Apparent responses of stomata to transpiration and humidity in a hybrid poplar canopy

It has been proposed that the stomatal response to humidity relies on sensing of the transpiration rate itself rather than relative humidity or the saturation deficit per se. We used independent measurements of stomatal conductance (g_s), transpiration (E), and leaf-to-air vapour pressure difference (V) in a hybrid poplar canopy to evaluate relationships between g_s and E and between g_s and V. Relationships between E, V and total vapour phase conductance or crown conductance (g_c) were also assessed. Conductance measurements were made on exposed and partially shaded branches over a wide range of incident solar radiation. In exposed branches, g_s appeared to decline linearly with increasing E and increasing V at both high and low irradiance. However, in a partially shaded branch, a bimodal relationship between g_s and E was observed in which g_s continued to decrease after E had reached a maximum value and begun to decrease. The relationship between g_s and V for this branch was linear. Plots of g_c against E always yielded bimodal or somewhat variable relationships, whereas plots of g_c against V were invariably linear. It was not possible to derive a unique relationship between conductance and E or V because prevailing radiation partially determined the operating range for conductance. Normalization of data by radiation served to linearize responses observed within the same day or type of day, but even after normalization, data collected on partly cloudy days could not be used to predict stomatal behaviour on clear days and vice versa. An additional unidentified factor was thus also involved in determining operating ranges of conductance on days with different overall radiation regimes. We suggest that the simplest mechanism to account for the observed humidity responses is stomatal sensing of the epidermal or cuticular transpiration rate rather than the bulk leaf or stomatal transpiration rate.     

Stomatal response of hybrid poplar to incident light, sudden darkening and leaf excision

Responses of abaxial and adaxial stomata of Populus trichocarpa Torr. & Gray. × P. deltoides Bartr. (ex Marsh.) cv. Unal to incident light, sudden darkening and leaf excision in the light and in the dark were studied on 5-year-old trees in the field using diffusion porometry. Stomatal closure in the dark was found to be incomplete in most cases studies. Stomata closed after leaf excision in the dark within 90 min. Stomatal closure after darkening of an entire tree or an entire branch (white the rest of the tree was in the light) was slower, and complete stomatal closure was noticed only for adaxial stomata after 3 h. Adaxial stomata were more reactive and sensitive than abaxial stomata to sudden darkening and leaf excision in the light and the dark. In all treatments, stomatal response was more responsive in mature leaves than in young, still expanding leaves.     

Unique occurrence of pectin-like fibrillar cell wall deposits in xylem fibres of poplar

Using light and electron microscopic techniques, we studied the unique occurrence of fibrillar cell wall deposits in mature xylem fibres from poplar. These cell wall deposits lined the lumen-facing side of the wall, mainly in fibres next to vessel elements. Different lines of evidence point to the pectin-like nature of these fibrillar cell wall deposits. First, specific staining by Alcian Blue 8GX, a dye with high affinity for pectic substances. Second, the strongly reduced staining of the cell wall deposits in microscopic sections treated with pectolytic enzyme. Third, concomitant staining of pits, which are known to consist mainly of pectic substances. Given the pectin-like nature of the fibrillar cell wall deposits as well as their preferred occurrence in fibres neighbouring water-conducting vessel elements, a function for the fibrillar cell wall deposits in lateral water diffusion and stem water storage is hypothesised. The hypothesis is supported by the increased abundance of these cell wall deposits in wood tissue of a drought-sensitive poplar species.     

杨树杂种无性系生长与光合生理遗传变异研究

以美洲黑杨与大青杨的27个杂种无性系1年生盆栽扦插苗为材料,以美洲黑杨无性系I-69为对照,对其生长性状、扦插成活率以及主要光合生理指标进行遗传变异分析,并利用分析结果对杂种无性系进行初步选择.结果表明:(1)27个杂种无性系间苗期生长性状及光合生理等12个性状指标差异极显著,无性系重复力均在0.7以上,最高达0.987,均受强遗传控制.(2)结合生长性状分析不同无性系的净光合速率,发现具有较高净光合速率的无性系,同样具有较大生长量和较高成活率.(3)经主成分分析和聚类分析,初选出7个生长快、成活率较高、光合作用能力较强的无性系(编号依次为135、141、153、155、165、177和193),7个无性系苗高超对照10%~33%,地径超对照11%~24%,成活率超对照30%~48%,净光合速率超对照7%~29%,且干形优美,适应性强,可作为进一步选育的材料.     

