AAP1 regulates import of amino acids into developing Arabidopsis embryos

The embryo of Arabidopsis seeds is symplasmically isolated from the surrounding seed coat and endosperm, and uptake of nutrients from the seed apoplast is required for embryo growth and storage reserve accumulation. With the aim of understanding the importance of nitrogen (N) uptake into developing embryos, we analysed two mutants of AAP1 (At1g58360), an amino acid transporter that was localized to Arabidopsis embryos. In mature and desiccated aap1 seeds the total N and carbon content was reduced while the total free amino acid levels were strongly increased. Separately analysed embryos and seed coats/endosperm of mature seeds showed that the elevated amounts in amino acids were caused by an accumulation in the seed coat/endosperm, demonstrating that a decrease in uptake of amino acids by the aap1 embryo affects the N pool in the seed coat/endosperm. Also, the number of protein bodies was increased in the aap1 endosperm, suggesting that the accumulation of free amino acids triggered protein synthesis. Analysis of seed storage compounds revealed that the total fatty acid content was unchanged in aap1 seeds, but storage protein levels were decreased. Expression analysis of genes of seed N transport, metabolism and storage was in agreement with the biochemical data. In addition, seed weight, as well as total silique and seed number, was reduced in the mutants. Together, these results demonstrate that seed protein synthesis and seed weight is dependent on N availability and that AAP1-mediated uptake of amino acids by the embryo is important for storage protein synthesis and seed yield.     

Contribution of Different Mechanisms to Zinc Efficiency in Bread Wheat During Early Vegetative Stage

Zinc (Zn) has a vast number of functions in plant metabolism and consequently Zn deficiency has a range of effects on plant growth. There are a number of different possible mechanisms by which plants tolerate Zn deficiency (generally expressed as Zn efficiency), such as Zn uptake, translocation to the shoot and physiological efficiency. However, there have been no direct comparisons of the relative importance of these possible mechanisms of Zn efficiency in a large set of genotypes of contrasting Zn efficiency. Soil and solution culture studies were conducted to examine the relative contribution of different mechanisms of Zn efficiency at the whole plant level in bread and durum wheat during early vegetative stage. Zn treatments were 0, 0.05, 0.1 and 1 mg/kg soil in the soil culture, and nil in the solution culture. Visual symptoms of Zn deficiency, dry matter production, Zn uptake, Zn distribution between roots and shoots, Zn utilization in roots and shoots and Zn remobilisation from the seed into growing parts were examined. Significant genotypic differences were observed in most criteria and responses differed with external Zn supply. The results of the present study suggest that while there are a number of different mechanisms contributing to Zn efficiency, uptake is the major mechanism and the effect of this is modified by the physiological efficiency within the shoot. Root:shoot partitioning was not strongly associated with Zn efficiency and seed Zn remobilisation was not linked to Zn efficiency. Visual symptoms of the severity of Zn deficiency was a good predictor of Zn efficiency and was correlated with Zn uptake.     

Seed zinc content influences early vegetative growth and zinc uptake in oilseed rape (Brassica napus and Brassica juncea) genotypes on zinc-deficient soil

Low-Zn seed (around 80 ng Zn per seed) and high-Zn seed (around 160 ng Zn per seed) of Zhongyou 821 (a traditional Brassica napus genotype from China found to be Zn-inefficient in our previous experiments), Narendra (Zn-efficient B. napus genotype from Australia) and CSIRO-1 (a Zn-efficient B. juncea genotype from Australia) oilseed rape genotypes were sown in pots containing Zn-deficient siliceous sand fertilized with low Zn supply (0.05 mg Zn kg^–1 soil) or high Zn supply (2.0 mg Zn kg^–1 soil) in a controlled environment. After six weeks, plants derived from the high-Zn seed had better seedling vigour, increased root and shoot growth, more leaf area and chlorophyll concentration in fresh leaf, and higher Zn uptake in shoot compared to those from low-Zn seed at low Zn supply; the impact of high-Zn seed was more marked in Zhongyou 821 compared with CSIRO-1 and Narendra. The influence of high-Zn seed was dissipated at high Zn supply. CSIRO-1 was superior in terms of shoot dry matter production and Zn uptake in shoots at low Zn supply. The results demonstrate that although oilseed rape has very small seeds (about 3 mg per seed weight) compared with wheat (30 mg per seed weight), Zn reserves present in this very small seed still have a strong impact on early vegetative growth as well as on Zn uptake of plants in Zn-deficient soils. The results suggest that sowing high-Zn seed coupled with growing Zn-efficient genotypes may help in sustaining the production of oilseed rape in Zn-deficient soils, and this has implications for improved seed technology.     

