Net O2 exchange rates under dark and light conditions across different stem compartments.

Woody plants display some photosynthetic activity in stems, but the biological role of stem photosynthesis and the specific contributions of bark and wood to carbon uptake and oxygen evolution remain poorly understood. We aimed to elucidate the functional characteristics of chloroplasts in stems of different ages in Fraxinus ornus. Our investigation employed diverse experimental approaches, including microsensor technology to assess oxygen production rates in whole stem, bark, and wood separately. Additionally, we utilized fluorescence lifetime imaging microscopy (FLIM) to characterize the relative abundance of photosystems I and II (PSI : PSII chlorophyll ratio) in bark and wood. Our findings revealed light-induced increases in O2 production in whole stem, bark, and wood. We present the radial profile of O2 production in F. ornus stems, demonstrating the capability of stem chloroplasts to perform light-dependent electron transport. Younger stems exhibited higher light-induced O2 production and dark respiration rates than older ones. While bark emerged as the primary contributor to net O2 production under light conditions, our data underscored that wood chloroplasts are also photosynthetically active. The FLIM analysis unveiled a lower PSI abundance in wood than in bark, suggesting stem chloroplasts are not only active but also acclimate to the spectral composition of light reaching inner compartments.

The effects of solar radiation on daily and seasonal stem increment of canopy trees in European temperate old-growth forests.

It is well established that solar irradiance greatly influences tree metabolism and growth through photosynthesis, but its effects acting through individual climate metrics have not yet been well quantified. Understanding these effects is crucial for assessing the impacts of climate change on forest ecosystems. To describe the effects of solar irradiance on tree growth, we installed 110 automatic dendrometers in two old-growth mountain forest reserves in Central Europe, performed detailed terrestrial and aerial laser scanning to obtain precise tree profiles, and used these to simulate the sum of solar irradiance received by each tree on a daily basis. Generalized linear mixed-effect models were applied to simulate the probability of growth and the growth intensity over seven growing seasons. Our results demonstrated various contrasting effects of solar irradiance on the growth of canopy trees. On the one hand, the highest daily growth rates corresponded with the highest solar irradiance potentials (i.e. the longest photoperiod). Intense solar irradiance significantly decreased tree growth, through an increase in the vapor pressure deficit. These effects were consistent for all species but had different magnitude. Tree growth is the most effective on long rainy/cloudy days with low solar irradiance.

Elevated aerosol enhances plant water-use efficiency by increasing carbon uptake while reducing water loss.

Aerosols could significantly influence ecosystem carbon and water fluxes, potentially altering their interconnected dynamics, typically characterized by water-use efficiency (WUE). However, our understanding of the underlying ecophysiological mechanisms remains limited due to insufficient field observations. We conducted 4-yr measurements of leaf photosynthesis and transpiration, as well as 3-yr measurements of stem growth (SG) and sap flow of poplar trees exposed to natural aerosol fluctuation, to elucidate aerosol's impact on plant WUE. We found that aerosol improved sun leaf WUE mainly because a sharp decline in photosynthetically active radiation (PAR) inhibited its transpiration, while photosynthesis was less affected, as the negative effect induced by declined PAR was offset by the positive effect induced by low leaf vapor pressure deficit (VPDleaf). Conversely, diffuse radiation fertilization (DRF) effect stimulated shade leaf photosynthesis with minimal impact on transpiration, leading to an improved WUE. The responses were further verified by a strong DRF on SG and a decrease in sap flow due to the suppresses in total radiation and VPD. Our field observations indicate that, contrary to the commonly assumed coupling response, carbon uptake and water use exhibited dissimilar reactions to aerosol pollution, ultimately enhancing WUE at the leaf and canopy level.

Blue light regulated lignin and cellulose content of soybean petioles and stems under low light intensity.

