In vitro growth and single-leaf photosynthetic response of Cymbidium plantlets to super-elevated CO2 under cold cathode fluorescent lamps

To examine the effectiveness of super-elevated (10,000 μmol mol⁻¹) CO₂ enrichment under cold cathode fluorescent lamps (CCFL) for the clonal propagation of Cymbidium, plantlets were cultured on modified Vacin and Went (VW) medium under 0, 3,000 and 10,000 μmol mol⁻¹ CO₂ enrichment and two levels of photosynthetic photon flux density (PPFD, 45 and 75 μmol m⁻² s⁻¹). Under high PPFD, 10,000 μmol mol⁻¹ CO₂ increased root dry weight and promoted shoot growth. In addition, a decrease in photosynthetic capacity and chlorosis at leaf tips were observed. Rubisco activity and stomatal conductance of these plantlets were lower than those of plantlets at 3,000 μmol mol⁻¹ CO₂ under high PPFD, which had a higher photosynthetic capacity. On the other hand, plantlets on Kyoto medium grown in 10,000 μmol mol⁻¹ CO₂ under high PPFD had a higher photosynthetic rate than those on modified VW medium; no chlorosis was observed. Furthermore, growth of plantlets, in particular the roots, was remarkably enhanced. This result indicates that a negative response to super-elevated CO₂ under high PPFD could be improved by altering medium components. Super-elevated CO₂ enrichment of in vitro-cultured Cymbidium could positively affect the efficiency and quality of commercial production of clonal orchid plantlets.     

Growth of In vitro banana (Musa SPP.) shoots under photomixotrophic and photoautotrophic conditions

Summary In vitro banana (Musa spp.) shoots were cultured under photomixotrophic (30 gl⁻¹ sucrose and 0.2 h⁻¹ number of air exchanges of culture vessels) and photoautotrophic (0 gl⁻¹ sucrose and 3.9 h⁻¹ number of air exchanges) conditions for 28 d in 370 cm³ Magenta boxes (GA7-type) containing 70 ml of half-strength Murashige and Skoog (MS) medium with 22.2 μM N⁶-benzyladenine (BA). The effects of varying CO₂ concentration (475 or 1340 μmol mol⁻¹) and light intensity (photosynthetic photon flux (PPF) of 100 or 200 μmol m⁻² s⁻¹) were investigated. Fresh and dry weights of banana shoots grown photomixotrophically were significantly greater on day 28 than those grown photoautotrophically. Photoautorophic shoots had a larger number of unfolded leaves and greater leaf area than photomixotrophic plants by days 14 and 28, regardless of CO₂ concentration. The shoot fresh and dry weights on day 14 in photoautotrophic conditions were significantly greater at PPF of 200 μmol m⁻² s⁻¹ than at 100 μmol m⁻² s⁻¹. The increase in net photosynthetic rate of photoautotrophic banana shoots was significant compared with photomixotrophic shoots. The multiplication ratio of in vitro banana shoots grown photoautotrophically in a 28-d culture period was the greatest at 100 μmol m⁻² s⁻¹ PPF and 475 μmol mol⁻¹ CO₂.     

Phytoplankton production after the collapse of the Larsen A Ice Shelf,Antarctica

Part of the Larsen A Ice Shelf (64°15′S to 74°15′S) collapsed during January 1995. A first oceanographic and biological data set from the newly free waters was obtained during December 1996. Typical shelf waters with temperatures near and below the freezing point were found. A nutrient-rich water mass (max: PO₄ ³⁻ 1.80 μmol L⁻¹ and NO₃ ⁻ 27.64 μmol L⁻¹) was found between 70 and 200 m depth. Chlorophyll-a (Chl-a) values (max 14.24 μg L⁻¹) were high; surface oxygen saturation ranged between 86 and 148%. Diatoms of the genera Nitzschia and Navicula and the prymnesiophyte Phaeocystis sp. were the most abundant taxa found. Mean daily primary production (Pc) estimated from nutrient consumption was 14.80 ± 0.17 mgC m⁻³ day⁻¹. Pc was significantly correlated with total diatom abundance and Chl-a. Calculated ΔpCO₂ (difference of the CO₂ partial pressure between surface seawater and the atmosphere) was –30.5 μatm, which could have contributed to a net CO₂ flux from the atmosphere to the sea and suggests the area has been a CO₂ sink during the studied period. High phytoplankton biomass and production values were found in this freshly open area, suggesting its importance for biological CO₂ pumping.     

