Exogenously applied nitrate improves the photosynthetic performance and nitrogen metabolism in tomato (<Emphasis Type="Italic">Solanum</Emphasis><Emphasis Type="Italic">lycopersicum</Emphasis> L. cv Pusa Rohini) under arsenic (V) toxicity

Tomato (Solanum lycopersicum L.) being a widespread and most commonly consumed vegetable all over the world has an important economic value for its producers and related food industries. It is a serious matter of concern as its production is affected by arsenic present in soil. So, the present study, investigated the toxicity of As(V) on photosynthetic performance along with nitrogen metabolism and its alleviation by exogenous application of nitrate. Plants were grown under natural conditions using soil spiked with 25 mg and 20 mM, As(V) and nitrate, respectively. Our results revealed that plant growth indices, photosynthetic pigments, and other major photosynthetic parameters like net photosynthetic rate and maximum quantum efficiency (F _v /F _m ) of photosystem II (PSII) were significantly (P ≤ 0.05) reduced under As(V) stress. However, nitrate application significantly (P ≤ 0.05) alleviated As(V) toxicity by improving the aforesaid plant responses and also restored the abnormal shape of guard cells. Nitrogen metabolism was assessed by studying the key nitrogen-metabolic enzymes. Exogenous nitrate revamped nitrogen metabolism through a major impact on activities of NR, NiR, GS and GOGAT enzymes and also enhanced the total nitrogen and NO content while malondialdehyde content, and membrane electrolytic leakage were remarkably reduced. Our study suggested that exogenous nitrate application could be considered as a cost effective approach in ameliorating As(V) toxicity.     

Effects of exogenous nitric oxide on the photosynthetic characteristics of bamboo (<Emphasis Type="Italic">Indocalamus barbatus</Emphasis> McClure) seedlings under acid rain stress

The effects of the exogenous application of nitric oxide (NO, in the form of sodium nitroprusside, SNP) on the diurnal variation in photosynthesis, chlorophyll content, chlorophyll fluorescence, light response curve and the net assimilation of CO₂ against intercellular CO₂ concentration (A-Ci) curve parameters were investigated in the leaves of bamboo (Indocalamus barbatus McClure) exposed to simulated acid rain (SAR, pH 3.0) stress. According to the results of the diurnal variation in photosynthesis, foliar applications of 100–400 mg/L SNP effectively inhibited the decrease in net photosynthetic rate (Pn) as a result of non-stomatal factors, and mitigated midday depression under acid rain stress. The mitigating effect was most pronounced at 400 mg/L SNP. However, at higher concentrations of SNP (700 and 1000 mg/L), the mitigating effect became weak and even counterproductive. The results of the chlorophyll content, light response and A-Ci curve parameters suggested that the regulating role of NO against acid rain in the photosynthetic processes occurs through improving not only the efficiency of the light-harvesting and the activity of photosynthetic apparatus, but also the absorption of CO₂ and the availability of CO₂ for photosynthesis. The results of the chlorophyll fluorescence investigation further indicated that NO protected PSII activity from the damage of acid rain toxicity by enhancing the electron transport activity and photochemical efficiency, especially concerning the increase in the proportion of PSII open reaction centers. Furthermore, NO induced an increase in photorespiration (Rp), rather than an increase in non-photochemical quenching (NPQ), to dissipate the excessive excitation energy, which provided some protection to the photosynthetic apparatus under acid rain stress.     

Comparison of Killing Activity of Micafungin Against Six <Emphasis Type="Italic">Candida</Emphasis> Species Isolated from Peritoneal and Pleural Cavities in RPMI-1640, 10 and 30% Serum