To improve light harvest and plant structural support under low light intensity, it is useful to investigate the effects of different ratios of blue light on petiole and stem growth. Two true leaves of soybean seedlings were exposed to a total light intensity of 200µmolm-2 s-1 , presented as either white light or three levels of blue light (40µmolm-2 s-1 , 67µmolm-2 s-1 and 100µmolm-2 s-1 ) for 15days. Soybean petioles under the low blue light treatment upregulated expression of genes relating to lignin metabolism, enhancing lignin content compared with the white light treatment. The low blue light treatment had high petiole length, increased plant height and improved petiole strength arising from high lignin content, thus significantly increasing leaf dry weight relative to the white light treatment. Compared with white light, the treatment with the highest blue light ratio reduced plant height and enhanced plant support through increased cellulose and hemicellulose content in the stem. Under low light intensity, 20% blue light enhanced petiole length and strength to improve photosynthate biomass; whereas 50% blue light lowered plants' centre of gravity, preventing lodging and conserving carbohydrate allocation.

Identification of genes associated with biosynthesis of bioactive flavonoids and taxoids in Taxus cuspidata Sieb. et Zucc. plantlets exposed to UV-B radiation.

UV-B radiation is a typical environmental stressor that can promote phytochemical accumulation in plants. Taxus species are highly appreciated due to the existence of bioactive taxoids (especially paclitaxel) and flavonoids. However, the effect of UV-B radiation on taxoid and flavonoid biosynthesis in Taxus cuspidata Sieb. et Zucc. is largely unknown. In the present work, the accumulation of taxoids and flavonoids in T. cuspidata plantlets was significantly induced by 12 and 24 h of UV-B radiation (3 W/m2), and a large number of significantly differentially expressed genes were obtained via transcriptomic analysis. The significant up-regulation of antioxidant enzyme- and flavonoid biosynthesis-related genes (phenylalanine ammonia lyase 1, chalcone synthase 2, flavonol synthase 1, and flavonoid 3', 5'-hydroxylase 2), suggested that UV-B might cause the oxidative stress thus promoting flavonoid accumulation in T. cuspidata. Moreover, the expression of some genes related to jasmonate metabolism and taxoid biosynthesis (taxadiene synthase, baccatin III-3-amino 3-phenylpropanoyltransferase 1, taxadiene-5α-hydroxylase, and ethylene response factors 15) was significantly activated, which indicated that UV-B might initiate jasmonate signaling pathway that contributed to taxoid enhancement in T. cuspidata. Additionally, the identification of some up-regulated genes involved in lignin biosynthesis pathway indicated that the lignification process in T. cuspidata might be stimulated for defense against UV-B radiation. Overall, our findings provided a better understanding of some potential key genes associated with flavonoid and taxoid biosynthesis in T. cuspidata exposed to UV-B radiation.

Effects of solar radiation on photosynthetic physiology of barren stalk differentiation in maize.

Barren stalks and kernel abortion are the major obstacles that hinder maize production. After many years of inbreeding, our group produced a pair of barren stalk/non-barren stalk near-isogenic lines SN98A/SN98B. Under weak light stress, the barren stalk rate is up to 98 % in SN98A but zero in SN98B. Therefore, we consider that SN98A is a weak light-sensitive inbred line whereas SN98B is insensitive. In the present study, the near-isogenic lines SN98A/SN98B were used as test materials to conduct cytological and photosynthetic physiological analyses of the physiological mechanism associated with the differences in maize barren stalk induced by weak light stress. The results showed that weak light stress increased the accumulation of reactive oxygen species (ROS), decreased the function of chloroplasts, destroyed the normal rosette structure, inhibited photosynthetic electron transport, and enhanced lipid peroxidation. The actual photochemical quantum efficiency for PSI (Y(I)) and PSII (Y(II)), relative electron transfer rate for PSI (ETR(I)) and PSII (ETR(II)), and the P700 activities decreased significantly in the leaves of SN98A and SN98B under weak light stress, where the decreases were greater in SN98A than SN98B. After 10 days of shading treatment, the O2·- production rate, H2O2 contents, the yield of regulated energy dissipation (Y(NPQ)), the donor side restriction for PSI (Y(ND)) and the quantum efficiency of cyclic electron flow photochemistry were always higher in SN98A than SN98B, and the antioxidant enzyme activities were always lower in SN98A than those in SN98B. These results show that SN98B has a stronger ability to remove ROS at its source, and maintain the integrity of the structure and function of the photosynthetic system. This self-protection mechanism is an important physiological reason for its adaptation to weak light.

