Response of rice to different forms of urea and phosphorus fertilization under intermediate deepwater conditions (15–50 cm)

Summary Under intermediate deepwater condition with water depths of 15–35 cm during most of the crop growth period, sulphur coated urea and urea supergranule placement was superior to prilled urea in increasing the relative uptake and grain yield (23–25%) of rice. A semi-tall variety (CR 1016) responded better to the nitrogen application than a tall variety (CR 1030).The crop fertilized with N produced more number of tillers and grain yield than the unfertilized crop under complete submergence for 6 days at seedling establishement stage (8 days after transplanting) followed by waterlogging of 25±5 cm throughout the crop growth period. Application of phosphorus together with nitrogen increased the grain yield (9–14%) over nitrogen alone. Crop fertilized with these two nutrients (NP) increased their uptake and yield components.     

Scale-specific determinants of a mixed beech and oak seedling–sapling bank under different environmental and biotic conditions

Based on the hypothesis that both plant size and local conspecific density influence allocation to female/male functions, we explored the relationship between plant height, local conspecific density, sexual expression, and fruit production in the andromonoecious shrub Caesalpinia gilliesii. We quantified the total number of perfect and staminate flowers, the pollen received and fruits produced per plant in two populations, and estimated phenotypic gender and fruit set. Local density failed to explain phenotypic gender, nevertheless, plant height and fruit set increased with local density in one population where, in addition, the slopes for the size-dependent sex allocation curve were steeper. As observed for other plant species, this suggests that between population differences in resource availability is the main underlying factor for the observed population differences in the size-dependent allocation pattern to flowers and fruits. On the other hand, the number of staminate and perfect flowers per plant increased with plant height and the fastest increase of staminate flowers resulted in a male-biased size-dependent sex allocation strategy in both populations. Since pollination intensity was not correlated with plant height in any population, the observed allocation strategy cannot be attributed to differences in pollen availability between different sized individuals, but to differences in plant size. Finally, because fruit set and total fruit number increased with plant height in one population, the obtained results provide further evidence that animal-pollinated, andromonoecious species may exhibit a male-biased size-dependent sex allocation strategy, which may favor female fecundity.     

Response of plant biomass to nitrogen addition and precipitation increasing under different climate conditions and time scales in grassland北大核心CSCD

Aims Plant biomass accounts for the main part of grassland productivity. The productivity of grassland regarded as one of important ecosystem function is always co-limited by nitrogen and water availability, therefore, how grasslands respond to atmosphic nitrogen (N) addition and precipitation increasing need to be systematically and quantitatively evaluated at different climate conditions and temporal scales. Methods To investigate the impact of nitrogen addition and precipitation increasing on grassland biomass over climate conditions and temproal scales, a meta-analysis was conducted based on 46 papers that were published during 1990-2017 involving 1 350 observations. Important findings Results showed that: (1) N addtion, precipitation increasing and the combinations of these two treatments significantly increased the aboveground biomass (37%, 41%, 104%), total biomass (32%, 23%, 60%) and the ratio of aboveground biomass to belowground biomass (29%, 25%, 46%) in grassland ecosystem. Belowground biomass showed no response to single N addtion, but could be significantly enhanced together with increaseing precipitation; (2) The response of grassland biomass under these N addtion and the increasing of precipitation showed obvious spatial pattern under different climate conditions. The N addition tended to increase more aboveground biomass, total biomass and the ratio of aboveground biomass to belowground biomass under high sites with high mean annual air temperature (MAT) and mean annual precipitation (MAP) while precipitation increasing tended to simulate more belowground biomass and total biomass under low MAT and MAP sites; (3) In addition, the response of grassland biomass under these two global change index showed obvious temporal pattern. With the increase of duration of N addition, the belowgound biomass tended to decrease, while the aboveground biomass, total biomass and the ratio of aboveground biomass to belowground biomass tended to increase under N addition. With the increase of duration of precipitation manipulation, the total biomass showed no response to precipitation increasing, while aboveground biomass, belowground biomass and the ratio of aboveground biomass to belowground biomass tended to be enhanced. The results indicated that aboveground biomass was more likely to be enhanced than belowground biomass under N addition or precipitation increasing in the long term. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

