This article summarizes allelochemicals’ active variety, its potential causes and function mechanisms. Allelochemicals’ activity varies with temperature, photoperiod, water and soils during natural processes, with its initial concentration, compound structure and mixed degree during functional processes, with plant accessions, tissues and maturity within-species, and with research techniques and operation processes. The prospective developmental aspects of allelopathy studies in the future are discussed. Future research should focus on: (1) to identify and purify allelochemicals more effectively, especially for agriculture, (2) the functions of allelopathy at the molecular structure level, (3) using allelopathy to explain plant species interactions, (4) allelopathy as a driving force of succession, and (5) the significance of allelopathy in the evolutionary processes.
The quality of seed deposition often involves habitat and microenvironment selection by seed-dispersing agents (e.g. birds and small rodents) and deposition patterns (e.g. burial of seeds). However, little is known where seeds and nuts are deposited by these animals after their shedding from parent trees. In this study, seed deposition patterns of oil tea (Camellia oleifera Abel., Theaceae) influenced by seed-caching rodents were studied by tracking individual oil tea seeds (labeled with small coded tin-tags) at two stands (secondary stand and primary stand) in an experimental forest of Dujiangyan City, Sichuan Province, China. We found that over 80% of the tagged seeds were well buried 0 – 60 mm deep in the soil and a small part of them were deposited on the soil surface with some leaf litter covering at both stands. Small rodents significantly preferred to select some specific microenvironments (e.g. shrub edge and under shrubs) to cache and eat seeds at each stand. In these microenvironments, they may experience less predation risk during the foraging process. We also found that the microenvironment distributions of caches changed slightly with cache order: a higher proportion of the cached seeds was deposited under shrubs or at shrub edge at higher order cache sites (i.e. secondary and tertiary caches) than at primary cache sites at both stands. Our results indicate that burial of oil tea seeds by small rodents might be a greater benefit for seed survival, seed germination and seedling establishment. Small rodents dispersed seeds from seed sources or parent trees to different microenvironments, which may be beneficial to seed germination and seedling establishment due to more seeds deposited in a favorable environment.
Through the field investigation and laboratory analysis, this paper describes the regular pattern of community succession on the deserted land of Shizishan copper tailings in Tongling City. There are 49 species of natural colonized plants on the wasteland, which are subordinate to 15 families and 38 genera. The main families are Compositae (12 species), Gramineae (11 species), Leguminosae (8 species) and Hippochaete ramosissimum, which belong to Equisetaceae. The extreme soil infertility and excessively concentration of heavy metals (especially Cu and Cd) are the main limiting factors to plants colonization. The vegetation on the deserted land of copper tailings is distributed in spot piece and scattered mainly with fewer species of plant, with lower species diversity. Annual and biennial herbs and grasses are dominant components. Cynodon dactylon, Imperata cylindrica var. major, Lespedeza chinensis, Erigeron annuus and H. ramosissimum etc. have a higher summed dominance ratio. The natural formation of plant community on the deserted land of copper tailings usually goes through seeds spread, invasion, ecesis, aggregation and species competition. After several years of primary natural restoration, 14 communities were formed. According to their community composition and structure level, the 14 communities are divided into three primary succession stages, namely monodominant, subdominant and codominant species communities. With the formation and succession of these communities, species were enriched and diversity increased, the margin of summed dominance ratio of species in each community decreased, and the composition or structure of community became complex.
Nanoneis was identified as a newly recorded diatom genus for China under transmission electron microscope (TEM) in the water samples from the East China Sea and Huanghai Sea (Yellow Sea). The valves of this diatom are bilaterally symmetrical and have a raphe extending through the middle of the valve from one pole to near the center. The raphe of the opposite valve on the same cell extends from the other pole to near the center. The alveoli or ribs of the valve face continue around the valve mantle. Two species were described in this paper, including Nanoneis longta sp. nov. as a new species and Nanoneis hasleae as a new recorded species for China. They have some distinctly different characteristics in the shape of valve surface, the ratio of length to width and the density of alveoli or ribs on valve face. Detailed description of the taxonomic characteristics with TEM photographs of these two species and their ecological distributions were given in this paper. N. longta sp. nov.: cells are narrowly linear in valve view and bilaterally symmetrical with convexity being present in the apices and in the middle of the valve. Cell length 1012 µm, width 1.01.5 µm. The ratio of length to width is about 10:1. Valve structure consisting of thickened ribs perpendicular to the apical axis alternating with thin areas, alveoli, in the greater length of the valve. Ribs and alveoli radically arranged in apical parts of valves. The density of the transapical ribs is approximately 60 in 10 µm. A simple raphe located in the middle of valve, extending from one pole to a point near to the median part of the valve. The opposite valve on the same cell with the raphe extended from the opposite pole to near the center. The specimens were collected from a 20-m layer at latitude 29º 6'' 31'''' N, longitude 126º 57'' 72'''' E, in Nov., 2000.
