Lower Rates Of Photosynthesis Research Articles

A Hydroponic System to Study the Effects of Root and Meristem Night Temperature on Growth, Photosynthesis Carbon Balance, and Antioxidant Enzymes in Rice

Nocturnal root and meristem temperature (RMT) can have a strong effect on rice growth and yield. However, underlying mechanisms are not well understood. To investigate the effects of night-time RMT on photosynthesis biomass allocation and activities of antioxidant enzymes, we designed a hydroponic system that maintained the following daily patterns of day/night temperature: 18/28 °C (HNT) or 28/18 °C (LNT). Rice plants cv. IR64 were grown in the greenhouse and subjected to either HNT or LNT. HNT stimulated growth and tillering but did not affect biomass allocation. HNT plants increased total biomass by 16 and 35%, depending on time of exposure. HNT increased rates of photosynthesis (Pn) compared to LNT plants in leaves of different ages. Overnight carbohydrate remobilisation was larger in HNT than in LNT plants, particularly at 16 days after treatment (dat), when Pn and relative growth rates were highest. Leaf soluble protein concentrations and specific leaf area were not affected by RMT, indicating higher photosynthetic nitrogen use efficiency in HNT plants. Super Oxide Dismutase, Ascorbate Peroxidase, and Glutathione Reductase activities did not respond to RMT, indicating no change in the production of reactive oxygen species in LNT plants despite lower photosynthesis rates. HNT increased sink demand by stimulating tillering, the increased sink demand upregulated the source activity through a larger leaf area per plant and a higher Pn throughout the canopy. The hydroponic system described here was able to control the temperature of the nutrient solution effectively, the installation of a second pump directly circulating the nutrient solution from and back to the reservoir through the cooling system allowed reaching the target temperature within 1 h. This system opens new opportunities to characterise plant responses to RMT alone or in combination with other environmental drivers.

Grain Yield, Biomass Accumulation, and Leaf Photosynthetic Characteristics of Rice under Combined Salinity-Drought Stress

Simultaneous stresses of salinity and drought often coincide during rice-growing seasons in saline lands, primarily due to insufficient water resources and inadequate irrigation facilities. Consequently, combined salinity-drought stress poses a major threat to rice production. In this study, two salinity levels (NS, non-salinity; HS, high salinity) along with three drought treatments (CC, control condition; DJ, drought stress imposed at jointing; DH, drought stress imposed at heading) were performed to investigate their combined influences on leaf photosynthetic characteristics, biomass accumulation, and rice yield formation. Salinity, drought, and their combination led to a shortened growth period from heading to maturity, resulting in a reduced overall growth duration. Grain yield was reduced under both salinity and drought stress, with a more substantial reduction under the combined salinity-drought stress. The combined stress imposed at heading caused greater yield losses in rice compared with the stress imposed at jointing. Additionally, the combined salinity-drought stress induced greater decreases in shoot biomass accumulation from heading to maturity, as well as in shoot biomass and nonstructural carbohydrate (NSC) content in the stem at heading and maturity. However, it increased the harvest index and NSC remobilization reserve. Salinity and drought reduced the leaf area index and SPAD value of flag leaves and weakened the leaf photosynthetic characteristics as indicated by lower photosynthetic rates, transpiration rates, and stomatal conductance. These reductions were more pronounced under the combined stress. Salinity, drought, and especially their combination, decreased the activities of ascorbate peroxidase, catalase, and superoxide dismutase, while increasing the contents of malondialdehyde, hydrogen peroxide, and superoxide radical. Our results indicated a more significant yield loss in rice when subjected to combined salinity-drought stress. The individual and combined stresses of salinity and drought diminished antioxidant enzyme activities, inhibited leaf photosynthetic functions, accelerated leaf senescence, and subsequently lowered assimilate accumulation and grain yield.

Exposed anthocyanic leaves of Prunus cerasifera are special shade leaves with high resistance to blue light but low resistance to red light against photoinhibition of photosynthesis.