Currently echinocandins are recommended in Candida peritonitis and pleuritis. We determined micafungin killing rates (k values) at therapeutic concentrations (0.25–2 mg/L) in RPMI-1640 with and without 10 and 30% serum mimicking in vivo conditions against six Candida species isolated from peritoneal and pleural fluid. In RPMI-1640, micafungin was fungicidal against C. glabrata, C. krusei and C. kefyr within 2.27?±?10.68, 2.69?±?10.29 and 3.10?±?4.41 h, respectively, while was fungistatic against C. albicans, C. tropicalis and C. parapsilosis. In 10% serum, ≥?0.25, ≥?0.5, ≥?0.5 and ≥?1 mg/L micafungin produced positive k values (killing) for all C. albicans, C. glabrata, C. kefyr and C. krusei, respectively. In 30% serum, 2 mg/L micafungin produced killing against all C. albicans, C. glabrata and C. kefyr isolates, but was ineffective against C. krusei, C. parapsilosis and 2 of 3 C. tropicalis. Micafungin exposure should be increased against non-albicans species to eradicate fungi from peritoneal and pleural cavities.     

Low concentrations of glycine inhibit photorespiration and enhance the net rate of photosynthesis in <Emphasis Type="Italic">Caragana korshinskii</Emphasis>

The inhibition of photorespiration can be used to improve plant carbon fixation. In order to compare the effects of three photorespiration inhibitors [glycine, NaHSO₃, and isonicotinyl hydrazide (INH)], photosynthetic parameters of leaves sprayed respectively with these chemicals were examined and their inhibiting efficiency was evaluated in Caragana korshinskii. Our results showed that 5 mM glycine could reduce the photorespiratory rate (P_R) effectively, while the net photosynthetic rate (P_N), stomatal conductance (g_s), and intercellular CO₂ concentration (Ci) significantly increased. The ratio of electron flow for ribulose-1,5-bisphosphate (RuBP) carboxylation to RuBP oxygenation was elevated markedly. NaHSO₃ and INH could also suppress the PR in some cases, whereas PN was not improved. The glyoxylate content increased considerably after application of low concentrations of glycine. These results suggested that low concentrations of glycine could suppress photorespiration by feed-back inhibition of glyoxylate and enhance photosynthesis by regulating g_s, C_i, and the distribution of electron flow in C. korshinskii.     

Physiological and Biochemical Mechanisms Preventing Cd Toxicity in the New Hyperaccumulator <Emphasis Type="Italic">Abelmoschus manihot</Emphasis>

Abelmoschus manihot, an ornamental plant, was examined for phytoremediation purposes in accordance with the ability to accumulate cadmium and physiological mechanisms of cadmium tolerance. A net photosynthetic rate (A _N) glasshouse experiment for 60 days was conducted to investigate the influence of different cadmium amounts (0–100 mg kg^?1) on the growth, biomass, photosynthetic performance, reactive oxygen species (ROS) production, antioxidative enzyme activities, Cd uptake and accumulation of A. manihot. Exposure to cadmium enhanced plant growth even at 100 mg kg^?1, without showing symptoms of visible damage. The cadmium concentration of shoots (stems or leaves) and roots was more than the critical value of 100 mg kg^?1 and reached 126.17, 185.26 and 210.24 mg kg^?1, respectively. BCF values of A. manihot plants exceeded the reference value 1.0 for all the Cd treatments, and TF values were greater than 1 at 15–60 mg kg^?1 Cd treatment. The results also showed that cadmium concentrations of 60 mg kg^?1 or less induced a significant enhancement in plant net photosynthetic rate (A _N), stomatal conductance (G _s), transpiration rate (T _r), photosynthetic pigments and F _v/F _m. These parameters were slightly decreased at the higher concentration (100 mg kg^?1). The ROS production (O₂ ^?, H₂O₂) and antioxidative response including SOD, CAT and POD were significantly enhanced by increasing cadmium. These results suggest that A. manihot can be considered as a Cd-hyperaccumulator and the hormetic effects may be taken into consideration in remediation of Cd contamination soil.     

