A Method to Estimate Practical Radial Oxygen Loss of Wetland Plant Roots

The estimation of practical radial oxygen loss (ROL) of wetland plant roots was attempted in this study. We have devised a new method to measure ROL of wetland plant roots. The whole root system was bathed in an anoxic nutrient solution. Oxygen released from the root was removed immediately by introducing oxygen-free nitrogen gas (O₂ < 4 nmol L⁻¹) to mimic natural habitats where released oxygen is consumed rapidly due to chemical and biological oxidation processes. Oxygen removed from the root-bathing chamber was simultaneously detected colorimetrically by use of the highly oxygen-sensitive anthraquinone radical anion (AQ·⁻) in a cell outside the root-bathing chamber, which decolorized by a rapid reaction with oxygen. An emergent macrophyte Typha latifolia L. was incubated, and its ROL was measured by both the new method and one of the conventional methods, the closed chamber/electrode method, by which the ROL of Typha latifolia L. had not yet been measured. The new method succeeded in detecting the ROL, whereas the conventional method was not able to detect oxygen, due to the level being below the detection limit of the oxygen electrode. The oxygen supply via the seedlings of Typha latifolia L. was ca. 10 times higher compared with control measurements without plant. Light illumination significantly enhanced the ROL of Typha latifolia L. (0.33 nmol O₂ g⁻¹ root dry weight s⁻¹ under light and 0.18 nmol O₂ g⁻¹ root dry weight s⁻¹ in the dark). Theses values fall between those previously reported by the closed chamber/titanium citrate method and the open chamber/electrode method.     

Microbial degradation of tetraethyl lead in soil monitored by microcalorimetry

Sieved agricultural soil samples were treated with the anti-knock agent tetraethyl lead (Et₄Pb), and the resulting effects were analyzed by microcalorimetry. Et₄Pb additions resulted in an increase of the heat production rate, provided that oxygen was present and that the soil was not autoclaved. The increased heat production rate was accompanied by degradation of Et₄Pb, as verified by speciation analysis (GC-MS) of the remaining Et₄Pb and its ionic degradation products (triethyl lead and diethyl lead cations). Conclusive evidence was obtained that these transformations were mediated mainly by microbes. At an initial Et₄Pb concentration of 2 g Pb/kg dry weight the biodegradation rate was about 780 μmol day⁻¹ kg dry weight⁻¹, whilst the chemical decomposition was only 50 μmol day⁻¹ kg dry weight⁻¹. A fivefold rise of the initial Et₄Pb concentration resulted in a decrease of the biodegradation rate to 600 μmol day⁻¹ kg dry weight⁻¹ and an increase of the chemical decomposition to 200 μmol day⁻¹ kg dry weight⁻¹. The biodegradation rate was not influenced by the addition of glucose, which means that no indication for a cometabolic attack of Et₄Pb was found. Received: 25 February 1997 / Received revision: 22 April 1997 / Accepted: 27 April 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.     

Physiological differences in the growth of <Emphasis Type="Italic">Sargassum horneri</Emphasis> between the germling and adult stages

The effects of temperature, irradiance, and daylength on Sargassum horneri growth were examined at the germling and adult stages to discern their physiological differences. Temperature–irradiance (10, 15, 20, 25, 30°C × 20, 40, 80 μmol photons m⁻²s⁻¹) and daylength (8, 12, 16, 24 h) experiments were carried out. The germlings and blades of S. horneri grew over a wide range of temperatures (10–25°C), irradiances (20–80 μmol photons m⁻²s⁻¹), and daylengths (8–24 h). At the optimal growth conditions, the relative growth rates (RGR) of the germlings were 21% day⁻¹ (25°C, 20 μmol photons m⁻²s⁻¹) and 13% day⁻¹ (8 h daylength). In contrast, the RGRs of the blade weights were 4% day⁻¹ (15°C, 20 μmol photons m⁻²s⁻¹) and 5% day⁻¹ (12 h daylength). Negative growth rates were found at 20 μmol photons m⁻²s⁻¹ of 20°C and 25°C treatments after 12 days. This phenomenon coincides with the necrosis of S. horneri blades in field populations. In conclusion, we found physiological differences between S. horneri germlings and adults with respect to daylength and temperature optima. The growth of S. horneri germlings could be enhanced at 25°C, 20 μmol photons m⁻²s⁻¹, and 8 h daylength for construction of Sargassum beds and restoration of barren areas.     

