Water stress is one of the most important environmental factors that affect plant growth and development, and limit plant production. Plants can respond and adapt to water stress by perceiving the stimulus, generating and transmitting the signals, and initiating various defense mechanisms. The plant hormone abscisic acid (ABA), as a stress signal, plays important roles in the regulation of plant responses to water stress. ABA not only regulates water balance by inducing stomatal closure, but also enhances water stress tolerance by inducing the expression of genes that encode dehydration tolerance proteins. Increasing evidence indicates that ABA-enhanced water stress tolerance is related to the induction of antioxidant defense systems by ABA. In this review, recent advances on the roles of ABA in the induction of the generation of reactive oxygen species (ROS), the expression of antioxidant enzyme genes, and the capacity of antioxidant defense systems are presented. Special attention is given to the cross-talk mecha-nisms between Ca2+ and ROS that originates from NADPH oxidase in the ABA-induced antioxidant defense in plants.
By using Thermal Asymmetric Interlaced PCR (TAIL-PCR) method, a DNA fragment of about 1 000 bp was amplified and cloned from a liverwort species (Lunularia cruciata (L.) Dum. ex Lindb). The nucleotide sequence of this fragment and its deduced amino acid sequence shared about 56% and 60% identity with those of exon 2 of CHS genes from vascular plants respectively. The four characteristic catalyzing sites of CHS were found conserved in the deduced amino acid sequences of the fragment when compared with other CHS sequences. This is the first report of cloning a CHS-like gene from liverworts, suggesting that the origin of CHS genes may predate liverworts. Using the CHS-like sequence from L. cruciata and CHS sequences from two fern-alien species, Psilotum nudum (L.) Griseb. and Equisetum arvense L., as outgroups, the phylogenetic trees of about 250 CHSs from 29 families of angiosperm plants were constructed by using the neighbour-joining (NJ), maximum parsimony (MP) and quartet puzzle (QP) methods. The results showed that the CHSs from most plant families were separated into two or more clades while sequences from the families Brassicaceae, Fabaceae and Poaceae were each grouped into an independent monophyletic clade. The relative base substitution rates were estimated for CHS genes in three plant families, Solanaceae, Convolvulaceae, and Asteraceae, where the heterogeneity rate was detected both within and among the families. Results indicated that CHS genes in angiosperm plants were greatly diverse in terms of copy number, base substitution rate, and duplication/deletion events, which might be correlated with the diversity of life history, habitat, floral characters, and defense system of angiosperm plants.
Knowledge of nitrous oxide (N2O) exchanges through soils and atmosphere in various ecosystems has been of great importance in global climate change studies. However, the relative magnitude of surface and subsurface N2O production sources from the alpine grassland ecosystem is unclear. In the present study, the N2O concentration profile from 1.5 m in depth in soil to 32 m in height in air was measured from July 2000 to July 2001 in alpine grassland located in the permafrost area of the Qinghai-Xizang Plateau, which revealed that N2O concentrations had a distinct variation pattern both in air and in soil during the study period. Mean N2O concentrations in the atmosphere were significantly lower than those in the soil, which induced the N2O emission from the alpine steppe soil into the atmosphere. Mean flux of N2O in this alpine grassland experiment site was 0.05×10-4 mmol·m-2·s-1. But the variation in N2O emissions did not show any clear trends over the whole-year experiment in our study site. The highest N2O concentration was found at the depth of 1.5 m in the soil while the lowest N2O concentration occurred at the height of 8 m in the atmosphere. Mean N2O concentrations in the soil increased significantly with depth. This was the influence of increasing soil moistures, which induced the increasing denitrification potential with depth. The mean N2O concentrations at different heights in the air remained a more steady state because of the atmospheric negotiability. Seasonal variations of N2O concentrations showed significant correlations between the neighbor layers both in the soil and in the atmosphere. The seasonal variations of N2O concentrations at all horizons in the soil showed very clear patterns, with the highest concentrations occurring from the onset of frost to the freeze-thaw period and lowest concentrations occurring during the spring and the summer. Further analyses showed that the seasonal variations of N2O concentrations in the soil were hardly explained by soil temperatures at any depth. Temporally, atmospheric N2O concentrations at all heights exhibited almost the same seasonal pattern with the soil N2O variations, while soil is believed to be the predominant natural source of atmospheric N2O near the earth surface in this alpine grassland area. Also, a significant correlation was found between N2O emissions and soil N2O concentrations at 0.2 m in depth during the study period. This implied the variation of N2O concentrations in the soil surface horizon was the most direct driving force of N2O exchanges between the soil and the atmosphere. Soil atmospheric N2O at surface layers is the main source of N2O emissions from the soil surface to the atmosphere. Soil N2O concentrations at deeper layers were all significantly higher than those at surface layers, which indicated that N2O was diffused from the deeper layers to the surface layers in the soil, and finally was emitted to the atmosphere.
