The effect of harvest time of forage on carbohydrate digestion in horses quantified by in vitro and mobile bag techniques

Carbohydrates in forages constitute an important part of the feed ration for all horses. The aim of the present study was to investigate the effect of harvest time on carbohydrate composition and digestion of various grass species. The experiment was divided into three parts 1) characterization of the chemical composition of experimental feeds (6 grass species: meadow fescue [MF], cocksfoot [CF], perennial ryegrass [PR], smooth bromegrass [SB], tall fescue [TF], and timothy [TI], and 3 harvest times: early, medium, and late first cut), 2) measurements of the in vitro digestion of selected experimental feeds (the 6 grass species, and 2 harvest times [early and late]) measured by in vitro gas production, and 3) in vivo digestion of selected experimental feeds (2 grass species: CF and PR, 2 harvest times [early and late]) measured by the mobile bag technique using caecum cannulated horses. An experimental field was established with plots containing each of the grass species in three replicate blocks. Grass samples were cut between 1200 and 1400 h at 4th of June (early first cut), 17th of June (medium first cut), and 1st of July (late first cut) and analyzed for crude protein (CP), neutral detergent fiber with heat stable amylase and free of residual ash (aNDFom) and water-soluble carbohydrates (WSC). The in vitro fermentation was investigated using the ANKOM RF gas production technique, where feeds were incubated for 48 h using horse caecal fluid as an inoculum. Gas production was modeled, and maximum gas production (MGP) was used to evaluate the potential digestibility of the feeds. Based on the chemical analyses and the in vitro experiment, early and late harvested CF and PR were selected for the in vivo experiment, which was conducted as a randomized 4 × 4 Latin square design including four periods, four horses and four feeds. In general, the CP content decreased whereas the aNDFom content increased as the grasses matured. The content of WSC increased in SB and TI, but decreased in CF, and fructans increased in SB, TI, PR, and TF as they matured. The in vitro MGP showed a clearer difference between harvest times than between grass species. Harvest time had larger effect on digestibility than grass species, and a high precaecal disappearance of the WSC fraction was measured by the mobile bag technique. Cocksfoot was identified as a grass species with potentially low digestibility and low WSC content and could potentially be used more for horses.

Grain-Filling Rate Improves Physical Grain Quality in Barley Under Heat Stress Conditions During the Grain-Filling Period

Heat stress is a primary constraint to Australia's barley production. In addition to impacting grain yield, it adversely affects physical grain quality (weight and plumpness) and market value. The incidence of heat stress during grain filling is rising with global warming. However, breeding for new superior heat-tolerant genotypes has been challenging due to the narrow window of sensitivity, the unpredictable nature of heat stress, and its frequent co-occurrence with drought stress. Greater scientific knowledge regarding traits and mechanisms associated with heat tolerance would help develop more efficient selection methods. Our objective was to assess 157 barley varieties of contrasting genetic backgrounds for various developmental, agro-morphological, and physiological traits to examine the effects of heat stress on physical grain quality. Delayed sowing (i.e., July and August) increased the likelihood of daytime temperatures above 30°C during grain-filling. Supplementary irrigation of field trials ensured a reduced impact of drought stress. Heat tolerance appeared to be the primary factor determining grain plumpness. A wide variation was observed for heat tolerance, particularly among the Australian varieties. Genotypic variation was also observed for grain weight, plumpness, grain growth components, stay-green and stem water-soluble carbohydrates (WSC) content, and mobilisation under normal and delayed sown conditions. Compared to normal sowing, delayed sowing reduced duration of developmental phases, plant height, leaf size, head length, head weight, grain number, plumpness, grain width and thickness, stem WSC content, green leaf area retention, and harvest index (HI), and increased screenings, grain length, grain-filling rate (GFR), WSC mobilisation efficiency (WSCME), and grain protein content. Overall, genotypes with heavier and plumper grains under high temperatures had higher GFR, longer grain-filling duration, longer green leaf area retention, higher WSCME, taller stature, smaller leaf size, greater HI, higher grain weight/plumpness potentials, and earlier flowering. GFR played a significant role in determining barley grain weight and plumpness under heat-stress conditions. Enhancing GFR may provide a new avenue for improving heat tolerance in barley.

