摘要:

ABSTRACTStimulation or light‐saturated rates of photosynthesis inEctocarpus siliculosus(Dillwyn) Lyngb. by blue light was eliminated by increasing dissolved inorganic carbon (DIC) or by lowering pH in natural seawater. The amplitude of the circadian rhythm of photosynthesis was also diminished under these conditions, and the pH compensation points in a closed system were higher in the presence of blue light and during the circadian day. These observations suggest that blue light and the circadian clock regulate the activity of a carbon acquisition system in these plants. The inhibitor of external carbonic anhydrase, acetazolamide, reduced overall rates of photosynthesis by only about 30%, but ethoxyzolamide suppressed the circadian rhythm of photosynthesis almost completely and markedly reduced the duration of responses to blue light pulses. Similar patterns were obtained when photosynthesis was measured in strongly limiting DIC concentrations (0–0.5 mol m−3). Since blue light stimulated photosynthesis under these conditions of strong carbon limitation, we suggest that blue light activates the release of CO2from an internal CO2store. We propose a metabolic pathway with similarities to that of CAM plants. Non‐photosynthetic fixation leads to the accumulation of a storage metabolite. The circadian clock and blue light control the mobilization of CO2at the site of decarboxylation of this metabolite. In the presence of continuous blue light the pathway is proposed to cycle and act as a pump for CO2into the chloroplasts. This hypothesis helps to explain a number of previously reported peculiarities of brown algal photosy

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00329.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTIn saturating irradiances of red light, photosynthesis ofLaminaria saccharina(L.) Lamouroux was stimulated by low irradiances of continuous blue light only when the supply of dissolved inorganic carbon (DIC) was limiting. The degree of this stimulation was inversely proportional to the logarithm of the concentration of free CO2, whether this was adjusted by varying the total DIC or the pH at a given DIC concentration. The final pH reached in a closed system was higher in blue light than in red light. Both acetazolamide and ethoxyzolamide suppressed the responses to blue light almost completely, but reduced photosynthesis in red light by only 30%. Buffering the pH of the seawater also suppressed the stimulation of photosynthesis by blue light without affecting the photosynthetic rate in red light. The transient stimulation of O2evolution by a blue light pulse was not accompanied by a corresponding increase in CO2consumption. These observations could be explained if, in analogy to the mechanism proposed for Ectocarpus (Schmid, Mills&Dring 1996,Plant Cell and Environment19,373–382, this issue, accompanying paper), photosynthesis was supported by a blue‐light‐activated release of CO2from an internal store. We suggest that the store is located in the vacuoles of the cortical tissue of the blades. The main photosynthetic tissue, however, is in the overlying meristoderm, and blue‐light‐activated mobilization of the store could stimulate O2evolution only if periplasmic carbonic anhydrase was available to facilitate CO2uptake from t

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00330.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe carbon isotope composition of C4grasses has the potential to be used as an indicator of changes in the isotopic composition and concentration of atmospheric CO2, especially for climate reconstruction. The usefulness of C4grasses for this purpose hinges on the assumption that their photosynthetic discrimination against13C remains constant in a wide range of environmental conditions. We tested this assumption by examining the effects of light and water stress on the carbon isotope composition of C4grasses using different biochemical subtypes (NADP‐ME, NAD‐ME, PCK) in glasshouse experiments. We grew 14 different C4grass species in four treatments: sun‐watered, sun‐drought, shade‐watered and shade‐drought. Carbon isotope discrimination (Δ) rarely remained constant. In general, Δ values were lowest in sun‐watered grasses, greater for sun‐drought plants and even higher for plants of the shade‐watered treatment. The highest Δ values were generally found in the most stressed grasses, the shade‐drought plants. Grasses of the NADP‐ME subtype were the least influenced by a change in environmental variables, followed by PCK and NAD‐ME subtypes. Water availability affected the carbon isotope discrimination less than light limitation in PCK and NAD‐ME subtypes, but similarly in NADP‐ME subtypes.In another experiment, we studied the effect of increasing light levels (150 to 1500 μmol photons m−2s−1) on the Δ values of 18 well‐watered C4grass species. Carbon isotope discrimination remained constant until photon flux density (PFD) was less than 700 μmol photons m−2s−1. Below this light level, Δ values increased with decreasing irradiance for all biochemical subtypes. The change in A was less pronounced in NADP‐ME and PCK than in NAD‐ME grasses. Grasses grown in the field and in the glasshouse showed a similar pattern. Thus, caution should be exercised when using C4 plants under varying environmental conditions to monitor the concentration or carbon isotopic composition of atmospheric CO2 in fi

