Quality and intensity of light affect <Emphasis Type="Italic">Lippia gracilis</Emphasis> Schauer plant growth and volatile compounds in vitro

The aim of this study was to evaluate the effects of different intensities and quality of light and explant type on the growth of and volatile compounds in Lippia gracilis in vitro. The treatments were as follows: light intensities of 26, 51, 69, 94, or 130 µmol m^?2 s^?1 from fluorescent lamps and light-emitting diode (LED) lamps at different wavelengths, namely, white, red, blue, and combinations of red and blue light at ratios of 2.5:1 and 1:2.5, respectively, and two explant types, namely, nodal and apical segments. On the 30th day of culture on half-strength Murashige and Skoog (Physiol Plant 15(3):473–497, 1962) medium, growth, production of photosynthetic pigments, chlorophyll a and b, total chlorophyll, carotenoids, and volatile constituents (using headspace gas chromatography-mass spectrometry) were analyzed. The light quality and intensity significantly influenced the in vitro growth of L. gracilis. The apical segments were superior in all parameters evaluated compared to nodal segments. The number of segments plantlet^?1, root length, and leaf, shoot, root, and total weight were higher with increasing light intensity, especially under the 94 µmol m^?2 s^?1 treatment, for both explant types. The red light showed the highest leaf (32.28 mg plantlet^?1) and total (58.33 mg plantlet^?1) dry weight of all the light qualities. Major constituents, namely, ρ-cymene, γ-terpinene, thymol, carvacrol, and E-caryophyllene, were identified, regardless of light conditions. The amount and composition of volatile compounds varied according to light intensity and quality. Low intensity (26 µmol m^?2 s^?1) increased γ-terpinene content (12.42%) and concomitantly decreased carvacrol (38.52%). Blue LED light showed higher production of carvacrol (48.11%).     

Enhancement of phenylpropanoid enzymes and lignin in Phalaenopsis orchid and their influence on plant acclimatisation at different levels of photosynthetic photon flux

Effects of three levels of photosynthetic photon flux (PPF: 60, 160 and 300 μmol m⁻²s⁻¹) were investigated in one-month-old Phalaenopsis plantlets acclimatised ex vitro. Optimal growth, chlorophyll and carotenoid concentations, and a high carotenoid:chlorophyll a ratio were obtained at 160 μmol m⁻²s⁻¹, while net CO₂ assimilation (A), stomatal conductance (g), transpiration rate (E) and leaf temperature peaked at 300 μmol m⁻²s⁻¹, indicating the ability of the plants to grow ex vitro. Adverse effects of the highest PPF were reflected in loss of chlorophyll, biomass, non-protein thiol and cysteine, but increased proline. After acclimatisation, glucose-6-phosphate dehydrogenase, shikimate dehydrogenase, phenylalanine ammonia-lyase (PAL) and cinnamyl alcohol dehydrogenase (CAD) increased, as did lignin. Peroxidases (POD), which play an important role in lignin synthesis, were induced in acclimatised plants. Polyphenol oxidase (PPO) and β-glucosidase (β-GS) activities increased to a maximum in acclimatised plants at 300 μmol m⁻²s⁻¹. A positive correlation between PAL, CAD activity and lignin concentration was observed, especially at 160 and 300 μmol m⁻²s⁻¹. The study concludes that enhancement of lignin biosynthesis probably not only adds rigidity to plant cell walls but also induces defence against radiation stress. A PPF of 160 μmol m⁻²s⁻¹was suitable for acclimatisation when plants were transferred from in vitro conditions.     

Effects of light intensity and quality on phycobiliprotein accumulation in the cyanobacterium <Emphasis Type="Italic">Nostoc sphaeroides</Emphasis> Kützing

Objectives

To assess the effects of light intensity and quality on the growth and phycobiliproteins (PBP) accumulation in Nostoc sphaeroides Kützing (N. sphaeroides).

