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.

A pivotal role of the jasmonic acid signal pathway in mediating radiation-induced bystander effects in Arabidopsis thaliana.

Although radiation-induced bystander effects (RIBE) in Arabidopsis thaliana have been well demonstrated in vivo, little is known about their underlying mechanisms, particularly with regard to the participating signaling molecules and signaling pathways. In higher plants, jasmonic acid (JA) and its bioactive derivatives are well accepted as systemic signal transducers that are produced in response to various environmental stresses. It is therefore speculated that the JA signal pathway might play a potential role in mediating radiation-induced bystander signaling of root-to-shoot. In the present study, pretreatment of seedlings with Salicylhydroxamic acid, an inhibitor of lipoxigenase (LOX) in JA biosynthesis, significantly suppressed RIBE-mediated expression of the AtRAD54 gene. After root irradiation, the aerial parts of A. thaliana mutants deficient in JA biosynthesis (aos) and signaling cascades (jar1-1) showed suppressed induction of the AtRAD54 and AtRAD51 genes and TSI and 180-bp repeats, which have been extensively used as endpoints of bystander genetic and epigenetic effects in plants. These results suggest an involvement of the JA signal pathway in the RIBE of plants. Using the root micro-grafting technique, the JA signal pathway was shown to participate in both the generation of bystander signals in irradiated root cells and radiation responses in the bystander aerial parts of plants. The over-accumulation of endogenous JA in mutant fatty acid oxygenation up-regulated 2 (fou2), in which mutation of the Two Pore Channel 1 (TPC1) gene up-regulates expression of the LOX and allene oxide synthase (AOS) genes, inhibited RIBE-mediated expression of the AtRAD54 gene, but up-regulated expression of the AtKU70 and AtLIG4 genes in the non-homologous end joining (NHEJ) pathway. Considering that NHEJ is employed by plants with increased DNA damage, the switch from HR to NHEJ suggests that over-accumulation of endogenous JA might enhance the radiosensitivity of plants in terms of RIBE.

Ultrasonic vibration-assisted (UV-A) pelleting of wheat straw: a constitutive model for pellet density.

Ultrasonic vibration-assisted (UV-A) pelleting can increase cellulosic biomass density and reduce biomass handling and transportation costs in cellulosic biofuel manufacturing. Effects of input variables on pellet density in UV-A pelleting have been studied experimentally. However, there are no reports on modeling of pellet density in UV-A pelleting. Furthermore, in the literature, most reported density models in other pelleting methods of biomass are empirical. This paper presents a constitutive model to predict pellet density in UV-A pelleting. With the predictive model, relations between input variables (ultrasonic power and pelleting pressure) and pellet density are predicted. The predicted relations are compared with those determined experimentally in the literature. Model predictions agree well with reported experimental results.

Changes in light- and nitrogen-use and in aboveground biomass allocation patterns along productivity gradients in grasslands.

Light- and nitrogen-use change was examined along productivity gradients in natural grasslands at Laelatu, western Estonia, both at community level and in most abundant species. Aboveground biomass (M) ranged from 341 to 503 g m(-2) in wet (W) and from 248 to 682 g m(-2) in dry (D) community. Aboveground leaf area ratio (aLAR) decreased with rising M in D site, while it increased in W site. In a high-aLAR W community (significantly higher compared to D), adjustment of leaf morphology through an increase in specific leaf area is responsible for an increase in aLAR with rising productivity. In low-aLAR stand, by contrast, adjustment of biomass allocation due to decrease in aboveground leaf mass fraction is primarily responsible for the tendency of aLAR to decline. In conclusion, a decrease in aLAR is not a universal response to increasing M. We hypothesise that there exists an optimum of light acquisition efficiency (ΦM) along a productivity gradient independent of community type. Aboveground nitrogen-use efficiency (aNUE) decreased in high-aLAR, W community with increasing M, while in low-aLAR, D site, there was no relationship along a gradient, although aNUE increased along six plots dominated by graminoids. A trade-off was established between leaf nitrogen content per unit leaf area (N A) and aLAR.

Ultrasonic vibration-assisted pelleting of wheat straw: a predictive model for energy consumption using response surface methodology.

