Mycological studies on the angiosperm root parasiteCynomorium coccineum L. and two of its halophytic hosts

The fungal colonization of the angiosperm root parasiteCynomorium coccineum and the halophytic hostsLimonium delicatulum andArthrocnemum glaucum were investigated in a Mediterranean salt marsh in March 1992. The main fungal inhabitants on the leaves or shoot surface of the test plants wereAspergillus niger, Penicillium chrysogenum andCladosporium herbarum. The qualitative analysis of the fungal species associating the parasite, the hosts and the non-infected plants showed similar pattern. However, the total population exhibited quantitative differences coupled with the amount and the chemical composition of the exudates on plant surface and the quantity of transpired water. The fungal catch from the aerial shoot (inflorescence) of the parasite was higher than that collected from either the leaves or aerial shoots of non-infected or host plants. The fungal density on the leaves ofL. delicatulum was higher than those isolated from the aerial shoots ofA. glaucum. Infection byC. coccineum caused a marked drop in the total fungal population on leaves or shoot surfaces of the hosts as compared to the corresponding non-infected individuals. The stimulative effect of washings on spore germination of some isolated fungal species was matched with the density of fungi on the target plants.     

Bimodal karyotype in Cynomorium coccineum L. and its systematic implications

The presence of a bimodal karyotype in Cynomorium coccineum (2n = 28) is used to support its separation from Balanophoraceae and the maintenance of Cynomoriaceae as a separate family.     

Competitiveness and dry matter allocation of oilseed rape (Brassica napus L.) and two mustards (Sinapis alba L. and S. arvensis L.) under water stress conditions

In Morocco, oilseed rape is commonly exposed to mustards competition which are not totally controlled by herbicides. To understand the competitiveness of each species, growth parameters should be studied notably dry matter allocation. The objective of this study was to confirm the competitiveness of oilseed rape with regard to Sinapis alba and S. arvensis and to investigate how the dry matter is allocated. A pot experiment was undertaken with a quartz sand as substrate. Two plant densities were tested (one and two plants). The binary density was either a monoculture or a mixture. Half the pots were maintained at field moisture capacity and the other half was irrigated up to 70% of its water holding capacity. Dry matter allocation of each species at density two was compared to that of the same species at density one. Results of replacement series diagrams and those of the relative crowding coefficient (based on total dry matter) showed that Brassica napus was more competitive than S. alba. S. arvensis was the least competitive. Under competition, B. napus irrigated at water holding capacity allocated more dry matter to stem when compared to its dry matter at density one. Under the same condition, when reducing water supply, B. napus allocated more dry matter to leaves. In case of S. alba, dry matter percent in leaves and roots were respectively low and high in normally irrigated plant and inversely under water shortage. S. arvensis allocated high and low dry matter percent respectively to root than to leaves when sufficiently irrigated. But no clear tendency was noticed under water shortage, for this species.     

Collection and composition of xylem sap and root structure in two halophytic species

Leptochloa fusca (L.) Kunth and Atriplex hortensis (L.) were grown on quartz sand or in liquid culture in the presence of varied concentrations of NaCl. Xylem sap was collected as (a) root pressure exudate, in L. fusca even at 100 mM NaCl, (b) by applying pressure to excised roots of L. fusca and (c) from leaves of the whole plant growing in quartz sand by pressurizing the root system. The latter procedure failed in L. fusca due to the passage of air and soil solution into the leaves. This was caused by an extensive aerenchyma in root cortex. In Atriplex hortensis remarkably high pressures were required to induce a flow of sap. The mineral cation and anion and the amino acid composition of the xylem sap obtained by the different methods was measured and is examined in view of using it for determining the flows of minerals in the whole plant and in relation to the effects of salinity. The spacious aerenchyma in roots of L. fusca has been found to persist also after prolonged exposure to dry air.Presented at the Fourth International Symposium on Structure and Function of Roots, Starà lesna, Slovak Republic. See also PLSO 167/1 (1994).     

Effects of nitrogen on leaves,dry matter allocation and regrowth dynamics in Trifolium repens L. and Lolium perenne L. in pure and mixed swards