9-β-L(+) Adenosine: A new naturally occurring plant growth substance elicited by triacontanol in rice

The naturally occurring plant growth substance elicited by triacontanol was found to be 9--L(+) adenosine by physical and spectral methods. At picomolar concentrations, 9--L(+) adenosine stimulated growth as determined by dry weight measurements of several plant species. Reaction of adenosine deaminase with adenosine from rice showed that small quantities of 9--L(+) adenosine exist in plants. We believe this is the first report of 9--L(+) adenosine as a natural product.     

The significance of denitrification of applied nitrogen in fallow and cropped rice soils under different flooding regimes I. Greenhouse experimènts

The role of nitrification-denitrification in the loss of nitrogen from urea applied to puddled soils planted to rice and subjected to continuous and intermittent flooding was evaluated in three greenhouse pot studies. The loss of N via denitrification was estimated indirectly using the¹⁵N balance, after either first accounting for NH₃ volatilization or by analyzing the¹⁵N balance immediately before and after the soil was dried and reflooded. When urea was broadcast and incorporated the loss of¹⁵N from the soil-plant systems depended on the soil, being about 20%–25% for the silt loams and only 10%–12% for the clay. Ammonia volatilization accounted for an average 20% of the N applied in the silt loam. Denitrification losses could not account for more than 10% of the applied N in any of the continuously flooded soil-plant systems under study and were most likely less than 5%. Intermittent flooding of soil planted to rice did not increase the loss of N. Denitrification appeared to be an important loss mechanism in continuously flooded fallow soils, accounting for the loss of approximately 40% of the applied¹⁵N. Loss of¹⁵N was not appreciably enhanced in fallow soils undergoing intermittent flooding. Apparently, nitrate formed in oxidized zones in the soil was readily denitrified in the absence of plant roots. Extensive loss (66%) of¹⁵N-labeled nitrate was obtained when 100 mg/pot of nitrate-N was applied to the surface of nonflooded soil prior to reflooding. This result suggests that rice plants may not compete effectively with denitrifiers if large quantities of nitrate were to accumulate during intermittent dry periods.     

Response of “criollo” maize to single and mixed species inocula of arbuscular mycorrhizal fungi

We tested the effect of two single species inocula and a mixed inoculum of the native population of arbuscular mycorrhizal (AM) fungi on the growth response of criollo maize (Zea mays L.). To determine the inocula that produced the highest response on maize growth, we conducted a greenhouse experiment at 3 levels of P fertilization (0, 40 and 80 kg ha^–1). Inoculation with Glomus mosseae (Nicolson and Gerdemann) Gerd. and Trappe (LMSS) produced the greatest shoot growth rates at the two lowest P fertilization levels. Inoculation with Acaulospora bireticulata Rothwell and Trappe (ABRT) and the native population (NP) resulted in similar shoot growth rates at all P levels. These rates were higher than the non-mycorrhizal control rate at the lowest P level but lower than the control at the highest P level. Also, ABRT and NP had significantly lower shoot growth rates than the inoculation treatment with G. mosseae at all P levels. The non-mycorrhizal control had the lowest growth rate at the lowest P level but its growth rate increased linearly with increased P fertilization. Inoculation with G. mosseae and A. bireticulata produced similar colonization rates which were lower than the native population colonization rate. There was no correlation between colonization and shoot growth rates.     

Occurrence of different trichothecenes and deoxynivalenol-3-β-d-glucoside in naturally and artificially contaminated Danish cereal grains and whole maize plants