Quantify the response of purslane plant growth,photosynthesis pigments and photosystem II photochemistry to cadmium concentration gradients in the soil

The cadmium (Cd), being a widespread soils pollutant and one of the most toxic heavy metals in the environment, adversely affects sustainable crop production and food safety. Pot experiment was conducted to quantify and simulate the response of purslane (Portulaca oleracea L.) plants to Cd toxicity. The purslane germinated seeds were cultivated in twelve Cd concentrations (from 0 to 300 mg/kg of Cd in soil) for six weeks and then some growth characteristics, photosynthesis pigments, and chlorophyll a fluorescence parameters were measured. The influence of Cd gradients in the soil on all growth parameters, photosynthesis pigments and chlorophyll a fluorescence parameters (except F_m and carotenoid content) were described by a segmented model. Furthermore, F_m and carotenoid contents were fitted to a linear model. The growth characteristics, chlorophyll content, photosynthetic pigments and some parameters of chlorophyll a fluorescence such as F_v, F_v/F_m, Y(II) and ETR decreased when Cd concentration increased. In contrast, F₀, Y(NPQ) and Y(NO) increased and F_m was not significantly affected. In general, most variations in the studied parameters were recorded with low concentrations of cadmium, which ranged from 0 to 125 mg/kg. Also, the growth characteristics (especially stem, leaf, and shoot dry weights) were more sensitive to Cd contamination than other parameters. Moreover, among chlorophyll fluorescence parameters, Y(NPQ) was the most sensitive to Cd concentration gradients in the soil that can be due to disturbances of antennae complex of PSII.     

Assessing biodegradation of furfuryl alcohol using <Emphasis Type="Italic">Pseudomonas putida</Emphasis> MTCC 1194 and <Emphasis Type="Italic">Pseudomonas aeruginosa</Emphasis> MTCC 1034 and its kinetics

The biodegradation of furfuryl alcohol (FA) in shake flask experiments using a pure culture of Pseudomonas putida (MTCC 1194) and Pseudomonas aeruginosa (MTCC 1034) was studied at 30 °C and pH 7.0. Experiments were performed at different FA concentrations ranging from 50 to 500 mg/l. Before carrying out the biodegradation studies, the bacterial strains were acclimatized to the concentration of 500 mg/l of FA by gradually raising 100 mg/l of FA in each step. The well acclimatized culture of P. putida and P. aeruginosa degraded about 80 and 66% of 50 mg/l FA, respectively. At higher concentration of FA, the percentage of FA degradation decreased. The purpose of this study was to determine the kinetics of biodegradation of FA by measuring biomass growth rates and concentration of FA as a function of time. Substrate inhibition was calculated from experimental growth parameters using the Haldane equation. Data for P. putida were determined as µ _max ?=?0.23 h^?1, K _s ?=?23.93 mg/l and K _i ?=?217.1 mg/l and for P. aeruginosa were determined as µ _max ?=?0.13 h^?1, K _s ?=?21.3 mg/l and K _i ?=?284.9 mg/l. The experimental data were fitted in Haldane, Aiba and Edwards inhibition models.     

Chlorophylls <Emphasis Type="Italic">d</Emphasis> and <Emphasis Type="Italic">f</Emphasis> and their role in primary photosynthetic processes of cyanobacteria

The finding of unique Chl d- and Chl f-containing cyanobacteria in the last decade was a discovery in the area of biology of oxygenic photosynthetic organisms. Chl b, Chl c, and Chl f are considered to be accessory pigments found in antennae systems of photosynthetic organisms. They absorb energy and transfer it to the photosynthetic reaction center (RC), but do not participate in electron transport by the photosynthetic electron transport chain. However, Chl d as well as Chl a can operate not only in the light-harvesting complex, but also in the photosynthetic RC. The long-wavelength (Q_y) Chl d and Chl f absorption band is shifted to longer wavelength (to 750 nm) compared to Chl a, which suggests the possibility for oxygenic photosynthesis in this spectral range. Such expansion of the photosynthetically active light range is important for the survival of cyanobacteria when the intensity of light not exceeding 700 nm is attenuated due to absorption by Chl a and other pigments. At the same time, energy storage efficiency in photosystem 2 for cyanobacteria containing Chl d and Chl f is not lower than that of cyanobacteria containing Chl a. Despite great interest in these unique chlorophylls, many questions related to functioning of such pigments in primary photosynthetic processes are still not elucidated. This review describes the latest advances in the field of Chl d and Chl f research and their role in primary photosynthetic processes of cyanobacteria.     

