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Phytate or phytic acid (PA), is a phosphorus (P) containing compound generated by the stepwise phosphorylation of myo-inositol. It forms complexes with some nutrient cations, such as Ca, Fe and Zn, compromising their absorption and thus acting as an anti-nutrient in the digestive tract of humans and monogastric animals. Conversely, PAs are an important form of P storage in seeds, making up to 90% of total seed P. Phytates also play a role in germination and are related to the synthesis of abscisic acid and gibberellins, the hormones involved in seed germination. Decreasing PA content in plants is desirable for human dietary. Therefore, low phytic acid (lpa) mutants might present some negative pleiotropic effects, which could impair germination and seed viability. In the present study, we review current knowledge of the genes encoding enzymes that function in different stages of PA synthesis, from the first phosphorylation of myo-inositol to PA transport into seed reserve tissues, and the application of this knowledge to reduce PA concentrations in edible crops to enhance human diet. Finally, phylogenetic data for PA concentrations in different plant families and distributed across several countries under different environmental conditions are compiled. The results of the present study help explain the importance of PA accumulation in different plant families and the distribution of PA accumulation in different foods.

Root–soil interactions in the rhizosphere are central to resource acquisition and crop production in agricultural systems. However, apart from studies in idealized experimental systems, rhizosphere processes in real agricultural soils in situ are largely uncharacterized. This limits the contribution of rhizosphere science to agriculture and the ongoing Green Revolution. Here, we argue that understanding plant responses to soil heterogeneity is key to understanding rhizosphere processes. We highlight rhizosphere sensing and root-induced soil modification in the context of heterogeneous soil structure, resource distribution, and root–soil interactions. A deeper understanding of the integrated and dynamic root–soil interactions in the heterogeneously structured rhizosphere could increase crop production and resource use efficiency towards sustainable agriculture.

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This study assessed the variations in the impacts of climate change on potential groundwater recharge from barley crop fields in fourteen UK administrative regions. Future climate data, based on the high, medium and low emissions scenarios (or HES, MES, and LES, respectively), were obtained from the UK Climate Projections 2009 (UKCP09) using the weather generator embedded therein. These were used, together with soil, field and calibrated data of the barley genotype Westminster, to simulate potential groundwater recharge in barley crop fields for the 2030s, 2040s, and 2050s. The results show significant variations in potential groundwater recharge for the regions and the emissions scenarios but not the time slices. There was no interaction effect between time and emissions scenarios. For all emissions scenarios, time slices and regions, the largest reduction and increase in potential groundwater recharge over baseline values were 38% and 41%, respectively. East Midlands had the largest reductions for all time slices and emissions scenarios while Southwest Scotland, Northwest Scotland, Northern Ireland and Wales had the largest increase in potential recharge over baseline values. Generally, reductions were prevalent in the south and the eastern regions of England. Reductions were also highest under HES and lowest under the LES. In the 2030 , the largest reductions were 37 mm (HES), 29 mm (MES), and 16 mm (LES). In the 2050 the largest reductions were 31 mm (HES), 27 mm (MES), and 19 mm (LES). It is concluded that the regional variations in potential recharge in arable crop fields during the spring-summer season can be a useful input in adaptation planning that integrates agriculture and water resources management in response to flood and drought risks, and water-food security needs.

Agricultural intensification driven by land-use changes has caused continuous and cumulative soil acidification (SA) throughout the global agroecosystem. Microorganisms mediate acid-generating reactions; however, the microbial mechanisms responsible for exacerbating SA feedback remain largely unknown. To determine the microbial community composition and putative function associated with SA, we conducted a metagenomic analysis of soils across a chronosequence that has elapsed since the conversion of rice-wheat (RW) to rice-vegetable (RV) rotations. Compared to RW rotations, soil pH decreased by 0.50 and 1.56 units (p0.05) in response to 10-year and 20-year RV rotations, respectively. Additionally, acid saturation ratios were increased by 7.3% and 36.2% (p0.05), respectively. The loss of microbial beta-diversity was a key element that contributed to the exacerbation of SA in the RV. Notably, the 20-year RV-enriched microbial taxa were more hydrogen (H

Yield loss in oilseed rape is caused by a decline in plant population density (PPD) due to nitrogen (N) insufficiency. The optimization of PPD is the foundation of the high and stable yield of winter oilseed rape. Field experiments were conducted with five contrasting N applications (0, 60, 120, 180 and 240 kg N ha−1, denoted by N0, N60, N120, N180 and N240, respectively) to identify the effect of different N application rates on PPD dynamics and the influence of PPD at harvest (PPDh) on seed yield. Oilseed rape yield was increased by the increase of PPDh and yield per plant as the N application rate added. The N deficiency decreased PPDh, resulting in a 35.1% and 17.1% yield loss in the N0 and N60 treatments compared to the PPDh of the treatment with the highest yield. This loss accounted for 30.9% and 20.6% of the total yield loss in the both treatments, respectively. PPD declined after the seedling emergence over the whole growing season, and the N application rate exhibited different effects at different growth stages. Sufficient N supplying suffered a sharp decline in PPD mainly during the seedling stage, accounting for approximately 46.1% ∼ 48.1% of the total mortality. As the N supply was insufficient, PPD declined dramatically both at the seedling stage and after the flowering stage, with the mortality proportion of 38.2% and 39.7% in the N0 treatment, respectively, resulting in greater mortality than the other stage over the growth period. A significant difference in the degree of PPD decline between sufficient and insufficient N treatments was observed since 150 days after sowing (DAS) till the harvest stage. Reduction in PPD was regulated by plant N status, and there was a negative relationship between N concentration and PPD. The minimum N concentrations of minimum decline in PPD from seedling emergency to 60 DAS and from 150 DAS to harvest were 4.11% and 2.44%, respectively. A lack of N increased plant mortality led to the reduced PPDh and decreased yield. PPDh should be optimized by the reasonable N management to promote individual growth, guarantee the group development, and achieve economic and efficient production.