Endosperm protein of wheat seed as a determinant of seedling growth

Seed of a Mexican semidwarf wheat (Triticum aestivum L. cv. Inia 66), was obtained from a nitrogen fertilizer field trial grown in Mexico. A high positive correlation was obtained between seed protein content and seedling dry weight after 3 weeks growth (r = +0.92^**). The seedling dry weight was positively related to the protein content of the aleurone layer and endosperm, but not to the embryo. Small, 35 milligrams, high protein seeds (4.7 milligrams protein per seed) produced larger seedlings than large, 45 milligrams, low protein seeds (4.3 milligram protein per seed). There was no difference in the weight or protein content of embryos from low and high protein seeds and their growth was similar. Composite seeds of the two protein levels were produced by transferring embryos from one endosperm type to the other. After 4 weeks, there was no difference between the different embryo types grown on the same endosperm type. High protein endosperm produced more vigorous seedlings regardless of the embryo type grown on it, indicating that the factor(s) responsible for the greater growth of high protein seed is in the endosperm.     

~(16)O~(8+)离子辐照普通小麦引起幼苗可溶性蛋白质的不同变化

利用不同能量、不同剂量的1 6 O8+ 离子辐照春麦。处理方式为离子贯穿种子 (75MeV u)以及离子注入胚和胚乳等种子的不同部位。然后分析其幼苗的可溶性蛋白质 (solubleprotein) ,根据其分子量大小不同 ,将其划分为五个区段并计算各组分的相对含量 ,结果表明 :1 同对照相比 ,随着辐照剂量的增加 ,所有辐照材料 (包括贯穿和注入 )第二区段 (分子量较高区段 )蛋白质组分的相对含量下降 ;而第五区段 (分子量最小区段 )蛋白质组分的相对含量升高。 2 种子的贯穿处理 ,同时也引起第一区段 (分子量最高区段 )和第三区段蛋白质组分相对含量的下降以及第四区段的升高 ;其中第三、四区段的变化明显区别于注入效应。 3 注入胚和胚乳的区别在于后者第一区段蛋白质组分相对含量的较大下降和第五区段的较大提高。 4 小剂量辐照的材料 ,可溶性蛋白质组分的变化异常 ,可能与低剂量辐射兴奋效应有关。在讨论中提出了注入胚的即时效应与注入胚乳的后期效应。     

Thioredoxin and germinating barley: targets and protein redox changes

The endosperm and embryo of barley ( Hordeum vulgare L.) grain were investigated to relate thioredoxin h and disulfide changes to germination and seedling development. The disulfide proteins of both tissues were found to undergo reduction following imbibition. Reduction reached a peak 1 day earlier in the embryo than in the endosperm, day 1 vs. day 2. The profile in both cases resembled those observed with wheat and rice, i.e., the reduction of the storage proteins increased initially and then declined during the period of seedling growth. The extent of the increase in reduction observed with barley endosperm was, however, less pronounced than with the other cereals. Also, unlike wheat and rice, the storage proteins of the endosperm were highly reduced in the dry seed and the sulfhydryl content of glutelins showed no appreciable change during this period. The relative abundance of thioredoxin h during germination and early seedling growth differed in the embryo and endosperm: a progressive decrease in the endosperm (as seen with wheat) vs. an increase in the embryo. Thioredoxin h was found in the major seed tissues in characteristic forms. Three forms were found in the scutellum and aleurone, whereas two, which may represent isoforms, were identified in the root and the shoot. Using a recently developed strategy based on two-dimensional gel electrophoresis, several proteins were identified as specific targets for thioredoxin in the embryo following oxidation with H(2)O(2), among them barley embryo globulin 1, peroxiredoxin and acidic ribosomal protein P(3). The results confirm earlier findings with the endosperm of other cereals and extend the importance of thioredoxin-linked redox change to the germinating embryo for functions that potentially include dormancy, protection against reactive oxygen species, translation and the mobilization of storage proteins.     