Cellulosic biomass can be used as a feedstock for biofuel manufacturing. Pelleting of cellulosic biomass can increase its bulk density and thus improve its storability and reduce the feedstock transportation costs. Ultrasonic vibration-assisted (UV-A) pelleting can produce biomass pellets whose density is comparable to that processed by traditional pelleting methods (e.g. extruding, briquetting, and rolling). This study applied response surface methodology to the development of a predictive model for the energy consumption in UV-A pelleting of wheat straw. Effects of pelleting pressure, ultrasonic power, sieve size, and pellet weight were investigated. This study also optimized the process parameters to minimize the energy consumption in UV-A pelleting using response surface methodology. Optimal conditions to minimize the energy consumption were the following: ultrasonic power at 20%, sieve size at 4 mm, and pellet weight at 1g, and the minimum energy consumption was 2.54 Wh.

Characterization of two Agrostis-Festuca alpine pastures and their influence on cheese composition.

Recently, there has been a renewed interest in mountain farming, and several studies have been carried out on milk and cheese obtained in the unique environmental conditions of the Alps, a 1300 km mountain chain, located in the north of Italy. In this paper, the influence, on some cheese constituents, of two very similar mountain grasslands, both dominated by Festuca - Agrostis , was investigated. The two pastures were located in the same area in the southeastern Italian alpine region and differed in sunshine orientation and exposure. Milk obtained from cows grazing on these pastures was used to produce a semi-hard traditional cheese. The differences observed between the cheeses of the two areas for both some hydrocarbons (1-phytene and 2-phytene) and trans-fatty acids can be explained by a different rumen environment created by the botanical composition of the two pastures. The multidisciplinary approach can be considered a successful strategy, suitable for studying markers of authenticity.

The effect of microwave pretreatment on biogas production from agricultural straws.

Biogas production from microwave-pretreated agricultural residual straws that are used as feedstock was investigated in a laboratory batch study. Barley, spring wheat, winter wheat and oat straw were examined. To investigate the effect of changing the physicochemical structure of the straws on biogas production, the pretreatment processes were applied to two sample groups. The first group contained milled straw and the second group comprised milled wet straw that was prepared by the addition of deionized water. Both groups were subjected to microwave irradiation until oven temperatures of 200 or 300 °C were attained. Sixty-six identical batch anaerobic reactors were run under mesophilic conditions for 60 days. Preliminary test results showed that the microwave pretreatment of the different straws did not improve their anaerobic digestion. An increase in the treatment temperature led to lower biogas production levels. An inverse relationship between the thermal conversion yield and cumulative biogas production was observed.

Oak loss increases foliar nitrogen, δ(15)N and growth rates of Betula lenta in a northern temperate deciduous forest.

Oak forests dominate much of the eastern USA, but their future is uncertain due to a number of threats and widespread failure of oak regeneration. A sudden loss of oaks (Quercus spp.) could be accompanied by major changes in forest nitrogen (N) cycles with important implications for plant nutrient uptake and tree species composition. In this study, we measured the changes in N use and growth rates of black birch trees (Betula lenta L.) following oak girdling at the Black Rock Forest in southeastern New York, USA. Data were collected from nine experimental plots composed of three treatments: 100% oaks girdled (OG), 50% oaks girdled (O50) and control (C). Foliar N concentration and foliar (15)N abundance increased significantly in the oak-girdled plots relative to the control, indicating that the loss of oaks significantly altered N cycling dynamics. As mineralization and nitrification rates increase following oak loss, black birch trees increase N absorption as indicated by higher foliar N content and increased growth rates. Foliar N concentration increased by 15.5% in the O50 and 30.6% in the OG plots relative to the control, while O50 and OG plots were enriched in (15)N by 1.08‰ and 3.33‰, respectively (P < 0.0001). A 641% increase in black birch growth rates in OG plots suggests that this species is able to respond to additional N availability and/or increased light availability. The loss of oaks and subsequent increase in black birch productivity may have a lasting impact on ecosystem form and function.

Rice MPR25 encodes a pentatricopeptide repeat protein and is essential for RNA editing of nad5 transcripts in mitochondria.