The effects of applied nitrogen (N) on dynamics of regrowth, dry matter (DM) allocation and leaf characteristics of grass and clover were investigated. Binary mixtures and monocultures of the diploid perennial ryegrass cultivars Barlet (erect) and Heraut (prostrate) and the white clovers cvs. Alice (large-leaved) and Gwenda (small-leaved) were established in a field experiment. Grass monocultures received three levels of N application (0, 140 or 280 kg N ha^–1), and mixtures 150 kg N ha^–1 (+N) or no N (–N). N was applied split over the season. Application of N reduced the average clover content in the DM of the mixtures from 43 to 12%. Due to defoliation, clover lost relatively more leaf area and less DM than grass, leading to a lower clover fraction in the leaf area index (LAI) of the stubble at the start of the next regrowth. In the –N mixtures, the clover fraction of the biomass and of the LAI increased within successive regrowth periods. In the +N mixtures, large-leaved Alice maintained its content during summer, mainly due to its greater petiole length which increased in response to N. The opposite was observed for Gwenda. At each harvest, the content of small-leaved Gwenda in the LAI and DM was lower than in the stubble at the start of regrowth. The allocation of DM to the petioles of Alice led to a decrease in the leaf weight ratio (LWR) in the +N mixtures, while Gwenda had a higher LWR and specific leaf area (SLA) in the +N mixtures than in the –N mixtures. There was little or no effect of ryegrass cultivar on competition with white clover.     

Ion channels in the plasma membrane of protoplasts from the halophytic angiosperm Zostera muelleri

Patch clamp studies show that there may be as many as seven different channel types in the plasma membrane of protoplasts derived from young leaves of the halophytic angiosperm Zostera muelleri. In whole-cell preparations, both outward and inward rectifying currents that activate in a timeand voltage-dependent manner are observed as the membrane is either depolarized or hyperpolarized. Current voltage plots of the tail currents indicate that both currents are carried by K⁺. The channels responsible for the outward currents have a unit conductance of approximately 70 pS and are five times more permeable to K⁺ than to Na⁺. In outside-out patches we have identified a stretch-activated channel with a conductance of 100 pS and a channel that inwardly rectifies with a conductance of 6 pS. The reversal potentials of these channels indicate a significant permeability to K⁺. In addition, the plasma membrane contains a much larger K⁺ channel with a conductance of 300 pS. Single channel recordings also indicate the existence of two Cl^– channels, with conductances of 20 and 80 pS with distinct substates. The membrane potential difference of perfused protoplasts showed rapid action potentials of up to 50 mV from the resting level. The frequency of these action potentials increased as the external osmolarity was decreased. The action potentials disappeared with the addition of Gd³⁺, an effect that is reversible upon washout.We would like to thank K. Morris and D. McKenzie for technical assistance and the Australian Research Council for financial support.     

Growth and root dry matter allocation by pasture legumes and a grass with contrasting external critical phosphorus requirements

Background and aims

This work aimed to quantify the critical external requirement for phosphorus (P) (i.e. extractable-P concentration required for 90 % of maximum yield) for a number of temperate legume species and understand differences in dry matter allocation, P distribution and P acquisition efficiency among these species.

Methods

Shoot and root growth of five legume and one grass species was assessed in response to six rates of P mixed into the top 45 mm of soil in a pot experiment. Dactylis glomerata and Trifolium subterraneum were used as benchmark species; they are commonly grown together in mixed temperate pastures and have low and high critical external requirements for P, respectively. Growth was compared with four alternative legume species: Ornithopus compressus, Ornithopus sativus, Biserrula pelecinus and Trifolium hirtum, that have root morphologies better suited to soil exploration and nutrient acquisition than that of Trifolium subterraneum.

Results

Dactylis glomerata, Ornithopus compressus and Ornithopus sativus had maximum yields equal to or greater than Trifolium subterraneum but achieved this at rates of P less than half that of Trifolium subterraneum. Biserrula pelecinus and Trifolium hirtum had critical P requirements between that of Trifolium subterraneum and the Ornithopus species, but also had lower yields. Root dry matter of Dactylis glomerata and the Ornithopus species in the fertilised soil layer was only marginally changed in response to low P supply. In contrast, Trifolium subterraneum, Trifolium hirtum and to a lesser extent Biserrula pelecinus markedly increased root dry matter allocation to this soil layer. Species with lower critical P requirements were able to take up more P per unit root dry mass than those with higher critical P requirements, particularly at lower levels of P addition.

Conclusions

The high P acquisition efficiencies of the Ornithopus species and Dactylis glomerata were likely to have contributed to their low critical external P requirements. It was surmised that differences in root morphology traits underpin the differences in acclimation to low P stress and P acquisition efficiency among the species.

     

Sink development and dry matter distribution in storage root crops

Events during early development are examined for their contribution to dry matter distribution in the mature plant. It is concluded that timing of initiation of the storage root is not a major cause of differences between cultivars of carrot. These may airse from differences in the control of partitioning of assimilate at storage organ initiation. Root crop species may be affected differently by environmental factors such as density as a result of different thresholds of response of sink development to source stimuli.     