Shoot and root growth and nutrients uptake of wheat as affected by soil layers

The effect of soil layering on the growth and nutrient content of wheat shoots and roots was studied. PVC containers (120 cm long and 25 cm inside diameter) were filled with layers of loam and loamy sand. Both roots and shoots dry weight increased as the thickness of loam layer increased. The root:shoot ratios decreased throughout the growing season. The N, P and K content of the shoots peaked at two weeks before anthesis, while shoot dry weight peaked at anthesis. The ranges of shoot content of N, P and K at anthesis for the different treatments were 6–25, 8–25 and 5–25% of the total plant nutrients, respectively. Late in the season the translocation rate of nutrients from the shoots to the seeds were in the following order N>P>K.     

Polyamines and Protein Metabolism in Maize Inbreds Differing in Seed Protein Content

Polyamine metabolism was evaluated in the embryo and the endosperm,during the early stages of seed germination, of two maize inbreds(Lo5 and B73) differing in the protein nitrogen content of thecaryopscs. On germination, the concentration of buffer-extractableproteins and of polyamines increases more quickly and to greatervalues in Lo5 than in B73. In the caryopses, the embryos havea higher polyamine content than the endosperms and in the seedlings,after three days of growth, the shoots show a higher polyaminecontent than in the case of the scutellum and the roots. Duringseed germination, spermidine is the main polyamine and its contentvaries while the spermine remains virtually constant. The polyaminesand protein pattern in the embryo and the endosperm of the twoinbreds are discussed in relation to the differences in theirgermination energy and early seedling growth.     

Dry matter production and distribution of zinc in bread and durum wheat genotypes differing in zinc efficiency

Six bread wheat (Triticum aestivum cvs. Kiraç-66, Gerek-79, Aroona, ES 91-12, ES-14 and Kirkpinar) and four durum wheat (Triticum durum cvs. BDMM-19, Kunduru-1149, Kiziltan-91 and Durati) genotypes were grown under controlled environmental conditions in nutrient solution for 20 days to study the effect of varied supply of Zn (0 to 1 µM) on Zn deficiency symptoms in shoots, root and shoot dry matter production, and distribution of Zn in roots and shoots.Visual Zn deficiency symptoms, such as whitish-brown lesions on leaves, appeared rapidly and severly in durum wheats, particularly in Kiziltan-91 and Durati. Among the durum wheats, BDMM-19 was less affected by Zn deficiency, and among the bread wheats Kiraç-66, ES 91-12, Aroona and Gerek-79 were less affected than ES-14 and Kirkpinar.Under Zn deficiency, shoot dry matter production was decreased in all genotypes, but more distinctly in durum wheat genotypes. Despite severe decreases in shoot growth, root growth of all genotypes was either not affected or even increased by Zn deficiency. Correspondingly, shoot/root dry weight ratios were lower in Zn-deficient than in Zn-sufficient plants, especially in durum wheat genotypes.The distinct differences among the genotypes in sensitivity to Zn deficiency were closely related with the Zn content (Zn accumulation) per shoot but not with the Zn concentration in the shoot dry matter. On average, genotypes with lesser deficiency symptoms contained about 42% more Zn per shoot than genotypes with severe deficiency symptoms. In contrast to shoots, the Zn content in roots did not differ between genotypes. Shoot/root ratios of total Zn content were therefore greater for genotypes with lesser deficiency symptoms than for genotypes with severe deficiency symptoms (i.e. all durum wheat genotypes).The results suggest that the enhanced capacity of genotypes for Zn uptake and translocation from roots to shoot meristems under deficient Zn supply might be the most important factor contributing to Zn efficiency in wheat genotypes. The results also demonstrate that under severe Zn deficiency, Zn concentration in the shoot dry matter is not a suitable parameter for distinguishing wheat genotypes in their sensitivity to Zn deficiency.     