Photons from NIR LEDs can delay flowering in short-day soybean and Cannabis: Implications for phytochrome activity.

Photons during the dark period delay flowering in short-day plants (SDP). Red photons applied at night convert phytochromes to the active far-red absorbing form (Pfr), leading to inhibition of flowering. Far-red photons (greater than 700 nm) re-induce flowering when applied after a pulse of red photons during the dark period. However, far-red photons at sufficiently high intensity and duration delay flowering in sensitive species. Mechanistically, this response occurs because phytochrome-red (Pr) absorbance is not zero beyond 700 nm. We applied nighttime photons from near infrared (NIR) LEDs (peak 850 nm) over a 12 h dark period. Flowering was delayed in Glycine max and Cannabis sativa (two photosensitive species) by 3 and 12 days, respectively, as the flux of photons from NIR LEDs was increased up to 83 and 116 µmol m-2 s-1. This suggests that long wavelength photons from NIR LEDs can activate phytochromes (convert Pr to Pfr) and thus alter plant development.

Allium sativum L. (Garlic) bulb enlargement as influenced by differential combinations of photoperiod and temperature.

Photoperiod and temperature are vital environmental factors that regulate plant developmental processes. However, the roles of these factors in garlic bulb enlargement are unclear. In this report, responses of garlic bulb morphology and physiology to combinations of photoperiod (light/dark: 10/14 h, 12/12 h, 14/10 h) and temperature (light/dark: 25/18 °C, 30/20 °C) were investigated. For garlic cultivar G103, bulb characteristics, phytohormones (IAA, ABA, ZT, tZR, JA), allicin and phenolic acids (p-coumaric and p-hydroxybenzoic) were highest under a photoperiod of 14 h at 30 °C. Maximum GA was observed under 14 h + 30 °C for cv. G2011-5. Maximum caffeic, ferulic and vanillic acids were detected for cv. G2011-5 at 14 h + 30 °C, 12 h + 25 °C and 14 h + 25 °C, respectively. Flavonoids (myricetin, quercetin, kaempferol and apigenin) were not detected in this trial. This is the first report describing the impact of long periods of light duration and higher temperatures on garlic morphology, phytohormones, phenolic acids and allicin content.

GmCRY1s modulate gibberellin metabolism to regulate soybean shade avoidance in response to reduced blue light.

Soybean is an important legume crop that displays the classic shade avoidance syndrome (SAS), including exaggerated stem elongation, which leads to lodging and yield reduction under density farming conditions. Here, we compared the effects of two shade signals, low red light to far-red light ratio (R:FR) and low blue light (LBL), on soybean status and revealed that LBL predominantly induces excessive stem elongation. We used CRISPR-Cas9-engineered Gmcry mutants to investigate the functions of seven cryptochromes (GmCRYs) in soybean and found that the four GmCRY1s overlap in mediating LBL-induced SAS. Light-activated GmCRY1s increase the abundance of the bZIP transcription factors STF1 and STF2, which directly upregulate the expression of genes encoding GA2 oxidases to deactivate GA1 and repress stem elongation. Notably, GmCRY1b overexpression lines displayed multiple agronomic advantages over the wild-type control under both dense planting and intercropping conditions. Our study demonstrates the integration of GmCRY1-mediated signals with the GA metabolic pathway in the regulation of LBL-induced SAS in soybean. It also provides a promising option for breeding lodging-resistant, high-yield soybean cultivars in the future.

