Poa annua L. in Antarctic: searching for the source of introduction

The level of polymorphism, genetic variability and relatedness of a population of Poa annua L. from South Shetlands Islands was studied and compared with results obtained for populations from two potential sources of introduction (Argentina—Ushuaia and Poland—Dziekanów Leśny) using the amplified fragment length polymorphism (AFLP) approach. Five primer pairs used for AFLP profiling amplified 226 scoreable DNA fragments that were used for Clustral and Factorial analyses. The level of molecular variability among all individuals from all the analysed populations reaches 30%. Clustral and Factorial analyses show that all populations formed clear-cut uniform groups according to their locations. However, population from King George Island show high variability. High genetic diversity may be related with escalated human activity at the area of Arctowski Station, favouring introductions of P. annua from many different sources and by many different vectors.     

Assimilation of 14CO2 by the Inflorescence of Poa annua L. and Lolium perenne L.

The relative assimilatory activity of the inflorescence, itsindividual components, and the leaves of flowering tillers ofPoa annua L. and Lolium perenneL. was determined over the periodfrom inflorescence emergence to seed shedding. The pattern of¹⁴CO₂ fixation was similar for both species and the inflorescencewas by far the most important assimilatory organ of the reproductivetiller, particularly over the latter period of seed developmentas leaf senescence progressed. With the exception of the seedsall parts of the inflorescence showed significant assimilatoryactivity and the lemmas and paleas accounted for 40–50per cent of the total ¹⁴C fixed by the inflorescence in bothspecies. The importance of the grass inflorescence as a photosyntheticstructure is discussed in relation to similar studies on cereals. Poa annua, Lolium perenne, carbon dioxide assimilation, inflorescence     

Compartmentation and fluxes of carbon in leaf blades and leaf sheaths of Poa annua L. and Poa x jemtlandica (Almq.) Richt

Abstract The allocation of photosynthetically fixed carbon in the leaf blades and sheaths of Poa annua (a ruderal grass) and Poa x jemtlandica (a sub-arctic grass) was followed over a light-dark cycle. Labelling with ¹⁴Carbon and gas exchange measurements provide data for an eight-compartment model describing the partitioning of carbon between spatially and chemically separated pools and their rates of turnover. Soluble sugars and fructans were turned over rapidly in the leaf blades of both species. The flux of carbon through pools of storage carbohydrates was higher in the leaves of P. x jemtlandica than in P. annua. The exchange of carbon between pools was slower in the sheath than the blade. Carbohydrates stored in the sheath appeared to have no significant role in metabolism over the light-dark cycle studied here.     

Mutant dn Influences Dry Matter Distribution, Assimilate Partitioning and Flowering in Lathyrus odoratus L.

The flowering mutant dn in sweet pea was used as a tool to study¹⁴C-assimilate and dry matter partitioning with respect to nutrientdiversion theories on the control of flower initiation. Wildtype plants (Dn^h) are photoperiodic and exhibit late floweringand profuse basal branching in short days while mutant plants(dn) are day neutral, early flowering and devoid of basal laterals.In short days, dn plants exported a significantly greater proportionof assimilate acropetally than (Dn^h) plants and the upper portionof dn plants had a greater dry weight. These differences werereduced dramatically when basal laterals were excised regularlyfrom the (Dn^h) plants although the difference in flowering remained.However, the effect of dn on resource allocation within theapical region may be more important in regard to flowering thanthe effect on acropetal versus basipetal movement. In shortdays, the dn plants partitioned significantly more resourcesinto their internodes and petioles, and less into their leaflets,than Dn^h plants as shown by dry weight and ¹⁴C-assimilate measurements.These differences were apparent from as early as node 7 up tothe node of flower initiation in dn plants (node 30) and theywere not eliminated by removal of basal laterals from Dn^h plants.Differences between dn and Dn^h plants in partitioning and floweringwere largely eliminated under long days. The fact that in thisspecies a single gene influences both resource allocation andflower initiation lends further support to nutrient diversionhypotheses on the control of flowering. Key words: Assimilate partitioning, branching, flowering, mutant, sweet pea     