Cell growth and nutritive value of the tropical benthic diatom, <Emphasis Type="Italic">Amphora</Emphasis> sp., at varying levels of nutrients and light intensity,and different culture locations

Two series of experiments were conducted to determine suitable growth factors for the mass propagation of the local algal isolate Amphora sp. A higher growth rate of 0.2 doubling (μ) day⁻¹ was attained at a lower photosynthetic photon flux density (PPFD; 11.4 μmol photon m⁻²s⁻¹) compared to cultures exposed to higher levels of PPFD (16.1 μmol photon m⁻²s⁻¹, −0.1 μ day ⁻¹; 31.3 μmol photon m⁻²s⁻¹, 0.0 μ day⁻¹). Cultures located inside the laboratory had a significantly higher cell density (133 × 10⁴ cells cm⁻²) and growth rate (0.3 μ day⁻¹) compared to those located outdoors (100 × 10⁴ cells cm⁻², 0.2 μ day⁻¹). A comparison of nutrient medium across two locations showed that lipid content was significantly higher in cultures enriched with F/2MTM (macronutrients + trace metals) and F/2MV (macronutrients + vitamins). Saturated fatty acids were also present in high concentrations in cultures enriched with F/2M (macronutrients only). Significantly higher amounts of saturated fatty acids were observed in cultures located outdoors (33.1%) compared to those located indoors (26.6%). The protein, carbohydrates and n-6 fatty acid content of Amphora sp. were influenced by the location and enrichment of the cultures. This study has identified growth conditions for mass culture of Amphora sp. and determined biochemical composition under those culture conditions. Presented at the 6th Meeting of the Asian Pacific Society of Applied Phycology, Manila, Philippines.     

Light-Dependency of Growth and Secondary Metabolite Production in the Captive Zooxanthellate Soft Coral Sinularia flexibilis

The branching zooxanthellate soft coral Sinularia flexibillis releases antimicrobial and toxic compounds with potential pharmaceutical importance. As photosynthesis by the symbiotic algae is vital to the host, the light-dependency of the coral, including its specific growth rate (μ day⁻¹) and the physiological response to a range of light intensities (10–1,000 μmol quanta m⁻² s⁻¹) was studied for 12 weeks. Although a range of irradiances from 100 to 400 μmol quanta m⁻² s⁻¹ was favorable for S. flexibilis, based on chlorophyll content, a light intensity around 100 μmol quanta m⁻² s⁻¹ was found to be optimal. The contents of both zooxanthellae and chlorophyll a were highest at 100 μmol quanta m⁻² s⁻¹. The specific budding rate showed almost the same pattern as the specific growth rate. The concentration of the terpene flexibilide, produced by this species, increased at high light intensities (200–600 μmol quanta m⁻² s⁻¹).     

Photosynthetic acclimation to photon irradiance and its relation to chlorophyll fluorescence and carbon assimilation in the halotolerant green alga Dunaliella viridis

This work describes the long-term acclimation of the halotolerant microalga Dunaliella viridis to different photon irradiance, ranging from darkness to 1500 μmol m⁻² s⁻¹. In order to assess the effects of long-term photoinhibition, changes in oxygen production rate, pigment composition, xanthophyll cycle and in vivo chlorophyll fluorescence using the saturating pulse method were measured. Growth rate was maximal at intermediate irradiance (250 and 700 μmol m⁻² s⁻¹). The increase in growth irradiance from 700 to 1500 μmol m⁻² s⁻¹ did not lead to further significant changes in pigment composition or EPS, indicating saturation in the pigment response to high light. Changes in Photosystem II optimum quantum yield (F_v/F_m) evidenced photoinhibition at 700 and especially at 1500 μmol m⁻² s⁻¹. The relation between photosynthetic electron flow rate and photosyntetic O₂ evolution was linear for cultures in darkness shifting to curvilinear as growth irradiance increased, suggesting the interference of the energy dissipation processes in oxygen evolution. Carbon assimilation efficiencies were studied in relation to changes in growth rate, internal carbon and nitrogen composition, and organic carbon released to the external medium. All illuminated cultures showed a high capability to maintain a C:N ratio between 6 and 7. The percentage of organic carbon released to the external medium increased to its maximum under high irradiance (1500 μmol m⁻² s⁻¹). These results suggest that the release of organic carbon could act as a secondary dissipation process when the xanthophyll cycle is saturated. This revised version was published online in June 2006 with corrections to the Cover Date.     