Molecular pathways regulating elongation of aerial plant organs: a focus on light, the circadian clock, and temperature.

Organs such as hypocotyls and petioles rapidly elongate in response to shade and temperature cues, contributing to adaptive responses that improve plant fitness. Growth plasticity in these organs is achieved through a complex network of molecular signals. Besides conveying information from the environment, this signaling network also transduces internal signals, such as those associated with the circadian clock. A number of studies performed in Arabidopsis hypocotyls, and to a lesser degree in petioles, have been informative for understanding the signaling networks that regulate elongation of aerial plant organs. In particular, substantial progress has been made towards understanding the molecular mechanisms that regulate responses to light, the circadian clock, and temperature. Signals derived from these three stimuli converge on the BAP module, a set of three different types of transcription factors that interdependently promote gene transcription and growth. Additional key positive regulators of growth that are also affected by environmental cues include the CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) and SUPPRESSOR OF PHYA-105 (SPA) E3 ubiquitin ligase proteins. In this review we summarize the key signaling pathways that regulate the growth of hypocotyls and petioles, focusing specifically on molecular mechanisms important for transducing signals derived from light, the circadian clock, and temperature. While it is clear that similarities abound between the signaling networks at play in these two organs, there are also important differences between the mechanisms regulating growth in hypocotyls and petioles.

Effects of tri-frequency ultrasound-ethanol pretreatment combined with infrared convection drying on the quality properties and drying characteristics of scallion stalk.

BACKGROUND: Having short drying time and attractive product quality are important in fruit and vegetable dehydration processing. In this work, tri-frequency (20, 40 and 60 kHz) ultrasound-ethanol pretreatment, ultrasound-water pretreatment and ethanol pretreatment were employed before infrared convection drying (ICD) of scallion stalks, which was aimed at improving the drying process and quality of the end products. The mass transfer, drying characteristics (moisture ratio and drying rate and quality properties of scallion (rehydration, color, flavor, optical microscope image, moisture distribution and microbiological quality) were analyzed. RESULTS: All pretreatments have decreased the drying time by 33.34-83.34% compared to the control, while ultrasound-ethanol pretreatment provided the highest time reduction (83.34%). The reason is that the volatility of ethanol have replaced air in the tissue, which produced a better osmotic dehydration effect and the cavitation effect of ultrasound changed the cell function of the material, so that the food tissue was rapidly compressed and expanded, resulting in damage to the cell structure. Ultrasonic-ethanol pretreatment has greatly reduced the water loss and dry matter of fresh scallion, improved the rehydration effect of dried scallion, better retained the color and flavor of scallion and effectively reduced the microbiological quality of the scallion. CONCLUSION: The tri-frequency ultrasound-ethanol pretreatment has effectively improved the drying process and quality characteristics of the dried scallion. Therefore, this research has a great contribution to the drying technology, as evident in the remarkable reduction in drying time and the improvement in the quality of the end product. © 2020 Society of Chemical Industry.

Low-light and its effects on crop yield: Genetic and genomic implications.

Shade indicates decreased sunlight. The agricultural importance of shade imparts to its deteriorative effect of crop yield. Rice is not only the most widely used food crop by a third of the population of the world, but it has also been established as the modelmonocot plant for study. This article describes several important aspects of shade on rice yield with appropriate examples in other plants such as Arabidopsis. To start with, how different environmental or growth conditions create shade is explained. Themorphological, physiological and biochemical characteristics due to different kinds of shade are selectively explained. The molecular characteristics of rice under shade from genetic, genomic and epigenetic studied are discussed. Signalling components for the manifestation of shade tolerance responses and their interconnection with other signalling networks and hormone pathway components are from recent reports. A list of genes, micro-RNAs and metabolites that are involved in shade responses is presented. Lastly, implications for sustainable yield under shade is discussed. This review will be useful not only for cutting-edge information on shade tolerance but will also build framework for upcoming new rice varieties with sustainable yield under shade.

