The contribution of roots and shoots to whole plant nitrate reduction in fast- and slow-growing grass species

The hypothesis was tested that slow-growing grass species perform a greater proportion of total plant NO3- reduction in their roots than do fast-growing grasses. Eight grass species were selected that differed in maximum relative growth rate (RGR) and net NO3- uptake rate (NNUR). Plants were grown with free access to nutrients in hydroponics under controlled-environment conditions. The site of in vivo NO3- reduction was assessed by combining in vivo NO3- reductase activity (NRA) assays with biomass allocation data, and by analysing the NO3- to amino acid ratio of xylem sap. In vivo NRA of roots and shoots increased significantly with increasing NNUR and RGR. The proportion of total plant NO3- reduction that occurs in roots was found to be independent of RGR and NNUR, with the shoot being the predominant site of NO3- reduction in all species. The theoretical maximum proportion of whole plant nitrogen assimilation that could take place in the roots was calculated using information on root respiration rates, RGR, NNUR, and specific respiratory costs associated with growth, maintenance and ion uptake. The calculated maximum proportion that the roots can contribute to total plant NO3- reduction was 0.37 and 0.23 for the fast-growing Dactylis glomerata L. and the slow-growing Festuca ovina L., respectively. These results indicate that slow-growing grass species perform a similar proportion of total plant NO3- reduction in their roots to that exhibited by fast-growing grasses. Shoots appear to be the predominant site of whole plant NO3- reduction in both fast- and slow-growing grasses when plants are grown with free access to nutrients.     

Why do fast- and slow-growing grass species differ so little in their rate of root respiration,considering the large differences in rate of growth and ion uptake?

Herbaceous plants grown with free access to nutrients exhibit inherent differences in maximum relative growth rate (RGR) and rate of nutrient uptake. Measured rates of root respiration are higher in fast-growing species than in slow-growing ones. Fast-growing herbaceous species, however, exhibit lower rates of respiration than would be expected from their high rates of growth and nitrate uptake. We investigated why the difference in root O₂ uptake between fast- and slow-growing species is relatively small. Inhibition of respiration by the build-up of CO₂ in closed cuvettes, diurnal variation in respiration rates or an increasing ratio of respiratory CO₂ release to O₂ uptake (RQ) with increasing RGR failed to explain the relatively low root respiration rates in fast-growing grasses. Furthermore, differences in alternative pathway activity can at most only partly explain why the difference in root respiration between fast- and slow-growing grasses is relatively small. Although specific respiratory costs for maintenance of biomass are slightly higher in the fast-growing Dactylis glomerata L. than those in the slow-growing Festuca ovina L., they account for 50% of total root respiration in both species. The specific respiratory costs for ion uptake in the fast-growing grass are one-third of those in the slow-growing grass [0·41 versus 1·22 mol O₂ mol (NO₃^–)^–1]. We conclude that this is the major cause of the relatively low rates of root respiration in fast-growing grasses.     

Relatively large nitrate efflux can account for the high specific respiratory costs for nitrate transport in slow-growing grass species