Background Selenium (Se) is not an essential element for plants, although it can benefit their growth and survival in some envionments. Excess tissue Se concentrations are toxic. The ability to sequester Se in vacuoles, synthesise non-toxic Se metabolites, or volatilise Se compounds determines maximum tissue Se concentrations and the ability to colonise seleniferous soils. Scope of review This review first classifies plant species on their abilities to accumulate Se in their tissues and to colonise seleniferous soils. It then presents our knowledge of Se uptake by roots and its movement within the plant, the primary and secondary metabolism of Se in plants, effects of Se on sulfur and nitrogen metabolism, and the detoxification of excessive Se by plants. Finally, it presents a current hypothesis for the evolution of seleniferous flora. Major conclusions Selenium and sulfur share the same primary metabolism. When grown in the same environment, most plant species have similar tissue Se/S quotients. However, Se-hyperaccumulator species, which can have tissue Se concentrations >1 mg g−1 dry matter, have larger Se/S quotients than other species. Secondary Se metabolism determines differences in tissue Se concentration among plant species. Among non-hyperaccumulator species, alliums and brassicas have particularly large tissue Se concentrations. Selenium hyperaccumulation results from the effective metabolic detoxification of Se in tissues. General significance Differences in Se metabolism determine the maximum Se concentrations in plant tissues, which is important for the delivery of Se to diets of herbivores and for the evolution of plant species to colonise seleniferous soils.

Urbanization is progressing rapidly. It can affect soils ecosystem services directly through land management and indirectly through changes in the socioeconomic environment, which eventually leads to an increase in emissions of greenhouse gases. Soil carbon (C) sequestration plays an important role in offsetting the anthropogenic C emissions. However, there is limited knowledge of how urbanization affects the soil C especially that in suburban. In this study, we studied changes in easily oxidizable organic C (EOC) and total organic C (TOC) of suburban soils (0–100 cm) in the rapid urbanising megacity Chengdu, China. The EOC stock and TOC stock decreased from the outer-suburb to the inner-suburb by 17.8–28.2% and 5.4–13.5%, respectively; particularly, the inner-suburb EOC decreased by 31.4–38.6% during the past 10 years. The quotient of EOC/TOC in the soil profile, reflecting the stability of soil C, declined from the outer-suburb (0.78) to the inner-suburb (0.20). Factors that influenced the EOC and TOC included the changes in economics (economic density, industrialization), farmland (cultivated area, farmland structure), urbanization (city size, population growth) and traffic flow. Among which, economic density growth was the primarily driver of the loss in TOC, explaining 31.6% of the variation in soil surface TOC and 16.0% of the variation in subsoil TOC; changes in farmland and urban expansion were the main factors contributing to the loss of subsoil EOC, with 40.4% explanatory ability. In addition, traffic flow also has contribution to the subsoil EOC loss. We concluded that the increasing soil C loss with decreasing distance from the city centre has a continuous contribution to C emission, and the C loss will persist until the suburbs are fully urbanized. The large losses of EOC and TOC caused by urbanization, and their contribution to global warming, necessitate their consideration in future appraisals of climate change and urban planning projects.

Ammonium (NH4+) and nitrate (NO3−) are the main nitrogen (N) sources accessible to plants. However, exclusive NH4+ may causes toxicity to crops. Transcriptomics in conjunction with metabolomics analysis in allotetraploid rapeseed under NH4+ stress showed that NH4+ taken up by roots was mainly transferred to leaves for assimilation. The concentrations of most amino acids, glucose, and glucose-6-phosphate increased whilst malate, succinate, and α-ketoglutarate concentrations decreased in NH4+-treated leaves. Moreover, NH4+ toxicity down-regulated genes related to photosynthesis and impaired the electron transport chain in chloroplasts. The expression of genes related to H2O2 decomposition, as well as the concentrations of monodehydro-ascorbic acid and ascorbic acid, reduced after exposure to NH4+-N, accompanied by higher O2 - and H2O2 accumulation. Taken together, our results indicated that the excessive accumulation of NH4+ in plants caused an imbalance of carbon and N metabolism, impaired photosystems and generated reactive oxygen species, which resulted in toxicity to rapeseed.

Crop production depends on the availability of water and mineral nutrients, and increased yields might be facilitated by a greater focus on roots–soil interactions. Soil properties affecting plant growth include drought, compaction, nutrient deficiency, mineral toxicity, salinity, and submergence. Plant roots respond to the soil environment both spatially and temporally by avoiding stressful soil environments and proliferating in more favorable environments. We observe that crops can be bred for specific root architectural and biochemical traits that facilitate soil exploration and resource acquisition, enabling greater crop yields. These root traits affect soil physical and chemical properties and might be utilized to improve the soil for subsequent crops. We argue that optimizing root–soil interactions is a prerequisite for future food security.

Rapeseed (Brassica napus L.) is extremely sensitive to both boron (B) and phosphorus (P) deficiencies. Application of chemical fertilizers is generally considered to be an effective agronomic practice to improve crop productivity, and it also affects soil bacterial community. However, there are few studies of the effects of balanced B and P fertilizer applications on crop yield and bacterial communities. In the present study, field experiments with five P application rates (0, 45, 90, 135 and 180 kg P2O5 ha−1) and four B application rates (0, 4.5, 9 and 18 kg Na2B4O7·5H2O ha−1) were conducted in 2016–2017 and 2017–2018 to investigate their effects on seed yield and P use efficiency (PUE) of B. napus. The smallest seed yields were obtained when B or P fertilizers were not applied (P90B0 or P0B9). Balanced B and P applications benefitted yields. The P45B4.5 treatment produced greater seed yield and PUE than the P45B18 treatment, and the P180B18 treatment produced greater seed yield and PUE than the P180B4.5 treatment. Sequencing of 16S rRNA genes revealed that the P90B9 treatment had greater soil bacterial diversity, and a different bacterial community composition, compared with the P90B0 or P0B9 treatments. Overall, our results underline the importance of balanced B and P nutrition for maximal seed yield of B. napus and the effects of B and P fertilizers on the soil bacterial community of B. napus.

