Topography-mediated light environment regulates intra-specific seasonal and diurnal patterns of photosynthetic plasticity and plant ecophysiological adaptation strategies.

Due to substantial topographic variations in the Himalaya, incident solar radiation in the forest canopy is highly unequal. This results in significant environmental differences at finer scales and may lead to considerable differences in photosynthetic productivity in montane forests. Therefore, local-scale ecophysiological investigations, may be more effective and instructive than landscape-level inventories and models. We investigated leaf ecophysiological differences and related adaptations between two Quercus semecarpifolia forests in aspect-mediated, significantly varying light regimes in the same mountain catchment. Seasonal and diurnal rates of photosynthesis (A) were significantly higher in south aspect (S) than the north (N). Although temperature was a key contributor to seasonal fluctuations in photosynthetic physiology, photoperiod significantly determined intraspecific variations in seasonal and diurnal plasticity of leaf ecophysiological traits between the two topography-mediated light environments. The regression model for A as a function of stomatal conductivity (gsw) explained the critical role of gsw in triggering photosynthetic plasticity as an adaptive function against varying environmental stresses due to seasonal solar differences. We also examined, modifications in chlorophyll content between the two light regimes across seasons to determine the chlorophyll adaptation strategy. The N aspect had higher leaf chl a, b, and chl a + b and a lower chl-allocation ratio (a/b) than S, which helped to optimize the required light reception in the photoreaction centers for improved photosynthetic performance. The leaf light response curves for A and gsw were observed against varying incident photosynthetic photon flux densities (0-2000 mol.m2 s-1 PPFD) for both aspects. We found that the same species developed significantly distinct light response strategies and photosynthetic capacities in S than in N for the given magnitudes of PPFD. Such acquired ecophysiological adaptations owing to varying light environments may provide significant clues for understanding the impact of future climate change on Himalayan tree species.

Oxidative stress and photoinhibition can be separated in the cyanobacterium Synechocystis sp. PCC 6803.

Roles of oxidative stress and photoinhibition in high light acclimation were studied using a regulatory mutant of the cyanobacterium Synechocystis sp. PCC 6803. The mutant strain ΔsigCDE contains the stress responsive SigB as the only functional group 2 σ factor. The ∆sigCDE strain grew more slowly than the control strain in methyl-viologen-induced oxidative stress. Furthermore, a fluorescence dye detecting H2O2, hydroxyl and peroxyl radicals and peroxynitrite, produced a stronger signal in ∆sigCDE than in the control strain, and immunological detection of carbonylated residues showed more protein oxidation in ∆sigCDE than in the control strain. These results indicate that ∆sigCDE suffers from oxidative stress in standard conditions. The oxidative stress may be explained by the findings that ∆sigCDE had a low content of glutathione and low amount of Flv3 protein functioning in the Mehler-like reaction. Although ∆sigCDE suffers from oxidative stress, up-regulation of photoprotective carotenoids and Flv4, Sll2018, Flv2 proteins protected PSII against light induced damage by quenching singlet oxygen more efficiently in ∆sigCDE than in the control strain in visible and in UV-A/B light. However, in UV-C light singlet oxygen is not produced and PSII damage occurred similarly in the ∆sigCDE and control strains. According to our results, resistance against the light-induced damage of PSII alone does not lead to high light tolerance of the cells, but in addition efficient protection against oxidative stress would be required.

Light-induced STOMAGEN-mediated stomatal development in Arabidopsis leaves.