Photosynthetic activity and components of the electron transport chain in the aerobic bacteriochlorophyll <Emphasis Type="Italic">a</Emphasis>-containing bacterium <Emphasis Type="Italic">Roseinatronobacter thiooxidans</Emphasis>

Bioenergetics of the aerobic bacteriochlorophyll a-containing (BCl a) bacterium (ABC bacterium) Roseinatronobacter thiooxidans is a combination of photosynthesis, oxygen respiration, and oxidation of sulfur compounds under alkaliphilic conditions. The photosynthetic activity of Rna. thiooxidans cells was established by the photoinhibition of cell respiration and reversible photobleaching discoloration of the BCl a of reaction centers (RC), connected by the chain of electron transfer with cytochrome c ₅₅₁ oxidation. The species under study, like many purple bacteria and some of the known ABC bacteria, possesses a light-harvesting pigment-protein (LHI) complex with the average number of 30 molecules of antenna BCl a per one photosynthetic RC. Under microaerobic growth conditions, the cells contained bc ₁ complex and two terminal oxidases: cbb ₃-cytochrome oxidase and the alternative cytochrome oxidase of the a ₃ type. Besides, Rna. thiooxidans was shown to have several different soluble low- and high-potential cytochromes c, probably associated with the ability of utilizing sulfur compounds as additional electron donors.     

Gas exchanges of an endangered species <Emphasis Type="Italic">Syringa pinnatifolia</Emphasis> and a widespread congener <Emphasis Type="Italic">S. oblata</Emphasis>

Net photosynthetic rate (P_N), transpiration rate (E), water use efficiency (WUE), stomatal conductance (g_s), and stomatal limitation (L_s) were investigated in two Syringa species. The saturation irradiance (SI) was 400 µmol m^-2s^-1 for S. pinnatifolia and 1 700 µmol m^-2s^-1 for S. oblata. Compared with S. oblata, S. pinnatifolia had extremely low g _s . Unlike S. oblata, the maximal photosynthetic rate (P_max) in S. pinnatifoliaoccurred around 08:00 and then fell down, indicating this species was sensitive to higher temperature and high photosynthetic photon flux density. However, such phenomenon was interrupted by the leaf development rhythms before summer. A relatively lower P_N together with a lower leaf area and shoot growth showed the capacity for carbon assimilation was poorer in S. pinnatifolia.     

Growth and photosynthetic activity of <Emphasis Type="Italic">Botryococcus braunii</Emphasis> biofilms

Botryococcus braunii is a green microalga capable of producing large amounts of external long-chain hydrocarbons suitable as a source of biofuel. There have been several studies indicating that cultures of B. braunii can reduce the energy and water requirement for mass biofuel production, especially if non-destructive extraction methods for milking hydrocarbons are used. Growing microalgae as a raw material for biofuel using conventional liquid-based cultivation (i.e., raceway ponds) has yet to be shown to be economically successful. An alternative solid growth (biofilm) cultivation method can markedly reduce the energy requirements and costs associated with the harvesting and dewatering processes. We evaluated the growth of biofilms of several strains of B. braunii (from races A, B, L and S) and found that three of the four tested races successfully grew to stationary phase in 10 weeks with no contamination. Among all races, B. braunii BOT22 (race B) reached the highest biomass and lipid yields (3.80 mg dry weight cm^?2 day^?1 and 1.11 mg dry weight cm^?2). Irrespective of the race, almost all photosynthetic parameters (F _V /F ₀ , PI_ABS and the OJIP curve) showed that the biofilm cultures were more stressed during lag and stationary phases than in logarithmic phase. We also studied the Botryococcus biofilm profiles using confocal microscopy and found that this method is suitable for estimating the overall biomass yield when compared with gravimetric measurement. In conclusion, the growth characteristics (biomass and lipid) and photosynthetic performance of all races indicated that B. braunii BOT22 is the most promising strain for biofilm cultivation.     