Oilseed rape (Brassica napus L.) is an important crop in China. Although its yields are restricted by phosphorus (P) supply, the response of its root system to P supply has not been explored systematically. This study aimed to investigate the contribution of root morphological and biochemical traits to P acquisition from soils with deficient P (30 kg P2O5 ha−1) and sufficient P (90 kg P2O5 ha−1) supplies in the field at the leaf development, stem elongation, flowering, pod development and ripening stages. The total root length and root surface area in the surface soil (0−10 cm soil layer) were both reduced significantly by decreasing P supply. However, a larger root/shoot ratio and root length ratio were observed in plants with the deficient P supply at the flowering stage. Roots of plants with a deficient P supply also secreted more acid phosphatase and organic acid into the rhizosphere from stem elongation to pod development than plants with a sufficient P supply. Seed yield (SY), shoot dry weight (SDW) and total P content (TPC) were strongly correlated with root morphological traits at the leaf development and flowering stages, especially with the coarse root length (CRL) and root surface area in the surface soil. However, there were no correlations between SDW or TPC and root biochemical traits (rhizosphere pH, acid phosphatase activity and organic acid content). It is hypothesized that greater CRL in the surface soil (0−10 cm soil layer) at the leaf development and flowering stages, served as a scaffold for fine roots, enhancing soil exploration and P acquisition, and, thereby, increasing seed yield.

Broccoli crops are produced throughout the year. They are grown under a wide range of environmental conditions, which results in large variation in the time to head initiation and in head growth after initiation. Mis-scheduling broccoli crops has financial consequences. Models to predict the harvest dates of broccoli crops allow growers to adapt their commercial strategies to maintain an appropriate supply of broccoli throughout the year in a cost-effective manner. The work described here developed models for the phenology and yields of Scottish broccoli crops using data from field trials and commercial crops that allow the prediction of harvest dates from observations or forecasts of daily temperatures and radiation. The models were validated using independent data obtained from commercial broccoli growers and used to explore the local, seasonal and year-to-year variation in the predicted harvest dates of broccoli in Scotland. The date of transplanting seedlings to the field had the largest effect on the time to harvest, although there was also considerable annual variation. Geographical location had least effect on the time to harvest.

The selectivity of cation uptake by radish (Raphanus sativus L.) growing in the field near Chernobyl varies during the growth season. It is hypothesised that this is a consequence of variation in (137)Cs (Csss) and potassium (Kss) concentrations in the soil solution or the amount of dissolved potassium available to the plants. In the experiments reported here, it was observed that (1) Csss and Kss were positively correlated, (2) the selectivity for uptake of (137)Cs versus potassium (r) increased exponentially with decreasing Csss and Kss, and (3) the (137)Cs concentration, but not the potassium concentration, in plant material, increased abruptly upon the simultaneous reduction of Kss and Csss below about 10 μg ml(-1) and 6.7 Bq l(-1), respectively. It is thought that potassium enters root cells from the soil solution through constitutively-expressed, inward rectifying K(+) channels (KIRC) and K(+)/H(+)-symporters, whose abundance increases when plants become potassium-deficient. Cesium is thought to enter root cells through non-specific cation channels (NSCC) and, in plants lacking sufficient potassium, through K(+)/H(+)-symporters. It is argued that the increase in r, together with the abrupt increase (137)Cs concentration in plant tissues, when Kss and Csss decrease simultaneously cannot be attributed to competition between Cs(+) and K(+) for transport though KIRC, NSCC or K(+)/H(+)-symporters and that the most plausible explanation of these phenomena is an increase in the abundance of K(+)/H(+)-symporters in plants exhibiting incipient potassium deficiency.

The flow of water through food commodity trade has been rationalized in the virtual water concept. Estimates of future virtual water flows under climate, land use, and population changes could have instrumental value for policy and strategic trade decisions. This paper estimated the virtual water flows associated with feed barley and meat imports to the UK under projected climate, land use, and population changes from the 2030s to the 2050s. The results show that future virtual water inflows associated with barley imports to balance domestic deficits are larger than total volume of water used in domestic barley production in the UK. Mean virtual water associated with total UK barley production ranged from 206 to 350 million m3. This is much less than the mean total virtual water associated with barley imports (if total barley produced in the UK is used for feed), which ranged from 2.5 to 5.6 billion m3 in the 2030s to the 2050s for all land use and climate change scenarios. If domestic barley production is distributed to the different end uses, the total virtual water inflows associated with imports to balance domestic feed barley supply could be as high as 7.4 billion m3. Larger virtual water inflows (as high as 9.9 billion m3) were associated with feed barley equivalent meat imports. While the UK barley production would be entirely green, imports of either barley or meat would result in large blue water inflows to the UK. Virtual water inflows increased across the time slices for all emissions scenarios, indicating weak effectiveness of yield or productivity gains to moderate virtual water inflows. While increase in yield and land allocated to barley production should be adaptive targets, the UK needs to take policy and strategic actions to diversify trade partners and shift imports away from countries where blue water flows can exacerbate existing or potential water stresses., Virtual water, Climate change, Land use change, Feed barley demand, Meat consumption, Population growth, Environmental science, Agriculture.

A shortage of water threatens agricultural sustainability in the Huang-Huai-Hai Plain of China. Effective water-saving technologies need to be developed urgently. The experiment reported here, conducted between 2010 and 2012, aimed to determine how the length of the micro-sprinkling hose delivering supplemental irrigation affected photosynthetsis, dry matter (DM) accumulation, grain filling, and yield of winter wheat. Four treatments were compared: rainfed (W0) and irrigated with micro-sprinkling hoses with lengths of 40 m (W40), 60 m (W60), and 80 m (W80). The relative soil water content in the 0–140 cm soil horizon (RSWC) did not differ between 0 and 40 m from the proximal border of irrigated plots either in W40 or W60, and no differences in RSWC were observed across four inter-rows, spaced 22.9 cm apart, from the micro-sprinkling hoses in W40. However, RSWC decreased significantly with increasing distance from the proximal border in W80. There were no differences in mean actual photochemical efficiency (ΦPSII), maximum quantum yield of the PSII ( F v/ F m), flag leaf photosynthetic rate ( P n) or canopy apparent photosynthetic rate (CAP) 20 days after anthesis (DAA) between plants from W40 and W60, but all were greater in plants from W40 and W60 than in plants from W80. The ΦPSII, Fv/Fm, Pn, and CAP in plants from W80, but not W40, decreased significantly with increasing distance from the proximal border from 20 DAA. The total DM and the harvest index of plants from W40 were greater than those of plants from W60 and W80. The grain filling rate in the middle and later filling stages, 1000-grain weight, grain yield and water use efficiency became less as the length of micro-sprinkling hose was increased from 40 m to 80 m. In this study, the optimum length of micro-sprinkling hoses for irrigating wheat after jointing was 40 m to 60 m. The results indicate the importance of uniformity of irrigation water distribution in increasing the productivity of winter wheat.