The study of microclimate in response to different plant community association in tropical moist deciduous forest from northern India

The data on microclimate were collected between 2010 and 2011 in five forest communities (dry miscellaneous, sal mixed, lowland miscellaneous, teak and savannah) in a tropical moist deciduous forest in Katerniaghat Wildlife Sanctuary, Uttar Pradesh, India to compare how vegetation structure affects microclimate. Diurnal variations in microclimatic variables [photosynthetically active radiation (PAR) at forest understory level, air temperature, soil surface temperature, ambient CO₂, air absolute humidity] were measured with LI-COR 840, LI-COR 191, LI-COR 190 SZ, LI-1400-101 and LI-1400-103 (LI-COR; Lincoln, NE, USA) at centre of three 0.5 ha plots in each forest community. The diurnal trend in microclimatic parameters showed wide variations among communities. PAR at forest floor ranged from 0.0024 to 1289.9 (μmol m⁻²s⁻¹) in post-monsoon season and 0.0012 to 1877.3 (μmol m⁻²s⁻¹) in mid-winter season. Among the five communities, the highest PAR value was observed in savannah and lowest in sal mixed forest. All the forest communities received maximum PAR at forest floor between 1000 and 1200 h. The ambient air temperature ranged from 19.15 to 26.69°C in post-monsoon season and 11.31 to 23.03°C in mid-winter season. Soil temperature ranged from 13.54 to 36.88°C in post-monsoon season and 6.39 to 29.17°C in mid-winter season. Ambient CO₂ ranged from 372.16 to 899.14 μmol mol⁻¹ in post-monsoon season and 396.65 to 699.65 μmol mol⁻¹ in mid-winter season. In savannah ecosystem, diurnal trend of ambient CO₂ was totally different from rest four communities. According to Canonical correspondence analysis, PAR and ambient CO₂ are most important in establishment of forest community, among microclimatic variables.     

Acclimation of the summer annual species, Lolium temulentum, to CO2 enrichment

Lolium temulentum L. Ba 3081 was grown hydroponically in air (350 μmol mol⁻¹ CO₂) and elevated CO₂ (700 μmol mol⁻¹ CO₂) at two irradiances (150 and 500 μmol m⁻² s⁻¹) for 35 days at which point the plants were harvested. Elevated CO₂ did not modify relative growth rate or biomass at either irradiance. Foliar carbon-to-nitrogen ratios were decreased at elevated CO₂ and plants had a greater number of shorter tillers, particularly at the lower growth irradiance. Both light-limited and light-saturated rates of photosynthesis were stimulated. The amount of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) protein was increased at elevated CO₂, but maximum extractable Rubisco activities were not significantly increased. A pronounced decrease in the Rubisco activation state was found with CO₂ enrichment, particularly at the higher growth irradiance. Elevated-CO₂-induced changes in leaf carbohydrate composition were small in comparison to those caused by changes in irradiance. No CO₂-dependent effects on fructan biosynthesis were observed. Leaf respiration rates were increased by 68% in plants grown with CO₂ enrichment and low light. We conclude that high CO₂ will only result in increased biomass if total light input favourably increases the photosynthesis-to-respiration ratio. At low irradiances, biomass is more limited by increased rates of respiration than by CO₂-induced enhancement of photosynthesis. Received: 23 February 1999 / Accepted: 15 June 1999     

Thidiazuron-induced high-frequency direct shoot organogenesis of <Emphasis Type="Italic">Cannabis sativa</Emphasis> L.

