Higher Photosynthetic Efficiency Research Articles

Renewable Sources of Plant Biostimulation: Microalgae as a Sustainable Means to Improve Crop Performance.

Plant biostimulants (PBs) attract interest in modern agriculture as a tool to enhance crop performance, resilience to environmental stress, and nutrient use efficiency. PBs encompass diverse organic and inorganic substances (humic acids and protein hydrolysates) as well as prokaryotes (e.g., plant growth promoting bacteria) and eukaryotes such as mycorrhiza and macroalgae (seaweed). Microalgae, which comprise eukaryotic and prokaryotic cyanobacteria (blue-green algae), are attracting growing interest from scientists, extension specialists, private industry and plant growers because of their versatile nature: simple unicellular structure, high photosynthetic efficiency, ability for heterotrophic growth, adaptability to domestic and industrial wastewater, amenability to metabolic engineering, and possibility to yield valuable co-products. On the other hand, large-scale biomass production and harvesting still represent a bottleneck for some applications. Although it is long known that microalgae produce several complex macromolecules that are active on higher plants, their targeted applications in crop science is still in its infancy. This paper presents an overview of the main extraction methods from microalgae, their bioactive compounds, and application methods in agriculture. Mechanisms of biostimulation that influence plant performance, physiology, resilience to abiotic stress as well as the plant microbiome are also outlined. Considering current state-of-the-art, perspectives for future research on microalgae-based biostimulants are discussed, ranging from the development of crop-tailored, highly effective products to their application for increasing sustainability in agriculture.

Fuzzy comprehensive evaluation of the effects of relative air humidity on the morpho-physiological traits of Pakchoi (Brassica chinensis L.) under high temperature

This study was conducted to investigate the effects of relative air humidity (RH) on morphological and physiological traits of Pakchoi (Brassica chinensis L.) under high temperature. Pakchoi was planted in climate chambers at 35/28 °C, day / night temperature, and the RH levels were 20%, 40%, 60%, 80%, and 95%. Most growth parameters peaked at 40–60% RH under high temperature. Biomass, leaf area, net photosynthetic rate (Pn), soluble sugar, and vitamin C were the highest at 60% RH, whereas total chlorophyll content, transpiration rate, and leaf air temperature were the highest at 40% RH. Superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities were the highest at 80% RH. All the above properties showed the lowest value at 95% RH. Malondialdehyde (MDA) peaked at 95% RH, and severe chlorosis was observed simultaneously. Based on our fuzzy comprehensive evaluation, the fuzzy value of production and intrinsic quality was the highest at 60% RH and lowest at 95% RH. RH does affect the temperature difference between leaf and air from the change of transpiration. Excessively high or low RH caused a significant reduction in biomass production and intrinsic quality. We found that 60% RH was the optimum level for growth of Pakchoi at high temperature. With 95% RH, the Pakchoi was damaged under high temperature; Pn, SOD, CAT, and POD activities were the lowest; and MDA content was the highest. Results suggested that proper RH level could reduce leaf temperature and maintain stomatal conductance, thereby maintaining the high yield of Pakchoi via higher photosynthetic efficiency at high temperature.

High photosynthetic rates associated with pico and nanophytoplankton communities and high stratification index in the North West Atlantic