Pentatricopeptide repeat (PPR) proteins are involved in the modification of organelle transcripts. In this study, we investigated the molecular function in rice of the mitochondrial PPR-encoding gene MITOCHONDRIAL PPR25 (MPR25), which belongs to the E subgroup of the PPR family. A Tos17 knockout mutant of MPR25 exhibited growth retardation and pale-green leaves with reduced chlorophyll content during the early stages of plant development. The photosynthetic rate in the mpr25 mutant was significantly decreased, especially under strong light conditions, although the respiration rate did not differ from that of wild-type plants. MPR25 was preferentially expressed in leaves. FLAG-tagged MPR25 accumulated in mitochondria but not in chloroplasts. Direct sequencing revealed that the mpr25 mutant fails to edit a C-U RNA editing site at nucleotide 1580 of nad5, which encodes a subunit of complex I (NADH dehydrogenase) of the respiratory chain in mitochondria. RNA editing of this site is responsible for a change in amino acid from serine to leucine. Recombinant MPR25 directly interacted with the proximal region of the editing site of nad5 transcripts. However, the NADH dehydrogenase activity of complex I was not affected in the mutant. By contrast, genes encoding alternative NADH dehydrogenases and alternative oxidase were up-regulated. The mpr25 mutant may therefore provide new information on the coordinated interaction between mitochondria and chloroplasts.

Ultraviolet-B radiation and nitrogen affect nutrient concentrations and the amount of nutrients acquired by above-ground organs of maize.

UV-B radiation effects on nutrient concentrations in above-ground organs of maize were investigated at silking and maturity at different levels of applied nitrogen under field conditions. The experiment simulated a 20% stratospheric ozone depletion over Portugal. At silking, UV-B increased N, K, Ca, and Zn concentrations, whereas at maturity Ca, Mg, Zn, and Cu increased and N, P and Mn decreased in some plant organs. Generally, at maturity, N, Ca, Cu, and Mn were lower, while P, K, and Zn concentrations in stems and nitrogen-use efficiency (NUE) were higher in N-starved plants. UV-B and N effects on shoot dry biomass were more pronounced than on nutrient concentrations. Nutrient uptake decreased under high UV-B and increased with increasing N application, mainly at maturity harvest. Significant interactions UV-B x N were observed for NUE and for concentration and mass of some elements. For instance, under enhanced UV-B, N, Cu, Zn, and Mn concentrations decreased in leaves, except on N-stressed plants, whereas they were less affected by N nutrition. In order to minimize nutritional, economical, and environmental negative consequences, fertiliser recommendations based on element concentration or yield goals may need to be adjusted.

Efficient bioconversion of rice straw to ethanol with TiO2/UV pretreatment.

Rice straw is a lignocellulosic biomass that constitutes a renewable organic substance and alternative source of energy; however, its structure confounds the liberation of monosaccharides. Pretreating rice straw using a TiO(2)/UV system facilitated its hydrolysis with Accellerase 1000(™), suggesting that hydroxyl radicals (OH·) from the TiO(2)/UV system could degrade lignin and carbohydrates. TiO(2)/UV pretreatment was an essential step for conversion of hemicellulose to xylose; optimal conditions for this conversion were a TiO(2) concentration of 0.1% (w/v) and an irradiation time of 2 h with a UV-C lamp at 254 nm. After enzymatic hydrolysis, the sugar yields from rice straw pretreated with these parameters were 59.8 ± 0.7% of the theoretical for glucose (339 ± 13 mg/g rice straw) and 50.3 ± 2.8% for xylose (64 ± 3 mg/g rice straw). The fermentation of enzymatic hydrolysates containing 10.5 g glucose/L and 3.2 g xylose/L with Pichia stipitis produced 3.9 g ethanol/L with a corresponding yield of 0.39 g/g rice straw. The maximum possible ethanol conversion rate is 76.47%. TiO(2)/UV pretreatment can be performed at room temperature and atmospheric pressure and demonstrates potential in large-scale production of fermentable sugars.

Microwave-assisted extraction of lignin from triticale straw: optimization and microwave effects.

Presently lignin is used as fuel but recent interests in biomaterials encourage the use of this polymer as a renewable feedstock in manufacturing. The present study was undertaken to explore the potential applicability of microwaves to isolate lignin from agricultural residues. A central composite design (CCD) was used to optimize the processing conditions for the microwave (MW)-assisted extraction of lignin from triticale straw. Maximal lignin yield (91%) was found when using 92% EtOH, 0.64 N H(2)SO(4), and 148 °C. The yield and chemical structure of MW-extracted lignin were compared to those of lignin extracted with conventional heating. Under similar conditions, MW irradiation led to higher lignin yields, lignins of lower sugar content, and lignins of smaller molecular weights. Except for these differences the lignins resulting from both types of heating exhibited comparable chemical structures. The present findings should provide a clean source of lignin for potential testing in manufacturing of biomaterials.