UV radiation increases phenolic compound protection but decreases reproduction in Silene littorea.

Plants respond to changes in ultraviolet (UV) radiation both morphologically and physiologically. Among the variety of plant UV-responses, the synthesis of UV-absorbing flavonoids constitutes an effective non-enzymatic mechanism to mitigate photoinhibitory and photooxidative damage caused by UV stress, either reducing the penetration of incident UV radiation or acting as quenchers of reactive oxygen species (ROS). In this study, we designed a UV-exclusion experiment to investigate the effects of UV radiation in Silene littorea. We spectrophotometrically quantified concentrations of both anthocyanins and UV-absorbing phenolic compounds in petals, calyces, leaves and stems. Furthermore, we analyzed the UV effect on the photosynthetic activity in hours of maximum solar radiation and we tested the impact of UV radiation on male and female reproductive performance. We found that anthocyanin concentrations showed a significant decrease of about 20% with UV-exclusion in petals and stems, and a 30% decrease in calyces. The concentrations of UV-absorbing compounds under UV-exclusion decreased by approximately 25% in calyces and stems, and 12% in leaves. Photochemical efficiency of plants grown under UV decreased at maximum light stress, reaching an inhibition of 58% of photosynthetic activity, but their ability to recover after light-stress was not affected. In addition, exposure to UV radiation did not affect ovule production or seed set per flower, but decreased pollen production and total seed production per plant by 31% and 69%, respectively. Our results demonstrate that UV exposure produced opposing effects on the accumulation of plant phenolic compounds and reproduction. UV radiation increased the concentration of phenolic compounds, suggesting a photoprotective role of plant phenolics against UV light, yet overall reproduction was compromised.

Differential UVR8 Signal across the Stem Controls UV-B-Induced Inflorescence Phototropism.

In the course of evolution, plants have developed mechanisms that orient their organs toward the incoming light. At the seedling stage, positive phototropism is mainly regulated by phototropin photoreceptors in blue and UV wavelengths. Contrasting with this, we report that UV RESISTANCE LOCUS8 (UVR8) serves as the predominant photoreceptor of UV-B-induced phototropic responses in Arabidopsis (Arabidopsis thaliana) inflorescence stems. We examined the molecular mechanisms underlying this response and our findings support the Blaauw theory (Blaauw, 1919), suggesting rapid differential growth through unilateral photomorphogenic growth inhibition. UVR8-dependent UV-B light perception occurs mainly in the epidermis and cortex, but deeper tissues such as endodermis can also contribute. Within stems, a spatial difference of UVR8 signal causes a transcript and protein increase of transcription factors ELONGATED HYPOCOTYL5 (HY5) and its homolog HY5 HOMOLOG at the UV-B-exposed side. The irradiated side shows (1) strong activation of flavonoid synthesis genes and flavonoid accumulation; (2) increased gibberellin (GA)2-oxidase expression, diminished GA1 levels, and accumulation of the DELLA protein REPRESSOR OF GA1; and (3) increased expression of the auxin transport regulator PINOID, contributing to diminished auxin signaling. Together, the data suggest a mechanism of phototropin-independent inflorescence phototropism through multiple, locally UVR8-regulated hormone pathways.

Pyrolysis, morphology and microwave absorption properties of tobacco stem materials.

