高光效作物基因工程中的几个问题

探讨了为提高作物光合作用效率的基因工程中存在的几个关键问题     

Surveying Rubisco Diversity and Temperature Response to Improve Crop Photosynthetic Efficiency

The threat to global food security of stagnating yields and population growth makes increasing crop productivity a critical goal over the coming decades. One key target for improving crop productivity and yields is increasing the efficiency of photosynthesis. Central to photosynthesis is Rubisco, which is a critical but often rate-limiting component. Here, we present full Rubisco catalytic properties measured at three temperatures for 75 plants species representing both crops and undomesticated plants from diverse climates. Some newly characterized Rubiscos were naturally “better” compared to crop enzymes and have the potential to improve crop photosynthetic efficiency. The temperature response of the various catalytic parameters was largely consistent across the diverse range of species, though absolute values showed significant variation in Rubisco catalysis, even between closely related species. An analysis of residue differences among the species characterized identified a number of candidate amino acid substitutions that will aid in advancing engineering of improved Rubisco in crop systems. This study provides new insights on the range of Rubisco catalysis and temperature response present in nature, and provides new information to include in models from leaf to canopy and ecosystem scale.In a changing climate and under pressure from a population set to hit nine billion by 2050, global food security will require massive changes to the way food is produced, distributed, and consumed (Ort et al., 2015). To match rising demand, agricultural production must increase by 50 to 70% in the next 35 years, and yet the gains in crop yields initiated by the green revolution are slowing, and in some cases, stagnating (Long and Ort, 2010; Ray et al., 2012). Among a number of areas being pursued to increase crop productivity and food production, improving photosynthetic efficiency is a clear target, offering great promise (Parry et al., 2007; von Caemmerer et al., 2012; Price et al., 2013; Ort et al., 2015). As the gatekeeper of carbon entry into the biosphere and often acting as the rate-limiting step of photosynthesis, Rubisco, the most abundant enzyme on the planet (Ellis, 1979), is an obvious and important target for improving crop photosynthetic efficiency.Rubisco is considered to exhibit comparatively poor catalysis, in terms of catalytic rate, specificity, and CO₂ affinity (Tcherkez et al., 2006; Andersson, 2008), leading to the suggestion that even small increases in catalytic efficiency may result in substantial improvements to carbon assimilation across a growing season (Zhu et al., 2004; Parry et al., 2013; Galmés et al., 2014a; Carmo-Silva et al., 2015). If combined with complimentary changes such as optimizing other components of the Calvin Benson or photorespiratory cycles (Raines, 2011; Peterhansel et al., 2013; Simkin et al., 2015), optimized canopy architecture (Drewry et al., 2014), or introducing elements of a carbon concentrating mechanism (Furbank et al., 2009; Lin et al., 2014a; Hanson et al., 2016; Long et al., 2016), Rubisco improvement presents an opportunity to dramatically increase the photosynthetic efficiency of crop plants (McGrath and Long, 2014; Long et al., 2015; Betti et al., 2016). A combination of the available strategies is essential for devising tailored solutions to meet the varied requirements of different crops and the diverse conditions under which they are typically grown around the world.Efforts to engineer an improved Rubisco have not yet produced a “super Rubisco” (Parry et al., 2007; Ort et al., 2015). However, advances in engineering precise changes in model systems continue to provide important developments that are increasing our understanding of Rubisco catalysis (Spreitzer et al., 2005; Whitney et al., 2011a, 2011b; Morita et al., 2014; Wilson et al., 2016), regulation (Andralojc et al., 2012; Carmo-Silva and Salvucci, 2013; Bracher et al., 2015), and biogenesis (Saschenbrecker et al., 2007; Whitney and Sharwood, 2008; Lin et al., 2014b; Hauser et al., 2015; Whitney et al., 2015).A complementary approach is to understand and exploit Rubisco natural diversity. Previous characterization of Rubisco from a limited number of species has not only demonstrated significant differences in the underlying catalytic parameters, but also suggests that further undiscovered diversity exists in nature and that the properties of some of these enzymes could be beneficial if present in crop plants (Carmo-Silva et al., 2015). Recent studies clearly illustrate the variation possible among even closely related species (Galmés et al., 2005, 2014b, 2014c; Kubien et al., 2008; Andralojc et al., 2014; Prins et al., 2016).Until recently, there have been relatively few attempts to characterize the consistency, or lack thereof, of temperature effects on in vitro Rubisco catalysis (Sharwood and Whitney, 2014), and often studies only consider a subset of Rubisco catalytic properties. This type of characterization is particularly important for future engineering efforts, enabling specific temperature effects to be factored into any attempts to modify crops for a future climate. In addition, the ability to coanalyze catalytic properties and DNA or amino acid sequence provides the opportunity to correlate sequence and biochemistry to inform engineering studies (Christin et al., 2008; Kapralov et al., 2011; Rosnow et al., 2015). While the amount of gene sequence information available grows rapidly with improving technology, knowledge of the corresponding biochemical variation resulting has yet to be determined (Cousins et al., 2010; Carmo-Silva et al., 2015; Sharwood and Whitney, 2014; Nunes-Nesi et al., 2016).This study aimed to characterize the catalytic properties of Rubisco from diverse species, comprising a broad range of monocots and dicots from diverse environments. The temperature dependence of Rubisco catalysis was evaluated to tailor Rubisco engineering for crop improvement in specific environments. Catalytic diversity was analyzed alongside the sequence of the Rubisco large subunit gene, rbcL, to identify potential catalytic switches for improving photosynthesis and productivity. In vitro results were compared to the average temperature of the warmest quarter in the regions where each species grows to investigate the role of temperature in modulating Rubisco catalysis.     