The biological dynamics of pelagic marine ecosystems are strongly influenced by the size structure and ecological succession of phytoplankton, which in turn modifies photosynthetic efficiency. Variability in photosynthetic rates is closely coupled with changes in community structure, but it is difficult to obtain coincident data at high enough resolution to characterise these changes. In this study, we employ hierarchical cluster analysis on chlorophyll-normalised high performance liquid chromatography (HPLC) pigment concentrations from the North West Atlantic, to identify seasonal successional trends amongst phytoplankton populations. Changes in phytoplankton community were also analysed as a function of mean equivalent spherical diameter (MESD) derived from absorption measurements, photosynthetic rates, water-column stratification and temperature. Well-mixed conditions in spring to early summer were associated with populations of large cells containing high concentrations of fucoxanthin, chlorophyll-c1 and chlorophyll-c2 relative to chlorophyll-a (Chl a). As stratification increased over the course of the summer, these cells were replaced by populations dominated by chlorophyll-b, 19'-hexanoyloxyfucoxanthin, 19'-butanoyloxyfucoxanthin and divinyl chlorophyll-a, indicative of small picophytoplankton. As stratification decreased in autumn, MESD and alloxanthin increased, suggesting the presence of cryptophytes. Positive relationships were found between MESD and the quantum yield of photosynthesis (φm) for 7 out of the 8 phytoplankton clusters identified, while negative relationships between mean mixed layer photosynthetically active radiation and φm and the light limited slope of photosynthesis (αB) were observed for 4 clusters, as a result of nutrient limitation and photo-protection. The highest photosynthetic rates were associated with a pico & nanophytoplankton communities, which increased from spring to late summer as stratification intensified. By contrast, diatom communities had the lowest photosynthetic rates throughout the year. These successional patterns in the dominant phytoplankton size-class and phenology support Margalef's mandala in terms of the relationship between turbulence and community structure. The study sheds new light on assemblages dominated by smaller cells, under warm, stratified conditions, having higher photosynthetic efficiencies, which has implications for the carbon flux in the NW Atlantic.

Photoacclimation of Arctic Ocean phytoplankton to shifting light and nutrient limitation

AbstractAs the physical environment of the Arctic Ocean shifts seasonally from ice‐covered to open water, the limiting resource for phytoplankton growth shifts from light to nutrients. To understand the phytoplankton photophysiological responses to these environmental changes, we evaluated photoacclimation strategies of phytoplankton during the low‐light, high‐nutrient, ice‐covered spring and the high‐light, low‐nutrient, ice‐free summer. Field results show that phytoplankton effectively acclimated to reduced irradiance beneath the sea ice by maximizing light absorption and photosynthetic capacity. In fact, exceptionally high maximum photosynthetic rates and efficiency observed during the spring demonstrate that abundant nutrients enable prebloom phytoplankton to become “primed” for increases in irradiance. This ability to quickly exploit increasing irradiance can help explain the ability of phytoplankton to generate massive blooms beneath sea ice. In comparison, phytoplankton growth and photosynthetic rates are reduced postbloom due to severe nutrient limitation. These results advance our knowledge of photoacclimation by polar phytoplankton in extreme environmental conditions and indicate how phytoplankton may acclimate to future changes in light and nutrient resources under continued climate change.

Compatibility of tomato cultivar Santa Cruz Kada grafted on different Solanaceae species and control of bacterial wilt

ABSTRACT The objective of this work was to evaluate the compatibility, gas exchange and yield of tomato cultivar Santa Cruz Kada, susceptible to bacterial wilt (Ralstonia solanacearum) when grafted on different Solanaceae species. Rootstock sources were the mini-tomato RVTC-66, Cayenne pepper, Jerusalem cherry (Solanum pseudocapsicum), sticky nightshade (Solanum sisymbriifolium), and cultivar Santa Cruz Kada itself (self-grafting). Two materials were tested to promote the union between rootstocks and scions: grafting clips and biodegradable tape (Parafilm). Grafting success index (GSI) was evaluated and, for treatments using biodegradable tape, grafting incompatibility, gas exchange, agronomic characteristics and bacterial wilt epidemiology were assessed throughout the cycle. The use of biodegradable tape favored graft healing. Cayenne pepper, Jerusalem cherry, and sticky nightshade should not be employed as rootstocks for scions of tomato cultivar Santa Cruz Kada. The mini-tomato accession RVTC-66 showed low graft incompatibility, high photosynthetic efficiency and, when compared to self-grafting, the same fruit production, but with higher plant health index concerning the bacterial wilt.

Exogenous melatonin enhances salt stress tolerance in maize seedlings by improving antioxidant and photosynthetic capacity.