Late-stage or later-successional ectomycorrhizal fungi, dominant ectomycorrhizal species in mature forest, are generally important symbiotic partners of dominant tree species in many forest ecosystems. Spatial patterns of fungal sporocarps of three families, i.e. Amanitaceae, Boletaceae and Russulaceae, in a subtropical forest in Dujiangyan were examined using second-order analysis in the present paper. The woody plant compositions of the plots associated with ectomycorrhizal fungi of three families were also compared using binary logistic regression analysis. Results indicated that presences of non-ectomycorrhizal and some ectomycorrhizal plants might have negative effects on the occurrence of ectomycorrhizas (ECM) fungal sporocarps and the characteristics in clonal growth of fungal taxa would not be the only determinant in the spatial pattern of ECM fungi. We suggest that besides host plants, non-ectomycorrhizal woody plants and interaction of ECM fungi should also be considered in spatial studies of ECM fungal communities in natural forests.
Effects of nutrients (compounds of macro- and micro-elements) supply without sulfur (T1) and with sulfur (T2) on the competition between Stipa grandis L. (C3) and Cleistogenes squarrosa L. (C4) were examined using a replacement series design in a greenhouse experiment over a period of 80 d. Blank treatment (nothing applied) (T0) was conducted simultaneously. It seems to be no inter-competition between S. grandis and C. squarrosa in all treatments. There was also no intra-competition for S. grandis in all treatments, and for C. squarrosa under T0 treatment because of low productivity. However, the intra-competition of aboveground of C. squarrosa was significant when nutrients were supplied regardless of sulfur (S) application. The interaction on dry weight of C. squarrosa per pot between S supply and proportion of C. squarrosa was observed. Under the treatments of T1 and T2 the shoot growth of S. grandis increased significantly compared with T0 treatment, but there was no significant difference between T1 and T2 treatments, indicating S had no effect on it. Root morphologies of S. grandis was not sensitive to nutrients added. Nutrients supply (T1 and T2 treatments) not only increased significantly the shoot growth of C. squarrosa, but also increased significantly its root growth. Sulfur increased significantly growth of the shoot and root of C. squarrosa. Nutrients supply decreased significantly ratio of root to shoot dry matter (RRS) of C. squarrosa regardless of S application, but the RRS of S. grandis was not affected by nutrients applied. Sulfur also decreased significantly the RRS of C. squarrosa in 100% and 75% proportions of C. squarrosa. The RRS of C. squarrosa was greater significantly in the 100% proportion than that in the 25% proportion of C. squarrosa for all treatments. Therefore, photosynthesis is more allocated to root in infertility soils than in fertility soils and the competition for nutrient resources stimulates root production. The degree of leaf greenness of C. squarrosa in T1 treatment was less significantly than that in T0 and T2 treatments, and it was greater significantly in the 25% proportion than in the 100% proportion of C. squarrosa under T1 and T2 treatments, indicating that nutrients supply increase chlorophyll content in plant and may accentuate S deficiency or low plant productivity alleviate S deficiency.
Synchrotron radiation extended X-ray absorption fine structure (SR EXAFS) was used to study the transformation of coordination and redox state of arsenic (As) in a newly discovered As hyperaccumulator, Pteris vittata L., which is considered to have great potential for phytoremediating the As contaminated soil. It is shown that the As in this plant was mainly coordinated with oxygen in the reduced state, As (Ⅲ), and the reduction of As (V) occurred in the root after it was taken up. No oxidation of As (Ⅲ) was found during the translocation of As, from root to shoot. Only a small amount of As was coordinated with sulfur in root and petiole, but not distinct in pinna.
The conversion from sucrose to starch in grains is a key process during yield formation of wheat. In a field study, diurnal changes in ATP content and activities of enzymes catalyzing starch synthesis in grains of two winter wheat (Triticum aestivum L.) cv. Lumai 22 and Lumai 14 were investigated. The enzymes included sucrose synthase (SS; EC 18.104.22.168), ADP-glucose pyrophosphorylase (ADPGPPase; EC 22.214.171.124), soluble starch synthase (SSS), and starch granule-bound synthase (GBSS; EC 126.96.36.199). Activities of these enzymes and ATP content showed obvious diurnal patterns. The enzyme activities were generally higher during the nighttime than the daytime, but ATP content showed an opposite pattern. It was found that the super-optimum air temperature could be partly responsible for the low enzyme activities during the daytime. The possible factors influenced the diurnal changes in activities of the enzymes for starch synthesis in wheat grain were discussed.
