Isolation and Characterization of Photosynthetically Active Cells from Submersed and Floating Leaves of the Aquatic Macrophyte Potamogeton nodosus Poir

Photosynthetically active cells were isolated by enzymic digestionof floating and submersed leaves of the heterophyllous aquaticmacrophyte Potamogeton nodosus Poir. The yields of cells isolatedfrom floating leaves represented approximately 25% of the leafprotein or chlorophyll, while cell yields from submersed leaveswere only 3%. Photosynthetic activity was maximal in cells isolatedfrom submersed leaves 10 to 14 days after germination of thewinterbuds. Floating leaves were induced by treatment of theplants with abscisic acid. Cells from induced floating leavesshowed maximum photo synthetic rates between 9 and 21 days posttreatment.Phosphoglycerate, fructose 1,6-bisphosphate, sulfate and phosphatewere without significant effect on photosynthesis in eithercell type indicating that the cells were substantially intact.Half-saturation of photosynthesis for bicarbonate was at 0.6mM (pH 7.6) for cells from both leaf types, and the maximumrate was greater for cells from floating leaves. The light intensityfor half-saturation of photosynthesis was approximately 95 µEm^–2s^–1 for cells from both leaf types, and the maximumrate was greater for cells from floating leaves. (Received September 19, 1984; Accepted December 6, 1984)     

Photosynthetic Metabolism and Activity of Carboxylating Enzymes in Emergent,Floating, and Submersed Leaves of Hydrophytes

Radioisotope techniques were used to compare photosynthetic CO₂ fixation, activities of carboxylating enzymes, and the composition of photosynthates in 42 species of aquatic plants (emergent, floating, and submersed hydrophytes) collected from rivers Sysert' and Iset' in Sverdlovsk oblast (Russia). The submersed leaves, in comparison with the emergent and floating leaves, featured lower rates of potential photosynthesis (by 2.2 mg CO²/(dm² h) on average), low content of the fraction I protein, and low activity of Rubisco and phosphoenolpyruvate carboxylase (PEPC). The averaged activities of Rubisco and PEPC were diminished in submersed leaves by 10 and 1 mg/(dm² h), respectively. Different hydrophyte groups showed similar composition of assimilates accumulated after 5-min photosynthesis and did not differ in this respect from terrestrial plants. However, the incorporation of ¹⁴C into sucrose and starch in submersed leaves (30 and 9% of total labeling, respectively) was lower than in emergent and floating leaves (45 and 15%, respectively). At the same time, the incorporation of ¹⁴C into C₄ acids (malate and aspartate) was 1.5 times higher in submersed leaves than in other leaf types. Analysis of leaf differentiation, the Rubisco/PEPC activity ratio, the PEPC activity, and the composition of primary photosynthates in the pulse–chase experiments revealed no evidence of the C₄ effect in the submersed hydrophytes examined. The adaptation of hydatophytes to specific conditions of an aquatic environment was structurally manifested in the reduction (by a factor of 3–5) in the number of chloroplasts per 1 cm² leaf area. This small number of chloroplasts was responsible for low photosynthetic rates in submersed leaves, although metabolic activities of individual chloroplasts were similar for all three hydrophyte groups.     

BIOCHEMICAL HETEROPHYLLY AND FLAVONOID EVOLUTION IN NORTH AMERICAN POTAMOGETON (POTAMOGETONACEAE)

Morphologically heterophyllous species of Potamogeton also commonly display biochemical heterophylly with respect to flavonoid compounds. Generally, floating leaves contain an assortment of flavonoids, whereas submersed leaves often exhibit reduced flavonoid profiles. In strictly submersed (homophyllous) species, two patterns occur. Linear-leaved species have few flavonoids and their biochemical profiles resemble those of submersed leaves of heterophyllous species. Broad-leaved homophyllous species possess flavonoid profiles more similar to those of the floating leaves of heterophyllous species. Numerical analysis of these chemical data is consistent with phylogenetic relationships within the genus derived independently on the basis of morphological and chromosomal data. Glycoflavones, which are probably maintained in floating leaves because of their UV filtering ability, exhibit the most pronounced biochemical heterophylly in Potamogeton. The lack of glycoflavones in submersed leaves of heterophyllous species and in linear-leaved homophyllous species is attributable to the ability of naturally colored water to significantly absorb harmful UV radiation. These observations provide strong support for earlier hypotheses suggesting the importance of flavonoid evolution in the conquest of exposed terrestrial habitats by plants.     