Induction of high-frequency shoot regeneration using nodal segments containing axillary buds from a 1-yr-old mother plants of Cannabis sativa was achieved on Murashige and Skoog (MS) medium containing 0.05–5.0 μM thidiazuron. The quality and quantity of regenerants were better with thidiazuron (0.5 μM thidiazuron) than with benzyladenine or kinetin. Adding 7.0 μM of gibberellic acid into a medium containing 0.5 μM thidiazuron slightly increased shoot growth. Elongated shoots when transferred to half-strength MS medium supplemented with 500 mg l⁻¹ activated charcoal and 2.5 μM indole-3-butyric acid resulted in 95% rooting. The rooted plants were successfully acclimatized in soil. Following acclimatization, growth performance of 4-mo-old in vitro propagated plants was compared with ex vitro vegetatively grown plants of the same age. The photosynthesis and transpiration characteristics were studied under different light levels (0, 500, 1,000, 1,500, or 2,000 μmol m⁻² s⁻¹). An increase in photosynthesis was observed with increase in the light intensity up to 1,500 μmol m⁻² s⁻¹ and then decreased subsequently at higher light levels in both types of plants. However, the increase was more pronounced at lower light intensities below 500 μmol m⁻² s⁻¹. Stomatal conductance and transpiration increased with light intensity up to highest level (2000 μmol m⁻² s⁻¹) tested. Intercellular CO₂ concentration (C _i) and the ratio of intercellular CO₂ concentration to ambient CO₂ (C _i/C _a) decreased with the increase in light intensity in both in vitro as well as ex vitro raised plants. The results show that in vitro propagated and hardened plants were functionally comparable to ex vitro plants of same age in terms of gas and water vapor exchange characteristics, within the limits of this study.     

Light acclimatisation of Elodea nuttallii grown under ambient DIC conditions

Light acclimatisation capabilities of Elodea nuttallii at nearly ambient DIC conditions were investigated by determining growth characteristics, main photosynthetic parameters and pigmentation of plants incubated at 5 different irradiances (10–146 μmol photons m⁻² s⁻¹). Positive net growth was observed under all light treatments tested. Maximum ratio root versus shoot (r:s) of 1.86 was achieved at medium irradiances (72–94 μmol photons m⁻² s⁻¹), whereas at low (10 μmol photons m⁻² s⁻¹) and high irradiances (146 μmol photons m⁻² s⁻¹) r:s was significantly lower (0.39 and 1.05, respectively). With respect to main photosynthetic parameters, an increase of light compensation points (E _c), attended by decreasing ratios of light saturation points of photosynthesis (E _k)/irradiance were observed. E _c values were comparable to other low-light adapted macrophytes, which indicate that E. nuttallii can be regarded as a low-light adapted plant, under photorespiratory conditions. This was also confirmed by maximum E _k values of just 73 μmol photons m⁻² s⁻¹. Further support was achieved from pigmentation and non-photochemical quenching (NPQ) data, both indicating rather limited acclimatisation ability at light treatments above 90 μmol photons m⁻² s⁻¹. These results are discussed with respect to the competitive abilities of E. nuttallii under nearly ambient (photorespiratory) DIC conditions, especially in dense stands and turbid phytoplankton-dominated waters.     

Seed germination and seedling physiology of Larix kaempferi and Pinus densiflora in seedbeds with charcoal and elevated CO2

We investigated the effect of ectomycorrhizal colonization, charcoal and CO₂ levels on the germination of seeds of Larix kaempferi and Pinus densiflora, and also their subsequent physiological activity and growth. The seeds were sown in brown forest soil or brown forest soil mixed with charcoal, at ambient CO₂ (360 μmol mol⁻¹) or elevated CO₂ (720 μmol mol⁻¹), with or without ectomycorrhiza. The proportions of both conifer seeds that germinated in forest soil mixed with charcoal were significantly greater than for seeds sown in forest soil grown at each CO₂ level (P < 0.05; t-test). However, the ectomycorrhizal colonization rate of each species grown in brown forest soil mixed with charcoal was significantly lower than in forest soil at each CO₂ treatment [CO₂] (P < 0.01; t-test). The phosphorus concentrations in needles of each seedling colonized with ectomycorrhiza and grown in forest soil were greater than in nonectomycorrhizal seedlings at each CO₂ level, especially for L. kaempferi seedlings (P < 0.05; t-test), but the concentrations in seedlings grown in brown forest soil mixed with charcoal were not increased at any CO₂ level. Moreover, the maximum net photosynthetic rate of each seedling for light and CO₂ saturation (P _max) increased when the seedlings were grown with ectomycorrhiza at 720 μmol mol⁻¹ [CO₂]. Ectomycorrhizal colonization led to an increase in the stem diameter of each species grown in each soil treatment at each CO₂ level. However, charcoal slowed the initial growth of both species of seedling, constraining ectomycorrhizal development. These results indicate that charcoal strongly assists seed germination and physiological activity.     