A Cascade of Sequentially Expressed Sucrose Transporters in the Seed Coat and Endosperm Provides Nutrition for the Arabidopsis Embryo

Developing plant embryos depend on nutrition from maternal tissues via the seed coat and endosperm, but the mechanisms that supply nutrients to plant embryos have remained elusive. Sucrose, the major transport form of carbohydrate in plants, is delivered via the phloem to the maternal seed coat and then secreted from the seed coat to feed the embryo. Here, we show that seed filling in Arabidopsis thaliana requires the three sucrose transporters SWEET11, 12, and 15. SWEET11, 12, and 15 exhibit specific spatiotemporal expression patterns in developing seeds, but only a sweet11;12;15 triple mutant showed severe seed defects, which include retarded embryo development, reduced seed weight, and reduced starch and lipid content, causing a “wrinkled” seed phenotype. In sweet11;12;15 triple mutants, starch accumulated in the seed coat but not the embryo, implicating SWEET-mediated sucrose efflux in the transfer of sugars from seed coat to embryo. This cascade of sequentially expressed SWEETs provides the feeding pathway for the plant embryo, an important feature for yield potential.     

Influence of aqueous leaf extract of common lambsquarters and NaCl salinity on the germination, growth, and nutrient content of wheat

Aqueous leaf extract of common lambsquarters (Chenopodium album L.) was evaluated alone or in combination with NaCl salinity for its influence on germination, seedling growth and contents of Na, K, and Ca by shoots and roots of wheat. The leaf extract and NaCl alone or in combination did not have any significant effect on germination, but the shoot and root lengths of seedlings and their dry weight decreased significantly by the treatments. Root growth was affected more than the shoot. The combination of leaf extract and NaCl drastically reduced the growth more than the separate effects of these stress treatments. The incorporation of leaf extract in the growth media decreased the content of Na by shoot, whereas the contents of K and Ca increased. NaCl treatments in combination with leaf extract increased the content of Na. Similar increases were observed for K and Ca in shoot, while these nutrients were increased in roots compared to control.     

Studies on the Physiology of Rice: XV. CHANGES IN THE NITROGEN METABOLISM OF SEEDS DURING GERMINATION AND THEIR RELATION TO THE APPLICATION OF GROWTH REGULATORS

Seeds of rice variety ‘Chinsurah Boro’ were treatedwith two concentrations of indoleacetic acid (IAA) and maleichydrazide (MH), 0.1 mg. per litre and 0.01 mg. per litre, duringthe first 7 days of germination, and the resulting changes innitrogen metabolism of both endosperm and embryo were determined.The seedling growth at different times during the treatmentwas recorded. Uptake of water by the embryo increased up to 72 hours, butthereafter the percentage water content fell, owing to large-scaletranslocation of dry matter to it. The endosperm showed increasingwater content for 5 days. There are two marked stages of nitrogen metabolism of the seedduring germination. During the first 72 hours hydrolysis ofprotein in the endosperm and translocation of soluble nitrogento the embryo are the predominant features. Thereafter the embryoactively synthesizes protein from the products of translocation. IAA and MH affected the seedling growth similarly. Initiallythere was a small retardation of leaf growth, but at later periodsrecovery took place. Root growth was more adversely affectedthan shoot growth, the effect also persisting longer. Thesechanges in growth were reflected in the nitrogen metabolismof the seedlings. For the first few days IAA and MH retardedthe supply of soluble nitrogen from the endosperm to the embryo,consequently there was less soluble nitrogen in the embryo thoughprotein synthesis there was affected only slightly. The differencein soluble nitrogen between the treated and untreated embryospersisted throughout the seven days. An attempt is made to explainthis on the basis that primarily IAA and MH retard the enzymaticactivity responsible for the hydrolysis of protein in the endosperm.     

Spatial X-ray fluorescence micro-imaging of minerals in grain tissues of wheat and related genotypes

Main conclusion

Wheat and its related genotypes show distinct distribution patterns for mineral nutrients in maternal and filial tissues in grains. X-ray-based imaging techniques are very informative to identify genotypes with contrasting tissue-specific localization of different elements. This can help in the selection of suitable genotypes for nutritional improvement of food grain crops.