Photosynthesis of submersed macrophytes in acidified lakes II. Carbon limitation and utilization of benthic CO2 sources

Photosynthetic characteristics of carbon-dioxide limitations were analyzed for leaf tissue in a Cartesian-diver system, in which irradiance could be stringently controlled, and with whole plants in electrode macrosystems for submerged macrophytes (Juncus bulbosus L., Sphagnum auriculatum Schimp. var. inundatum (Russow) M. O. Hill) and other benthic moss and algae (Drepanocladus, Batrachospermum, and an algal mat) from acidified lakes. Light compensation points were extremely low for Juncus (1.5–6 μE m^?2 s^?1) and Sphagnum (3–10), and higher for shallow-inhabiting Batrachospermum (22–33). Leaf tissue, whole plants, and algal populations were rapidly limited by CO₂ availability under closed submersed, acidified conditions (pH 4–6).Controlled and in situ experiments were performed, in which the rooting tissue of Juncus bulbosus was partitioned from the leaves and the rates of photosynthetic carbon fixation of the foliage, utilizing dissolved inorganic ¹⁴C-carbon from the water, were analyzed under different conditions of CO₂ enhancement in the rhizosphere of the sediments. Results demonstrated that: (a) from 25 to 40% of the carbon fixed in the leaves can originate from the rhizosphere, diffuse to the leaves via internal gas lacunae, and be fixed photosynthetically; (b) photosynthetic utilization of CO₂ from the water surrounding the leaves is reduced markedly when the CO₂ concentration of the rhizosphere was increased by direct additions of CO₂, bacteria, or organic compounds (glucose, acetate) that stimulate bacterial growth. Shifts to predominance of submersed benthic primary producers with low light compensation points and adapted to acidified lakes are related in part to circumvention of carbon limitation in the water by utilization of enhanced CO₂ availability in the rhizosphere and at the sediment—water interface from bacterial degradation of organic matter, and in part to physiological mechanisms that conserve and recycle CO₂ of respiration and photorespiration.     

Growth and turion formation of Potamogeton crispus in response to different phosphorus concentrations in water

The vegetative growth and turion formation of Potamogeton crispus, a submersed aquatic macrophyte, was investigated under a range of phosphorus (P) concentrations (0.025, 0.25, 2.5 and 25 mg P L^?1) in the ambient water free of algae, aiming to identify the responses of submersed aquatic macrophytes to nutrient enrichment, a common eutrophication problem in China and worldwide. Plant growth was not affected by different P concentrations in terms of biomass accumulation of stems and leaves. However, the contents of chlorophyll a and starch in plants decreased with increasing water P levels, whereas chlorophyll b and carotenoids declined with P level ranging from 0.025 to 2.5 mg P L^?1. The soluble sugar content decreased when water P concentration increased up to 2.5 mg L^?1. The P content in plants increased with increasing water P levels, whereas plant N content decreased and soluble protein increased when water P concentration increased over 0.25 mg L^?1, implying that P. crispus may have modified its metabolism to adapt to water P availability. When P concentration increased to 25 mg L^?1, the number and dry matter production of turions per plant decreased significantly. Meanwhile, there was a significant reduction in turion weight and the accumulations of soluble sugar and starch in turion, when water P concentration was over 0.25 mg L^?1. The results suggest that turion formation in P. crispus is sensitive to P concentration in the ambient water, and high P levels may lead to decreases in P. crispus populations due to the decline in turion production.     

