The vegetative nitrogen response of sorghum lines containing different alleles for nitrate reductase and glutamate synthase

Improving the nitrogen (N) responsiveness of crops is crucial for food security and environmental sustainability, and breeding N use efficient (NUE) crops has to exploit genetic variation for this complex trait. We used reverse genetics to examine allelic variation in two N metabolism genes. In silico analysis of the genomes of 44 genetically diverse sorghum genotypes identified a nitrate reductase and a glutamate synthase gene that were under balancing selection in improved sorghum cultivars. We hypothesised that these genes are a potential source of differences in NUE, and selected parents and progeny of nested association mapping populations with different allelic combinations for these genes. Allelic variation was sourced from African (Macia) and Indian (ICSV754) genotypes that had been incorporated into the Australian elite parent R931945-2-2. Nine genotypes were grown for 30 days in a glasshouse and supplied with continuous limiting or replete N, or replete N for 27 days followed by 3 days of N starvation. Biomass, total N and nitrate contents were quantified together with gene expressions in leaves, stems and roots. Limiting N supply universally resulted in less shoot and root growth, increased root weight ratio and reduced tissue nitrate and total N concentrations. None of the tested genotypes exceeded growth or NUE of the elite parent R931945-2-2 indicating that the allelic combinations did not confer an advantage during early vegetative growth. Thus, the next steps for ascertaining potential effects on NUE include growing plants to maturity. We conclude that reverse genetics that take advantage of rapidly expanding genomic databases enable a systematic approach for developing N-efficient crops.     

Identification of QTLs associated with potassium use efficiency and underlying candidate genes by whole-genome resequencing of two parental lines in Brassica napus

Breeding crops that acquire and/or utilize potassium (K) more effectively could reduce the use of K fertilizers. Sixteen traits affecting K use efficiency (KUE) at the seedling stage were investigated in a B. napus double haploid population grown at an optimal K supply (OK) and a low K supply (LK) in a hydroponic culture system. In total, 50 and 62 QTLs associated with these traits were identified at OK and LK, respectively. A total of 25 orthologues of 23 Arabidopsis genes regulating K transport were identified in the confidence intervals of nine QTLs impacting shoot dry weight at LK, and 22 of these showed variations in coding sequences and/or exhibited significant differences in mRNA abundances in roots at LK between the two parental lines. This study provided insights to the genetic basis of KUE in B. napus, which will accelerate the breeding of K-efficient rapeseed cultivars by marker-assisted selection.     

Carbon distribution in grass (Festuca pratensis L.) during regrowth after cutting—utilization of stored and newly assimilated carbon

Distribution of net assimilated C in meadow fescue (Fectuca pratensi L.) was followed before and after cutting of the shoots. Plants were continuously labelled in a growth chamber with ¹⁴C-labelled CO₂ in the atmosphere from seedling to cutting and with ¹³C-labelled CO₂ in the atmosphere during regrowth after the cutting. Labelled C, both ¹⁴C and ¹³C, was determined at the end of the two growth periods in shoots, crowns, roots, soil and rhizosphere respiration. Distribution of net assimilated C followed almost the same pattern at the end of the two growth periods, i.e. at the end of the ¹⁴C- and the ¹³C-labelling periods. Shoots retained 71–73% of net assimilated C while 9% was detected in the roots and 11–14% was released from the roots, determined as labelled C in soil and as rhizosphere respiration. At the end of the 2nd growth period, after cutting and regrowth, 21% of the residual plant ¹⁴C at cutting (¹⁴C in crowns and roots) was found in the new shoot biomass. A minor part of the residual plant ¹⁴C, 12%, was lost from the plants. The decreases in ¹⁴C in crowns and roots during the regrowth period suggest that ¹⁴C in both crowns and roots was translocated to new shoot tissue. Approximately half of the total root C at the end of the regrowth period after cutting was ¹³C-labelled C and thus represents new root growth. Root death after cutting could not be determined in this experiment, since the decline in root ¹⁴C during the regrowth period may also be assigned to root respiration, root exudation and translocation to the shoots. ei]{gnH}{fnLambers} ei]{gnA C}{fnBorstlap}     