Exploring the Limits of Crop Productivity : I. Photosynthetic Efficiency of Wheat in High Irradiance Environments

The long-term vegetative and reproductive growth rates of a wheat crop (Triticum aestivum L.) were determined in three separate studies (24, 45, and 79 days) in response to a wide range of photosynthetic photon fluxes (PPF, 400-2080 micromoles per square meter per second; 22-150 moles per square meter per day; 16-20-hour photoperiod) in a near-optimum, controlled-environment. The CO₂ concentration was elevated to 1200 micromoles per mole, and water and nutrients were supplied by liquid hydroponic culture. An unusually high plant density (2000 plants per square meter) was used to obtain high yields. Crop growth rate and grain yield reached 138 and 60 grams per square meter per day, respectively; both continued to increase up to the highest integrated daily PPF level, which was three times greater than a typical daily flux in the field. The conversion efficiency of photosynthesis (energy in biomass/energy in photosynthetic photons) was over 10% at low PPF but decreased to 7% as PPF increased. Harvest index increased from 41 to 44% as PPF increased. Yield components for primary, secondary, and tertiary culms were analyzed separately. Tillering produced up to 7000 heads per square meter at the highest PPF level. Primary and secondary culms were 10% more efficient (higher harvest index) than tertiary culms; hence cultural, environmental, or genetic changes that increase the percentage of primary and secondary culms might increase harvest index and thus grain yield. Wheat is physiologically and genetically capable of much higher productivity and photosynthetic efficiency than has been recorded in a field environment.     

The Influence of Increased Solar UV-B Radiation on Magnesium-Deficient Cowpea Seedlings: Changes in the Photosynthetic Characteristics

The influence of increased solar UV-B radiation on the photosynthetic characteristics in cowpea seedlings (Vigna unguiculata) grown at optimal (Mg_s) and low (Mg_d) Mg levels were studied. Both higher UV-B and Mg_d treatments caused significant drops of photochemical activities and net CO₂ uptake rates (P_N). Yet the UV-B-induced decrease in the photosynthetic efficiency was lesser in Mg_d seedlings. The leaf Chl a fluorescence measurements proved that after receiving an enhanced UV-B radiation these seedlings showed a significant enhancement in their variable parts. The PSM oscillation of slow fluorescence kinetics was remarkably altered by both treatments. The P_N also followed a typical inhibitory pattern as seen in photochemical activities. Concentrations of several chloroplast proteins in trifoliate leaves were significantly reduced by Mg_d treatment and unaffected by the other two treatments. Whereas the contents of 43-47 kDa polypeptides in primary leaves were markedly reduced with a maximal effect in Mg_d seedlings, no major difference was noted for combined stress. This revised version was published online in September 2006 with corrections to the Cover Date.     