The photoprotective role of foliar anthocyanins has long been ambiguous: exacerbating, being indifferent to or ameliorating the photoinhibition of photosynthesis. The photoinhibitory light spectrum and failure to separate photo-resistance from repair, as well as the different methods used to quantify the photo-susceptibility of the photosystems, could lead to such a discrepancy. We selected two congeneric deciduous shrubs, Prunus cerasifera with anthocyanic leaves and Prunus triloba with green leaves, grown under identical growth conditions in an open field. The photo-susceptibilities of photosystem II (PSII) and photosystem I (PSI) to red light and blue light, in the presence of lincomycin (to block the repair), of exposed leaves were quantified by a non-intrusive P700+ signal from PSI. Leaf absorption, pigments, gas exchange and Chl a fluorescence were also measured. The content of anthocyanins in red leaves (P. cerasifera) was >13 times greater than that in green leaves (P. triloba). With no difference in maximum quantum efficiency of PSII photochemistry (Fv/Fm) and apparent CO2 quantum yield (AQY) in red light, anthocyanic leaves (P. cerasifera) showed some shade-acclimated suites, including lower Chl a/b ratio, lower photosynthesis rate, lower stomatal conductance and lower PSII/PSI ratio (on an arbitrary scale), compared with green leaves (P. triloba). In the absence of repair of PSII, anthocyanic leaves (P. cerasifera) showed a rate coefficient of PSII photoinactivation (ki) that was 1.8 times higher than that of green leaves (P. triloba) under red light, but significantly lower (-18 %) under blue light. PSI of both types of leaves was not photoinactivated under blue or red light. In the absence of repair, anthocyanic leaves exhibited an exacerbation of PSII photoinactivation under red light and a mitigation under blue light, which can partially reconcile the existing controversy in terms of the photoprotection by anthocyanins. Overall, the results demonstrate that appropriate methodology applied to test the photoprotection hypothesis of anthocyanins is critical.

Salinity‐induced limits to mangrove canopy height

AbstractAimMangrove canopy height is a key metric to assess tidal forests' resilience in the face of climate change. In terrestrial forests, tree height is primarily determined by water availability, plant hydraulic design, and disturbance regime. However, the role of water stress remains elusive in tidal environments, where saturated soils are prevalent, and salinity can substantially affect the soil water potential.LocationGlobal.Time PeriodThe canopy height dataset provides a global snapshot of the maximum mangrove height geographical distribution for the year 2000. Climate and environmental variables extend over the period 1970–2018.Major Taxa StudiedMangroves.MethodsWe use global observations of maximum canopy height, species richness, air temperature, and seawater salinity—a proxy of soil water salt concentration—to explore the causal link between salinity and mangrove stature.ResultsOur findings suggest that salt stress limits mangrove height. High salinity favours more salt‐tolerant species, narrowing the spectrum of viable traits. Highly salt‐tolerant mangroves have evolved to cope with high salt concentrations in the soil, but this adaptation comes at a cost. They typically have lower rates of photosynthesis and growth, resulting in reduced productivity and smaller stature compared to more salt‐sensitive mangrove species. This suggests a causal link between salinity, biodiversity, and tree height, where high salinity selects for more salt‐tolerant species that tend to be less productive and shorter.ConclusionsWe hypothesize that the salinity‐induced limit to mangrove canopy height is the direct result of a reduction of primary productivity, an increment in the risk of xylem cavitation, and an indirect consequence of the decrease in biodiversity. As sea‐level rise enhances coastal salinisation, failure to account for these effects can lead to incorrect estimates of future carbon stocks in Tropical coastal ecosystems and endanger preservation efforts.

Physiological, transcriptome and co-expression network analysis of chlorophyll-deficient mutants in flue-cured tobacco