In vitro regeneration and optimization of factors affecting <Emphasis Type="Italic">Agrobacterium</Emphasis> mediated transformation in <Emphasis Type="Italic">Artemisia Pallens</Emphasis>, an important medicinal plant

Artemisia pallens is an important medicinal plant. In-vitro regeneration and multiplication of A. pallens have been established using attached cotyledons. Different growth regulators were considered for regeneration of multiple shoots. An average of 36 shoots per explants were obtained by culturing attached cotyledons on Murashige and Skoog’s medium containing 2 mg/L BAP and 0.1 mg/L NAA, after 45 days. The shoots were rooted best on half Murashige and Skoog’s medium with respect to media containing 1 mg/L IBA or 1 mg/L NAA. Different parameters such as type of bacterial strains, OD₆₀₀ of bacterial culture, co-cultivation duration, concentration of acetosyringone and explants type were optimized for transient expression of the reporter gene. Agrobacterium tumefaciens harbouring pCambia1301 plasmid carrying β-glucuronidase as a reporter gene and hygromycin phosphotransferase as plant selectable marker genes were used for genetic transformation of A. pallens. Hygromycin lethality test showed concentration of 15 mg/L were sufficient to inhibit the growth of attached cotyledons and multiple shoot buds of nontransgenics in selection media. Up to 83 % transient transformation was found when attached cotyledons were co-cultivated with Agrobacterium strain AGL1 for 2 days at 22 °C on shoot induction medium. The bacterial growth was eliminated by addition of cefotaxime (200 mg/L) in selection media. T₀ transgenic plants were confirmed by GUS histochemical assay and further by polymerase chain reaction (PCR) using uidA and hpt gene specific primers. The study is useful in establishing technological improvement in A. pallens by genetic engineering.     

<Emphasis Type="Italic">Terminalia arjuna</Emphasis> bark extract alleviates nickel toxicity by suppressing its uptake and modulating antioxidative defence in rice seedlings

Terminalia arjuna (Ta) bark contains various natural antioxidants and has been used to protect animal cells against oxidative stress. In the present study, we have examined alleviating effects of Ta bark aqueous extract against Ni toxicity in rice (Oryza sativa L.). When rice seedlings were raised for 8 days in hydroponics in Yoshida nutrient medium containing 200 μM NiSO₄, a decline in height, reduced biomass, increased Ni uptake, loss of root plasma membrane integrity, increase in the level of O₂˙^?, H₂O₂ and ˙OH, increased lipid peroxidation, decline in photosynthetic pigments, increase in the level of antioxidative enzymes superoxide dismutase, catalase and glutathione peroxidase and alterations in their isoenzyme profile patterns were observed. Transmission electron microscopy (TEM) showed damage to chloroplasts marked by disorganised enlarged starch granules and disrupted thylakoids under Ni toxicity. Exogenously adding Ta bark extract (3.2 mg ml^?1) to the growth medium considerably alleviated Ni toxicity in the seedlings by reducing Ni uptake, suppressing generation of reactive oxygen species, reducing lipid peroxidation, restoring level of photosynthesis pigments and ultrastructure of chloroplasts, and restoring levels of antioxidative enzymes. Results suggest that Ta bark extract considerably alleviates Ni toxicity in rice seedlings by preventing Ni uptake and reducing oxidative stress in the seedlings.     

Sequencing of the plastome in the leafless green mycoheterotroph <Emphasis Type="Italic">Cymbidium macrorhizon</Emphasis> helps us to understand an early stage of fully mycoheterotrophic plastome structure

To date, plastome studies of mycoheterotrophic orchids have focused on nongreen mycoheterotrophic or partially mycoheterotrophic species. Cymbidium macrorhizon is a fully mycoheterotrophic orchid that lacks leaves and roots, although its inflorescence rachis is pale green. It has degraded stomata, specific fungal partners, and high concentrations of heavy stable nitrogen and carbon isotopes. Therefore, the plastome of this species is expected to represent an early stage of a fully mycoheterotrophic plastome. In this study, we sequenced the plastomes of C. macrorhizon and closely related species (C. ensifolium, C. kanran, and C. lancifolium). Plastomes of the four Cymbidium species were almost identical structurally, but differed somewhat from those of previously studied species. The genes for the photosynthetic subunits of NADH dehydrogenase, ndhF and ndhH, were absent from all four newly sequenced plastomes, whereas only ndhJ was absent from C. ensifolium. In section Pachyrhizanthe (C. lancifolium and C. macrorhizon), ndhE, ndhI, and ndhJ were pseudogenized. With the exception of ndh and ycf, 64 protein-coding genes in C. macrorhizon were apparently functional. Most of them were highly conserved and under purifying selection. Therefore, no direct evidence is available to suggest that genes related to photosynthesis have lost their functions in C. macrorhizon. This discordance between molecular and physiological features for the trophic status of C. macrorhizon might result from a lag between photosynthetic function loss and relaxed purifying selection.     