Melatonin (N-acetyl-5-methoxytryptamine) is an important biological hormone in many abiotic stress responses and developmental processes. In this study, the protective roles of melatonin were investigated by measuring the antioxidant defense system and photosynthetic characteristics in maize under salt stress. The results indicated that NaCl treatment led to the decrease in plant growth, chlorophyll contents and photochemical activity of photosystem II (PSII). However, the levels of reactive oxygen species increased significantly under salt stress. Meanwhile, we found that application of exogenous melatonin alleviated reactive oxygen species burst and protected the photosynthetic activity in maize seedlings under salt stress through the activation of antioxidant enzymes. In addition, 100 μM melatonin-treated plants showed high photosynthetic efficiency and salinity. Immunoblotting analysis of PSII proteins showed that melatonin application alleviated the decline of 34 kDa PSII reaction center protein (D1) and the increase of PSII subunit S protein. Taken together, our study promotes more comprehensive understanding in the protective effects of exogenous melatonin in maize under salt stress, and it may be involved in activation of antioxidant enzymes and regulation of PSII proteins.

Functional and ecophysiological traits of Halimione portulacoides and Sarcocornia perennis ecotypes in Mediterranean salt marshes under different tidal exposures

AbstractThe present paper aims to discuss the functional and ecophysiological traits of two abundant succulent halophytes in Mediterranean salt marsh systems, considering two ecotypes differing on their tidal exposure. In Halimione portulacoides the higher root/shoot (R/S) biomass ratio verified in low inundation frequency (LF) marshes, as compared with that in high inundation frequency (HF), indicates an optimal partitioning strategy, inducing differential allocation patterns along with varying environmental factors. Conversely, Sarcocornia perennis appear to have an isometric allocation strategy, based on intrinsic biomass allocation mechanisms independent from the surrounding environmental conditions. Similarly, the photosynthetic traits appear to reflect the intrinsic ecology of the species. Sarcocornia perennis habitat adaptation to HF conditions is clearly revealed by its high photosynthetic efficiency under HF conditions. On the other hand, the cosmopolitan H. portulacoides shows no differences between ecotypes, in which concerns this trait, mostly due to the high carotenoid content of the HF ecotype, which allows this specie to counteract the stress generated during submersion. Additionally, anti‐oxidant enzymatic activities revealed that S. perennis presents a high degree of stress tolerance under HF conditions, while H. portulacoides is highly adapted to LF conditions. These functional (biomass‐related) and physiological traits determine the optimal habitats for H. portulacoides and S. perennis. While H. portulacoides optimal biomass partitioning, along with its efficient anti‐oxidant defence system, makes this species fitter to LF conditions, S. perennis isometric allocation strategy, along with a higher photosynthetic efficiency under frequent flooding conditions, provides this species the mechanisms to efficiently colonize the intertidal habitat.

Microalgae: Potential precursors of CO2 adsorbents

With faster growth rates and higher photosynthetic efficiencies than other terrestrial plants, microalgae biomass could be considered as a green, low-cost, alternative carbon source. This paper explores the potential use of various species of microalgae as activated carbon precursors. Chlorella and Spirulina were evaluated both as freeze-dried microalgae and in fresh paste form, while Acutodesmus Obliquus and Coelastrella sp. were studied only as paste.Activated carbons were produced using the selected species of microalgae as well as mixtures of pine sawdust and microalgae. Two different preparation routes were compared: with and without hydrothermal carbonization pretreatment before physical activation with CO2 in a single step. All samples were conformed into pellets prior to CO2 activation.The CO2 adsorption capacity of the microalgae derived carbons was assessed in conditions representative of a flue gas (10.5 vol.% CO2 at atmospheric pressure and 50 °C). Significant differences in terms of CO2 adsorption capacity, carbon yield and pellet density were obtained among the species studied. These preliminary results showed that activated carbons produced from microalgae mixed with pine sawdust and directly activated with CO2 are among the most promising adsorbents to capture CO2 from flue gas.

