Allocation pattern,ion partitioning,and chlorophyll a fluorescence in Arundo donax L. in responses to salinity stress

Biometric and physiological analyses of salt stress responses were performed in two time-course experiments on giant reed (Arundo donax L). Experiment I evaluated biomass production in plants exposed to 128, 256, 512 mM NaCl for 84 days. For Experiment II, plants grown under 256 mM NaCl were further assessed for chlorophyll a fluorescence, ionic partitioning, and proline content at 14 and 49 days after treatment (DAT). Biomass allocation was affected with all the concentrations of NaCl used from 28 DAT onward. Proline biosynthesis in leaves was more stimulated than that in roots after salt stress. Photosynthetic efficiency of photosystem II (PSII) was not affected by salt stress up to 42 DAT, while 49 DAT plants exhibited a significant reduction of both potential (Φ_PSII) and maximal (F_v/F_m) PSII quantum yield. A. donax resulted a moderately sensitive species in response to 256 and 512 mM NaCl, concentrations that are however higher than that commonly found in most marginal lands (such as 128 mM or lower), where the biomass yield is appreciable, especially in short-term cultivation (56 DAT here). Altogether, this study indicates that A. donax can be considered as a promising and valuable energy crop for exploiting the Mediterranean marginal land.     

Cytogenetics of modern sugar canes

Modern sugar cane varieties are derived from interspecific crosses involving as many as four species. Because a chromosome increase accompanies certain crosses and backcrosses, modern varieties have very high aneuploid chromosome numbers and complicated genetics. Despite this complexity, the chromosome behavior of some modern varieties approaches that of allopolyploids. In achieving homozygosity, therefore, such varieties should respond to inbreeding almost like diploids. The meiotic chromosome behavior of F₁ hybrids and modern varieties indicates little or no genetic exchange between chromosomes ofSaccharum officinarum andS. spontaneum. Irradiation may break linkages between desirable and undesirableS. spontaneum genes not ordinarily broken by crossing-over between the chromosomes of the two species. The quick success of nobilizingS. spontaneum (recurrently back-crossing to “noble canes”) depends on a peculiar increase of the chromosomes ofS. officinarum. Experience with nobilizingS. spontaneum should not make breeders impatient when they turn to interspecific crosses unaccompanied by chromosome increases.     

Triterpene methyl ethers in leaf waxes of Saccharum and related genera

The triterpene methyl ethers in the leaf waxes of over 80 clones of Saccharum officinarum, S. edule, S. robustum, S. spontaneum and a limited number of related species were compared as possible chemotaxonomic markers by GLC. The principal components were arundoin, crusgallin and cylindrin. The overall interspecific variation was small, but arundoin was particularly characteristic of S. officinarum. However, each species showed marked interclonal variation, which was related to chromosome numbers and geographical origin. Most S. spontaneum clones from India were atypical containing no triterpene methyl ethers.     

NaCl胁迫加重强光胁迫下超大甜椒叶片的光系统II和光系统I的光抑制

快速叶绿素荧光动力学可以在无损情况下探知叶片光合机构的损伤程度, 快速叶绿素荧光测定和分析技术(JIP-test)将测量值转化为多种具有生物学意义的参数, 因而被广泛应用于植物光合机构对环境的响应机制研究。该文研究了超大甜椒(Capsicum annuum)幼苗在强光及不同NaCl浓度胁迫下的荧光响应情况。与单纯强光胁迫相比, NaCl胁迫引起了叶绿素荧光诱导曲线的明显改变, 光系统II (PSII)光抑制加重, 同时PSII反应中心和受体侧受到明显影响, 而且高NaCl浓度胁迫下PSII供体侧受伤害明显, 同时PSI反应中心活性(P700⁺)在盐胁迫下明显降低。这些结果表明, NaCl胁迫会增强强光对超大甜椒光系统的光抑制, 并且浓度越高抑制越明显, 但对PSI的抑制作用低于PSII。高NaCl浓度胁迫易对PSII供体侧造成破坏, 且PSI光抑制严重。     

Arundo donax L.: A non-food crop for bioenergy and bio-compound production

Arundo donax L., common name giant cane or giant reed, is a plant that grows spontaneously in different kinds of environments and that it is widespread in temperate and hot areas all over the world. Plant adaptability to different kinds of environment, soils and growing conditions, in combination with the high biomass production and the low input required for its cultivation, give to A. donax many advantages when compared to other energy crops. A. donax can be used in the production of biofuels/bioenergy not only by biological fermentation, i.e. biogas and bio-ethanol, but also, by direct biomass combustion. Both its industrial uses and the extraction of chemical compounds are largely proved, so that A. donax can be proposed as the feedstock to develop a bio-refinery.     