BackgroundPhotosynthetic pigments in higher plants, including chlorophyll (Chl) and carotenoids, are crucial for photosynthesis and photoprotection. Chl-deficient tobacco seedlings generally have a lower photosynthesis rate and higher nitrate-nitrogen (NO3-N) content, which causes a profound influence on tobacco yield and quality. In this study, a stable albino leaf mutant (Al) and slight-green leaf mutant (SG) obtained from the common flue-cured tobacco (Nicotiana tabacum L.) cultivar ‘Zhongyan 100’ (ZY100) by mutagenesis with ethyl methanesulfonate (EMS) were used as materials. The differences between the Chl-deficient mutants and the wild-type (WT) were analyzed in terms of biomass, photosynthetic fluorescence parameters, and carbon- and nitrogen-related physiological parameters. RNA sequencing (RNA-seq) and weighted gene co-expression network analysis (WGCNA) were used to explore the key pathways and candidate genes regulating differentiated chlorophyll and nitrate content.ResultsThe results showed that, when compared to the WT, the Chl content and biomass of mutant plants were considerably lower while the NO3-N content was substantially elevated. The net photosynthetic rate, photosynthetic fluorescence parameters, carbohydrate, soluble protein, and carbon- and nitrogen-related enzyme activities all decreased in leaves of mutants and the development of chloroplasts was abnormal. Applying more nitrogen improved the growth and development of mutants, whereas NO3-N content distinctively increased compared with that of the WT. Through transcriptome sequencing, the downregulated genes in mutants were enriched in plant hormone signal transduction and nitrogen metabolism, which are involved in pigment biosynthesis and the carbon fixation pathway. In addition, two hub genes and seven transcription factors identified from the blue module through WGCNA were likely to be key candidate factors involved in chlorophyll synthesis and nitrate accumulation.ConclusionOur results demonstrated that differences in chlorophyll and nitrate content were caused by the combined effects of chloroplast development, photosynthesis, as well as related biological activity. In addition, transcriptome results provide a bioinformatics resource for further functional identification of key pathways and genes responsible for differences in chlorophyll and nitrate content in tobacco plants.

Assessment of Biometric Parameters and Health of Canna’s Cultivars as Plant Useful in Phytoremediation of Degraded Agrocenoses

Recently, the ecological awareness of society and the need to take care of our surroundings and the natural environment has significantly increased. There is also an urgent problem of searching for new, environmentally friendly techniques for its purification (soil, ground and surface waters, sewage sludge and air) with the use of living organisms, especially higher plants. One plant species investigated for phytoremediation is canna. Ten varieties of canna, grown on degraded and garden soil, were tested in this respect. The disease index and species composition of fungi inhabiting its organs, growth dynamics, parameters of photosynthesis and gas exchange were determined. The conducted research showed that cannas are able to satisfactorily grow even in seemingly unfavorable soil conditions with its strong degradation. Among a total of 24 species of fungi obtained from its organs, genus Fusarium, considered as pathogenic for canna, Alternaria alternata, and, less frequently, Thanatephorus cucumeris and Botrytis cinerea, dominated. The cultivars ‘Picasso’, ‘Cherry Red’, ‘President’ and ‘La Boheme’ had lower rates of photosynthesis and gas exchange than the least affected ‘Botanica’, ‘Wyoming’, ‘Robert Kemp’ and ‘Lucifer’ cultivars. Those turned out to be the most beneficial and they can be recommended for cultivation on strongly degenerated soils.

Physiological performance of green soybean seeds: a systematic review

The production of seeds, mainly of oilseed species, requires that the stages of maturation and harvest occur under optimal conditions, with mild temperatures and dry climatic conditions, avoiding biotic or abiotic stresses, which result in premature death or forced maturation, producing seeds and grains. greenish, with reduced physiological and organoleptic qualities. Greenish seeds are the result of very rapid translocation of reserves and lower rates of photosynthesis, preventing chlorophyll degradation. These levels of chlorophyll present in the seeds can be affected by the genotype and the climate, being an enzymatic process, evidenced by the increase of chlorylides, resulting in an increase of pheophytins and other derivatives. Green seeds, when destined for the production of vegetable oil, resulted in a product with higher acidity and higher refining cost.

Promoter replacement of ANT1 induces anthocyanin accumulation and triggers the shade avoidance response through developmental, physiological and metabolic reprogramming in tomato.

The accumulation of anthocyanins is a well-known response to abiotic stresses in many plant species. However, the effects of anthocyanin accumulation on light absorbance and photosynthesis are unknown . Here, we addressed this question using a promoter replacement line of tomato constitutively expressing a MYB transcription factor (ANTHOCYANIN1, ANT1) that leads to anthocyanin accumulation. ANT1-overexpressing plants displayed traits associated with shade avoidance response: thinner leaves, lower seed germination rate, suppressed side branching, increased chlorophyll concentration, and lower photosynthesis rates than the wild type. Anthocyanin-rich leaves exhibited higher absorbance of light in the blue and red ends of the spectrum, while higher anthocyanin content in leaves provided photoprotection to high irradiance. Analyses of gene expression and primary metabolites content showed that anthocyanin accumulation produces a reconfiguration of transcriptional and metabolic networks that is consistent with, but not identical to those described for the shade avoidance response. Our results provide novel insights about how anthocyanins accumulation affects the trade-off between photoprotection and growth.