Cloning of metallothionein genes from <Emphasis Type="Italic">Arachis hypogaea</Emphasis> and characterization of <Emphasis Type="Italic">AhMT2a</Emphasis>

Seven cDNA sequences putatively encoding metallothionein (MT) proteins were isolated from peanut (Arachis hypogaea L.). We analyzed the sequences of the deduced amino acids and characterized one of these genes, AhMT2a. Northern blot analysis indicates that the accumulation of AhMT2a mRNA was found in stems, young roots, and young leaves, and AhMT2a mRNA levels were up-regulated by cadmium, copper, ABA, H₂O₂, and heat shock. The metal-binding properties of the recombinant protein expressed in E. coli was investigated, and the results show that bacteria harboring AhMT2a exhibited increased tolerance to cadmium, copper, and lead, and the metal accumulation was also higher than the controls. Taken together, our results suggest that the AhMT2a protein might function in both detoxification of heavy metals and scavenging of reactive oxygen species in peanut. Published in Russian in Fiziologiya Rastenii, 2007, Vol. 54, No. 5, pp. 755–762. The text was submitted by the authors in English.     

Distinct responses to ozone of abaxial and adaxial stomata in three Euramerican poplar genotypes

Ozone induces stomatal sluggishness, which impacts photosynthesis and transpiration. Stomatal responses to variation of environmental parameters are slowed and reduced by ozone and may be linked to difference of ozone sensitivity. Here we determine the ozone effects on stomatal conductance of each leaf surface. Potential causes of this sluggish movement, such as ultrastructural or ionic fluxes modification, were studied independently on both leaf surfaces of three Euramerican poplar genotypes differing in ozone sensitivity and in stomatal behaviour. The element contents in guard cells were linked to the gene expression of ion channels and transporters involved in stomatal movements, directly in microdissected stomata. In response to ozone, we found a decrease in the stomatal conductance of the leaf adaxial surface correlated with high calcium content in guard cells compared with a slight decrease on the abaxial surface. No ultrastructural modifications of stomata were shown except an increase in the number of mitochondria. The expression of vacuolar H⁺/Ca²⁺‐antiports (CAX1 and CAX3 homologs), β‐carbonic anhydrases (βCA1 and βCA4) and proton H⁺‐ATPase (AHA11) genes was strongly decreased under ozone treatment. The sensitive genotype characterized by constitutive slow stomatal response was also characterized by constitutive low expression of genes encoding vacuolar H⁺/Ca²⁺‐antiports.     

Effects of low level O3 exposure on leaf diffusive conductance and water-use efficiency in hybrid poplar

Abstract Young, amphistomatous hybrid poplar (Populus deltoides x trichocarpa) plants were exposed daily to either background (0.025 cm³ m^-3) or elevated (0.125 cm³ m^-3) concentrations of O₃. Levels of abaxial and adaxial leaf conductance were affected interactively by pollutant treatment, leaf age, and photon fluence rate. Consequently, conductance in O₃-treated leaves was sometimes higher and sometimes lower than in comparable control leaves, depending on leaf age or level of photon fluence rate. For example, at low photon fluence rate or in the dark, conductance was greater in O₃-treated than in control plants, while at high photon fluence rate that relationship was reversed. Exposure to O₃ also reduced the water-use efficiency and range of leaf conductance of individual leaves, and altered the relationship between the conductances of the two leaf surfaces (the ratio of abaxial to adaxial leaf conductance was increased). Furthermore, O₃ treatment resulted in diminished stomatal control of water loss; excised O₃-treated leaves had higher conductances and wilted sooner than excised control leaves of identical ages. Overall, the data indicate that exposure to O₃ resulted in impaired stomatal function.     

Molecular characterization and expression of metallothionein from freshwater pearl mussel,Hyriopsis schlegelii

Two metallothionein genes (HsMT1 and HsMT2) were first identified and described from Hyriopsis schlegelii. The open reading frame of HsMT1 and HsMT2 were 216 and 222 bp, encoding a protein of 71 and 73 amino acid residues. The deduced amino acid sequences showed they contained parts of typical MT characteristics, apart from HsMT2 lacked Cys–Cys motifs. The phylogenetic tree showed HsMT1 shared a high similarity with that of other molluscs, but HsMT2 was split into a distinct group separated from known molluscan MTs. HsMT1 exhibited constitutive expression in all examined tissues and the highest expression occurred in hepatopancreas, however, nearly all HsMT2 was just detected in gonad. After Cd exposure, their mRNA levels presented similar expression patterns. The transgenic bacteria of HsMT1 showed higher tolerance than HsMT2 in Cd environment. It was implied that HsMT1 and HsMT2 were involved in metal response but HsMT2 might have other physiological functions.     

