Transition of Ethiopian highland forests to agriculture-dominated landscapes shifts the soil microbial community composition

Background

Land use changes and related land management practices significantly alter soil physicochemical properties; however, their effects on the soil microbial community structure are still unclear. In this study, we used automated ribosomal intergenic spacer analysis to determine the fungal and bacterial community composition in soils from different land use areas in the Ethiopian highlands. Soil samples were collected from five areas with different land uses, natural forest, eucalyptus plantation, exclosure, grassland and cropland, which had all historically been natural forest.

Results

Our results showed a significant shift in the soil bacterial and fungal community composition in response to land use change. We also identified soil physicochemical factors corresponding to the changes in bacterial and fungal communities. Although most soil attributes, including soil organic carbon, total soil nitrogen, labile P, soil pH and soil aggregate stability, were related to the change in bacterial community composition, the total soil nitrogen and soil organic carbon had the strongest relationships. The change in fungal community composition was correlated with soil nutrients, organic carbon, soil nitrogen and particularly the labile P concentration.

Conclusions

The fungal community composition was likely affected by the alteration of vegetation cover in response to land use change, whereas the bacterial communities were mainly sensitive to changes in soil attributes. The study highlights the higher sensitivity of fungal communities than bacterial communities to land use changes.

     

Soil Ecosystem Changes During the Transition to No-Till Cropping

Summary

Growers in the United States and worldwide are adopting no-tillage (no-till) cropping to reduce soil erosion, improve soil quality, increase water infiltration, and reduce number of passes with farm equipment over their fields. Soil erosion from dry farmed (i.e., non-irrigated) cropland in most regions of the United States exceeds the tolerable rate. An understanding of the changes in the soil ecosystem with changing tillage practices is needed to minimize the impact of agriculture on the environment and foster the use of sustainable agricultural practices. The soil biota is critical to the functioning of any agro-ecosystem, but studying the soil biota is difficult due to the diversity and the challenges associated with isolating and identifying these organisms. Soil disturbance or lack of disturbance can have a profound effect on biotic populations, processes and community structure. This contribution examines changes that occur in soil during the transition to no-till cropping, interrelations among organisms in the soil food web, and the relationships between organisms and their environment. As interest grows in sustainable cropping systems that mimic processes and soil organic matter turnover of native, undisturbed systems, it is imperative to understand how the transition to no-till affects an organism's niche, or functional role within the soil environment. Ecosystem investigations will enhance the understanding of changes that occur with the adoption of reduced tillage and no-till cropping systems so that these systems become increasingly viable.     

Weed Seed Bank Dynamics

Summary

Weeds continue to have major impacts on crop production in spite of efforts to eliminate them. Most weed species rely on seed for regeneration and persistence. The species composition and density of weed seed in the soil vary greatly and are closely linked to the cropping history of the land. Altering tillage practices changes patterns of soil disturbance and weed seed depth in the soil, which plays a role in weed species shifts. Crop rotation and weed control practices also impact the weed seed bank in the soil. Information on the weed seed bank should be a useful tool for integrated weed management. Decision aid models are being developed that use information on the composition of the weed seed bank to estimate weed populations, crop yield loss, and to recommend weed control tactics. Understanding weed seed bank dynamics can also be used to guide management practices. Improving and applying our understanding of weed seed and seed bank dynamics is essential to developing improved weed management systems.     