Fermentation of rice hull by Aspergillus japonicus under ultrasonic pretreatment.

The application of ultrasound for treating rice hull used as the fermentation substrate for xylooligosaccharides production was investigated. Aspergillus japonicus CY6-1 was selected to produce cellulolytic and xylanolytic enzymes from untreated rice hull (RH) and rice hull treated with ultrasound (USRH-M). The hemicellulose yield was increased to 1.4-fold with ultrasound, and treatment time was greatly shortened from 24h to 1.5h at 80 °C and 300 W/28 kHz. The morphology of RH from various pretreatments was observed with field emission scanning electron microscope (FESEM), revealing the surface structure of USRH-M smoother than that of RH. USRH-M was much easier to be utilized by fungi, to extend the stability of enzyme activity and to increase activities of CMCase, ß-glucosidase, and xylanase compared with those of untreated RH. The final fermentative products were xylotetraose, xylohexaose, and higher molecular weight xylooligosaccharides, achieving xylohexaose yield for USRH-M 80% higher than that for RH group.

SCAR mediates light-induced root elongation in Arabidopsis through photoreceptors and proteasomes.

The ARP2/3 complex, a highly conserved nucleator of F-actin, and its activator, the SCAR complex, are essential for growth in plants and animals. In this article, we present a pathway through which roots of Arabidopsis thaliana directly perceive light to promote their elongation. The ARP2/3-SCAR complex and the maintenance of longitudinally aligned F-actin arrays are crucial components of this pathway. The involvement of the ARP2/3-SCAR complex in light-regulated root growth is supported by our finding that mutants of the SCAR complex subunit BRK1/HSPC300, or other individual subunits of the ARP2/3-SCAR complex, showed a dramatic inhibition of root elongation in the light, which mirrored reduced growth of wild-type roots in the dark. SCAR1 degradation in dark-grown wild-type roots by constitutive photomorphogenic 1 (COP1) E3 ligase and 26S proteasome accompanied the loss of longitudinal F-actin and reduced root growth. Light perceived by the root photoreceptors, cryptochrome and phytochrome, suppressed COP1-mediated SCAR1 degradation. Taken together, our data provide a biochemical explanation for light-induced promotion of root elongation by the ARP2/3-SCAR complex.

Red and blue pulse timing control for pulse width modulation light dimming of light emitting diodes for plant cultivation.

A pulse width modulation (PWM) light dimming system containing red and blue light emitting diodes was designed and constructed. Cultivation of the plant Arabidopsis thaliana under various light dimming wave patterns was compared. Control of the pulse timing (phase of wave pattern) between red and blue light in PWM light dimming was examined. Different plant growth was obtained by changing the phase of red and blue pulses. Pulse timing control of PWM light dimming for plant cultivation has the potential to act as a method for probing photosynthesis.

The time course of long-distance signaling in radiation-induced bystander effect in vivo in Arabidopsis thaliana demonstrated using root micro-grafting.

The radiation-induced bystander effect has been demonstrated in whole organisms as well as in multicellular tissues in vitro and single-cell culture systems in vitro. However, the time course of bystander signaling, especially in whole organisms, is not clear. Long-distance bystander/abscopal effects in vivo in plants have been demonstrated by our group. Plant grafting is a useful experimental tool for studying the root-shoot signaling of plants. In the present study, we developed a root micro-grafting technique with young seedlings of Arabidopsis thaliana in which the bystander signaling communication of root-to-shoot could easily be stopped or started at specific times after root irradiation. Using this methodology, we demonstrated the time course of long-distance signaling in radiation-induced bystander effects at the level of the organism using the expression level of the AtRAD54 gene as a biological end point. Briefly, an 8-h accumulation of damage signals in bystander parts after irradiation was essential for eliciting a bystander response. The protraction of signal accumulation was not related to the transmission speed of signaling molecules in plants and did not result from the delayed initiation of bystander signals in targeted root cells. It was suggested that the bystander effect might be induced jointly by multiple bystander signals initiated at different stages after irradiation. Moreover, reactive oxygen species (ROS) were shown to be implicated in the response process of bystander cells to radiation damage signals rather than in the generation of bystander signals in targeted cells.

Light stress is not effective to enhanced crassulacean acid metabolism.

