黄瓜MTP基因家族分析及重金属胁迫下表达特征

该研究以模式物种(拟南芥、水稻、玉米)的MTP序列作为种子序列,对黄瓜MTP基因家族(CsMTP)成员进行了系统鉴定和分析;并以Zn~(2+)、Cd~(2+)、Mn~(2+)、Cu~(2+)、Fe~(2+)和Mo~(2+)处理后的黄瓜叶片和根系为材料,对CsMTP响应金属离子的表达模式进行了研究,为探究该基因家族对黄瓜重金属胁迫调控机制提供理论依据。结果表明:(1)黄瓜含有10个CsMTP,可进一步分为Fe/Zn-CDF(2个)、Mn-CDF(3个)和Zn-CDF(5个)三个亚家族,Mn-CDF成员含有保守基序DxxxD,Zn-CDF和Fe/Zn-CDFs成员含有保守基序HxxxD,大部分CsMTP成员含有6个跨膜结构域。(2)RNA-seq数据分析表明,CsMTP具备组织特异性表达和响应不同处理的特征,CsMTP11、CsMTP3和CsMTP7在不同组织和处理下普遍高水平表达,且外源化学试剂处理可诱导同一基因的不同表达模式。(3)RT-PCR分析表明,CsMTPs可被不同重金属离子诱导差异表达,包括不是MTP家族潜在底物的重金属。     

Abscisic acid alleviates iron deficiency by promoting root iron reutilization and transport from root to shoot in Arabidopsis

Abscisic acid (ABA) has been demonstrated to be involved in iron (Fe) homeostasis, but the underlying mechanism is largely unknown. Here, we found that Fe deficiency induced ABA accumulation rapidly (within 6 h) in the roots of Arabidopsis. Exogenous ABA at 0.5 μM decreased the amount of root apoplastic Fe bound to pectin and hemicellulose, and increased the shoot Fe content significantly, thus alleviating Fe deficiency‐induced chlorosis. Exogenous ABA promoted the secretion of phenolics to release apoplastic Fe and up‐regulated the expression of AtNRAMP3 to enhance reutilization of Fe stored in the vacuoles, leading to a higher level of soluble Fe and lower ferric–chelate reductase (FCR) activity in roots. Treatment with ABA also led to increased Fe concentrations in the xylem sap, partially because of the up‐regulation of AtFRD3, AtYSL2 and AtNAS1, genes related to long‐distance transport of Fe. Exogenous ABA could not alleviate the chlorosis of abi5 mutant resulting from the significantly low expression of AtYSL2 and low transport of Fe from root to shoot. Taken together, our data support the conclusion that ABA is involved in the reutilization and transport of Fe from root to shoot under Fe deficiency conditions in Arabidopsis.     

Iron deficiency stress can induce MxNAS1 protein expression to facilitate iron redistribution in Malus xiaojinensis

• Iron (Fe) is a vital trace element in plants, and deficiency of this element in apple trees can reduce fruit quality. Nicotianamine (NA) is known to play an important role in Fe transport and endogenous hormone balance. In the present study, we investigated the role of a nicotianamine synthase 1 gene (MxNas1) in an apple species, Malus xiaojinensis, that has a more Fe‐efficient genotype than other apple species and ecotypes.
• To characterise the response of M. xiaojinensis to Fe deficiency, we used quantitative Q‐PCR to determine the level of expression of MxNas1 and Western blot to measure protein levels. Immunohistochemical staining and GFP fluorescence localisation of the MxNAS1 protein were also carried out. HPLC and polarised absorption spectrophotometry were performed to investigate the effects of overexpression of MxNas1 in order to elucidate the role of MxNAS1 in the cellular uptake of active Fe in tobacco suspension cells.
• We found that MxNas1 expression and protein levels were higher under Fe deficiency stress than under Fe sufficiency. Immunohistochemical staining showed that MxNAS1 was localised mainly in the epidermal and vascular tissues of the roots, vascular tissues of the stem and palisade cells of mature leaves, and in parenchyma cells of young leaves. MxNAS1 was mainly localised in the plasma membranes and vesicles of protoplasts. In addition, overexpression of MxNas1 in stable transgenic tobacco cells increased NA and active Fe content under Fe sufficiency.
• The results suggest that MxNas1 expression in M. xiaojinensis is induced in response to Fe deficiency stress, resulting in higher levels of the protein. MxNAS1 may be involved in the redistribution of Fe in M. xiaojinensis under Fe deficiency.