In this paper we address the question why slow-growing grass species appear to take up nitrate with greater respiratory costs than do fast-growing grasses when all plants are grown with free access to nutrients. Specific costs for nitrate transport, expressed as moles of ATP per net mole of nitrate taken up, were 1.5 to 4 times higher in slow-growing grasses than in fast-growing ones (Scheurwater et al., 1998, Plant, Cell & Environ. 21, 995–1005). The net rate of nitrate uptake is determined by two opposing nitrate fluxes across the plasma membrane: influx and efflux. To test whether differences in specific costs for nitrate transport are due to differences in the ratio of nitrate influx to net rate of nitrate uptake, nitrate influx and the net rate of nitrate uptake were measured in the roots of two fast-growing ( Dactylis glomerata L. and Holcus lanatus L.) and two slow-growing (Deschampsia flexuosa L. and Festuca ovina L.) grass species at four points during the diurnal cycle, using ¹⁵NO₃ ^-. Efflux was calculated by subtraction of net uptake from influx; it was assumed that efflux of nitrogen represents the flux of nitrate. Transfer of the plants to the solution containing the labelled nitrate did not significantly affect nitrate uptake in the present grass species. The net rate of nitrate uptake was highest during the middle of the light period in all species. Diurnal variation in the net rate of nitrate uptake was mostly due to variation in nitrate influx. Variation in nitrate efflux did not occur in all species, but efflux per net mole of nitrate taken up was higher during darkness than in the light in the slow-growing grasses. The two fast-growing species, however, did not show diurnal variation in the ratio of efflux to net nitrate uptake. Integrated over 24 hours, the slow-growing grasses clearly exhibited higher ratios of influx to net uptake than the fast-growing grass species. Our results indicate that the higher ratio of nitrate influx to net nitrate uptake can account for higher specific costs for nitrate transport in slow-growing grass species compared with those in their fast-growing counterparts, possibly in combination with greater activity of the non-phosphorylating alternative respiratory path. Therefore, under our experimental conditions with plants grown at a non-limiting nitrate supply, nitrate uptake is less efficient (from the point of ATP consumption) in slow-growing grasses than in fast-growing grass species. This revised version was published online in June 2006 with corrections to the Cover Date.     

Respiratory energy requirements of roots vary with the potential growth rate of a plant species

The rates of growth, net rate of nitrate uptake and root respiration of 24 wild species were compared under conditions of optimum nutrient supply. The relative growth rate (RGR)of the roots of these species varied between 110 and 370 mg g^-1 day^-1 and the net rate of nitrate uptake between 1 and 7 mmol (g root dry weight)^-1 day^-1. The rate of root respiration was positively correlated with the RGR of the roots. Root respiration was also calculated from the measured rate of growth and nitrate uptake, using previously determined values for the costs of maintenance, growth and ion uptake of two slow-growing species. The calculated rate of respiration was slightly lower than the measured one for slow-growing species, but twice as high as measured rates for rapid-growing species. This discrepancy was not due to a relatively smaller electron flow through the alternative pathway and, consequently, a more efficient ATP production in the fast-growing species. Neither could variation in specific costs for root growth or maintenance explain these differences. Therefore, we conclude that fast-growing species have lower specific respiratory costs for ion uptake than slow-growing ones. Due partly to these lower specific costs of nutrient uptake, the fraction of respiration that rapid-growing species spend on anion uptake is lower than that of slow-growing species, in spite of the much higher rate of ion uptake of the fast-growing ones.     

Endophytic fungi in wild and cultivated grasses in Finland

We examined the occurrence of vertically via host seeds transmitted endophyte infections of 14 grass species in natural populations in Finland and totally 97 agricultural cultivars of 13 grass species. Although endophyte infections were widespread in native grass species, overall endophyte occurrence and frequencies were lower than published reports have suggested. In natural populations, 10 out of 14 grass species examined harbor fungal endophytes in their seeds. The highest species-specific mean incidences of endophyte infected plants in infected populations were found in Agrostis capillaris. Festuca arundinacea. F. ovina. F. Pratensis. F. rubra and Phleum pratense (67%, 98%, 29%., 42%. 32% and 33%, respectively). Mean incidences were < 20% in Dactylis glomerata. Deschampsia flexuosa. D. cespitosa and Elymus repens. and no infections were detected in Calamagrostis lapponica. C. epigejos. Alopecurus pratensis and Phalaris arundinacea. However, we detected a very high variation in infection incidences among natural populations and a large proportion of populations was, indeed, endophyte-free. This supports the ideas that 1) endophytic fungi provide selective advantage of infected grasses to their uninfected eonspecifics in some habitats, and/or 2) fungi are occasionally transmitted horizontally by spores. In grass cultivars, endophyte infected seeds were detected only in F. Pratensis and Lolium perenne. and endophyte frequencies were either very high or very low. Cultivars of 11 other grass species were endophyte-free.     