Molecular Diversity Among Members of the Saccharum Complex Assessed Using TRAP Markers Based on Lignin-Related Genes

In addition to the cultivation of sugarcane for sugar, the crop is considered seriously as an important bioenergy grass crop for its high biomass production ability. But, lignin is a serious bottleneck in the bioconversion of lignocellulosic biomass to ethanol. Hence, genetic relationships among 64 genotypes within the Saccharum complex were studied with respect to lignin-related genes using target region amplified polymorphic (TRAP) primers derived from caffeic acid O-methyltransferase (COMT), cinnamoyl alcohol dehydrogenase (CAD), cinnamoyl coA reductase (CCR), and ferrulate 5-hydroxylase (F5H) genes. While the average polymorphism detected by the TRAP markers was 43%, the markers derived from F5H gene (34%) were less polymorphic in comparison to those derived from COMT (46%), CCR (44%), and CAD (46%) genes. The lignin gene-based TRAP markers differentiated members of the Saccharum complex broadly according to previously established genetic relationships in the order of Miscanthus?>?Erianthus?>?Saccharum spontaneum?>?Saccharum robustum/Saccharum barberi/Saccharum sinense?>?Saccharum officinarum/cultivars. Principal coordinate analysis showed that 29% of the total variation was explained by the genotypes with respect to the lignin-related genes. The association of genetic variation revealed in this study with the biomass composition-related genes of the genotypes within a species will be helpful to design breeding strategies to develop superior energy cane cultivars with improved biomass quality of the sugarcane.     

Reorganization of Thylakoid Components during Chloroplast Development in Higher Plants after Transfer to Darkness : Changes in Photosystem I Unit Components, and in Cytochromes

It was shown earlier that in etiolated bean (Phaseolus vulgaris, var. red kidney) leaves exposed to continuous light for a short time and then transferred to darkness a reorganization of their photosystem II (PSII) unit components occurs. This reorganization involves disorganization of the light-harvesting complex of PSII (LHC-II), destruction of its chlorophyll b and the 25 kilodalton polypeptide, and reuse of its chlorophyll a for the formation of additional, small in size, PSII units (Argyroudi-Akoyunoglou, Akoyunoglou, Kalosakas, Akoyunoglou 1982 Plant Physiol 70: 1242-1248). The present study further shows that parallel to the PSII unit reorganization a reorganization of the PSI unit components also occurs: upon transfer to darkness the 24, 23, and 21 kilodalton polypeptides, components of the light-harvesting complex of PSI (LHC-I), are decreased, the 69 kilodalton polypeptide, component of the chlorophyll a-rich P700-protein complex (CPI), is increased and new smallsized PSI units are formed. Concomitantly, the cytochrome f/chlorophyll and the cytochrome b/chlorophyll ratios are gradually increased. This suggests that the concentration of the electron transport components is also modulated in darkness to allow for adequate electron flow to occur between the newly synthesized PSII and PSI units.     