     

Influence of iron and pH on the yield and iron,manganese, zinc,and sulfur concentrations of carrots grown on sphagnum peat soil

Summary In two greenhouse experiments, sphagnum peat, adjusted to various pH levels, was used to study the effect of various levels of Fe on the growth of carrots (Daucus carota L., var. sativa D.C.). The Fe was added to the medium as sequesterine 330 chelate. Maximum carrot root and top tissue yields were obtained at soil pH 6.6 and 7.1. At soil pH 5.2 and 7.8 the yields were in the intermediate range. The yields were low at pH 4.3, 4.5 and 8.1 and at pH 8.4 the carrots did not grow. The chlorotic symptoms on carrot leaves, accom-panied by reduced yields, were associated with 39 to 82 ppm Fe and > 332 ppm Mn in the leaf and were likely due to Mn toxicity. Toxic levels of Mn in tissue were found even at soil pH 8.1 and were associated with reduced carrot yields. The leaf tissue concentrations of Fe and Mn decreased as the pH of soil increased; however, at pH 5.2, 7.8, and 8.1 the tissue Mn concentration increased. The added Fe had no effect on the Fe concentration but decreased the Mn and Zn concentration of leaf tissue and increased carrot root yields. There was a significant interaction between added lime and Fe, whereby the decrease in leaf tissue Mn concentration and increases in root yields with added Fe were much greater at pH 4.5 and 5.2 than at pH values of 6.6 and 7.8. The S concentration in the leaf tissue decreased with added Fe and lime. The leaf tissue Zn concentrations of 184 to 490 ppm and S concentrations of 0.32 to 0.63%, as found here, are considered to be high but not in the toxic range.Contribution No. 321, Research Station, Charlottetown, P.E.I. and No. 1534, Research Station, Kentville, N.S.Contribution No. 321, Research Station, Charlottetown, P.E.I. and No. 1534, Research Station, Kentville, N.S.     

Isolation and functional analysis of MdNAS1, with functions in improved iron stress tolerance and abnormal flower in transgenic tobacco

Metal elements are essential micronutrients required by all plants for natural physiological activities. Nicotianamine is considered as the chelate substance in the transport of metal ions. In the present study, a new gene encoding NA synthase was isolated from Malus domestica (L.) Borkh and designated as MdNAS1. The expression levels of MdNAS1 were enriched in leaf, and phloem which were highly affected by Fe stress, indoleacetic acid (IAA) and abscisic acid (ABA) treatments in M. domestica seedlings. Subcellular localization research revealed that MdNAS1 was localized in cytoplasmic membrane. Overexpression of MdNAS1 in transgenic tobaccos increased the tolerance to Fe stress, but also contributes to higher chlorophyll, NA, Fe, Mn, Cu and Zn contents and abnormal flowers. Moreover, the MdNAS1-OE tobaccos had the increased expression levels of Fe uptake and transport related genes (NtFRO, NtIRT1, NtVIT, NtNRAMP1, and NtYSL).     