Variation in nitrogen use efficiency among soft red winter wheat genotypes

Summary Nitrogen use efficiency (NUE), defined as grain dry weight or grain nitrogen as a function of N supply, was evaluated in 25 soft red winter wheat genotypes for two years at one location. Significant genotypic variation was observed for NUE, nitrogen harvest index, and grain yield. Genotype x environment interaction for these traits was not significant. Several variables including N uptake efficiency (total plant N as a function of N supply), grain harvest index, and N concentration at maturity were evaluated for their role in determining differences in NUE. Nitrogen uptake efficiency accounted for 54% of the genotypic variation in NUE for yield and 72% of the genotypic variation in NUE for protein. A path coefficient analysis revealed that the direct effect of uptake efficiency on NUE was high relative to indirect effects.The investigation reported in this paper (No. 85-3-122) is in connection with a project of the Kentucky Agricultural Experiment Station and is published with approval of the Director     

Short-term UV-B radiation and ozone exposure effects on aromatic secondary metabolite accumulation and shoot growth of flavonoid-deficient Arabidopsis mutants

The presence of UV-absorptive substances in the epidermal cells of leaves is thought to protect mesophyll tissues from the harmful effects of UV-B radiation. We examined the influence of short-term UV-B exposures on UV-absorptive (330 nm) sinapates and flavonols, and on shoot growth of the Arabidopsis wild type ecotype Landsberg erecta and two mutants. 114 deficient in chalcone synthase, and 115 , deficient in chalcone/flavonone isomerase. Sequential ozone exposures were used to determine the effects of oxidative stress The levels of sinapates and flavonols on a leaf fresh weight basis increased substantially in the wild type and sinapates increased in the 114 mutant in vegetative vegetative/reproductive transitional and reproductive stage plants in response to short-term (48h) UV-B radiation. When UV-B was discontinued the levels generally decreased lo pre-exposure levels after 48 h in vegetative/reproductive but not in reproductive plants. Exposure to ozone before or alter UV-B treatment did not consistently affect the levels of these UV-absorptive compounds. Dry matter accumulation was less affected by UV-B at the vegetative and reproductive stages than at the vegetative/reproductive stage. At the vegetative/reproductive stage, shoot growth of all 3 genotypes was retarded by UV-B. Growth was not retarded by short-term ozone exposure alone but when exposure to ozone followed UV-B exposure, growth was reduced in all genotypes. Leaf cupping appeared on 115 plants exposed to UV-B.     

Association and path-coefficient studies on vegetatively propagating and sexually reproducing parts in ramie (Boehmeria nivea L. Gaud.)

Summary In 30 genotypes of ramie (Boehmeria nivea L. Gaud.) there were significant genotypic differences in the weight of reproductive parts (male + female flowers), vegetatively propagating parts (clump and rhizome) and non-propagating vegetative parts (leaf and root). The weight of reproductive parts was significantly and positively associated with the weight of vegetatively propagating parts. Path-coefficient analysis revealed that the selection of genotypes with a high weight of reproductive parts should be based on genotypes with a high weight of vegetatively propagating parts.     

Yield responses of Nepalese spring wheat (Triticum aestivum L.) cultivars to inoculation with Azospirillum spp. of Nepalese origin

Azosprilla were collected in wheat fields from subtropical and temperate soils of central Nepal at various elevations. Different wheat cultivars responded positively and significantly in grain yield, grain N-yield, and total N-yield in plant shoots to the inoculation with Nepalese isolate Azospirillum 10SW. Nepalese wheat cv. Seto responded significantly better with Azospirillum 10SW than with the Brasilian isolate A. lipoferum Sp 108 st, a strain which was found highly efficient in earlier experiments with German wheat cultivars, especially cv. Turbo. Yield of Turbo was increased by inoculations of both Azospirillum strains too, but it showed no significant differences depending from the inoculum used. The higher efficacy of combining Azospirillum 10SW and Seto, both collected from the same locality, indicates the possibility of improved associations using traditional cultivars and local bacteria. ei]{gnR O D}{fnDixon}     

Reproductive trade-offs in genetically distinct clones ofVaccinium macrocarpon,the American cranberry