Variation in C:N:S Stoichiometry and Nutrient Storage Related to Body Size in a Holometabolous Insect (Curculio davidi) (Coleoptera: Curculionidae) Larva

Body size can be an important factor controlling consumer stoichiometry. In holometabolous insects, body size is typically associated with nutrient storage. Consumer stoichiometry is known to vary within species across a range of body sizes; however, the contribution of nutrient storage to this variation is not well understood. We used the fifth-instar larvae of the oak weevil (Coleoptera: Curculio davidi Fairmaire), which is characterized by a high capacity for nutrient storage, to investigate the effect of shifts in nutrient storage with body mass on variations in larva stoichiometry. Our results showed that weevil larvae with larger body mass had a lower carbon (C) content, reflecting decreases in the sequestration rate of C-rich lipids. Larger larvae had elevated concentrations of nitrogen (N), sulfur (S), and protein. The similar patterns of variation in elemental composition and macromolecule storage with body weight indicate that the shift in nutrient storage is the main factor causing the variation in larval stoichiometry with body weight. This finding was further supported by the low variation in residual larval biomass C, N, and S concentrations after lipid extraction. These results help decipher the physiological mechanism of stoichiometric regulation in growing organisms.     

Gastrointestinal complaints in shift-working and day-working nurses in Iran

Background

There is evidence in the scientific literature of the adverse physiological and psychological effects of shift work. The work of nurses in hospitals is connected with shift and night work. Several publications have described gastrointestinal disturbances in shift workers. The aim of this study was to compare the frequency of gastrointestinal (GI) complaints of nurses on a rotating shift with that of nurses on a regular day shift.

Methods

The study involved 160 nurses (133 working in shifts and at night and 27 working on day shifts) in the Shahid Beheshti Hospital in Kashan, Iran. These nurses answered a Gastrointestinal Symptom Questionnaire regarding the presence of gastrointestinal symptoms (including heartburn, regurgitation, constipation, diarrhea and bloating). Positive responses required frequent symptom occurrence in the past 4 weeks. Significance of group differences was assessed by chi-square and Fisher-exact tests.

Results

Prevalence of GI symptoms was significantly higher (p = 0.009) in rotating-shift nurses (81.9%) than in day-shift nurses (59.2%). Irregular meal consumption (p = 0.01) and GI medications (p = 0.002) were all significantly higher among the rotating shift nurses. In both groups, regurgitation was the most common symptom.

Conclusion

Nurses on rotating shifts in Iran experience more GI disturbances than do nurses on day shifts.     

The effect of Calluna vulgaris cover on the performance and intake of ewes grazing hill pastures in northern Spain

The effect of the proportion of Calluna vulgaris cover on diet composition, intake and performance of sheep grazing hill vegetation communities in northern Spain is examined. A total of 591 non‐lactating Gallega ewes grazed for five consecutive grazing seasons (June to September) on replicated plots of hill pastures (1700 m.a.s.l.) composed principally of Festuca, Agrostis, Nardus and Calluna spp. but with different proportions of Calluna vulgaris cover, either 0·3 (C_0·3) or 0·7 (C_0·7) of the total area. In 1 year, twenty‐eight ewes suckling single lambs also grazed the plots. The mean stocking density over the 5 years was 8·7 ewes ha^–1. On treatment C_0·3, daily liveweight gains (33 g d^–1) of non‐lactating ewes were significantly (P < 0·001) greater than on treatment C_0·7 (12 g d^–1). Likewise in lactating ewes the difference in mean daily liveweight change was 40 g d^–1 (–5 vs. –45 g d^–1 for C_0·3 and C_0·7 treatments respectively; P < 0·001). Liveweight gains of lambs were only 80–100 g d^–1 from June to August and lambs only maintained live weight during August and September. The effect of lactational status on liveweight changes was not significant. Liveweight gains of non‐lactating ewes increased significantly (P < 0·001) from the first to the last year of the experiment on both treatments. The composition of the diet was significantly affected by treatment (P < 0·001), with a higher proportion of grass species on the C_0·3 treatment and a higher digestibility of the diet in the first half of the grazing season (P < 0·001). The proportion of C. vulgaris in the diet was significantly (P < 0·001) higher on the C_0·7 treatment and increased significantly (P < 0·001) from July to September on both treatments. There were no significant differences in the composition of the diet selected by lactating and non‐lactating ewes. The results demonstrate that on hill vegetation communities, in which the grass components (Festuca rubra, Agrostis capillaris, and Nardus stricta) cover at least 0·3 of the area and on which the preferred grass component (Festuca and Agrostis spp.) is maintained at a sward height of at least 2·5 cm, non‐lactating ewes can increase their live weight and body condition, but this increase is influenced by the proportion and quantity of species of grass in the diet, which is affected in turn by the species of grass available and their nutritive quality. However, ewes suckling lambs were not able to maintain their live weight and body condition except when Calluna cover was 0·3 and grass height was more than 3·5 cm. It is concluded that these indigenous vegetation communities can be used in sheep production systems to complement the use of improved pastures at other times of year. In particular, they can be utilized during the non‐lactating period (summer) to increase body condition before the beginning of the mating period in autumn.     