Successful Reproduction Requires the Function of Arabidopsis YELLOW STRIPE-LIKE1 and YELLOW STRIPE-LIKE3 Metal-Nicotianamine Transporters in Both Vegetative and Reproductive Structures

Several members of the Yellow Stripe-Like (YSL) family of proteins are transporters of metals that are bound to the metal chelator nicotianamine or the related set of mugineic acid family chelators known as phytosiderophores. Here, we examine the physiological functions of three closely related Arabidopsis (Arabidopsis thaliana) YSL family members, AtYSL1, AtYSL2, and AtYSL3, to elucidate their role(s) in the allocation of metals into various organs of Arabidopsis. We show that AtYSL3 and AtYSL1 are localized to the plasma membrane and function as iron transporters in yeast functional complementation assays. By using inflorescence grafting, we show that AtYSL1 and AtYSL3 have dual roles in reproduction: their activity in the leaves is required for normal fertility and normal seed development, while activity in the inflorescences themselves is required for proper loading of metals into the seeds. We further demonstrate that the AtYSL1 and AtYSL2 proteins, when expressed from the AtYSL3 promoter, can only partially rescue the phenotypes of a ysl1ysl3 double mutant, suggesting that although these three YSL transporters are closely related and have similar patterns of expression, they have distinct activities in planta. In particular, neither AtYSL1 nor AtYSL2 is able to functionally complement the reproductive defects exhibited by ysl1ysl3 double mutant plants.The transition metals iron (Fe), copper (Cu), and zinc (Zn) are among the most important and most problematic of all the micronutrients used by plants. The importance of these metals stems from their roles as essential cofactors for cellular redox reactions involved in photosynthesis, respiration, and many other reactions. The problematic nature of these metals stems from the same distinct chemical properties that make them so valuable to living systems. These metals, particularly Cu and Fe, are highly reactive and, if overaccumulated, can cause cellular redox damage. Fe presents an additional problem for plants, because it is also only sparingly soluble in aqueous solution and thus is typically not “bioavailable” in soil (Guerinot and Yi, 1994). As a response to these key properties, plants have evolved multifaceted systems to control metal uptake by the root, translocation through the plant body, storage within tissues, and remobilization during reproduction and times of nutrient stress.The nonproteinogenic amino acid nicotianamine (NA) is a strong complexor of various transition metals, particularly Fe(II) (Anderegg and Ripperger, 1989) and Fe(III) (von Wiren et al., 1999), as well as Cu(II), Ni(II), Co(II), Mn(II), and Zn(II) (Anderegg and Ripperger, 1989). NA is present in shoots and roots at concentrations ranging between 20 and 500 nm g⁻¹ fresh weight (Stephan et al., 1990) and is present in both xylem (approximately 20 μm [Pich and Scholz, 1996]) and phloem (approximately 130 μm [Schmidke and Stephan, 1995]), suggesting that it is a major complexor of metals throughout the plant. Much of what we know about NA function in plants comes from studies of a mutant of tomato (Solanum lycopersicum) called chloronerva, in which the single gene encoding NA synthase is disrupted (Herbik et al., 1999; Higuchi et al., 1999; Ling et al., 1999). The chloronerva phenotype is complex. Plants exhibit interveinal chlorosis in young leaves and constitutively activate their root Fe uptake systems, indicating that they have inadequate Fe. However, mature leaves of chloronerva mutants contain excess Fe, implying that the Fe that is present is not being properly localized in the absence of NA. These chloronerva plants also have severe defects in translocation of Cu in the xylem, indicating a clear role for NA in Cu transport. The plants are sterile, indicating that NA is important during plant reproduction. Complementing these classical studies on chloronerva, Takahashi et al. (2003) have developed tobacco (Nicotiana tabacum) plants that heterologously express a barley (Hordeum vulgare) gene encoding the enzyme NA aminotransferase, which converts NA into a nonfunctional intermediate. Recently, the phenotype of quadruple NA synthase mutants was described in Arabidopsis (Arabidopsis thaliana; Klatte et al., 2009). In both studies, the plants exhibited many of the defects caused by the chloronerva mutation, including chlorosis and an array of reproductive abnormalities.Several members of the well-conserved Yellow Stripe-Like (YSL) family of proteins function as metal-NA transporters (DiDonato et al., 2004; Koike et al., 2004; Roberts et al., 2004; Schaaf et al., 2004; Murata et al., 2006; Gendre et al., 2007). The founding member of the YSL family, maize (Zea mays) Yellow Stripe1 (ZmYS1), is the primary means by which roots of grasses take up Fe from the soil. The grasses, a group that includes most of the world’s staple grains (e.g. rice [Oryza sativa], wheat [Triticum aestivum], and maize), use