Patterns of resource allocation to growth, current reproduction, and potential future reproduction were quantified in six genetically distinct cultivars ofVaccinium macrocarpon. For all cultivars (genotypes), vegetative size is positively correlated with some measures of current reproduction (fruit and flower number) but negatively correlated with others (seed number per fruit, seed weight per fruit). Vegetative growth in the current year is significantly related to the production of reproductive terminal buds, a measure of the potential for reproduction in the following year. Stems with low levels of current reproduction — lower flower number, fruit number, and seed weight — were more likely to form reproductive terminal buds than stems with higher levels of current reproduction. Individual genotypes differed significantly for vegetative size, fruit number, fruit weight, seed number, and seed weight, as well as for the frequency of fruiting stems and reproductive terminal buds produced. Genotypes were segregated in principal component space, indicating overall differences between them in allocation to the suite of variables measured. These results indicate the possibility of fitness differences among cultivars due to genetically determined allocation strategy, which has implications for fitness differences among genotypes within natural populations.     

Root growth and water uptake in winter wheat under deficit irrigation

Root growth is critical for crops to use soil water under water-limited conditions. A field study was conducted to investigate the effect of available soil water on root and shoot growth, and root water uptake in winter wheat (Triticum aestivum L.) under deficit irrigation in a semi-arid environment. Treatments consisted of rainfed, deficit irrigation at different developmental stages, and adequate irrigation. The rainfed plots had the lowest shoot dry weight because available soil water decreased rapidly from booting to late grain filling. For the deficit-irrigation treatments, crops that received irrigation at jointing and booting had higher shoot dry weight than those that received irrigation at anthesis and middle grain filling. Rapid root growth occurred in both rainfed and irrigated crops from floral initiation to anthesis, and maximum rooting depth occurred by booting. Root length density and dry weight decreased after anthesis. From floral initiation to booting, root length density and growth rate were higher in rainfed than in irrigated crops. However, root length density and growth rate were lower in rainfed than in irrigated crops from booting to anthesis. As a result, the difference in root length density between rainfed and irrigated treatments was small during grain filling. The root growth and water use below 1.4 m were limited by a caliche (45% CaCO₃) layer at about 1.4 m profile. The mean water uptake rate decreased as available soil water decreased. During grain filling, root water uptake was higher from the irrigated crops than from the rainfed. Irrigation from jointing to anthesis increased seasonal evapotranspiration, grain yield, harvest index and water-use efficiency based on yield (WUE), but did not affect water-use efficiency based on aboveground biomass. There was no significant difference in WUE among irrigation treatments except one-irrigation at middle grain filling. Due to a relatively deep root system in rainfed crops, the higher grain yield and WUE in irrigated crops compared to rainfed crops was not a result of rooting depth or root length density, but increased harvest index, and higher water uptake rate during grain filling.     

植物养分高效利用机制研究进展

长期进化和环境适应导致不同植物或同种植物不同基因型间养分利用效率(NUE)差异明显,研究筛选植物养分高效利用基因型至关重要,其极大的增产潜力可补充代替传统植物栽培方法所需的能源.目前人们对于植物NUE概念的理解存在一定差异,造成众多研究成果缺乏可比性.通过对植物NUE的概念及其描述方式难以统一原因的分析,提出人工林NUE应采用干材生物量与林分养分总量的比值表示.综合评述了植物体内养分高效利用及植物对生长介质中养分高效吸收的生物生理学适应性机制.对养分逆境植物养分高效利用适应性策略的整个过程进行了描述,进一步阐明了Ca2+在化学通讯机制中的生物功能,指出Ca2+可能是启动植物养分高效利用挽救机制的主要调控因子,并就该领域今后研究工作的特点作了展望.     

内蒙古中东部草原不同生境克氏针茅（Stipa krylovii Roshev.）种群的形态差异分析

对内蒙古中东部草原分布的克氏针茅进行了种群内和种群间的形态差异分析。结果表明：（1）种群内不同的形态性状存在不同程度的差异;（2）种群间生殖枝中的一部分形态性状以及营养枝高度和营养枝干重均存在较大差异;（3）每穗小花数、每穗籽粒数、每穗小穗数、生殖枝高、穗干重、生殖枝干重、每穗种子重、种子重/生殖枝重比等性状的变化趋势相同,均表现为随生境条件变差而增加,即在生殖上投入增加以增大适合度;（4）主成分分析表明穗长、种子重/生殖枝重比、每穗小花数、每穗籽粒数、生殖枝高、基盘长、第二芒柱长、营养枝高、千粒重、芒针长是不同种群差异的主要指标。这些形态性状的差异可以看作克氏针茅对不同生境的适应性表现。     