Fast cyclic electron transport around photosystem I in leaves under far-red light: a proton-uncoupled pathway?

Fast cyclic electron transport (CET) around photosystem I (PS I) was observed in sunflower (Helianthus annuus L.) leaves under intense far-red light (FRL) of up to 200 μmol quanta m⁻² s⁻¹. The electron transport rate (ETR) through PS I was found from the FRL-dark transmittance change at 810 and 950 nm, which was deconvoluted into redox states and pool sizes of P700, plastocyanin (PC) and cytochrome f (Cyt f). PC and P700 were in redox equilibrium with K _e = 35 (ΔE _m = 90 mV). PS II ETR was based on O₂ evolution. CET [(PS I ETR) − (PS II ETR)] increased to 50–70 μmol e⁻ m⁻² s⁻¹ when linear electron transport (LET) under FRL was limited to 5 μmol e⁻ m⁻² s⁻¹ in a gas phase containing 20–40 μmol CO₂ mol⁻¹ and 20 μmol O₂ mol⁻¹. Under these conditions, pulse-saturated fluorescence yield F _m was non-photochemically quenched; however, F _m was similarly quenched when LET was driven by low green or white light, which energetically precluded the possibility for active CET. We suggest that under FRL, CET is rather not coupled to transmembrane proton translocation than the CET-coupled protons are short-circuited via proton channels regulated to open at high ΔpH. A kinetic analysis of CET electron donors and acceptors suggests the CET pathway is that of the reversed Q-cycle: Fd → (FNR) → Cyt c_n → Cyt b_h → Cyt b_l → Rieske FeS → Cyt f → PC → P700 →→ Fd. CET is activated when PQH₂ oxidation is opposed by high ΔpH, and ferredoxin (Fd) is reduced due to low availability of e⁻ acceptors. The physiological significance of CET may be photoprotective, as CET may be regarded as a mechanism of energy dissipation under stress conditions.     

Characterization of PSI recovery after chilling-induced photoinhibition in cucumber (<Emphasis Type="Italic">Cucumis sativus</Emphasis> L.) leaves

By simultaneously analyzing the chlorophyll a fluorescence transient and light absorbance at 820 nm as well as chlorophyll fluorescence quenching, we investigated the effects of different photon flux densities (0, 15, 200 μmol m⁻² s⁻¹) with or without 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU) on the repair process of cucumber (Cucumis sativus L.) leaves after treatment with low temperature (6°C) combined with moderate photon flux density (200 μmol m⁻² s⁻¹) for 6 h. Both the maximal photochemical efficiency of Photosystem II (PSII) (F _v/F _m) and the content of active P700 (ΔI/I _o) significantly decreased after chilling treatment under 200 μmol m⁻² s⁻¹ light. After the leaves were transferred to 25°C, F _v/F _m recovered quickly under both 200 and 15 μmol m⁻² s⁻¹ light. ΔI/I _o recovered quickly under 15 μmol m⁻² s⁻¹ light, but the recovery rate of ΔI/I _o was slower than that of F _v/F _m. The cyclic electron transport was inhibited by chilling-light treatment obviously. The recovery of ΔI/I _o was severely suppressed by 200 μmol m⁻² s⁻¹ light, whereas a pretreatment with DCMU effectively relieved this suppression. The cyclic electron transport around PSI recovered in a similar way as the active P700 content did, and the recovery of them was both accelerated by pretreatment with DCMU. The results indicate that limiting electron transport from PSII to PSI protected PSI from further photoinhibition, accelerating the recovery of PSI. Under a given photon flux density, faster recovery of PSII compared to PSI was detrimental to the recovery of PSI or even to the whole photosystem.     