Water- and ethanol-soluble carbohydrates of temperate grass pastures: a review of factors affecting concentration and composition

Temperate grasses contain both water- and ethanol-soluble carbohydrates. Water-soluble carbohydrates (WSCs) of temperate grasses include glucose, fructose, sucrose, and fructans (fructose polymers) of varying lengths. Ethanol-soluble carbohydrates (ESCs) consist of glucose, fructose, sucrose, and shorter fructans. WSCs and ESCs have been implicated in equine pasture-associated laminitis and other metabolic disorders. In this paper, the peer-reviewed literature of the past decade was summarized for selected factors influencing concentrations and composition of WSCs and ESCs in temperate grasses. WSC concentrations tended to increase under cool temperatures and during cooler seasons. WSC and ESC concentrations generally increased from morning to evening with a range of -20 to 74 g/kg DM for WSCs. Cultivar choice had variable effects on WSC concentrations. Frequent defoliation usually lowered WSC and fructan concentrations. Nitrogen application increased or decreased WSC concentrations, depending on the amount applied and the grass cultivars. Water stress had variable effects on WSC concentration and composition. Multiple factors should be considered before assuming how certain management or environmental conditions will affect WSCs, ESCs, or individual carbohydrates.

A review on the potentials of using feeds rich in water-soluble carbohydrates to enhance rumen health and sustainability of dairy cattle production

Cows are adapted to degrade structural plant carbohydrates (SC), such as cellulose and hemicelluloses, prevailing in grasses. Yet, the need for energy-dense diets in many intensive dairy production systems has shifted the dairy cattle's diet from SC-rich to high levels of starch. Feeding of starch-rich diets increases the risk of ruminal acidosis in cows, and feeding starch in the form of grains intensifies the competition over cereal grains and arable land among different livestock species, as well as between livestock and humans. Besides cellulose and hemicelluloses, grasses are also often rich in water-soluble carbohydrates (WSC), which comprise mono-, di-, oligo- and polysaccharides (fructans). Although the ruminal fermentation profile of mono- and disaccharides resembles that of starch, the degradation of oligo- and polysaccharides is slower, and their fermentation elicits a rather protecting effect on ruminal pH. When harvested in an early phase (i.e. ear emergence), grass hay and silages can reach WSC levels up to 150-200 g kg^-1 dry matter and energy levels close to starch-rich diets, allowing a significantly reduced inclusion of concentrate supplements. By doing so, this will enhance both rumen health and the sustainability of milk production. However, because the WSC are chemically very heterogeneous, the patterns and extent of their ruminal fermentation are difficult to predict without a clear analytical characterization. This review article aims to summarize both the benefits and potentials, as well as the challenges, with respect to using WSC-rich feedstuffs in the nutrition of dairy cattle and their effects on ruminal fermentation characteristics and milk production. © 2021 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Evolutionary and ecological perspectives on the wheat phenotype

Technologies, from molecular genetics to precision agriculture, are outpacing theory, which is becoming a bottleneck for crop improvement. Here, we outline theoretical insights on the wheat phenotype from the perspective of three evolutionary and ecologically important relations-mother-offspring, plant-insect and plant-plant. The correlation between yield and grain number has been misinterpreted as cause-and-effect; an evolutionary perspective shows a striking similarity between crop and fishes. Both respond to environmental variation through offspring number; seed and egg size are conserved. The offspring of annual plants and semelparous fishes, lacking parental care, are subject to mother-offspring conflict and stabilizing selection. Labile reserve carbohydrates do not fit the current model of wheat yield; they can stabilize grain size, but involve trade-offs with root growth and grain number, and are at best neutral for yield. Shifting the focus from the carbon balance to an ecological role, we suggest that labile carbohydrates may disrupt aphid osmoregulation, and thus contribute to wheat agronomic adaptation. The tight association between high yield and low competitive ability justifies the view of crop yield as a population attribute whereby the behaviour of the plant becomes subordinated within that of the population, with implications for genotyping, phenotyping and plant breeding.