Fusarium mycotoxins such as deoxynivalenol (DON) can occur in cereals conjugated to glucose and probably also to other sugars. These conjugates, which are often referred to as ??masked mycotoxins??, will not be detected with routine analytical techniques. Furthermore, it is suspected that the parent toxin may again be released after hydrolysis in the digestive tracts of animals and humans. Today, our knowledge of the occurrence of these compounds in cereal grains is limited. In this paper, a LC-MS/MS method for the simultaneous determination of DON, deoxynivalenol-3-??-d-glucoside (DON-3-glucoside), 3 acetyl-DON, nivalenol, fusarenon-X, diacetoxyscirpenol, HT-2 toxin, and T-2 toxin in naturally (n?=?48) and artificially (n?=?30) contaminated cereal grains (wheat, barley, oat, rye triticale) is reported. The method has also been applied to whole fresh maize plant intended for production of maize silage (n?=?10). The samples were collected from the harvest years 2006?C2010, The results show that DON-3-glucoside and DON co-occurred in cereal grains and, especially in several of the highly contaminated samples, the concentration of the glucoside can be relatively high, corresponding to over 37?% of the DON concentration. The DON-3-glucoside levels in both the naturally and in the artificially grain inoculated with Fusarium were second only to DON, and were generally higher than those of the other tested trichothecenes, which were found at low concentrations in most samples, in many cases even below the detection limit of the method. This argues for the importance of taking DON-3-glucoside into account in the ongoing discussion within the European Community concerning exposure re-evaluations for setting changed values for the tolerable intake for DON. Our results indicate that, in the naturally contaminated grains and in the Fusarium infested cereal grains (winter and spring wheat, oat, triticale), the concentration level of DON-3-glucoside is positively correlated to the DON content. When the DON concentration is high, then the content of DON-3-glucoside will most probably also be high and vice versa.     

Syntrophic oxidation of propionate in rice field soil at 15 and 30°C under methanogenic conditions

Propionate is one of the major intermediary products in the anaerobic decomposition of organic matter in wetlands and paddy fields. Under methanogenic conditions, propionate is decomposed through syntrophic interaction between proton-reducing and propionate-oxidizing bacteria and H(2)-consuming methanogens. Temperature is an important environmental regulator; yet its effect on syntrophic propionate oxidation has been poorly understood. In the present study, we investigated the syntrophic oxidation of propionate in a rice field soil at 15°C and 30°C. [U-(13)C]propionate (99 atom%) was applied to anoxic soil slurries, and the bacteria and archaea assimilating (13)C were traced by DNA-based stable isotope probing. Syntrophobacter spp., Pelotomaculum spp., and Smithella spp. were found significantly incorporating (13)C into their nucleic acids after [(13)C]propionate incubation at 30°C. The activity of Smithella spp. increased in the later stage, and concurrently that of Syntrophomonas spp. increased. Aceticlastic Methanosaetaceae and hydrogenotrophic Methanomicrobiales and Methanocellales acted as methanogenic partners at 30°C. Syntrophic oxidation of propionate also occurred actively at 15°C. Syntrophobacter spp. were significantly labeled with (13)C, whereas Pelotomaculum spp. were less active at this temperature. In addition, Methanomicrobiales, Methanocellales, and Methanosarcinaceae dominated the methanogenic community, while Methanosaetaceae decreased. Collectively, temperature markedly influenced the activity and community structure of syntrophic guilds degrading propionate in the rice field soil. Interestingly, Geobacter spp. and some other anaerobic organisms like Rhodocyclaceae, Acidobacteria, Actinobacteria, and Thermomicrobia probably also assimilated propionate-derived (13)C. The mechanisms for the involvement of these organisms remain unclear.     

β-Galactosidase activity of Escherichia coli under long-term starvation, alterations in temperature, and different nutrient conditions in lake water

β-Galactosidase activity of Escherichia coli was investigated in response to long-term starvation, changes in temperature and the presence of certain nutrient sources in lake water. β-Galactosidase activity decreased markedly in filtered-autoclaved lake water at 25 °C and 37 °C, whereas it remained almost constant at 4 °C and 15 °C for 60 days. Increases in β-galactosidase activity were observed in response to the following nutrient sources: glycine, serine, methionine and ammonium sulfate at 4 °C; glycine and ammonium sulfate at 15 °C; glycine, serine, methionine and ammonium sulfate at 30 °C. Glycine addition led to an increase in β-galactosidase activity of almost five and seven orders of magnitude at 15 °C and 30 °C, respectively. In addition, L-methionine had the strongest influence on β-galactosidase activity, which was detected as an increase of seven and eleven orders of magnitude at 4 °C and 30 °C, respectively. The effect of several amino acids and other nitrogen sources depended on the concentration of the nutrient source and the temperature. The results showed that, in lake water, long-term starvation, temperature change, and variations in nitrogen sources alter β-galactosidase activity. Those effects should be taken into account when monitoring coliforms from the environment. Electronic Publication     