Respiratory energy costs for the maintenance of biomass, for growth and for ion uptake in roots of Carex diandra and Carex acudformis

van der Werf, A., Kooijman, A., Welschen, R. and Lambers, H. 1988. Respiratory energy costs for the maintenance of biomass, for growth and for ion uptake in roots of Carex diandra and Carex acutiformis. - Physiol. Plant. 72: 483–491. The respiratory characteristics of the roots of Carex diandra Schrank and Carex acutiformis Ehrh. were investigated. The aims were, firstly to determine the respiratory energy costs for the maintenance of root biomass, for root growth and for ion uptake, and secondly to explain the higher rate of root respiration and ATP production in C. diandra. The three respiratory energy components were derived from a multiple regression analysis, using the relative growth rate and the net rate of nitrate uptake as independent variables and the rate of ATP production as a dependent variable. Although the rate of root respiration and ATP production was significantly higher in C. diandra than in C. acutiformis, the two species showed no significant difference in their rate of ATP production for the maintenance of biomass, in the respiratory energy coefficient for growth (the amount of ATP production per unit of biomass produced) and the respiratory energy coefficient for ion uptake (amount of ATP production per unit of ions absorbed). It is concluded that the higher rate of root respiration of C. diandra is caused by a higher rate of nitrate uptake. At relatively high rates of growth and nitrate uptake, the contribution of the rate of ATP production for ion uptake to the total rate of ATP production amounted to 38 and 25% for C. diandra and C. acutiformis, respectively. At this growth rate, the respiratory energy production for growth contributed 37 and 50%, respectively, to the total rate of ATP production. The relative contribution of the rate of ATP production for the maintenance of biomass increased from 25 to 70% with increasing plant age for both species. The results suggest that ion uptake is one of the major sinks for respiratory energy in roots. These experimentally derived values for the rate of ATP production for the maintenance of biomass, the respiratory energy coefficient for growth and the respiratory energy coefficient for ion uptake are discussed in relation to other experimentally and theoretically derived values.     

Estimation of the turnover number of bovine heart F0F1 complexes for ATP synthesis

In mitochondria and submitochondrial particles (SMP), the rate of ATP synthesis is restricted by the rate of energy production by the respiratory chain. Fractional inactivation of the ATP synthase complexes (F0F1) of bovine heart SMP by covalent modifiers increased the rate of ATP synthesis per mole of active F0F1. Thus, by use of SMP containing fractionally inactivated F0F1 complexes, a synthetic rate of 420 mol of ATP (mol of F0F1.s)-1 was measured, which extrapolated to a Vmax of 440 s-1. At this extrapolated point, the turnover rate of F0F1 complexes was independent of the rate of energy production by the respiratory chain. These results have been discussed in relation to the effect of fractional inactivation of the F0F1 complexes of SMP on the steady-state free energy of the system. The above rate of ATP synthesis is comparable to the rate of ATP hydrolysis by SMP (400-520 s-1) in the absence of energy coupling constraints and control by the ATPase inhibitor protein. More interestingly, this rate is also comparable to the rate of ATP synthesis by chloroplast F0F1 under high light intensity (approximately 420 s-1). Under the conditions specified, bovine heart SMP and chloroplasts show similar apparent Km values for ADP. Thus, it appears that the mammalian and chloroplast ATP synthase complexes are similar not only in structure but also in catalytic efficiency for ATP synthesis.     

Na2SO4胁迫对四种抗盐性不同牧草膜脂过氧化和活性氧清除系统的影响

 经过1%和2%的Na2SO4胁迫后,草原绢蒿,圆叶蒿,苇状羊茅和鸭茅4种牧草的膜脂过氧化程度和质膜的透性都增加,但抗盐性较强的草原绢蒿和苇状羊茅的膜脂过氧化程度及质膜透性分别低于同科中抗盐性较差的圆叶蒿和鸭茅。随着Na2SO4胁迫浓度的增加,两种禾本科牧草的超氧化物歧化酶(SOD)及过氧化氢酶(CAT)的活性逐渐升高,两种菊科牧草的SOD及CAT的活性却逐渐下降,但禾本科中抗盐性较强的苇状羊茅的SOD及CAT活性的增长率要大于抗盐性较差的鸭茅,菊科中抗盐性较强的草原绢蒿的SOD及CAT活性的下降率要小于抗盐性较差的圆叶蒿。在Na2SO4胁迫下,两种抗盐性较强牧草的类胡萝卜素的相对含量要分别高于同科中抗盐性较差的牧草。     