The development of water-saving irrigation techniques is required for future food and ecological security in the Huang-Huai-Hai Plain of China, which suffers from severe water shortage. Field experiments were performed over two years (2010/2012) with the high-yielding winter wheat cultivar Jimai22 to examine the effects of supplemental irrigation (SI) with micro-sprinkling hoses on water distribution in soil and grain yield of winter wheat. Five irrigation treatments were tested: rainfed (T0), and irrigated with micro-sprinkling hoses with minimum sprinkling angles (i.e. the angle between the tangent of the initial water jet and the horizontal) of 35° (T1), 50° (T2), 65° (T3) and 80° (T4). The SI brought soil water content in the 0–140 cm profile to 75% field capacity (FC) at jointing and 70% FC at anthesis in 2010/2011, and 70% FC at both jointing and anthesis in 2011/2012. The distribution uniformity of irrigation water (Cμ) in soil after irrigation at jointing and anthesis was increased by increasing sprinkling angle from 35° to 80°. The increase in the soil water content in the 0–40 cm soil layer of the inter-rows decreased significantly with increasing distance from the micro-sprinkling hose in T1, T2 and T3, but there was no significant difference between inter-rows in T4. As sprinkling angle was increased from 35° to 80°, the amount of SI required (CIR), soil water consumption (ΔW) and crop evapotranspiration (ETc) decreased. The grain filling rate at the later filling stage, 1000-kernel weight, dry matter accumulation (DM), grain yield, and agronomic water use efficiency (AWUE) were significantly higher in T4 than in T1, T2 and T3. The CIR, ΔW and ETc had significant, negative, linear relationships with Cμ. However, DM, grain yield, and AWUE had significant, positive, linear relationships with Cμ with mean correlation coefficients of 0.60, 0.91 and 0.91, respectively. In this study, the optimum sprinkling angle of micro-sprinkling hoses for irrigating wheat after jointing was 80°.

Food security in the Huang-Huai-Hai Plain of China is threatened by water shortages and the early senescence of wheat induced by water deficit. However, effective water-saving irrigation techniques based on the consideration of precipitation, soil water storage and crop requirements are rudimentary. Information on the responses of transpiration, photosynthesis and plant senescence to Supplemental Irrigation (SI) at different stages of crop development is urgently required. Field experiments were performed in 2007–2008 and 2008–2009 to provide this information. Four irrigation treatments were tested: rainfed (W0), SI at Zadoks stage 31 (Z31) and Z60 (W1), SI at Z34 and Z69 (W2), and SI at Z39 and Z77 (W3). The SI brought soil water content in the 0–140 cm profile to 75% field capacity. Supplemental Irrigation increased grain yields and the scheduling of SI affected yield components. Delaying SI from Z31 and Z60 (W1) to Z34 and Z69 (W2) decreased the number of spikes, but increased the number of grains per spike, 1000-grain weight and crop yield. Activities of superoxide dismutase (SOD) and catalase (CAT) in flag leaves of plants from the W2 treatment were greater, and malondialdehyde (MDA) concentrations in flag leaves were lower, than those from the W3 treatment until 24 days after anthesis and those from the W1 and W0 treatments throughout anthesis. Although SI increased both photosynthetic rate (Pn) and transpiration rate ( E ), the net effect was greater instantaneous water use efficiency (WUE leaf = Pn/ E ). Supplemental Irrigation also increased agronomic Water Use Efficiency (grain yield/crop evapotranspiration). Delaying SI decreased the grain filling rate at the beginning of grain filling in 2007–2008, but increased the grain filling rate later in grain filling in both 2007–2008 and 2008–2009. An appropriate delay in SI (W2) increased grain yield substantially, but if SI was applied too late (W3), there was less effect on grain yield, probably because of an inhibition of assimilate remobilization to the grain due to delayed senescence.

A retrospective analysis of the effects of nearly 75 years of breeding on the nitrogen use efficiency (NUE) of spring barley ( Hordeum vulgare L.) was undertaken to identify physiological mechanisms governing NUE and targets for future improvement. Fifteen varieties, selected to be as genetically dissimilar as possible and to represent the breeding period from 1931 to 2005, were grown at three site-year combinations in the NE of Scotland. Varieties were grown with zero or 110 kg N ha −1 supplied as ammonium nitrate. Averaged across site-years, breeding was shown to increase yield and NUE (grain yield N supply −1 ) by 1 and 1.2% per year respectively in the presence of fertilizer. Mean grain weight was larger in modern compared to old varieties grown both with and without N fertilizer. The greater response of yield to fertilizer in modern varieties was associated with the production of more grains m −2 . Significant variation was found between genotypes in efficiencies of N uptake (NupE; N offtake per unit N supply) and N utilization (NutE g , grain yield per unit N offtake). Differences in NutE g contributed 60% to the variation in NUE, whilst NupE contributed 40%. The improvement in NutE g was mostly the result of increases in harvest index (HI) and was stable across environments. NupE was positively correlated with post-anthesis, but not pre-anthesis, dry matter accumulation and N uptake, which suggests that greater NupE of some varieties was the result of an increased N demand from a large grain sink. Across all varieties NupE was not related to NutE g suggesting that improvements in each may be selected independently. The results also indicated possible opportunities for improving the efficiency of pre-anthesis N uptake.