Setaria viridis: A Model for C4 Photosynthesis

C₄ photosynthesis drives productivity in several major food crops and bioenergy grasses, including maize (Zea mays), sugarcane (Saccharum officinarum), sorghum (Sorghum bicolor), Miscanthus x giganteus, and switchgrass (Panicum virgatum). Gains in productivity associated with C₄ photosynthesis include improved water and nitrogen use efficiencies. Thus, engineering C₄ traits into C₃ crops is an attractive target for crop improvement. However, the lack of a small, rapid cycling genetic model system to study C₄ photosynthesis has limited progress in dissecting the regulatory networks underlying the C₄ syndrome. Setaria viridis is a member of the Panicoideae clade and is a close relative of several major feed, fuel, and bioenergy grasses. It is a true diploid with a relatively small genome of ~510 Mb. Its short stature, simple growth requirements, and rapid life cycle will greatly facilitate genetic studies of the C₄ grasses. Importantly, S. viridis uses an NADP-malic enzyme subtype C₄ photosynthetic system to fix carbon and therefore is a potentially powerful model system for dissecting C₄ photosynthesis. Here, we summarize some of the recent advances that promise greatly to accelerate the use of S. viridis as a genetic system. These include our recent successful efforts at regenerating plants from seed callus, establishing a transient transformation system, and developing stable transformation.     

Predicting the Impacts of Climate Change on the Potential Distribution of Major Native Non-Food Bioenergy Plants in China

Planting non-food bioenergy crops on marginal lands is an alternative bioenergy development solution in China. Native non-food bioenergy plants are also considered to be a wise choice to reduce the threat of invasive plants. In this study, the impacts of climate change (a consensus of IPCC scenarios A2a for 2080) on the potential distribution of nine non-food bioenergy plants native to China (viz., Pistacia chinensis, Cornus wilsoniana, Xanthoceras sorbifolia, Vernicia fordii, Sapium sebiferum, Miscanthus sinensis, M. floridulus, M. sacchariflorus and Arundo donax) were analyzed using a MaxEnt species distribution model. The suitable habitats of the nine non-food plants were distributed in the regions east of the Mongolian Plateau and the Tibetan Plateau, where the arable land is primarily used for food production. Thus, the large-scale cultivation of those plants for energy production will have to rely on the marginal lands. The variables of “precipitation of the warmest quarter” and “annual mean temperature” were the most important bioclimatic variables for most of the nine plants according to the MaxEnt modeling results. Global warming in coming decades may result in a decrease in the extent of suitable habitat in the tropics but will have little effect on the total distribution area of each plant. The results indicated that it will be possible to grow these plants on marginal lands within these areas in the future. This work should be beneficial for the domestication and cultivation of those bioenergy plants and should facilitate land-use planning for bioenergy crops in China.     

Photosynthetic Gas Exchange and Chlorophyll a Fluorescence in Salicornia brachiata (Roxb.) Under Osmotic Stress

Osmotic stress negatively affects the photosynthetic efficiency and cause a significant loss of crop productivity. Salicornia brachiata (Roxb.) is a eu-halophyte. We hereby report on photosynthetic gas exchange and chlorophyll fluorescence in S. brachiata under sodium chloride (NaCl), seawater and polyethylene glycol (PEG) induced osmotic stress. It grows luxuriantly and exhibited a higher tolerance index and better accumulation of organic solutes under 100% strength of seawater (32.5 ppt) and 0.5 M NaCl salinity. It exhibited comparatively better gas exchange, stomatal conductance, PSII photochemistry and electron transfer under 100% strength of seawater salinity. Higher chlorophyll a/b ratio under stress conditions indicated a lower ratio of PSII to PSI and balanced excitation of PSI and PSII in S. brachiata resulting in efficient photosynthetic processes. The lower total chlorophyll/carotenoids ratio and higher non-photochemical quenching indicated the photo-protection and safer dissipation of heat energy in S. brachiata under stress. The 100% strength of seawater and 0.5 M NaCl salinity in S. brachiata did not cause significant changes in antenna size, connectivity between PSII reaction centres (RCs) and reduction of electrons on PSII donor side. The 20% PEG induced the inactivation of RCs and cause damage to PSII RCs in S. brachiata thus reduced the electron transfer from QA^– to QB pool-sized and activity of water-splitting complex. Higher φ(P₀) and F_V/F_M in S. brachiata under seawater salinity indicated a comparatively better quantum yield of primary photochemistry. The higher PI_Total in S. brachiata under 100% strength of seawater and 0.5 M NaCl stress indicated a better energy flux reaching to PSII RCs, electron transport and performance of RCs. The higher strengths of osmotic stress cause reduction in the quantum yield of PSII electron transport and capturing efficiency of excitation energy by open PSII RCs in S. brachiata.