Raman spectroscopic study of rice globulin

The conformation of rice globulin was studied by Fourier-transform Raman spectroscopy as influenced by different buffer environments and heat treatments. The Raman spectrum of the native protein showed a predominance of α-helical structures as indicated by major amide I and III bands at 1657 and 1270 cm⁻¹, respectively. Highly acidic and alkaline pH conditions induced band shifts and intensity changes in amide I, amide III, and C–H (bending and stretching) vibrations, indicating protein denaturation. Addition of dithiothreitol and β-mercaptoethanol led to changes in S–S stretching vibration, whereas ethylene glycol and urea caused marked changes in tryptophan, tyrosine Fermi doublet and C–H band intensities. Heating at 100 °C resulted in progressive denaturation as indicated by band shifts and intensity changes of major spectral regions. Our results revealed that hydrophobic interactions and disulfide bonds play a major role in stabilizing the conformation and in thermal aggregation of rice globulin.     

Spatial structure and nest demography reveal the influence of competition, parasitism and habitat quality on slavemaking ants and their hosts

Background

Stable isotope ratios (¹³C/¹²C and ¹⁸O/¹⁶O) in fossil teeth and bone provide key archives for understanding the ecology of extinct horses during the Plio-Pleistocene in South America; however, what happened in areas of sympatry between Equus (Amerhippus) and Hippidion is less understood.

Results

Here, we use stable carbon and oxygen isotopes preserved in 67 fossil tooth and bone samples for seven species of horses from 25 different localities to document the magnitude of the dietary shifts of horses and ancient floral change during the Plio-Pleistocene. Dietary reconstructions inferred from stable isotopes of both genera of horses present in South America document dietary separation and environmental changes in ancient ecosystems, including C₃/C₄ transitions. Stable isotope data demonstrate changes in C₄ grass consumption, inter-species dietary partitioning and variation in isotopic niche breadth of mixed feeders with latitudinal gradient.

Conclusions

The data for Hippidion indicate a preference varying from C₃ plants to mixed C₃-C₄ plants in their diet. Equus (Amerhippus) shows three different patterns of dietary partitioning Equus (A.) neogeus from the province of Buenos Aires indicate a preference for C₃ plants in the diet. Equus (A.) andium from Ecuador and Equus (A.) insulatus from Bolivia show a preference for to a diet of mixed C₃-C₄ plants, while Equus (A.) santaeelenae from La Carolina (sea level of Ecuador) and Brazil are mostly C₄ feeders. These results confirm that ancient feeding ecology cannot always be inferred from dental morphology. While the carbon isotope composition of horses skeletal material decreased as latitude increased, we found evidence of boundary between a mixed C₃/C₄ diet signal and a pure C₄ signal around 32° S and a change from a mixed diet signal to an exclusively C₃ signal around 35°S. We found that the horses living at high altitudes and at low to middle latitude still have a C₄ component in their diet, except the specimens from 4000 m, which have a pure C₃ diet. The change in altitudinal vegetation gradients during the Pleistocene is one of several possibilities to explain the C₄ dietary component in horses living at high altitudes. Other alternative explanations imply that the horses fed partially at lower altitudes.     