Four field experiments were performed in the UK in harvest seasons 2007 and 2008. Each experiment consisted of 10 winter oilseed rape varieties grown at a low level of available nitrogen (N) and at a high level of available N intended to replicate commercial practice. A combined analysis of three of the experiments with significant yield differences between the N treatments showed a significant interaction between N availability and variety for yield. Across these three experiments the proportion of yield lost when crops were grown at low N compared with high N ranged from 0.23 to 0.35 among varieties. The proportion of yield lost at low N was negatively associated with crop N uptake. There was also an interaction between N supply and variety for N use efficiency (kg of seed dry matter/kg available N) within these three experiments. Varietal differences in yield at low N correlated most closely, and positively, with crop N uptake, final crop dry matter and seeds/m2, but not N utilisation (kg seed/kg N uptake). Every additional kilogram of N taken up by the crop increased yield at low N by 0.020 t/ha. The amount of N taken up after flowering was the most important phase of N uptake for determining yield differences between the varieties, with every additional kilogram of N taken up after flowering associated with a yield increase of 0.016 t/ha. Each additional 1000 seeds/m2 was associated with an additional 1.4 kg N/ha taken up after flowering. There was no correlation between yield at low N or late N uptake and individual seed size.

The Richards equation has been widely used for simulating soil water movement. However, the take-up of agro-hydrological models using the basic theory of soil water flow for optimizing irrigation, fertilizer and pesticide practices is still low. This is partly due to the difficulties in obtaining accurate values for soil hydraulic properties at a field scale. Here, we use an inverse technique to deduce the effective soil hydraulic properties, based on measuring the changes in the distribution of soil water with depth in a fallow field over a long period, subject to natural rainfall and evaporation using a robust micro Genetic Algorithm. A new optimized function was constructed from the soil water contents at different depths, and the soil water at field capacity. The deduced soil water retention curve was approximately parallel but higher than that derived from published pedo-tranfer functions for a given soil pressure head. The water contents calculated from the deduced soil hydraulic properties were in good agreement with the measured values. The reliability of the deduced soil hydraulic properties was tested in reproducing data measured from an independent experiment on the same soil cropped with leek. The calculation of root water uptake took account for both soil water potential and root density distribution. Results show that the predictions of soil water contents at various depths agree fairly well with the measurements, indicating that the inverse analysis is an effective and reliable approach to estimate soil hydraulic properties, and thus permits the simulation of soil water dynamics in both cropped and fallow soils in the field accurately.

Models for water transfer in the crop–soil system are key components of agro-hydrological models for irrigation, fertilizer and pesticide practices. Many of the hydrological models for water transfer in the crop–soil system are either too approximate due to oversimplified algorithms or employ complex numerical schemes. In this paper we developed a simple and sufficiently accurate algorithm which can be easily adopted in agro-hydrological models for the simulation of water dynamics. We used a dual crop coefficient approach proposed by the FAO for estimating potential evaporation and transpiration, and a dynamic model for calculating relative root length distribution on a daily basis. In a small time step of 0.001 d, we implemented algorithms separately for actual evaporation, root water uptake and soil water content redistribution by decoupling these processes. The Richards equation describing soil water movement was solved using an integration strategy over the soil layers instead of complex numerical schemes. This drastically simplified the procedures of modeling soil water and led to much shorter computer codes. The validity of the proposed model was tested against data from field experiments on two contrasting soils cropped with wheat. Good agreement was achieved between measurement and simulation of soil water content in various depths collected at intervals during crop growth. This indicates that the model is satisfactory in simulating water transfer in the crop–soil system, and therefore can reliably be adopted in agro-hydrological models. Finally we demonstrated how the developed model could be used to study the effect of changes in the environment such as lowering the groundwater table caused by the construction of a motorway on crop transpiration.

Controlled atmosphere storage (CA) is used to increase the storage life of onions; however detrimental effects on the shelf-life have been reported. The effect of the transition between CA (5 kPa CO 2 , 3 kPa O 2 ) and air (and vice versa) on onion cvs. Renate, Carlos and SS1 in terms of the respiration rate, sprout growth, dry weight, firmness, pungency, total soluble solids, abscisic acid concentration and non-structural carbohydrate composition was assessed. Removal of bulbs from CA storage resulted in an immediate increase in the respiration rate (measured in air), which then reverted to a lower rate following subsequent storage under air conditions for 21 days. In some cultivars, this could be sufficient to trigger the onset of sprouting and thus account for the detrimental effect of CA storage on shelf-life. Delaying the start of CA storage of onions cv. SS1 for 21 days was as effective in suppressing sprout growth as CA storage for 42 days. Further investigation into the use of CA storage in this manner with relation to the optimum time to begin CA conditions could decrease the cost of CA storage without compromising storage life. Abscisic acid concentration has been associated with storage life of onions. There was a significant decrease in the bulb ABA concentration between the time of harvest and the beginning of storage. This is likely to be due to the effects of curing and suggests that current curing practices are having a detrimental effect on storage potential.

There is a paucity of information on the role of ethylene in onion bulb dormancy, and the available literature is conflicting. Onion cv. SS1 bulbs were treated with 1 μl l −1 1-MCP for 24 h at 20 °C and then stored at 4, 12 or 20 °C. Sprout growth was reduced in onions treated with 1-MCP and stored at 4 or 12 °C, but not when stored at 20 °C. Greater concentrations of sucrose, glucose and fructose were measured in 1-MCP treated bulbs stored at 12 °C as compared with untreated bulbs. Dry weight was also maintained in onions treated with 1-MCP. Abscisic acid (ABA) concentration before storage has previously been shown to be correlated with storage life, but there were no differences in the ABA concentration between 1-MCP treated and untreated bulbs. It appeared that 1-MCP reduced the rate of carbon utilisation. The mechanism by which this occurred is unknown although it is unlikely to be mediated by ABA.