Redirecting carbon to bioproduction via a growth arrest switch in a sucrose-secreting cyanobacterium

Cyanobacteria are microbes with high photosynthetic efficiencies, making them a promising target for the production of sustainable bioproducts directly from solar energy and carbon dioxide. The most common efforts to increase cyanobacterial bioproduction involve diverting cellular resources away from cellular biomass and towards a heterologous pathway, for example through nutrient starvation or knockout of genes in competing metabolic pathways. Here we show that an inducible cell growth arrest switch can be used to increase the partitioning of carbon to an engineered sucrose sink. Specifically, we show that overexpression of Regulator of Phycobilisome-Associated B (RpaB), an essential response regulator in Synechococccous elongatus PCC 7942, allows for inducible arrest of cell growth and is associated with a > 2-fold higher specific productivity of a heterologous sucrose secretion pathway. Finally, we show that sucrose export can partially relieve photosynthetic feedback inhibition imposed by the RpaB dependent growth arrest, allowing sucrose-secreting strains to maintain higher photosynthetic efficiencies. This work provides a novel conceptual framework for improving photosynthetic productivity and cyanobacterial bioproduction.

Eudicots from severely phosphorus-impoverished environments preferentially allocate phosphorus to their mesophyll.

Plants allocate nutrients to specific leaf cell types, with commelinoid monocots preferentially allocating phosphorus (P) to the mesophyll and calcium (Ca) to the epidermis, whereas the opposite is thought to occur in eudicots. However, Proteaceae from severely P-impoverished habitats present the same P-allocation pattern as monocots. This raises the question of whether preferential P allocation to mesophyll cells is a phylogenetically conserved trait, exclusive to commelinoid monocots and a few Proteaceae, or a trait that has evolved multiple times to allow plants to cope with very low soil P availability. We analysed the P-allocation patterns of 16 species from 10 genera, eight families and six orders within three major clades of eudicots across different P-impoverished environments in Australia and Brazil, using elemental X-ray mapping to quantitatively determine leaf cell-specific nutrient concentrations. Many of the analysed species showed P-allocation patterns that differed substantially from that expected for eudicots. Instead, P-allocation patterns were strongly associated with the P availability in the natural habitat of the species, suggesting a convergent evolution of P-allocation patterns at the cellular level, with P limitation as selective pressure and without a consistent P-allocation pattern within eudicots. Here, we show that most eudicots from severely P-impoverished environments preferentially allocated P to their mesophyll. We surmise that this preferential P allocation to photosynthetically active cells might contribute to the very high photosynthetic P-use efficiency of species adapted to P-impoverished habitats.

GABA Shunt in Durum Wheat.

Plant responses to salinity are complex, especially when combined with other stresses, and involve many changes in gene expression and metabolic fluxes. Until now, plant stress studies have been mainly dealt only with a single stress approach. However, plants exposed to multiple stresses at the same time, a combinatorial approach reflecting real-world scenarios, show tailored responses completely different from the response to the individual stresses, due to the stress-related plasticity of plant genome and to specific metabolic modifications. In this view, recently it has been found that γ-aminobutyric acid (GABA) but not glycine betaine (GB) is accumulated in durum wheat plants under salinity only when it is combined with high nitrate and high light. In these conditions, plants show lower reactive oxygen species levels and higher photosynthetic efficiency than plants under salinity at low light. This is certainly relevant because the most of drought or salinity studies performed on cereal seedlings have been done in growth chambers under controlled culture conditions and artificial lighting set at low light. However, it is very difficult to interpret these data. To unravel the reason of GABA accumulation and its possible mode of action, in this review, all possible roles for GABA shunt under stress are considered, and an additional mechanism of action triggered by salinity and high light suggested.

Evaluation of growth and phycobiliprotein composition of cyanobacteria isolates cultivated in different nitrogen sources