Development of upland rice introgression lines and identification of QTLs for basal root thickness under different water regimes

Introgression lines (ILs) are valuable materials for identifying quantitative trait loci (QTLs),evaluating genetic interactions,and marker assisted breeding.A set of 430 ILs (BC5F3) containing segments from upland tropical japonica cultivar IRAT109 in a lowland temperate japonica cultivar Yuefu background were developed.One hundred and seventy-six polymorphic markers were used to identify introgressed segments.No segment from IRAT 109 was found in 160 lines.Introgressed segments of the other 270 lines covered 99.1％ of the donor genome.The mean number of introgressed donor segments per individual was 3.3 with an average length of 14.4 cM.QTL analysis was conducted on basal root thickness (BRT) of the 270 ILs grown under irrigated lowland,upland and hydroponic conditions.A total of 22 QTLs affecting BRT were identified,six QTLs (qBRT3.1,qBRT3.2,qBRT6.1,qBRT8.2,qBRT9.1,and qBRT9.2) were consistently expressed under at least two environments (location and water regime),and qBRT7.2 was a new BRT QTL identified under lowland conditions.IL255 containing qBRT9.1 showed an increase of 10.09％ and 7.07％ BRT over cultivar Yuefu when grown under upland and lowland conditions,respectively.Using a population of 304 F2:3 lines derived from the cross IL255 × Yuefu,qBRT9.1 was validated and mapped to a 1.2 cM interval between RM24271 and RM566.The presence of qBRT9.1 explained 12％ of BRT variation.The results provide upland rice ILs and BRT QTLs for analyzing the genetic basis of drought resistance,detecting favorable genes from upland rice,and rice drought resistance breeding.     

Effects of environmental conditions on cell growth and poly-β-hydroxybutyrate accumulation in Alcaligenes eutrophus

Influences of the control of glucose and oxygen concentrations on cell growth and poly--hydroxybutyrate (PHB) accumulation in Alcaligenes eutrophus were studied. Glucose affects both biosynthesis and glycolysis directly and the other pathways indirectly. PHB accumulation could also be stimulated under oxygen limitation conditions, but the final PHB content within the cells was less than in the case of nitrogen limitation. When the culture was shifted from the PHB accumulation state to balanced growth conditions, PHB degradation occurred in the cells. The cell growth was inhibited by high PHB content within the cells.     

Identification of QTLs with main, epistatic and QTL?×?environment interaction effects for salt tolerance in rice seedlings under different salinity conditions

Salt tolerance of rice (Oryza sativa L.) at the seedling stage is one of the major determinants of its stable establishment in saline soil. One population of recombinant inbred lines (RILs, F (2:9)) derived from a cross between the salt-tolerant variety Jiucaiqing and the salt-sensitive variety IR26 was used to determine the genetic mechanism of four salt tolerance indices, seedling height (SH), dry shoot weight (DSW), dry root weight (DRW) and Na/K ratios (Na/K) in roots after 10 days in three salt concentrations (0.0, 0.5 and 0.7 % NaCl). The main effect QTLs (M-QTLs) and epistatic QTLs (E-QTLs) were detected by QTL IciMapping program using single environment phenotypic values. Eleven M-QTLs and 11 E-QTLs were identified for the salt tolerance indices. There were six M-QTLs and two E-QTLs identified for SH, three M-QTLs and five E-QTLs identified for DSW, two M-QTLs and one E-QTL identified for DRW, and three E-QTLs identified for Na/K. The phenotypic variation explained by each M-QTL and E-QTL ranged from 7.8 to 23.9 % and 13.3 to 73.7 %, respectively. The QTL-by-environment interactions were detected by QTLNetwork program in the joint analyses of multi-environment phenotypic values. Six M-QTLs and five E-QTLs were identified. The phenotypic variation explained by each QTL and QTL × environment interaction ranged from 0.95 to 6.90 % and 0.02 to 0.50 %, respectively. By comparing chromosomal positions of these M-QTLs with those previously identified, five M-QTLs qSH1.3, qSH12.1, qSH12.2, qDSW12.1 and qDRW11 might represent novel salt tolerance genes. Five selected RILs with high salt tolerance had six to eight positive alleles of the M-QTLs, indicating that pyramiding by marker-assisted selection (MAS) of M-QTLs can be applied in rice salt tolerance breeding programs.     