The initiation of stomata, microscopic valves in the epidermis of higher plants that control of gas exchange, requires a co-ordinated sequence of asymmetric and symmetric divisions, which is under tight environmental and developmental control. Arabidopsis leaves grown under elevated photosynthetic photon flux density have a higher density of stomata. STOMAGEN encodes an epidermal patterning factor produced in the mesophyll, and our observations indicated that elevated photosynthetic irradiation stimulates STOMAGEN expression. Our analysis of gain and loss of function of STOMAGEN further detailed its function as a positive regulator of stomatal formation on both sides of the leaf, not only in terms of stomatal density across the leaf surface but also in terms of their stomatal index. STOMAGEN function was rate limiting for the light response of the stomatal lineage in the adaxial epidermis. Mutants in pathways that regulate stomatal spacing in the epidermis and have elevated stomatal density, such as stomatal density and distribution (sdd1) and too many mouth alleles, displayed elevated STOMAGEN expression, suggesting that STOMAGEN is either under the direct control of these pathways or is indirectly affected by stomatal patterning, suggestive of a feedback mechanism. These observations support a model in which changes in levels of light irradiation are perceived in the mesophyll and control the production of stomata in the epidermis by mesophyll-produced STOMAGEN, and whereby, conversely, stomatal patterning, either directly or indirectly, influences STOMAGEN levels.

Acclimation of C4 metabolism to low light in mature maize leaves could limit energetic losses during progressive shading in a crop canopy.

C4 plants have a biochemical carbon-concentrating mechanism that increases CO2 concentration around Rubisco in the bundle sheath. Under low light, the activity of the carbon-concentrating mechanism generally decreases, associated with an increase in leakiness (ϕ), the ratio of CO2 retrodiffusing from the bundle sheath relative to C4 carboxylation. This increase in ϕ had been theoretically associated with a decrease in biochemical operating efficiency (expressed as ATP cost of gross assimilation, ATP/GA) under low light and, because a proportion of canopy photosynthesis is carried out by shaded leaves, potential productivity losses at field scale. Maize plants were grown under light regimes representing the cycle that leaves undergo in the canopy, whereby younger leaves initially developed under high light and were then re-acclimated to low light (600 to 100 µE·m(-2)·s(-1) photosynthetically active radiation) for 3 weeks. Following re-acclimation, leaves reduced rates of light-respiration and reached a status of lower ϕ, effectively optimizing the limited ATP resources available under low photosynthetically active radiation. Direct estimates of respiration in the light, and ATP production rate, allowed an empirical estimate of ATP production rate relative to gross assimilation to be derived. These values were compared to modelled ATP/GA which was predicted using leakiness as the sole proxy for ATP/GA, and, using a novel comprehensive biochemical model, showing that irrespective of whether leaves are acclimated to very low or high light intensity, the biochemical efficiency of the C4 cycle does not decrease at low photosynthetically active radiation.

Enhancement of crop photosynthesis by diffuse light: quantifying the contributing factors.

BACKGROUND AND AIMS: Plants use diffuse light more efficiently than direct light. However, experimental comparisons between diffuse and direct light have been obscured by co-occurring differences in environmental conditions (e.g. light intensity). This study aims to analyse the factors that contribute to an increase in crop photosynthesis in diffuse light and to quantify their relative contribution under different levels of diffuseness at similar light intensities. The hypothesis is that the enhancement of crop photosynthesis in diffuse light results not only from the direct effects of more uniform vertical and horizontal light distribution in the crop canopy, but also from crop physiological and morphological acclimation. METHODS: Tomato (Solanum lycopersicum) crops were grown in three greenhouse compartments that were covered by glass with different degrees of light diffuseness (0, 45 and 71 % of the direct light being converted into diffuse light) while maintaining similar light transmission. Measurements of horizontal and vertical photosynthetic photon flux density (PPFD) distribution in the crop, leaf photosynthesis light response curves and leaf area index (LAI) were used to quantify each factor's contribution to an increase in crop photosynthesis in diffuse light. In addition, leaf temperature, photoinhibition, and leaf biochemical and anatomical properties were studied. KEY RESULTS: The highest degree of light diffuseness (71 %) increased the calculated crop photosynthesis by 7·2 %. This effect was mainly attributed to a more uniform horizontal (33 % of the total effect) and vertical PPFD distribution (21 %) in the crop. In addition, plants acclimated to the high level of diffuseness by gaining a higher photosynthetic capacity of leaves in the middle of the crop and a higher LAI, which contributed 23 and 13 %, respectively, to the total increase in crop photosynthesis in diffuse light. Moreover, diffuse light resulted in lower leaf temperatures and less photoinhibition at the top of the canopy when global irradiance was high. CONCLUSIONS: Diffuse light enhanced crop photosynthesis. A more uniform horizontal PPFD distribution played the most important role in this enhancement, and a more uniform vertical PPFD distribution and higher leaf photosynthetic capacity contributed more to the enhancement of crop photosynthesis than did higher values of LAI.