The shoot branching patterns of the two-year-old branches of peach trees (Prunus persica (L.) Batsch cv. Elberta) were compared with different pruning measures. The branches were divided into a basal non-branching zone, a proleptic branching zone, a sylleptic branching zone and the part removed. We used the hidden semi-Markov model to capture the branching patterns. The final results showed that theoretical probability distributions of diverse lateral shoots of the parent branches calculated on the basis of the parameters of the hidden semi-Markov chain model were in good agreement with probabilities extracted from the observed data. This paper described the quantitative effects of pruning on branching architecture of a parent branch, taking into account of branch morphology. Results suggest that the hidden semi-Markov model could be used as an effective tool to describe the branching patterns. In addition, the application of hidden semi-Markov models to predict the effects of pruning on peach tree branching pattern based on growth parameters was discussed.
Recalcitrant seeds of Trichilia dregeana Sond. were used as experimental material, and desiccation sensitivity of T. dregeana axes and antioxidant role of ascorbic acid were studied. Desiccation tolerance of T. dregeana axes progressively declined with dehydration, water content at which 50% of axes has been killed by dehydration (W50) was about 0.16 g H2O/g DW. During dehydration, electrolyte leakage rate of axes gradually increased, the activities of superoxide dismutase (SOD), ascorbate peroxidase (APX), catalase (CAT), glutathione reductase (GR) and dehydroascorbate reductase (DHAR) declined, and content of thiobarbituric acid (TBA)-reactive products increased. Two point five-10 mmol/L ascorbic acid (AsA) treatment could significantly increase desiccation tolerance and activities of SOD, APX, CAT and GR in axes, and decrease electrolyte leakage rate and content of TBA-reactive products in axes. The results showed that desiccation tolerance of T. dregeana axes was strongly correlated with the increase in the activities of antioxidant enzymes and the decrease in lipid peroxidation.
The effects of salt stress on photosynthesis, Mehler-peroxidase reaction (MPR) and the susceptibility of PSⅡ to photoinhibition were investigated in Rumex K-1 leaves. Salt stress resulted in dramatic decrease in photosynthesis, but had no significant effect on maximal photochemistry of PSⅡ (Fv/Fm). During photosynthetic induction, a considerable electron flow was transported to oxygen in MPR both in control and salt-stressed leaves. Under steady state photosynthesis, enhanced electron flow to oxygen in MPR was observed only in salt-stressed leaves. The enhanced MPR in salt-stressed leave was accompanied by enhanced activities of scavenging enzymes, i.e. superoxidase dismutase (SOD) and ascor-bate peroxidase (APX). In the presence of saturating CO2, decreasing oxygen concentration from 21% to 2% did not affect the susceptibility to photoinhibition in control leaves, but largely increased the suscep-tibility to photoinhibition in salt-stressed leaves. Based on these results, it is concluded that the enhanced MPR in salt-stressed Rumex leaves serves as a sink to drain the excess electrons off the electron chain and thus mitigates photoinhibition.
Salicylic acid (SA) plays an important role in mediating some biotic and abiotic stress-induced oxidative stresses in plants. However, it remains unknown about the role of SA in mediating oxidative stress induced by aluminum. In this study, we investigated the changes in concentrations of H2O2 and O2-, some antioxidative enzyme activities and several physiological parameters involved in oxidative damage to plasma membrane in the root tips of Cassia tora L. Results indicated that 20 mmol/L aluminum (Al) caused increases in electrolytes leakage, malondlaldehyde (MDA) content and intense staining with Evans blue in root tips, while treatment with 5 mmol/L SA suppressed the Al-induced increase in MDA. Examination of H2O2 and O2-, the major ROS responsible for lipid peroxidation indicated that root tips challenged with Al in the presence of SA contained significantly lower contents of H2O2 and O2- than those with Al alone. However, the reduced levels of H2O2 appeared not to be correlated with enhanced activities of ROS-scavenging enzymes like catalase (CAT), ascorbate peroxidase (APX) and glutathione reductase (GR), but with increased activities of guaiacol peroxidase (POD). SA-induced reduction of H2O2 was also correlated with suppression of O2- accumulation and superoxide dismutase (SOD) activities. From the results, it is concluded that SA might activate an H2O2-mediated pathway, which in turn initiated a POD-dependent antioxidative mechanism for retarding lipid peroxidation or preserving membrane integrity in root tips of C. tora. We presented the evidence of time-dependent changes in endogenous SA in root tips exposed to 20 mmol/L Al.