Responses of poplar to chilling temperatures: proteomic and physiological aspects

Abstract: The effects of cold acclimation on primary metabolism in actively growing poplar ( Populus tremula L. × P. tremuloides Michaux) were studied. Three-month-old poplar plants were exposed to chilling stress (4 °C) and compared to plant material kept at a control temperature (23 °C). This treatment did not affect the survival of the plants but growth was almost stopped. The freezing tolerance of the adult leaves increased from - 5.7 °C for the control plants to - 9.8 °C after 14 days of exposure to 4 °C. During acclimation, the evolution of soluble carbohydrate contents was followed in the leaves. Sucrose, glucose, fructose and trehalose accumulated rapidly under chilling conditions, while raffinose content increased after one week at 4 °C. Proteomic analyses, by bidimensional electrophoresis, performed during this stage revealed that a large number of proteins had higher expression, while much less proteins disappeared or had a lower abundance. MALDI-TOF-MS analyses enabled ca. 30 spots to be proposed for candidate proteins. Among the accumulating or appearing proteins proposed, about a third presented similarities with chaperone-like proteins (heat shock proteins, chaperonins). In addition, dehydrins and other late embryogenesis abundant proteins, i.e., stress-responsive proteins, detoxifying enzymes, proteins involved in stress signalling and transduction pathways were also activated or newly synthesised. Finally, cold exposure induced a decrease in the candidate proteins involved in cell wall or energy production.     

Cloning and identification of methionine synthase gene from Pichia pastoris

Methionine synthase (MS) is grouped into two classes. Class One MS (MetH) and Class Two MS (MetE) share no homology and differ in their catalytic model. Based on the conserved sequences of metE genes from different organisms, a segment of the metE gene was first cloned from Pichia pastoris genomic DNA by PCR, and its 5‘ and 3‘ regions were further cloned by 5‘- and 3‘-rapid amplification of cDNA ends (RACE), respectively. The assembled sequence reveals an open reading frame encoding a polypeptide of 768 residues, and the deduced product shares 76% identity with MetE of Saccharomyces cerevisiae. P. pastoris methionine synthase (PpMetE) consists of two domains common to MetEs. The active site is located in the C-terminal domain, in which the residues involved in the interaction of zinc with substrates are conserved. Homologous expression of PpMetE in P. pastoris was achieved, and the heterologous expression of PpMetE in the S. cerevisiae strain XJB3-1D that is MetE-defective restored the growth of the mutant on methionine-free minimal media. The gene sequence has been submitted to GenBank/EMBL/DDBJ under accession No. AY601648.     

5个毛果杨PtrZFP基因的鉴定和表达分析

ZFP转录因子是植物中的一类具有指环结构域的转录因子。从毛果杨中鉴定出5条ZFP基因（命名为PtrZFP1-5）,对其特性和表达模式进行了分析,以期初步了解这些基因是否能对胁迫做出应答。对PtrZFP1-5基因进行生物学分析,进一步利用qRT-PCR技术分析NaCl、PEG₆₀₀₀和ABA胁迫处理后毛果杨根、茎和叶中5条基因的表达情况。PtrZFP1-5基因编码蛋白氨基酸残基数为258~338 aa,编码蛋白的分子量为27.7~37.3 kDa,理论等电点为4.87~8.61,5个基因不均等的分布在毛果杨基因组的3条染色体上。qRT-PCR结果显示,0.2 mol·L^-1 NaCl、15%（w/v）PEG6000和100 μmol·L^-1 ABA胁迫处理后,5个PtrZFP基因在毛果杨根、茎和叶中的表达模式明显不同。PtrZFP1基因在3种胁迫后毛果杨中均被明显的上调表达;PtrZFP2基因在盐、渗透和ABA胁迫处理后,叶中的表达都明显被抑制;PtrZFP3基因受到干旱胁迫时在根中的响应最为明显;而叶和茎中,表达量在大部分胁迫的大部分时间点无明显改变。PtrZFP4基因也能在根和茎中对干旱胁迫做出明显应答。PtrZFP5基因在经受盐和ABA胁迫后,在叶中的表达受到明显抑制。PtrZFP1-5这5个基因至少能在一种器官中对一种胁迫处理做出应答,但参与的胁迫应答类型和机制可能不同。     

Comparative expression analysis of genes encoding metallothioneins in response to heavy metals and abiotic stresses in rice (Oryza sativa) and Arabidopsis thaliana

To get insights into the functions of metallothionein (MT) in plant response to multiple stresses, expressions of 10 rice MT genes (OsMTs) and 7 Arabidopsis MT genes (AtMTs) were comprehensively analyzed under combined heavy metal and salt stress. OsMT1a, OsMT1b, OsMT1c, OsMT1g, and OsMT2a were increased by different heavy metals. Notably, ABA remarkably increased OsMT4 up to 80-fold. Combined salt and heavy metals (Cd, Pb, Cu) synergistically increased OsMT1a, OsMT1c, and OsMT1g, whereas combined salt and H₂O₂ or ABA synergistically increased OsMT1a and OsMT4. Heavy metals decreased AtMT1c, AtMT2b, and AtMT3 but cold or ABA increased AtMT1a, AtMT1c, and AtMT2a. AtMT4a was markedly increased by salt stress. Combined salt and other stresses (Pb, Cd, H₂O₂) synergistically increased AtMT4a. Taken together, these findings suggest that MTs in monocot and dicot respond differently to combined stresses, which provides a valuable basis to further determine the roles of MTs in broad stress tolerance.     