Phycobiliproteins, light-harvesting pigments found in cyanobacteria and in some eukaryotic algae, have numerous commercial applications in food, cosmetic, and pharmaceutical industries. Colorant production from cyanobacteria offers advantages over their production from higher plants, as cyanobacteria have fast growth rate and high photosynthetic efficiency and require less space. In this study, three cyanobacteria strains were studied for phycobiliprotein production and the influence of sodium nitrate, potassium nitrate and ammonium chloride on the growth and phycobiliprotein composition of the strains were evaluated. In the batch culture period of 12 days, Phormidium sp. and Pseudoscillatoria sp. were able to utilize all tested nitrogen sources; however, ammonium chloride was the best nitrogen source for both strains to achieve maximum growth rate μ = 0.284 ± 0.03 and μ = 0.274 ± 0.13 day−1, chlorophyll a 16.2 ± 0.5 and 12.2 ± 0.2 mg L−1, and phycobiliprotein contents 19.38 ± 0.09 and 19.99 ± 0.14% of dry weight, whereas, for Arthrospira platensis, the highest growth rate of μ = 0.304 ± 0.0 day−1, chlorophyll a 19.1 ± 0.5 mg L−1, and phycobiliprotein content of 22.27 ± 0.21% of dry weight were achieved with sodium nitrate. The phycocyanin from the lyophilized cyanobacterial biomass was extracted using calcium chloride and food grade purity (A620/A280 ratio > 0.7) was achieved. Furthermore, phycocyanin was purified using two-step chromatographic method and the analytical grade purity (A620/A280 ratio > 4) was attained. SDS-PAGE demonstrated the purity and presence of two bands corresponding to α- and β-subunits of the C-phycocyanin. The results showed that Phormidium sp. and Pseudoscillatoria sp. could be good candidates for phycocyanin production.

Improved photosynthesis in Arabidopsis roots by activation of GATA transcription factors

Plant cells plastically change their functions according to the environment. Although Arabidopsis roots are heterotrophic organs, they increase photosynthetic capacity after shoot removal. Transcription factors regulating chloroplast development are involved in this response downstream of positive cytokinin and negative auxin regulation. To dissect the crosstalk of these regulators after shoot removal, we analyzed photosynthetic parameters in roots with chloroplast development enhanced by shoot removal, overexpression of transcription factors, or hormonal treatment. Our data suggest that shoot removal improves electron transfer downstream of PSII in roots, with a decrease in nonregulated energy dissipation. Cytokinin, auxin, and transcription factors affect the photosynthetic capacity of roots in a highly complex manner. Overexpression of two different types of transcription factors (GOLDEN 2-LIKE 1 and class-B GATAs) synergistically increased root chlorophyll content while maintaining high photosynthetic efficiency. Our data demonstrate the flexible regulation of the photosynthetic machinery by hormone signaling and downstream transcription factors.

Proteaceae from phosphorus-impoverished habitats preferentially allocate phosphorus to photosynthetic cells: An adaptation improving phosphorus-use efficiency.

Plants allocate nutrients to specific leaf cell types; eudicots are thought to predominantly allocate phosphorus (P) to epidermal/bundle sheath cells. However, three Proteaceae species have been shown to preferentially allocate P to mesophyll cells instead. These Proteaceae species are highly adapted to P-impoverished habitats, with exceptionally high photosynthetic P-use efficiencies (PPUE). We hypothesized that preferential allocation of P to photosynthetic mesophyll cells is an important trait in species adapted to extremely P-impoverished habitats, contributing to their high PPUE. We used elemental X-ray mapping to determine leaf cell-specific nutrient concentrations for 12 Proteaceae species, from habitats of strongly contrasting soil P concentrations, in Australia, Brazil, and Chile. We found that only species from extremely P-impoverished habitats preferentially allocated P to photosynthetic mesophyll cells, suggesting it has evolved as an adaptation to their extremely P-impoverished habitat and that it is not a family-wide trait. Our results highlight the possible role of soil P in driving the evolution of ecologically relevant nutrient allocation patterns and that these patterns cannot be generalized across families. Furthermore, preferential allocation of P to photosynthetic cells may provide new and exciting strategies to improve PPUE in crop species.

Sugarcane can afford a cleaner energy profile in Latin America & Caribbean

Abstract Latin American and Caribbean's (LAC) external dependency on fossil fuels and the pursuit for renewable energy leads to the need for a strategy to afford a cleaner and reliable domestic energy supply. Sugarcane presents high photosynthetic efficiency and it is a well-spread crop in LAC. Our study aims to explore the potential of different approaches of modern energy production from sugarcane, at a national level, and its implication to the environmental aspects. We found that Guatemala, Nicaragua and Cuba would be able to replace 10% of the gasoline and about 2–3% of the diesel consumption by only using the current molasses. With a slight expansion on sugarcane production, Bolivia can replace 20% of the gasoline and diesel, besides providing surplus ethanol for exportation or other purposes. With a minor investment, bagasse may enlarge the electricity access in many countries whereas in other may represent an alternative to replace fossil fuel sources. We also found relevant potential on reducing the GHG emissions specially in Bolivia, Paraguay and Nicaragua. However, the implementation of such strategies must be supported by appropriate policies to ensure competitive prices, overcome opportunity costs, and stimulate investments.

