-Derived Foliar Methyl Acetate Emissions a Tracer of Acetate-Mediated Drought Survival in Plants?

Upregulation of acetate fermentation in plants has recently been described as an evolutionarily conserved drought survival strategy, with the amount of acetate produced directly correlating to survival. However, destructive measurements are required to evaluate acetate-linked drought responses, limiting the temporal and spatial scales that can be studied. Here, 13C-labeling studies with poplar (Populus trichocarpa) branches confirmed that methyl acetate is produced in plants from the acetate-linked acetylation of methanol. Methyl acetate emissions from detached leaves were strongly stimulated during desiccation, with total emissions decreasing with the leaf developmental stage. In addition, diurnal methyl acetate emissions from whole physiologically active poplar branches increased as a function of temperature, and light-dark transitions resulted in significant emission bursts lasting several hours. During experimental drought treatments of potted poplar saplings, light-dark methyl acetate emission bursts were eliminated while strong enhancements in methyl acetate emissions lasting > 6 days were observed with their initiation coinciding with the suppression of transpiration and photosynthesis. The results suggest that methyl acetate emissions represent a novel non-invasive tracer of acetate-mediated temperature and drought survival response in plants. The findings may have important implications for the future understanding of acetate-mediated drought responses to transcription, cellular metabolism, and hormone signaling, as well as its associated changes in carbon cycling and water use from individual plants to whole ecosystems.