Seasonal Variation in the Faecal Microbiota of Mature Adult Horses Maintained on Pasture in New Zealand

Simple Summary

Ten horses were kept on pasture for one year, with hay provided from June to October. Each month we measured how much pasture was present and collected pasture and hay samples to assess their nutrient content, and faecal samples from all horses to investigate the diversity of the bacterial species present using next-generation sequencing technology. The population of faecal bacteria was more diverse during the months when the horses were kept exclusively on pasture compared to the months when pasture was supplemented with hay. The diet offered, and the season and the month we sampled the paddock all had a major influence on the diversity of the species of bacteria in the faeces. While there were some differences between the horses, generally the bacterial populations could be grouped together in samples obtained during May, June, and July (late-autumn to winter period), and January, February, and March (a period of drought). More specifically we were able to show an association between specific bacterial species, nutrients (dry matter, protein, and structural carbohydrates), and climatic conditions (rainfall and temperature). Our study showed that the diversity and composition of the bacterial population of horses kept on pasture changes over a 12-month period, and this reflects changes in the nutrient composition of the pasture, which in turn is influenced by climate. The findings of this study may have implications for managing horses on pasture and the use of forages for horses susceptible to digestive problems.

Abstract

Seasonal variation in the faecal microbiota of forage-fed horses was investigated over a 12-month period to determine whether the bacterial diversity fluctuated over time. Horses (n = 10) were maintained on pasture for one year, with hay supplemented from June to October. At monthly intervals, data were recorded on pasture availability and climate (collected continuously and averaged on monthly basis), pasture and hay samples were collected for nutrient analysis, and faecal samples were collected from all horses to investigate the diversity of faecal microbiota using next-generation sequencing on the Illumina MiSeq platform. The alpha diversity of bacterial genera was high in all samples (n = 118), with significantly higher Simpson’s (p < 0.001) and Shannon-Wiener (p < 0.001) diversity indices observed during the months when horses were kept exclusively on pasture compared to the months when pasture was supplemented with hay. There were significant effects of diet, season, and month (ANOSIM, p < 0.01 for each comparison) on the beta diversity of bacterial genera identified in the faeces. While there was some inter-horse variation, hierarchical clustering of beta diversity indices showed separate clades originating for samples obtained during May, June, and July (late-autumn to winter period), and January, February, and March (a period of drought), with a strong association between bacterial taxa and specific nutrients (dry matter, protein, and structural carbohydrates) and climate variables (rainfall and temperature). Our study supports the hypothesis that the diversity and community structure of the faecal microbiota of horses kept on pasture varied over a 12-month period, and this variation reflects changes in the nutrient composition of the pasture, which in turn is influenced by climatic conditions. The findings of this study may have implications for grazing management and the preparation of conserved forages for those horses susceptible to perturbations of the hindgut microbiota.

Bottlenecks and opportunities in field-based high-throughput phenotyping for heat and drought stress

Flowering and grain-filling stages are highly sensitive to heat and drought stress exposure, leading to significant loss in crop yields. Therefore, phenotyping to enhance resilience to these abiotic stresses is critical for sustaining genetic gains in crop improvement programs. However, traditional methods for screening traits related to these stresses are slow, laborious, and often expensive. Remote sensing provides opportunities to introduce low-cost, less biased, high-throughput phenotyping methods to capture large genetic diversity to facilitate enhancement of stress resilience in crops. This review focuses on four key physiological traits and processes that are critical in understanding crop responses to drought and heat stress during reproductive and grain-filling periods. Specifically, these traits include: (i) time of day of flowering, to escape these stresses during flowering; (ii) optimizing photosynthetic efficiency; (iii) storage and translocation of water-soluble carbohydrates; and (iv) yield and yield components to provide in-season yield estimates. Moreover, we provide an overview of current advances in remote sensing in capturing these traits, and discuss the limitations with existing technology as well as future direction of research to develop high-throughput phenotyping approaches. In the future, phenotyping these complex traits will require sensor advancement, high-quality imagery combined with machine learning methods, and efforts in transdisciplinary science to foster integration across disciplines.

Suppressed ABA signal transduction in the spike promotes sucrose use in the stem and reduces grain number in wheat under water stress

Water stress is a primary trigger for reducing grain number per spike in wheat during the reproductive period. However, under stress conditions, the responses of plant organs and the interactions between them at the molecular and physiological levels remain unclear. In this study, when water stress occurred at the young microspore stage, RNA-seq data indicated that the spike had 970 differentially expressed genes, while the stem, comprising the two internodes below the spike (TIS), had 382. Abscisic acid (ABA) signal transduction genes were down-regulated by water stress in both these tissues, although to a greater extent in the TIS than in the spike. A reduction in sucrose was observed, and was accompanied by increases in cell wall invertase (CWIN) and sucrose:sucrose 1-fructosyl-transferase (1-SST) activities. Hexose and fructan were increased in the TIS but decreased in the spike. ABA was increased in the spike and TIS, and showed significant positive correlation with CWIN and 1-SST activities in the TIS. Overall, our results suggest that water stress induces the conversion of sucrose to hexose by CWIN, and to fructan by 1-SST, due to increased down-regulation of ABA signal transduction related-genes in the TIS; this leads to deficient sucrose supply to the spike and a decrease in grain number.

