Requirement for far-red light to maintain secondary needle extension growth in northern but not southern populations of Pinus sylvestris (Scots pine)

Extension growth of secondary needles is under photoperiodic control in Pinus sylvestris . To test for the effects of far-red light on maintaining this extension growth, seedlings of six populations originating from latitudes between 57° and 67°N were raised for 11 weeks in continuous incandescent (metal halogen) light at 300 µmol m⁻² s⁻¹ and 20°C and then transferred at the same temperature to a daily regime of 8 h incandescent light (230 µmol m⁻² s⁻¹) followed by a 16 h day extension with cool white fluorescent light (40 µmol m⁻² s⁻¹, R/FR ratio 7.5) or with incandescent lamps (20 µmol m⁻² s⁻¹, R/FR ratio 2.0). For the seedlings from the three populations north of 64°, needle extension growth over 42 days in the FR-poor day extension treatment was lower by up to 40% than in the FR-rich day extension treatment, whereas for the seedlings from the three southern populations the needle extension growth was similar in both day extension treatments. The requirement for FR in day extensions is characteristic of 'light-dominant' photoperiodic control mechanisms. It appears that P. sylvestris changes from dark-dominant night timekeeping to light-dominant day timekeeping with increasing latitude, as with the photoperiodic control of budset in Picea abies .     

Phytochrome control of hypocotyl extension in light-grown Chenopodium rubrum

The regulation of hypocotyl extension in light-grown Chenopodium rubrum L. seedlings by light analogous to dense vegetation canopy shade has been monitored. Hypocotyl extension was controlled by both the quantity and quality of the actinic light. At the higher of the two background photon fluence rates which were used (10.0 μmol m⁻²s⁻¹ in the 400–700 nm waveband), increasing the proportion of phytochrome calculated to exist as Pfr resulted in greater inhibition of growth. At the lower photon fluence rate (1.0 μmol m⁻²s⁻¹ in the 400–700 nm waveband), a biphasic response was observed in which minimum inhibition was observed at intermediate photoequilibria. Although photosynthesis was not directly involved in the photomorphogenetic responses, it did play an indirect quantitative role in determining the response.     

Photomorphogenic regulation of increases in UV-absorbing pigments in cucumber (Cucumis sativus) and Arabidopsis thaliana seedlings induced by different UV-B and UV-C wavebands

Brief (1–100 min) irradiations with three different ultraviolet-B (UV-B) and ultraviolet-C (UV-C) wave bands induced increases the UV-absorbing pigments extracted from cucumber ( Cucumis sativus L.) and Arabidopsis . Spectra of methanol/1% HCl extracts from cucumber hypocotyl segments spanning 250–400 nm showed a single defined peak at 317 nm. When seedlings were irradiated with 5 kJ m⁻² UV-B radiation containing proportionally greater short wavelength UV-B (37% of UV-B between 280 and 300 nm; full-spectrum UV-B, FS-UVB), tissue extracts taken 24 h after irradiation showed an overall increase in absorption (91% increase at 317 nm) with a second defined peak at 263 nm. Irradiation with 1.1 kJ m⁻² UV-C (254 nm) caused similar changes. In contrast, seedlings irradiated with 5 kJ m⁻² UV-B including only wavelengths longer than 290 nm (8% of UV-B between 290 and 300 nm; long-wavelength UV-B, LW-UVB) resulted only in a general increase in absorption (80% at 317 nm). The increases in absorption were detectable as early as 3 h after irradiation with FS-UVB and UV-C, while the response to LW-UVB was first detectable at 6 h after irradiation. In extracts from whole Arabidopsis seedlings, 5 kJ m⁻² LW-UVB caused only a 20% increase in total absorption. Irradiation with 5 kJ m⁻² FS-UVB caused the appearance of a new peak at 270 nm and a concomitant increase in absorption of 72%. The induction of this new peak was observed in seedlings carrying the fah 1 mutation which disrupts the pathway for sinapate synthesis. The results are in agreement with previously published data on stem elongation indicating the existence of two response pathways within the UV-B, one operating at longer wavelengths (>300 nm) and another specifically activated by short wavelength UV-B (<300 nm and also by UV-C).     

