Regulation of Light Absorption and Energy Dissipation in Sweet Sorghum Under Climate-Relevant CO2 and Temperature Conditions

Effects of Free Air Carbon-Dioxide Enrichment (FACE) and drought on PSII photochemistry, carbon assimilation (A) and photoprotection in leaves of Sorghum bicolor has been examined. In the drought-stressed plants (drys) growth under elevated CO2 increased the quantum yield of PSII (fPSII) throughout the day. This enhancement of fPSII is attributed to increases in both photochemical quenching (qp) and the effective quantum yield of PSII (Fv¢ /Fm¢ ). CO2 enhancement of fPSII in the well-watered plants (wets) occurred only during midday measurements and was entirely attributed to changes in qp. Non-photochemical quenching (NPQ) was higher in the drys but was reduced by elevated CO2 in both water treatments. Drought increased the total xanthophyll cycle pigments relative to total chlorophyll but was unaffected by growth [CO2]. The de-epoxidation state of the xanthophyll pool, DPS (A+Z/V+A+Z), was high under field conditions but showed no treatment differences. To further characterize the relationships between NPQ and DPS measurements were made on excised leaves in a controlled laboratory environment. There was no water treatment effect on NPQ, however, NPQ rates were reduced under elevated [CO2]. Conversely, growth [CO2] had no effect on DPS, however, the drys had a 57% higher DPS then the wets. Growth under elevated CO2 enhances C4 photosynthesis when A is limited by drought and/or midday conditions. Additionally, elevated CO2 and water-stress differently affected NPQ and pigment composition. Low NPQ under high CO2 did not correlate with DPS which maybe attributed to a reduced thylakoid D pH sufficient to alleviate NPQ but not DPS.

Sweet pearl millet [Pennisetum glaucum (L.) R. Br.] and sweet sorghum [Sorghum bicolor (L.) Moench], previously tested for ethanol production, were evaluated as high sugar crops for animal feeds to possibly replace silage corn (Zea mays L.). We compared the forage yield, nutritive value, and ensilability of one hybrid of sweet pearl millet and two of sweet sorghum to a locally adapted silage corn hybrid in five Canadian ecozones. Forage yields of sweet pearl millet and sorghum were similar to that of silage corn in the Boreal Shield, Mixedwood Plain, and Atlantic Maritime ecozones, greater in the Prairies, and lower in the Pacific Maritime ecozone. Across sites, forage dry matter concentration was less for sweet pearl millet (289 g kg−1) and sweet sorghum (245 g kg−1) than for silage corn (331 g kg−1). Sweet pearl millet had a lower total digestible nutrient (TDN) concentration (452 g kg−1 DM) and aNDF digestibility (NDFd) than sweet sorghum and silage corn along with greater neutral detergent fibre (aNDF) and water-soluble carbohydrate (WSC) concentrations than silage corn. Sweet sorghum had greater aNDF and WSC, lower starch, and similar TDN (534 g kg−1 DM) concentrations, but greater NDFd compared with silage corn. Sweet pearl millet and sorghum fermented as well as silage corn, reaching low pH values and acceptable concentrations of lactic and volatile fatty acids. Sweet sorghum is therefore a viable alternative to silage corn in Canada except in the Pacific Maritime ecozone, but early-maturing hybrids with acceptable DM concentration at harvest are required.

Sweet sorghum is a C4 grass which is traditionally cultivated for making syrup from the sugars in the stalks. Sweet and grain sorghum are in the same species, Sorghum bicolor (L.) Moench. In optimum conditions, sweet sorghum can grow 4.5 meters tall and produce 45 to 110 Mg of fresh weight biomass per hectare with less N and water than maize. Ethanol can be produced from sweet sorghum stalks by extracting the juice and fermenting the sugars with yeast. Bagasse remaining after extraction can be fed to livestock or converted to useable energy by burning to produce steam for generating electricity, anaerobic digestion to make methane, or reacting with oxygen at high temperature to produce synthetic gas. Sweet sorghum can be grown in most climates. Some cultivars will grow as far north and south as the 45° latitude. It is normally grown as an annual crop. But, in warm climates, a single seed planting can be managed for two or three years by leaving lower stalks and roots at harvest to produce new tillers for the next growing cycle. Rotating sweet sorghum in alternate years with a non-grass crop is an effective management tool for reducing insect, weed, and disease pests. Nitrogen fertilizer can often be reduced when sweet sorghum is planted after a legume crop such as soybean. Most of the sugar for syrup and ethanol from sweet sorghum is currently produced with open pollinating cultivars. Recently, hybrid sweet sorghums with increased sugar content and biomass yield have been developed in India, China, and the United States.