Atmospheric CO2 and VPD alter the diel oscillation of leaf elongation in perennial ryegrass: compensation of hydraulic limitation by stored-growth

We explored the effects of atmospheric CO₂ concentration (C_a ) and vapor pressure deficit (VPD) on putative mechanisms controlling leaf elongation in perennial ryegrass. Plants were grown in stands at a C_a of 200, 400 or 800 μmol mol^-1 combined with high (1.17 kPa) or low (0.59 kPa) VPD during the 16 h-day in well-watered conditions with reduced nitrogen supply. We measured day : night-variation of leaf elongation rate (LER_day  : LER_night ), final leaf length and width, epidermal cell number and length, stomatal conductance, transpiration, leaf water potential and water-soluble carbohydrates and osmotic potential in the leaf growth-and-differentiation zone (LGDZ). Daily mean LER or morphometric parameters did not differ between treatments, but LER_night strongly exceeded LER_day , particularly at low C_a and high VPD. Across treatments LER_day was negatively related to transpiration (R²  = 0.75) and leaf water potential (R²  = 0.81), while LER_night was independent of leaf water potential or turgor. Enhancement of LER_night over LER_day was proportional to the turgor-change between day and night (R²  = 0.93). LGDZ sugar concentration was high throughout diel cycles, providing no evidence of source limitation in any treatment. Our data indicate a mechanism of diel cycling between daytime hydraulic and night-time stored-growth controls of LER, buffering C_a and daytime VPD effects on leaf elongation.

Water-soluble carbohydrates in Patzkea paniculata (L.): a plant strategy to tolerate snowpack reduction and spring drought in subalpine grasslands

In subalpine grasslands of the central French Alps, cessation of traditional mowing promotes dominance of Patzkea paniculata (L.) G.H.Loos (Poaceae) tussocks, with high biomass but low fodder quality. Mowing limits P. paniculata abundance through the depletion of its water-soluble carbohydrate (WSC) reserves, which sustain early spring growth initiation. However, the effectiveness of mowing effects is modulated by grassland functional composition, fertilization and climate change, as WSC compounds, and notably fructans, support plant physiological responses to climate stresses such as drought or frost. To characterize the mechanisms underpinning the control of P. paniculata under global change, we tested the effects of climate manipulation (combined snow removal and drought) and management (cutting and fertilization) alone or in combination on P. paniculata WSC storage in assembled grassland communities of varying functional composition. Management and climate treatments individually decreased seasonal fructan storage, with neither additive nor synergic effects between them, primarily due to the dominance of management over climate effects. Fructan amounts were higher in individuals growing in unmanaged exploitative communities compared to unmanaged conservative communities, regardless of climate treatments, but management overrode these differences. Our findings suggest that reduction by combined snow removal and drought of P. paniculata carbon allocation to WSC storage may similarly limit its dominance to that in current mowing practices.

Effect of heat wave on N2 fixation and N remobilisation of lentil (Lens culinaris MEDIK) grown under free air CO2 enrichment in a mediterranean-type environment

The stimulatory effect of elevated [CO₂ ] (e[CO₂ ]) on crop production in future climates is likely to be cancelled out by predicted increases in average temperatures. This effect may become stronger through more frequent and severe heat waves, which are predicted to increase in most climate change scenarios. Whilst the growth and yield response of some legumes grown under the interactive effect of e[CO₂ ] and heat waves has been studied, little is known about how N₂ fixation and overall N metabolism is affected by this combination. To address these knowledge gaps, two lentil genotypes were grown under ambient [CO₂ ] (a[CO₂ ], ~400 µmol·mol^-1 ) and e[CO₂ ] (~550 µmol·mol^-1 ) in the Australian Grains Free Air CO₂ Enrichment facility and exposed to a simulated heat wave (3-day periods of high temperatures ~40 °C) at flat pod stage. Nodulation and concentrations of water-soluble carbohydrates (WSC), total free amino acids, N and N₂ fixation were assessed following the imposition of the heat wave until crop maturity. Elevated [CO₂ ] stimulated N₂ fixation so that total N₂ fixation in e[CO₂ ]-grown plants was always higher than in a[CO₂ ], non-stressed control plants. Heat wave triggered a significant decrease in active nodules and WSC concentrations, but e[CO₂ ] had the opposite effect. Leaf N remobilization and grain N improved under interaction of e[CO₂ ] and heat wave. These results suggested that larger WSC pools and nodulation under e[CO₂ ] can support post-heat wave recovery of N₂ fixation. Elevated [CO₂ ]-induced accelerated leaf N remobilisation might contribute to restore grain N concentration following a heat wave.