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00331.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTEffects of canopy structure on microclimate, energy budget and CO2exchange were analysed in a pasture, two hay meadows, a tall herb community and a dwarf shrub community in the subalpine belt of the Central Caucasus. The results show that canopy structure exerts a marked influence on the distribution of photon flux density, temperature and canopy photosynthesis Ac. Three canopy types were distinguished. Type 1 (pasture) has a small LAI (leaf area index) and more than two‐thirds of the phytomass is concentrated in the lowest few cm of the canopy, mainly as planophile leaves. This results in (1) a low degree of utilization of photosynthetic photon flux density (PPFD) by assimilatory plant components, (2) high leaf temperatures and a high soil heat flux during the phase of incoming radiation, and (3) a relatively low Ac/ LAI ratio. Type 2 (meadows), in spite of its erect leaves, which at high solar elevations permit light to penetrate to the lower canopy layers, is characterized by (1) marked effects of mutual shading in the lower canopy layers for most of the day, and thus (2) only slight variations in air and leaf temperatures and (3) a comparatively lowAc/LAI ratio. In canopies of type 3 (tall herb and dwarf shrub communities), there is a concentration of flat leaves in the upper layers. This results in (1) very good utilization of PPFD; (2) no strong fluctuations in canopy temperature as the flat leaves act as a buffer, reducing the amounts of incoming and outgoing radiation in lower canopy layers, and (3) high values of theAc/LAI ratio. The energy budgets of the canopies investigated are governed not so much by their spatial structure, but rather indirectly by LAI and the degree of coupling of the canopy with the atmospher

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00332.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTPedunculate oak (Quercus roburL.) was germinated and grown at ambient CO2concentration and 650 μmol mol−1CO2in the presence and absence of the ectomycorrhizal fungusLaccaria laccatafor a total of 22 weeks under nonlimiting nutrient conditions. Sulphate uptake, xylem loading and exudation were analysed in excised roots. Despite a relatively high affinity for sulphate (KM= 1.6 mmol m−3), the rates of sulphate uptake by excised lateral roots of mycorrhizal oak trees were low as compared to herbaceous plants. Rates of sulphate uptake were similar in mycorrhizal and non‐mycorrhizal roots and were not affected by growth of the trees at elevated CO2. However, the total uptake of sulphate per plant was enhanced by elevated CO2and further enhanced by elevated CO2and mycorrhization. Sulphate uptake seemed to be closely correlated with biomass accumulation under the conditions applied.The percentage of the sulphate taken up by mycorrhizal oak roots that was loaded into the xylem was an order of magnitude lower than previously observed for herbaceous plants. The rate of xylem loading was enhanced by mycorrhization and, in roots of mycorrhizal trees only, by growth at elevated CO2. On a whole‐plant basis this increase in xylem loading could only partially be explained by the increased growth of the trees. Elevated CO2and mycorrhization appeared to increase greatly the sulphate supply of the shoot at the level of xylem loading. For all treatments, calculated rates of sulphate exudation were significantly lower than the corresponding rates of xylem loading of sulphate. Radiolabelled sulphate loaded into the xylem therefore seems to be readily diluted by unlabelled sulphate during xylem transport.Allocation of reduced sulphur from oak leaves was studied by flap‐feeding radiolabelled GSH to mature oak leaves. The rate of export of radioactivity from the fed leaves was 4–5 times higher in mycorrhizal oak trees grown at elevated CO2than in those grown at ambient CO2. Export of radiolabel proceeded almost exclusively in a basipetal direction to the roots. From these experiments it can be concluded that, in mycorrhizal oak trees grown at elevated CO2, the transport of sulphate to the shoot is increased at the level of xylem loading to enable increased sulphate reduction in the leaves. Increased sulphate reduction seems to be required for the enhanced allocation of reduced sulphur to the roots which is observed in trees grown at elevated CO2. These changes in sulphate and reduced sulphur allocation may be a prerequisite for the positive effect of elevated CO2on growth of oak trees previou

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00333.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTPressure probe measurements have been interpreted as showing that xylem pressures below c. –0.4 MPa do not exist and that pressure chamber measurements of lower negative pressures are invalid. We present new evidence supporting the pressure chamber technique and the existence of xylem pressures well below –0.4 MPa. We deduced xylem pressures in water‐stressed stem xylem from the following experiment: (1) loss of hydraulic conductivity in hydrated stem xylem (xylem pressure = atmospheric pressure) was induced by forcing compressed air into intact xylem conduits; (2) loss of hydraulic conductivity from cavitation and embolism in dehydrating stems was measured, and (3) the xylem pressure in dehydrated stems was deduced as being equal and opposite to the air pressure causing the same loss of hydraulic conductivity in hydrated stems. Pressures determined in this way are only valid if cavitation was caused by air entering the xylem conduits (air‐seeding). Deduced xylem pressure showed a one‐to‐one correspondence with pressure chamber measurements for 12 species (woody angiosperms and gymnosperms); data extended to c. –10 MPa. The same correspondence was obtained under field conditions inBetula occidentalisHook., where pressure differences between air‐ and water‐filled conduits were induced by a combination ofin situxylem water pressure and applied positive air pressure. It is difficult to explain these results if xylem pressures were above –0.4 MPa, if the pressure chamber was inaccurate, and if cavitation occurred by some mechanism other than air‐seeding. A probable reason why the pressure probe does not register large negative pressures is that, just as cavitation within the probe limits its calibration to pressures above c. –0.5 MPa, cavitation limits its m