The energy crop sweet sorghum (Sorghum bicolor L. Moench) is raising considerable interest as a source of either fermentable free sugars or lignocellulosic feedstock with the potential to produce fuel, food, feed and a variety of other products. Sweet sorghum is a C4 plant with many potential advantages, including high water, nitrogen and radiation use efficiency, broad agro-ecological adaptation as well as a rich genetic diversity for useful traits. For developing countries sweet sorghum provides opportunities for the simultaneous production of food and bioenergy (e.g. bio-ethanol), thereby contributing to improved food security as well as increased access to affordable and renewable energy sources. In temperate regions (e.g. in Europe) sweet sorghum is seen as promising crop for the production of raw material for 2nd generation bio-ethanol. The project SWEETFUEL (Sweet Sorghum: An alternative energy crop) is supported by the European Commission in the 7th Framework Programme to exploit the advantages of sweet sorghum as potential energy crop for bio-ethanol production. Thereby, the main objective of SWEETFUEL is to optimize yields in temperate and semi-arid regions by genetic enhancement and the improvement of cultural and harvest practices. (Resume d'auteur)

Compared to grain sorghums, sweet sorghums typically have lower grain yield and thick, tall stalks which accumulate high levels of sugar (sucrose, fructose and glucose). Unlike commercial grain sorghum (S. bicolor ssp. bicolor) cultivars, which are usually F1 hybrids, commercial sweet sorghums were selected as wild accessions or have undergone limited plant breeding. Although all sweet sorghums are classified within S. bicolor ssp. bicolor, their genetic relationship with grain sorghums is yet to be investigated. Ninety-five genotypes, including 31 sweet sorghums and 64 grain sorghums, representing all five races within the subspecies bicolor, were screened with 277 polymorphic amplified fragment length polymorphism (AFLP) markers. Cluster analysis separated older sweet sorghum accessions (collected in mid 1800s) from those developed and released during the early to mid 1900s. These groups were emphasised in a principle component analysis of the results such that sweet sorghum lines were largely distinguished from the others, particularly by a group of markers located on sorghum chromosomes SBI-08 and SBI-10. Other studies have shown that QTL and ESTs for sugar-related traits, as well as for height and anthesis, map to SBI-10. Although the clusters obtained did not group clearly on the basis of racial classification, the sweet sorghum lines often cluster with grain sorghums of similar racial origin thus suggesting that sweet sorghum is of polyphyletic origin within S. bicolor ssp. bicolor

Comparative expression analysis of microRNAs and their targets in emerging bio-fuel crop sweet sorghum (Sorghum bicolor L.)

Sorghum, the fifth largest global cereal crop, comprises various types, such as grain, sweet, forage, and biomass sorghum, delineated by their designated end uses. Among these, sweet sorghum (Sorghum bicolor (L.) Moench) stands out for its unique versatility, exceptional abiotic stress tolerance and large biomass serving the multi-purpose of high-sugar forage, syrup, and biofuel production. Despite its significance, functional genomic research and biotechnological breeding in sweet sorghum are still in nascent stages, necessitating more efficient genetic transformation and genome-editing techniques. This study unveils Gaoliangzhe (GZ), an elite sweet sorghum variety for heightened resistance to salinity and drought. Through the establishment of an Agrobacterium tumefaciens‐mediated genetic transformation and CRISPR/Cas9-based genome-editing system in GZ, a breakthrough is achieved. Using genome-editing technology, we first produced a fragrant sweet sorghum line by targeting the BETAINE ALDEHYDE DEHYDROGENASE 2 (SbBADH2) gene. Our results establish a strong foundation for further functional genomic research and biotechnological breeding of sweet-sorghum varieties.