A FeMoco-deficient DnifH Av1 was partially purified from a nifH deleted mutant DJ54 of Azotobacter vinelandii Lipmann grown in NH3-limited medium. By using the same purification method, DnifE Av1 and NifB-Av1 were obtained from DJ35 and UW45, respectively. The latter two proteins were obviously much purer than DnifH Av1. Under a suitable condition for crystallization, dark brown short rhombohedron crystals could be obtained from the three proteins. Like NifB-Av1, the time for formation of DnifH Av1 crystal was longer than that of DnifE Av1. But the optimal concentrations of precipitant and buffer for crystallization of DnifH Av1 were similar to those of DnifE Av1. SDS-PAGE analysis showed that the crystalline DnifH Av1 was similar in the composition to OP Av1. It indicates that the crystal formed in DnifH Av1 solution could be the protein crystal.
A simple in vitro system was employed for ectomycorrhizal synthesis of Abies firma Sieb. et Zucc. with Laccaria bicolor (Maire) Orton. The aim of this present study was to study whether the symbiosis of A. firma broad occurred with L. bicolor and whether the symbiosis of A. firma only occurred at the whole plant level. The results of the study show that the typical ectomycorrhizal structures, i.e. thick mantle and intracortical Hartig net, were observed in the lateral roots of A. firma after incubation of 10 weeks. In case of callus, three weeks following incubation, fungal hyphae were visible within the intercellular spaces of the callus cells and Hartig net-like structures were observed in transverse section. This was the first report of aseptic ectomycorrhization of A. firma seedlings, and ectomycorrhizal colonization on A. firma callus by L. bicolor. These results suggested that the callus system might be a useful tissue system for mycorrhiza synthesis in the present study. This model system may facilitate detailed studies on ectomycorrhizal development of Abies species.
Potassium pyroantimonate precipitation method was used for ultracytochemical localization of calcium in microsporangia of Prince Rupprecht Larch (Larix principis-rupprechtii Mayr) at different developmental stages. During meiosis, calcium precipitates were abundant on the cell wall and intercellular space among cells of the epidermis and middle layers of the microsporangium wall. Calcium precipitates were only found on the cell wall of the outer tangential membrane of the tapetal cells, but few was found in microspore mother cells. At tetrad stage, a large amount of calcium precipitates were observed on the callose wall of each tetraspore as well as the wall surrounding the whole tetrad. The quantity of calcium precipitates decreased at free microspore stage and then gradually increased till pollen maturation. Calcium around the Ubisch bodies increased from the tetrad stage till pollen maturation. This study also discusses the relation between the distribution of calcium precipitates on the tetrad walls and the formation of pollen wall, as well as the possible function of epidermis, middle cells, tapetum and Ubisch bodies in transportation of Ca2+ to the pollen.
The ultrastructural characteristics and the subcellular localization of vegetative storage proteins (VSPs) of Ginkgo biloba L. were systematically studied under the electron microscope. Results indicated that the VSPs of G. biloba were mostly distributed in the small vacuoles of the phloem parenchyma cells. The VSPs of phloem parenchyma cells were produced in cytoplasm, then separated by the inflated cisternae of endoplasmic reticulum (ER), plasmalemma invagination or Golgi body vesicles, resulting in the formation of vacuole filled with proteins. Three kinds of VSPs were detected: granular, floccular and massive VSPs, which were distributed in different tissue cells and different cells of the same tissue or vacuoles of the same cells. VSPs accumulated in autumn and kept at high level throughout the winter. In the following spring, the bud started growing and VSPs were completely mobilized. With new shoots growth, VSPs resumed accumulating in late summer and early autumn.
Embryological investigation was carried out on apomixis in Eulaliopsis binata (Rotz) C. E. Hubb by using paraffin section method. The results indicated that the development pattern of the embryo sac was apospory. In the early stage of the ovule development, a few of the nucellar cells developed into aposporous initial cells, which differentiated later into two forms of mature embryo sac: (1) one form of the mature embryo sac contained one egg cell, one synergid and two polar nuclei; (2) another form possessed one egg cell, two synergids and one polar nucleus. The former occupied about 67.6% and the later only 32.4%. The development pattern of the aposporous embryo sac resembled the Panicum type. Multiple initial cells of apospory might undergo development simultaneously to form two- or multiple-embryo sacs. The ratio of multiple mature embryo sacs in one ovule was 17.7%. No sexual embryo sac was found in the observed ovules. The genesis of the embryo could be classified into two types according to their initial time: (1) the pre-genesis embryo (74%), which originated from unreduced egg cell before the division of the polar nucleus, was observed at one to two days earlier than anthesis. (2) the late-genesis embryo (26%) which was observed at one or two days after anthesis and formation of free endosperm nuclei. The endosperm was derived from the polar nucleus or secondary nucleus without fertilization. The process of the embryonic development followed the sequence of the sexual embryo. The frequency of polyembryony observed was 13%.