Results

Dry weights, dry matter, protein, chlorophyll and PBP contents were higher under 90 μmol m^?2 s^?1 than under other intensities (both higher and lower). Phycocyanin and allophycocyanin increased with light intensity while phycoerythrin decreased. Fresh weights, protein and PBP contents increased at the highest rates under blue light. Red light resulted in higher values of dry matter, phycocyanin and chlorophyll a.

Conclusion

White light at 90 μmol m^?2 s^?1 or blue light 30 μmol m^?2 s^?1 were optimal for the growth and phycobiliprotein accumulation in N. sphaeroides.

     

Photosynthetic capacity of the capsule wall and its contribution to carbon fixation and seed yield in castor (<Emphasis Type="Italic">Ricinus communis</Emphasis> L.)

Defoliation occurs in castor due to several reasons, but the crop has propensity to compensate for the seed yield. Photosynthetic efficiency in terms of functional (gas exchange and chlorophyll fluorescence) and structural characteristics (photosynthetic pigment profiles and anatomical properties) of castor capsule walls under light- and dark-adapted conditions was compared with that of leaves. Capsule wall showed high intrinsic efficiency of photosystem II (F _v/F _m, 0.82) which was comparable to leaves (F _v/F _m, 0.80). With increasing photon flux densities (PFD), actual quantum yields and photochemical quenching coefficients of the capsule walls were similar to that in leaves, while electron transport rates reached a maximum corresponding to about 118 % of the leaves. However, maximum net photosynthetic rate of the capsule walls (2.60 µmol CO₂ m^?2 s^?1) was less than one-fourth of the leaves (15.67 µmol CO₂ m^?2 s^?1) at the CO₂ concentration of 400 µmol mol^?1, and the difference was attributed to about 80 % lower stomatal density and the 75 % lower total chlorophyll content of capsule walls than the leaves. Furthermore, seed weight in dark-adapted capsules was 2.70–12.42 % less as compared to the capsules developed under light. The results indicate that castor capsule walls are photosynthetically active (about 15–30 % of the leaves) and contribute significantly to carbon fixation and seed yield accounting for 10 % photoassimilates towards seed weight.     

Mammalian <Emphasis Type="Italic">CYP2E1</Emphasis> gene triggered changes of relative ions fluxes,CaM content and genes expression profiles in <Emphasis Type="Italic">Petunia hybrida</Emphasis> cells to enhance resistance to formaldehyde

The influence of light quality and cytokinin content in media on growth, development, photosynthetic pigments and secondary metabolite content of Myrtus communis L. was evaluated in an in vitro culture. Various treatments with light emitting diodes (LEDs): 100% blue (B), a mix of 70% red and 30% blue (RB) and 100% red were applied and compared with a traditional fluorescent lamp as control. Axillary shoots were incubated on Murashige and Skoog medium with 30 g dm^?3 sucrose, 0.5% BioAgar, 0.5 μM 1-naphthaleneacetic acid and different concentrations of 6-benzyladenine (BA): 1, 2.5 and 5 µM. Cultures were maintained for 6 weeks in 23/21?±?1 °C (day/night), 80% relative humidity and 16/8 h photoperiod; photosynthetic photon flux density (PPFD) was 35 µmol m^?2 s^?1 in all treatments. Light spectra and BA content in media affected biometrical and phytochemical M. communis properties. Red LEDs and 5 µM BA resulted in the highest multiplication rate. The highest shoots were obtained under red LEDs, but with the lowest concentration of cytokinin in media. Fresh weight was greatest on LEDs containing blue light in the spectrum (B and RB); moreover, 5 µM BA increased dry weight. Photosynthetic pigment levels were lower under LED light compared to control lamps. Phenolic acids and flavonoids were identified in M. communis leaf extracts. Myricetin was the major constituent with highest concentration under red LEDs and highest BA level.     