Rice β-Glucosidase 4 (Os1βGlu4) Regulates the Hull Pigmentation via Accumulation of Salicylic Acid.

Salicylic acid (SA) is a stress hormone synthesized in phenylalanine ammonia-lyase (PAL) and the branching acid pathway. SA has two interconvertible forms in plants: SAG (SA O-β-glucoside) and SA (free form). The molecular mechanism of conversion of SA to SAG had been reported previously. However, which genes regulate SAG to SA remained unknown. Here, we report a cytoplasmic β-glucosidase (β-Glu) which participates in the SA pathway and is involved in the brown hull pigmentation in rice grain. In the current study, an EMS-generated mutant brown hull 1 (bh1) displayed decreased contents of SA in hulls, a lower photosynthesis rate, and high-temperature sensitivity compared to the wild type (WT). A plaque-like phenotype (brown pigmentation) was present on the hulls of bh1, which causes a significant decrease in the seed setting rate. Genetic analysis revealed a mutation in LOC_Os01g67220, which encodes a cytoplasmic Os1βGlu4. The knock-out lines displayed the phenotype of brown pigmentation on hulls and decreased seed setting rate comparable with bh1. Overexpression and complementation lines of Os1βGlu4 restored the phenotype of hulls and normal seed setting rate comparable with WT. Subcellular localization revealed that the protein of Os1βGlu4 was localized in the cytoplasm. In contrast to WT, bh1 could not hydrolyze SAG into SA in vivo. Together, our results revealed the novel role of Os1βGlu4 in the accumulation of flavonoids in hulls by regulating the level of free SA in the cellular pool.

Plastid development of albino viviparous propagules in the woody mangrove species of Kandelia obovata.

The process of plastids developing into chloroplasts is critical for plants to survive. However, this process in woody plants is less understood. Kandelia obovata Sheue, Liu & Yong is a viviparous mangrove species; the seeds germinate on the maternal tree, and the hypocotyls continue to develop into mature propagules. We identified rare albino propagules through field observation among normal green and brown ones. Toward unveiling the propagule plastid development mechanism, albino propagule leaves only have etioplasts, low photosynthesis rates, and drastically reduced chlorophyll a/b and carotenoid contents, but with increased superoxide dismutase activities. To identify candidate genes controlling propagule plastid development, a genome-wide association study (GWAS) was performed between the albino and green propagules. Twenty-five significant single nucleotide polymorphisms (SNPs) were associated with albino propagule plastid development, the most significant SNPs being located on chromosomes 1 and 5. Significant differentially expressed genes were identified in porphyrin and chlorophyll metabolisms, carotenoid and flavonoid biosynthesis by combining transcriptome and GWAS data. In particular, KoDELLAs, encoding a transcription factor and KoCHS, encoding chalcone synthase, may be essential to regulate the albino propagules plastid development through weakened chlorophyll and flavonoid biosynthesis pathways while promoting chlorophyll degradation. Our results provide insights into genetic mechanisms regulating propagule plastid development in woody plants.

Molecular, physiological and agronomic assessment of genetic diversity in rice varieties in relation to drought treatment

The study presents the morpho-physiological performance under induced drought condition and molecular marker based genetic variability amongst 13 rice varieties released for cultivation in Uttar Pradesh, India. An attempt was made to identify suitable genotypes for drought affected areas, based on their morpho-physiological characteristics and genetic diversity. The physiological parameters of photosynthesis rate (A), transpiration rate (E), water use efficiency (WUE), along with the yield parameters and genetic diversity by simple sequence repeats marker (SSR) profile were analysed. The rice varieties PR-115 and PR-113 exhibited high water use efficiency, suggesting its possible advantageous response to drought due to low transpiration and high rate of net photosynthesis. The varieties, PR-115 and PR-113 were also found to be best performer in terms of yield under drought conditions. However, the more widely cultivated varieties namely Basmati, IR-36 and IR-20 were found to be intermediate in their response to drought for both yield and physiological parameters. The 19 simple sequence repeats marker (SSR) produces a total of 64 alleles across the 13 varieties, with alleles ranging from 2 to 7 per locus (average 3 alleles). The Polymorphic information content (PIC) value ranged from 0.13 to 0.78 with an average of 0.45 ± 0.19.