a chelation strategy for primary Fe uptake. In response to Fe starvation, grasses secrete phytosiderophores (PS): derivatives of the mugineic acid family that are structurally similar to NA and that form stable Fe(III) chelates in soil (Tagaki et al., 1984). This accomplishes solubilization of the otherwise nearly insoluble soil Fe. The YS1 protein, located at the root surface, then moves the Fe(III)-PS complexes from the rhizosphere into root cells (Romheld and Marchner, 1986; Curie et al., 2001; Roberts et al., 2004)Arabidopsis has eight YSL genes. Three of these (AtYSL1, At4g24120; AtYSL2, At5g24380; and AtYSL3, At5g53550) are expressed strongly in the xylem parenchyma of leaves and are down-regulated during Fe deficiency (DiDonato et al., 2004; Waters et al., 2006). We have previously shown that double mutant plants with lesions in both AtYSL1 and AtYSL3 display strong interveinal chlorosis. We have hypothesized that the function of these YSL transporters in vegetative tissues is to take up Fe that arrives in leaves via the xylem (Waters et al., 2006). All of the defects displayed by ysl1ysl3 double mutants can be alleviated if excess Fe is applied to the soil, demonstrating that these growth defects are caused primarily by a lack of Fe. Intriguingly, although Fe deficiency appears to be the basis of the double mutant phenotype, the concentrations of several metals are specifically altered in the double mutants (Waters et al., 2006). AtYSL1 single mutant plants have subtle phenotypes, the most striking of which is a decrease in both NA and Fe in seeds (Le Jean et al., 2005). Interestingly, leaves of these mutants contain excess NA, while Fe levels are normal. These observations are consistent with the more obvious and extensive phenotypes exhibited by the ysl1ysl3 double mutant and highlight the idea that AtYSL proteins affect the homeostasis of both Fe and NA.In addition to the vegetative defects mentioned above, the ysl1ysl3 double mutant has multiple defects in reproduction. Double mutant flowers produce few functional pollen grains and thus exhibit greatly reduced fertility. Many of the seeds that these plants do manage to produce are small and contain embryos arrested at various immature stages, which often fail to germinate. These fertility defects can be reversed by application of Fe-ethylenediamine-N,N′-bis(2-hydroxyphenylacetic acid) solution to the soil, again demonstrating that these growth defects are caused by a lack of Fe (Waters et al., 2006). Expression of YSL1 and YSL3 is very limited in flowers and developing siliques; furthermore, the patterns of expression of YSL1 and YSL3 are distinct and largely nonoverlapping in these structures. However, expression of AtYSL1 and AtYSL3 increases markedly during leaf senescence, a period in which many minerals are remobilized from leaves, presumably for delivery into developing seeds (Himelblau and Amasino, 2001). This model is in good agreement with the accepted model for nutrient loading into seeds proposed originally by Hocking and Pate (1977, 1978), which suggests that metals mobilized from vegetative structures account for 20% to 30% of the content in seeds. Direct measurements of metals in senescing and younger leaves demonstrated that double mutants failed to mobilize Zn and Cu from leaves. Seeds produced by the double mutant plants contained reduced levels of Zn and Cu, the same metals that failed to be mobilized out of the leaves (Waters et al., 2006). This led us to propose a model in which the activity of AtYSL1 and AtYSL3 in leaves was required for correct localization of metals into the seeds. However, seeds also had low Fe levels, even though Fe appeared to be mobilized normally from leaves of the double mutants.Here, we further investigate the role(s) of AtYSL1 and AtYSL3 in the allocation of metals into various organs of Arabidopsis. AtYSL1 and AtYSL3 are localized to the plasma membrane, and each is capable of suppressing the growth defect of yeast lacking normal Fe uptake, indicating that the most likely biochemical function for these proteins is in uptake of Fe(II)-NA complexes. We have used inflorescence grafting to determine the relative roles of AtYSL1 and AtYSL3 in leaves and inflorescences during seed development. These proteins are found to have dual roles: activity in the leaves is required for normal inflorescence development, while activity in the inflorescences themselves is required for proper loading of metals into the seeds. We have further examined the effect of overexpressing AtYSL3, which resulted in a small increase in Cu in shoots, and have demonstrated that the AtYSL1 protein, when expressed from the AtYSL3 promoter, can only partially rescue the phenotypes of the ysl1ysl3 double mutant, indicating that these proteins have distinct biochemical activities. A third AtYSL from the same subgroup of the YSL family, AtYSL2, also only partially complements the phenotypes of ysl1ysl3 double mutants, suggesting that although these three YSL transporters are closely related, they have distinct activities in planta.     