Phenology of Chondrus ocellatus in Cheongsapo Near Busan, Korea

The reproductive phenology of Chondrus ocellatus and the effects of temperature and light on its growth were examined in Cheongsapo near Busan, Korea, from September 1994 to August 1995. The vegetative plants dominated over the year, with a peak occurrence in January. Gameto- and tetrasporophytes were most abundant in November and August. All vegetative and reproductive plants had a peak both in length and weight in October, when seawater temperature was highest (24°C). In laboratory culture, the maximum relative growth rate (RGR) of 2.94% day⁻¹ was obtained at 20°C and 100 μmol photons m⁻² s⁻¹, whereas the lowest value was recorded at 25°C and 100 μmol photons m⁻² s⁻¹ in a 12: 12 h LD photoperiod regime. Among the three photoperiod regimes (8:16 h, 12:12 h, 16:8 h LD) tested, there was evidence of a higher RGR in the 12:12 h LD cycle. This result suggests that the growth and reproduction of C. ocellatus are correlated with the seawater temperature based on laboratory culture and field observations.     

Photosynthetic CO2 affinity of the aquatic carnivorous plant Utricularia australis (Lentibulariaceae) and its investment in carnivory

Aquatic carnivorous plants usually grow in shallow dystrophic waters poor in inorganic N and P. Utricularia australis was chosen as a model plant for its prolific distribution and great ecological plasticity. The photosynthetic CO₂ compensation point and factors associated with investment in carnivory and capture of prey were measured in 17 U. australis micropopulations in Třeboň basin, Czech Republic, together with water chemistry factors at these sites differing greatly in their trophic level, water hardness, and prey availability. Apical shoot growth rate was estimated at some oligotrophic sites. The micropopulations differed greatly in the proportion of traps with animal prey (2.7–70%, mean 26%), trap proportion to total biomass (1.4–42%, mean 26%), mean trap biomass (0.7–63 μg trap⁻¹, mean 19 μg), and maximum trap size (1–3 mm, mean 2.0 mm). CO₂ compensation points ranged from 0.7 to 6.1 μM (mean 2.6 μM). A weak HCO₃ ⁻ use (compensation point 0.51 mM) was found in plants growing in alkaline water. Trap biomass proportion did not correlate significantly with prey capture and CO₂ compensation points with ambient [CO₂]. A very rapid apical growth (2.5–4.2 new nodes day⁻¹) occurred in sand pits. Thus, HCO₃ ⁻ use in U. australis can be induced by growing at very high pH. CO₂ compensation points resembled those known in other aquatic non-carnivorous plants. They did not reflect carnivory. In spite of very rapid apical shoot growth, the relative growth rate of U. australis can be zero in oligotrophic habitats without prey.     

Response of Photosynthetic Apparatus of Spring Barley (Hordeum vulgare L.) to Combined Effect of Elevated CO2 Concentration and Different Growth Irradiance

The response of barley (Hordeum vulgare L. cv. Akcent) to various photosynthetic photon flux densities (PPFDs) and elevated [CO₂] [700 μmol (CO₂) mol⁻¹; EC] was studied by gas exchange, chlorophyll (Chl) a fluorescence, and pigment analysis. In comparison with barley grown under ambient [CO₂] [350 μmol (CO₂) mol⁻¹; AC] the EC acclimation resulted in a decrease in photosynthetic capacity, reduced stomatal conductance, and decreased total Chl content. The extent of acclimation depression of photosynthesis, the most pronounced for the plants grown at 730 μmol m⁻² s⁻¹ (PPFD₇₃₀), may be related to the degree of sink-limitation. The increased non-radiative dissipation of absorbed photon energy for all EC plants corresponded to the higher de-epoxidation state of xanthophylls only for PPFD₇₃₀ barley. Further, a pronounced decrease in photosystem 2 (PS2) photochemical efficiency (given as F_V/F_M) for EC plants grown at 730 and 1 200 μmol m⁻² s⁻¹ in comparison with AC barley was related to the reduced epoxidation of antheraxanthin and zeaxanthin back to violaxanthin in darkness. Thus the EC conditions sensitise the photosynthetic apparatus of high-irradiance acclimated barley plants (particularly PPFD₇₃₀) to the photoinactivation of PS2. This revised version was published online in August 2006 with corrections to the Cover Date.     