Enzymatic isolation of cells from aquatic macrophytes

Cells were isolated by enzymic digestion from a number of aquatic macrophytes and their photosynthetic activities were determined. Eichhornia crassipes (Mart.) Solms, Myriophyllum spicatum L. and M. brasiliense Cambess provided photosynthetically-active cells after digestion with commercial pectinase. Cells from emergent leaves of M. brasiliense were approximately 3 times more active than cells from submersed leaves (56.1 vs. 17.4 μmoles CO₂ mg^?2 Chl h^?1). Cells could be isolated from E. crassipes by grinding as well as by digestion, but the former were less active (3.1 vs. 24.2 μmoles CO₂ mg Chl h^?1). Attempts to isolate cells from Hydrilla verticillata (L.f.) Royle or Potamogeton pectinatus L. were not successful.     

Regulation of shoot growth, root development and manganese allocation in wheat (Triticum aestivum) genotypes by light intensity

The objective of this study was to assess effects of different light intensities on shoot growth, root development and allocation of root-borne solutes via the transpiration stream to various shoot parts of young wheat plants (Triticum aestivum L.). Hydroponic culture allowed direct access to the roots and shoots throughout the experiment. Under low light intensity (100?μmol photons m^?2?s^?1), shoot growth was restricted, less (but larger) leaves were produced at the main shoot and only a few tillers became visible as compared to plants under high light intensity (380?μmol photons m^?2?s^?1). The root system was indirectly also affected by the illumination of the aerial parts. A larger number of shorter roots were produced under high light leading to a denser root system, while only a small number of longer roots were present under low light. The distribution of ⁵⁴Mn (xylem-mobile, but essentially phloem-immobile in wheat) from the roots to the shoot lead to the conclusion that light regime strongly influences the distribution of root-borne solutes within the shoots. Labels introduced into the roots may allow a deeper insight into the transfer of solutes from the root system to the various shoot parts under different light regimes.     

Comparative feeding selectivity of herbivorous insects on water lilies: aquatic vs. semi‐terrestrial insects and submersed vs. floating leaves

1. The rate of grazing damage experienced by submersed and floating leaves of water lilies (Nuphar variegata and Nymphaea odorata) was monitored in lakes in the Upper Peninsula of Michigan, U.S.A. Herbivores damaged 0.2–1.7% of the leaf surface of water lilies per day. These grazing rates differed between plant species, between submersed and floating leaves, and between lakes. Some leaves had more than 60% of their surface damaged and an overall mean of 16% damage occurred during the 2–3 week monitoring period of this study. 2. Snapshot measurements of grazing damage on randomly collected submersed and floating leaves of Nuphar showed that submersed leaves were more damaged (11.0 ± 1.6%, n = 84) than floating leaves (3.8 ± 0.6%, n = 92). Overall, these 176 Nuphar leaves had 7.2% of their area damaged. 3. Five species of herbivorous insects were commonly found on water lilies (Nymphaeacea). One primarily aquatic insect (sensu 1 ), a caddisfly larva (Trichoptera: Limniphilidae), had a generalized diet of water lilies, other macrophytes, algae, and detritus. Four of the five insects were from primarily terrestrial insect groups (Coleoptera and Diptera;‘secondary invaders’, sensu 1 ) and consumed only water lilies in food preference experiments. 4. The feeding preferences of the generalist trichopteran were altered when the macrophytes were freeze-dried, ground into a powder, and reconstituted in an alginate gel. This suggests that plant structure may be an important feeding determinant for this insect. In contrast, a specialist weevil preferred its host plant in choice assays, regardless of whether fresh tissue or reconstituted macrophytes were used, suggesting this insect cued on a unique, non-structural property of its host plant. 5. These results suggest that herbivory on freshwater macrophytes is of a similar magnitude to that on terrestrial plants. The findings of this study are consistent with the hypothesis that herbivorous insects of primarily terrestrial groups have a narrower diet breadth than insects of primarily aquatic groups.     