Band Edge Modulated Polymer Layer to Decrease Back Electron Transfer and Increase Efficiency in Sensitized Solar Cells

Recombination of charges residing in the TiO₂ and redox electrolyte is one of the factors affecting the efficiency of dye sensitized solar cells (DSSCs). To circumvent this recombination, inorganic oxide barrier layers and organic silanes have been coated on TiO₂/dyes. Due to the insulating nature of these layers, the efficiency increase is not very impressive. Conducting polymers with different band edges are used to suppress the charge recombination. Amongst the four polymers that are used as barrier layers, a polymer with a highest occupied molecular orbital energy at ?5.8 eV and lowest unoccupied molecular orbital at ?3.1 eV is found to increase the electron life time at TiO₂ and decrease the charge recombination. The electron life time is found to be 88 ms. In addition to the long electron life time, the recombination resistance of this polymer is also high (91 Ω). This resistance is 18% higher than that measured for DSSCs without polymer barrier layer. These factors impact the efficiency of DSSCs. DSSCs fabricated with this polymer as barrier layer exhibit an efficiency of 9.2%, which is 22% higher than that of DSSCs without polymer barrier layer.     

Semiarid Crop Production from a Hydrological Perspective: Gap between Potential and Actual Yields

Rapid population growth in the dry climate regions, arable land scarcity, and irrigation expansion limitations direct our interest to possibilities of yield increase in rainfed agriculture. Literature, however, indicates large differences between actual and potential yields, and between yields on farmers’ fields and research stations. This article focuses on the determinants of these yield gaps and the windows of opportunity for yield increase on the farmer's field together with the agricultural challenges involved. The study links the conventional approach to estimate crop water requirements and dry spell effects on biomass production to a conceptual Green Water Crop Model. This model addresses the effects on crop yields of the sequential diversions of infiltrating rainfall (rainwater partitioning into runoff, plant available soil water, and deep percolation) and of different relations between nonproductive evaporation flow and productive transpiration flow, defined together as green water flow. Also, the effects of droughts and dry spells are analyzed. The model is used to demonstrate typical situations for semiarid and dry subhumid conditions (lengths of growing period (LGP) of 90 and 179 days, respectively) for maize (Zea mays (L.)) under on-station agricultural conditions. Based on detailed water flow analysis in a 3-year on-farm case study in the Sahel on pearl millet (Pennisetum glaucum (L.) Br.), the model is used to clarify the large scope for improved yield levels, achievable through land and water management securing that runoff losses and deep percolation are reduced and nonproductive evaporation losses minimized. The analysis indicates that poor rainwater partitioning and low plant water uptake capacity alone reduces estimated on-farm grain yields to 1/10th of the potential yields. This suggests that lack of water per se not necessarily is the primary constraint to crop growth even in drought prone areas of sub-Saharan Africa. The conclusion is that even a doubling of crop yields would be agro-hydrologically possible with relatively small manipulations of rainwater partitioning in the water balance.     

Transferability of Microsatellite Markers from Brachypodium distachyon to Miscanthus sinensis,a Potential Biomass Crop

Miscanthus sinensis has high biomass yield and contributed two of the three genomes in M.x giganteus,a bioenergy crop widely studied in Europe and North America,and thus is a potential biomass crop and an important germplasm for Miscanthus breeding.Molecular markers are essential for germplasm evaluation,genetic analyses and new cultivar development in M.sinensis.In the present study,we reported transferability of simple sequence repeat (SSR) markers from Brachypodium distachyon to M.sinensis.A set of 57 SS...     

自花授粉作物杂交育种组合潜势的预测和比较

在黄花烟草Nicotiana russica中,开花期这一性状用V_5作亲本可能产生较大变异,无论是选择早开花的还是选择迟开花的,都有较大机会得到理想目标株系;对于株高这一性状,含有V(?)的组合可望有较大机会产生高于标准品种的株系。通过组合间育种潜势的比较,能了解各亲本中基因分布的基本情况,进而进行客观评价并对杂交组合做出取舍。试验证明,用一个组合的早期世代的参数m和D来预测高世代或纯系的育种潜势是可行的。     

Photosynthetic Efficiency, and Photodamage by UV and Visible Radiation, in Red versus Green Leaf Coleus Varieties

The maximum quantum yield for photosynthetic O₂ evolution inred leaf coleus varieties having anthocyanin in their upperepidermis is much lower in green light and slightly lower inwhite light than in a green leaf variety lacking anthocyanin.A similar degree of photoinhibition occurred under excess visiblelight in the red versus green varieties; whereas, the red leafvarieties were less damaged by UV-B and UV-C radiation suggestingprotection by anthocyanin in their epidermal tissue. (Received October 3, 1995; Accepted February 7, 1996)     

On the Photosynthetic Potential in the Very Early Archean Oceans

In this work we apply a mathematical model of photosynthesis to quantify the potential for photosynthetic life in the very Early Archean oceans. We assume the presence of oceanic blockers of ultraviolet radiation, specifically ferrous ions. For this scenario, our results suggest a potential for photosynthetic life greater than or similar to that in later eras/eons, such as the Late Archean and the current Phanerozoic eon.     