Plants constantly sense the changes in their environment; when mineral elements are scarce, they often allocate a greater proportion of their biomass to the root system. This acclimatory response is a consequence of metabolic changes in the shoot and an adjustment of carbohydrate transport to the root. It has long been known that deficiencies of essential macronutrients (nitrogen, phosphorus, potassium and magnesium) result in an accumulation of carbohydrates in leaves and roots, and modify the shoot-to-root biomass ratio. Here, we present an update on the effects of mineral deficiencies on the expression of genes involved in primary metabolism in the shoot, the evidence for increased carbohydrate concentrations and altered biomass allocation between shoot and root, and the consequences of these changes on the growth and morphology of the plant root system.

Onion bulbs (Allium cepa L.) of cultivars with long-, medium- and short-storage lives, viz. Renate, Ailsa Craig and SS1, respectively, were stored in controlled atmosphere (CA) conditions (3.03 kPa CO2; 5.05 kPa O2; 2 °C). Bulb abscisic acid (ABA) concentration, pyruvate, fructans, total soluble solids (TSS) and firmness were measured throughout storage. In all cultivars, bulb ABA concentration declined exponentially during storage. The greatest decrease in ABA concentration occurred during the first 80 days of storage. Although the pattern of decline was similar for the long-, medium- and short-storing onion bulbs, onion cv. SS1 bulbs had the lowest initial ABA concentration. Onion bulb ABA concentration at harvest (measured on a fresh weight basis) may prove to be a better indicator of storage life. The ABA concentration at harvest (DW) may be indicative of a greater difference in sprouting during storage between cv. SS1 and the other cultivars than between cvs. Renate and Ailsa Craig. It is hypothesised that the storage potential of bulbs of different onion cultivars is inversely related to the time at which they reach a minimal ABA content. Thus, the storage life of short-storing cultivars (e.g. cv. SS1) might be prolonged by slowing the decline in ABA concentration. This could help extend the period for supplying these onions from temperate regions. Onion bulbs of cvs. Renate, Ailsa Craig and SS1 were characterised by high, intermediate and low concentrations of pyruvate, fructan and total soluble solids, respectively.

In plant cells, Ca(2+) is required for both structural and biophysical roles. In addition, changes in cytosolic Ca(2+) concentration ([Ca(2+)](cyt)) orchestrate responses to developmental and environmental signals. In many instances, [Ca(2+)](cyt) is increased by Ca(2+) influx across the plasma membrane through ion channels. Although the electrophysiological and biochemical characteristics of Ca(2+)-permeable channels in the plasma membrane of plant cells are well known, genes encoding putative Ca(2+)-permeable channels have only recently been identified. By comparing the tissue expression patterns and electrophysiology of Ca(2+)-permeable channels in the plasma membrane of root cells with those of genes encoding candidate plasma membrane Ca(2+) channels, the genetic counterparts of specific Ca(2+)-permeable channels can be deduced. Sequence homologies and the physiology of transgenic antisense plants suggest that the Arabidopsis AtTPC1 gene encodes a depolarisation-activated Ca(2+) channel. Members of the annexin gene family are likely to encode hyperpolarisation-activated Ca(2+) channels, based on their corresponding occurrence in secretory or elongating root cells, their inhibition by La(3+) and nifedipine, and their increased activity as [Ca(2+)](cyt) is raised. Based on their electrophysiology and tissue expression patterns, AtSKOR encodes a depolarisation-activated outward-rectifying (Ca(2+)-permeable) K(+) channel (KORC) in stelar cells and AtGORK is likely to encode a KORC in the plasma membrane of other Arabidopsis root cells. Two candidate gene families, of cyclic-nucleotide gated channels (CNGC) and ionotropic glutamate receptor (GLR) homologues, are proposed as the genetic correlates of voltage-independent cation (VIC) channels.

Agro-hydrological models have widely been used for optimizing resources use and minimizing environmental consequences in agriculture. SMCR_N is a recently developed sophisticated model which simulates crop response to nitrogen fertilizer for a wide range of crops, and the associated leaching of nitrate from arable soils. In this paper, we describe the improvements of this model by replacing the existing approximate hydrological cascade algorithm with a new simple and explicit algorithm for the basic soil water flow equation, which not only enhanced the model performance in hydrological simulation, but also was essential to extend the model application to the situations where the capillary flow is important. As a result, the updated SMCR_N model could be used for more accurate study of water dynamics in the soil–crop system. The success of the model update was demonstrated by the simulated results that the updated model consistently out-performed the original model in drainage simulations and in predicting time course soil water content in different layers in the soil–wheat system. Tests of the updated SMCR_N model against data from 4 field crop experiments showed that crop nitrogen offtakes and soil mineral nitrogen in the top 90 cm were in a good agreement with the measured values, indicating that the model could make more reliable predictions of nitrogen fate in the crop–soil system, and thus provides a useful platform to assess the impacts of nitrogen fertilizer on crop yield and nitrogen leaching from different production systems.

The effect of plant growth temperature on the lipid composition and ATPase activity associated with tonoplast and plasma-membrane fractions from roots of rye ( Secale cereale cv. ‘Rheidol’) was investigated to try and explain the rapid ( K m ), sensitivity to specific inhibitors (nitrate or vanadate), stimulation by KCI and activation energy ( E a ) of the plasma-membrane and tonoplast ATPases were unaffected. The only apparent difference between growth temperature pretreatments was an increase in the specific activity of the plasma-membrane ATPase, but not that of the tonoplast, after long term ( > 3 day) cooling of plant roots. It appears, therefore, that the enhancement of ion transport capacity which is evident upon cooling rye roots is not mediated by changes in activity or properties of the ATPases.