The expression of heterologous Fe (III) phytosiderophore transporter HvYS1 in rice increases Fe uptake,translocation and seed loading and excludes heavy metals by selective Fe transport

Many metal transporters in plants are promiscuous, accommodating multiple divalent cations including some which are toxic to humans. Previous attempts to increase the iron (Fe) and zinc (Zn) content of rice endosperm by overexpressing different metal transporters have therefore led unintentionally to the accumulation of copper (Cu), manganese (Mn) and cadmium (Cd). Unlike other metal transporters, barley Yellow Stripe 1 (HvYS1) is specific for Fe. We investigated the mechanistic basis of this preference by constitutively expressing HvYS1 in rice under the control of the maize ubiquitin1 promoter and comparing the mobilization and loading of different metals. Plants expressing HvYS1 showed modest increases in Fe uptake, root‐to‐shoot translocation, seed accumulation and endosperm loading, but without any change in the uptake and root‐to‐shoot translocation of Zn, Mn or Cu, confirming the selective transport of Fe. The concentrations of Zn and Mn in the endosperm did not differ significantly between the wild‐type and HvYS1 lines, but the transgenic endosperm contained significantly lower concentrations of Cu. Furthermore, the transgenic lines showed a significantly reduced Cd uptake, root‐to‐shoot translocation and accumulation in the seeds. The underlying mechanism of metal uptake and translocation reflects the down‐regulation of promiscuous endogenous metal transporters revealing an internal feedback mechanism that limits seed loading with Fe. This promotes the preferential mobilization and loading of Fe, therefore displacing Cu and Cd in the seed.     

The isochorismate pathway is negatively regulated by salicylic acid signaling in O<Subscript>3</Subscript>-exposed <Emphasis Type="Italic">Arabidopsis</Emphasis>

Phytochelatins (PCs) are heavy metal binding peptides that play an important role in sequestration and detoxification of heavy metals in plants. In this study, our goal was to develop transgenic plants with increased tolerance for and accumulation of heavy metals from soil by expressing an Arabidopsis thaliana AtPCS1 gene, encoding phytochelatin synthase (PCS), in Indian mustard (Brassica juncea L.). A 35S promoter fused to a FLAG–tagged AtPCS1 cDNA was expressed in Indian mustard, and transgenic lines, designated pc lines, were evaluated for tolerance to and accumulation of Cd and Zn. Transgenic plants with moderate AtPCS1 expression levels showed significantly higher tolerance to Cd and Zn stress, but accumulated significantly less Cd and Zn than wild type plants in both shoot and root tissues. However, transgenic plants with highest expression of the transgene did not exhibit enhanced Cd and Zn tolerance. Shoots of Cd-treated pc plants had significantly higher levels of phytochelatins and thiols than wild-type plants. Significantly lower concentrations of gluthatione in Cd-treated shoot and root tissues of transgenic plants were observed. Moderate expression levels of phytochelatin synthase improved the ability of Indian mustard to tolerate certain levels of heavy metals, but at the same time did not increase the accumulation potential for Cd and Zn.     