CO<Subscript>2</Subscript>-enriched microenvironment affects sucrose and macronutrients absorption and promotes autotrophy in the <Emphasis Type="Italic">in vitro</Emphasis> culture of kiwi (<Emphasis Type="Italic">Actinidia deliciosa</Emphasis> Chev. Liang and Ferguson)

In traditional in vitro culture, the low CO₂ concentration inside the vessels restricts photosynthesis and necessitates the addition of sucrose to the culture medium as the main energy source, thus bringing about changes in the absorption of mineral elements from the culture medium. In this study, we investigated macronutrient absorption and sugar consumption in Actinidia deliciosa Chevalier Liang and Ferguson cv. Hayward (kiwi), cultured on medium supplemented with varying amounts of sucrose (0, 10, and 20 g l⁻¹) under both heterotrophy and autotrophy, flushed with different concentrations of CO₂ (non-ventilation, 300, 600, and 2,000 μl l⁻¹). In ventilated systems with 20 g l⁻¹ of sucrose, sucrose absorption was less than under non-ventilation. The lowest rate of sucrose absorption was recorded when the explants were cultured on medium supplemented with 20 g l⁻¹ of sucrose and flushed with 600 μl l⁻¹ CO₂. Absorption of NO₃ ⁻, PO₄ ³⁻, and Mg²⁺ were high (maximum) at the end of the culture period (40 d) in explants flushed with 600 μl l⁻¹ CO₂ that have been cultured 20 d in the presence of sucrose and then transferred to a sucrose-free medium. These autotrophic conditions promoted maximum plant growth in terms of both fresh and dry mass as well as the length and number of shoots and leaves. The study shows that to maintain an optimum regime of mineral nutrition for prolonged culture of kiwi in vitro, an increased amount of these three ions should be supplemented in Murashige and Skoog’s medium.     

Physiological responses of Spartina alterniflora to varying environmental conditions in Virginia marshes

Physiological measurements were used to investigate the dependence of photosynthesis on light, temperature, and intercellular carbon dioxide (CO₂) levels in the C₄ marsh grass Spartina alterniflora. Functional relationships between these environmental variables and S. alterniflora physiological responses were then used to improve C₄-leaf photosynthesis models. Field studies were conducted in monocultures of S. alterniflora in Virginia, USA. On average, S. alterniflora exhibited lower light saturation values (~1000 μmol m⁻² s⁻¹) than observed in other C₄ plants. Maximum carbon assimilation rates and stomatal conductance to water vapor diffusion were 36 μmol (CO₂) m⁻² s⁻¹ and 200 mmol (H₂O) m⁻² s⁻¹, respectively. Analysis of assimilation-intercellular CO₂ and light response relationships were used to determine Arrhenius-type temperature functions for maximum rate of carboxylation (V _cmax), phosphoenolpyruvate carboxylase activity (V _pmax), and maximum electron transport rate (J _max). Maximum V _cmax values of 105 μmol m⁻² s⁻¹ were observed at the leaf temperature of 311 K. Optimum V _pmax values (80.6 μmol m⁻² s⁻¹) were observed at the foliage temperature of 308 K. The observed V _pmax values were lower than those in other C₄ plants, whereas V _cmax values were higher, and more representative of C₃ plants. Optimum J _max values reached 138 μmol (electrons) m⁻² s⁻¹ at the foliage temperature of 305 K. In addition, the estimated CO₂ compensation points were in the range of C₃ or C₃–C₄ intermediate plants, not those typical of C₄ plants. The present results indicate the possibility of a C₃–C₄ intermediate or C₄-like photosynthetic mechanism rather than the expected C₄-biochemical pathway in S. alterniflora under field conditions. In a scenario of atmospheric warming and increased atmospheric CO₂ concentrations, S. alterniflora will likely respond positively to both changes. Such responses will result in increased S. alterniflora productivity, which is uncharacteristic of C₄ plants.     

Photosynthetic Response of Carrots to Varying Irradiances

Response to irradiance of leaf net photosynthetic rates (P _N) of four carrot cultivars: Cascade, Caro Choice (CC), Oranza, and Red Core Chantenay (RCC) were examined in a controlled environment. Gas exchange measurements were conducted at photosynthetic active radiation (PAR) from 100 to 1 000 μmol m⁻² s⁻¹ at 20 °C and 350 μmol (CO₂) mol⁻¹(air). The values of P _N were fitted to a rectangular hyperbolic nonlinear regression model. P _N for all cultivars increased similarly with increasing PAR but Cascade and Oranza generally had higher P _N than CC. None of the cultivars reached saturation at 1 000 μmol m⁻² s⁻¹. The predicted P _N at saturation (P _Nmax) for Cascade, CC, Oranza, and RCC were 19.78, 16.40, 19.79, and 18.11 μmol (CO₂) m⁻² s⁻¹, respectively. The compensation irradiance (I _c) occurred at 54 μmol m⁻² s⁻¹ for Cascade, 36 μmol m⁻² s⁻¹ for CC, 45 μmol m⁻² s⁻¹ for Oranza, and 25 μmol m⁻² s⁻¹ for RCC. The quantum yield among the cultivars ranged between 0.057–0.033 mol(CO₂) mol⁻¹(PAR) and did not differ. Dark respiration varied from 2.66 μmol m⁻² s⁻¹ for Cascade to 0.85 μmol m⁻² s⁻¹ for RCC. As P _N increased with PAR, intercellular CO₂ decreased in a non-linear manner. Increasing PAR increased stomatal conductance and transpiration rate to a peak between 600 and 800 μmol m⁻² s⁻¹ followed by a steep decline resulting in sharp increases in water use efficiency. This revised version was published online in August 2006 with corrections to the Cover Date.     