Abiotic stresses affect crop productivity worldwide. Plants have developed defense mechanisms against environmental stresses by altering the gene expression pattern which leads to regulation of certain metabolic and defensive pathways. Sorghum [Sorghum bicolor (L.) Moench] is an important crop in those regions irrigated by salty water. Sweet sorghum is a variant of common grain sorghum and is relatively more adapted to marginal growing conditions. Here, we compared the different response to salt stress of sweet and grain sorghum. We investigated six traits related with seed germination under salt-stress and normal conditions, conducted a genome-wide research on the salt effect on the gene expression of a landrace sweet and two grain sorghum by RNA-sequencing at seedling stage. The results showed that salt stress had significant inhibition to sorghum seed germination capability, and the inhibition to grain sorghum was greater. By comparing sweet and grain sorghum and the KEGG pathway analysis based on the DEGs, six genes involved in flavonoid biosynthesis pathway to tannins and anthocyanins from phenylalanine were identified in the landrace sweet sorghum, which expression was significant different with that in grain sorghum. Quantitative real-time PCR (qRT-PCR) data were closely in accordance with the transcript patterns estimated from the RNA-seq data. Tannins accumulation changes were associated with the genes expression under salt stress and control. These suggested that flavonoid biosynthesis pathway was involved in the sorghum resistance to salt stress. The present results suggested that flavonoid biosynthesis plays an important role in the sweet sorghum capacity for salt tolerance.

BackgroundSorghum (Sorghum bicolor L. Moench) cultivars store non-structural carbohydrates predominantly as either starch in seeds (grain sorghums) or sugars in stems (sweet sorghums). Previous research determined that sucrose accumulation in sweet sorghum stems was not correlated with the activities of enzymes functioning in sucrose metabolism, and that an apoplasmic transport step may be involved in stem sucrose accumulation. However, the sucrose unloading pathway from stem phloem to storage parenchyma cells remains unelucidated. Sucrose transporters (SUTs) transport sucrose across membranes, and have been proposed to function in sucrose partitioning differences between sweet and grain sorghums. The purpose of this study was to characterize the key differences in carbohydrate accumulation between a sweet and a grain sorghum, to define the path sucrose may follow for accumulation in sorghum stems, and to determine the roles played by sorghum SUTs in stem sucrose accumulation.ResultsDye tracer studies to determine the sucrose transport route revealed that, for both the sweet sorghum cultivar Wray and grain sorghum cultivar Macia, the phloem in the stem veins was symplasmically isolated from surrounding cells, suggesting sucrose was apoplasmically unloaded. Once in the phloem apoplasm, a soluble tracer diffused from the vein to stem parenchyma cell walls, indicating the lignified mestome sheath encompassing the vein did not prevent apoplasmic flux outside of the vein. To characterize carbohydrate partitioning differences between Wray and Macia, we compared the growth, stem juice volume, solute contents, SbSUTs gene expression, and additional traits. Contrary to previous findings, we detected no significant differences in SbSUTs gene expression within stem tissues.ConclusionsPhloem sieve tubes within sweet and grain sorghum stems are symplasmically isolated from surrounding cells; hence, unloading from the phloem likely occurs apoplasmically, thereby defining the location of the previously postulated step for sucrose transport. Additionally, no changes in SbSUTs gene expression were detected in sweet vs. grain sorghum stems, suggesting alterations in SbSUT transcript levels do not account for the carbohydrate partitioning differences between cultivars. A model illustrating sucrose phloem unloading and movement to stem storage parenchyma, and highlighting roles for sucrose transport proteins in sorghum stems is discussed.Electronic supplementary materialThe online version of this article (doi:10.1186/s12870-015-0572-8) contains supplementary material, which is available to authorized users.