Supplemental greenhouse lighting increased the water use efficiency, crop growth, and cutting production in Cannabis sativa.

The expanding cannabis production sector faces economic challenges, intensified by freshwater scarcity in the main US production areas. Greenhouse cultivation harnesses sunlight to reduce production costs, yet the impact of greenhouse light levels on crucial production components, such as plant growth, branching, and water use efficiency (WUE), remains poorly understood. This study aimed to assess the effects of combined sunlight and supplemental lighting on the crop's main production components and leaf gas exchange of Cannabis sativa 'Suver Haze' in the vegetative stage. Within a greenhouse, LED lighting provided at intensities of ~150, 300, 500, and 700 µmol m-2 s-1 (18-hour photoperiod), combined with solar radiation, resulted in average daily light integrals of 17.9, 29.8, 39.5, and 51.8 mol m-2 d-1. Increasing light levels linearly increased biomass, leaf area, and the number of branches per plant and square meter, with respective rates of 0.26 g, 32.5 cm2, and 0.41 branches per mole of additional light. As anticipated, crop evapotranspiration increased by 1.8-fold with the increase in light intensity yet crop WUE improved by 1.6-fold when comparing the lowest and highest light treatments. Moreover, water requirements per unit of plant biomass decreased from 0.37 to 0.24 liters per gram when lighting increased from ~18 to 52 mol m-2 d-1, marking a 35% reduction in evapotranspiration. These results were supported by increments in leaf photosynthesis and WUE with light enhancement. Furthermore, our findings indicate that even 52 mol m-2 d-1 of supplemental lighting did not saturate any of the crop responses to light and can be economically viable for cannabis nurseries. In conclusion, light supplementation strongly enhanced photosynthesis and plant growth while increasing WUE. Additionally, a comprehensive discussion highlights the shared physiological mechanisms governing WUE in diverse plant species and their potential for water conservation under enhanced lighting conditions.

Effect of light-induced changes in leaf anatomy on intercellular and cellular components of mesophyll resistance for CO2 in Fagus sylvatica.

Mesophyll resistance for CO2 diffusion (rm) is one of the main limitations for photosynthesis and plant growth. Breeding new varieties with lower rm requires knowledge of its distinct components. We tested new method for estimating the relative drawdowns of CO2 concentration (c) across hypostomatous leaves of Fagus sylvatica. This technique yields values of the ratio of the internal CO2 concentrations at the adaxial and abaxial leaf side, cd/cb, the drawdown in the intercellular air space (IAS), and intracellular drawdown between IAS and chloroplast stroma, cc/cbd. The method is based on carbon isotope composition of leaf dry matter and epicuticular wax isolated from upper and lower leaf sides. We investigated leaves from tree-canopy profile to analyse the effects of light and leaf anatomy on the drawdowns and partitioning of rm into its inter- (rIAS) and intracellular (rliq) components. Validity of the new method was tested by independent measurements of rm using conventional isotopic and gas exchange techniques. 73% of investigated leaves had adaxial epicuticular wax enriched in 13C compared to abaxial wax (by 0.50‰ on average), yielding 0.98 and 0.70 for average of cd/cb and cc/cbd, respectively. The rIAS to rliq proportion were 5.5:94.5% in sun-exposed and 14.8:85.2% in shaded leaves. cc dropped to less than half of the atmospheric value in the sunlit and to about two-thirds of it in shaded leaves. This method shows that rIAS is minor but not negligible part of rm and reflects leaf anatomy traits, i.e. leaf mass per area and thickness.