Effects of host plant drought stress on the performance of the bird cherry-oat aphid, Rhopalosiphum padi (L.): a mechanistic analysis

Abstract.  1. The growth (increase in height and leaf number) of four grass species was reduced by a −0.5 MPa drought stress, but the performance of an associated herbivore, Rhopalosiphum padi (L.), was not affected consistently. The intrinsic rate of increase of R. padi was reduced by drought stress on three grass species, including Dactylis glomerata (L.), but was unaffected on Arrhenatherum elatius (L.). Therefore, there is no general relationship in the effect of plant drought on an insect herbivore, even among closely related host plant species.
2. Drought stress increased the quality of plant phloem sap, as indicated by increased sieve element osmotic pressure and essential amino acid concentrations. Thus, diet quality could not account for the reduced performance of R. padi under drought stress. The concentration of essential amino acids in the phloem of well-watered A. elatius was, however, lower than that of well-watered D. glomerata , correlating with the decreased performance of aphids on well-watered A. elatius .
3. There were no differences in aphid feeding duration between watering treatments or plant species but sap ingestion rates were reduced significantly under drought stress.
4. Using the measure of dietary amino acid concentrations and the estimate of sap ingestion, the essential amino acid flux through aphids was calculated. Compared with the flux through aphids feeding on well-watered D. glomerata , there was a reduction in aphids feeding on drought-stressed D. glomerata and drought-stressed A. elatius due to lower sap ingestion rates. The flux through aphids on well-watered A. elatius was also reduced due to low phloem essential amino acid concentrations. Thus, the performance of an aphid is correlated with the availability and accessibility of essential amino acids.     

Root respiratory characteristics associated with plant adaptation to high soil temperature for geothermal and turf-type Agrostis species

Respiration is a major avenue of carbohydrates loss. The objective of the present study was to examine root respiratory characteristics associated with root tolerance to high soil temperature for two Agrostis species: thermal Agrostis scabra, a species adapted to high-temperature soils in geothermal areas in Yellowstone National Park, and two cultivars ('L-93' and 'Penncross') of a cool-season turfgrass species, A. stolonifera (creeping bentgrass), that differ in their heat sensitivity. Roots of thermal A. scabra and both creeping bentgrass cultivars were exposed to high (37 degrees C) or low soil temperature (20 degrees C). Total root respiration rate and specific respiratory costs for maintenance and ion uptake increased with increasing soil temperatures in both species. The increases in root respiratory rate and costs for maintenance and ion uptake were less pronounced for A. scabra than for both creeping bentgrass cultivars (e.g. respiration rate increased by 50% for A. scabra upon exposure to high temperature for 28 d, as compared with 99% and 107% in 'L-93' and 'Penncross', respectively). Roots of A. scabra exhibited higher tolerance to high soil temperature than creeping bentgrass, as manifested by smaller decreases in relative growth rate, cell membrane stability, maximum root length, and nitrate uptake under high soil temperature. The results suggest that acclimation of respiratory carbon metabolism plays an important role in root survival of Agrostis species under high soil temperatures, particularly for the thermal grass adaptation to chronically high soil temperatures. The ability of roots to tolerate high soil temperatures could be related to the capacity to control respiratory rates and increase respiratory efficiency by lowering maintenance and ion uptake costs.     

Partitioning of Carbon and Nitrogen During Growth and Development of Pigeonpea (Cajanus cajan L.)