APⅣ is a rice mutant that develops poly-egg apparatus in its embryo sac. All the eggs that make up the poly-egg apparatus can be fertilized respectively resulting in the development of polyembryony. The routes taken in the development of polyembryony appear to fall mainly into three variant polygonum pattern types, designated as 5-2-1 , 5-3-0 and 6-2-0 types. Out of the embryo sacs of APⅣ studied about 50% exhibited variant polygonum type with associated abnormal nuclear behavior and microtubule organizational changes. Some of the major abnormal features shown by the three variant polygonum types were described and they included the following: For the 5-2-1 type At the beginning of the four-nucleate embryo sac development, one pair of nuclei became located to the micropylar end and the other pair to the chalazal end. As embryo sac further developed, long connecting microtubule (MT) bundles that existed between the two nuclei in the chalazal end play a role in the movement and positioning of that nucleus. As a result of the activities of these MT, one of the nuclei in the chalazal end moved to the micropylar end resulting in the micropylar end having three nuclei and the chalazal end only one. For the 5-3-0 type In the two-nucleate embryo sac of the 5-3-0 type, one nucleus remained at the micro-pylar end, while the other one became located near the central region. In the four-nucleate embryo sac, the pair of nuclei aligned in parallel to the micropylar-chalazal axis often having one of its nuclei relocated to the micropylar end as a result of associated MT activities. For the 6-2-0 type All the nuclei in the megaspore, two- and four-nucleate embryo sacs became located to the micropylar end. At the early stages of the eight-nucleate embryo sac development, the two nuclei in the central region of the embryo sac (originally at the micropylar end) became polar nuclei. All the other nuclei remained at the micropylar end were surrounded by reticulate MT. The relationship between abnormal behavior of nuclei and MT organi-zation in the development of rice embryo sac was discussed.
The ovule of Doritis pulcherrima Lindl. is anatropous, tenuinucellate and bitegmic. The mature megagametophyte is composed of seven cells with eight nuclei and its formation belongs to Allium type. Its embryo sac matures about 45 d after pollination. The megasporogenesis in vitro by ovule culture can be induced on all media whether with exogenous hormones or not 3 d after inoculation, but the later megagametogenesis will stop on the medium without hormone or only with auxin or cytokinin. Mature embryo sac can form from megaspore mother cell on the modified VW medium supplemented with 0.5 mg/L BA and 0.1 mg/L NAA.
五唇兰(Doritis pulcherrima Lindl.)的胚珠属于倒生型，具薄珠心，两层珠被。胚囊发育类型为双孢子葱型，授粉后约45 d形成七细胞八核的成熟胚囊。五唇兰未受精胚珠在离体培养初期对外源激素的依赖性很小，在没有外源激素的培养基上，大孢子母细胞也能经过减数分裂发育为二核胚囊。在培养后期，外源激素对胚囊发育的影响很大。在培养基无外源激素或仅含生长素或细胞分裂素时，雌配子体的发生过程不能顺利完成；在改良VW培养基上添加0.5 mg/L BA和0.1 mg/L NAA时，形成成熟胚囊。
The Arabidopsis gene UPRIGHT ROSETTE (URO) was previously identified as a leaf developmental regulator, as all rosette leaves of the semi-dominant upright rosette (uro) mutant grow uprightly at seedling stages. Here, we report more detailed phenotypic characterizations of the uro mutant and show that the URO gene has multiple functions in plant development. In addition to its aberrant leaf-growing pattern, the uro mutant displayed pleiotropic phenotypes. Both uro/+ and uro/uro plants showed a loss of apical dominance, while such a phenotype in the uro/uro plants appeared more severe. Some secondary branches of the uro/uro plants were replaced by leaves, for which petioles were attached to the abaxial side of leaves. Flowers often exhibited varying abnormalities, with altered numbers of petals and stamens and abnormally fused organs. Stems of the uro mutant were soft, which was caused by lacking interfascicular fiber. In addition, vascular differentiation in mutant stem was delayed. The loss of apical dominance and the defects in vascular development and interfascicular fiber formation suggest that the URO function might be associated with auxin-mediated plant development. To provide more direct evidence whether the URO is involved in auxin action, we examined the URO function in auxin polar transportation pathway by analyzing pinformed1 (pin1) uro double mutant. Phenotypes of the double mutant suggest that URO and PINFORMED1 (PIN1) have partial genetic interactions in plant development, which further supports the hypothesis that the URO gene may play an important role in the auxin regulatory pathway.