Graphic Abstract

     

Response of the Photosynthetic Apparatus in Dunaliella salina (Green Algae) to Irradiance Stress

The response of the photosynthetic apparatus in the green alga Dunaliella salina, to irradiance stress was investigated. Cells were grown under physiological conditions at 500 millimoles per square meter per second (control) and under irradiance-stress conditions at 1700 millimoles per square meter per second incident intensity (high light, HL). In control cells, the light-harvesting antenna of photosystem I (PSI) contained 210 chlorophyll a/b molecules. It was reduced to 105 chlorophyll a/b in HL-grown cells. In control cells, the dominant form of photosystem II (PSII) was PSII_α(about 63% of the total PSII) containing >250 chlorophyll a/b molecules. The smaller antenna size PSII_β centers (about 37% of PSII) contained 135 ± 10 chlorophyll a/b molecules. In sharp contrast, the dominant form of PSII in HL-grown cells accounted for about 95% of all PSII centers and had an antenna size of only about 60 chlorophyll a molecules. This newly identified PSII unit is termed PSII_γ. The HL-grown cells showed a substantially elevated PSII/PSI stoichiometry ratio in their thylakoid membranes (PSII/PSI = 3.0/1.0) compared to that of control cells (PSII/PSI = 1.4/1.0). The steady state irradiance stress created a chronic photoinhibition condition in which D. salina thylakoids accumulate an excess of photochemically inactive PSII units. These PSII units contain both the reaction center proteins and the core chlorophyll-protein antenna complex but cannot perform a photochemical charge separation. The results are discussed in terms of regulatory mechanism(s) in the plant cell whose function is to alleviate the adverse effect of irradiance stress.     

Salinity improves chilling resistance in Suaeda salsa

Suaeda salsa L., a C3 euhalophytic herb, is native to saline soils, demonstrates high resistance to salinity stress. The effect of chilling stress on S. salsa under high salinity, particularly the change in unsaturated fatty acid content within membrane lipids, has not been investigated. After a 12 h chilling treatment (4 °C) performed under low irradiance (100 μmol m^?2 s^?1), the chlorophyll contents, maximal photochemical efficiency of photosystem II (F _v/F _m) and actual PSII efficiency (ΦPSII) were determined. These measurements were significantly decreased in S. salsa leaves in the absence of salt treatment yet there were no significant changes with a 200 mM NaCl treatment. Chlorophyll contents, F _v/F _m and ΦPSII in S. salsa under 200 mM NaCl were higher than those without salt treatment. The unsaturated fatty acid content and the double bond index (DBI) of major membrane lipids of monogalactosyldiacylglycerols, digalactosyldiacylglycerols (DGDG), sulphoquinovosyldiacylglycerols and phosphatidylglycerols (PG) significantly increased following the chilling treatment (4 °C) (with 12 h of low irradiance and 200 mM of NaCl). The DBI of DGDG and PG was decreased in the absence of the salt treatment. These results suggest that in the euhalophyte S. salsa, a 200 mM NaCl treatment increases chilling tolerance under conditions of low irradiance (100 μmol m^?2 s^?1).     

Sugarcane Underground Organs: Going Deep for Sustainable Production

Sugarcane breeding has greatly advanced in recent decades, but many aspects of sugarcane physiology are still poorly understood, including the root-shoot relationships that ultimately affect yield. Traditional methods for studying root systems are imprecise due to methodological difficulties of in situ assessment and sampling; this seems especially true for the sugarcane root system. Studies on sugarcane roots lag well behind those on other crops, in part due to the large plant stature and long crop cycle. Commercial sugarcane cultivars are hybrids from crosses mostly between Saccharum officinarum and S. spontaneum made by breeders at the beginning of the last century. These hybrids have a genomic structure composed of 80% S. officinarum, 10% S. spontaneum and 10% recombinants of these two species. S. spontaneum is included in large part for the robustness of its underground organs (root and rhizome). The S. spontaneum genes controlling these characteristics may be lost during recurrent backcrosses with S. officinarum to increase sugar content and yield. Thus, ratooning ability is one of the most desired traits. Ratooning ability comes mainly from the rhizomatousness of S. spontaneum, but this trait has been diluted during the selection process so that the stubble of hybrids does not have rhizomes sensu stricto. In this review, we revisit some basic aspects of the sugarcane root system, mainly from an ecophysiological view, and point out considerations for breeders to consider in designing the architecture of a new sugarcane cultivar that can meet the need for sustainable agricultural production.     