Budgets for C and N were computed for pigeonpea (Cajanus cajanL.) at 15 d intervals, for the entire life cycle. Maximum Cand N in dry matter was observed at 90 d after sowing. Of theplants total respiratory loss during the vegetative phase, shoots,roots and nodules accounted for 65%, 23% and 12%, respectively.During the reproductive phases, the respiratory burden of theroots increased, while that of shoots and nodules decreased.Total respiratory loss as a proportion of net photosynthateremained more or less constant until ‘flowering and pod-setting’but increased heavily during seed filling, losing nearly 75%of the photosynthate in respiration. The efficiency of nitrogenfixation, in relation to respiratory output of the whole plantand nodulated roots, decreased during the period 60–90d after sowing, while that of nodules decreased from day 45onwards. Photosynthate supply to nodules and nodulated rootsincreased up to 75 d and 90 d after sowing, respectively. During45–90 d, nodules were fixing a constant proportion ofN per unit of C translocated (0.2 mg N mg^–1 C). Nodulatedroots, on an average, fixed 0.07 mg N mg^–1 C translocatedin the vegetative phase and this value decreased considerablyduring the subsequent phases. The crop produced during its lifecycle 50.4 g of glucose equivalents and yielded 3.8 g seed drymatter and 0.8 g seed protein giving an average of 13.2 g g^–1seed dry matter and 62.8 g g^–1 seed protein. Selectioncriteria for the improvement of C, N economy in pigeonpea havebeen suggested. Key words: Cajanus cajan, Carbon, Nitrogen, Dry weight, Plant parts, Growth, Development, Models     

Symbiotic N2 fixation activity in relation to C economy of Pisum sativum L. as a function of plant phenology

The relationships between symbiotic nitrogen fixation (SNF) activity and C fluxes were investigated in pea plants (Pisum sativum L. cv. Baccara) using simultaneous 13C and 15N labelling. Analysis of the dynamics of labelled CO2 efflux from the nodulated roots allowed the different components associated with SNF activity to be calculated, together with root and nodule synthetic and maintenance processes. The carbon costs for the synthesis of roots and nodules were similar and decreased with time. Carbon lost by turnover, associated with maintenance processes, decreased with time for nodules while it increased in the roots. Nodule turnover remained higher than root turnover until flowering. The effect of the N source on SNF was investigated using plants supplied with nitrate or plants only fixing N2. SNF per unit nodule biomass (nodule specific activity) was linearly related to the amount of carbon allocated to the nodulated roots regardless of the N source, with regression slopes decreasing across the growth cycle. These regression slopes permitted potential values of SNF specific activity to be defined. SNF activity decreased as the plants aged, presumably because of the combined effects of both increasing C costs of SNF (from 4.0 to 6.7 g C g-1 N) and the limitation of C supply to the nodules. SNF activity competed for C against synthesis and maintenance processes within the nodulated roots. Synthesis was the main limiting factor of SNF, but its importance decreased as the plant aged. At seed-filling, SNF was probably more limited by nodule age than by C supply to the nodulated roots.     

Respiratory energy requirements and rate of protein turnover in vivo determined by the use of an inhibitor of protein synthesis and a probe to assess its effect

Protein turnover is generally regarded as a major maintenance process, but experimental evidence to support this contention is scarce. Here we quantify the component of dark respiration rate associated with overall protein turnover of tissues in vivo. The effect of an inhibitor of cytosolic protein synthesis (cycloheximide, CHM) on dark respiration was tested on a cell suspension from potato ( Solanum tuberosum L.) and quantified on leaf discs of expanding and full-grown primary leaves of bean ( Phaseolus vulgaris L.). The in vivo effect of CHM on protein biosynthesis was assessed by monitoring the inhibition of the induction of the ethylene-forming enzyme (EFE) activity. The present method yields the energy costs of turnover of the total pool of proteins irrespective of their individual turnover rates. Average turnover rates were derived from the respiratory costs and the specific costs for turnover.
Inhibition of respiration by CHM was readily detectable in growing-cell suspensions and discs of expanding leaves, The derived respiratory costs of protein turnover in expanding leaves were maximally 17–37% of total respiration. Turnover costs in full-grown primary leaves of bean amounted to 17–21% of total dark respiration. The maximum degradation constants (i.e. K_d-values) derived for growing and full-grown leaves were up to 2.42 × 10⁻⁶ and 1.12 × l0⁻⁶ s⁻¹, respectively.     

The influence of 3,3',5-triiodo-L-thyronine on growth survival and body composition of slow-growing development elvers (Anguilla rostrata L.)