The AtNHX1 gene and hygromycin phosphotransferase (hpt) gene were introduced into the embryonic callus cells of maize (Zea mays L.) elite inbred lines DH4866, Qi 319 and Luyuan 16106 by Agrobacterium-mediated method. Plantlets were obtained from the hygromycin-resistant calli after screening. PCR analysis and Southern blot hybridization indicated that there were 22.8% transgenic plants among the regenerated plants. The transformation frequencies were obviously affected by Agrobacterium concentration, the genotype of callus and co-cultivation duration. The segregations of AtNHX1 gene in the progeny were not easily to be elucidated, and some lines showed Mendelian segregations. The screening of salt tolerance indicated that the salt tolerance of some transgenic plants and their progenies were improved significantly and the seeds of some lines were able to germinate and grow in the presence of 0.8%-1.0% sodium chloride. Northern blotting analysis of T2 transgenic plants indicated that the salt tolerance of plants was correlative with the transcription level of AtNHX1 in the leaves.
A new inducible Cre/lox system was constructed in transgenic tobacco (Nicotiana tabacum L.) plants. The inducer-treatment of tobacco callus mediates an excision event in which the selectable marker gene and Cre gene between two lox sites were deleted. A chloroacetanilide-induced promoter (In5-2) was used to control the expression of Cre gene in this system. Molecular analysis of transgenic tobacco plants showed the interested gene, b-glucuronidase (gus), was integrated into the genome whether removing has been successful, and forty-five out of forty-eight T0 plants were transgenic tobacco without the marker gene, hpt. This system uses a single vector to circumvent the flaw of other dual recombinase vector systems.
A powdery mildew resistance gene in a BC3F2 population, derived from a cross made between an amphidiploid of Triticum durum Desf.-Aegilops caudata L. and T. aestivum L. cv. Laizhou 953, was identified. Genetic analysis of resistance to powdery mildew in BC3F2 population and derived BC3F3 families indicated a single dominant gene controlled the resistance. By bulk segregation analysis, two microsatellite markers, Xgwm311 and Xgwm382, were identified to be closely linked to the resistance gene with genetic distance of 5.9 cM and 4.9 cM, respectively. DNA from T. durum accession DR147, Ae. caudata acc. Ae14, and recurrent parent wheat (Triticum aestivum L.) cv. Laizhou 953 were amplified with primer pairs WMS311 and WMS382, the specific bands related to the resistance gene were only present in T. durum acc. DR147. Results showed that the resistance gene originated in T. durum acc. DR147. Based on the location of the linked microsatellite markers, the resistance gene was located on the telomeric region of chromosome 2AL in wheat. Temporarily, the resistance gene was designated as PmDR147. The relation of this gene and Pm4 was discussed.
The gene encoding sorghum NADP malic enzyme, which plays a key role in C4 photosynthetic pathway, was isolated by RT-PCR and cDNA library screening. The 2 139 bp cDNA sequence obtained includes a 1 911-bp open reading frame that encodes 636 amino acids and a terminating codon (GenBank accession number: AY274836). It was then introduced into Nongken 58, a rice variety, using an Agrobacterium-mediated system. Southern hybridization, Northern hybridization and enzyme activity determination all confirmed the effective expression of sorghum (Sorghum vulgare L.) C4 type NADP-ME in rice, with the enzyme activity being elevated 1–7 folds. However, no appreciable change was demonstrated in carbon assimilation of the transgenic rice though increased photoinhibition was noted under high light intensity.
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