Photosynthetic responses of the low intertidal macroalga Sargassum fusiforme (Sargassaceae) to saline stress

Sargassum fusiforme, a species of brown seaweed with economic importance, inhabits lower intertidal zones where algae are often exposed to various stresses. In this study, changes in the photosynthetic performance of S. fusiforme under saline stress were investigated. The PSII performance in S. fusiforme significantly improved, when the thalli were exposed to 0% salinity, and remained high with prolonging treatment time. In contrast, the PSII activity declined considerably under salinities of 4.5 and 6%. The PSI activity did not change remarkably under saline stress, thus demonstrating higher tolerance to saline stress than PSII. In addition, the PSI activity could be also restored after saline treatments, when PSII was inhibited by 3-(3,4-dichlorophenyl)-1,1-dimethylurea. It might be as a result of changes in the NAD(P)H content in the thalli under saline stress. Our results suggested that PSI was much more tolerant to different saline stress than PSII in S. fusiforme. We demonstrated that S. fusiforme was much more tolerant to hyposaline than to hypersaline stress.     

Tissue chemistry and morphology affect root decomposition of perennial bioenergy grasses on sandy soil in a sub‐tropical environment

Second‐generation biofuels and bio‐based products derived from lignocellulosic biomass are likely to replace current fuels derived from simple sugars and starch because of greater yield potential and less competition with food production. Besides the high aboveground biomass production, these bioenergy grasses also exhibit extensive root systems. The decomposition of root biomass greatly influences nutrient cycling and microbial activity and subsequent accumulation of carbon (C) in the soil. The objective of this research was thus to characterize root morphological and chemical differences in six perennial grass species in order to better understand root decomposition and belowground C cycling of these bioenergy cropping systems. Giant reed (Arundo donax), elephantgrass (Pennisetum purpureum), energycane (Saccharum spp.), sugarcane (Saccharum spp.), sweetcane (Saccharum arundinaceum), and giant miscanthus (Miscanthus × giganteus) were established in Fall 2008 in research plots near Gainesville, Florida. Root decomposition rates were measured in situ from root decomposition bags over 12 months along with initial and final root tissue composition. Root potential decomposition rate constant (K) was higher in elephantgrass (3.64 g kg^?1 day^?1) and sweetcane (2.77 g kg^?1 day^?1) than in sugarcane (1.62 g kg^?1 day^?1) and energycane (1.48 g kg^?1 day^?1). Notably, K was positively related to initial root tissue total C (Total C), total fiber glucose (TFG), total fiber xylose (TFX), and total fiber carbohydrate (TFC) concentrations, but negatively related to total fiber arabinose (TFA) and lignin (TL) concentrations and specific root volume (SRV). Among the six species, elephantgrass exhibited root traits most favorable for fast decomposition: high TFG, high TFX, high TFC, high specific root length (SRL), and a low SRV, whereas giant reed, sugarcane, and energycane exhibited slow decomposition rates and the corresponding root traits. Thus, despite similar aboveground biomass yields in many cases, these species are likely to differentially affect soil C accumulation.     