Expression and characterization of glutamate decarboxylase from <Emphasis Type="Italic">Lactobacillus brevis</Emphasis> HYE1 isolated from <Emphasis Type="Italic">kimchi</Emphasis>

A putative gene (gadlbhye1) encoding glutamate decarboxylase (GAD) was cloned from Lactobacillus brevis HYE1 isolated from kimchi, a traditional Korean fermented vegetable. The amino acid sequences of GADLbHYE1 showed 48% homology with the GadA family and 99% identity with the GadB family from L. brevis. The cloned GADLbHYE1 was functionally expressed in Escherichia coli using inducible expression vectors. The expressed recombinant GADLbHYE1 was successfully purified by Ni–NTA affinity chromatography, and had a molecular mass of 54 kDa with optimal hydrolysis activity at 55 °C and pH 4.0. Its thermal stability was determined to be higher than that of other GADs from L. brevis, based on its melting temperature (75.18 °C). Kinetic parameters including K_m and V_max values for GADLbHYE1 were 4.99 mmol/L and 0.224 mmol/L/min, respectively. In addition, the production of gamma-aminobutyric acid in E. coli BL21 harboring gadlbhye1/pET28a was increased by adding pyridoxine as a cheaper coenzyme.     

Nisin Z produced by <Emphasis Type="Italic">Lactococcus lactis</Emphasis> from bullfrog hatchery is active against <Emphasis Type="Italic">Citrobacter freundii</Emphasis>, a red-leg syndrome related pathogen

Lactococcus lactis subsp. lactis CRL 1584 isolated from a bullfrog hatchery produces a bacteriocin that inhibits both indigenous Citrobacter freundii (a Red-Leg Syndrome related pathogen) and Lactobacillus plantarum, and Listeria monocytogenes as well. Considering that probiotics requires high cell densities and/or bacteriocin concentrations, the effect of the temperature on L. lactis growth and bacteriocin production was evaluated to find the optimal conditions. Thus, the growth rate was maximal at 36 °C, whereas the highest biomass and bacteriocin activity was achieved between 20 and 30 °C and 20–25 °C, respectively. The bacteriocin synthesis was closely growth associated reaching the maximal values at the end of the exponential phase. Since bacteriocins co-production has been evidenced in bacterial genera, a purification of the bacteriocin/s from L. lactis culture supernatants was carried out. The active fraction was purified by cationic-exchange chromatography and then, a RP-HPLC was carried out. The purified sample was a peptide with a 3353.05 Da, a molecular mass that matches nisin Z, which turned out to be the only bacteriocin produced by L. lactis CRL 1584. Nisin Z showed bactericidal effect on C. freundii and L. monocytogenes, which increased in the presence l-lactic acid?+?H₂O₂. This is the first report on nisin Z production by L. lactis from a bullfrog hatchery that resulted active on a Gram-negative pathogen. This peptide has potential probiotic for raniculture and as food biopreservative for bullfrog meat.     