How do steppe plants follow their optimal environmental conditions or persist under suboptimal conditions? The differing strategies of annuals and perennials

For a species to be able to respond to environmental change, it must either succeed in following its optimal environmental conditions or in persisting under suboptimal conditions, but we know very little about what controls these capacities. We parameterized species distribution models (SDMs) for 135 plant species from the Algerian steppes. We interpreted low false‐positive rates as reflecting a high capacity to follow optimal environmental conditions and high false‐negative rates as a high capacity to persist under suboptimal environmental conditions. We also measured functional traits in the field and built a unique plant trait database for the North‐African steppe. For both perennial and annual species, we explored how these two capacities can be explained by species traits and whether relevant trait values reflect species strategies or biases in SDMs. We found low false‐positive rates in species with small seeds, flowers attracting specialist pollinators, and specialized distributions (among annuals and perennials), low root:shoot ratios, wide root‐systems, and large leaves (perennials only) (R² = .52–58). We found high false‐negative rates in species with marginal environmental distribution (among annuals and perennials), small seeds, relatively deep roots, and specialized distributions (annuals) or large leaves, wide root‐systems, and monocarpic life cycle (perennials) (R² = .38 for annuals and 0.65 for perennials). Overall, relevant traits are rarely indicative of the possible biases of SDMs, but rather reflect the species' reproductive strategy, dispersal ability, stress tolerance, and pollination strategies. Our results suggest that wide undirected dispersal in annual species and efficient resource acquisition in perennial species favor both capacities, whereas short life spans in perennial species favor persistence in suboptimal environmental conditions and flowers attracting specialist pollinators in perennial and annual species favor following optimal environmental conditions. Species that neither follow nor persist will be at risk under future environmental change.     

Homologous expression of γ-glutamylcysteine synthetase increases grain yield and tolerance of transgenic rice plants to environmental stresses

Various environmental stresses induce reactive oxygen species (ROS), causing deleterious effects on plant cells. Glutathione (GSH), a critical antioxidant, is used to combat ROS. GSH is produced by γ-glutamylcysteine synthetase (γ-ECS) and glutathione synthetase (GS). To evaluate the functional roles of the Oryza sativa L. Japonica cv. Ilmi ECS (OsECS) gene, we generated transgenic rice plants overexpressing OsECS under the control of an inducible promoter (Rab21). When grown under saline conditions (100 mM) for 4 weeks, 2-independent transgenic (TGR1 and TGR2) rice plants remained bright green in comparison to control wild-type (WT) rice plants. TGR1 and TGR2 rice plants also showed a higher GSH/GSSG ratio than did WT rice plants in the presence of 100 mM NaCl, which led to enhanced redox homeostasis. TGR1 and TGR2 rice plants also showed lower ion leakage and higher chlorophyll-fluorescence when exposed to 10 μM methyl viologen (MV). Furthermore, the TGR1 and TGR2 rice seeds had approximately 1.5-fold higher germination rates in the presence of 200 mM salt. Under paddy field conditions, OsECS-overexpression in transgenic rice plants increased rice grain yield (TGW) and improved biomass. Overall, our results show that OsECS overexpression in transgenic rice increases tolerance and germination rate in the presence of abiotic stress by improving redox homeostasis via an enhanced GSH pool. Our findings suggest that increases in grain yield by OsECS overexpression could improve crop yields under natural environmental conditions.     