Clusia minor L., a C3-CAM intermediate, and Clusia multiflora H. B. K., a C3 obligate, present two physiotypes of a similar morphotype occurring sympatrically in the field. Both species, exposed 2 days to high light, show similar responses to this kind of stress: (i) the level of xanthophyll pigments in tested plants during the daycourse adapts to stress, (ii) the levels of antheraxanthin and zeaxanthin clearly increase during the afternoon showing increased de-epoxidation, (iii) the changes in the xanthophyll cycle are similar. Exposure to high light increases the malate levels in C. minor during the afternoon while decreases the day/night changes of the malate levels, and hence the Crassulacean Acid Metabolism (CAM) expression. It can be concluded that strong light applied as a single stress factor to well-watered plants is not effective in strengthing the CAM metabolism in a C3-CAM intermediate plant but rather suppresses the CAM activity despite exposure to high light energy. It is suggested that, when water supply is not limiting and other stresses do not prevail, C3 allows to use up the citrate pool, especially in the afternoon and enables a superior daily photon utilization.

Simulation of wheat growth and development based on organ-level photosynthesis and assimilate allocation.

Intimate relationships exist between form and function of plants, determining many processes governing their growth and development. However, in most crop simulation models that have been created to simulate plant growth and, for example, predict biomass production, plant structure has been neglected. In this study, a detailed simulation model of growth and development of spring wheat (Triticum aestivum) is presented, which integrates degree of tillering and canopy architecture with organ-level light interception, photosynthesis, and dry-matter partitioning. An existing spatially explicit 3D architectural model of wheat development was extended with routines for organ-level microclimate, photosynthesis, assimilate distribution within the plant structure according to organ demands, and organ growth and development. Outgrowth of tiller buds was made dependent on the ratio between assimilate supply and demand of the plants. Organ-level photosynthesis, biomass production, and bud outgrowth were simulated satisfactorily. However, to improve crop simulation results more efforts are needed mechanistically to model other major plant physiological processes such as nitrogen uptake and distribution, tiller death, and leaf senescence. Nevertheless, the work presented here is a significant step forwards towards a mechanistic functional-structural plant model, which integrates plant architecture with key plant processes.

Analysis of glutamate homeostasis by overexpression of Fd-GOGAT gene in Arabidopsis thaliana.

Glutamate plays a central role in nitrogen flow and serves as a nitrogen donor for the production of amino acids. In plants, some amino acids work as buffers: during photorespiration, ammonium derived from the conversion of glycine to serine is promptly reassimilated into glutamate by the glutamine synthetase (GS-2)/ferredoxin-dependent glutamate synthase (Fd-GOGAT) cycle. The glutamate concentration is relatively stable compared with those of other amino acids under environmental changes. The few studies dealing with glutamate homeostasis have but all used knockouts or mutants of these enzymes. Here, we generated Fd-GOGAT (GLU1)-overexpressing Arabidopsis plants to analyze changes in the amino acid pool caused by glutamate overproduction under different ammonium conditions controlled by CO(2) concentration, light intensity and nitrate concentration. Under photorespiratory conditions with sufficient ammonium supply, aspartate increased and glutamine and glycine decreased, but glutamate barely changed. Under non-photorespiratory conditions, however, glutamate and most other amino acids increased. These results suggest that the synthesized glutamate is promptly converted into other amino acids, especially aspartate. In addition, ammonium supply by photorespiration does not limit glutamate biosynthesis, but glutamine and glycine are important. This study will contribute to the understanding of glutamate homeostasis in plants.

Improved enzymatic hydrolysis yield of rice straw using electron beam irradiation pretreatment.

Rice straw was irradiated using an electron beam at currents and then hydrolyzed with cellulase and beta-glucosidase to produce glucose. The pretreatment by electron beam irradiation (EBI) was found to significantly increase the enzyme digestibility of rice straw. Specifically, when rice straw that was pretreated by EBI at 80 kGy at 0.12 mA and 1 MeV was hydrolyzed with 60 FPU of cellulase and 30 CBU of beta-glucosidase, the glucose yield after 132 h of hydrolysis was 52.1% of theoretical maximum. This value was significantly higher than the 22.6% that was obtained when untreated rice straw was used. In addition, SEM analysis of pretreated rice straw revealed that EBI caused apparent damage to the surface of the rice straw. Furthermore, EBI pretreatment was found to increase the crystalline portion of the rice straw. Finally, the crystallinity and enzyme digestibility were found to be strongly correlated between rice straw samples that were pretreated by EBI under different conditions.