Sweet sorghum, a C4 crop of tropical origin, is gaining momentum as a multipurpose feedstock to tackle the growing environmental, food and energy security demands. Under temperate climates sweet sorghum is considered as a potential bioethanol feedstock, however, being a relatively new crop in such areas its physiological and metabolic adaptability has to be evaluated; especially to the more frequent and severe drought spells occurring throughout the growing season and to the cold temperatures during the establishment period of the crop. The objective of this thesis was to evaluate some adaptive photosynthetic traits of sweet sorghum to drought and cold stress, both under field and controlled conditions. To meet such goal, a series of experiments were carried out. A new cold-tolerant sweet sorghum genotype was sown in rhizotrons of 1 m3 in order to evaluate its tolerance to progressive drought until plant death at young and mature stages. Young plants were able to retain high photosynthetic rate for 10 days longer than mature plants. Such response was associated to the efficient PSII down-regulation capacity mediated by light energy dissipation, closure of reaction centers (JIP-test parameters), and accumulation of glucose and sucrose. On the other hand, when sweet sorghum plants went into blooming stage, neither energy dissipation nor sugar accumulation counteracted the negative effect of drought. Two hybrids with contrastable cold tolerance, selected from an early sowing field trial were subjected to chilling temperatures under controlled growth conditions to evaluate in deep their physiological and metabolic cold adaptation mechanisms. The hybrid which poorly performed under field conditions (ICSSH31), showed earlier metabolic changes (Chl a + b, xanthophyll cycle) and greater inhibition of enzymatic activity (Rubisco and PEPcase activity) than the cold tolerant hybrid (Bulldozer). Important insights on the potential adaptability of sweet sorghum to temperate climates are given.

SbCASP4 improves the salt tolerance of sweet sorghum [Sorghum bicolor (L.) Mocnch] by enhancing the root apoplastic barrier and blocking the transport of sodium ions to the shoot. Sweet sorghum [Sorghum bicolor (L.) Mocnch] is a C4 crop with high biomass and tolerance to abiotic stresses such as salt, drought, and waterlogging. Sweet sorghum is widely used in bioenergy production, as a forage crop, and in liquors and beer. Root salt exclusion has been reported to underlie the salt tolerance of sweet sorghum. The Casparian strip has a key role in root salt exclusion, and the membrane domain protein (CASP) family participates in Casparian strip aggregation. However, the function and the regulatory mechanisms of SbCASP in response to salt stress in sweet sorghum are unclear. In the current study, we cloned SbCASP4 and determined that it is induced by salt stress and expressed in the endodermis cells of sweet sorghum. Histochemical staining and physiological indicators showed that heterologous expression of SbCASP4 significantly increased the tolerance to salt stress in transgenic Arabidopsis thaliana. Compared with wild type and casp5 mutants, under 50 mM NaCl treatment, SbCASP4-expression lines had the less leaf Na+, lower PI accumulation in stele, smaller oxidative damage and higher salinity threshold, longer root length and higher expression levels of the genes related to Casparian strip formation.

Sorghum (Sorghum bicolor L. Moench) has high water use efficiency, and is therefore widely cultivated in the Southern High Plains (SHP). Interest in sorghums for biofuel feedstock has increased recently as ethanol demand expands. Unlike grain sorghum, little data are available on N fertilizer requirements for ethanol production from sweet or forage sorghum production. Our objective was to compare ethanol yields and determine optimal N fertilizer needs for ethanol production from sweet sorghum and photoperiod sensitive (PPS) sorghum with limited irrigation in the SHP. Nitrogen fertilizer rates from 0 to 168 N kg ha−1 were tested on four sorghum cultivars (two sweet and two PPS) on Acuff sandy clay loam near Lubbock, TX in 2008 and 2009. Total dry matter (TDM) yields averaged 13 Mg ha−1 across years, cultivars, and N rates. Nitrogen fertilizer response in TDM was observed only in 2009, but bagasse yields responded to N fertilizer in both years. Cellulosic ethanol yields were greater with PPS sorghums than with sweet sorghums in both years. However, total ethanol yields were greater with sweet sorghums than PPS sorghums. Cellulosic ethanol and total ethanol yields responded to N in 2009 only. High preplant soil NO3 in 2008 apparently precluded TDM and ethanol yield response to N fertilizer. The optimum agronomic N fertilizer rate for ethanol and TDM across all four sorghums was 108 kg ha−1 respectively in 2009. The optimum N fertilizer rate for maximum profit with $ 0.70 kg N−1 and $.50 L−1 ethanol was 101 kg ha−1