Characteristics of soil CO2 efflux variability in an aseasonal tropical rainforest in Borneo Island

Although soil carbon dioxide (CO₂) efflux from tropical forests may play an important role in global carbon (C) balance, our knowledge of the fluctuations and factors controlling soil CO₂ efflux in the Asian tropics is still poor. This study characterizes the temporal and spatial variability in soil CO₂ efflux in relation to temperature/moisture content and estimates annual efflux from the forest floor in an aseasonal intact tropical rainforest in Sarawak, Malaysia. Soil CO₂ efflux varied widely in space; the range of variation averaged 17.4 μmol m⁻² s⁻¹ in total. While most CO₂ flux rates were under 10 μmol m⁻² s⁻¹, exceptionally high fluxes were observed sporadically at several sampling points. Semivariogram analysis revealed little spatial dependence in soil CO₂ efflux. Temperature explained nearly half of the spatial heterogeneity, but the effect varied with time. Seasonal variation in CO₂ efflux had no fixed pattern, but was significantly correlated with soil moisture content. The correlation coefficient with soil moisture content (SMC) at 30 and 60 cm depth was higher than at 10 cm depths. The annual soil CO₂ efflux, estimated from the relationship between CO₂ efflux and SMC at 30 cm depth, was 165 mol m⁻² year⁻¹ (1,986 g C m⁻² year⁻¹). As this area is known to suffer severe drought every 4–5 years caused by the El Nino-Southern Oscillation, the results suggest that an unpredictable dry period might affect soil CO₂ efflux, leading an annual variation in soil C balance.     

Growth and net photosynthetic rates of <Emphasis Type="Italic">Hosta</Emphasis> ‘blue vision’ during acclimatization in bright,natural light with CO<Subscript>2</Subscript> enrichment

Summary Hosta ‘Blue Vision’, a shade-adapted perennial, was successfully acclimatized in high, natural light conditions in the research Acclimatron^TM at Clemson University, Clemson, SC during the summer of 2000. The supplemental CO₂ levels achieved during acclimatization were 710±113, 2396±121, and 5641±119 μmol mol⁻¹, approximately 2×, 6×, and 15× ambient CO₂. Plants were maintained in H₂O-saturated atmospheres and protected from temperature increases associated with high light intensity. In the 5 wk following ex vitro transfer, plantlet roots grew at the 2× CO₂ level, but shoot biomass was unaffected. Results for the 6× and 15× CO₂ levels were comparable and provided the best plantlet growth. The “doubling time’ that is characteristic of exponential growth was 10.8 and 9.8 d for root and shoot dry weights, respectively. There was no indication of light saturation of net photosynthetic rate (NPR) over the photosynthetic photon flux density (PPFD) range of 100–1200 μmolm⁻²s⁻¹ experienced during this study. An interaction between CO₂ and light intensity levels was detected for NPR of Hosta ‘Blue Vision’ with CO₂ saturation occurring at approximately 2800 μmol mol⁻¹. regardless of light level. Furthermore, at the optimal CO₂ level, NPR increased quadratically as light intensity increased, and NPR was greatest at the maximum light intensity (PPFD: 1200 μmol m⁻²s⁻¹).     