大豆高光效育种研究进展

多年的研究证明 ,提高光合效率是提高大豆产量的重要途径。在高产条件下 ,高光效大豆 (GlycinemaxL .Merr.)品种与一般品种相比可提高产量 30 %～ 40 %,表明高光效育种有着广阔的发展前景。高光效育种虽然未能缩短育种时间 ,但为达到预定的高光效目标提供了“实时”监测 ,可免除目标的偏离 ,从而达到高光效与高产的同步提高。大豆叶片与豆荚均存在着高活性的有限的C4 途径循环 ,因此 ,通过常规育种或基因工程技术提高C4 途径酶的表达能力 ,可能是提高C3 植物光合效率的新突破点。     

大豆高光效育种研究进展

多年的研究证明,提高光合效率是提高大豆产量的重要途径.在高产条件下,高光效大豆(Glycine max L. Merr.)品种与一般品种相比可提高产量30%～40%,表明高光效育种有着广阔的发展前景.高光效育种虽然未能缩短育种时间,但为达到预定的高光效目标提供了"实时"监测,可免除目标的偏离,从而达到高光效与高产的同步提高.大豆叶片与豆荚均存在着高活性的有限的C4途径循环,因此,通过常规育种或基因工程技术提高C4途径酶的表达能力,可能是提高C3植物光合效率的新突破点.     

Efficiency Boost in All-Small-Molecule Organic Solar Cells: Insights from the Re-Ordering Kinetics

Achieving high-performance in all-small-molecule organic solar cells (ASM-OSCs) significantly relies on precise nanoscale phase separation through domain size manipulation in the active layer. Nonetheless, for ASM-OSC systems, forging a clear connection between the tuning of domain size and the intricacies of phase separation proves to be a formidable challenge. This study investigates the intricate interplay between domain size adjustment and the creation of optimal phase separation morphology, crucial for ASM-OSCs’ performance. It is demonstrated that exceptional phase separation in ASM-OSCs’ active layer is achieved by meticulously controlling the continuity and uniformity of domains via re-packing process. A series of halogen-substituted solvents (Fluorobenzene, Chlorobenzene, Bromobenzene, and Iodobenzene) is adopted to tune the re-packing kinetics, the ASM-OSCs treated with CB exhibited an impressive 16.2% power conversion efficiency (PCE). The PCE enhancement can be attributed to the gradual crystallization process, promoting a smoothly interconnected and uniformly distributed domain size. This, in turn, leads to a favorable phase separation morphology, enhanced charge transfer, extended carrier lifetime, and consequently, reduced recombination of free charges. The findings emphasize the pivotal role of re-packing kinetics in achieving optimal phase separation in ASM-OSCs, offering valuable insights for designing high-performance ASM-OSCs fabrication strategies.     

Photosynthetic Potential and Light-Dependent Oxygen Consumption in a Benthic Cyanobacterial Mat

The potential to carry out oxygenic photosynthesis after prolonged burial below the photic zone was studied at 0.1-mm depth intervals in the thick, laminated Microcoleus chthonoplastes mats growing in Solar Lake, Sinai. The buried mat community lost about 20% of its photosynthetic potential with depth per annual layer down to 8- to 10-year-old layers at a 14-mm depth. In some of the older layers, below a 30-mm depth, light-dependent oxygen consumption which increased with increasing light intensity was observed. Possible mechanisms for this phenomenon are (i) pseudocyclic electron transport (Mehler reaction), (ii) interactions between respiratory electron transport and photosynthetic electron transport, (iii) photorespiration, and (iv) photooxidation.     