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00334.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTVariations in stable carbon isotope discrimination (δ) were investigated across the thalli of several lichen species possessing different photobiont associations. Lichens containing (i) green algae (phycobiont), (ii) green algae in association with cyanobacteria confined in cephalodia, or (iii) cyanobacteria (cyanobiont) as the photobiont partner were studied. Carbon isotope discrimination was analysed in different thallus sections, which varied in distance from the margin and in age. The marginal thallus region is considered to be youngest, while the central region is thought to be oldest. This analysis showed a clear variation in δ across the thallus related to distance from the growing margin. In most of the species examined, the highest δ values were found in marginal regions (younger), while the central and basal regions (older) showed significantly lower δ. To investigate the effects of the historical increase in atmospheric CO2concentration and the concurrent decrease in the13C content of atmospheric CO2on the δ of lichens, experiments were carried out on herbarium samples ofLobaria pulmonariacollected from the mid 19th Century to 1953. The results obtained showed a pattern of variation of δ consistent with that of freshly collected samples; δ decreased substantially with increasing distance from the thallus margin, irrespective of the collection date. Moreover, no consistent variation of discrimination was found among different collection dates. These results demonstrate that the observed variation in δ is caused by age‐related changes in the physiological behaviour of different thallus sections, and that the past 150 years of increasing CO2concentration have not had significant effects on A inL. pulmonaria. Photosynthesis measurements, chlorophyll analysis and observations using optical microscopy, performed on freshly collected lichens, showed significant changes in morphological and physiological characteristics across the thallus. Particularly, remarkable variations in thickness were found across the thallus. These anatomical changes may be responsible for the variation in δ, through variations in CO2 transfer resistance and, consequently, in CO2availability across the thallus. The lack of age‐dependent variation in δ in cyanobiont lichens is possibly attributable to the operation of a CO2‐coneentrating mechanism and, therefore, to a more constant CO2environment across the thallus in th

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00335.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTAs a first step towards transferring a tetracycline (Tc)‐inducible gene expression system to tomato, we have transformed tomato plants with the Tn10‐encoded tet repressor gene (tetR). Homozygous transformed plants with high expression oftetR mRNA show a deleterious phenotype, having reduced shoot dry weights and leaf chlorophyll content, an even more marked reduction in root dry weight and leaf size, and altered photosynthetic physiology. It appears that TetR protein exerts its toxicity only when expressed beyond a threshold level and by interacting with a process that is non‐limiting under slow growth conditions. The deleterious phenotype was almost completely reversed by the application of 1 mg dm−3Tc to plants grown in sand. The possiblity is discussed that TetR causes these symptoms by binding to a specific DNA sequence functioning as a Tet operator.The effect of Tc on growth and physiology in wild‐type plants grown in sand or rockwool is described. Tc at 0.1 mg cm−3had no effect. Tc at 1 mg dm−3caused a small reduction in root growth, while 5 and 20 mg dm−3Tc caused large reductions in growth and photosynth

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00336.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTWetting of the upper needle surface ofAbies grandisLindl. by aqueous solutions of different pH values was investigated. With increasing needle age, contact angles decreased significantly from about 75° on current‐year needles to values lower than 30° on 4‐year‐old needles. On older needles, contact angles were significantly lower, by more than 10°, when aqueous solutions of pH9‐0 were used compared with those of pH3‐0. On the surfaces of older needles, contact angle titrations were carried out, contact angles being measured with aqueous solutions covering a pH range from 3.0 to 11.0. Measured titration curves showed clear inflection points around pH 7.0, indicating the existence of ionizable carboxylie groups in the interface between needle surface and atmosphere. The evidence seems convincing that the pronounced pH dependence of wetting is mainly due to the presence and/or activity of epiphyllic micro‐organisms, whereas the cuticular wax composition of Abies grandis needles does not appear to contribute significantly to this phenomenon. Thus, the results presented here allow the general conclusion that changes of contact angles measured on leaf surfaces may not always be due to changes in the leaf surface chemistry and/or the fine structure of leaf surface waxes, but may also be due to increased amounts of epiphyllic micro‐organisms significantly altering the leaf surface we

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00337.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY

摘要:

ABSTRACTThe plant polypeptide signal systemin induces proteinase inhibitor synthesis in tomato leaves. We show here that systemin elicits a transient depolarization of the tomato mesophyll cell membrane. Furthermore it triggers a transient decrease in the external pH of the mesophyll tissue which is followed by a sustained pH increase. In the presence of fusicoccin (which has been shown to antagonize the synthesis of proteinase inhibitors) the depolarization and transient H+efflux are attenuated whereas the slower phase of the sustained electroneutral H+influx persists. These results suggest that systemin‐induced changes in ion transport play a role in the early phases of systemin signal transductio

ISSN:0140-7791    

DOI:10.1111/j.1365-3040.1996.tb00338.x

出版商:Blackwell Publishing Ltd    

年代:1996

数据来源: WILEY