Photosystem I acceptor side limitation is a prerequisite for the reversible decrease in the maximum extent of P700 oxidation after short-term chilling in the light in four plant species with different chilling sensitivities

Changes in the extent of P700 oxidation (P700⁺) were investigated after chilling of barley, rice, pumpkin, and cucumber leaf segments at 4°C for 1 h under light with various photon flux densities. At 50 µmol photons m⁻² s⁻¹, the decrease in P700⁺ was observed only in cucumber, but at 150 µmol photons m⁻² s⁻¹, it was found in all plants except barley, revealing their expected chilling sensitivities. However, the decrease in P700⁺ by this short-term chilling was reversible in the presence of 3-(3',4'-dichlorophenyl)-1,1-dimethylurea or methyl viologen, and it did not show any causal relationship with the decrease in the electron transfer rate nor with the down-regulation of photosystem II through the accumulation of zeaxanthin and the development of non-photochemical quenching. These results led to the suggestion that photosystem I (PSI) acceptor side limitation is a prerequisite for the decrease of P700⁺. Furthermore, PSI acceptor side limitation could be mainly due to limitation of electron-sink pathways such as CO₂ assimilation and ascorbate–glutathione cycle, because treatment with glycolaldehyde which inhibits the former pathway, and with KCN which inhibits both pathways, decreased P700⁺ by 20–30% in barley leaves after chilling in the light.     

Responses of Antarctic Iridaea cordata (Rhodophyta) tetraspores exposed to ultraviolet radiation

In Antarctica ozone depletion is highest during spring, coinciding with the reproduction of many seaweed species. Propagules are the life-stage of an alga most susceptible to environmental perturbations. Therefore, fertile thalli of Iridaea cordata (Turner) Bory (Rhodophyta) were collected in the eulittoral of King George Island (Antarctica) to examine spore susceptibility to ultraviolet radiation (UVR). In the laboratory, freshly released tetraspores were exposed to photosynthetically active radiation (PAR) (400–700 nm), PAR+UV-A (320–700 nm) or PAR+UV-A+UV-B (280–700 nm). Photosynthetic efficiency was measured during 1–8 h of exposure and after 48 h of recovery. Additionally, mycosporine-like amino acids (MAAs) and DNA damage were determined. Saturating irradiance of photosynthesis of freshly released tetraspores was 57 µmol photons m⁻² s⁻¹. Exposure to increasing fluence of PAR reduced photosynthetic efficiency. UVR further decreased the photosynthetic efficiencies of the tetraspores but spores were able to recover completely after UVR exposure and 2 days post-cultivation under low PAR. DNA damage was minimal and lesions were effectively repaired under photoreactivating light. Concentrations of the MAAs shinorine and palythine were higher in tetraspores treated with UVR than in spores only exposed to PAR. Generally, the tetraspores show a good UV tolerance. This flexible response of the tetraspores of this species to changing radiation conditions enables the alga to grow along a considerable depth gradient from the sublittoral to the eulittoral where they can be exposed to enhanced UVBR under conditions of stratospheric ozone depletion.     

Influence of solar ultraviolet radiation on photosynthesis and motility of marine phytoplankton

Abstract: The effects of solar ultraviolet radiation (UV) on carbon uptake, oxygen evolution and motility of marine phytoplankton were investigated in coastal waters at Kristineberg Marine Research Station on the west coast of Sweden (58° 30'N, 11° 30'E). The mean irradiances at noon above the water surface during the investigation period were: photosynthetic active radiation (PAR, 400–700 nm) 1670 μmol m⁻² s⁻¹; ultraviolet-A radiation (UV-A, 320–400 nm) 35.9 W m⁻² and ultraviolet-B radiation (UV-B, 280–320 nm) 1.7 W m⁻². UV-B radiation was much more attenuated with depth in the water column than were PAR and UV-A radiation. UV-B radiation could not be detected at depths greater than 100–150 cm. Inhibition of carbon uptake by UV-A and UV-B in natural phytoplankton populations was greatest at 50 cm depth and the effects of UV-B were greater than those of UV-A. At depths greater than 50 cm there was almost no effect of ultraviolet radiation on carbon uptake. PAR, UV-A and UV-B decreased oxygen evolution by the dinoflagellate Prorocentrum minimum . Inhibition of oxygen evolution was greater after 4 h than 2 h but it was not possible to distinguish the negative effects of the different light regimes. The motility of P. minimum was not affected by PAR, UV-A and UV-B. The importance of exposure of phytoplankton to different light regimes before being exposed to natural solar radiation is discussed.     