The effect of varying LED light sources and influent carbon/nitrogen ratios on treatment of synthetic sanitary sewage using Chlorella vulgaris

Sanitary sewage can create serious environmental problems if discharged directly into natural waters without appropriate treatment. This study showed that red light is the optimum light wavelength for growing microalgae Chlorella vulgaris in microalgae biological wastewater treatment systems, given a harvest time of 144 h. Only moderate light intensities (1,000, 1,500, 2,000, and 2,500 μmol m^?2 s^?1) were able to remove nutrients from synthetic sanitary sewage, but higher light intensity led to better nutrient removal effects. Because of economic considerations, the optimum light intensity range for efficient nutrient removal was determined to be between 1,500 and 2,000 μmol m^?2 s^?1. Furthermore, nutrient removal efficiency was significantly affected by light wavelength, light intensity, the interaction of these two factors, and the interaction among light wavelength, light intensity, and influent carbon/nitrogen (C/N) ratios. Total nitrogen and total phosphorus removal efficiency was also significantly affected by influent C/N ratios. Appropriate control of carbon and nitrogen source concentrations enabled optimal nutrient removal. The optimal influent C/N ratio was determined to be 6:1.     

A fully in vitro protocol towards large scale production of recombinant inbred lines in wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.)

A bottleneck for genetic research and breeding of crop plants is the time taken to producing large pure line segregating populations so called recombinant inbred lines (RILs). One way to overcome this problem is through use of the single-seed-decent (SSD) process under in vitro conditions. A number of factors that may affect in vitro SSD approach of wheat including temperature, light duration and intensity, salt strength and carbohydrate concentration were investigated in this study. Under the in vitro conditions, 45 days per generation was achieved for an early flowering wheat genotype Emu Rock, allowing eight generations per annum; 58 days per generation was achieved for mid flowering genotypes, allowing six generations per annum. The results showed that a variation of growth environment before and after three-leaf stage allowed in vitro seed-set with a relatively short generation time. Specifically, the plantlets were first grown under 22?°C with a light intensity of 145 μmol m^?2 s ^?1 (16 h d^?1) for 20 days (around three-leaf stage), and then moved to an environment of 28?°C and 500 μmol m^?2 s^?1 (20 h d^?1) light. The culture medium was 1/2 strength Murashige and Skoog (MS) with modification of adding ten times of extra KH₂PO₄ and 4% sucrose. The fully in vitro protocol resulted in 100% flowering rate and average seed set rate of 91.5% in Emu Rock and Zippy. It can be further fine-tuned to suit different genotypes and it has a potential for factory scale mass-production of RILs for genetic studies and practical breeding programs.     

The paths of Andrew A. Benson: a radio-autobiography

Among marine phytoplankton groups, diatoms span the widest range of cell size, with resulting effects upon their nitrogen uptake, photosynthesis and growth responses to light. We grew two strains of marine centric diatoms differing by ~4 orders of magnitude in cell biovolume in high (enriched artificial seawater with ~500 µmol L^?1 µmol L^?1 NO₃ ^?) and lower-nitrogen (enriched artificial seawater with <10 µmol L^?1 NO₃ ^?) media, across a range of growth light levels. Nitrogen and total protein per cell decreased with increasing growth light in both species when grown under the lower-nitrogen media. Cells growing under lower-nitrogen media increased their cellular allocation to RUBISCO and their rate of electron transport away from PSII, for the smaller diatom under low growth light and for the larger diatom across the range of growth lights. The smaller coastal diatom Thalassiosira pseudonana is able to exploit high nitrogen in growth media by up-regulating growth rate, but the same high-nitrogen growth media inhibits growth of the larger diatom species.     

Functional characteristics of a fruticose type of lichen, Stereocaulon foliolosum Nyl. in response to light and water stress