Genome-wide identification and characterization of the Prunus persica ferredoxin gene family and its role in improving heat tolerance.

Ferredoxin is involved in many biological processes, such as carbon fixation, nitrogen assimilation, chlorophyll metabolism, and fatty acid synthesis, and it plays a role in plant resistance to stress. However, the functions of Fds in peach during stress are unclear. In this study, 11 members of the peach Fd gene family were identified and divided into six groups (I- VI). We carried out bioinformatics analysis on these sequences, analyzed the physical and chemical properties of PpFd protein and the cis-elements in its promoter region, and predicted and compared the differences in gene structure and conserved protein motifs among groups. The results showed that the PpFd protein was highly conserved in plant species. In addition, overexpression of PpFd08 significantly increased the tolerance of transgenic tomato to high-temperature stress. The transcriptome analysis and qRT-PCR results of PpFd08 transgenic apple calli showed that PpFd08 might enhance heat resistance by modulating the expression of heat tolerance related genes. The results of this study provide a new understanding for the further study of the function of PpFd protein in peach and a candidate gene for improving the heat resistance of peach.

Impact of Different Daily Light Integrals and Carbon Dioxide Concentrations on the Growth, Morphology, and Production Efficiency of Tomato Seedlings.

Indoor growing systems with light-emitting diodes offer advantages for the growth of tomato seedlings through uniform and optimized environmental conditions which increase consistency between plants and growing cycles. CO2 enrichment has been shown to improve the yield of crops. Thus, this research aimed to characterize the effects of varied light intensities and CO2 enrichment on the growth, morphology, and production efficiency of tomato seedlings in indoor growing systems. Four tomato cultivars, "Florida-47 R," "Rebelski," "Maxifort," and "Shin Cheong Gang," were subjected to three different daily light integrals (DLIs) of 6.5, 9.7, and 13 mol m-2 d-1 with a percent photon flux ratio of 40 blue:60 red and an end-of-day far-red treatment of 5 mmol m-2 d-1. The plants were also subjected to three different CO2 concentrations: 448 ± 32 (400-ambient), 1010 ± 45 (1000), and 1568 ± 129 (1600) µmol mol-1. Temperature was maintained at 24.3°C ± 0.48/16.8°C ± 1.1 (day/dark; 22.4°C average) and relative humidity at 52.56 ± 8.2%. Plant density was 1000 plants m-2 until canopy closure. Morphological measurements were conducted daily to observe the growth response over time. In addition, data was collected to quantify the effects of each treatment. The results showed increases in growth rate with increases in the DLI and CO2 concentration. In addition, CO2 enrichment to 1000-1600 µmol mol-1 increased the light use efficiency (gDM mol-1 applied) by 38-44%, and CO2 enrichment to 1600 µmol mol-1 did not result in any additional increase on shoot fresh mass, shoot dry mass, and stem extension. However, the net photosynthetic rate obtained with 1600 µmol mol-1 was 31 and 68% higher than those obtained with 1000 and 400 µmol mol-1, respectively. Furthermore, the comparison of the light and CO2 treatment combinations with the control (13 mol m-2 d-1-400CO2) revealed that the plants subjected to 6.5DLI-1600CO2, 9.7DLI-1000CO2, and 9.7DLI-1600CO2 treatment combinations exhibited the same growth rate as the control plants but with 25-50% less DLI. Furthermore, two treatment combinations (13.0DLI-1000CO2 and 13.0DLI-1600CO2) were associated with the consumption of comparable amount of energy but increased plant growth by 24-33%.

Continuous Lighting and High Daily Light Integral Enhance Yield and Quality of Mass-Produced Nasturtium (Tropaeolum majus L.) in Plant Factories.