Changing Significance of Inland Fisheries for Livelihoods and Nutrition in Bangladesh

SUMMARY

Fish is an essential and irreplaceable food in the rural Bangladesh diet. Inland capture fisheries are still the main source of fish in the diet. Although wetlands and fish habitat have been lost to drainage and flood control, the contribution of aquaculture to total fish production has been increasing in the last two decades.

The contribution of different species to fish intake as well as micro-nutrient intakes has been investigated based on food consumption studies. The main distinction is between small indigenous fish species (SIS), which typically are caught in open waters and floodplains, and larger species including carps (which are now largely cultured in ponds) and other fishes. The contribution of nutrient-minerals and especially vitamin A–from SIS is particularly important. Some SIS have very high vitamin A contents, whereas other fish, including carps have low vitamin A content. SIS that are eaten whole are also an important source of calcium. In addition, fish as part of a meal can enhance the intake of minerals present in other foods. Lastly, SIS are well-liked by the rural poor and are considered tasty and nutritious.

Case studies of fisheries and aquaculture interventions in Bangladesh indicate that SIS still contribute more to fish consumption than do cultured species for both poor and rich households. Fish consumption levels and the proportion of SIS in the diet are seasonal, peaking in and immediately after the wet season. Examples of community initiatives to protect over-wintering fish in local sanctuaries and to restore fish habitat and migration routes appear to have increased fish catches and consumption. Where beel (lake) fisheries were enhanced by stocking carps, the user communities benefited from higher catches and incomes. However, it seemed that fish consumption for non-participants increase where fishing was not limited, but fell where they were excluded from fishing by participants.

Extension efforts have encouraged rapid growth in aquaculture production in the last two decades. A case study indicated that increases in production were sustained and that practices had spread from extension participants. Declining capture fisheries and increasing carp production mean that carps have become relatively cheaper, and it has been seen that the proportion of carps to other fish sold doubled in less than a decade in some local markets. However, poor rural consumers without ponds are now more dependent on purchased fish, and increased production of carp from ponds does not compensate for substantial declines in their SIS catches from open waters. Aquaculture in flooded rice fields would normally exclude the poor, but there have been attempts where NGOs have organized landless people to benefit from stocking carps.

SIS can be included in pond aquaculture systems, and on-farm experiments show this can complement carp production by increasing production and cash returns. A focus on incorporating vitamin A rich SIS in aquaculture combined with widespread and concerted efforts to restore and sustainably manage the floodplain fisheries (which are dominated by SIS) can result in an important food-based strategy to improve micro-nutrient deficiencies in poor people in Bangladesh and similar flood-plains.     

Long-Term Changes in the Soil Properties and the Soil Macrofauna and Mesofauna of an Agricultural Field in Northern Japan During Transition from Chemical-Intensive Farming to Nature Farming

Summary

This paper reports the changes in soil chemical and physical properties, and in the populations and diversity of the soil macrofauna and mesofauna that occurred during the 10 years (1976-1986) following the initiation of nature farming practices on this once chemically-managed field in Northern Japan.     