The recent development of microwave radiation technology has increased the application possibilities of waste tobacco stems (WTSs). In this study, the morphology and microwave absorption properties of tobacco stem materials as well as the pyrolysis of the resultant biomass (BMTS) were studied via thermogravimetry-differential scanning calorimetry (TG-DSC), scanning electron microscopy (SEM), mercury intrusion porosimetry (MIP), and a vector network analysis (VNA). The results show that the BMTS pyrolysis involves four stages in air: dehydration, heat transfer, pyrolysis, and carbonisation, and it involves three stages in N2: moisture evaporation, de-volatilization, and charring. The microwave-assisted expansion of WTSs can improve the pore diameter and total porosity of the expanded tobacco stems (ETSs) and BMTS. The latter is a macroporous material with a total porosity of 78.2% and a probable pore size of 29.5 µm. Its pore size distribution ranges from 10.7 nm to 227 µm. The microwave absorption properties of the WTSs are affected by the moisture content, bulk density, and grain size; the properties can be enhanced by decreasing the grain size and increasing the moisture content and bulk density within the experimental range. The 3 dB bandwidth and amplitude vary by 0.45 MHz and - 0.406 dB per 1% increase in the moisture content of the materials, respectively. Our results demonstrate that tobacco stem materials with different moisture contents and grain sizes should be classified before the expansion or re-drying steps to ensure heating uniformity and product quality during the microwave radiation treatment.

Influence of enhanced ultraviolet-B radiation during rice plant growth on rice straw decomposition with nitrogen deposition.

Although straw decomposition is important for ecosystem fertility and carbon balance, influence of ultraviolet-B (UV-B) radiation and nitrogen (N) deposition on this process is unclear. In this study, UV-B-exposed rice straw was decomposed under different N addition treatments for 15 months to investigate the indirect effects of UV-B radiation on straw chemistry and direct effects of N deposition on decomposition. UV-B exposure during rice plant growth changed the rice straw chemical composition, increasing the concentrations of acid-insoluble fraction (AIF), acid-soluble fraction, and UV-B-absorbing compounds. High N content had a negative effect on decomposition of rice straw exposed to enhanced and ambient UV-B radiation. Both AIF concentration and FTIR peak intensities indicated that lignin in rice straw was selectively preserved following N addition and UV-B radiation, reducing straw decomposition rate, which corresponded to lower activities of lignin-degrading enzymes in the later stage of decomposition. Thus, enhanced UV-B radiation during rice plant growth produced more recalcitrant substrates (lignin) and N reacted with lignin to produce more resistant compounds, further decreasing straw decomposition rate. UV-B radiation during plant growth and N deposition inhibit litter decomposition in agroecosystem, and their effects should be considered when establishing biogeochemical models in response to global changes.

Whole-plant reddening in Silene germana is due to anthocyanin accumulation in response to visible light.

The phenology of anthocyanin accumulation in leaves has been widely studied in perennial plants; several hypotheses have been proposed to explain their adaptive significance. Here, we explored the photoprotection hypothesis in Silene germana, a Mediterranean annual plant with late-spring/summer flowering. We analysed the temporal patterns of anthocyanin accumulation in photosynthetic calyces, leaves and stems and throughout the reproductive season, and their relationship with flower abortion, florivory and plant mortality due to drought. In addition, the flavonoid production and the photoinhibitory response were measured in a shading experiment. The whole plant becomes red at the end of the flowering and remains red until fruiting and senescence. Calyces were redder on the side with more sun exposition. Aborted flowers showed redder calyces than those of fruiting flowers. No effect of plant redness on florivory or plant mortality was found. The shading experiment showed a positive relationship between anthocyanin accumulation and intensity of solar radiation, but plants growing in absence of UV showed similar redness than full sunlight plants. Plants growing in natural shade lack anthocyanins but produced the same amount of non-anthocyanin flavonoids. Anthocyanic and non-anthocyanic plants showed similar photochemical efficiency (Fv /Fm ) after sun exposition, but in early morning, the former showed lower Fv /Fm values. Plants growing in full sunlight produced more fruits than those of natural shade plants. Whole-plant reddening during fruiting and senescence appears to be a property of S. germana. Our results suggest that anthocyanin accumulation depends on sunlight intensity, but non-anthocyanin flavonoids are produced constitutively.

Accelerated diversification and functional trait evolution in Velloziaceae reveal new insights into the origins of the campos rupestres' exceptional floristic richness.