Allelopathy: a tool for weed management in forest restoration

Forest restoration uses active management to re-establish natural forest habitat after disturbance. However, competition from early successional species, often aggressively invasive exotic plant species, can inhibit tree establishment and forest regeneration. Ideally, restoration ecologists can plant native tree species that not only establish and grow rapidly, but also suppress exotic competitors. Allelopathy may be a key mechanism by which some native trees could reduce the abundance and impact of exotic species. Allelopathy is a recognized tool for weed management in agriculture and agroforestry, but few studies have considered how allelopathic interactions may aid restoration. Here we introduce the “Homeland Security” hypothesis, which posits that some naïve exotic species may be particularly sensitive to allelochemicals produced by native species, providing a tool to reduce the growth and impacts of invasive exotic species on reforestation. This article explores how exploiting allelopathy in native species could improve restoration success and the re-establishment of natural successional dynamics. We review the evidence for allelopathy in agroforestry systems, and consider its relevance for reforestation. We then illustrate the potential for this approach with a case study of tropical forest restoration in Panama. C₄ grasses heavily invade deforested areas in the Panama Canal watershed, especially Saccharum spontaneum L. We measured the effect of leaf litter from 17 potential restoration tree species on the growth of invasive C₄ grasses. We found that leaf litter from legume trees had a greater inhibitory effect on performance of S. spontaneum than did litter from non-legume trees. However, allelopathic effects varied greatly among species within tree functional groups. Further evaluation of intra- and inter-specific interactions will help to improve our selection of restoration species.     

Connectivity between electron transport complexes and modulation of photosystem II activity in chloroplasts

In chloroplasts, photosynthetic electron transport complexes interact with each other via the mobile electron carriers (plastoquinone and plastocyanin) which are in surplus amounts with respect to photosystem I and photosystem II (PSI and PSII), and the cytochrome b ₆ f complex. In this work, we analyze experimental data on the light-induced redox transients of photoreaction center P₇₀₀ in chloroplasts within the framework of our mathematical model. This analysis suggests that during the action of a strong actinic light, even significant attenuation of PSII [for instance, in the result of inhibition of a part of PSII complexes by DCMU or due to non-photochemical quenching (NPQ)] will not cause drastic shortage of electron flow through PSI. This can be explained by “electronic” and/or “excitonic” connectivity between different PSII units. At strong AL, the overall flux of electrons between PSII and PSI will maintain at a high level even with the attenuation of PSII activity, provided the rate-limiting step of electron transfer is beyond the stage of PQH₂ formation. Results of our study are briefly discussed in the context of NPQ-dependent mechanism of chloroplast protection against light stress.     

Photosynthetic acclimation to drought stress in Agave salmiana Otto ex Salm-Dyck seedlings is largely dependent on thermal dissipation and enhanced electron flux to photosystem I

Agave salmiana Otto ex Salm-Dyck, a crassulacean acid metabolism plant that is adapted to water-limited environments, has great potential for bioenergy production. However, drought stress decreases the requirement for light energy, and if the amount of incident light exceeds energy consumption, the photosynthetic apparatus can be injured, thereby limiting plant growth. The objective of this study was to evaluate the effects of drought and re-watering on the photosynthetic efficiency of A. salmiana seedlings. The leaf relative water content and leaf water potential decreased to 39.6 % and ?1.1 MPa, respectively, over 115 days of water withholding and recovered after re-watering. Drought caused a direct effect on photosystem II (PSII) photochemistry in light-acclimated leaves, as indicated by a decrease in the photosynthetic electron transport rate. Additionally, down-regulation of photochemical activity occurred mainly through the inactivation of PSII reaction centres and an increased thermal dissipation capacity of the leaves. Prompt fluorescence kinetics also showed a larger pool of terminal electron acceptors in photosystem I (PSI) as well as an increase in some JIP-test parameters compared to controls, reflecting an enhanced efficiency and specific fluxes for electron transport from the plastoquinone pool to the PSI terminal acceptors. All the above parameters showed similar levels after re-watering. These results suggest that the thermal dissipation of excess energy and the increased energy conservation from photons absorbed by PSII to the reduction of PSI end acceptors may be an important acclimation mechanism to protect the photosynthetic apparatus from over-excitation in Agave plants.     

Hydrocarbons in leaf waxes of Saccharum and related genera

The composition of the n-alkanes in the leaf waxes of over 80 clones of Saccharum officinarum, S. edule, S. robustum, S. spontaneum and from a number of related species have been compared by GLC. The waxes contain predominantly odd alkanes, C₂₇–C₃₅, the major components being C₂₉ and C₃₁. In a number of clones, particularly of S. edule, a homologous series of alkenes was also present. No chemotaxonomic relationship could be derived from the compositions as the intraspecific variation was greater than the interspecific variations.