Morphactin effects on soybean leaf anatomy and chlorophyll content

The effect of chlorflurenol (methyl 2-chloro-9-hydroxyfluorene-9-carboxylate) (CF) on chlorophyll (chl) content was studied in intact plants and floating leaf disks. For intact soybean (Glycine max (L.) Merrill) plants grown in the growth chamber, 2.5 μg/ml CF applied 10 to 20 d after planting retarded chl decline in senescing tissues such as cotyledons and unifoliate leaves and increased chl content in recently expanded tissues such as trifoliate leaves. CF did not retard chl decline in the dark unless regulator application was followed by a period of 24 h in the light prior to darkness. In floating leaf disk tests, CF retarded chl decline in dock (Rumex obtusifolius L.) and radish (Raphanus sativus L.) at concentrations of 10^?4 M, but was ineffective at lower concentrations. Chl decline was significantly hastened by CF in tobacco (Nicotiana tabacum L.) and soybean, but was unchanged in barley (Hordeum vulgare L.). CF treatment increased tissue weight (g fresh wt/cotyledon; g dry wt/ cm² for unifoliate and trifoliate leaves), decreased moisture content, and increased leaf thickness, palisade layer thickness, and palisade and spongy mesophyll cell counts. We conclude that plants treated with morphactins show greater green coloration predominantly because of growth effects, and only in small part because of prevention of chl decline in senescing tissues.     

The Effect of Leaf Water Potential, Leaf Temperature and Light Intensity on Leaf Diffusion Resistance and the Transpiration of Leaves of Malus sylvestris

The relationship between leaf resistance to water vapour diffusion and each of the factors leaf water potential, light intensity and leaf temperature was determined for leaves on seedling apple trees (Malus sylvestris Mill. cv. Granny Smith) in the laboratory. Leaf cuticular resistance was also determined and transpiration was measured on attached leaves for a range of conditions. Leaf resistance was shown to be independent of water potential until potential fell below — 19 bars after which leaf resistance increased rapidly. Exposure of leaves to CO₂-free air extended the range for which resistance was independent of water potential to — 30 bars. The light requirement for minimum leaf resistance was 10 to 20 W m^?2 and at light intensities exceeding these, leaf resistance was unaffected by light intensity. Optimum leaf temperature for minimum diffusion resistance was 23 ± 2°C. The rate of change measured in leaf resistance in leaves given a sudden change in leaf temperature increased as the magnitude of the temperature change increased. For a sudden change of 1°C in leaf temperature, diffusion resistance changed at a rate of 0.01 s cm^?1 min^?1 whilst for a 9°C leaf temperature change, diffusion resistance changed at a rate of 0.1 s cm^?1 min^?1. Cuticular resistance of these leaves was 125 s cm^?1 which is very high compared with resistances for open stomata of 1.5 to 4 s cm^?1 and 30 to 35 s cm^?1 for stomata closed in the dark. Transpiration was measured in attached apple leaves enclosed in a leaf chamber and exposed to a range of conditions of leaf temperature and ambient water vapour density. Peak transpiration of approximately 5 × 10^?6 g cm^?2 s^?1 occurred at a vapour density gradient from the leaf to the air of 12 to 14 g m^?3 after which transpiration declined due presumably to increased stomatal resistance. Leaves in CO₂-free air attained a peak transpiration of 11 × 10^?6 g cm^?2 s^?1 due to lower values of leaf resistance in CO₂ free air. Transpiration then declined in these leaves due to development of an internal leaf resistance (of up to 2 s cm^?1). The internal resistance was masked in leaves at normal CO₂ concentrations by the increase in stomatal resistance.     

Carotenoid composition in Zea mays developed at sub-optimal temperature and different light intensities