Salinity improves growth, photosynthesis and bioenergy characteristics of Phragmites karka

Based on biomass composition of plants collected from saline habitats, Phragmites karka (Retz.) Trin. ex Steud. has emerged as a suitable feedstock for biofuel. In the present study, plant growth, eco-physiological responses and bioenergy characteristics of P. karka grown under conditions ranging from non-saline to ~80% seawater salinity are reported. Moderate salinity (NaCl at 100 mol m–3) increased plant fresh weight (20%), number of leaves (25%) and specific plant length, which were directly linked with increased net photosynthetic rate (25%) and stomatal conductance (25%) compared with the non-saline control. Higher photosynthetic efficiency was achieved by increasing electron transport rate (ETR, 20%), effective quantum yield (YII, 21%) and maximum efficiency of photosystem II (Fv/Fm, 20%). Decreased non-photochemical quenching (Y(NPQ)) and malondialdehyde content (18%) indicated an oxidative balance, which was also reflected in total carotenoids and chlorophylls. These eco-physiological parameters worked together to increase cellulose (34%) and hemicellulose (70%) at NaCl concentrations up to 200 mol m–3. Decreased growth under higher salinity could be linked with photosynthesis inhibition, due to stomatal closure and co-occurring reduction in CO2 uptake. Lower stomatal conductance increased water-use efficiency but led to over-production of reactive oxygen species, which disturbed oxidative stability (increasing ETR/PN) and imposed membrane leakage. Consequently, plants accumulated more carotenoids and soluble carbohydrates to stabilise PSII machinery (Fv/Fm, YII and Y(NPQ)), and to survive under high salinity. Such adaptations, however, led to growth penalty and reduced quality of lignocellulosic biomass. The above findings suggest that P. karka qualifies as a suitable raw material for biofuel under moderate salinity.

Responses of growth and photosynthetic fluorescent characteristics in Ottelia acuminata to a water-depth gradient

ABSTRACTTo assess the response of Ottelia acuminata to a water-depth gradient, we investigated the plant growth and leaf photosynthesis by setting three water depths (0.5, 1.0, and 1.5 m) in situ in Yilong Lake, Yunnan Province, China. The results showed that the growth and photosynthetic fluorescent characteristics of O. acuminata exhibited different responses to the water-depth gradient. The plant height, fresh weight, root length, and leaf number of O. acuminata, varied significantly with changes in the water depth. With regard to the photosynthetic fluorescent characteristics of leaves, the maximum quantum yield half-saturation light intensity and fluorescence parameter of photosystem II markedly improved with increasing water depth. The increase of photosynthetically active radiation resulted in a decreased photochemical quenching coefficient (qP). In contrast, the nonphotochemical quenching coefficient was relatively high in the leaves of O. acuminata in shallow water under high photosynthetically active radiation. The chlorophyll content of the leaves varied significantly with changes in the water depth. Higher chlorophyll a, chlorophyll b, and carotenoid contents were detected in the leaves of O. acuminata at the water depth of 1.5 m. The results of the growth and photosynthetic fluorescent characteristics of O. acuminata indicate a better protection mechanism against high light in the leaves of O. acuminata in shallow water and a higher photosynthetic efficiency, as well as a greater photosynthetic potential, in the leaves of O. acuminata in deep water.

Physiological and transcriptomic analyses of a yellow-green mutant with high photosynthetic efficiency in wheat (Triticum aestivum L.).