Nasturtium (Tropaeolum majus L.), as a medicinal plant, has a high phenolic content in its leaves and flowers. It is often used in salads as a dietary vegetable. Attracting strong demand, it could be a good candidate crop for a plant factory with artificial lighting (PFAL) that can achieve the mass production of high-quality crops with high productivity by regulating environmental conditions such as light. In this study, two experiments were conducted to investigate the effects of continuous lighting (CL) and different daily light integrals (DLIs) under CL on the growth, secondary metabolites, and light use efficiency (LUE) of nasturtium, all of which are essential in the successful cultivation in PFALs. In Experiment 1, two lighting models, the same DLI of 17.3 mol m-2 d-1 but different light periods (24 and 16 h) with different light intensities (200 and 300 µmol m-2 s-1, respectively), were applied to nasturtium. The results showed that leaf production, secondary metabolites, and LUE were higher under the 24-h CL treatment than under the 16-h non-CL treatment. In Experiment 2, three DLI levels (17.3, 25.9, and 34.6 mol m-2 d-1) under the CL condition were applied. The results showed that the growth parameters were positively correlated with the DLI levels under CL. The lowest DLI had the highest LUE. We conclude that the mass production of nasturtium under CL in PFALs is feasible, and the yield increases as DLI increases from 17.3 to 34.6 mol m-2 d-1 under CL without causing physiological stress on plants.

Cannabis Yield, Potency, and Leaf Photosynthesis Respond Differently to Increasing Light Levels in an Indoor Environment.

Since the recent legalization of medical and recreational use of cannabis (Cannabis sativa) in many regions worldwide, there has been high demand for research to improve yield and quality. With the paucity of scientific literature on the topic, this study investigated the relationships between light intensity (LI) and photosynthesis, inflorescence yield, and inflorescence quality of cannabis grown in an indoor environment. After growing vegetatively for 2 weeks under a canopy-level photosynthetic photon flux density (PPFD) of ≈425 µmol·m-2·s-1 and an 18-h light/6-h dark photoperiod, plants were grown for 12 weeks in a 12-h light/12-h dark "flowering" photoperiod under canopy-level PPFDs ranging from 120 to 1,800 µmol·m-2·s-1 provided by light emitting diodes. Leaf light response curves varied both with localized (i.e., leaf-level) PPFD and temporally, throughout the flowering cycle. Therefore, it was concluded that the leaf light response is not a reliable predictor of whole-plant responses to LI, particularly crop yield. This may be especially evident given that dry inflorescence yield increased linearly with increasing canopy-level PPFD up to 1,800 µmol·m-2·s-1, while leaf-level photosynthesis saturated well-below 1,800 µmol·m-2·s-1. The density of the apical inflorescence and harvest index also increased linearly with increasing LI, resulting in higher-quality marketable tissues and less superfluous tissue to dispose of. There were no LI treatment effects on cannabinoid potency, while there were minor LI treatment effects on terpene potency. Commercial cannabis growers can use these light response models to determine the optimum LI for their production environment to achieve the best economic return; balancing input costs with the commercial value of their cannabis products.

Green Light Improves Photosystem Stoichiometry in Cucumber Seedlings (Cucumis sativus) Compared to Monochromatic Red Light.

It has been shown that monochromatic red and blue light influence photosynthesis and morphology in cucumber. It is less clear how green light impacts photosynthetic performance or morphology, either alone or in concert with other wavelengths. In this study, cucumber (Cucumis sativus) was grown under monochromatic blue, green, and red light, dichromatic blue-green, red-blue, and red-green light, as well as light containing red, green, and blue wavelengths, with or without supplemental far-red light. Photosynthetic data collected under treatment spectra at light-limiting conditions showed that both red and green light enhance photosynthesis. However, photosynthetic data collected with a 90% red, 10% blue, 1000 µmol photons m-2 s-1, saturating light show significantly lower photosynthesis in the green, red, and red-green treatments, indicating a blue light enhancement due to photosystem stoichiometric differences. The red-green and green light treatments show improved photosynthetic capacity relative to red light, indicating partial remediation by green light. Despite a lower quantum efficiency and the lowest ambient photosynthesis levels, the monochromatic blue treatment produced among the tallest, most massive plants with the greatest leaf area and thickest stems.