Stereocaulon foliolosum a fruticose type of lichen under its natural habitat is subjected to low temperature, high light conditions and frequent moisture stress due its rocky substratum. To understand as to how this lichen copes up with these stresses, we studied the reflectance properties, light utilization capacity and the desiccation tolerance under laboratory conditions. S. foliolosum showed light saturation point for photosynthesis at 390 μmol CO₂ m^?2 s^?1 and the light compensation point for photosynthesis at 64 μmol CO₂ m^?2 s^?1. Our experiments show that S. foliolosum has a low absorptivity (30–35 %) towards the incident light. The maximum rates of net photosynthesis and apparent electron transport observed were 1.9 μmol CO₂ m^?2 s^?1 and 45 μmol e^? m^?2 s^?1, respectively. The lichen recovers immediately after photoinhibition under low light conditions. S. foliolosum on subjecting to desiccation results in the decrease of light absorptivity and the reflectance properties associated with water status of the thalli show a change. During desiccation, a simultaneous decrease in photosynthesis, dark respiration and quenching in the fluorescence properties was observed. However, all the observed changes show a rapid recovery on rewetting the lichen. Our study shows that desiccation does not have a severe or long-term impact on S. foliolosum and the lichen is also well adapted to confront high light intensities.     

Effects of various LED light wavelengths and light intensity supply strategies on synthetic high-strength wastewater purification by Chlorella vulgaris

Chemical fertilizer agricultural wastewater is a typical high-strength wastewater that has dramatically triggered numerous environmental problems in China. The Chlorella vulgaris microalgae biological wastewater treatment system used in this study can effectively decontaminate the high-strength carbon and nitrogen wastewater under an optimum light wavelength and light intensity supply strategy. The descending order of both the dry weight for C. vulgaris reproduction and wastewater nutrient removal efficiency is red > white > yellow > purple > blue > green, which indicates that red light is the optimum light wavelength. Furthermore, rather than constant light, optimal light intensity is used for the incremental light intensity strategy. The phases for the optimal light intensity supply strategy are as follows: Phase 1 from 0 to 48 h at 800 μmol m^?2 s^?1; Phase 2 from 48 to 96 h at 1,200 μmol m^?2 s^?1; and Phase 3 from 96 to 144 h at 1,600 μmol m^?2 s^?1. Additionally, the optimal cultivation time is 144 h.     

Acclimations to light quality on plant and leaf level affect the vulnerability of pepper (<Emphasis Type="Italic">Capsicum annuum</Emphasis> L.) to water deficit

We investigated the influence of light quality on the vulnerability of pepper plants to water deficit. For this purpose plants were cultivated either under compact fluorescence lamps (CFL) or light-emitting diodes (LED) providing similar photon fluence rates (95 µmol m^?2 s^?1) but distinct light quality. CFL emit a wide-band spectrum with dominant peaks in the green and red spectral region, whereas LEDs offer narrow band spectra with dominant peaks at blue (445 nm) and red (665 nm) regions. After one-week acclimation to light conditions plants were exposed to water deficit by withholding irrigation; this period was followed by a one-week regeneration period and a second water deficit cycle. In general, plants grown under CFL suffered more from water deficit than plants grown under LED modules, as indicated by the impairment of the photosynthetic efficiency of PSII, resulting in less biomass accumulation compared to respective control plants. As affected by water shortage, plants grown under CFL had a stronger decrease in the electron transport rate (ETR) and more pronounced increase in heat dissipation (NPQ). The higher amount of blue light suppressed plant growth and biomass formation, and consequently reduced the water demand of plants grown under LEDs. Moreover, pepper plants exposed to high blue light underwent adjustments at chloroplast level (e.g., higher Chl a/Chl b ratio), increasing the photosynthetic performance under the LED spectrum. Differently than expected, stomatal conductance was comparable for water-deficit and control plants in both light conditions during the stress and recovery phases, indicating only minor adjustments at the stomatal level. Our results highlight the potential of the target-use of light quality to induce structural and functional acclimations improving plant performance under stress situations.     