The content and composition of pigments were examined in the third leaf of Zea mays L. plants grown under controlled environment at near-optimal temperature (24°C) or sub-optimal temperature (14°C) at a light intensity of either 200 or 600 μmol m^?2 s^?1. Compared to leaves grown at 24°C, leaves grown at 14°C showed a large reduction in the chlorophyll (Chl) content, a marked decrease in the Chl a/b ratio, and a large increase in the ratio of total carotenoids/Chl a+b. Leaves grown at 14°C showed a much lower content of β-carotene than leaves grown at 24°C, while the content of the carotenoids of the xanthophyll cycle (violaxanthin [V] + antheraxanthin [A] + zeaxanthin [Z]) was markedly higher in the former leaves as compared to the latter leaves; neoxanthin and lutein were affected by the growth temperature to a much lesser extent. The xanthophylls/β-carotene ratio was about three times higher in leaves grown at 14°C as compared to leaves grown at 24°C. On a chlorophyll basis, the two types of leaves hardly differed in their level of β-carotene, while the levels of the xanthophylls (including lutein and neoxanthin) were higher in 14°C-grown leaves as compared to 24°C-grown leaves. In leaves grown at 14°C, 40 and 56% of the V+A+Z pool was in the form of zeaxanthin at low light intensity and high light intensity, respectively. Only trace amounts of zeaxanthin, if any, were present in leaves grown at 24°C. The changes in the pigment composition induced by growth at sub-optimal temperature were more pronounced at a light intensity of 600 as compared to 200 μmol m^?2 s^?1. In the given range, the light intensity slightly affected the composition of pigments in leaves grown at 24°C. The physiological significance of the modifications to the pigment composition induced by growth at sub-optimal temperature is discussed.     

Rapid, reversible alterations in spinach thylakoid appression upon changes in light intensity

Changes in light quantity and quality cause structural changes within the thylakoid membrane; long‐term responses have been described for so‐called ‘sun’ and ‘shade’ leaves. Many leaves, however, experience changes in irradiance on a time scale of minutes due to self‐shading and sun flecks. In this study, mature, attached spinach leaves were grown at 300 µmol photons m^?2 s^?1 then rapidly switched to a different light treatment. The treatment irradiances were 10, 800 or 1500 µmol m^?2 s^?1 for 10 min, or 10 or 20 min of self‐shading (about 10 µmol m^?2 s^?1). Image analysis of transmission electron micrographs revealed that a 10 min switch to a lower light intensity increased grana size and number per chloroplast profile by 10–20%. Returning the leaves to 300 µmol m^?2 s^?1 for 10 min reversed the phenomenon. Chlorophyll fluorescence measurements of detached, intact leaves at 77 K were suggestive of a transition from state 2 to state 1 upon shading. Diurnal ultrastructural measurements of granal size and number did not reveal a significant net change in ultrastructure over the time scale of hours. It is concluded that spinach chloroplasts can alter the degree of thylakoid appression in response to irradiance changes on a time scale of minutes. These ultrastructural responses are caused by biochemical and biophysical adjustments within the thylakoid membrane that serve to maximize photosynthesis and minimize photo‐inhibition under rapidly fluctuating light environments.     

In Vivo Measurements of the Photo-Oxidation of Chlorophyll Pigments in Dark Grown Wheat Leaves after Treatment with δ-Aminolevulinic Acid

Dark-grown leaves of wheat fed with δ-aminolevulinic acid accumulate protochlorophyllide₆₃₆ in excess. After the leaves had been illuminated with high intensity red light (154 W × m^?2) for half a minute, a treatment which blocks the phototrans-formation protochlorophyllide chlorophyllide, the sensitivity of chlorophyllide and protochlorophyllide to light was examined. The decrease in pigment content, caused by photo-oxidation was found to be very close to a second order reaction. The second order “rate constant” for decrease in absorbance was found to be eight times greater for the formed chlorophyllide than for protochlorophyllide. The light intensity dependence of the decomposition was found to be linear within the intensity range used (E= 25 – 154 W × m^?2). In samples in which the pigments had been heat denatured, it was possible to photodecompose the chlorophyllide without affecting the protochlorophyllide. The results are discussed in connection with the theory of a photodynamic action involving oxygen in the singlet state (¹ΔO₂).     