Optimizing nitrogen supply promotes biomass, physiological characteristics and yield components of soybean (Glycine max L. Merr.).

Avoidable or inappropriate nitrogen (N) fertilizer rates harmfully affect the yield production and ecological value. Therefore, the aims of this study were to optimize the rate and timings of N fertilizer to maximize yield components and photosynthetic parameter of soybean. This field experiment consists of five fertilizer N rates: 0, 75, 150, 225 and 300 kg N ha-1 arranged in main plots and four N fertilization timings: V5 (trifoliate leaf), R2 (full flowering stage) and R4 (full poding stage), and R6 (full seeding stage) growth stages organized as subplots. Results revealed that 225 kg N ha-1 significantly enhanced grain yield components, total chlorophyll (Chl), photosynthetic rate (P N), and total dry biomass and N accumulation by 20%, 16%, 28%, 7% and 12% at R4 stage of soybean. However, stomatal conductance (g s ), leaf area index (LAI), intercellular CO2 concentration (Ci) and transpiration rate (E) were increased by 12%, 88%, 10%, 18% at R6 stage under 225 kg N ha-1. Grain yield was significantly associated with photosynthetic characteristics of soybean. In conclusion, the amount of nitrogen 225 kg ha-1 at R4 and R6 stages effectively promoted the yield components and photosynthetic characteristics of soybean.

Comparison of the Photoautotrophic Growth Regimens of Chlorella sorokiniana in a Photobioreactor for Enhanced Biomass Productivity.

Microalgae have a wide industrial potential because of their high metabolic diversity and plasticity. Selection of optimal cultivation methods is important to optimize multi-purpose microalgal biotechnologies. In this research, Chlorella sorokiniana AM-02 that was isolated from a freshwater lake was cultured under various high photosynthetic photon flux density (PPFD) conditions and CO2 gas levels in standard Bold's basal medium (BBM). Furthermore, a wide range of nitrate levels (180-1440 mg L-1) was tested on the growth of C. sorokiniana. Microalgae growth, pigment concentration, medium pH, exit gas composition, as well as nitrate, phosphate, and sulfate levels were measured during an experimental period. The preferred high PPFD and optimal CO2 levels were found to be 1000-1400 µmol photons m-2 s-1 and 0.5-2.0% (v/v), respectively. The addition of nitrate ions (up to 1440 mg L-1) to the standard growth medium increased final optical density (OD750), cell count, pigment concentration, and total biomass yield but decreased the initial growth rate at high nitrate levels. Our findings can serve as the basis for a robust photoautotrophic cultivation system to maximize the productivity of large-scale microalgal cultures.

Spectral comparison of diffuse PAR irradiance under different tree and shrub shading conditions and in cloudy days.

Spectral Solar Photosynthetically Photon Flux Density (PPFD) (380 to 780 nm) reaching the surface of a plant in different lighting conditions has been analyzed in order to better understand the different photosynthetic performance of plants depending on their spatial situation and the vegetation surrounding. A comparison between the shadow of several trees in a sunny day and the case of a cloudy day in an open space has been studied. Three isolated trees (a palm tree, an olive tree and a shrub oleander) and a tipuana grove have been studied. The study has been developed in Valencia (Spain) during January and February 2017. A portable Asensetek Standard ALP-01 spectrometer with a measurement wavelength range of 380 to 780 nm, has been used. Conditions with higher PPFD received are found to be, apart from those of a sunny day, those for cloudy day (with a spectral maximum in the Green region of the spectrum), and those for individual trees and shrub shadows in a sunny day (with a spectral maximum in the Blue region). The case in which less amount of PPFD is received is that under the shadow of tipuana grove (with a spectral maximum in the Infrared region of the spectrum). In fact the order of magnitude in which the PPFD in a cloudy day exceeds the PPFD under the tipuana grove shade is up to 20.