Biomass production of Tolypothrix tenuis as a basic component of a cyanobacterial biofertilizer

The influence of artificial illumination on upstream and downstream operations for biomass production of Tolypothrix tenuis as a basic component of a powdered cyanobacterial biofertilizer was studied. Cultures were operated semi-continuously for 18 months at harvesting frequencies of 4, 7, 10, and 14 days in two vertical plate photobioreactors of 1.5 and 5 cm of light path and illuminated at two different light intensities: high (290 μmol photons m^?2 s^?1) and normal (60 μmol photons m^?2 s^?1). Biomass was separated by self-flocculation and finally processed as a dried powder. The cellular concentration and volumetric productivity were superior in photobioreactors of short light path at high light intensity, while the overall areal productivity was higher in the photobioreactor of 5 cm at normal light intensity with weekly harvest frequency. The viability preservation of the dried and milled biomass was greatly enhanced by the use of halogen lamps and subsequent ionic flocculation with 10 mM MgSO₄ plus 10 mM CaCl₂. An optimum value of the retained viability index (RVI₁₀) was maintained for 24 months, while a sharp viability declination and cellular death were produced after 12 months with fluorescent tubes, which represents a relevant aspect in the commercialization step of this type of biofertilizer.     

Effects of macrophyte leachate on <Emphasis Type="Italic">Anabaena</Emphasis> sp. and <Emphasis Type="Italic">Chlamydomonas moewusii</Emphasis> growth in freshwater tropical ecosystems

This study reports on the effects of dissolved organic matter (DOM) derived from the aquatic macrophyte Pistia stratiotes (collected from a tropical reservoir) on the mixotrophic growth of two phytoplankton species (Chlamydomonas moewusii and Anabaena sp.). The DOM from P. stratiotes had a mainly aliphatic structure, low molecular weight, low cellulose and lignin content and high carbon content. The addition of DOM (5% v/v) significantly decreased the growth rate of Anabaena sp. but increased the chlorophyll a concentration of C. moewusii. Higher light intensity (100 versus 30 µmol m^?2 s^?1) was important for Anabaena sp., increasing its growth rate and chlorophyll content. The use of DOM from P. stratiotes to mitigate cyanobacterial blooms should be further explored in future studies.     

Influence of thidiazuron (TDZ) pretreatment of shoot tips on shoot multiplication and ex vitro acclimatization of Harpagophytum procumbens

The effects of thidiazuron (TDZ) pretreatment of shoot tips on Harpagophytum procumbens shoot proliferation and successive stages of micropropagation, i.e. rooting of regenerated shoots and acclimatization of plantlets to ex vitro conditions, were described in the present study. The best response in terms of shoot proliferation (about seven shoots/explant) and shoot length (3.2 ± 0.4 cm) was obtained when explants pretreated with 25 µmol L^?1 TDZ for 6 h were cultured on Schenk and Hildebrandt medium containing indole-3-acetic acid (IAA) (0.57 µmol L^?1) and 6-benzylaminopurine (BAP) (8 µmol L^?1). Under these conditions, a 330 % increase in shoot multiplication over TDZ non-pretreatment culture was achieved and TDZ pretreatment shoots were longer compared to those in control culture (2.6 ± 0.3 cm). The TDZ pretreatment did not affect the percentage of rooted shoots, length of roots and number of roots formed per shoot. The rooted plantlets were transplanted from in vitro to pots with soil and grown during 1 year in the greenhouse. The hardening process was difficult and time-consuming. We found that the plants developed from the TDZ pretreated culture were superior to plants from non-pretreated culture in terms of survival rate and morphological features, such as shoot length, leaf size, flowering and earlier root tuberisation. Random amplified polymorphic DNA and inter-simple sequence repeat analyses of pretreatment with TDZ plants showed genetic similarity to non-pretreatment plants. We conclude that applying the strategy of initial explant pretreatment with TDZ may be valuable for the improvement in H. procumbens in vitro propagation.     

Chloroplast changes and differentiation of callus cells in Eckloniopsis radicosa (Kjellman) Okamura (Phaeophyta, Laminariales)

Excised rectangular blade pieces of young sporophytes of Eckloniopsis radicosa (Kjellman) Okamura were cultured at four different temperatures (10, 15, 20, 25 °C) and light intensities (10, 20, 40, 80 μmol photon m⁻² s⁻¹) to observe callus cell propagation and differentiation. Although rapidly propagating callus cells were observed at a low temperature (15 °C) and low light intensities of (10–20 μmol photon m⁻² s⁻¹), differentiation to bladelets was only observed at higher temperatures and light intensities. In rapidly propagating callus cells, the chloroplasts decreased in both size and number. When callus cells with few chloroplasts were exposed to high temperature and light intensity, the chloroplasts gradually increased in number and size until they were the same size as found in cells from young blades. Finally, these cells differentiated and produced bladelets. This is the first report describing a relationship between differentiation and chloroplast size and number in the callus cells on E. radicosa. This revised version was published online in September 2006 with corrections to the Cover Date.     