Protein,fatty acid,and pigment content of <Emphasis Type="Italic">Chlorella vulgaris</Emphasis> under different light regimes

The effects of irradiance and photoperiod on growth rates, chlorophyll a, β-carotene, total protein, and fatty acid content of Chlorella vulgaris were determined. The maximum growth rate (1.13 day⁻¹) was at 100 μmol photons m⁻² s⁻¹ and 16:8-h light/dark photoperiod. Chlorophyll a and β-carotene contents significantly differed under different light regimes with chlorophyll a content lower at high irradiance and longer light duration, while β-carotene showed the inverse trend. The total protein and fatty acid content also significantly differed in different light regimes; the maximum percentage of protein (46%) was at 100 μmol photons m⁻² s⁻¹ and 16:8 h photoperiod, and minimum (33%) was at 37.5 μmol photons m⁻² s⁻¹ and 8:16 h photoperiod; the total saturated fatty acids increased, while monounsaturated and polyunsaturated fatty acids decreased with increasing irradiance and light duration.     

Phenol biodegradation by the thermoacidophilic archaeon <Emphasis Type="Italic">Sulfolobus solfataricus</Emphasis> 98/2 in a fed-batch bioreactor

Toxic at low concentrations, phenol is one of the most common organic pollutants in air and water. In this work, phenol biodegradation was studied in extreme conditions (80°C, pH = 3.2) in a 2.7 l bioreactor with the thermoacidophilic archaeon Sulfolobus solfataricus 98/2. The strain was first acclimatized to phenol on a mixture of glucose (2000 mg l⁻¹) and phenol (94 mg l⁻¹) at a constant dissolved oxygen concentration of 1.5 mg l⁻¹. After a short lag-phase, only glucose was consumed. Phenol degradation then began while glucose was still present in the reactor. When glucose was exhausted, phenol was used for respiration and then for biomass build-up. After several batch runs (phenol < 365 mg l⁻¹), specific growth rate (μ_X) was 0.034 ± 0.001 h⁻¹, specific phenol degradation rate (q_P) was 57.5 ± 2 mg g⁻¹ h⁻¹, biomass yield (Y_X/P) was 52.2 ± 1.1 g mol⁻¹, and oxygen yield factor ( \textY_{\textX/\textO 2} ) \left( {{\text{Y}}_{{{\text{X}}/{\text{O}}_{ 2} }} } \right) was 9.2 ± 0.2 g mol⁻¹. A carbon recovery close to 100% suggested that phenol was exclusively transformed into biomass (35%) and CO₂ (65%). Molar phenol oxidation constant ( \textY_{\textO 2 /\textP} ) \left( {{\text{Y}}_{{{\text{O}}_{ 2} /{\text{P}}}} } \right) was calculated from stoichiometry of phenol oxidation and introducing experimental biomass and CO₂ conversion yields on phenol, leading to values varying between 4.78 and 5.22 mol mol⁻¹. Respiratory quotient was about 0.84 mol mol⁻¹, very close to theoretical value (0.87 mol mol⁻¹). Carbon dioxide production, oxygen demand and redox potential, monitored on-line, were good indicators of growth, substrate consumption and exhaustion, and can therefore be usefully employed for industrial phenol bioremediation in extreme environments.     

Leaf photosynthesis, plant growth and nitrogen allocation in rice under different irradiances

The photosynthetic rates and various components of photosynthesis including ribulose-1,5-bisphosphate carboxylase (Rubisco; EC 4.1.1.39), chlorophyll (Chl), cytochrome (Cyt) f, and coupling factor 1 (CF₁) contents, and sucrose-phosphate synthase (SPS; EC 2.4.1.14) activity were examined in young, fully expanded leaves of rice (Oryza sativa L.) grown hydroponically under two irradiances, namely, 1000 and 350 μmol quanta · m⁻² · s⁻¹, at three N concentrations. The light-saturated rate of photosynthesis measured at 1800 μmol · m⁻² · s⁻¹ was almost the same for a given leaf N content irrespective of growth irradiance. Similarly, Rubisco content and SPS activity were not different for the same leaf N content between irradiance treatments. In contrast, Chl content was significantly greater in the plants grown at 350 μmol · m⁻² · s⁻¹, whereas Cyt f and CF₁ contents tended to be slightly smaller. However, these changes were not substantial, as shown by the fact that the light-limited rate of photosynthesis measured at 350 μmol · m⁻² · s⁻¹ was the same or only a little higher in the plants grown at 350 μmol · m⁻² · s⁻¹ and that CO₂-saturated photosynthesis did not differ between irradiance treatments. These results indicate that growth-irradiance-dependent changes in N partitioning in a leaf were far from optimal with respect to N-use efficiency of photosynthesis. In spite of the difference in growth irradiance, the relative growth rate of the whole plant did not differ between the treatments because there was an increase in the leaf area ratio in the low-irradiance-grown plants. This increase was associated with the preferential N-investment in leaf blades and the extremely low accumulation of starch and sucrose in leaf blades and sheaths, allowing a more efficient use of the fixed carbon. Thus, morphogenic responses at the whole-plant level may be more important for plants as an adaptation strategy to light environments than a response of N partitioning at the level of a single leaf. Received: 23 February 1997 / Accepted: 8 May 1997     