Microbial transformations of (−)-α- and (+)-β-thujone by fungi of Absidia species

The microbial transformations of (−)-α- and (+)-β-thujone (1a and 1b) in cultures of Absidia species: Absidia coerulea AM93, Absidia glauca AM254 and Absidia cylindrospora AM336 were studied. The biotransformations of (−)-α-thujone (1a), by these fungi strains, afforded mixtures of 4-hydroxy- and 7-hydroxy-α-thujone (2 and 3). Aforementioned fungi strains were also able to hydroxylate of (+)-β-thujone at C-7 position. Only A. glauca AM254 transformed 1b to 8-hydroxy-β-thujone (7) and (2S)-2-hydroxyneoisothujol (6). The (4R)-4-hydroxyisothujole (5) was identified as one of the major metabolite of (+)-β-thujone (1b) in culture of A. cylindrospora AM336. This strain was also able to introduce hydroxy group to C-4 position in 1b without reduction of carbonyl group at C-3. The absolute configuration of all chiral centers of new (4R)-4-hydroxyisothujol (5) and (2S)-2-hydroxyneoisothujol (6) were established taking into account the configuration of (+)-β-thujone (1b) and their spectral data.     

Extent of heterosis in rice (Oryza sativa L.) under cold stress conditions — yield and its components

Summary The nature and extent of heterosis for grain yield and its component characters was estimated in a seven-parent F₁-diallel cross in rice under the cold stress conditions of Palampur, representing sub-temperate climate of the mid hills of Himachal Pradesh. The highest heterotic effects for grain yield were observed in Himalaya 1/Phul Patas 72 and China 988/Himdhan hybrids, which gave 60.36 and 32.48% heterosis, respectively, over mid parent, 38.76 and 26.86% heterosis, respectively, over high parent and 32.30 and 26.86% heterosis, respectively, over the best variety, Himdhan. Heterosis for grain yield in these crosses was due to an increase in tiller number, panicle length, spikelets/panicle and 1,000-grain weight. Large number of crosses exhibited significant heterosis for high spikelet sterility and the majority of them had significant heterosis for late flowering, taking more than 120 days to flower, which resulted in lack of heterosis for grain yield in such crosses due to cold stress at the reproductive stage.Part of the thesis submitted by the senior author to Himachal Pradesh Agricultural University, Palampur (H.P.) India, in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Agriculture     

Rapid desensitization of α1β1 GABAA receptors expressed in Sf9 cells under optimized conditions

₁ and ₁ subunits of human GABA_A receptors were expressed in Sf9 cells using the Sf9-baculovirus system. Better expression was obtained by manipulating the system. Cell growth phase at the time of infection determined the practical range of virus titre, the period postinfection during which cells were useful for signal detection and the maximal current obtained. Cells in the early exponential phase were relatively insensitive to multiplicity of infection (MOI) whereas cells in the midto late-exponential phase were highly dependent on MOI and they responded with the largest Cl–} current generated by GABA. Channels activated by GABA were chloride-selective. Half the maximum peak whole-cell current was obtained with 11 m GABA. The time course of Cl–} currents activated by saturating GABA concentrations in cells infected with ₁₁recombinant viruses was examined employing a rapid perfusion system which allowed whole-cell solution exchange in less than 1 msec. The current decay could be fitted by 3 to 4 exponentials for the first 8 sec. The initial fast current decrease had a time constant of about 23 msec. No voltage dependence of time constants was detected but the whole-cell IV relation showed outward rectification. Currents were depressed by bicuculline, penicillin and picrotoxin and potentiated by pentobarbitone.We are grateful to I. Woo and B. MacLachlan for their expert technical assistance and L. Hardy for secretarial assistance. This work was generously supported by: Sir Rutherford Robertson, Sir John Pround, The Raymond E. Purves Foundation, The James N. Kirby Foundation, C. H. Warman and the Brace and Joy Reid Foundation.     