Effect of 3,3',5-triiodo-L-thyronine (T3) on survival, growth and body composition (protein, fat and ash) of slow-growing (Anguilla rostrata L.) elvers was investigated. A significant increase was found in the mean weight of slow growing elvers receiving diets containing 20 ppm T3 and held in the low water turnover system. A significant increase was also found in the weight of slow-growing elvers receiving diets containing 40 or 60 ppm T3 and held in the high water turnover system. Percentage protein (dry weight basis) was significantly correlated to body weight, but was not significantly correlated to concentration of T3 in the diet. There were no significant differences between the total fat content of slow-growing elvers when compared to the total body fat of control elvers.     

Root carbon and protein metabolism associated with heat tolerance

Extensive past efforts have been taken toward understanding heat tolerance mechanisms of the aboveground organs. Root systems play critical roles in whole-plant adaptation to heat stress, but are less studied. This review discusses recent research results revealing some critical physiological and metabolic factors underlying root thermotolerance, with a focus on temperate perennial grass species. Comparative analysis of differential root responses to supraoptimal temperatures by a heat-adapted temperate C3 species, Agrostis scabra, which can survive high soil temperatures up to 45 °C in geothermal areas in Yellow Stone National Park, and a heat-sensitive cogeneric species, Agrostis stolonifera, suggested that efficient carbon and protein metabolism is critical for root thermotolerance. Superior root thermotolerance in a perennial grass was associated with a greater capacity to control respiratory costs through respiratory acclimation, lowering carbon investment in maintenance for protein turnover, and efficiently partitioning carbon into different metabolic pools and alternative respiration pathways. Proteomic analysis demonstrated that root thermotolerance was associated with an increased maintenance of stability and less degradation of proteins, particularly those important for metabolism and energy production. In addition, thermotolerant roots are better able to maintain growth and activity during heat stress by activating stress defence proteins such as those participating in antioxidant defence (i.e. superoxide dismutase, peroxidase, glutathione S-transferase) and chaperoning protection (i.e. heat shock protein).     

Chemical composition of 24 wild species differing in relative growth rate

The chemical composition of 24 plant species which showed a three-fold range in potential growth rate was investigated. The carbon content of whole plants was lower for fast-growing species than for slow-growing ones. Fast-growing species accumulated more organic N-compounds, organic acids and minerals, whereas slow-growing species accumulated more (hemi)cellulose, insoluble sugars and lignin. No correlations with relative growth rate were found for soluble phenolics, soluble sugars and lipids. The costs to construct 1 g of plant biomass were rather similar for fast- and slow-growing species, both when expressed as C needed for C-skeletons, as glucose to provide ATP and NAD(P)H, and as total glucose costs. Therefore, we conclude that, despite the differences in chemical composition between fast- and slow-growing species, variation in the costs of synthesis of whole plant biomass cannot explain interspecific variation in relative growth rate of herbaceous species.     

Enhanced Water Use Efficiency in Dry Loess Grassland Species Grown at Elevated Air CO2 Concentration

Net CO2 assimilation rate (PN), stomatal conductance (gs), transpiration rate (E), and water use efficiency (WUE) in four perennial C3 species (grasses: Dactylis glomerata, Festuca rupicola, dicots: Filipendula vulgaris, Salvia nemorosa) grown for 231 d in open-top chambers at ambient (CA, 350 µmol mol-1) or elevated (CE, 700 µmol mol-1) CO2 concentrations were compared. When measured at CE, PN was significantly higher in CE plants of all four species than in the CA ones. The increase in PN was less prominent in the two grasses than in the two dicots. The E was significantly higher in the CE-grass F. rupicola and CE-dicot F. vulgaris than in the CA plants. There was no change in E owing to CE in the other grass and dicot. The gs in F. vulgaris and F. rupicola increased, while there was a decrease in D. glomerata and no change in S. nemorosa. WUE increased in all species grown in CE: four- to five-fold in the dicots and less than two-fold in the grasses. The increase in WUE was primarily due to an increase in PN and not to a decrease in E.     