Effect of Wild Lactobacillus buchneri Strains on the Fermentation Profile and Microbial Populations of Sugarcane Silage

BACKGROUND

Sugarcane silage has been increasing as a feed in the tropics by dairy farmers. However, sugarcane normally had high yeast population that leads to intense alcoholic fermentation and excessive Dry-Matter (DM) loss during ensilage and after air exposure, as well. There are several patents that have recently shown the benefits of applying Lactobacillus buchneri in forage preservation.

OBJECTIVE

This study aimed to investigate the changes in pH, DM, Water-Soluble Carbohydrates (WSC) and fermentation end product concentrations that occur in sugarcane silage with or without inoculation with L. buchneri after 45 days of ensiling.

METHODS

Sugarcane plants were harvested with approximately 16 months of growth and chopped at 2 cm. Four strains of wild L. buchneri (56.1, 56.4, 56.9 and 56.26) and the commercial inoculant "Lalsil Cana" were evaluated. For all treatments, the theoretical application rate was 1.0 × 106 colony- forming units (cfu) per g of fresh weight. Data from the silo openings were analysed as a completely randomized design, with four replicates per treatment (inoculants).

RESULTS

The treatment with L. buchneri affected the DM content, pH, Lactic Acid Bacteria (LAB) population, DM recovery, and concentrations of WSC, lactic acid, acetic acid and ethanol of sugarcane silage after 45 days of ensiling. Yeasts and molds populations and the concentrations of propionic and butyric acids were not affected by the treatments.

CONCLUSION

Lactobacillus buchneri 56.1 and 56.4 are considered the most suitable strains for improving the fermentation of sugarcane silage and thus are potential inoculants for silage production. At present, we are preparing the patent application.

An Approach of Utilizing Water-Soluble Carbohydrates in Lignocellulose Feedstock for Promotion of Cellulosic l-Lactic Acid Production

Agricultural lignocellulose biomass generally contains certain amounts of water-soluble carbohydrates (WSC) such as glucose, fructose, or sucrose. These sugars are generally degraded in pretreatment at high temperature or discharged with wastewater in a detoxification process. This study proposed an approach of utilizing frequently ignored water-soluble carbohydrates for promotion of cellulosic l-lactic acid production. A simple solid state fermentation was performed during a corn stover storage period to convert the sugars into l-lactic acid and then a dry biorefining technology was applied to convert cellulose and hemicellulose fractions into the same l-lactic acid product. The 5-hydroxymethylfurfural (HMF) formation in pretreatment was significantly reduced and the consequent biodetoxification time was shortened. l-Lactic acid production was increased from 130.2 g/L to 139.0 g/L, and the minimum l-lactic acid selling price was reduced by 5.9%. This study provided an important option of biorefinery processing technology for production of value added biochemicals.

Water Stress Scatters Nitrogen Dilution Curves in Wheat

Nitrogen dilution curves relate a crop's critical nitrogen concentration (%N_c) to biomass (W) according to the allometric model %N_c = a W ^-b . This model has a strong theoretical foundation, and parameters a and b show little variation for well-watered crops. Here we explore the robustness of this model for water stressed crops. We established experiments to examine the combined effects of water stress, phenology, partitioning of biomass, and water-soluble carbohydrates (WSC), as driven by environment and variety, on the %N_c of wheat crops. We compared models where %N_c was plotted against biomass, growth stage and thermal time. The models were similarly scattered. Residuals of the %N_c - biomass model at anthesis were positively related to biomass, stem:biomass ratio, Δ¹³C and water supply, and negatively related to ear:biomass ratio and concentration of WSC. These are physiologically meaningful associations explaining the scatter of biomass-based dilution curves. Residuals of the thermal time model showed less consistent associations with these variables. The biomass dilution model developed for well-watered crops overestimates nitrogen deficiency of water-stressed crops, and a biomass-based model is conceptually more justified than developmental models. This has implications for diagnostic and modeling. As theory is lagging, a greater degree of empiricism might be useful to capture environmental, chiefly water, and genotype-dependent traits in the determination of critical nitrogen for diagnostic purposes. Sensitivity analysis would help to decide if scaling nitrogen dilution curves for crop water status, and genotype-dependent parameters are needed.