Aluminium (Al) toxicity limits crop productivity on acid soils. Consequently, it is hoped that an understanding of the physiology of plants endemic to acid soils might help in the development of Al-tolerant crops. Such plants either exclude Al from their foliage or detoxify Al within their tissues. The mechanisms that plants use to exclude Al have been studied intensively. It is now known that the entry of Al to Al-tolerant plants is prevented by secreting organic acids into the soil solution, binding Al to negatively charged components of the root cell wall and mucilage, or by alkalinizing the rhizosphere. By contrast, how some plants manage to accumulate Al to concentrations that are toxic to most organisms is unknown.To investigate the physiology of Al accumulation, Steven Jansen and colleagues [1xAluminum hyperaccumulation in angiosperms: a review of its phylogenetic significance. Jansen, S. et al. Bot. Rev. 2002; 68: 235–269CrossrefSee all References[1] have compiled a list of 45 angiosperm families (scattered over >20 orders) that ‘hyperaccumulate’ Al to concentrations exceeding 1000 ppm in their dry matter. Their list is based primarily on previous studies assaying Al concentrations in dried herbarium samples, using simple semi-quantitative tests. They have mapped this list onto a recent angiosperm phylogeny to reveal that Al hyperaccumulation is a simple, primitive trait that has not only arisen independently several times during evolution but has also been lost independently in many derived taxa. Aluminium hyperaccumulation occurs at the base of many major clades, such as the basal angiosperms (Laurales), rosids (Malphigiales, Oxidales and Myrtales) and asterids (Cornales, Ericales, Gentianales, Aquifoliales). In general, species that hyperaccumulate Al are perennial, woody plants that inhabit tropical or subtropical regions. The low incidence of Al hyperaccumulation in evolutionarily advanced groups, and also in the monocots, appears to be correlated with their herbaceous habit. Intriguingly, Al accumulation is correlated with the incidence of blue fruits in eudicots.By placing the trait of Al accumulation in a sound phylogenetic framework, the work of Jansen and colleagues should enable researchers to formulate and test a variety of physiological, ecological and evolutionary hypotheses. Because this trait characterizes certain species, genera and families, it has a certain taxonomic utility. Within this taxonomy, it might be worthwhile investigating the selective advantage that is conferred by Al hyperaccumulation: either by acting as a defence or deterrence to pathogens and herbivores or simply by enabling plants to grow on acid soils. Finally, knowing the phylogeny of Al hyperaccumulation should allow researchers to identify closely related species suitable for comparative physiological studies to determine the mechanisms used by plants to detoxify and accumulate Al within their tissues. Unfortunately, although this might eventually allow the genes enabling Al accumulation to be cloned, it is unlikely that these genes could be used in crop improvement programs, given the toxicity of Al to animals.‘Intriguingly, Al accumulation is correlated with the incidence of blue fruits in eudicots.’

The biotrophic fungus Cladosporium fulvum causes leaf mould in tomatoes. Certain cultivars show resistance, and about a dozen dominant genes have been identified that provide resistance against various races of the pathogen. The interaction between C. fulvum and tomatoes has provided an excellent model system to investigate the gene-for-gene model of pathogen resistance whereby specific structures or metabolites from the pathogen are recognized by host receptors to generate an intracellular signal that initiates plant defence responses. It has also proven useful in unravelling the early intracellular signalling events following pathogen attack. An immediate perturbation in cytosolic Ca2+ concentration ([Ca2+]cyt) is implicated in these events, and modifications of protein phosphorylation status have frequently been observed. Activation of these signal transduction cascades ensures that cellular responses to the pathogen are coordinated, appropriate and timely, and that defence responses are induced systemically in other parts of the plant. Interestingly, diverse biotic agents (and also mechanical injury) induce many of the same (wounding) responses, including an oxidative burst, strengthening of the cell wall and release of antimicrobial compounds. This suggests that plant signalling cascades converge upon key elements and, by comparison of individual cascades, researchers hope to identify key cellular controls that enable plant protection.The experiments of Jose Chico and colleagues [1xA calcium-dependent protein kinase is systemically induced upon wounding in tomato plants. Chico, J.M et al. Plant Physiol. 2002; 128: 256–270Crossref | PubMedSee all References][1] have given us an insight into the link between [Ca2+]cyt and protein phosphorylation following wounding. They have isolated a complementary DNA (cDNA) encoding a calcium-dependent protein kinase (CDPK1) that contains a Ser/Thr kinase catalytic domain and a calmodulin-like domain (CLD) with four calcium-binding motifs from a cDNA library of tomato cell cultures exposed to C. fulvum elicitors for 1.5 h. They observed low, constitutive expression of CDPK1 throughout the plant. However, when detached leaves were exposed to conidiospores of the fungus Colletotrichum coccodes (which causes anthracnose of tomato), or to the non-specific elicitors chitosan and polygalacturonide, or to signalling intermediates, such as H2O2, CDPK1 expression increased rapidly and transiently, reaching a maximum after ∼4 h. Cutting a leaflet also increased the expression of CDPK1 transiently, with a similar timecourse. Furthermore, cutting induced transient CDPK1 expression systemically in neighbouring non-wounded leaflets, which exhibited maximal expression after 12 h, and in other leaflets with a delay proportional to their distance from the site of injury. The expression of CDPK1 was paralleled by an increase in soluble CDPK activity, and an antibody raised to the CLD of a soybean CDPK indicated that the abundance of soluble CDPK protein increased upon wounding. A small increase in membrane-bound CDPK protein 20 min after injury was also noted.It is hoped that an understanding of the molecular mechanisms by which plants activate their defence responses will enable the bioengineering of plant protection and disease resistance. Chico and colleagues have identified a novel element of these signalling cascades in tomato. The induction of CDPK1 both locally and systemically in non-wounded leaflets by mechanical injury, diverse elicitors and H2O2, suggests that it might be a key regulator of non-specific responses to wounding. Perhaps, as suggested by Chico et al., signal transduction cascades triggered both by biotic agents and by mechanical wounding are interlinked by this kinase, in which case, it would make an excellent target for bioengineering.