Rate of soil egestion by larvae of Hylamorpha elegans (Burm.) and Phytoloema hermanni Germ. (Coleoptera: Scarabaeidae)

Larvae of Hylamorpha elegans (Burm.) and Phytoloema herrmanni Germ. feed on roots, although many Scarabaeidae species are able to feed and survive on soil without living roots. In this study we evaluated the potential of H. elegans and P. herrmanni to ingest soil by estimating the rate of soil egestion. In the laboratory, the rate of soil egestion was determined from gut content and gut transit time of 3rd-instar larvae feeding on soil without roots. The soil egestion rate was 14-21 mg g(-1) d(-1) for H. elegans and 11-16 mg g(-1) d(-1) for P. herrmanni. The gut transit time (time of soil passage from mouth to anus) was 2-3 d for both species and the gut content was 41±2 mg g(-1) for H. elegans and 32±2 mg g(-1) for P. herrmanni. The quantitative importance of feeding activity on soil depends upon the population density of larvae in the field, which ranges from 1 to 25 larvae m(-2), but in severe outbreaks can reach 300 larvae m(-2). High population densities could result in soil egestion rates reaching 20 kg d(-1) ha(-1) for P. herrmanni and 30 kg d(-1) ha(-1) for H. elegans.     

ON THE HOST RANGE AND SYSTEMATIC POSITION OF THE BACTERIA RESPONSIBLE FOR THE YELLOW SLIME DISEASES OF WHEAT (TRITICUM VULGARE VILL.) AND COCKSFOOT GRASS (DACTYLIS GLOMERATA L.)

Inoculations with Corynebacterium rathayi (E. F. Sm.) Dowson, alone or combined with the eelworm Anguina tritici into the leaves and shoots of cocksfoot grass ( Dactylis glomerata L.) and wheat ( Triticum vulgare Vill.), fail to cause infection. Inoculations made through the soil with Corynebactmim rathuyi and C. tritici (Hutchinson) Burkh. plua Anguina tritici cause infection in wheat but not in cocksfoot grass. The symptoms produced on wheat resemble those of yellow slime disease of cocksfoot grass. Successful infection of wheat with Corynebacterium rathay. or C. tritici is dependent on the presence, in the soil surrounding the plants, of Anguina tritici together with one of these bacterial species, which are considered to be so closely related as to suggest that Corynebacterium tritici is but a geographical variety of C. rathayi.     

Temperature dependency of bark photosynthesis in beech (Fagus sylvatica L.) and birch (Betula pendula Roth.) trees

Temperature dependencies of stem dark respiration (R(d)) and light-driven bark photosynthesis (A(max)) of two temperate tree species (Fagus sylvatica and Betula pendula) were investigated to estimate their probable influence on stem carbon balance. Stem R(d) was found to increase exponentially with increasing temperatures, whereas A(max) levelled off or decreased at the highest temperatures chosen (35-40 degrees C). Accordingly, a linear relationship between respiratory and assimilatory metabolism was only found at moderate temperatures (10-30 degrees C) and the relationship between stem R(d) and A(max) clearly departed from linearity at chilling (5 degrees C) and at high temperatures (35-40 degrees C). As a result, the proportional internal C-refixation rate also decreased non-linearly with increasing temperature. Temperature response of photosystem II (PSII) photochemistry was also assessed. Bark photochemical yield (Delta F/F(m)') followed the same temperature pattern as bark CO(2) assimilation. Maximum quantum yield of PSII (F(v)/F(m)) decreased drastically at freezing temperatures (-5 degrees C), while from 30 to 40 degrees C only a marginal decrease in F(v)/F(m) was found. In in situ measurements during winter months, bark photosynthesis was found to be strongly reduced. Low temperature stress induced an active down-regulation of PSII efficiency as well as damage to PSII due to photoinhibition. All in all, the benefit of bark photosynthesis was negatively affected by low (<5 degrees C) as well as high temperatures (>30 degrees C). As the carbon balance of tree stems is defined by the difference between photosynthetic carbon gain and respiratory carbon loss, this might have important implications for accurate modelling of stem carbon balance.