Effects of different light quality on growth, chlorophyll concentration and chlorophyll biosynthesis precursors of non-heading Chinese cabbage (Brassica campestris L.)

The aim of this study was to evaluate the effects of different light quality of light emitting diode (LED) on the growth, concentration of chlorophyll and chlorophyll biosynthesis precursors of non-heading Chinese cabbage (Brassica campestris L.). Seedlings of the cultivar Te Ai Qing were cultured for 28 days under 6 treatments: red light (R), blue light (B), green light (G), yellow light (Y), red plus blue light (RB) and dysprosium lamp (CK). Lighting experiments were performed under controlled conditions (photon flux density 150 μmol m^?2 s^?1; 12 h photoperiod; 18–20 °C). The fresh and dry mass were the greatest under RB, which were significantly higher than other light treatments. The fresh mass under RB was almost twice higher compared to other light treatments. Plant height was highest under R treatment and was lowest under B. RB treatment also lowered the plant height significantly. The highest soluble sugar concentration was observed under B. The soluble protein concentration was the greatest under RB. The R treatment was adverse to pigment accumulation. The concentration of photosynthetic pigments and chlorophyll biosynthesis precursors were higher under RB. The RB treatment was beneficial to pigment accumulation.     

A novel inhibitor of cytokinin degradation (INCYDE) influences the biochemical parameters and photosynthetic apparatus in NaCl-stressed tomato plants

The effect of 2-chloro-6-(3-methoxyphenyl)aminopurine [inhibitor of cytokinin degradation (INCYDE)] at 10 nM on growth, biochemical and photosynthetic efficiency in sodium chloride (NaCl)-stressed (75, 100 and 150 mM) tomato plants was investigated. NaCl-induced decline in plant vigor index was slightly reversed by both drenching and foliar application of INCYDE. Foliar application of INCYDE significantly increased the flower number in the control and 75 mM NaCl-supplemented plants, while drenching was more effective in 150 mM NaCl-stressed plants. Antioxidant enzymes (peroxidase, catalase and superoxide dismutase) were enhanced in the presence of INCYDE in the control and NaCl-stressed plants. Higher concentration of malondialdehyde (MDA) associated with oxidative (lipid peroxidation) damage in leaf tissue which was evident in the presence of NaCl stress was significantly attenuated with the drenching and foliar application of INCYDE. Regardless of NaCl concentration, application of INCYDE had no significant influence on maximum quantum efficiency of photosystem II. However, the reduced quantum yield of photosystem II and coefficient of photochemical quenching under continuous illumination with actinic light at four intensities (264, 488, 800 and 1,200 µmol m^?2 s^?1) in NaCl-stressed (100 and 150 mM) tomato plants were significantly alleviated by drenching application with INCYDE. Non-photochemical quenching of the singlet excited state of chlorophyll a and relative electron transfer rate were generally higher in INCYDE-treated plants than in the controls. From an agricultural perspective, these findings indicate the potential of INCYDE in protecting plants against NaCl stress and the possibility of enhanced productivity.     