Background and Aims: The greater diversity of plant clades in the Neotropics compared to their relatives in Africa is a pervasive pattern in biogeography. To better understand the causes of this imbalance, we studied the diversification dynamics of the monocot family Velloziaceae. In addition to being conspicuously richer in the Neotropics compared to the Palaeotropics, many species of Velloziaceae exhibit extreme desiccation tolerance (i.e. 'resurrection' behaviour), and other ecological specializations to life on rocky outcrops, poor sandy soils, open vegetation and seasonally dry climates. Velloziaceae is also ecologically dominant in the campos rupestres, a habitat having exceptionally high plant diversity and endemism in Brazil. Methods: We reconstructed a densely sampled time-calibrated molecular phylogeny and used state-dependent and state-independent models to estimate rates of lineage diversification in relation to continent-scale geographical occurrence and functional traits associated with desiccation tolerance and water storage capacity. Key Results: Independent shifts to faster diversification occurred within two Neotropical lineages, Vellozia and Barbacenia. The Vellozia radiation was associated with the presence of conspicuous aerial stems, and was followed by decreasing diversification rates during the Oligocene, a time of rising global temperatures and expanding open areas around the world. The Barbacenia radiation was faster and more recent, occurring during the cooling conditions of the Miocene, and associated with the acquisition of aquiferous parenchyma on the leaves. Conclusions: High species richness of Velloziaceae in South America has been driven by faster diversification in lineages predominantly occurring in the campos rupestres, putatively by the evolution of adaptive strategies in response to independent climatic events. The radiation of Vellozia in particular might have played a key role in the assembly of the campos rupestres vegetation.

More than just CO2 -recycling: corticular photosynthesis as a mechanism to reduce the risk of an energy crisis induced by low oxygen.

Reassimilation of internal CO2 via corticular photosynthesis (PScort ) has an important effect on the carbon economy of trees. However, little is known about its role as a source of O2 supply to the stem parenchyma and its implications in consumption and movement of O2 within trees. PScort of young Populus nigra (black poplar) trees was investigated by combining optical micro-optode measurements with monitoring of stem chlorophyll fluorescence. During times of zero sap flow in spring, stem oxygen concentrations (cO2 ) exhibited large temporal changes. In the sapwood, over 80% of diurnal changes in cO2 could be explained by respiration rates (Rd(mod) ). In the cortex, photosynthetic oxygen release during the day altered this relationship. With daytime illumination, oxygen levels in the cortex steadily increased from subambient and even exhibited a diel period of superoxia of up to 110% (% air sat.). By contrast, in the sapwood, cO2 never reached ambient levels; the diurnal oxygen deficit was up to 25% of air saturation. Our results confirm that PScort is not only a CO2 -recycling mechanism, it is also a mechanism to actively raise the cortical O2 concentration and counteract temporal/spatial hypoxia inside plant stems.

Separate and Combined Response to UV-B Radiation and Jasmonic Acid on Photosynthesis and Growth Characteristics of Scutellaria baicalensis.

The negative effects of enhanced ultraviolet-B (UV-B) on plant growth and development have been reported with many species. Considering the ability of jasmonic acid (JA) to improve plant stress tolerance, the hypothesis that JA pretreatment could alleviate the adverse effects of UV-B on S. baicalensis was tested in this study with photosynthesis and growth characteristics. The results showed that UV-B or JA alone both induced photosynthesis inhibition and decreased biomass in stems and leaves. However, the photosynthetic reduction caused by increased UV-B was mainly related to the effect of nonstomatal-limitation, while that of JA was a stomatal-limitation effect. JA pretreatment prior to UV-B could remit the photosynthetic inhibition via the recovery of chlorophyll content, stomatal conductance; and intercellular CO2 concentration (especially the maximum electron transport rate increase). Furthermore, the coaction of JA and enhanced UV-B alleviated some disadvantageous effects on the leaf and did not aggravate the growth damage induced by their separate actions.