Inhibition of hypocotyl elongation by ultraviolet-B radiation in de-etiolating tomato seedlings. I. The photoreceptor

Broad-band UV-B radiation inhibited hypocotyl elongation in etiolated tomato ( Lycopersicon esculentum Mill. cv. Alisa Craig) seedlings. This inhibition could be elicited by < 3 μmol m⁻² s⁻¹ of UV-B radiation provided against a background of white light (> 620 μmol m⁻² s⁻¹ between 320 and 800 nm), and was similar in wild-type and phytochrome-1-deficient aurea mutant seedlings. These observations suggest that the effect of UV-B radiation is not mediated by phytochrome. An activity spectrum obtained by delivering 1 μmol m⁻² s⁻¹ of monochromatic UV radiation against a while light background (63 μmol m⁻² s⁻¹ showed maximum effectiveness around 300 nm, which suggests that DNA or aromatic residues in proteins are not the chromophores mediating UV-B induced inhibition of elongation. Chemicals that affect the normal (photo)chemistry of flavins and possibly pterins (KI, NaN, and phenylacetic acid) largely abolished the inhibitor) effect of broad-hand UV-B radiation when applied to the root zone before irradiation. KI was effective at concentrations < 10⁻⁴ M , which have been shown in vitro to be effective in quenching the triplet excited stales of flavins but not fluorescence from pterine or singlet states of flavins. Elimination of blue light or reduction of UV-A, two sources of flavin excitation, promoted hypocotyl elongation, but did not affect the inhibition of elongation evened by UV-B. Kl applied after UV-B irradiation had no effect on the inhibition response. Taken together these findings suggest that the chromophore of the photoreceptor system invoked in UV-B perception by tomato seedlings during de-etiolation may be a flavin.     

Overexpression of light-dependent PORA or PORB in plants depleted of endogenous POR by far-red light enhances seedling survival in white light and protects against photooxidative damage

The structurally related light-dependent protochlorophyllide (Pchlide) oxidoreductases PORA and PORB mediate the only light-requiring step in chlorophyll (Chl) biosynthesis in higher plants. Correlative evidence suggests that some in vivo functions of PORA and PORB may be unique, including a postulated photoprotective role for PORA. For example, wild-type Arabidopsis thaliana seedlings grown in non-photooxidative far-red light (cFR) resemble those grown in white light (WL), but they are yellow and do not green normally thereafter in WL. This defect is accompanied by the absence of detectable PORA and reduced levels of PORB expression. Here, direct evidence is provided that the presence of POR, either as PORA or PORB, can confer photoprotection in plants. In contrast to the wild-type, the plastids of transgenic PORA- or PORB-overexpressing Arabidopsis seedlings grown in cFR possess extensive prolamellar bodies. Upon a subsequent shift to WL, POR-overexpressing seedlings develop thylakoid membranes, accumulate large amounts of Chl and are viable at fluence rates lethal to the wild-type. Intriguingly, the plastid membrane architectures of greening transgenic seedlings seem to depend on whether PORA or PORB has been overproduced. POR-overexpressing seedlings shifted from cFR to WL of fluence rates from 20 to 500 μE m^–2 sec^–1 accumulate substantially higher amounts of Chl than does the wild-type. Furthermore, the WL fluence rate that permits maximal Chl accumulation increases from 8 μE m^–2 sec^–1 in the wild-type to 125 μE m^–2 sec^–1 in transgenic seedlings. POR overexpression during growth in cFR also correlates with a fourfold decrease in the steady-state content of Pchlide, a potentially lethal photosensitizer.     

Endonuclease activity from tobacco nuclei specific for ultraviolet radiation-damaged DNA

Endonuclease activity specific for UV damaged DNA was isolated from tobacco leaf nuclei and detected by relaxation of supercoiled pUC 19 plasmid DNA. The activity did not require divalent cations or ATP. It acted on photoproducts induced by as little as 24 J m⁻² of UV-C (primarily 254 nm) radiation. but not on photoproducts produced by UV-B (290–320 nm) radiation in the presence of acetophenone and a N₂ atmosphere or by UV-A (320–400 nm) radiation in the presence of 4'-methoxy-methyltrioxsalen in a N₂ atmosphere and not on the products of OsO₄ oxidation of the DNA. Using end-labeled DNA of defined sequence, it was possible to identify sites in UV-C-irradiated DNA that were cut by the endonuclease preparation: most sites were assocrated with pyrimidine pairs. Cleavage by the tobacco endonuclease was not eliminated by treatment with Escherichia coli photolyase and light, suggesting that the endonuclease did not recognize cyclobutadipyrimidines.     