Channel proteins form aqueous pores that allow ions to cross membranes down their electrochemical gradients. ‘Highly-selective’ K+ channels are characterized by the amino acid sequence Gly-Tyr-Gly-Asp (GYGD) in their pore structure. There are 15 genes encoding such K+ channels in Arabidopsis thaliana, which includes those for channels facilitating K+ influx (KIR) and K+ efflux (KOR) across the plasma membrane belonging to the ‘Shaker’ channel family. Plasma membrane K+ channels serve both to generate the osmotic changes required for turgor regulation, nastic movements or growth, and to balance the charge of other ions moving across the plasma membrane during, for example, nutrient uptake or cell signalling. The seven KIR channels in Arabidopsis can be divided into proteins that possess an ankyrin domain at their C-terminal (AKT1, AKT2/3, AKT5 and AKT6), which allows interactions with the cytoskeleton, and those that do not (KAT1, KAT2 and KAT3). The physiological roles of these channels are being elucidated through studies of their expression patterns, electrophysiological characteristics (following expression in heterologous systems and corroboration in appropriate plant cell types), and through the use of mutants lacking, or expressing mutant, channel proteins. From many such studies it has been suggested that (1) AKT1 is the dominant KIR channel expressed in roots and is responsible for K+ uptake from ammoniacal solutions, (2) AKT2/3 is expressed in the leaf vasculature, where it can provide a counter K+ current that facilitates sucrose loading into the phloem, and (3) KAT1 and KAT2 are co-expressed in guard cells where they form an oligomeric channel responsible for K+ uptake during stomatal opening. Now, in a most comprehensive study, Karine Mouline and colleagues have elucidated the function of AKT6 [1xPollen tube development and competitive ability are impaired by disruption of a Shaker K+ channel in Arabidopsis. Mouline, K et al. Genes Dev. 2002; 16: 339–350Crossref | PubMed | Scopus (138)See all References][1].Because AKT6 is expressed solely in pollen tubes, Mouline et al. have called its gene product SPIK, for Shaker pollen inward K+ channel. When expressed in mammalian COS cells, SPIK behaves as a typical KIR channel. It opens at extremely negative voltages and is blocked by extracellular Cs+ at mm concentrations. It is insensitive to extracellular Ca2+ in the range 1–10 mm, but is activated at more positive voltages when the extracellular medium is acidified. Mouline et al. confirmed that this electrophysiological behaviour corresponded to the KIR channels recorded in native pollen grains and argue that, because the membrane potential of pollen tubes is sufficiently negative for SPIK to open, this channel could drive pollen tube elongation by catalysing K+ uptake. Consistent with their argument, was the demonstration that pollen tubes of mutants lacking AKT6 (spick-1) had reduced KIR currents and restricted growth, resulting in a decline in pollen competitive ability and reproductive success.It is noteworthy that the expression of AKT6 is restricted to a particular cell type. Indeed, it is startling that each KIR-channel gene in Arabidopsis encodes a protein with unique biophysical properties that is expressed in specific cell types or at certain stages of development. The reason for this functional differentiation of KIR channels has yet to be resolved. Perhaps the answer lies in a necessity for precisely controlled cation fluxes, or the strict coordination of KIR channel expression in cells experiencing contrasting extracellular ionic conditions or conflicting environmental or developmental cues. The answer might also lie in the exact role of the KIR channel in cellular or plant physiology. Whatever the reason, it is nevertheless clear that many cell types possess a unique complement of KIR channels and that the K+ transport capabilities of different cell types can never be assumed.

Auxin is the name given to a specific group of compounds that control cell division, cell differentiation and cell elongation in plants. This group includes the natural phytohormone indole acetic acid (IAA), phenylacetic acid and several synthetic compounds frequently used to manipulate plant growth. IAA is a small molecule with a planar indole ring system and a carboxylic acidic side chain. It orchestrates a multitude of developmental and morphological phenomena in plants, most notably those involved in apical dominance, root initiation and a variety of tropisms. Ever since the action of hormones in animal cells was ascribed to specific receptor proteins, botanists have searched for a receptor for IAA. It is thought that the clue to the design of future agrochemicals lies in the structure of the receptor's IAA-binding site. At present, the best candidate for an auxin receptor is auxin binding protein 1 (ABP1), which appears to be necessary both for cell division and for auxin-induced cell elongation.Jim Warwicker1xModelling of auxin-binding protein 1 suggests that its C terminus and auxin could compete for a binding site that incorporates a metal ion and tryptophan residue 44. Warwicker, J. Planta. 2001; 212: 343–347Crossref | PubMed | Scopus (18)See all References1 has now predicted the three-dimensional structure of the auxin-binding site in ABP1 based on its similarity with proteins of the cupin and vicilin superfamily. He suggests that ABP1 forms a β-barrel structure, with a cluster of amino acids that could bind a metal ion at its centre. This metal ion could complement the carboxylic acid group of IAA and an adjacent tryptophan could provide a hydrophobic platform for its indole ring. Thus, an auxin-binding site is formed. The predicted geometry of this site can accommodate an indole or napthalene ring system with a carboxylic acid side-chain whose acidic group is perpendicular to the ring system. Such a structure is consistent with the specificity of ABP1 for binding ligands. Warwicker's proposed structure for ABP1 is also consistent with a physiological model for auxin perception and signal transduction, in which IAA displaces the C-terminus of ABP1 from the auxin-binding site to force a conformational change in the protein and initiate a physiological response.Elucidating the three-dimensional structure of the auxin-binding site of ABP1 provides an insight of great consequence. It can be used not only in the computer-aided design of auxin mimetics, such as the next generation of herbicides or plant growth regulators, but also in defining how ABP1 could be modified to alter the competition between auxin and the C-terminal domain or the geometry of the auxin-binding site. Such modifications could be useful in manipulating the responsiveness or specificity of cell division and cell elongation to auxins. However, although clues to the structure of the auxin-binding site of ABP1 obtained by modelling are exciting, they remain predictions. Fortuitously, Eui-Jeon Woo and colleagues2xCrystallisation and preliminary X-ray analysis of the auxin receptor ABP1. Woo, E-J. et al. Acta Crystallogr. Sect. D. 2000; 56: 1476–1478Crossref | PubMed | Scopus (14)See all References2 have recently succeeded in producing crystals of ABP1. With crystals diffracting to 1.9 A, it should not be long before a definitive structure is available against which such predictions can be tested.

Summary One of the major proteins in human serum capable of binding DNA (designated DBP-1) has been identified as β1H of the alternative complement pathway. The two proteins exhibit the same molecular weight and amino acid composition. When compared directly using immunoassays, DBP-1 and β1H appear immunologically identical. Finally, although isolated as a complement component and not as a DNA-binding protein, β1H demonstrates an affinity for DNA comparable to that of DBP-1.