Physiological basis of chilling tolerance and early-season growth in miscanthus

BACKGROUND AND AIMS

The high productivity of Miscanthus × giganteus has been at least partly ascribed to its high chilling tolerance compared with related C4 crops, allowing for a longer productive growing season in temperate climates. However, the chilling tolerance of M. × giganteus has been predominantly studied under controlled environmental conditions. The understanding of the underlying mechanisms contributing to chilling tolerance in the field and their variation in different miscanthus genotypes is largely unexplored.

METHODS

Five miscanthus genotypes with different sensitivities to chilling were grown in the field and scored for a comprehensive set of physiological traits throughout the spring season. Chlorophyll fluorescence was measured as an indication of photosynthesis, and leaf samples were analysed for biochemical traits related to photosynthetic activity (chlorophyll content and pyruvate, Pi dikinase activity), redox homeostasis (malondialdehyde, glutathione and ascorbate contents, and catalase activity) and water-soluble carbohydrate content.

KEY RESULTS

Chilling-tolerant genotypes were characterized by higher levels of malondialdehyde, raffinose and sucrose, and higher catalase activity, while the chilling-sensitive genotypes were characterized by higher concentrations of glucose and fructose, and higher pyruvate, Pi dikinase activity later in the growing season. On the early sampling dates, the biochemical responses of M. × giganteus were similar to those of the chilling-tolerant genotypes, but later in the season they became more similar to those of the chilling-sensitive genotypes.

CONCLUSIONS

The overall physiological response of chilling-tolerant genotypes was distinguishable from that of chilling-sensitive genotypes, while M. × giganteus was intermediate between the two. There appears to be a trade-off between high and efficient photosynthesis and chilling stress tolerance. Miscanthus × giganteus is able to overcome this trade-off and, while it is more similar to the chilling-sensitive genotypes in early spring, its photosynthetic capacity is similar to that of the chilling-tolerant genotypes later on.

Genome-Wide Associations for Water-Soluble Carbohydrate Concentration and Relative Maturity in Wheat Using SNP and DArT Marker Arrays

Improving water-use efficiency by incorporating drought avoidance traits into new wheat varieties is an important objective for wheat breeding in water-limited environments. This study uses genome wide association studies (GWAS) to identify candidate loci for water-soluble carbohydrate accumulation-an important drought-avoidance characteristic in wheat. Phenotypes from a multi-environment trial with experiments differing in water availability and separate single nucleotide polymorphism (SNP) and diversity arrays technology (DArT) marker sets were used to perform the analyses. Significant associations for water-soluble carbohydrate accumulation were identified on chromosomes 1A, 1B, 1D, 2D, and 4A. Notably, these loci did not collocate with the major loci identified for relative maturity. Loci on chromosome 1D collocated with markers previously associated with the high molecular weight glutenin Glu-D1 locus. Genetic × environmental interactions impacted the results strongly, with significant associations for carbohydrate accumulation identified only in the water-deficit experiments. The markers associated with carbohydrate accumulation may be useful for marker-assisted selection of drought tolerance in wheat.

Coordinated nitrogen and carbon remobilization for nitrate assimilation in leaf, sheath and root and associated cytokinin signals during early regrowth of Lolium perenne

Background and Aims

The efficiency of N assimilation in response to defoliation is a critical component of plant regrowth and forage production. The aim of this research was to test the effect of the internal C/N balance on NO3- assimilation and to estimate the associated cytokinin signals following defoliation of perennial ryegrass ( Lolium perenne L. 'Grasslands Nui') plants.