Phytoplankton primary production: 14C-in situ and 14C-incubator methods compared

Abstract We estimated phytoplankton depth-integrated primary production rates at an open sea station in the northern Baltic Proper in 2004–2009 by parallel in situ and ship-board incubations in an “ICES incubator”. Observations were strongly linearly related (r2 = 0.67, p < 0.00001) and produced similar seasonal signals, but incubator estimates were significantly lower in spring (∼5–20%, March–May) and summer (∼30%, June–August), but not in autumn (September–October). Incubator PBmax was significantly lower in all seasons (∼10, 23, and 14% in spring, summer, and autumn), and the initial slope of the PB/E-curve (αB) was two-thirds of in-situ αB in spring and autumn, and half in summer, but not significantly different in autumn, and had an order of magnitude lower standard deviation. Parallel incubations of mixed 0–10 m hose samples at discrete depths in situ and in the incubator gave similar differences in PBmax and αB. This strongly suggests that the main factor causing the lower photosynthesis rates in the incubator was light quality, since all other potential sources of variability were similar. However, we cannot rule out that the lower incubator PBmax was partly due to insufficient light compared to in situ, particularly in summer. Our results suggest that a major challenge to the harmonization of 14C in situ, and artificial light and deck incubator measurements, is to simulate spectral composition changes with depth or, alternatively, use phytoplankton action spectra or constructed action spectra that are less complicated and time-consuming to establish (Kyewalyanga et al., 1997).

Foliar respiration is related to photosynthetic, growth and carbohydrate response to experimental drought and elevated temperature.

Short-term plant respiration (R) increases exponentially with rising temperature, but drought could reduce respiration by reducing growth and metabolism. Acclimation may alter these responses. We examined if species with different drought responses would differ in foliar R response to +4.8°C temperature and -45% precipitation in a field experiment with mature piñon and juniper trees, and if any differences between species were related to differences in photosynthesis rates, shoot growth and nonstructural carbohydrates (NSCs). Short-term foliar R had a Q10 of 1.6 for piñon and 2.6 for juniper. Piñon foliar R did not respond to the +4.8°C temperatures, but R increased 1.4× for juniper. Across treatments, piñon foliage had higher growth, lower NSC content, 29% lower photosynthesis rates, and 44% lower R than juniper. Removing 45% precipitation had little impact on R for either species. Species differences in the response of R under elevated temperature were related to substrate availability and stomatal response to leaf water potential. Despite not acclimating to the higher temperature and having higher R than piñon, greater substrate availability in juniper suggests it could supply respiratory demand for much longer than piñon. Species responses will be critical in ecosystem response to a warmer climate.

Exogenous ethylene reduces growth via alterations in central metabolism and cell wall composition in tomato (Solanum lycopersicum)

Ethylene is a gaseous hormone with a well-established role in the regulation of plant growth and development. However, its role in the modulation of carbon assimilation and central metabolism remains unclear. Here, we investigated the morphophysiological and biochemical responses of tomato plants (Solanum lycopersicum) following the application of ethylene in the form of ethephon (CEPA - 2-chloroethylphosphonic acid), forcing the classical triple response phenotype. CEPA-treated plants were characterized by growth inhibition, as revealed by significant reductions in both shoot and root dry weights, coupled with a reduced number of leaves and lower specific leaf area. Growth inhibition was associated with a reduction in carbon assimilation due to both lower photosynthesis rates and stomatal conductance, coupled with impairments in carbohydrate turnover. Furthermore, exogenous ethylene led to the accumulation of cell wall compounds (i.e., cellulose and lignin) and phenolics, indicating that exposure to exogenous ethylene also led to changes in specialized metabolism. Collectively, our findings demonstrate that exogenous ethylene disrupts plant growth and leaf structure by affecting both central and specialized metabolism, especially that involved in carbohydrate turnover and cell wall biosynthesis, ultimately leading to metabolic responses that mimic stress situations.