How yield relates to ash content, ��13C and ��18O in maize grown under different water regimes

Background and Aims

Stable isotopes have proved a valuable phenotyping tool when breeding for yield potential and drought adaptation; however, the cost and technical skills involved in isotope analysis limit its large-scale application in breeding programmes. This is particularly so for Δ¹⁸O despite the potential relevance of this trait in C₄ crops. The accumulation of minerals (measured as ash content) has been proposed as an inexpensive way to evaluate drought adaptation and yield in C₃ cereals, but little is known of the usefulness of this measure in C₄ cereals such as maize (Zea mays). The present study investigates how yield relates to ash content, Δ¹³C and Δ¹⁸O, and evaluates the use of ash content as an alternative or complementary criterion to stable isotopes in assessing yield potential and drought resistance in maize.

Methods

A set of tropical maize hybrids developed by CIMMYT were subjected to different water availabilities, in order to induce water stress during the reproductive stages under field conditions. Ash content and Δ¹³C were determined in leaves and kernels. In addition, Δ¹⁸O was measured in kernels.

Key Results

Water regime significantly affected yield, ash content and stable isotopes. The results revealed a close relationship between ash content in leaves and the traits informing about plant water status. Ash content in kernels appeared to reflect differences in sink–source balance. Genotypic variation in grain yield was mainly explained by the combination of ash content and Δ¹⁸O, whilst Δ¹³C did not explain a significant percentage of such variation.

Conclusions

Ash content in leaves and kernels proved a useful alternative or complementary criterion to Δ¹⁸O in kernels for assessing yield performance in maize grown under drought conditions.     

Does perianth colour affect the seed germination of two desert shrubs under different storage periods and conditions?

Haloxylon salicornicum and Salsola vermiculata (Amaranthaceae) are two perennial shrubs producing fruits with differently coloured perianths (yellow vs pink) on separate individuals. To test the impact of different storage periods (four, eight and twelve months) and temperature conditions (freezing, room temperature and natural field temperatures) on the seed germination of the two seed categories, germination tests were carried out on both species. For both species, collected from wild plants in the Arabian desert (Qatar), seed germination was tested under two photoperiods (light 12/12; dark 24 hours) at 20/30°C for winged (intact) and de‐winged seeds. For each species, all the considered factors (perianth colour, wing presence, photoperiod, storage period and storage conditions) had significant effects on seed germination (p < 0.001), while the interactions among factors varied in their level of significance depending on the species. In both species, yellow seeds germinated considerably better than the pink ones, the presence of wings slowed the germination, and both storage period and temperature conditions highly influenced their germination ability. Our results indicate that seeds from different perianth colours have different germination strategies to delay their germination and distribute the species through time by escaping germination time by imposing some kind of after‐ripening or seed dormancy. The variation in storage time and storage conditions might help in extending their germination period, where one set of seeds germinate immediately, and the other set of seeds becomes dormant and thus contributes to the formation of a soil seed bank for the long‐term recruitment of seedlings. This study highlights an ecological advantageous strategy for these two species growing in the unpredictable desert habitat.     

Iron-induced oxidation of (all-E)-β-carotene under model gastric conditions: kinetics,products, and mechanism

The stability of (all-E)-β-carotene toward dietary iron was studied in a mildly acidic (pH 4) micellar solution as a simple model of the postprandial gastric conditions. The oxidation was initiated by free iron (Fe^II, Fe^III) or by heme iron (metmyoglobin, MbFe^III). Fe^II and metmyoglobin were much more efficient than Fe^III at initiating β-carotene oxidation. Whatever the initiator, hydrogen peroxide did not accumulate. Moreover, β-carotene markedly inhibited the conversion of Fe^II into Fe^III. β-Carotene oxidation induced by Fe^II or MbFe^III was maximal with 5–10 eq Fe^II or 0.05–0.1 eq MbFe^III and was inhibited at higher iron concentrations, especially with Fe^II. UPLC/DAD/MS and GC/MS analyses revealed a complex distribution of β-carotene-derived products including Z-isomers, epoxides, and cleavage products of various chain lengths. Finally, the mechanism of iron-induced β-carotene oxidation is discussed. Altogether, our results suggest that dietary iron, especially free (loosely bound) Fe^II and heme iron, may efficiently induce β-carotene autoxidation within the upper digestive tract, thereby limiting its supply to tissues (bioavailability) and consequently its biological activity.