Overexpression of a <Emphasis Type="Italic">Panax ginseng</Emphasis> tonoplast aquaporin alters salt tolerance,drought tolerance and cold acclimation ability in transgenic <Emphasis Type="Italic">Arabidopsis</Emphasis> plants

Water movement across cellular membranes is regulated largely by a family of water channel proteins called aquaporins (AQPs). Since several abiotic stresses such as, drought, salinity and freezing, manifest themselves via altering water status of plant cells and are linked by the fact that they all result in cellular dehydration, we overexpressed an AQP (tonoplast intrinsic protein) from Panax ginseng, PgTIP1, in transgenic Arabidopsis thaliana plants to test its role in plant’s response to drought, salinity and cold acclimation (induced freezing tolerance). Under favorable conditions, PgTIP1 overexpression significantly increased plant growth as determined by the biomass production, and leaf and root morphology. PgTIP1 overexpression had beneficial effect on salt-stress tolerance as indicated by superior growth status and seed germination of transgenic plants under salt stress; shoots of salt-stressed transgenic plants also accumulated greater amounts of Na⁺ compared to wild-type plants. Whereas PgTIP1 overexpression diminished the water-deficit tolerance of plants grown in shallow (10 cm deep) pots, the transgenic plants were significantly more tolerant to water stress when grown in 45 cm deep pots. The rationale for this contrasting response, apparently, comes from the differences in the root morphology and leaf water channel activity (speed of dehydration/rehydration) between the transgenic and wild-type plants. Plants overexpressed with PgTIP1 exhibited lower (relative to wild-type control) cold acclimation ability; however, this response was independent of cold-regulated gene expression. Our results demonstrate a significant function of PgTIP1 in growth and development of plant cells, and suggest that the water movement across tonoplast (via AQP) represents a rate-limiting factor for plant vigor under favorable growth conditions and also significantly affect responses of plant to drought, salt and cold stresses.     

Copper Uptake and Its Effect on Metal Distribution in Root Growth Zones of Commelina communis Revealed by SRXRF

To explore the copper uptake mechanisms by the Cu-tolerant plant Commelina communis, the contents of Cu and other metals (including Fe, Zn, and Mn) in roots were detected using atomic absorption spectrometer under transporter inhibitors, partial element deficiency, or Cu excess treatments, while distribution characters of Cu and other metals in root growth zones were investigated by synchrotron radiation X-ray fluorescence spectroscopy (SRXRF). Cu uptake was inhibited by the uncoupler DNP and P-type ATPase inhibitor Na₃VO₄, not by the Ca²⁺ ion channel inhibitor LaCl₃, suggesting that Cu could probably be assimilated actively by root and be related with P-type ATPase, but not through Ca²⁺ ion channel. Fe or Zn deficiency could enhance Cu uptake, while 100 μM Cu inhibited Fe, Zn, and Mn accumulation in roots significantly. Metal distribution under 100 μM Cu treatment was investigated by SRXRF. High level of Cu was found in the root meristem, and higher Cu concentrations were observed in the vascular cylinder than those in the endodermis, further demonstrating the initiative Cu transport in the root of C. communis. Under excess Cu stress, most Fe was located in the epidermis, and Fe concentrations in the endodermis were higher than those in the vascular cylinder, suggesting Cu and Fe competition not only in the epidermal cells but also for the intercellular and intracellular transport in roots. Zn was present in the meristem and the vascular cylinder similar to Cu. Cu and Zn showed a similar pattern. Mn behaves as Zn does, but not like Fe.     