Sweet sorghum (Sorghum bicolor) has been grown in the southeastern United States for more than 150 years on a relatively limited scale, primarily for forage and for the production of table syrup. However, interest in the crop has increased recently due to its potential as a feedstock for biofuels. Colletotrichum sublineola is the causal agent of anthracnose on cultivated sorghum and on the wild sorghum relative Johnsongrass (S. halepense). Anthracnose is an important disease of grain sorghum worldwide, but little is known about its impact on sweet sorghum in the U.S. The aggressiveness of four C. sublineola isolates collected from sweet and grain sorghum and from Johnsongrass at various locations across Kentucky was measured as disease incidence and severity on the susceptible heirloom sweet sorghum inbred Sugar Drip in inoculated field trials. The isolate from sweet sorghum was the most aggressive, while the two Johnsongrass isolates caused only minimal disease symptoms. Disease incidences of up to 99%, and severities of up to 16.7% of leaf area affected, had no negative effect on the yield of biomass, grain, juice, or Brix. Removal of sorghum seed heads increased Brix in the stalks and leaves, but did not affect susceptibility to anthracnose. The same group of fungal isolates was evaluated for aggressiveness in greenhouse assays on juvenile plants, and in the laboratory on seedlings and detached leaf sheaths. These protocols will be useful for prescreening sorghum germplasm for new sources of resistance or for characterizing the aggressiveness of new fungal isolates.

Sweet sorghum [Sorghum bicolor (L.) Moench] cultivars have been bred for high sugar content; with accompanying adequate forage yield, the crop may offer potential for ensiling. “Wray”; sweet sorghum, a good sugar producer, was grown under field conditions to determine nutritional quality and subsequent animal performance of silage from the yield. In one experiment, “Wray”; was compared to “FS‐5”;, medium‐tall forage sorghum, at four reproductive stages of growth, in regard to agronomic characteristics and chemical composition. In another study, the “Wray”; sweet sorghum was harvested in early and late reproductive stages and stored in experimental silos. Ensiling losses were measured; in addition, the silages were offered to sheep to determine in vivo digestibility (IVODMD) and intake. In the first experiment, dry matter yields of both sweet and forage sorghum increased during the reproductive period, from 6.2 to 11.9 and 7.7 to 13.9 Mg/ha, respectively; at maturity, grain yields were 651 and 3,5...