Genetic diversity of Poa annua in western Oregon grass seed crops

The genetic diversity of Poa annua L.populations collected from western Oregon grass-seed fields was surveyed using 18 randomly amplified polymorphic DNA (RAPD) markers. Markers from 1357 individual plants from 47 populations collected at three sampling dates (fall, winter, and spring) for 16 sites were used to measure genetic diversity within and among populations. Site histories varied from low to high herbicide selection pressure, and some sites were subdivided by 3 years of differing post-harvest residue management. Gene diversity statistics, simple frequency of haplotype occurrence, and analysis of molecular variance (AMOVA) revealed the presence of significant variability in P. annua among sites, among collection dates within sites, and within collection dates. Nei gene-diversity statistics and population-differentiation parameters indicated that P. annua populations were highly diverse. Mean Nei gene diversity (h) for all 47 populations was 0.241 and total diversity (H_T) was 0.245. A greater proportion of this diversity, however, was within (H_S=0.209) rather than among (G_ST=0.146) populations. When populations were grouped by season of collection, within-group diversity was H_S=0.241, while among-group diversity was G_ST=0.017. When populations were grouped by site, within-group diversity was H_S=0.224, while among-group diversity was G_ST=0.087. The diversity among populations within season for fall, winter, and spring collections was G_ST=0.121, 0.142, and 0.133, respectively. Populations collected from fields with histories of high herbicide selection pressure showed low differentiation among collection dates, with G_ST as low as 0.016, whereas those collected from fields with low herbicide selection pressure showed greater differentiation among collection dates, with G_ST as high as 0.125. At high selection-pressure sites, populations were also lower in gene diversity (as low as h=0.155), while at low selection-pressure sites there was higher gene diversity (as high as h=0.286). The site to site variability was greater for the high selection-pressure sites (G_ST=0.107 or 69% of the total among-population variance), while the season of germination variability was greater at sites of low herbicide-selection pressure (G_ST=0.067, or 70% of the total among-population variance). High initial diversity coupled with a long-term re-supply of genotypes from the seed bank must have been factors in maintaining the genetic diversity of this weed despite the intensive use of herbicides. Knowledge of the genetic diversity of Willamette Valley P. annua should help in formulating more effective strategies for managing this weed. Received: 24 July 1999 / 11 November 1999     

Zur Biologie derPoa annua L.

Ohne Zusammenfassung     

Preliminary test of arsenic and mercury uptake by Poa annua

Arsenic (As) and mercury (Hg) are among the most dangerous heavy metals to humans and the environment because of their toxicity towards all living organisms and their related accumulation capability. It is known that some plant species are able to detoxify water and soil from some pollutants. In this paper we strive to investigate how a common plant species is able to accumulate these metals.In this research we considered Poa annua, a plant species easily growing in Italy and deeply involved in the food chain, to understand problems related to its use as fodder for wild and farm animals (i.e. cattle) and suitability to be used for phytoremediation purposes.Hydroponic experiments were set up; P. annua was seeded in different substrates: gravel and zeolite, alone and mixed at different percentage.For each metal three different levels of contamination were chosen, for As 0.25, 0.5 and 5 mg L^?1, for Hg 0.1, 0.2 and 2 mg L^?1. No substantial difference in metal absorption among plant samples watered with different As and Hg concentrations, was observed during the testing phase.Nevertheless, results show that concentrations of As and Hg accumulated in P. annua increase with the increasing contamination exposure.     

Nitrogen deprivation induces cross-tolerance of Poa annua callus to salt stress

Alternative respiration pathway (AP) is an important pathway which can be induced by environment stresses in plants. In the present study, we show a new mechanism involving the AP in nitrogen deprivation-induced tolerance of Poa annua callus to salt stress. The AP capacity markedly increased under a 600 mM NaCl treatment or nitrogen deprivation pretreatment and reached a maximum under the nitrogen deprivation pretreatment combined with the NaCl treatment (–N+NaCl). Malondialdehyde (MDA) and H₂O₂ content and Na⁺/K⁺ ratio significantly increased under the 600 mM NaCl treatment but less under the–N+NaCl treatment. Moreover, both the nitrogen deprivation and the NaCl stress stimulated the plasma membrane (PM) H⁺-ATPase activity and increased pyruvate content. The maximal stimulating effect was found under the–N+NaCl treatment. When the AP capacity was reduced by salicylhydroxamic acid (SHAM, an inhibitor of AP), content of MDA and H₂O₂ and Na⁺/K⁺ ratio dramatically increased, whereas PM H⁺-ATPase activity decreased. Moreover, exogenous application of pyruvate produced a similar effect as the nitrogen deprivation pretreatment. The effects of SHAM on the Poa annua callus were counteracted by catalase (a H₂O₂ scavenger) and diphenylene iodonium (a plasma membrane NADPH oxidase inhibitor). Taken together, our results suggest that the nitrogen deprivation enhanced the capacity of AP by increasing pyruvate content, which in turn prevented the Poa annua callus from salt-induced oxidative damages and Na⁺ over-uptake.     

Metabolic engineering of artemisinin biosynthesis in Artemisia annua L.

Artemisinin, a sesquiterpene lactone isolated from the Chinese medicinal plant Artemisia annua L., is an effective antimalarial agent, especially for multi-drug resistant and cerebral malaria. To date, A. annua is still the only commercial source of artemisinin. The low concentration of artemisinin in A. annua, ranging from 0.01 to 0.8% of the plant dry weight, makes artemisinin relatively expensive and difficult to meet the demand of over 100 million courses of artemisinin-based combinational therapies per year. Since the chemical synthesis of artemisinin is not commercially feasible at present, another promising approach to reduce the price of artemisinin-based antimalarial drugs is metabolic engineering of the plant to obtain a higher content of artemisinin in transgenic plants. In the past decade, we have established an Agrobacterium-mediated transformation system of A. annua, and have successfully transferred a number of genes related to artemisinin biosynthesis into the plant. The various aspects of these efforts are discussed in this review.     