Impact of CO2 Enrichment and Variable Nitrogen Supplies on Composition and Partitioning of Essential Nutrients of Wheat

This study was conducted to determine effects of nitrogen supply (75 and 150 kg(N) ha⁻¹) and CO₂ enrichment on partitioning of macro and micro nutrients in wheat (Triticum aestivum L. cv. HD-2285). Plants were grown from seedling emergence to maturity inside open top chambers under ambient CO₂ (CA, 350 ± 50 μmol mol⁻¹) and elevated CO₂ (CE, 600 ± 50 μmol mol⁻¹). Leaves, stems and roots of the same physiological age were analyzed for carbon, nitrogen, calcium, copper, iron, zinc and manganese content at 40, 60 and 90 d after germination. C, Cu, Mn and Zn content was higher in the stem, leaves and roots on dry mass basis under CE than CA. However, N and Fe contents decreased in CE grown plants. Ca content was unaffected due to CE and variable N supplies. This revised version was published online in July 2006 with corrections to the Cover Date.     

Extracellular Matrix in Early Stages of Direct Somatic Embryogenesis in Leaves of Drosera spathulata

The growth and water relations of Paulownia fortunei in photoautotrophic cultures (nutrient medium lacking sucrose and growth regulator) with CO₂ enrichment (PWAH) or without CO₂ enrichment (PWAL) were compared with those in photomixotrophic shoot (PWC; 30 g dm⁻³ sucrose and 0.3 mg dm⁻³ N⁶-benzyladenine) and root cultures (PWR; 0.3 mg dm⁻³ indole-3-butyric acid). The photoautotrophic and photomixotrophic cultures were incubated under photosynthetic photon flux 125 and 60 μmol m⁻² s⁻¹, respectively. 100 % sprouting and significantly higher number of shoots (1.6) were obtained with PWAH as compared to PWAL and PWC. PWAH and PWAL stimulated spontaneous rooting from the cut end of axillary shoots. In PWAH, 84 % of shoots rooted with an average of 5.9 roots per shoot and 4.0 cm of root length in 21 d. Rooting of photomixotrophic shoot cultures were stimulated by an auxin treatment. In this case, 98.3 % of shoots were rooted with an average of 4.6 roots per shoot and 1.9 cm length. A microscopic observation on leaf abaxial surface prints from photomixotrophic shoot and root cultures showed widely open (6 – 8 μm) spherical stomata (12 – 14 μm) and from photoautotrophic cultures elliptical stomata (10 – 12 μm) with narrow openings (3 – 4 μm). Leaves from photomixo-trophic cultures had higher stomatal index as compared to photoautotrophic cultures. The rate of moisture loss from detached leaves was not varying significantly in different cultures. This revised version was published online in July 2006 with corrections to the Cover Date.     

Micropropagation of Gymea Lily (<Emphasis Type="Italic">Doryanthes excelsa</Emphasis> Corrêa) from New South Wales,Australia

The physiological effects of three auxins [indole-3-butyric acid (IBA), α-naphthaleneacetic acid (NAA) and 2,4-dichlorophenoxyacetic acid (2,4-d)] and two cytokinins [thidiazuron (TDZ) and N⁶-benzylaminopurine (NAA)] on in vitro morphogenesis of Doryanthes excelsa were measured. Longitudinal bud sections derived from immature inflorescences were used as a source of explants. Callus regeneration was observed at the highest frequencies (46.2%) when grown on media containing 50 μmol L^-1 NAA and 0.5 μmol L⁻¹ TDZ. Adventitious shoot organogenesis was observed at the highest frequency (56.8%) when grown on media containing 0.5 μmol L⁻¹ NAA and 50 μmol L⁻¹ TDZ. Regenerated shoots were rooted ex vitro after 6 weeks when dipped in a solution of 50 μmol L⁻¹ NAA or no plant growth regulators were applied.     

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.     