为给地表太阳辐射减弱和O₃浓度增加等大气环境变化条件下我国粮食生产和安全提供安全评估依据，利用开顶式气室（OTC）和黑色遮光网开展了1种熏气水平和2种辐射减弱程度的大田试验（野外CK，T1：遮光20%，T2：遮光40%，T3：O₃浓度100 nL/L，T4：O₃浓度100 nL/L与遮光20%复合，T5：O₃浓度100 nL/L与遮光40%复合）。结果表明：T1、T2和T4组的<em>Fv/Fm</em>、<em>L</em>_（PFD）与CK均相似且变化不明显，Yield、<em>qP</em>、<em>Y</em>（<em>NO</em>）、（1-<em>qP</em>）/<em>NPQ</em>分别较CK不同程度下降，而<em>NPQ</em>和<em>Y</em>（<em>NPQ</em>）较CK分别较大程度升高；T3-T5组的<em>Fv/Fm</em>，<em>L</em>_（PFD） 、Yield、<em>qP</em>、<em>Y</em>（<em>NO</em>）和（1-<em>qP</em>）/<em>NPQ</em>较CK不同程度降低，而<em>NPQ</em>和<em>Y</em>（<em>NPQ</em>）较CK分别显著升高且T5增幅显著大于T1-T4组。综上表明，复合胁迫下，冬小麦光能更多地向调节性热耗散途径分配，辐射减弱效应能使臭氧胁迫下冬小麦较好地自我调节以更好地适应逆境环境。尽管冬小麦对复合胁迫具有一定的适应能力，地表臭氧浓度升高和辐射减弱仍然是我国粮食生产中面临的一个重要问题。;At present, the aerosol radiative effect is the focus of many scholars and the solar radiation attenuated by direct or indirect effect to cause crop photosynthetic capacity decreased, resulting in crop production; At the same time the surface concentration of O₃ continuously increased, O₃ has strong negative effect on crop growth and metabolic processes and O₃ was direct threat to food safety to crops. Providing the basis for the security of National grain assessments and production under the conditions of reduced solar irradiance and elevated ozone concentration and other changes in atmospheric. Used open-top chamber (OTC) and black shading network to launch a fumigation level and two kinds of irradiance reduction degree. (field: CK, T1: shading 20%, T2: shading 40%, T3: 100nL/L O₃ concentration, T4: 100nL/L O₃ concentration and shading 20% compound, T5: 100nL/L O₃ concentration and shading 40% compound). The results showed that contrasting to CK, the <em>Fv/Fm</em>(PSⅡ maximum quantum yield), <em>L</em>_(PFD) (the relative limit of Photosynthetic function) of T1 treatment are similar and had no obvious changes, but the Yield, <em>qP</em>(Photochemical quenching coefficient), <em>Y(NO)</em> (the non regulation of energy dissipation in quantum yield), (1-<em>qP</em>)/<em>NPQ</em>(Light quantum excess degree) are decreased by 1.3%-21.5%, 7.5%-21.2%, 14.8%-20.6%, 27.7%-51.4% and NPQ(non photochemical quenching coefficient), <em>Y (NPQ)</em>(regulation of energy dissipation in quantum yield) are increased by 12.0%-31.9%, 53.4%-116%. Fv/Fm of T2 treatment had no significant changes, The Yield, <em>qP</em>, <em>L</em>_(PFD), <em>Y(NO)</em>, (1-<em>qP</em>)/<em>NPQ</em> were decreased by 13.2%-34.0%, 16.9%-36.2%, 6.8%-8.3%, 2.8%-16.0%, 23.1%-32.7%, The <em>NPQ</em>, <em>Y(NPQ)</em> were increased downby 15.9%-38.2% 39.5%-65.4%. The <em>Fv/Fm</em>, Yield(Optical system II actual photochemical efficiency), <em>qP</em> of T3 treatment were decreased by 11.8%-12.6%, 19.1%-28.0%, 15.6%-43.1%. The <em>L</em>_(PFD), <em>NPQ</em>, <em>Y</em>(<em>NPQ</em>), <em>Y</em>(<em>NO</em>), (1-<em>qP</em>)/<em>NPQ</em> increased by 1.1%-7.2%, 20.8%-83.6%, 12.6%-40.3%, 3.9%-22.2% obviously, 0.6%-34.1%. <em>Fv/Fm</em>, <em>L</em>_(PFD) of T4 treatment were similar to CK and compared with CK, the Yield, <em>qP</em>, <em>Y(NO)</em>, (1-<em>qP</em>)/<em>NPQ</em> decreased by 12.7%-42.8%, 7.2%-14.4% 18.8%-27.5%, 16.4%-45.1% and <em>NPQ, Y(NPQ)</em> increased by 13.4%-45.2% 6.9%-110.8%. <em>Fv/Fm</em>, Yield, <em>qP</em>, <em>L</em>_(PFD), </em>Y(NO)</em>, (1-<em>qP</em>)/<em>NPQ</em> of T5 treatment compared with CK, decreased by 30.4%-50.9%, 27.7%-43.2%, 2.2%-4.9%, 2.2%-10.2%, 23.3%-26.2%, 47.1%-61.6% and <em>NPQ</em>, <em>Y(NPQ)</em> increased by 27.5%-51.6% 63.3%-142.7%. Those results showed that (1) the single factor of Ozone significantly changed photosynthetic activity and distribution of light energy of winter wheat leaves but the single factor of reduced solar radiation alleviated negative effect photosynthesis restriction of winter wheat to a certain extent. (2) Further, under the combined stress, the light energy of winter wheat distributed more to regulatory heat dissipation. Composite action enhanced obviously the heat dissipation capability of winter wheat Radiation attenuation effect could cause winter wheat at the ozone stress self-regulated to better adapt to the adverse environment. Reducing appropriate the amount of solar radiation under Ozone stress could alleviate and reduce the light injury of winter wheat leaves. (3) Reducing solar radiation under the Ozone stress could inhibition the light injury and ensure the winter wheat optical system function normally and the normal growth of Winter Wheat. (4) In spite of winter wheat on composite stress has a certain ability to adapt; the reduced solar irradiance and elevated ozone concentration are still an important issue facing national grain production.