Abstract

Understanding mineral localization in cereal grains is important for their nutritional improvement. Spatial distribution of mineral nutrients (Mg, P, S, K, Ca, Fe, Zn, Mn and Cu) was investigated between and within the maternal and filial tissues in grains of two wheat cultivars (Triticum aestivum Cv. WH291 and WL711), a landrace (T. aestivum L. IITR26) and a related wild species Aegilops kotschyi, using micro-proton-induced X-ray emission (µ-PIXE) and micro-X-ray fluorescence (µ-XRF). Aleurone and scutellum were major storage tissues for macro (P, K, Ca and Mg) as well as micro (Fe, Zn, Cu and Mn) nutrients. Distinct elemental distribution patterns were observed in each of the four genotypes. A. kotschyi, the wild relative of wheat and the landrace, T. aestivum L. IITR26, accumulated more Zn and Fe in scutellum and aleurone than the cultivated wheat varieties, WH291 and WL711. The landrace IITR26, accumulated far more S in grains, Mn in scutellum, aleurone and embryo region, Ca and Cu in aleurone and scutellum, and Mg, K and P in scutellum than the other genotypes. Unlike wheat, lower Mn and higher Fe, Cu and Zn concentrations were noticed in the pigment strand of A. kotschyi. Multivariate statistical analysis, performed on mineral distribution in major grain tissues (aleurone, scutellum, endosperm and embryo region) resolved the four genotypes into distinct clusters.     

Postanthesis remobilisation and losses of nitrogen in wheat in relation to applied nitrogen

A ¹⁵N leaf feeding technique was used to measure the extent of remobilisation and loss of nitrogen (N) that had been accumulated prior to anthesis in wheat plants that received three rates of N fertilizer. Uptake of postanthesis N to the heads was reduced as the quantity of applied N was increased. This reduction of postanthesis N uptake did not affect the quqntity of N in the heads because the loss of preanthesis accumulated N was reduced and the extent of remobilised preanthesis N increased at higher rates of N application. At the lowest rate of N application the increase in ¹⁵N in the heads of fertile shoots arose chiefly from the remobilisation of N in the stem supporting the head. At higher rates of N application this source of N was increasingly supplemented by N remobilised from infertile tillers and roots.     

Accumulation and distribution of Zn in the shoots and reproductive structures of the halophyte plant species Kosteletzkya virginica as a function of salinity

Kosteletzkya virginica is a wetland halophyte that is a good candidate for rehabilitation of degraded salt marshes and production of oil as biodiesel. Salt marshes are frequently contaminated by heavy metals. The distribution of Zn in vegetative and reproductive organs of adult plants, and the NaCl influence on this distribution remain unknown and were thus explored in the present study. Plants were cultivated in a nutrient film technique system, from seedling stage until seed maturation in a control, Zn (100 μM), NaCl (50 mM) or Zn + NaCl medium. Photosynthesis, ion nutrition, malondialdehyde and non-protein thiol concentrations were quantified. Zinc distribution in reproductive organs was estimated by a laser ablation-inductively coupled plasma-mass spectrometry procedure (LA-ICP-MS). Adult plants accumulated up to 2 mg g^?1 DW Zn in the shoots. Zinc reduced plant growth, inhibited photosynthesis and reduced seed yield. Zinc accumulation in the seeds was only two times higher in Zn-treated plants than in controls. Exogenous NaCl neutralized the damaging action of Zn and modified the Zn distribution through a preferential accumulation of toxic ions in older leaves. Zinc was present in seed testa, endosperm and, to a lower extent, in embryo. Additional NaCl induced a chalazal retention of Zn during seed maturation and reduced final Zn seed content. It is concluded that NaCl 50 mM had a positive impact on the response of K. virginica to Zn toxicity and acts through a modification in Zn distribution rather than a decrease in Zn absorption.     