Soil Weed Seed Banks and Weed Management

Abstract

Studies of soil weed seed banks are of relatively recent origin considering their importance as sources of diversity and continued occupation of many types of habitats, including agroecosystems. The management of weed seed banks is based on knowledge and modification of the behavior of seeds within the soil seed bank matrix. The behavior of seeds defines the phenotypic composition of the floral community of a field. Selection and adaptation over time have led to the highly successful weed populations that exploit resources unused by crops. The weed species infesting agricultural seed banks are those populations that have found successful trait compromises within and between the five roles of seeds: dispersal and colonization, persistence, embryonic food supply, display of genetic diversity, and as a means of species multiplication. Diverse weed seed populations provide seed banks the opportunity to exploit any change in conditions to ensure their enduring survival and spread. The soil seed bank matrix is the spatial arrangement of environmental and physical factors over time. The behavior of soil seed banks at any level of biological, spatial, or temporal organization is a consequence of the accumulated, emergent behavior at lower levels of organization. Weed seed behavior arises from their sensitivity to environmental conditions within the physical structure of the soil seed bank. This sensitivity is reflected in changes of short duration (e.g., germination), during the annual life cycle, over multiple years (e.g., population shifts), and over evolutionary time. Understanding the processes that drive and control seed behavior will allow us to manipulate and manage weed seed banks in an economic and sustainable manner. This knowledge will allow us to implement improved, more informed, weed management systems and strategies. Important weed bank management strategies include prevention of seed introduction on farm, acquisition of weed biology information (including predictive tools), decision making about weed seed infestation levels and their implementation (eradication, reduction, tolerance), weed seed population shifts (within the seed bank, between species, increased diversity), and manipulations encouraging beneficial weed species. Environmental modification and changes in cropping systems can also be of considerable strategic importance in weed management.     

Comparative studies of the influence of sward conditions on the ingestive behaviour of cows and sheep

Separate groups of non-lactating cows and wether sheep grazed at similar herbage allowances for two successive 5-d periods on swards that had previously been grazed frequently or infrequently with the intention of creating differences in canopy structure. Measurements were made of sward structure and composition, ingestive behaviour and diet composition. The preliminary treatments had little effect upon either sward conditions or animal behaviour.
Herbage mass was reduced from 4020 kg dry matter (DM) ha⁻¹ to 3290 kg DM ha⁻¹ on average over a 5-d grazing period as a consequence of the relatively low grazing pressure imposed. This resulted in a mean decline in intake per bite of 28%, and the changes for cattle and sheep did not differ significantly. However, there was a marked difference in the other behavioural responses of the two species; in the sheep biting rate fell and grazing time increased with declining herbage mass, particularly in the sward previously grazed infrequently, whereas the changes in the cattle were small.
Differences in the botanical composition of the herbage eaten by cattle and sheep were minor, but there was a small but consistent advantage to the sheep in the digestibility of the herbage eaten.
In the first of the two periods the variation in surface height after grazing was substantially greater for sheep-grazed than for cattle-grazed swards, indicating more patchy grazing by the sheep.
Estimates of daily herbage organic matter (OM) intake calculated from ingestive behaviour variables were high (means 38 and 32 g (kg LW) ⁻¹ for cattle and sheep respectively) and usually declined substantially over a grazing period.     

Ultrastructure of Fusion Product between Protoplasts from C3 and C4 Species of Amaranthaceae

Summary

This paper describes the ultrastructure of the electric field-induced fusion products of C₃ and C₄ species of Amaranthaceae at the early developmental stage. Protoplasts of C₃ species were isolated from a Ceiosia cristata L. cell suspension and, those of C₄ species were isolated from an Amaranthus tricolor L. cotyledon. Incompatibility occurred in the C₃/C₄ hybrid. The incompatibility reactions were detected in the newly formed hybrid cells accompanied with significant changes in the nucleolus (segregation of nucleolar components) and plastids (cup-like shape or amoeboid plastid enclosing cytoplasmic materials) of C₃ species parent. The structural changes in the organelles of the C₄ partner were less marked. After 5 days of culture, most organelles showed high cellular activity, and a normal dedifferentiation process of mesophyll chloroplasts was observed. At this stage nucleolar segregation was not detected and the C₃ species plastids were difficult to distinguish from the proplastids formed from mesophyll chloroplasts. In addition, some mitochondria showed bursting-like structure. However, under the culture condition used these somatic incompatibility did not seem to impair further growth of fusion products since they were still proliferating well resulting in callus formation.     