Soil nutrient patchiness affects nutrient use efficiency,though not photosynthesis and growth of parental Glechoma longituba ramets: both patch contrast and direction matter

Aims Most plants are clonal in nature. Clonal ramets can share water, nutrients and photosynthate, especially when they experience patchy resources. Patch contrast (i.e. a difference in resources among patches) and patch direction (i.e. source–sink relations) are among the basic attributes of spatial patchiness. Here, I hypothesize that young established ramets in nutrient-rich patches support old ramets in nutrient-poor patches when ramets are subjected to different patch contrasts and patch directions.Methods In a greenhouse experiment, old and young ramets of Glechoma longituba were grown in four combinations consisting of patch contrast and patch direction. Minus patch direction refers to a patch combination in which parent ramets grow in nutrient-rich patches while connected daughter ramets grow in nutrient-poor ones and plus patch direction is the opposite direction. I measured photosynthesis and fluorescence traits, harvested all ramets, took morphological measures, weighed their dry mass and determined their nutrient uptake and use.Important findings For parental ramets of G. longituba, patch contrast and patch direction and their interactions had no significant effects on net photosynthetic rate, maximal fluorescence yield, photochemical quenching (quenching refers to any process which decreases the fluorescence intensity of a given substance), non-photochemical quenching, nutrient uptake, biomass and stolon weight ratio. Patch direction alone significantly affected root weight ratio. Large patch contrast enhanced N use efficiency (NUE) and P use efficiency (PUE); plus patch direction decreased NUE, but increased PUE; the patch contrast by patch direction interaction affected PUE and K use efficiency (KUE). There were significant interactions between patch direction and patch contrast on PUE and KUE. It is concluded that soil nutrient patchiness may influence nutrient use strategies, but not nutrient uptake, photosynthesis and growth of parent ramets of G. longituba connected to daughter ramets, and that patch contrast and patch direction jointly affect PUE and KUE.     

Reproductive allocation of biomass and nitrogen in annual and perennial Lesquerella crops

* BACKGROUND AND AIMS: The use of perennial crops could contribute to increase agricultural sustainability. However, almost all of the major grain crops are herbaceous annuals and opportunities to replace them with more long-lived perennials have been poorly explored. This follows the presumption that the perennial life cycle is associated with a lower potential yield, due to a reduced allocation of biomass to grains. The hypothesis was tested that allocation to perpetuation organs in the perennial L. mendocina would not be directly related to a lower allocation to seeds. * METHODS: Two field experiments were carried on with the annual Lesquerella fendleri and the iteroparous perennial L. mendocina, two promising oil-seed crops for low-productivity environments, subjected to different water and nitrogen availability. * KEY RESULTS: Seed biomass allocation was similar for both species, and unresponsive to water and nitrogen availability. Greater root and vegetative shoot allocation in the perennial was counterbalanced by a lower allocation to other reproductive structures compared with the annual Lesquerella. Allometric relationships revealed that allocation differences between the annual and the perennial increased linearly with plant size. The general allocation patterns for nitrogen did not differ from those of biomass. However, nitrogen concentrations were higher in the vegetative shoot and root of L. mendocina than of L. fendleri but remained stable in seeds of both species. * CONCLUSIONS: It is concluded that vegetative organs are more hierarchically important sinks in L. mendocina than in the annual L. fendleri, but without disadvantages in seed hierarchy.     

Relationship between the photosynthetic activity and the performance of Cakile maritima after long-term salt treatment