Spatio-temporal variation in macroinvertebrate assemblages of glacial streams in the Swiss Alps

1. Changes in water chemistry, benthic organic matter (BOM), and macroinvertebrates were examined in four different glacial streams over an annual cycle. The streams experienced strong seasonal changes in water chemistry that reflected temporal changes in the influence from the source glacier, especially in water turbidity, particulate phosphorus and conductivity.
2. Nitrogen concentrations were high (nitrate-N values were 130–274 μg L^–1), especially during spring snowmelt runoff. Benthic organic matter attained >600 g m^–2 dry mass at certain times, peaks being associated with seasonal blooms of the alga Hydrurus foetidus .
3. Macroinvertebrate taxon richness was two to three times higher (also numbers and biomass) in winter than summer suggesting winter may be a more favourable period for these animals. Benthic densities averaged 1140–3820 ind. m^–2, although peaking as high as 9000 ind. m^–2. Average annual biomass ranged from 102 to 721 mg m^–2, and reached >2000 mg m^–2 at one site in autumn.
4. Taxa common to all sites included the dipterans Diamesa spp. and Rhypholophus sp., the plecopterans Leuctra spp. and Rhabdiopteryx alpina , and the ephemeropterans Baetis alpinus and Rhithrogena spp. Principal components analysis clearly separated winter assemblages from those found in summer.     

Effect of light quality (blue, red) and fluence rate on the synthesis of pigments and pigment-proteins in maize and black pine mesophyll chloroplasts

Maize ( Zea mays L. hybrid ZP-704) and black pine ( Pinus nigra Arn.) were grown for five days at low fluence rate (0.4–4.0, μmol m^–2 s⁻¹) in blue or red light. Compared to red light of the same fluence rate, blue light effects in maize were repressive for the accumulation of Chita, b , carotenoids and light-harvesting complex-2 (LHC-2) proteins. The maximal reduction of proteins bound to the light-harvesting complex of photosystem 2 and pigments was attained at different fluence rate levels. In black pine, blue light compared to the red of the same fluence rate level either activated or reduced accumulation of pigments and LHC proteins, the effect being dependent on its fluence rate level. At fluence less than 3.0 μmol m⁻² s⁻¹ blue light was more efficient for the synthesis of Chi a, b and carotenoids, hut for LHC-2 complexes, fluence rates between 0.4 and 1.5 [μmol m⁻² s⁻¹ were more effective. In pine the effects of the two lights on the accumulation of pigments and LHC proteins were demonstrated separately and were dependent on fluence rate level. This suggests irradianoe-controlled activation/deactivation of the photoreceptor at the level of the cell.     

Latitudinal cline of requirement for far‐red light for the photoperiodic control of budset and extension growth in Picea abies (Norway spruce)

To test for the effects of far‐red light on preventing budset in Picea abies , seedlings of six populations originating from latitudes between 67°N and 47°N were grown for 4–8 weeks in continuous incandescent (metal halogen) light at 300 µmol m⁻² s⁻¹ and 20°C and then transferred, at the same temperature, to a daily regime of 8 h incandescent light (300 µmol m⁻² s⁻¹) followed by 16 h cool white fluorescent light (40 µmol m⁻² s⁻¹). (Cool white lamps are deficient in far‐red light, with a R/FR ratio of 7.5 compared with 2.0 for the incandescent lamps.) All the seedlings from 67° and 80% of those from 64° stopped extension growth and set terminal buds within 28 days of the change of regime. The seedlings from 61° and further south continued growing, as did control seedlings from 67° grown as above but with incandescent light at 20 µmol m⁻² s⁻¹ replacing cool white illumination. To distinguish between a clinal and ecotypic pattern of variation, the interval between 64° and 59° was investigated by growing populations originating from that area in the same regimes as before. After 28 days in the cool white day‐extension regime, the percentage budset was 86 for the population from 64°, 0 for the population from 59° and 25–50 for the intermediate populations; i.e. the populations showed a clinal variation in requirement for far‐red light according to latitude. Thus northern populations of Picea abies appear to behave as 'light‐dominant' plants for the photoperiodic control of extension growth and budset, whereas the more southern populations behave as 'dark‐dominant' plants.     