Microgravity effects on thylakoid,single leaf,and whole canopy photosynthesis of dwarf wheat

The concept of using higher plants to maintain a sustainable life support system for humans during long-duration space missions is dependent upon photosynthesis. The effects of extended exposure to microgravity on the development and functioning of photosynthesis at the leaf and stand levels were examined onboard the International Space Station (ISS). The PESTO (Photosynthesis Experiment Systems Testing and Operations) experiment was the first long-term replicated test to obtain direct measurements of canopy photosynthesis from space under well-controlled conditions. The PESTO experiment consisted of a series of 21–24 day growth cycles of Triticum aestivum L. cv. USU Apogee onboard ISS. Single leaf measurements showed no differences in photosynthetic activity at the moderate (up to 600 μmol m⁻² s⁻¹) light levels, but reductions in whole chain electron transport, PSII, and PSI activities were measured under saturating light (>2,000 μmol m⁻² s⁻¹) and CO₂ (4000 μmol mol⁻¹) conditions in the microgravity-grown plants. Canopy level photosynthetic rates of plants developing in microgravity at ∼280 μmol m⁻² s⁻¹ were not different from ground controls. The wheat canopy had apparently adapted to the microgravity environment since the CO₂ compensation (121 vs. 118 μmol mol⁻¹) and PPF compensation (85 vs. 81 μmol m⁻² s⁻¹) of the flight and ground treatments were similar. The reduction in whole chain electron transport (13%), PSII (13%), and PSI (16%) activities observed under saturating light conditions suggests that microgravity-induced responses at the canopy level may occur at higher PPF intensity.     

Improved in vitro shoot multiplication and rooting of <Emphasis Type="Italic">Dendrocalamus hamiltonii</Emphasis> Nees et Arn. Ex Munro: production of genetically uniform plants and field evaluation

An efficient in vitro regeneration protocol and field performance of a multipurpose bamboo species Dendrocalamus hamiltonii Nees et Arn. Ex Munro has been demonstrated using single node cuttings taken from the lateral branches of a 20-year-old bush. Axillary buds on the nodal explant sprouted within 10 days of culture on Murashige and Skoog (MS) medium without any plant growth substance. High-frequency proliferation was induced on the propagules (small clusters with 3–5 multiple shoots and rhizomatous portions). Subsequent removal of the shoots (about 1.5 cm) from the rhizomatous portion of propagules (shoot cut) influenced the plantlet formation capacity. A multiplication of about 20-folds was achieved on MS medium supplemented with 8 μM BAP and 1 μM NAA. Rooting efficiency was also markedly enhanced (>90%) when the propagules, following shoot cut, were placed on to MS medium supplemented with 100 μM IBA for 10 days and then transferred to IBA-free medium. This is the first report from this species where 20-fold increment in multiplication was observed at the end of second subculture followed by >90% rooting. The hardened plants, established in the field, exhibited normal growth; their physiological performance has been monitored at 6-month intervals. The rate of photosynthesis increased from 3.55 μmol CO₂ m⁻² s⁻¹ (hardened, ready for field transfer) to 5.44 μmol m⁻² s⁻¹ (6 months of field transfer); following a year of plantation net photosynthesis recorded was 14.0 μmol CO₂ m⁻² s⁻¹ while after 1.5 years it was 12.76 μmol CO₂ m⁻² s⁻¹. These values were compared with those observed for the mother bush. Genetic fidelity of these regenerants was established by RAPD analysis advocating clonal propagation of this species through nodal segment culture and its commercial cultivation.