Methods

Plants, manipulated to have contrasting internal N content and contrasting availability of water soluble carbohydrates (WSCs), were obtained by exposure to either continuous light or short days (8:16 h light-dark), and watered with modified N-free Hoagland medium containing either high (5 m m ) or low (50 μ m ) NO3- as sole N source. Half of the plants were defoliated and the root, sheath and leaf tissue were harvested at 8, 24 and 168 h after cutting. The spatiotemporal changes in WSCs, synthesis of amino acids and associated cytokinin content were recorded after cutting.

Key Results

Leaf regrowth following defoliation involved changes in the low- and high-molecular weight WSCs. The extent of the changes and the partitioning of the WSC following defoliation were dependant on the initial WSC levels and the C and N availability. Cytokinin levels varied in the sheath and root as early as 8 h following defoliation and preceded an overall increase in amino acids at 24 h. Subsequently, negative feedback brought the amino acid response back towards pre-defoliation levels within 168 h after cutting, a response that was under control of the C/N ratio.

Conclusions

WSC remobilization in the leaf is coordinated with N availability to the root, potentially via a systemic cytokinin signal, leading to efficient N assimilation in the leaf and the sheath tissues and to early leaf regrowth following defoliation.

Fall-grown oat to extend the fall grazing season for replacement dairy heifers

Our objective was to assess the pasture productivity and forage characteristics of 2 fall-grown oat (Avena sativa L.) cultivars, specifically for extending the grazing season and reducing reliance on harvested forages by replacement dairy heifers. A total of 160 gravid Holstein heifers (80 heifers/yr) were stratified by weight, and assigned to 1 of 10 identical research pens (8 heifers/pen). Initial body weights were 480 ± 43.5 kg in 2011 and 509 ± 39.4 kg in 2012. During both years of the trial, four 1.0-ha pasture replicates were seeded in August with Ogle oat (Schumitsch Seed Inc., Antigo, WI), and 4 separate, but similarly configured, pasture replicates were seeded with Forage Plus oat (Kratz Farms, Slinger, WI). Heifer groups were maintained as units, assigned to specific pastures, and then allowed to graze fall-oat pastures for 6h daily before returning to the barn, where they were offered a forage-based basal total mixed ration. Two heifer groups were retained in confinement (without grazing) as controls and offered the identical total mixed ration as pasture groups. During 2011, available forage mass increased with strong linear and quadratic effects for both cultivars, peaking at almost 9 Mg/ha on October 31. In contrast, forage mass was not affected by evaluation date in 2012, remaining ≤ 2,639 kg/ha across all dates because of droughty climatic conditions. During 2012, Ogle exhibited greater forage mass than Forage Plus across all sampling dates (2,678 vs. 1,856 kg/ha), largely because of its more rapid maturation rate and greater canopy height. Estimates of energy density for oat forage ranged from 59.6 to 69.1% during 2011, and ranged narrowly from 68.4 to 70.4% during 2012. For 2011, responses for both cultivars had strong quadratic character, in which the most energy-dense forages occurred in mid November, largely due to accumulation of water-soluble carbohydrates that reached maximum concentrations of 18.2 and 15.1% for Forage Plus and Ogle, respectively. Across the 2-yr trial, average daily gain for grazing heifer groups tended to be greater than heifers remaining in confinement (0.85 vs. 0.74 kg/d), but both management strategies produced weight gains within reasonable proximity to normal targets for heifers in this weight range. Fall-grown oat should be managed as stockpiled forage for deferred grazing, and good utilization of fall-oat forage can be accomplished by a one-time removal of standing forage, facilitated by a single lead wire advanced daily to prevent waste.

Abiotic stress-induced accumulation of raffinose in Arabidopsis leaves is mediated by a single raffinose synthase (RS5, At5g40390)

BACKGROUND

The sucrosylgalactoside oligosaccharide raffinose (Raf, Suc-Gal1) accumulates in Arabidopsis leaves in response to a myriad of abiotic stresses. Whilst galactinol synthases (GolS), the first committed enzyme in Raf biosynthesis are well characterised in Arabidopsis, little is known of the second biosynthetic gene/enzyme raffinose synthase (RS). Conflicting reports suggest the existence of either one or six abiotic stress-inducible RSs (RS-1 to -6) occurring in Arabidopsis. Indirect evidence points to At5g40390 being responsible for low temperature-induced Raf accumulation in Arabidopsis leaves.