Optimization of cryopreservation of Artemisia annua L. callus

Cryopreservation of callus tissue of Artimisia annua L. was optimized. Two lines of calli were precultured on MS medium with 5% (v/v) dimethyl sulfoxide, and protected by a cryoprotectant containing 15% (v/v) ethylene glycol, 15% (v/v) dimethyl sulfoxide, 30% (v/v) glycerol and 13.6% (w/v) sucrose. The highest survival rate of callus A201 reached 87% after it was pretreated at 25°C, cryopreserved by liquid nitrogen, recovered in water bath at 25°C and reloaded at 25°C with 34% (w/v) sucrose solution, and that of callus A202 reached 78% after it was treated as callus A201, except pretreated at 35°C, recovered at 35°C and reloaded with 47.8% (w/v) sucrose solution.     

Artemisia annua L.: dedifferentiated and differentiated cultures

Dedifferentiated and differentiated tissue cultures ofArtemisia annua L. for artemisinin production were carried out. The calluses were initiated on MS medium supplemented with sucrose (30 g l^-1), myoinositol (100 mg l^-1) and RT vitamins. The auxins used were naphtaleneacetic acid (NAA), indoleacetic acid (IAA), indolebutyric acid (IBA) and 2,4-dichlorophenoxyacetic acid (2,4-d). These were added to the basal medium either singly or in combination. The best results were obtained with 2.4-d (4.5 M : 0.02 d^-1) and NAA (5.4 M : 0.06 d^-1). Cell suspensions were established on the same media without agar. Suspension cultures showed different morphological characteristics according to the plant growth regulator supplied. Organized cultures were initiated from callus obtained on 2,4-d (4.5 M) and from bud cultures. Medium containing 6-benzylaminepurine (BA) (8.9 M)+NAA (0.54 M); Zeatin (45.62 M)+NAA (5.37 M) or BA (8.9 M) stimulated both organogenesis in callus (frequency of induction =50%) and semi-organized tissue in shoot buds. BA (13.32 M)+NAA (1.08 M) or BA (13.32 M) only stimulated multiple shoot cultures (frequency of induction =80%). Regarding artemisinin content, while the values obtained were 1.13 and 0.78 mg gDW^-1 in primary callus, artemisinin was not detected in cell suspension and only traces of it were found in multiple shoot cultures.     

Transgenic approach to increase artemisinin content in Artemisia annua L.

Artemisinin, the endoperoxide sesquiterpene lactone, is an effective antimalarial drug isolated from the Chinese medicinal plant Artemisia annua L. Due to its effectiveness against multi-drug-resistant cerebral malaria, it becomes the essential components of the artemisinin-based combination therapies which are recommended by the World Health Organization as the preferred choice for malaria tropica treatments. To date, plant A. annua is still the main commercial source of artemisinin. Although semi-synthesis of artemisinin via artemisinic acid in yeast is feasible at present, another promising approach to reduce the price of artemisinin is using plant metabolic engineering to obtain a higher content of artemisinin in transgenic plants. In the past years, an Agrobacterium-mediated transformation system of A. annua has been established by which a number of genes related to artemisinin biosynthesis have been successfully transferred into A. annua plants. In this review, the progress on increasing artemisinin content in A. annua by transgenic approach and its future prospect are summarized and discussed.     

青蒿组织培养及其快速繁殖研究

以青蒿幼叶、叶柄为外植体,研究其离体培养和试管苗再生途径。结果表明,以青蒿嫩叶为外植体,在MS+6-BA0.5mg/L+IBA0.5mg/L的培养基中可诱导出愈伤组织,诱导率达87%,并在此培养基中可以分化出芽,分化率为85%,将分化苗转移到MS+IBA0.5mg/L的培养基上,生根率高达93%。     

反相高效液相色谱法测定青蒿中青蒿酸的含量

本文建立了反相高效液相色谱快速测定青蒿中青蒿酸含量的方法。色谱条件为:Diamonsil C18色谱柱(250 mm×4.6 mm,5μm),柱温为(30±1)℃,流动相采用乙腈与0.2%磷酸水溶液混合液(体积比65:35),流速1 mL/min,检测波长220 nm。标准曲线回归方程:Y=8.784573×10-8X-6.443559×10-5,r=0.9997,青蒿酸回收率为102.4%。实验证明该方法稳定可靠、精密度高、重现性好、简单可行,适用于青蒿酸的分析检测。