Effect of Solar UV-B Radiation on a Phyllosphere Bacterial Community

The effect of solar UV-B radiation on the population dynamics and composition of the culturable bacterial community from peanut (Arachis hypogeae L.) was examined in field studies using plants grown under UV-B−transmitting (UV-B+) or UV-B−excluding (UV-B−) plastic filters. Our data demonstrate that solar UV-B selection alters phyllosphere bacterial community composition and that UV tolerance is a prevalent phenotype late in the season. The total bacterial population size was not affected by either UV-B treatment. However, isolates from the UV-B+ plots (n = 368) were significantly more UV tolerant than those from the UV-B− (n = 363) plots. UV sensitivity was determined as the minimal inhibitory dose of UV that resulted in an inhibition of growth compared to the growth of a nonirradiated control. The difference in minimal inhibitory doses among bacterial isolates from UV-B+ and UV-B− treatments was mainly partitioned among nonpigmented isolates, with pigmented isolates as a group being characterized as UV tolerant. A large increase in UV tolerance was observed within isolate groups collected late (89 and 96 days after planting) in the season. Identification of 200 late-season isolates indicated that the predominant UV-tolerant members of this group were Bacillus coagulans, Clavibacter michiganensis, and Curtobacterium flaccumfaciens. We selected C. michiganensis as a model UV-tolerant epiphyte to study if cell survival on UV-irradiated peanut leaves was increased relative to UV survival in vitro. The results showed an enhancement in the survival of C. michiganensis G7.1, especially following high UV-C doses (300 and 375 J m⁻²), that was evident between 24 and 96 h after inoculation. A dramatic increase in the in planta/in vitro survival ratio was observed over the entire 96-h experiment period for C. michiganensis T5.1.     

Salt Tolerance and Crop Potential of Halophytes

Although they represent only 2% of terrestrial plant species, halophytes are present in about half the higher plant families and represent a wide diversity of plant forms. Despite their polyphyletic origins, halophytes appear to have evolved the same basic method of osmotic adjustment: accumulation of inorganic salts, mainly NaCl, in the vacuole and accumulation of organic solutes in the cytoplasm. Differences between halophyte and gly-cophyte ion transport systems are becoming apparent. The pathways by which Na⁺ and Cl^? enters halophyte cells are not well understood but may involve ion channels and pinocytosis, in addition to Na⁺ and Cl^? transporters. Na⁺ uptake into vacuoles requires Na⁺/H⁺ antiporters in the tonoplast and H⁺ ATPases and perhaps PP_i ases to provide the proton motive force. Tonoplast antiporters are constitutive in halophytes, whereas they must be activated by NaCl in salt-tolerant glycophytes, and they may be absent from salt-sensitive glycophytes. Halophyte vacuoles may have a modified lipid composition to prevent leakage of Na⁺ back to the cytoplasm. Becuase of their diversity, halophytes have been regarded as a rich source of potential new crops. Halophytes have been tested as vegetable, forage, and oilseed crops in agronomic field trials. The most productive species yield 10 to 20 ton/ha of biomass on seawater irrigation, equivalent to conventional crops. The oilseed halophyte, Sali-cornia bigelovii, yields 2?t/ha of seed containing 28% oil and 31% protein, similar to soybean yield and seed quality. Halophytes grown on seawater require a leaching fraction to control soil salts, but at lower salinities they outperform conventional crops in yield and water use efficiency. Halophyte forage and seed products can replace conventional ingredients in animal feeding systems, with some restrictions on their use due to high salt content and antinutritional compounds present in some species. Halophytes have applications in recycling saline agricultural wastewater and reclaiming salt-affected soil in arid-zone irrigation districts.     