Impact of Global Change on Biological Processes in Soil

SUMMARY

The Earth is undergoing rapid environmental changes due to human activities. Three components of the ongoing global change, elevated atmospheric CO₂, N deposition, and global warming, may significantly impact soil biota directly through modifying the physical and chemical environment, and indirectly through altering aboveground plant growth and community composition. The biomass, community structure, and activities of microbes and animals in soil as well as their interactions will likely be affected, leading to changes in ecological processes and functions. Biological processes that may be modified by global change include organic matter decomposition, N mineralization, food web interaction, and biotic N fixation. Lack of the complexity in agroecosystems may amplify the effects of global change on many biological processes in agricultural soils. However, minimizing human disturbance and thus increasing the complexity of agroecosystems may enhance the potential of C sequestration in agricultural soils and the stability of belowground systems, thereby contributing to ecological sustainability.     

Effect on man's serum lipids of a faba-bean protein concentrate

The hypocholesterolemic effect of a vegetable dietary protein was studied by comparing egg white protein and faba-bean protein concentrate in 4 hyperchol-esterolemic persons (3 type IIA, 1 type IIB) and 1 normal individual. To maintain stable body weight, participants were kept for 1 month on an isocaloric diet (20% protein, 48% CHO, 32% fat, P/S=2) and then hospitalized for two consecutive cross-over periods of 18 days each, when they again received an isocaloric diet but of different composition (15% protein, 59% CHO, 26% fat, P/S=2), with the two protein sources as the basis of the cross-over. Serum total, LDL-, VLDL- and HDL-cholesterol and total and VLDL-triglycerides were analyzed every three days. Compared to baseline values, serum total and LDL-cholesterol decreased during both diets, reaching statistical significance for the egg white diet; serum HDL-cholesterol significantly decreased on the faba-bean diet; serum total and VLDL-Tg did not show any significant changes. Comparisons of lipid values at the end of each diet (faba-bean vs. egg white) showed small differences in mean values, none statistically significant. In conclusion, evidence was not obtained that the faba-bean diet produced a significant lowering of serum total and LDL-cholesterol.     

Growth,hormonal status and protein turnover in rats fed on a diet containing peas (Pisum sativum L.) as the source of protein

The inclusion of peas (Pisum sativum L.) as the source of protein in the diet of growing rats brings about a reduction in growth rate as well as the impairment in the liver, muscle and spleen weights as compared with casein fed controls. Also, a fall in plasma glucose, triglycerides and protein was observed in the legume fed animals, while no changes in cholesterol levels were found. Furthermore, the rats fed on the diet containing peas showed lower levels of plasma insulin, corticosterone, IGF-I and T₄ as compared with casein controls. Liver and muscle total protein (mg) and total DNA (mg) were markedly decreased in the legume fed animals, but DNA/g, protein/DNA and RNA/protein ratios were similar in both dietary groups. Likewise, liver and muscle fractional synthesis rates were similar in the casein and legume groups, while the whole body protein synthesis is assumed to be lower in the legume fed animals due to differences in body weights. It is concluded that animals fed on a diet containing peas (Pisum sativum L.) as the only source of protein showed less adverse effects than those found with other legumes such asVicia faba L. orPhaseolus vulgaris L., in which protein quality, antinutritional factors and nutrient availability could be involved.     

Effects of Whole Grain Wheat Bread on Visceral Fat Obesity in Japanese Subjects: A Randomized Double-Blind Study

Metabolic syndrome is a risk factor for cardiovascular diseases and has become increasingly common in Japan. Epidemiological studies show inverse associations between intake of whole wheat grains and metabolic syndrome, but few dietary intervention trials have investigated the effect of whole wheat grain consumption. It was investigated whether a diet in which refined wheat bread (RW diet) was substituted by whole grain wheat bread (WW diet) would reduce visceral fat obesity in Japanese subjects. A randomized double-blind placebo-controlled intervention study was conducted in 50 Japanese subjects with body mass index (BMI)?≥?23 kg/m². Subjects were randomly assigned WW (WW group) or RW diets (RW group) for 12 weeks. Blood samples and computed tomography scans were obtained every 6th week. The WW group showed decrease (?4 cm²) in visceral fat area (VFA) (p <?0.05), whereas the RW group showed no significant changes. These time-dependent changes were significantly different between the groups. WW diet led to significant and safe reductions in VFA in subjects with BMI?≥?23 kg/m². WW diet may contribute to preventing visceral fat obesity.     