For salinity stress tolerance in plants, the vacuolar type H+-ATPase (V-H+-ATPase) is of prime importance in establishing an electrochemical H+-gradient across tonoplast that energizes sodium sequestration into the central vacuole. In this paper, the sequence of a cDNA encoding the B subunit of the vacuolar-type H+-ATPase from Suaeda salsa L., a plant that can survive in seawater was reported. The B subunit cDNA is 1 974 nucleotides long and include a 18 bp poly(A+) tail together with a complete 1 470 bp coding region for a 489 amino acid with a conservative ATP binding site and a predicted molecular mass of 54.29 kD. Northern and Western blotting analyses indicated that the expression of B subunit was significantly up-regulated by NaCl treatment. Moreover, the expressions of B subunit were coordinated with c subunit of V-H+-ATPase at transcript and translation levels under NaCl stress. The increased V-H+-ATPase subunit amounts and activity of Suaeda salsa provide the energy for the compartmentation of sodium in response to salinity.
Heritable alteration in DNA methylation patterns was detected in all five rice lines with introgressed DNA segments from wild rice (Zizania latifolia (Griseb.)) by DNA gel blotting analysis with an endogenous retrotransposon Tos17 as a probe. The changing patterns include simultaneous loss of parental fragments and appearance of novel fragments in each of the four methylation-sensitive enzyme digests. Methylation modifications include cytosines at both symmetrical and asymmetrical sites, as well as adenine bases. Sequence analysis at two critical regions of Tos17, i.e. the 5''-LTR region (region Ⅰ) and the reverse transcriptase region (region Ⅱ) showed complete conservation for all five introgression lines compared with the parent. Sequence-specific PCR assay, however, confirmed that methylation changes occurred in both regions. Moreover, concordance in the collective methylation changes between 5''-LTR and RT regions was observed in two of the introgression lines. The methylation changes are stably inherited to the next generation. Because earlier studies showed that there had been activation and mobilization of Tos17 in these introgression lines following alien DNA integration, it appears likely that DNA methylation may have played some roles in controlling activity of Tos17 in rice, although the exact relationship between the two phenomena remains to be established.
hloroplast microsatellite primers of wheat (Triticum aestivum L.) and random primers were employed to identify the chloroplast and nuclear genomes of three selfed linesⅡ-2, Ⅱ-Ⅰ-8 (F2-F6) and 8-1 (F3-F6) ( segregated from Ⅱ-Ⅰ-8 of F2), which were derived from the same asymmetric somatic hybrid clone between Triticum aestivum L. cv. Jinan 177 and Agropyron elongatum (Host) Nevski. The results showed that the chloroplast genomic components of the three lines were consistent and dominated by that of wheat. Bands characteristic to both parents were only detected in the sequence of the intergenic region between rpl14 and rpl16 of the chloroplast genome, suggesting the existence of chloroplast DNA of A. elongatum in those hybrids. Furthermore, this exogenous integration of chloroplast DNA was passed to F6 stably. RAPD analysis showed that there were different DNA fragments of A. elongatum in different lines. However, the nuclear genome basically remained stable during passage.
Transgenic tobacco (Nicotiana tabacum L. cv. Xanthi) plants which express coat protein (CP) gene (cp) of potato virus X (PVX) were generated via Agrobacterium tumefaciens-mediated gene transfer. Northern blotting analysis indicated that cp silencing happened in three transformants, and Run on assay showed that the cp silencing was at post-transcriptional level. The result of cp methylation assay showed different degree of methylation existed in coat protein gene coding sequences. cp methylation was also analyzed during virus-induced gene silencing (VIGS), and results suggested that methylation pre-existed in cp non-silenced transgenic plants, while virus infection increase the methylation degree, which indicated DNA methylation in VIGS was not a de novo DNA methylation process.
A new bibenzyl derivative, moniliformine, along with six known compounds, was isolated from a orchid Dendrobium moniliforme (L.) Sw. The new compound was identified as 3,4-dihydroxy-5,4''-dimethoxy bibenzyl on the basis of 1D and 2D NMR experiments. The six known compounds were determined to be a-dihydropicrotoxinin, n-triacontyl p-hydroxy-cis-cinnamate, n-octacostyl ferulate, b-sitosterol, daucosterol and n-nonacosane, respectively. Among them, a-dihydropicrotoxinin was isolated for the first time from the plant kingdom.
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