Early Shoot Development Affects Carbohydrate Supply and Fruit Quality of Red-Fleshed Actinidia chinensis var. chinensis ‘Zes008’

Fruit quality characteristics are highly variable across kiwifruit vines due to complex source-sink interactions. We investigated how variation in fruit quality of Actinidia chinensis (Planch.) var. chinensis ‘Zes008’ was influenced by different shoot types (short, medium or long) and rootstocks types (Actinidia chinensis (Planch.) var. deliciosa (A. Chev.) ‘Bruno’ or Actinidia macrosperma C.F. Liang). Short shoots had smaller leaves (−30 to −50%) and lower photosynthesis rates (−0.70 to −3.34 µmol m−2 s−1) in the first cluster of nine leaves (Zone 1) compared with leaves on medium or long shoots. Later in the season, photosynthesis rates in Zone 1 declined with leaf age, but photosynthesis rates were higher (+0.5 to +6.1 µmol m−2 s−1) in later developing leaves on medium or long shoots. Fruit from short shoots had lower dry matter (−0.3 percent units) and lower outer pericarp flesh red pigment scores than fruit from medium or long shoots. At harvest, fruit from vines on ‘Bruno’ rootstocks were larger (+3.7 g), had higher dry matter (+1.3 percent units), soluble solids concentration (+1.7° Brix) and firmness (+0.4 kgf) than fruit from vines on A. macrosperma rootstocks. Factors that prioritised early development of source leaves had a direct impact on the carbohydrate supply from photosynthesis to support flower and fruit development.

The apple DNA-binding one zinc-finger protein MdDof54 promotes drought resistance

DNA-binding one zinc-finger (Dof) proteins constitute a family of transcription factors with a highly conserved Dof domain that contains a C2C2 zinc-finger motif. Although several studies have demonstrated that Dof proteins are involved in multiple plant processes, including development and stress resistance, the functions of these proteins in drought stress resistance are largely unknown. Here, we report the identification of the MdDof54 gene from apple and document its positive roles in apple drought resistance. After long-term drought stress, compared with nontransgenic plants, MdDof54 RNAi plants had significantly shorter heights and weaker root systems; the transgenic plants also had lower shoot and root hydraulic conductivity, as well as lower photosynthesis rates. By contrast, compared with nontransgenic plants, MdDof54-overexpressing plants had higher photosynthesis rates and shoot hydraulic conductivity under long-term drought stress. Moreover, compared with nontransgenic plants, MdDof54-overexpressing plants had higher survival percentages under short-term drought stress, whereas MdDof54 RNAi plants had lower survival percentages. MdDof54 RNAi plants showed significant downregulation of 99 genes and significant upregulation of 992 genes in response to drought, and 366 of these genes were responsive to drought. We used DAP-seq and ChIP-seq analyses to demonstrate that MdDof54 recognizes cis-elements that contain an AAAG motif. Taken together, our results provide new information on the functions of MdDof54 in plant drought stress resistance as well as resources for apple breeding aimed at the improvement of drought resistance.

Bacterial production prevails over photo- and chemosynthesis in a eutrophic tropical lagoon

Dark carbon fixation is a combination of processes performed by microorganisms to fix inorganic carbon driven the energy generated by chemical reactions. Our study quantified microbial primary and secondary production rates to evaluate the relative importance of dark carbon fixation in relation to photosynthetic rates and heterotrophic bacterial production and their contribution to the carbon cycle in a tropical eutrophic and human-impacted lagoon (Rodrigo de Freitas Lagoon, Brazil). Samples were collected daily at a fixed point to assess short-term temporal variations and at six different stations to assess spatial variability. Water samples were incubated using 14C-bicarbonate at 100% of light and in the dark to quantify photosynthesis and dark carbon fixation, respectively; and 3H-leucine incubations were performed to measure bacterial production. Environmental parameters (temperature, salinity, dissolved oxygen, dissolved organic carbon and inorganic nutrients) were measured to characterize the hydrology of the studied area, and to evaluate their influence on the microbial production rates. There were no significant changes in production rates over time or within different depths. Bacterial production rates varied significantly over space, and were correlated with nitrogen compounds, temperature, salinity and pH. However, a short rainfall event, although not strong or extreme, promoted rapid changes in the shallow water column, such as a decrease in temperature and nitrogen compounds, inducing responses to microbial production rates, such as higher rates of dark carbon fixation and bacterial production at the bottom and lower rates of photosynthesis. Heterotrophic bacterial production was significantly higher than dark and light carbon fixation, being the most important carbon-cycling process in Rodrigo de Freitas Lagoon, possibly favored by the high allochthonous organic matter and nutrient inputs. This study showed that, on average, dark carbon fixation accounted for 30% at the surface and 43% near the bottom of the total primary production and up to 10% of heterotrophic production in the water column, which may be related to the availability of ammonia and methane. We concluded that, even for this short-term temporal and spatial assessment, dark carbon fixation is relevant, although usually disregarded, and this process should be taken into account when evaluating carbon budgets, metabolic balance and ecosystem functioning in tropical coastal lagoons.