NMR imaging of developing barley grains

NMR imaging was used for the non-invasive acquisition of three-dimensional images of developing barley grains from anthesis to maturity, 40 days after anthesis. Quantitative T₂ maps were generated, and chemical shift imaging detected changes in the tissue distribution of water, soluble carbohydrate and lipids. Complete 3D data are accessible on a website.     

Antihyperlipidemic Effect of Methanolic Extract from Opuntia joconostle Seeds in Mice Fed a Hypercholesterolemic Diet

The purpose of this study was to evaluate the hypolipidemic effect of a methanolic extract from Opuntia joconostle seeds fed to mice in a hypercholesterolemic diet. Acute toxicity of the methanolic extract was investigated by an established method. Phenolic composition and antioxidant activity were determined by high-performance liquid chromatography and DPPH, respectively. The total phenolic content of Opuntia joconostle seeds was 47.85?±?1.29 mg gallic acid equivalents/g dry weight. The main phenolic compounds were identified as quercetin, rutin, and cafeic acid. Percent inhibition of DPPH⁺ was 49.76?±?0.49 %. The oral LD₅₀ for the methanolic extract from the Opuntia joconostle seeds was >5,000 mg/kg BW. Mice fed a hypercholesterolemic diet for six days exhibited significantly (P?≤?0.001) higher plasma lipid levels than mice fed a normal diet. Remarkably, supplementation with methanolic extract from Opuntia joconostle at doses of 1, 2, and 5 g/kg body weight significantly (P?≤?0.001) prevented the increase in total cholesterol, low-density lipoprotein cholesterol, triglycerides level, and atherogenic index. Similar concentrations of the HDL cholesterol were observed in both treated and control groups. A significant dose-dependent reduction in lipid levels was noted for treated groups compared to the hypercholesterolemic group. We attribute this result to the seeds’ phenolic composition. This methanolic extract has potential to be included in short-term hypercholesterolemia treatment regimens as it exhibits hypolipidemic activity with no apparent toxic manifestations.     

Varietal Differences in Cell Wall β-(1→3),(1→4)-Glucan and Nonstructural Carbohydrate in Rice Stems during the Grain Filling Stage

Abstract

The contribution of cell wall components and nonstructural carbohydrate (NSC) to grain filling in rice (Oryza sativa L.) was clarified by investigating the differences in the dynamics of hemicellulose, sugar composition of hemicellulose, β-(1→3),(1→4)-glucan, and NSC among cultivars with different grain filling capacities. This investigation was performed using the stems of standard, high yield and low harvest index (HI) cultivars. Hemicellulose concentration in stems tended to decrease slightly during the grain filling stage. This decrease was attributed to a decrease in β-(1→3),(1→4)-glucan concentration, which was detected as a decrease in glucose composition of hemicellulose in the stems during the grain filling stage. The rate of decrease and decrease in the amount of β-(1→3),(1→4)-glucan in the stems differed among the cultivars. These were higher in high yield and high HI cultivars than in relatively low yield and low HI cultivars. Moreover, a positive correlation was observed between the rate of decrease in β-(1→3),(1→4)-glucan and NSC, indicating similarities in the dynamics of β-(1→3),(1→4)-glucan and NSC among the cultivars. When the top half of panicle was removed, β-(1→3),(1→4)-glucan and NSC concentrations in the culm and leaf sheath did not decrease during the grain filling stage. Therefore, the β-(1→3),(1→4)-glucan in stems might be one of the sources that supply substrate to panicle as well as NSC.