Efficient tissue culture and <Emphasis Type="Italic">Agrobacterium</Emphasis>-mediated transformation of haploid poplar derived from anthers

Calli were induced from anthers of Populus simonii × P. nigra. Haploid plants were then regenerated from the callus and multiplied efficiently by culturing leaf explants. The presence of both haploid and diploid cells in the same plant revealed spontaneous chromosome doubling in haploid cells. The haploid plants were transformed with the nptII gene by Agrobacterium-mediated method using leaf explants, and five independent kanamycin-resistant lines were obtained, with a transformation frequency more than 6%. Further PCR test indicated that the exogenous betA gene was transferred into these kanamycin-resistant lines, which were still haploid. Thus, the efficient tissue culture system and transformation of haploid poplar plants were achieved. Our study will contribute to forest improvement via the haploid culture and transgenic technology. Published in Russian in Fiziologiya Rastenii, 2007, Vol. 54, No. 4, pp. 629–633. The text was submitted by the authors in English.     

Stimulation of hybrid poplar growth in petroleum-contaminated soils through oxygen addition and soil nutrient amendments

Hybrid poplar trees (Populus deltoides x nigra DN34) were grown in a green-house using hydrocarbon-contaminated soil from a phytoremediation demonstration site in Health, Ohio. Two independent experiments investigated the effect of nutrient addition on poplar growth and the importance of oxygen addition to root development and plant growth. Biomass measurements, poplar height, and leaf color were used as indicators of plant health in the selection of a 10/5/5 NPK fertilizer applied at 1121 kg/ha (112 kg-N, 24.4 kg-P, 46.5 kg-K per ha) to enhance hybrid poplar growth at the Health site. Five passive methods of oxygen delivery were examined, including aeration tubes, gravel addition, and an Oxygen Release Compound (ORC). When ORC was placed in coffee filters above hydrocarbon-contaminated soil, a statistically significant increase of 145% was observed in poplar biomass growth, relative to unamended controls. The ORC in filters also stimulated significant increases in root density. A 15.2-cm interval of soil directly below ORC addition exhibited an increase from 2.6 +/- 1.0 mg/cm3 to 4.8 +/- 1.0 mg/cm3, showing stimulation of root growth in hydrocarbon-stained soil. The positive response of hybrid poplars to oxygen amendments suggests that overcoming oxygen limitation to plants should be considered in phytoremediation projects when soil contamination exerts a high biochemical oxygen demand, such as in former refinery sites.     

Flavonoid data and populational observations in support of hybrid status for Populus acuminata

Flavonoid distribution and populational composition at the collection sites of several samples of Populus acuminata strongly suggest that this taxon is an inter-sectional hybrid between P. angustifolia, sect. Tacamahaca and any one of two or three different species of the section Aigeiros, when the entire range is considered. In the vicinity of the type locality, the Aigeiros parent is P. sargentii. Within any population, foliage of trees of P. acuminata is characterized by morphological intermediacy and an essentially additive flavonoid profile, as compared to the two parental taxa present. In habit the trees resemble those of P. sargentii, and habitats at the collection sites were found to be somewhat intermediate. Fifteen flavonoid compounds were consistently present in samples of the putative hybrid. Twelve of these had diagnostic value because they were absent in one of the parental species. One compound, apigenin 7-O-diglucoside, was found only in P. acuminata. In part, our identifications correspond to compounds reported by Crawford in a morphological and chemical study of P. acuminiata.     

Cloning,expression and function of phosphate transporter encoded gene in Oryza sativa L.

OsPT6:1,a phosphate transporter encoding gene from the leaf samples of Oryza sativa, was identified through PCR with specifically designed primers.The phylogenetic analysis and the conserved amino acid residue site detection suggested OsPT6:1 a possible high-affinity phosphate transporter encoding gene.In situ hybridization and RT-PCR demonstrated the expression of OsPT6:1 in both roots and leaves.The peak expression signal was observed in mesophyll cells under low phosphorus(P)induction.A homologous recombination study indicated that OsPT6:1 can enhance the Pi uptake efficiency of Pichia pastoris.At the meantime,the introduction of OsPT6:1 was able to complement the Pi uptake function of yeast cells with high-affinity phosphate transporters de- ficient.Those results substantiated our contention that OsPT6:1 encoded a high-affinity phosphate transporter of Oryza sativa.