过表达或沉默棉花GhPCBER基因株系的获得及其茎叶木质素和木脂素含量研究

编码苯基香豆满苄基醚还原酶(phenylcoumaran benzylic ether reductase,PCBER)的基因PCBER属于PIP亚家族,是苯丙烷代谢途径中参与木脂素合成的关键基因。该研究构建了棉花GhPCBER基因的植物过表达载体并转化拟南芥,同时构建了VIGS(virus induced gene silencing,病毒诱导的基因沉默)载体转化棉花,采用实时荧光定量PCR技术对GhPCBER基因在不同组织中的表达进行分析;对野生型和转基因植株茎叶组织中的木质素和木脂素含量进行测定分析。结果表明:(1)成功构建了GhPCBER植物过表达载体pGWB17-GhPCBRE以及基因沉默重组载体pTRV2-GhPCBER;经遗传转化获得6株转棉花GhPCBER基因抗性拟南芥植株,同时获得15株GhPCBER基因沉默棉花植株(5株为一组)。(2)PCR检测表明,6株转基因拟南芥均为过表达株系,其中株系1、2、3相对表达量更高,且在茎、叶组织中的表达量分别较野生型提高了7～14倍和6～16倍,表明GhPCBER基因成功在拟南芥中过表达;GhPCBER基因沉默棉花植株的茎、叶组织中的表达量分别比野生型棉株约下降12%和26%,表明烟草脆裂病毒(TRV)体系(pTRV2-GhPCBER)成功抑制了GhPCBER基因的表达。(3)转GhPCBER基因拟南芥茎、叶中木质素和木脂素含量较野生型均显著降低;GhPCBER基因沉默棉花植株茎、叶中木质素和木脂素含量较野生型均极显著降低;组织化学染色观察发现GhPCBER基因沉默棉花植株茎秆颜色明显比野生型染色浅,也证明沉默基因棉花植株茎秆中的木质素含量减少。(4)苯丙烷代谢通路中8个相关基因的实时荧光定量PCR分析发现,过表达或抑制GhPCBRE基因均会导致苯丙烷代谢途径发生重新定向。     

Heterologous Expression of the Wheat Aquaporin Gene TaTIP2;2 Compromises the Abiotic Stress Tolerance of Arabidopsis thaliana

Aquaporins are channel proteins which transport water across cell membranes. We show that the bread wheat aquaporin gene TaTIP2;2 maps to the long arm of chromosome 7b and that its product localizes to the endomembrane system. The gene is expressed constitutively in both the root and the leaf, and is down-regulated by salinity and drought stress. Salinity stress induced an increased level of C-methylation within the CNG trinucleotides in the TaTIP2;2 promoter region. The heterologous expression of TaTIP2;2 in Arabidopsis thaliana compromised its drought and salinity tolerance, suggesting that TaTIP2;2 may be a negative regulator of abiotic stress. The proline content of transgenic A. thaliana plants fell, consistent with the down-regulation of P5CS1, while the expression of SOS1, SOS2, SOS3, CBF3 and DREB2A, which are all stress tolerance-related genes acting in an ABA-independent fashion, was also down-regulated. The supply of exogenous ABA had little effect either on TaTIP2;2 expression in wheat or on the phenotype of transgenic A. thaliana. The expression level of the ABA signalling genes ABI1, ABI2 and ABF3 remained unaltered in the transgenic A. thaliana plants. Thus TaTIP2;2 probably regulates the response to stress via an ABA-independent pathway(s).     

Effects of pH and bicarbonate on the nutrient status and growth of three Lupinus species

Aims

High pH, and high bicarbonate (HCO₃⁻) and calcium (Ca) availability characterise calcareous soils. High [Ca] only partially explains why some Lupinus species are calcifuge, so we explored high [HCO₃⁻] and high pH.

Methods

We grew six Lupinus genotypes in hydroponics with pH 5, 6.5 and 8^a (adjusted by KOH), and 8^b (adjusted by KHCO₃). Leaf symptoms and areas, root appearance and biomass were recorded; whole leaf and root nutrient concentrations, and leaf cellular phosphorus (P), Ca and potassium (K) concentrations were determined using elemental X-ray microanalysis.