Effects of aquatic vegetation type on denitrification

In a microcosm ¹⁵N enrichment experiment we tested the effect of floating vegetation (Lemna sp.) and submerged vegetation (Elodea nuttallii) on denitrification rates, and compared it to systems without macrophytes. Oxygen concentration, and thus photosynthesis, plays an important role in regulating denitrification rates and therefore the experiments were performed under dark as well as under light conditions. Denitrification rates differed widely between treatments, ranging from 2.8 to 20.9 ??mol N m^?2 h^?1, and were strongly affected by the type of macrophytes present. These differences may be explained by the effects of macrophytes on oxygen conditions. Highest denitrification rates were observed under a closed mat of floating macrophytes where oxygen concentrations were low. In the light, denitrification was inhibited by oxygen from photosynthesis by submerged macrophytes, and by benthic algae in the systems without macrophytes. However, in microcosms with floating vegetation there was no effect of light, as the closed mat of floating plants caused permanently dark conditions in the water column. Nitrate removal was dominated by plant uptake rather than denitrification, and did not differ between systems with submerged or floating plants.     

Acclimation of photosynthesis to lightflecks in tomato leaves: interaction with progressive shading in a growing canopy

Plants in natural environments are often exposed to fluctuations in light intensity, and leaf‐level acclimation to light may be affected by those fluctuations. Concurrently, leaves acclimated to a given light climate can become progressively shaded as new leaves emerge and grow above them. Acclimation to shade alters characteristics such as photosynthetic capacity. To investigate the interaction of fluctuating light and progressive shading, we exposed three‐week old tomato (Solanum lycopersicum ) plants to either lightflecks or constant light intensities. Lightflecks of 20 s length and 1000 μmol m^?2 s^?1 peak intensity were applied every 5 min for 16 h per day, for 3 weeks. Lightfleck and constant light treatments received identical daily light sums (15.2 mol m^?2 day^?1). Photosynthesis was monitored in leaves 2 and 4 (counting from the bottom) during canopy development throughout the experiment. Several dynamic and steady‐state characteristics of photosynthesis became enhanced by fluctuating light when leaves were partially shaded by the upper canopy, but much less so when they were fully exposed to lightflecks. This was the case for CO₂‐saturated photosynthesis rates in leaves 2 and 4 growing under lightflecks 14 days into the treatment period. Also, leaf 2 of plants in the lightfleck treatment showed significantly faster rates of photosynthetic induction when exposed to a stepwise change in light intensity on day 15. As the plants grew larger and these leaves became increasingly shaded, acclimation of leaf‐level photosynthesis to lightflecks disappeared. These results highlight continuous acclimation of leaf photosynthesis to changing light conditions inside developing canopies.     

Fertile sediment and ammonium enrichment decrease the growth and biomechanical strength of submersed macrophyte Myriophyllum spicatum in an experiment

Decline of submersed macrophytes has occurred in eutrophic lakes worldwide. Little is known about effects of nutrient enrichment on biomechanical properties of submersed macrophytes. In a 30-day experiment, Myriophyllum spicatum was cultured in aquaria containing two types of sediment (mesotrophic clay vs. fertile loam) with contrasting water NH₄ ⁺ concentrations (0 vs. 3.0 mg L^?1 NH₄–N). The plant growth, shoot and root morphology, stem biomechanical properties, and stem total nonstructure carbohydrates content (TNC) were examined. The NH₄ ⁺-enriched water, particularly combined with the fertile sediment, caused adverse effects on M. spicatum as indicated by reductions in the growth, stem biomechanical properties (tensile force, bending force and structural stiffness), and TNC content. These results indicate that increased sediment fertility and water NH₄ ⁺-enrichment made the plant more fragile and vulnerable to hydraulic damage, particularly for the upper stem, implying that M. spicatum was prone to uprooting and fracture by hydraulic force, and the broken fragment from parent shoot of M. spicatum might have low-survival potential due to its low-TNC content. This may be a mechanical aspect for the decline of submersed macrophytes and makes it more difficult to restore submersed vegetation in the eutrophic lakes.     

Photosynthesis and respiration in a fast growing strain of Gigartina exasperata (Harvey and Bailey)

Photosynthesis and respiration rates of blades from a selected, fast growing strain of the marine red alga. Gigartina exasperata Harvey and Bailey, a carrageenan producer, were measured with an oxygen electrode and compared with rates similarly obtained from wild material of the same species. The measurements, expressed as μl O₂ · mg chl a^?1, min^?1. were made over a light intensity range from 5 to 800 μE · m^?2 · sec^?1 and a temperature range of 6 to 16°C. The photosynthesis light intensity data are best described by hyperbolic functions.     