Photosynthetic and leaf anatomical characteristics of Castanea sativa: a comparison between in vitro and nursery plants

The anatomic and functional leaf characteristics related to photosynthetic performance of Castanea sativa growing in vitro and in nursery were compared. The irradiance saturated photosynthesis in in vitro grown plantlets was significantly lower compared to nursery plants (65 vs. 722 μmol m⁻² s⁻¹). The maximum photosynthetic rate (P_Nmax) was 4.0 and 10.0 μmol(CO₂) m⁻² s⁻¹ in in vitro microshoots and nursery plant leaves, respectively. Carboxylation efficiency (C_E) and electron transport rate (ETR) were three-folds higher in nursery plants than in microshoots. The nonphotochemical quenching (NPQ) was saturated at 80 μmol m⁻² s⁻¹ in microshoots suggesting limited photoprotection by thermal dissipation. The microshoots had wide open, spherical stomata and higher stomatal density than nursery plants and they had almost no epicuticular wax. Consequently, the microshoots had high stomatal conductance and high transpiration rate. These anatomic and functional leaf characteristics are likely major causes of the low survival rates of plantlets after ex vitro transfer.     

Factors influencing shoot regeneration from cotyledons of tetraploid <Emphasis Type="Italic">Isatis indigotica</Emphasis> fort

Summary An efficient in vitro plant regeneration system from cotyledons was established in tetraploid Isatis indigotica Fort. Factors influencing shoot regeneration from cotyledons, including culture medium type, combinations of plant growth regulators, and sucrose concentrations in the medium, as well as illumination were investigated. Murashige and Skoog's (MS) medium was found to be best for promoting shoot regeneration, followed by Gamborg's B₅ and White's medium. The highest shoot regeneration frequency was achieved from cotyledons cultured on MS medium supplemented with 2.0 mgl⁻¹ (8.9 μM) 6-benzyladenine and 1.0 mgl⁻¹ (5.4 μM) α-naphthaleneacetic acid (NAA), with 97.9% regeneration, associated with a high number of multiple shoots developed per explant (8.6 shoots per explant). A sucrose concentration of 3% present in the medium and light conditions were beneficial for shoot regeneration. The shoots developed were rooted in a half-strength MS medium supplemented with 1.0 mgl⁻¹ (5.4 μM) NAA and successfully transplanted in soil in pots with over 85% survival. The establishment of an efficient plant regeneration procedure from cotyledons provides a basis for the rapid in vitro multiplication of tetraploid Isatis indigotica Fort., one of the most extensively used medicinal plants in China currently under great shortage.     

Combined effect of temperature and light intensity on growth and extracellular polymeric substance production by the cyanobacterium Arthrospira platensis

The effects of light intensity and temperature on Arthrospira platensis growth and production of extracellular polymeric substances (EPS) in batch culture were evaluated using a three-level, full-factorial design and response surface methodology. Three levels were tested for each parameter (temperature: 30, 35, 40°C; light intensity: 50, 115, 180 μmol photons m⁻² s⁻¹). Both growth and EPS production are influenced mainly by the temperature factor but the interaction term temperature*light intensity also had a significant effect. In addition, conditions optimising EPS production are different from those optimising growth. The highest growth rate (0.414 ± 0.003 day⁻¹) was found at the lowest temperature (30°C) and highest light intensity (180 μmol photons m⁻² s⁻¹) tested, no optima were detectable within the given test range. Obviously, optima for growth must be at a temperature lower than 30°C and a light intensity higher than 180 μmol photons m⁻² s⁻¹. For EPS production, light intensity had a positive linear effect (optimum obviously higher than 180 μmol photons m⁻² s⁻¹), but for the temperature parameter a maximum effect was detectable at 35°C.     

Life-history, thallus ontogeny, and the effects of temperature, irradiance and salinity on growth of the edible green seaweed Gayralia spp. (Chlorophyta) from Southern Brazil

Gayralia K.L. Vinogr. is a monostromatic green alga of commercial importance in the southern Brazil, and its cultivation is being considered. This paper reports some basic aspects of the biology of this poorly known genus. Two populations of Gayralia spp., from outer and inner sectors of Paranaguá Bay, showed an asexual life history with a distinct pattern of thallus ontogeny. In one population (Gayralia sp. 1), zooids developed an expanded monostromatic blade directly, while in the other (Gayralia sp. 2) zooids produced an intermediate saccate stage, before giving rise to a monostromatic blade. Thalli of the two species differ in size and in cell diameter. The effects of temperature (16–30°C), irradiance (50–100 μmol photons m⁻² s⁻¹), and salinity (5–40 psu) on the growth of both populations were assessed. Plantlets of Gayralia sp. 1 from in vitro cultures showed a broader tolerance to all salinity and irradiance levels tested, with the highest growth rate (GR; mean 17% day⁻¹) at 21.5°C and 100 μmol photons m⁻² s⁻¹. Plantlets of Gayralia sp. 1 collected during the winter in the field showed higher GR, ranging from 5% day⁻¹ to 7.5% day⁻¹ in salinities from 20 to 40 psu, and 2.0% day⁻¹ and 4.3% day⁻¹ for plantlets collected during the summer. Gayralia sp. 2 from the field showed highest GR at salinity of 15 psu. These results suggest distinct physiological responses of the two species, in accordance with their distribution: Gayralia sp. 2 is limited to the inner areas of the estuary, while Gayralia sp. 1 grows in outer areas, where salinity values are higher than 20 psu. These data indicate that Gayralia sp. 1 has a higher potential for aquaculture than Gayralia sp. 2 due to its larger thalli, higher GR, and wider tolerance to environmental variations.     