The parasitic angiosperm Striga hermonthica can reduce photosynthesis of its sorghum and maize hosts in the field

Two cultivars of sorghum (CK60 and Ochuti) and one cultivarof maize (H511) were grown in field plots in western Kenya inthe presence or absence of the parasitic angiosperm Striga hermonthica,with or without a single addition of nitrogen fertilizer (150kg N ha^–1) using a factorial design. A progressive declinein rates of photosynthesis of Striga-infected plants were observedfor the sorghum cultivar CK60 from 30 d after planting (DAP)and for maize from 40 DAP, until measurements ended 63 DAP.At this time photosynthetic rates were 46% and 31% lower inthe Striga-infected sorghum and maize cultivars, respectively,compared to uninfected control plants. No decline in photosynthesiswas observed in the second sorghum cultivar studied, Ochuti,a local land race reported to show some tolerance to the parasite.The trends in photosynthesis reflected stunting of the cereals,as determined by the height of the youngest emerged ligule,however, only the grain yield of the sorghum cultivar CK60 wassignificantly reduced by the presence of the parasite. The nitrogenapplication influenced neither the growth nor the photosyntheticparameters measured, and possible explanations for the absenceof responses are discussed. It is concluded that S. hermonthicacan reduce photosynthetic rates of field-grown sorghum and maize,and suggest that an ability to maintain high rates of photosynthesiswhilst infected may be an important correlate of tolerance tothe parasite. Key words: Parasitic angiosperm, photosynthesis, nitrogen, tropical weeds, tropical agriculture     

Physiology of the interaction of angiosperm parasites and their higher plant hosts

Abstract. Interactions between parasitic angiosperms and their hosts occur at the level of seed germination, haustorial development and resource transfer. Chemicals released from the host function as cues for host recognition, and trigger germination as well as haustorial initiation. Transpiration is a key process regulating solute transfer from host to parasite, and some parasitie plants have unusual stomatal characteristics. Although solute transfer is apoplastic, the haustorium appears to play a role in regulating solute composition. Host responses to infection are reviewed, and it is concluded that competition for water and solutes are unlikely to play a major role in determining reductions in host productivity: metabolic incompatability is suggested to be the major cause of this.     

Early growth,dry matter allocation and water use efficiency of two sympatric Populus species as affected by water stress

We exposed cuttings of two sympatric species of Sect. Tacamahaca Spach, Populus cathayana Rehder and Populus przewalskii Maximowicz, to two watering regimes in a greenhouse. In the semi-controlled environmental study, two watering treatments which were watered to 100 and 25% of field capacity were used, respectively. The effects of water deficit on early growth, biomass allocation and water use efficiency (WUE) were investigated. We found that there were significant interspecific differences in early growth, dry matter allocation and water use efficiency between two sympatric Populus species. Compared with P. cathayana, P. przewalskii showed higher shoot height, dry matter accumulation, number of leaves, total leaf area, fine root mass, fine root/total root ratio and water use efficiency under both well-watered and water-stressed treatments. On the other hand, P. przewalskii also showed higher root mass/foliage area ratio, root/shoot ratio and carbon isotope composition than P. cathayana under water-stressed treatment. The results suggested that there were different water-use strategies between two sympatric Populus species, P. przewalskii with higher drought tolerance may employ a conservative water-use strategy, whereas P. cathayana with lower drought tolerance may employ a prodigal water-use strategy. The findings confirm the existence of interspecific genetic differences in early growth, dry matter allocation and water use efficiency as affected by water stress, these variations in drought responses may be used as criteria for species selection and tree improvement.     

Micro-Nutrient Deficiency and Transpiration in Tropaeolum majus L.

The transpiration of Tropaeolum plants, grown in water culture,on full nutrient solutions and on solutions deficient in oneof the following, i.e. boron, copper, manganese, and zinc, wasstudied. The transpiration rate of the control plants grownon the full nutrient solution was significantly higher thanthat of the deficient ones. The more acute the deficiency, thegreater was the disparity. Under the condition of the experiment, the control plants weresmaller in size, having fewer and smaller leaves than the deficientones, but the foliage was much greener and healthier in appearance.     

Biochemical aspects of parasitism by the angiosperm parasites I. Phosphate fractions in the leaves of loranthus and hosts

The leaves of Dendrophthoe falcata growing on different trees had differing dry solid content. With 1 exception, the parasite leaf contained less dry solid than host leaf.

A characteristic feature of the loranthus parasite was the accumulation of phosphate in excess of that present in host leaves. Expressed as percent of the total phosphorus, the parasite tissue contained significantly less acid-insoluble phosphate than the host leaves. When the acid-insoluble material was fractionated into phospholipid, RNA, DNA and phosphoprotein, every component was found to be present in a smaller amount in parasite than in host leaf, expressed as percent of total phosphate in leaves.