Ecological implications of seed characteristics of the native Prosopis cineraria and the alien P. juliflora

Seed weight, percentage germination, seedling growth, and nutrient concentrations (Mg, Na, K, Zn, Cu and P) of whole seeds, and of seed coats and embryos separately of two tree species, the native Prosopis cineraria and the invasive alien P. juliflora from semi-arid and arid areas of north and north-west India, were analysed to understand the differences in their ecology. Seeds of P. cineraria were heavier than those of P. juliflora. Percent germination was similar in the two species, but seedling growth was faster in P. juliflora than in P. cineraria. Nutrient concentrations of seeds of the two species were similar (except Cu). Nutrient concentrations in the embryo were higher in P. cineraria, while those in the seed coat were higher in P. juliflora. The relative allocation of nutrients to seed coat was higher in P. juliflora than in P. cineraria. Nutrient-rich embryos and slow growth, along with a staggered seed germination pattern in the native P. cineraria could be linked to delayed establishment as well, in the substratum. Faster growth of the nutrient-poor embryos in P. juliflora along with its simultaneous seed germination pattern, and creation of a favourable microenvironment through leaching of nutrients from a nutrient-rich seed coat can facilitate immediate and successful establishment of this alien species in the invaded habitats.     

Importance of seed Zn content for wheat growth on Zn-deficient soil

Seed nutrient reserves may be important for an early establishment of crops on low-fertility soils. This glasshouse pot study evaluated effects of seed Zn content on vegetative growth of two wheat (Triticum aestivum L.) genotypes differing in Zn efficiency. Low-Zn (around 250 ng Zn per seed) and high-Zn seed (around 700 ng Zn per seed on average) of Excalibur (Zn efficient) and Gatcher (Zn inefficient) wheats were sown in a Zn-deficient siliceous sand fertilised with 0, 0.05, 0.2, 0.8 or 3.2 mg Zn kg^-1 soil. After 3 weeks, plants derived from the high-Zn seed had better root and shoot growth; the cv. Excalibur accumulated more shoot dry matter than the cv. Gatcher. After 6 weeks, greater root and shoot growth of plants grown from the high-Zn seed compared to those from the low-Zn seed was obvious only at nil Zn fertilisation. A fertilisation rate of 0.2 mg Zn kg^-1 soil was required for achieving 90% of the maximum yield for plants grown from the high-Zn seed compared to 0.8 mg Zn kg^-1 soil for plants derived from the low Zn seed. The critical Zn level in youngest expanded leaves for 90% maximum yield was 16 mg Zn kg^-1 dry matter for both genotypes. Zn-efficient Excalibur had greater net Zn uptake rates compared to Zn-inefficient Gatcher after 3 weeks but they were not different at the 6-week harvest. Zinc-deficient plants had greater net uptake rates of Cu, Mn, B, P, and K but a reduced uptake rate of Fe. It is concluded that higher seed Zn content acted similar to a starter-fertiliser effect by improving vegetative growth and dissipating differences in Zn efficiency of wheat genotypes.     

Free and bound amino acids during germination of maize seeds with implemented foreign prolamines

Wheat prolamines were preincorporated into the endosperm of maize seed, and concentrations of free and bound amino acids were measured in the endosperm and seedlings during seed germination. Incorporation of foreign prolamines lowered the decrease rate of free proline concentration in both the endosperm (sprouting and shoots) and the embryo (sprouting). The seedlings at the stage of shoots were characterized by higher concentrations of aspartic acid, glutamic acid, and tyrosine. At the stage of transition to autotrophic nutrition, the pool of amino acids that are physiologically important for the plant growth was greater in maize seedlings with incorporated wheat prolamines.     

Abortive seed development in Ulmus minor (Ulmaceae)

Three genotypes of field elm ( Ulmus minor ) were studied to determine the structural basis of seed abortion in this species. In the non-abortive control, P-VV1, the pattern of seed development is similar to many flowering plants. The embryo progresses through defined morphological stages leading to developmental arrest as the seed matures. Storage products are abundant within embryo cells. Endosperm development is similar to the nuclear type; however, a more extensive cellularization of the endosperm occurs prior to it being crushed by the expanding embryo. For the abortive genotypes, M-SF1 and V-JR1, abnormalities in endosperm development are found. This is judged by the early cellularization and the massive synthesis of the PAS-positive material in the cellular endosperm. In these abortive genotypes, embryo development is delayed and storage products failed to accumulate within embryo cells. After seed desiccation, no living embryo tissue remains within the seed coat in the abortive genotypes.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 145 , 455–467.