Cakile maritima is a halophyte with potential for ecological, economical and medicinal uses. We address here the impact of salinity on its growth, photosynthesis and seed quality. Whole plant growth rate and shoot development were stimulated at moderate salinity (100–200 m M NaCl) and inhibited at higher salt concentrations. Although diminished in the presence of salt, potassium and calcium uptake per unit of root biomass was maintained at relatively high value, while nutrient-use efficiency (NUE) was improved in salt-treated plants. Chl and carotenoid concentrations decreased at extreme salinities, but anthocyanin concentration continuously grew with salinity. Net photosynthetic rate (A), stomatal conductance, maximum quantum efficiency of PSII and quantum yield were stimulated in the 100–200 m M NaCl range. Higher salinity adversely affected gas exchange and changed PSII functional characteristics, resulting in a reduction of A per leaf area unit. This phenomenon was associated with increased non-photochemical quenching. Harvest index, silique number and seeds per fruit valve were maximal at 100 m M NaCl. Despite the decreasing salt accumulation gradient from the vegetative to the reproductive organs, high salinities were detrimental for the seed viability and increased the proportion of empty siliques. Overall, the salt-induced changes in the plant photosynthetic activity resulted into analogous responses at the vegetative and reproductive stages. The enhancement of NUE, the absence of pigment degradation, the reduction of water loss and the concomitant PSII protection from photodamage through thermal dissipation of excess excitation significantly accounted for Cakile survival capacity at high salinity.     

Dynamics of nitrogen uptake and partitioning in early and late fruit ripening peach (Prunus persica) tree genotypes under a mediterranean climate

The dynamics of N uptake and N partitioning in peach (Prunus persica, Batsch) trees of a very early (cv. Flordastar) and a very late (cv. Tudia) fruit ripening varieties grown under a mediterranean climate was assessed during one season. Labelled N was applied to two-year old potted trees which were destructively harvested at regular intervals during the vegetative and reproductive cycle. Tree phenology as well as vegetative and reproductive growth of the two genotypes strongly differed: bud burst started in late January in Flordastar and late March in Tudia. Leaf senescence in Flordastar was almost complete by mid October, while Tudia still retained a significant fraction of leaves at the December harvest. Fruit yield averaged 4.0 and 6.9 kg tree^–1 (fresh weight) in cv. Flordastar and Tudia, respectively, and fruit size was within commercial standards for the two genotypes. After growth resumption, shoot and fruit growth mainly relied on N remobilised from reserves, which accounted for 72–80% of total N in new growth. Nitrogen uptake by both genotypes was relatively low in the first month after bud burst, then was more rapid until the end of the season. Total labelled N uptake did not differ between the two genotypes and accounted on average for 65–70% of total N supplied. The kinetics of labelled N uptake were similar in the two varieties despite the great difference in the timing of their fruit ripening. Leaves were the main sink for N during much of the experimental period. The fruits, when present, also used a significant fraction of the absorbed N, which was almost constant until fruit ripening in Flordastar. Nitrogen partitioning to leaves declined progressively after summer, when a greater fraction of the absorbed N was recovered in the twigs, the trunk, the fine roots and especially in the coarse roots. The data provide evidence for guiding the kinetics of N supply to peach orchards under a Mediterranean climate.     

Phenotypic plasticity in vegetative and reproductive traits in an invasive weed, Lythrum salicaria (Lythraceae), in response to soil moisture

In colonizing species, high phenotypic plasticity can contribute to survival and propagation in heterogenous adventive environments, and it has been suggested as a predictor of invasiveness. Observation of natural populations of an invasive species, Lythrum salicaria salicaria, indicated extensive variation in its growth and reproductive traits. Phenotypic plasticity of different life history traits of L. salicaria was investigated using vegetative clones of each of 12 genotypes from one population in Ontario, Canada. We chose soil moisture as the treatment factor because of its importance in wetland species and raised all 12 genotypes in each of four soil moisture treatments. We examined an array of vegetative and reproductive traits, including root and shoot mass, shoot and inflorescence length, total seed set, floral mass, and morphometric variables. All observed vegetative as well as reproductive traits demonstrated significant phenotypic plasticity in response to soil moisture treatment. Even the stigma-anther separation involved significant genotype by environment interactions, suggesting that soil moisture may modify the relative positions of anthers and stigma. Compared to vegetative traits, most reproductive traits demonstrated crossing reaction norms, implying that the average differences in those traits among genotypes vary with the environment maintaining the genetic variation in a population.     