RESULTS

By heterologously expressing At5g40390 in E.coli, we demonstrate that crude extracts synthesise Raf in vitro, contrary to empty vector controls. Using two independent loss-of-function mutants for At5g40390 (rs 5-1 and 5-2), we confirm that this RS is indeed responsible for Raf accumulation during low temperature-acclimation (4°C), as previously reported. Surprisingly, leaves of mutant plants also fail to accumulate any Raf under diverse abiotic stresses including water-deficit, high salinity, heat shock, and methyl viologen-induced oxidative stress. Correlated to the lack of Raf under these abiotic stress conditions, both mutant plants lack the typical stress-induced RafS activity increase observed in the leaves of wild-type plants.

CONCLUSIONS

Collectively our findings point to a single abiotic stress-induced RS isoform (RS5, At5g40390) being responsible for Raf biosynthesis in Arabidopsis leaves. However, they do not support a single RS hypothesis since the seeds of both mutant plants still contained Raf, albeit at 0.5-fold lower concentration than seeds from wild-type plants, suggesting the existence of at least one other seed-specific RS. These results also unambiguously discount the existence of six stress-inducible RS isoforms suggested by recent reports.

Developmental and growth controls of tillering and water-soluble carbohydrate accumulation in contrasting wheat (Triticum aestivum L.) genotypes: can we dissect them?

In wheat, tillering and water-soluble carbohydrates (WSCs) in the stem are potential traits for adaptation to different environments and are of interest as targets for selective breeding. This study investigated the observation that a high stem WSC concentration (WSCc) is often related to low tillering. The proposition tested was that stem WSC accumulation is plant density dependent and could be an emergent property of tillering, whether driven by genotype or by environment. A small subset of recombinant inbred lines (RILs) contrasting for tillering was grown at different plant densities or on different sowing dates in multiple field experiments. Both tillering and WSCc were highly influenced by the environment, with a smaller, distinct genotypic component; the genotype × environment range covered 350-750 stems m(-2) and 25-210 mg g(-1) WSCc. Stem WSCc was inversely related to stem number m(-2), but genotypic rankings for stem WSCc persisted when RILs were compared at similar stem density. Low tillering-high WSCc RILs had similar leaf area index, larger individual leaves, and stems with larger internode cross-section and wall area when compared with high tillering-low WSCc RILs. The maximum number of stems per plant was positively associated with growth and relative growth rate per plant, tillering rate and duration, and also, in some treatments, with leaf appearance rate and final leaf number. A common threshold of the red:far red ratio (0.39-0.44; standard error of the difference=0.055) coincided with the maximum stem number per plant across genotypes and plant densities, and could be effectively used in crop simulation modelling as a 'cut-off' rule for tillering. The relationship between tillering, WSCc, and their component traits, as well as the possible implications for crop simulation and breeding, is discussed.

Escape from water or remain quiescent? Lotus tenuis changes its strategy depending on depth of submergence

BACKGROUND AND AIMS

Two main strategies that allow plants to cope with soil waterlogging or deeper submergence are: (1) escaping by means of upward shoot elongation or (2) remaining quiescent underwater. This study investigates these strategies in Lotus tenuis, a forage legume of increasing importance in areas prone to soil waterlogging, shallow submergence or complete submergence.

METHODS

Plants of L. tenuis were subjected for 30 d to well-drained (control), waterlogged (water-saturated soil), partially submerged (6 cm water depth) and completely submerged conditions. Plant responses assessed were tissue porosity, shoot number and length, biomass and utilization of water-soluble carbohydrates (WSCs) and starch in the crown.

KEY RESULTS

Lotus tenuis adjusted its strategy depending on the depth of submergence. Root growth of partially submerged plants ceased and carbon allocation prioritized shoot lengthening (32 cm vs. 24.5 cm under other treatments), without depleting carbohydrate reserves to sustain the faster growth. These plants also developed more shoot and root porosity. In contrast, completely submerged plants became quiescent, with no associated biomass accumulation, new shoot production or shoot elongation. In addition, tissue porosity was not enhanced. The survival of completely submerged plants is attributed to consumption of WSCs and starch reserves from crowns (concentrations 50-75 % less than in other treatments).

CONCLUSIONS

The forage legume L. tenuis has the flexibility either to escape from partial submergence by elongating its shoot more vigorously to avoid becoming totally submerged or to adopt a non-elongating quiescent strategy when completely immersed that is based on utilizing stored reserves. The possession of these alternative survival strategies helps to explain the success of L. tenuis in environments subjected to unpredictable flooding depths.