Toxic metals accumulation in <Emphasis Type="Italic">Trichoderma asperellum</Emphasis> and <Emphasis Type="Italic">T. harzianum</Emphasis>

Heavy metal contamination represents an important environmental issue due to the toxic effects of metals on different organisms. Filamentous fungi play an important impact in the bioremediation of heavy metal-contaminated wastewater and soil. The purpose of this investigation was to observe fungal uptake behavior toward heavy metal. For this aim Trichoderma asperellum TS141 and T. harzianum TS103 at growth period were screened for their tolerance and uptake capability of cadmium (Cd), lead (Pb) and nickel (Ni) at different concentrations (0, 25, 50, 100, and 200 mg/L) in PDB media (potato dextrose broth as a complex medium). Results showed that both fungi were able to survive at the maximum concentration of 200 mg/L of the heavy metals, and remove them. T. asperellum had a better uptake capacity for Cd compared to Pb and Ni in the highest metal concentration in media. Maximum removal efficiency of Pb (68.4%) at 100 mg/L and Ni (78%) at 200 mg/L was performed by T. asperellum. For Cd, the highest removal efficiency (82.1%) was recorded by T. harzianum at 200 mg/L Cd in aqueous solution. The uptake of Cd was highly dependent on pH of solution than Pb and Ni so that the optimal pH of Cd uptake was 9 for T. asperellum and 4 for T. harzianum. Also, optimal temperature was 35°C for Cd and Pb uptake in both fungi, whereas for Ni uptake was 30 and 35°C in T. harzianum and T. asperellum, respectively. We propose that T. asperellum TS141 and T. harzianum TS103 can be used as a bioremediation agent for metal remediation from wastewater and heavy metal-contaminated soils.     

Effects of low nocturnal temperature on photosynthetic characteristics and chloroplast ultrastructure of winter rapeseed

We investigated the effects of low nocturnal temperature on photosynthetic apparatus of winter rapeseed (Brassica campestris L.). An artificial climate chamber was used to simulate the effects of low nocturnal temperature on seedling and stomatal morphology, chloroplast ultrastructure, photosynthetic parameters, and dry matter distribution and accumulation in two winter rapeseed cultivars, Longyou-7 (ultra coldresistant) and Tianyou-2 (weak cold resistance). Compared with those at diurnal/nocturnal temperatures of 20°/10°C (control), rapeseed seedlings at 20°/5°C had increased leaf chlorophyll content, deepened green leaf color, decreased stomatal conductance (G_s), intercellular CO₂ concentration (C_i), and photosynthetic rate (P_n), and improved root/shoot ratio; the majority of stomata remained open in Longyou-7 while those in Tianyou-2 were mostly closed or semi-closed. At diurnal/nocturnal temperatures of 20°/–5°C, rapeseed seedlings had decreased leaf chlorophyll content with increased C_i but decreased G_s and P_n; Tianyou-2 exhibited ruptured chloroplast membrane, dissolved grana, broken stroma lamella, and decreased root/shoot ratio, whereas Longyou-7 had chloroplasts retaining partial structure of grana with a small amount of starch granules in guard cells. Low nocturnal temperature damaged the photosynthetic membrane of chloroplasts and reduced P_n in the leaves of winter rapeseed influencing photosynthetic processes in this crop. The reduction of P_n was mainly related to stomatal limitation at diurnal/nocturnal temperatures of 20°/5°C and non-stomatal limitation at diurnal/nocturnal temperatures of 20°/–5°C.     

Growth and photosynthetic response of two larches exposed to O<Subscript>3</Subscript> mixing ratios ranging from preindustrial to near future

In this study, we questioned whether ground-level ozone (O₃) induces hormesis in Japanese larch (Larix kaempferi) and its hybrid F₁ (L. gmelinii var. japonica × L. kaempferi). In order to answer the question, we exposed seedlings of both taxa to four O₃ treatments [ranging from ≈10 to 60 nmol(O₃) mol^–1] in open-top chambers for two consecutive growing seasons. We found a hormetic response in maximum photosynthetic rate (P_Nmax) at 1700 μmol(CO₂) mol^–1 and maximum rates of carboxylation (V_cmax) and electron transport (J_max) in both larches. Stimulation of P_Nmax, V_cmax, and J_max did not lead to suppressed plant productivity in Japanese larch, which followed a stress-tolerant strategy, but it did lead to suppressed plant productivity in hybrid larch which followed a competitive strategy. These findings are the first to suggest that stimulation of physiological functions by low O₃ exposures may have negative consequences for larch reproduction.