Results

Chlorosis was observed in young leaves at high pH for L. angustifolius and L. cosentinii, and P deficiency at high pH for all genotypes. High pH decreased iron (Fe) and zinc (Zn) uptake in all genotypes. It also decreased lateral root growth, the uptake of P, K, Ca, and manganese (Mn) by all sensitive species; and translocation of P, Fe, Zn, Mn, and Ca to leaves in most sensitive species. However, leaf [Ca], leaf [K], [K] within each measured cell type, and translocation of K and Ca to leaves of L. pilosus and L. cosentinii at pH 8 were greater than at pH 5 and 6.5. Compared with pH 8^a, all L. angustifolius genotypes translocated more P, Fe, Zn, Mn and K from roots to leaves at pH 8^b. High pH did not affect the leaf cell types that accumulated P and Ca, but decreased the leaf cellular [P].

Conclusions

Lupinus angustifolius and L. cosentinii were sensitive to high [HCO₃⁻] and/or high pH; L. pilosus was relatively tolerant. High pH decreased lateral root growth and nutrient uptake, inhibiting growth of sensitive species. High [HCO₃⁻] diminished the negative effect of pH 8 on nutrient translocation to leaves in most L. angustifolius genotypes. This knowledge provides critical insights into the habits of Lupinus species to guide breeding of calcicole plants.

     

Functional analyses of TaHMA2, a P1B‐type ATPase in wheat

Currently, there are few studies concerning the function of heavy metal ATPase 2 (HMA2), particularly in monocotyledons, and the potential application of this protein in biofortification and phytoremediation. Thus, we isolated and characterized the TaHMA2 gene from wheat (Triticum aestivum L.). Our results indicate that TaHMA2 is localized to the plasma membrane and stably expressed, except in the nodes, which showed relatively high expression. Zinc/cadmium (Zn/Cd) resistance was observed in TaHMA2‐transformed yeast. The over‐expression of TaHMA2 increased the elongation and decreased the seed‐setting rate in rice (Oryza sativa L.), but not Arabidopsis thaliana, tobacco (Nicotiana tabacum L.) or wheat. TaHMA2 over‐expression also improved root‐shoot Zn/Cd translocation, especially in rice. The seeds of transgenic rice and wheat, not tobacco, showed decreased Zn concentrations. The Zn concentration was decreased in all parts of the transgenic rice seeds, but was decreased only in the ventral endosperm of wheat, which showed an increased Zn concentration in the embryo and aleurone. The over‐expression of TaHMA2 improved plant tolerance under moderate Zn stress and Zn deficiency, but Zn and Cd resistance decreased under high levels of Zn and Cd stress, respectively. The Cd concentration in transgenic rice seedlings was dramatically increased under Zn deficiency. Thus, over‐expression of TaHMA2 showed a more obvious phenotype in monocotyledons than in dicotyledons. These findings provide important information for TaHMA2, and more efforts should be made in the future to characterize the reduced Zn concentration in TaHMA2 transgenic grains and the diversity of TaHMA2 substrate specificity.     

不同土壤和微量元素对车桑子幼苗生长的影响

为了解微量元素对车桑子(Dodonaea viscosa)生长的作用,研究添加微量元素(硼B、铁Fe、锰Mn、锌Zn)对车桑子生长和叶绿素荧光特性的影响。结果表明,除Mn外,B、Zn和Fe均对车桑子的生长和叶绿素荧光参数有显著促进作用(P<0.05);且添加B的车桑子具有更高的生物量积累,比对照显著提高了133.61%。微量元素与土壤类型对叶片磷(P)含量和叶片氮磷比(N/P)具有显著的交互作用(P<0.05),紫色土添加Zn、黄棕壤添加Fe均显著降低了叶片N/P。燥红土和黄棕壤上车桑子的株高、叶面积和生物量积累均高于紫色土,但紫色土和黄棕壤上车桑子的根冠比和叶片N/P显著高于燥红土(P<0.001)。这表明微量元素对干热河谷车桑子生长具有重要作用,在植被恢复过程中可通过添加B、Fe、Zn尤其是B来促进植物生长。