Different sealing materials for petri dishes strongly affect shoot regeneration and development from leaf explants of quince ‘BA 29’

Summary The effect of different sealing materials [i.e., polyvinyl chloride (PVC) transparent film, and Parafilm (PARA) for Petri dishes was investigated on shoot regeneration from quince (Cydonia oblonga L.) ‘BA 29’ leaf explants. Leaves were excised from proliferating shoot cultures, transversally scored, and placed with the abaxial side down in 60-mm Petri dishes containing 10 ml of Murashige and Skoog modified medium, with 5.4 μM α-naphthaleneacetic acid, 4.5 μM thidiazuron, 200 mg l⁻¹ cefotaxime, and 0.25% (w/v) Phytagel (IM medium) for shoot bud induction, and cultured in darkness at 22±2°C for 28 d. Then the explants were transferred to standard conditions (16-h photoperiod at 30 μmol m⁻² s⁻¹ photosynthetically active radiation) on a medium similar to IM, except for lack of NAA, and with 0.65% (w/v) agar instead of Phytagel, for an additional 15–28 d. The sealing combinations PARA-PARA, PARA-PVC, PVC-PARA, and PVC-PVC (in the induction-expression phases) were compared during regeneration and for their carry-over effect on shoot development after transfer of explants to an elongation medium (0.9 μM 6-benzyladenine). Carbon dioxide accumulated at 27.2 mmol mol⁻¹ at the end of induction, and gradually decreased from 35.4 mmol mol⁻¹ on day 9 to 22.5 mmol mol⁻¹ on day 28 of the expression phase in PARA-sealed Petri dishes, being always much higher than after sealing with PVC (1–2 mmol mol⁻¹). Ethylene concentration was 0.1 and 0.04 μmol mol⁻¹ in the first part of the induction and expression phase, respectively, in PARA-sealed Petri dishes, and slightly decreased with duration of exposure to light during expression; while it was absent in most PVC-sealed dishes. The PARA-PARA and PVC-PVC (induction-expression) combinations gave, respectively, the worst and best results of regeneration and successive shoot development.     

Seasonal variations of microsite light availability within aMiscanthus sinensis canopy

Photosynthetic photon flux density (PPFD) at 15 cm above the ground was measured at 20 microsites in gaps and grass patches within aMiscanthus sinensis Anderss community at 10 s intervals during 5 days every month from May to September 1989. Microsite light availability, which was characterized by daily total PPFD, sunfleck PPFD (PPFD above a threshold value of 50 or 400 μmol m⁻² s⁻¹) and the diffuse site factor, showed evident seasonal changes, with a marked reduction between June and July due to the rapid growth of the grass canopy. The monthly median value of daily total PPFD among the microsites decreased from 10.3 mol m⁻² day⁻¹ in May to 0.77 mol m⁻² day⁻¹ in September, with a reduction in the diffuse site factor from 31 to 4%. During the summer, the median value of the total time of sunflecks exceeding 50 μmol m⁻² s⁻¹ contributed 7–18% of measurement time, but the contribution of these sunflecks to daily total PPFD ranged from 29 to 59%. There was considerable microsite variation in light availability throughout the measurement period. Rank correlation analysis revealed that some microsites, such as those in gaps, consistently received more total PPFD, more sunfleck PPFD and had a higher diffuse site factor than those in grass patches. The diffuse site factor had a linearly positive relationship with daily total PPFD and total sunfleck PPFD for the 20 microsites during the measurement period, confirming that the diffuse site factor is a useful index for microsite light availability withinM. sinensis canopies.