Photophobic stop-response in a dinoflagellate: Modulation by preirradiation

Gyrodinium dorsum Kofoid responds photophobically to flashes of blue light. The photophobic response consists of a cessation of movement (stop-response). Without background light and after a flash fluence above 10 J m⁻², 75–85% of the cells show a stop-response, while only 50% of the cells show this response at 5 J m⁻². With a flash fluence of 5 J m⁻², background light of different wavelengths either increases (614 nm. 5.5–18.2 μmol m⁻² s⁻¹) or decreases (700 nm, 18.4–36.0 μmol m⁻² s⁻¹) the stop-response. Two hypotheses for the mechanism of the modulation by background light of the photophobic response are discussed: an effect of light on the balance of the photosynthetic system (PS I/PS II) or an effect on a phytochrome-like pigment (P_r/P_fr). This study supports the idea that a phytochrome-like pigment works in combination with a blue light-absorbing pigment. It was also found that cells of Gyrodinium dorsum cultured in red light (39.8 μmol m⁻²) had a higher absorption in the red region of the absorption spectra than those cultured in white light (92.7 μmol m⁻²).     

An estimate of the sustainable rate of shell extraction from the Dutch Wadden Sea

1. Shell production by cockles Cerastoderma edule was studied to examine whether or not the present licensed rate of shell extraction in the Dutch Wadden Sea exceeds the current rate of shell addition to the exploitable stocks.
2. Long-term data on numbers of cockles and weights of their shells were used to estimate their annual production on Balgzand, a 50-km² tidal flat area in the western-most part of the Wadden Sea. During the 1969–97 period, it amounted to an average of 125 g m^–2, including 107 g m^–2 of shells large enough to be exploitable for shell-lime fishery.
3. The very irregular annual recruitment of cockles was the main cause of the wide 95% confidence limits (74 and 140 g m^–2 year^–1) of this 28-year estimate. Moreover, high mortality rates in severe winters substantially reduced production per recruit in some year classes.
4. About one-third of the estimated production does not reach exploitable stocks, because it is fragmented by birds (particularly eider ducks), permanently buried in the sediment, or removed by the fishery for live cockles.
5. During the last few decades, the estimated mean amount added annually to the exploitable stocks was 88 million kg or 132 000 m³ of large cockle shells. This amount compares favourably with the current annual level of removal of 134 000 m³ of shells, three-quarters of which are cockles.
6. Even at temporarily lower production rates, the exploitation of shell stocks at its present rate is not expected to lead to a rapid exhaustion of the existing stocks in the tidal inlets of the Dutch Wadden Sea, as these stocks will be in the order of a few million m³.     

Thermogenesis of three species of Arum from Crete

Inflorescences of arum lilies have a three-part spadix with a scent-producing, sterile appendix above two bands of fertile male and female florets. The appendix and male florets are thermogenic, but with different temporal patterns. Heat-production was measured in Arum concinnatum , A. creticum and A. idaeum . The male florets of A. concinnatum showed a 3 d continuous episode of thermogenesis with three waves, and the appendix warmed in a single, 6 h episode. Maximum fresh-mass-specific CO₂ production rate was 0.17  µ mol s⁻¹ g⁻¹ to achieve a 10.9 °C temperature elevation by the appendix, and 0.92  µ mol s⁻¹ g⁻¹ to achieve a 4.8 °C elevation by male florets. Reversible, physiological temperature regulation was not evident in either tissue. Respiration increased with tissue temperatures with Q₁₀ values of 1.8–3.9, rather than less than 1.0 as occurs in thermoregulatory flowers. Experimental step changes in temperature of appendix and male floret tissues also failed to show thermoregulatory responses. The patterns of thermogenesis therefore appear to be fixed by the temporal sequence of blooming. Thermogenesis in the alpine species, A. creticum and A. idaeum , was significantly lower than in the lowland A. concinnatum , possibly related to difficulty in raising floral temperature in their cold and windy habitat.     