Optimization of Light-Harvesting Pigment Improves Photosynthetic Efficiency

Maximizing light capture by light-harvesting pigment optimization represents an attractive but challenging strategy to improve photosynthetic efficiency. Here, we report that loss of a previously uncharacterized gene, HIGH PHOTOSYNTHETIC EFFICIENCY1 (HPE1), optimizes light-harvesting pigments, leading to improved photosynthetic efficiency and biomass production. Arabidopsis (Arabidopsis thaliana) hpe1 mutants show faster electron transport and increased contents of carbohydrates. HPE1 encodes a chloroplast protein containing an RNA recognition motif that directly associates with and regulates the splicing of target RNAs of plastid genes. HPE1 also interacts with other plastid RNA-splicing factors, including CAF1 and OTP51, which share common targets with HPE1. Deficiency of HPE1 alters the expression of nucleus-encoded chlorophyll-related genes, probably through plastid-to-nucleus signaling, causing decreased total content of chlorophyll (a+b) in a limited range but increased chlorophyll a/b ratio. Interestingly, this adjustment of light-harvesting pigment reduces antenna size, improves light capture, decreases energy loss, mitigates photodamage, and enhances photosynthetic quantum yield during photosynthesis. Our findings suggest a novel strategy to optimize light-harvesting pigments that improves photosynthetic efficiency and biomass production in higher plants.The tremendous increase in world population and environmental deterioration pose serious challenges to agricultural production and food security (Ray et al., 2013). To meet this challenge, crops with high yield potential need to be developed (Long et al., 2015). However, the yield traits that have played key roles during the green revolution have had their potential nearly exhausted; thus, new strategies are needed. Photosynthesis, the unique biological process responsible for the conversion of light energy to chemical forms, is the ultimate basis of crop yield (Zhu et al., 2010). Theoretically, enhancing photosynthetic efficiency should be an excellent strategy to increase crop yield. However, the improvement of photosynthetic efficiency has played only a minor role in the remarkable crop productivity improvement achieved in the last half-century (Zhu et al., 2010; Ort et al., 2015).In the light reactions of photosynthesis, light energy is used by chlorophyll and associated pigments, water is split, and electron transport on the chloroplast membrane reduces NADP, resulting in a proton gradient that powers the phosphorylation of ADP. NADPH and ATP power the Calvin cycle, which assimilates and reduces carbon dioxide to carbohydrate (Ort et al., 2015). Strategies to improve photosynthesis mainly include the optimization of light capture, light energy conversion in the light reaction, and carbon capture and conversion in the dark reaction (Ort et al., 2015). Previous research focused mainly on the optimization of dark reactions through the improvement of carbon capture and conversion to directly increase biomass (Miyagawa et al., 2001; Kebeish et al., 2007; Lin et al., 2014; Ort et al., 2015). However, less effort has been spent to optimize light capture and light energy conversion in the light reactions to improve the whole photosynthetic efficiency (Ort et al., 2015).Maximizing light capture by the adjustment of antenna size can optimize light capture and light energy conversion, but it is difficult to achieve (Blankenship and Chen, 2013). Antenna in photosynthetic systems typically consist of pigments specifically bound to membrane-associated proteins. These antenna pigment-protein complexes closely associate with the reaction center complexes and deliver absorbed energy to the reaction centers, where some of the energy originally in the photon is captured by electron-transfer processes (Blankenship, 2002; Green and Parson, 2003). However, light saturation could take place at intensities much lower than would be expected if every chlorophyll was able to carry out photosynthesis by itself (Blankenship, 2002). The light saturation problem also has been addressed from the antenna perspective, and many efforts are under way to truncate the antenna system in photosynthetic microorganisms. A smaller antenna associated with each reaction center will, in principle, also shift the light-response curve, so that light saturation sets in at higher intensities, thereby reducing excess light and increasing productive light. While the concept of increased efficiency due to reduced antenna size is simple, reaching this goal has not yet been achieved (Blankenship and Chen, 2013). In green algae, the reduction of light-harvesting pigments by decreasing the expression of the chlorophyll a oxygenase gene, which is responsible for the synthesis of chlorophyll b via the oxidation of chlorophyll a (Czarnecki and Grimm, 2012), led to efficient photosynthesis due to the balance between captured light and photochemical reactions (Perrine et al., 2012). However, there is still no success in higher plants.In this study, we performed a large-scale genetic screen using the model organism Arabidopsis (Arabidopsis thaliana) and identified two independent alleles of an uncharacterized gene that we named HIGH PHOTOSYNTHETIC EFFICIENCY1 (HPE1), whose mutation confers improved photosynthetic efficiency by optimizing light-harvesting pigment. A deficiency of HPE1 shows higher light reaction activity of photosynthesis, more efficient carbon fixation, and significantly increased biomass production. Interestingly, HPE1 encodes a chloroplast protein containing an RNA recognition motif and regulates the splicing of RNAs of plastid genes by directly associating with target RNAs. HPE1 mutation results in a splicing deficiency of plastid genes that may alter the expression of chlorophyll-related genes, probably through plastid-to-nucleus signaling. Altered expression of chlorophyll-related genes changes the content of light-harvesting pigments and optimizes the light-harvesting system. Our characterization of HPE1 mutants suggests a novel strategy to optimize light harvesting and improve photosynthetic efficiency in higher plants.     

Photosynthetic Efficiency in Lawson's Bay on the East Coast of India

Seasonal variations in the efficiency of utilization of radiant energy by phytoplankton photosynthesis in a tropical embayment followed the same pattern as that of primary production. showing that incident radiation did not limit phytoplankton production. Peak values in primary production and photosynthetic efficiency coincided with periods of nutrient enrichment caused either by upwelling during the southwest monsoon or by run-off during the northeast, monsoon. A world-wide comparison of published data on photosynthetic efficiencies in different latitudes showed that higher efficiency is achieved in the tropics, where the values are similar to those observed on phytoplankton cultures. Based on the maximum efficiency of photosynthesis attained, three regimes can be recognized in tropical waters: 1) regions of upwelling with a maximum of 6%,. 2) coastal bays with 0.7%, 3) oceanic regions with 0.24%.