Born to revive: molecular and physiological mechanisms of double tolerance in a paleotropical and resurrection plant.

Resurrection plants recover physiological functions after complete desiccation. Almost all of them are native to tropical warm environments. However, the Gesneriaceae include four genera, remnant of the past palaeotropical flora, which inhabit temperate mountains. One of these species is additionally freezing-tolerant: Ramonda myconi. We hypothesise that this species has been able to persist in a colder climate thanks to some resurrection-linked traits. To disentangle the physiological mechanisms underpinning multistress tolerance to desiccation and freezing, we conducted an exhaustive seasonal assessment of photosynthesis (gas exchange, limitations to partitioning, photochemistry and galactolipids) and primary metabolism (through metabolomics) in two natural populations at different elevations. R.myconi displayed low rates of photosynthesis, largely due to mesophyll limitation. However, plants were photosynthetically active throughout the year, excluding a reversible desiccation period. Common responses to desiccation and low temperature involved chloroplast protection: enhanced thermal energy dissipation, higher carotenoid to Chl ratio and de-epoxidation of the xanthophyll cycle. As specific responses, antioxidants and secondary metabolic routes rose upon desiccation, while putrescine, proline and a variety of sugars rose in winter. The data suggest conserved mechanisms to cope with photo-oxidation during desiccation and cold events, while additional metabolic mechanisms may have evolved as specific adaptations to cold during recent glaciations.

Nutrient uptake of different contingent crops under delayed sowings in changed climate in rainfed agriculture

A field experiment was conducted during kharif 2018 at Dryland Agriculture Project, All India Coordinated Research Project (AICRP) on Dryland Agriculture, University of Agricultural Sciences, GKVK, Bengaluru, Karnataka. The experiment comprised of two factors laid out in Factorial Randomized Complete Block Design (FRCBD) with three replications. Treatments consist of three sowing windows viz., August 2nd fortnight, September 1st fortnight and September 2nd fortnight and five crops viz foxtail millet, finger millet, field bean, french bean and quiona. Delayed dates of sowing caused drop in growth parameters which may be due to unfavorable weather conditions to the plants as well as high temperature which might have caused in lower rate of photosynthesis and lower uptake of nutrients led to reduced accumulation of food materials. Among the contingent crops and delayed sowings in kharif season under dryland condition, August 2nd fortnight sowing recorded significantly higher availability of nitrogen, phosphorous and potassium by crops and it was decreasing with delayed sowing of contingent crops. Field bean and french bean were improved the availability of nutrients in the soil after the harvest of crops than remaining crops.

Chloroplastic Os3BGlu6 contributes significantly to cellular ABA pools and impacts drought tolerance and photosynthesis in rice.

Cellular abscisic acid (ABA) concentration is determined by both de novo biosynthesis and recycling via β-glucosidase(s). However, which rice β-glucosidase(s) are involved in this process remains unknown. Here, we report on a chloroplastic β-glucosidase isoenzyme, Os3BGlu6, that functions in ABA recycling in rice. Disruption of Os3BGlu6 in rice resulted in dwarfism, lower ABA content in leaves, drought-sensitivity, lower photosynthesis rate and higher intercellular CO2 concentration. Os3BGlu6 could hydrolyze ABA-GE to ABA in vitro. The reversion and overexpression rice lines restored or increased the drought tolerance as shown by the higher β-glucosidase activity, ABA concentrations and expressions of ABA- and drought-responsive genes. Drought induced Os3BGlu6 to form dimers, and the degree of polymerization correlated well with the increase in cellular ABA concentrations and drought tolerance in rice. Os3BGlu6 was responsive to drought and ABA treatments, and the protein was localized to the chloroplast. Disruption of Os3BGlu6 resulted in the increased stomatal density and impaired stomatal movement. Transcriptomics revealed that disruption of Os3BGlu6 resulted in chloroplastic oxidative stress and lowered Rubisco activity even under normal conditions. Taken together, these results suggest that chloroplastically localized Os3BGlu6 significantly affects cellular ABA pools, thereby affecting drought tolerance and photosynthesis in rice.