Physiological responses of spring rapeseed (Brassica napus) to red/far‐red ratios and irradiance during pre‐ and post‐flowering stages

Early shade signals promote the shade avoidance syndrome (SAS) which causes, among others, petiole and shoot elongation and upward leaf position. In spite of its relevance, these photomorphogenic responses have not been deeply studied in rapeseed (Brassica napus). In contrast to other crops like maize and wheat, rapeseed has a complex developmental phenotypic pattern as it evolves from an initial rosette to the main stem elongation and an indeterminate growth of floral raceme. In this work, we analyzed (1) morphological and physiological responses at individual level due to low red/far‐red (R/FR) ratio during plant development, and (2) changes in biomass allocation, grain yield and composition at crop level in response to high R/FR ratio and low irradiance in two modern spring rapeseed genotypes. We carried out pot and field experiments modifying R/FR ratios and irradiance at vegetative or reproductive stages. In pot experiments, low R/FR ratio increased the petiole and lamina length, upward leaf position and also accelerated leaf senescence. Furthermore, low R/FR ratio reduced main floral raceme and increased floral branching with higher remobilization of soluble carbohydrates from the stems. In field experiments, low irradiance during post‐flowering reduced grain yield, harvest index and grain oil content, and high R/FR ratio reaching the crop partially alleviated such effects. We conclude that photomorphogenic signals are integrated early during the vegetative growth, and irradiance has stronger effects than R/FR signals at rapeseed crop level.     

Tolerance of peanut to excess boron

The tolerance ofArachis hypogaea cv. Shulamit to high concentrations of B in nutrient solution, [B]o, was determined under greenhouse conditions that promoted the production of vegetative dry matter. Plants grew in large containers in which a root zone of nutrient solution was separated from a pod zone of soil. Grain yield was reduced at a calculated [B]o-threshold of 0.29 mM, which was associated with a concentration of B in the vegetative shoots that was approximately four times larger than the control. Symptoms of B toxicity occurred on leaves as young as the third unfolded leaf from the shoot apex before the [B]o-threshold. Excess B caused a relatively larger decrease in pod number than in vegetative shoot weight, which was high in all treatments (78 g d.wt/plant) and it did not decrease single grain weight. It was suggested that the tolerance of grain development to excess B was a consequence of the high ratio of vegetative matter to pod number.     

Effects of water stress on N2 fixation and grain yield of Phaseolus vulgaris L.

Most dry bean production in Mexico is under non-irrigated conditions in the semi-arid highlands. One of the most limiting factors is insufficient moisture during the reproductive stage and sometimes during the vegetative stage. The objective of this experiment was to study the effect of drought on nodulation, N₂ fixation and grain yield of beans. The cultivars evaluated were: Flor de Mayo Bajio, Bayocel, Bat-477 and Honduras-35. The treatments were water stress treatments during vegetative or reproductive stage and a control of minimal stress. To measure N₂ fixation, ¹⁵N-labelled fertilizer was used. Data for soil moisture, nodule number and nodule dry weight, as well as, straw and grain yield and total N were taken. The results indicated that water stress during vegetative stage depressed nodulation temporarily, but after watering regularly plants not only recovered completely but were nodulated better than the control. Water stress during the reproductive stage depressed nodulation and after watering there was no recovery. Grain yield was not affected by water stress during vegetative stage but it was reduced when water stress was imposed during the reproductive stage. The percentage of N derived from fixation varied among cultivars but was not affected by water stress treatment. The highest N₂ fixation occurred in Bayocel and Bat-477 and the lowest in Honduras-35 and F.M. Bajio, although the amounts were not as low as in some other reports.     

Response of three wheat genotypes grown under saline medium to low/high potassium levels

A water culture experiment was conducted, to study the response of three wheat genotypes (Sarsabz, Kiran-95 and Pasban-90) to low and high potassium levels, (0.01 and 10 mM KC1) grown under two salinity concentrations (50 mM and 150 mM, NaCI). The results showed that the presence of sufficient potassium in the growth medium was found to bring good effects on plant growth. The data showed that shoot length of Kiran-95 growing under two salinities and associated with low and high potassium was quite satisfactory followed by Sarsabz and Pasban-90. Ionic content in plant shoots also varied with the increase in salinity levels of the medium. Potassium content in plant shoot was strongly regulated by Na⁺ ions, showing gradually decrease in K with the increase in Na accumulation in shoot. Under high salinities Kiran-95 had maximum K content in both low/high K supply, followed by Sarsabz and Pasban-90. This ability of Kiran-95 to maintain optimum K level may be the reason of its better survival.