Growth and Accumulation of Secondary Metabolites in Perilla as Affected by Photosynthetic Photon Flux Density and Electrical Conductivity of the Nutrient Solution.

The global demand for medicinal plants is increasing. The quality of plants grown outdoors, however, is difficult to control. Myriad environmental factors influence plant growth and directly impact biosynthetic pathways, thus affecting the secondary metabolism of bioactive compounds. Plant factories use artificial lighting to increase the quality of medicinal plants and stabilize production. Photosynthetic photon flux density (PPFD) and electrical conductivity (EC) of nutrient solutions are two important factors that substantially influence perilla (Perilla frutescens, Labiatae) plant growth and quality. To identify suitable levels of PPFD and EC for perilla plants grown in a plant factory, the growth, photosynthesis, and accumulation of secondary metabolites in red and green perilla plants were measured at PPFD values of 100, 200, and 300 µmol m-2 s-1 in nutrient solutions with EC values of 1.0, 2.0, and 3.0 dS m-1. The results showed significant interactive effects between PPFD and EC for both the fresh and dry weights of green perilla, but not for red perilla. The fresh and dry weights of shoots and leafy areas were affected more by EC than by PPFD in green perilla, whereas they were affected more by PPFD than by EC in red perilla. Leaf net photosynthetic rates were increased as PPFD increased in both perilla varieties, regardless of EC. The perillaldehyde concentration (mg g-1) in red perilla was unaffected by the treatments, but accumulation in plants (mg per plant) was significantly enhanced as the weight of dry leaves increased. Perillaldehyde concentrations in green perilla showed significant differences between combinations of the highest PPFD with the highest EC and the lowest PPFD with the lowest EC. Rosmarinic acid concentration (mg g-1) was increased in a combination of low EC and high PPFD conditions. Optimal cultivation conditions of red and green perilla in plant factory will be discussed in terms of plant growth and contents of medicinal ingredients.

Cytokinins and Abscisic Acid Act Antagonistically in the Regulation of the Bud Outgrowth Pattern by Light Intensity.

Bud outgrowth is a key process in the elaboration of yield and visual quality in rose crops. Although light intensity is well known to affect bud outgrowth, little is known on the mechanisms involved in this regulation. The objective of this work was to test if the control of bud outgrowth pattern along the stem by photosynthetic photon flux density (PPFD) is mediated by sugars, cytokinins and/or abscisic acid in intact rose plants. Rooted cuttings of Rosa hybrida 'Radrazz' were grown in growth chambers under high PPFD (530 µmol m-2 s-1) until the floral bud visible stage. Plants were then either placed under low PPFD (90 µmol m-2 s-1) or maintained under high PPFD. Bud outgrowth inhibition by low PPFD was associated with lower cytokinin and sugar contents and a higher abscisic acid content in the stem. Interestingly, cytokinin supply to the stem restored bud outgrowth under low PPFD. On the other hand, abscisic acid supply inhibited outgrowth under high PPFD and antagonized bud outgrowth stimulation by cytokinins under low PPFD. In contrast, application of sugars did not restore bud outgrowth under low PPFD. These results suggest that PPFD regulation of bud outgrowth in rose involves a signaling pathway in which cytokinins and abscisic acid play antagonistic roles. Sugars can act as nutritional and signaling compounds and may be involved too, but do not appear as the main regulator of the response to PPFD.

In vitro regeneration of shoots and ex vitro rooting of an important medicinal plant Passiflora foetida L. through nodal segment cultures.