Effect of light quality on Bacillus amyloliquefaciens JBC36 and its biocontrol efficacy

Light is one of the most important environmental signals regulating physiological processes of many microorganisms. However, very few studies have been reported on the qualitative or quantitative effects of light on control of postharvest spoilage using antagonistic bacteria. In this study, we investigated the effects of white, red, green, and blue light at photon flux densities of 40, 240, and 360 μmol m^?2 s^?1 on Bacillus amyloliquefaciens JBC36 (JBC36), which has been reported as a promising candidate for biocontrol of green and blue mold on mandarin fruit. With the exception of blue light at 240 and 360 μmol m^?2 s^?1, light generally stimulated growth of JBC36 compared to the controls grown in the dark. Red light increased swarming motility irrespective of intensity and significantly enhanced biofilm formation at 240 μmol m^?2 s^?1. Production of antifungal metabolites and antifungal activity on Penicillium digitatum was also affected by light quality. Interestingly, antifungal activity was significantly increased when JBC36 and P. digitatum was co-incubated under red and green light at an intensity of 240 μmol m^?2 s^?1. We also demonstrated that the quality of light resulted in changes in colonization of JBC36 on mandarin fruit and control of green mold. In particular, red light increased the population level on mandarin fruit and biocontrol efficacy against green mold. These results represent the first report on the effect of light quality on an antagonistic bacterium for the control of postharvest spoilage. We believe that an improved understanding of the JBC36 response to light quality may help in the development of strategies to increase biocontrol efficacy of postharvest spoilage.     

Heterophylly in the yellow waterlily, Nuphar variegata (Nymphaeaceae): effects of [CO2], natural sediment type, and water depth

We transplanted Nuphar variegata with submersed leaves only into natural lake sediments in pH-, [CO(2)]-, depth-, and temperature-controlled greenhouse tanks to test the hypotheses that more fertile sediment, lower free [CO(2)], and shallower depth would all stimulate the development of floating leaves. Sediment higher in porewater [NH(4)(+)] favored floating leaf development. Low CO(2)-grown plants initiated floating leaf development significantly earlier than high CO(2)-grown plants, which produced significantly more submersed leaves and fewer floating leaves. Mean floating leaf biomass was significantly greater than mean submersed leaf biomass but was not influenced by CO(2) enrichment, whereas mean submersed leaf biomass increased 88% at high [CO(2)]. At the shallower depth (35 cm), floating leaves required 50% less biomass investment per leaf than at 70 cm, and a significantly greater proportion of plants had floating leaves (70 vs. 23-43% at 35 vs. 70 cm, respectively) for the last three of the eight leaf censuses. Sediment type, water depth, and especially free [CO(2)] all can influence leaf morphogenesis in Nuphar variegata, and the development of more and larger submersed leaves with CO(2) enrichment favors the exploitation of high [CO(2)] when it is present in the water column.     

Division and growth of mesophyll cells isolated from Psoralea bituminosa leaves

Mesophyll cells have been isolated from Psoralea bituminosa plant by gentle homogenization in a liquid nutrient medium. Between 60 and 70% of the cells can be isolated from leaves using this method, of which 50 to 60% can be recovered morphologically intact. Under light the separated cells have rates of oxygen evolution under light of 3500 μl O₂ mg^?1 chlorophyll h^?1 (measured with a Clark-type electrode). During growth, this rate decreases rapidly, as does cell pigments (chlorophylls and carotenoids). As a first step in obtaining a photoautotrophic cell suspension, growth factors affecting cell division in free sugar medium were investigated. The starting culture contained between 1 and 2 × 10⁶ cells ml^?1. The best increase in cell number was obtained on a medium composed of Joshi and Ball's elements and vitamins and containing 1 mg l^?1 of naphthalene acetic acid, 0.1 mg l^?1 of benzylaminopurine and the grinding juice. The optimum culture pH was between 5 and 5.3.