Stable Transformation of Three Cultivars of Kentucky Bluegrass (Poa pratensis L.) by Particle Bombardment of Mature Seed-Derived Highly Regenerative Callus

High embryogenic calli of three cutivars of Kentucky bluegrass, Md, Bd, and Gm, were induced from mature embryos, and were proliferated on medium K3 and K5. Embryogenic calli were transformed with plamids pDM803 and pBY520 by microprojectile bombardment. Fourty-two transgenic lines had been obtained. The highest efficiency of transformation reached to 3.7% for cv. Md, 2.8% for cv. Gm, and 5 % for cv. Bd. The micro nutriment of Cupric had significant effect on transformation. The embryogenic callus cultured in dim-light condition had higher transformation efficiency than the green callus cultured in light condition for one month before transformation. The selective regime and selective pressure on the putative transgenic plants were important for obtaining the desire number of transgenic plants. It also affected the copy number of integrated genes in the genomic DNA of transgenic plants.

Analysis of drought resistance HVA1 gene under drought stress in different Poa pratensis cultivars

Total RNA from leaves of Poapratensis cultivars under drought stress was extracted for reversing transcription to cDNA and then cDNA as template for PCR reaction by designing primer of cds of Hordeum valgare HVA1 drought resistance gene from GenBank. The amplified products were positive recon identified by using procedures of recovery, connection, transformation and enzyme separation. The length of cloned gene sequence was 324 bp, identity reached 79.27% with Barley HVA1 gene that meaned the cloned gene sequence was the partial HVA1 gene of Poapratensis.

Callus induction and plant regeneration from mature bluegrass (Poa pratensis L.) seeds

A protocol was discussed for high efficient plant regeneration from seven bluegrass （Poa pratensis L.） cultivars via an in- direct callus induction and somatic embryogenesis method. Mature seeds were used as explants for callus initiation. Callus induction and proliferation efficiencies were investigated on NB, modified MS （MMS） and MS media, supplemented with 2.0 mg·L^-1 2,4-dichlorophenoxyacetic acid （2,4-D）. The MMS medium performed best. Based on the MMS medium, direct and indirect callus induction effects of bluegrass from mature seeds were compared at the range of 1-5 mg·L^-1 2,4-D contained in the medium. Under the direct callus induction method, the most suitable 2,4-D concentrations varied among cultivars. Under the indirect callus induction method, a significantly high callus induction frequency （93.33%-98.33%） was obtained and there were barely any statistically sig- nificant differences among the tested genetically diverse cultivars. Somatic embryos were promoted on the MMS medium supple- mented with 3 mg·L^-1 2,4-D, 0.1 mg·L^-1 kinetin and 0.8 mg·L^-1 CuSO4. Embryogenetic calli developed into plantlets on the MMS medium containing different concentrations of thidiazuron （TDZ）, and the differentiation frequencies varied in the range from 20.15% to 77.65%. The 0.25 mg·L^-1 TDZ was generally the most suitable concentration for the tested cultivars.

Agrobacterium-mediated Transformation of Kentucky Bluegrass

Embryogenic calli of Kentucky bluegrass, named Md, were induced from mature seeds and embryos, and proliferated on medium K3 containing 2,4-dichlorophenoxyacetic acid (2,4-D, 10.0 mumol/L), 6-benzylaminopurine (BAR, 0.5 mumol/L) and K5 which was the K3 medium supplemented with cupric sulfa (0.5 mumol/L) under dim-light condition (20-30 mumol.m(-2).s-1, 16 h light) at 24 degreesC. Embryogenic calli were transformed with plasmids pDM805 Carring bar and gus genes, Which was mediated by an Agrobacterium strain AGL1, four transgenic lines were obtained. The important factors that affect the transformation efficiency and obtain desirable number of transgenic plants included: (1) the quality of embryogenic calli; (2) light condition and time of co-cultivation; (3) concentration of antibiotics used for suppressing the overgrowth of Agrobacterium in the course of transformed plant regeneration; (4) selection pressure, etc. The micro nutrient of cupric had significant influence on the quality of embryogenic calli. This presentation is the first successful protocol of Kentucky bluegrass transformation mediated by Agrobacterium.