Methods were developed in the present investigation for cloning and large scale plant production of Passiflora foetida L. germplasm selected from the East-Coast region of South India. Nodal shoot segments were used as explants. The explants were dressed and surface sterilized with 0.1% (w/v) HgCl2. Multiple shoots were induced (6.13 ± 0.22 shoots per explant) by proliferation of nodal shoot meristems on Murashige and Skoog (MS) semi-solid medium + 2.0 mg l-1 6-benzylaminopurine (BAP). The shoots of P. foetida were further multiplied (16.45 ± 0.44 shoots per explant) on MS medium + 0.5 mg l-1 each of BAP and Kinetin (Kin). The in vitro generated shoots were rooted on half-strength MS medium containing 2.5 mg l-1 indole-3 butyric acid (IBA). By this method 67% shoots were rooted. About 97% shoots were rooted ex vitro (8.33 ± 0.29 roots per shoot) when the cut ends of the shoots were treated with 300 mg l-1 IBA for 5 min. The in vitro rooted plants were hardened and acclimatized in the greenhouse and successfully (100%) transplanted to the field.

Differences in photosynthetic performance between cyanobacterial and green algal components of lichen photosymbiodemes measured in the field.

Photosymbiodemes are lichens which contain a single mycobiont but have cyanobacteria and green algae as primary photobionts in different parts of the thallus. Members of a photosymbiodeme can be found as separate, free-living lichen species. The photosynthesis of the components of two Pseudocyphellaria photosymbiodemes were studied in the natural forest environment in New Zealand. It was found that the green algal component had a large photosynthetic advantage when thallus water contents were low and the thalli were in equilibrium with atmospheric humidity. The cyanobacterial components were at an advantage when thallus water contents were very high. The environment in which photosymbiodemes are found, forest margins in high humidity areas, seems to provide the correct combination of thallus water contents so that neither component has a major advantage. The photosymbiodemes appear to be models, preserved by the special habitat and showing a possible early stage in the evolution before the definite separation of ecologically specialised green algal and cyanobacterial species.

Acclimation of photosystem II in a cyanobacterium and a eukaryotic green alga to high and fluctuating photosynthetic photon flux densities, simulating light regimes induced by mixing in lakes.

Photoacclimation of Scenedesmus protuberans Fritsch and Microcystis aeruginosa Kützing emend. Elenkin to high and fluctuating PPFD was studied in continuous cultures with computer-controlled variable light regimes. The aim of the work was to provide a better understanding of species-specific acclimation to high PPFD (as encountered by cyanobacteria in surface waterblooms), and of suppression of the growth of colony-forming cyanobacteria during periods of prolonged mixing in lakes. The dynamics of a set of variables was followed during the light period, including pigment composition, maximum rate, efficiency and minimum quantum requirement of photosynthesis, PS II cross-sections, and fluorescence variables. Both the green alga and the cyanobacterium displayed strong photo-inhibition of photosynthesis in the sinusoidal light regime, which simulated a natural light regime in the absence of mixing. Pmax , α, QR and the ratio of variable to maximum fluorescence declined, and the number of inactive PS II centres and PS IIß centres increased towards midday. Introduction of oscillations in the diurnal light regime, simulating different intensities of wind-induced mixing in lakes, mitigated photo-inhibition. Microcystis showed a prompt non-photochemical quenching of fluorescence in all light regimes, even at low to moderate PPFD. The sustained presence of zeaxanthin in Microcystis possibly induced instant, thermal dissipation of excitation energy from the antenna. Microcystis also exhibited a more reluctant acclimation to fluctuating PPFD. Growth rate of Scenedesmus was higher in all light regimes. This implied that if (known) differences in loss processes were ignored, Scenedesmus would outcompete Microcystis in lakes. The results underlined the importance of buoyancy regulation in increasing the daily light dose of cyanobacteria (but at the same time preventing over-excitation), and ultimately in the success in Microcystis in stable lakes.