A comparative study of the phosphate fractions in the infected and uninfected branch of infected host tree revealed that, without exception, there was a demonstrable increase in the DNA content of the infected branch.

     

Light-dependent conversion of carotenoids in the parasitic angiosperm Cuscuta reflexa L.

The parasitic angiosperm Cuscuta reflexa contains unusually high amounts of the carotenoids lutein-5,6-epoxide and 9- cis -violaxanthin. In this study the light-dependent conversions of these carotenoids in entire plant tissue and purified LHCII b was compared with that of the xanthophyll cycle carotenoid violaxanthin when plants are exposed to high irradiance followed by low irradiance. In entire tissue under high irradiance, similar conversion kinetics and stoichiometry with de-epoxidation products suggest that both lutein-5,6-epoxide and all- trans -violaxanthin are equally suitable substrates for de-epoxidase. This is not the case under low irradiance as, although epoxidation of zeaxanthin and antheraxanthin rapidly restores the violaxanthin pool, the recovery of the lutein-5,6-epoxide pool is comparatively slow and has no stoichiometric relationship with its de-epoxidation product, lutein. Light-dependent changes in the concentration of 9- cis -violaxanthin mimic violaxanthin. However, the inability to detect de-epoxidation products or to de-epoxidize 9- cis -violaxanthin in vitro suggests that it is not subject to de-epoxidation and, instead, its concentration changes may reflect the equilibrium between isomers of violaxanthin. Light exposure did not affect the composition of carotenoids bound to purified LHCII b , indicating that these bound carotenoids are not subject to de-epoxidation and do not contribute to the isomer pool equilibrium. The biosynthetic origins of lutein-5,6-epoxide and the potential role of these carotenoid cycles in photoprotection are discussed.     

不同施肥配比对麦冬幼苗光合特性及干物质分配的影响

运用L9(33)正交实验设计、采用盆栽法研究了不同浓度N(15、30和45 mmol·L-1)、P(1、3和5 mmol·L-1)和K(6、12和24 mmol·L-1)配施对麦冬〔Ophiopogon japonicus (Linn. f.) Ker-Gawl.〕幼苗光合特性和干物质分配的影响。结果表明：N肥对麦冬幼苗叶片光合特性的影响最大,其中对叶绿素a含量、净光合速率、气孔导度、胞间CO2浓度和蒸腾速率的影响均达到显著水平,以45 mmol·L-1 N的促进作用最为明显;P肥对麦冬幼苗叶片光合参数均无显著影响;K肥仅对麦冬幼苗叶片类胡萝卜素含量有显著影响,以12 mmol·L-1 K处理组类胡萝卜素含量为最高。 N肥对麦冬幼苗地上部分和地下部分含水量的影响较大,K肥对二者的影响次之,P肥的影响较小。 N肥对麦冬幼苗地上部分和地下部分干物质分配指数以及根冠比的影响较大,P肥和K肥的影响较小。综合分析结果表明：45 mmol·L-1 N、1 mmol·L-1 P和12 mmol·L-1 K配施条件下麦冬幼苗叶片光合色素含量和植株含水量均较高,45 mmol·L-1 N、3 mmol·L-1 P和6 mmol·L-1 K配施条件下麦冬幼苗叶片光合参数较高,30 mmol·L-1 N、5 mmol·L-1 P和6 mmol·L-1 K配施条件下麦冬幼苗地下部分干物质分配比例较高。在麦冬的不同种植阶段可据此合理配施肥料以达到增加产量和提高品质的目的。     

Short-term accumulation of organic matter and nutrient contents in two dry sand ecosystems

Inland dunes in northwestern Europe support a number of dry vegetation types. These ecosystems are poor in nutrients and it has been suggested that accumulation of nutrients triggers succession in such systems.We studied the accumulation of organic matter and N and P over a 30 months period in two adjacent ecosystems, the Spergulo-Corynephoretum and the Genisto-Callunetum. Amounts of plant matter and soil organic matter significantly accumulated during the sampling period in the Genisto-Callunetum but not in the Spergulo-Corynephoretum. While nutrient concentrations of live and dead phytomass in the Spergulo-Corynephoretum were significantly higher than in the Genisto-Callunetum, total nutrient contents in the systems showed the opposite pattern. N and P concentrations in litter were relatively high compared with the other fractions of plant matter and the amount of N significantly increased in both ecosystems during the sampling period. Soil moisture contents showed a seasonal pattern. It was highest in the top soil layer and higher in the Genisto-Callunetum than in the Spergulo-Corynephoretum.The estimated annual increase of total N in these two ecosystems was consistent with rates of atmospheric N deposition (wet fall + dry fall) measured in comparable Dutch sites.