The responses of a lotic mayfly Nousia sp. (Ephemeroptera: Leptophlebiidae) to moving water and light of different wavelengths

1. Although laboratory studies of the behaviour of aquatic macroinvertebrates are common, there has been little critical evaluation of the importance of test conditions to them. We used a common Australian leptophlebiid mayfly, Nousia sp., to investigate responses to light, wavelength of light, presence or absence of cover and still or flowing water.
2. Nousia sp. showed substantial qualitative differences in behaviour, as measured by movement, when there was no refuge (in the form of a crevice beneath a tile) present in the experimental arena.
3. We found no evidence of diel periodicity in activity in Nousia sp.
4. Nousia sp. did not respond to infra-red, red or green light at a flux density of 18–19 μmol m^–2 s^–1.
5. Nymphs were three times more likely to remain stationary in flowing water (mean velocity 0.10 m s^–1) than in still water.
6. We conclude that generalized assumptions about test conditions for experiments designed to quantify laboratory behaviour in benthic macroinvertebrates are unjustified and that evaluation of the individual requirements of test species should be conducted routinely.     

Spatial variations in nutrient supply to the red algae Eucheuma serra (J. Agardh) J. Agardh

The nutrient supply rates within the canopy of the economically important red algal species, Eucheuma serra J. Agardh were determined experimentally in a recirculating flow-chamber. A single individual was placed in the working section of the 2000 × 200 × 250 mm³ acrylic flow-chamber and subjected to unidirectional water velocities from 1.0 to 9.3 cm s⁻¹. Rates of nutrient supply were determined using 9.7 mm diameter CaSO₄ (gypsum) spheres that were attached to the thallus inside and outside of the canopy. The supply rates within the canopy were 56% less than outside of the canopy. Increases in internal and external water velocity asymptotically increased the nutrient supply rates regardless of location. A model was developed to examine how changes in ammonium and nitrate supply compared with the physiologically maximum uptake rates of these nutrients. The results suggest that when the ammonium concentration in the water was 20 µmol L⁻¹ uptake rates were limited by the supply rate especially at velocities below 5 cm s⁻¹, whereas in the case of 20 µmol L⁻¹ of nitrate, the supply of nitrate was more than adequate to maximize nutrient uptake.     

Relative effectiveness and interaction of ultraviolet-B, red and blue light in anthocyanin synthesis of apple fruit

The effect of light on anthocyanin production in apple ( Malus pumila Mill. cv. Jonathan) skin disks was investigated, with prolonged irradiation from different light sources. High fluence rates of white light provided from a xenon lamp were unable to produce large amounts of anthocyanin, and anthocyanin production became saturated at about 30 W m⁻². When UV-B light, provided by a fluorescent lamp which had an emission peak at 312 nm, was combined with the white light, anthocyanin production was synergistically stimulated and increased up to the highest fluence rates of white light tested (44 W m⁻²). This UV-B light was more effective than red and blue light provided from fluorescent lamps, but anthocyanin production became saturated at about 1.7 W m⁻². However, simultaneous irradiation with red and UV-B light had a synergistic effect. UV-B light was also effective in increasing anthocyanin production in whole fruit. Therefore this synergism seemed to have an important role in the development of the desirable red skin color under field light conditions. The results of aminoethoxyvinylglycine treatment suggested that ethylene was not involved in the stimulative effect of UV-B light.     

Low irradiance modifies the effect of water stress on survival and growth-related parameters during the early developmental stages of buckwheat (Fagopyrum esculentum)

In order to characterize physiological modifications encountered by buckwheat plants exposed to both drought and low-light stresses, seedlings (cv. La Harpe) were exposed under controlled environmental conditions, to a progressive decline in soil volumetric water content under two light regimes: low irradiance (80 µmol m⁻² s⁻¹) or moderate irradiance (160 µmol m⁻² s⁻¹). Phenological evolution of the whole plant until the macroscopic appearance of the reproductive structure and physiological properties of leaves in relation to their position on the main axis were quantified. Water stress reduced net assimilation rate (NAR) before specific leaf area (SLA) and induced a decrease in stomatal conductance (g_l) and carbon isotope discrimination (Δ). Water consumption by stressed plants was similar under both light treatments. Water-stressed plants under moderate irradiance exhibited higher growth, NAR, osmotic adjustment, and lower SLA than plants maintained under low irradiance. However, the former died after 27 days of treatment while the latter still remained alive until the experiment was discontinued (40 days). We concluded that the physiological strategy adopted by the water-stressed plants maintained under moderate irradiance did not afford a long-term advantage in terms of survival. The effects of a combination of low-light and water stress on chlorophyll concentration and carbon isotope discrimination (Δ) are discussed in relation to growth parameters.