Optimizing the antenna size by reducing the chlorophyll (Chl) content is an effective strategy to improve solar energy conversion efficiencies in dense crop monocultures. To elucidate the physiological and molecular mechanisms that regulate Chl biosynthesis and understand the effects of lower Chl content on the photosynthetic process, a light-intensity-dependent yellow-green wheat mutant (Jimai5265yg) was characterized to determine its morphological, histological, physiological, and transcriptional differences with wild type. In addition to lower Chl content with a higher Chl a/b ratio, Jimai5265yg has spherical chloroplasts with few plastoglobule. It is counterintuitive that the photochemical quantum yield of both photosystem I and photosystem II and the following CO2 assimilation rate significantly increased, but the value of nonphotochemical quenching decreased, indicating a reduction of the photoprotective capacity of this yellow-green mutant. Analysis of intermediate pools and the expression of genes in the Chl synthesis pathway indicated that Mg-protoporphyrin IX (Mg-Proto IX) synthesis was partially blocked due to the imbalanced expression of Mg-chelatase subunits. Interestingly, the expression of photosynthesis-associated nuclear genes (PhANGs) was upregulated, resembling gun mutants which have defects in the Mg-Proto IX-mediated plastid-to-nucleus signaling pathway. A genetic analysis indicated that the yellow-green phenotype was controlled by two nuclear recessive genes located on chromosomes 4AL and 4BL. Jimai5265yg is a novel chlorina mutant which could be used for understanding photosynthesis improvement mechanisms.

Effect of iron on the growth of Phaeodactylum tricornutum via photosynthesis.

Iron is a limiting factor that controls the phytoplankton biomass in the modern ocean, and iron fertilization of the ocean could lead to blooms dominated by diatoms. Thus, iron plays an important role in controlling the distribution of diatoms. In this study, we measured the growth rate and photosynthetic activity of the model diatom Phaeodactylum tricornutum cultured under different iron concentrations and found that it grew more rapidly and had a much higher photosynthetic efficiency under higher iron concentrations. In order to explore the unique mechanism of the response of diatoms to iron, a proteomic analysis was carried out, and the results indicated that iron promotes the Calvin cycle of P.tricornutum. Diatoms can tolerate the pressure of iron limitation by replacing iron-rich proteins with flavodoxin, and so on. Moreover, we found that the photosystem I (PSI) activity of iron-limited algae that were treated by N',N',N',N'-tetramethyl-p-phenylenediamine (TMPD) was increased significantly. As TMPD plays the role of a cytochrome b6 /f complex that transfers electrons from photosystem II to PSI, the cytochrome b6 /f complex is the key to photosynthesis regulation. Iron could influence the growth of P.tricornutum by regulating its biosynthesis. All of the results suggest that iron might affect the growth of diatoms through the Calvin cycle and the cytochrome b6 /f complex.

Adaptation of Arabidopsis Plants to Tropical Aeroponics Using Cool Root Zone Temperatures

Arabidopsis thaliana (L.) Heyhn. is a well known model plant in plant research. However, its growth conditions and diminutive stature associated with low biomass at maturity make it a challenging species for physiological studies. While in the tropical countries, it can only be grown either by tissue cultures or in growth chambers under controlled conditions. An aeroponic technique with 20°C ± 2°C and 30°C ± 2°C root-zone temperatures (RZT) was used to grow Arabidopsis (Columbia ecotype) in a tropical greenhouse with natural irradiance and high ambient temperature (38°C/28°C day/night). Seedlings germinated in growth chambers at 20°C or 30°C. At 6 to 8 leaf stage, they were transferred to the aeroponic troughs with their roots exposed to constant temperature of 20°C ± 2°C and 30°C ± 2°C while their aerial parts were subjected to fluctuating ambient temperature from 28°C to 38°C. After a week, plants have acclimatised to both RZTs and started developing normal rosettes, bolted and yielded viable seeds. However, 20°C ± 2°C RZT allowed them to recover from turgor pressure despite of wilting, and significantly increased biomass. Mature plants grown in each RZTs were compared morphologically and physiologically to the plants grown in growth chamber (GC) at 20°C (root and shoot) temperature with 60% relative humidity. Aeroponically grown plants did not experience photoinhibition, and also exhibited higher photosynthetic light usage efficiency and higher capacities of heat dissipation, compared to GC plants. This aeroponics with cool RZTs can allow the use of Arabidopsis as a model plant even under tropical climate.