Effect of light and natural ventilation systems on the growth parameters and carvacrol content in the in vitro cultures of <Emphasis Type="Italic">Plectranthus amboinicus</Emphasis> (Lour.) Spreng

The aim of the current study is to investigate the influence of light intensity, quality of light and alternative membrane sytems on the growth and headspace-GC/MS chemical analysis of Plectranthus amboinicus cultivated in vitro. Nodal segments were grown under light intensities (26, 51, 69, 94 and 130 µmol m^?2 s^?1) provided by cool-white fluorescent lamps. Apical segments were grown under light-emitting diodes blue; red; 1 blue/2.5 red; 2.5 blue/1 red; 1 blue/1 red and white fluorescent lamps. Apical and nodal segments were grown under alternative membrane and membrane-free systems. One, two or four PTFE membranes were used on the lid of the culture vessel. The membranes provided natural ventilation and worked as filters. The results have shown significant differences in the growth and carvacrol content, as well as in the content of carvacrol precursors (γ-terpinene and p-cymene) in different treatments. Among all tested light intensities, the significant increase in the dry weight and in the carvacrol content of plantlets derived from the nodal segments was recorded at 69 µmol m^?2 s^?1. The monochromatic red led to greater shoot length and higher dry weight in plantlets derived from the apical segments, as well as to carvacrol accumulation greater than that provided by the fluorescent lamps. The culture vessel enclosure by one and two membranes led to higher dry weight in plantlets derived from the apical and nodal segments, respectively. They also showed higher carvacrol content. Thus, it is possible optimizing the growth and carvacrol content in P. amboinicus cultivated in vitro by adjusting these environmental parameters.     

Genetic engineering of polyamine metabolism changes <Emphasis Type="Italic">Medicago truncatula</Emphasis> responses to water deficit

In the current scenario of climate change and increasing water scarcity there is an increased need to combine research efforts for the development of abiotic stress resistant crops, specifically plants able to support water deficit (WD). Polyamines (PAs) have been described as being involved in the regulation of many physiological processes and a variety of stress responses in plants. Arginine decarboxylase (ADC) is considered a key enzyme of the polyamine (PA) biosynthetic pathway. In this study, a T₂ transgenic homozygous line of Medicago truncatula expressing the oat Adc under the control of CaMV 35S was obtained and was shown to have higher leaf accumulation of putrescine, spermidine and norspermidine compared to wild type plants. The photosynthetic parameters, leaf internal CO₂ concentration (Ci), net CO₂ assimilation rate (A), transpiration (E) and stomatal conductance (gs) of transformed and untransformed lines during WD and water deficit recovery experiments were measured by IRGA (infrared gas analyzer) and compared over time. Two light intensities were used, growth light intensity (391 μmol m^?2 s^?1) and saturating light intensity (1044 μmol m^?2 s^?1). Independently of the light intensity, and under WD, the transgenic line stood out with increased Ci, A, E and gs; suggesting a possible benefit of the augmented PAs under such disturbing environmental conditions. We showed that the constitutive expression of the oat Adc gene improve the physiological responses to WD and that WD recovered transgenic plants had higher seed yield, suggesting a possible benefit of PA metabolism manipulation in legumes.     

Differences in the success of sugar maple and red maple seedlings on acid soils are influenced by nutrient dynamics and light environment

Variation in tolerance to nutrient limitations may contribute to the differential success of sugar maple ( Acer saccharum Marsh.) and red maple ( Acer rubrum L.) on acid soils. The objectives of this study were to examine these relationships as influenced by light environment and test whether sensitivity to nutrient stress is mediated by oxidative stress. First-year sugar maple and red seedlings were grown on forest soil cores contrasting in nutrient availability under high or low light intensity. Foliar nutrition, photosynthesis, growth and antioxidant enzyme activity were assessed. Photosynthesis and growth of sugar maple were significantly lower on nutrient-poor soils and were correlated with leaf nutrient status with Ca and P having the strongest influence. For red maple, only chlorophyll content showed sensitivity to the nutrient-poor soils. High light exacerbated the negative effects of nutrient imbalances on photosynthesis and growth in sugar maple. Antioxidant enzyme activity in sugar maple was highest in seedlings growing on nutrient-poor soils and was inversely correlated with photosynthesis, Ca, P, and Mg concentrations. These results suggest that: (1) sugar maple is more sensitive to nutrient stresses associated with low pH soils than red maple; (2) high light increases sugar maple sensitivity to nutrient stress; (3) the negative effects of nutrient imbalances on sugar maple may be mediated by oxidative stress.