Effects of Drought Stress on Photosynthetic Characteristics of Kentucky Bluegrass

Drought stress is one of the major constraints on turf growth and performance in northern China. Based on previous assessments of drought tolerance levels, four varieties of Kentucky bluegrass （Poa pratensis L.） representing different types （＇Baron＇, BVMG type; ＇Blackstone＇, Cheri type; ＇Kenblue＇, Midwest type; and ＇Bluemoon＇, Midnight type） were chosen for this study. Grass materials were established in a glasshouse, and the changes in their photosynthetic and metabolic characteristics were analyzed during a period of imposed drought stress. Drought stress led to decrease in chlorophyll content, photosynthetic rate, stomatal conductance and transpiration rate in all four cultivars, but the relative changes in each characteristic varied among varieties. The results also showed that changes in the photosynthetic and metabolic characteristics of different varieties under drought stress were related to the morphological characteristics of the plants. Varieties with longer narrow leaves, longer roots, higher root-to-shoot ratios, and higher chlorophyll contents showed greater rates of photosynthesis and stomatal conductance, and lower transpiration rates.

Arbuscular mycorrhizal fungi in the rhizosphere soil of poisonous plants depressed the growth of pasture grasses in the Tibetan Plateau Alpine meadow

In order to explore the influence of arbuscular mycorrhizal(AM)fungi in the rhizosphere of poisonous plants on the neighboring pasture grasses in the Tibetan Plateau Alpine meadow ecosystem,rhizosphere soils were collected from eight different poisonous plants in degraded grasslands and one from pasture grass in non-degraded grasslands(CK).The collected soils were used as inocula to assess the influence of indigenous AM fungi on the growth of two typical pasture grass species,Elymus nutans and Poa pratensis,in a bioassay experiment.Five growth parameters and two AM parameters were determined.The mycorrhizal responsiveness and the importance value were calculated.Significant differences between the eight poisonous plants and CK were observed.Compared to CK,rhizosphere soil from the eight poisonous plants had lower AM fungal spore densities.The growth of E.nutans and P.pratensis seedlings was depressed with the inoculation from poisonous plants rhizosphere soil.This study demonstrated that the presence of poisonous plants with grassland degradation altered inherent AM fungal community abundance,and could exert inhibition effects on the growth of pasture grasses.It may attribute to discover the important role of rhizosphere soil of different poisonous plants to AM fungal community on the Alpine meadow.

Soil space and nutrients differentially promote the growth and competitive advantages of two invasive plants

Aims Invasive plants commonly occupy disturbed soils,thereby provid-ing a stage for understanding the role of disturbance-enhanced resources in plant invasions.Here,we addressed how soil space and soil nutrients affect the growth and competitive effect of inva-sive plants and whether this effect varies with different invaders.Methods We conducted an experiment in which two invasive plants(Bromus tectorum and Centaurea maculosa)and one native species(Poa pratensis)were grown alone or together in four habitats consisting of two levels of soil space and nutrients.at the end of the experiment,we determined the total biomass,biomass allocation and relative interaction intensity of B.tectorum,C.maculosa and P.pratensis.Important Findingsacross two invaders,B.tectorum and C.maculosa,increased soil nutrients had greater positive effects on their growth than increased soil space,the effects of soil space on root weight ratio were greater than those of soil nutrients,and their competitive effect decreased with soil space but increased with soil nutrients.these findings sug-gest that changing soil space and nutrients differentially influence the growth and competitive advantages of two invaders.Bromus tectorum benefited more from increased soil resources than C.mac-ulosa.soil space and nutrients affected the biomass allocation of C.maculosa but not B.tectorum.the competitive effect of B.tecto-rum was unaffected by soil space and soil nutrients,but the opposite was the case for C.maculosa.thus,the effects of soil space and nutrients on growth and competitive ability depend on invasive species identity.