High-light Plants Research Articles

Impact of dye treatment as management strategy on available light may favour a highly invasive alien aquatic plant

Attempts to control massive proliferations of invasive alien aquatic plants (IAAP) are often ineffective. A renewed interest for dye treatment is emerging aiming to control the submerged macrophyte Myriophyllum heterophyllum in France. We aimed to understand the effects of dye on this plant knowing about its adaptation to low light. In a 2 × 2 factorial design experiment, we assessed the effect of a dye mixture based on Brilliant Blue (E133) and Allura Red (E129) at high and low light intensities on light quantity and quality and how this might affect the plant’s performance by measuring morphological and physiological traits. A multivariate analysis identified three groups – high light (HL) plants, plants in high light with dye (HLD) or low light (LL), and low light with dye (LLD) plants. HL plants performed well but showed stress signs, with a reduced main shoot length, a higher leaf dry matter content (LDMC) and a lower nitrogen content (N), not observed in plants grown in HLD or LL. HLD and LL plants exhibited a comparable total length growth rate to those in HL, but had lower LDMC and higher N contents. LLD plants performed poorly with the lowest growth and signs of physiological stress. Dye-induced changes in light quality only marginally affected the absorbance range of chlorophyll b, which apparently did not affect photosynthesis. Commercially available dyes currently used to control nuisance aquatic plants thus seem to have little or no effect on submerged macrophytes. The presence of dye may exacerbate negative effects of very low light intensities on the plant’s growth. However, these very low intensities would only be reached during high-water levels or in winter, periods where the dye would rapidly be diluted. During summer, however, the application of dye may protect the plant from damaging light intensities and thus not be a good management strategy to control low light adapted invasive submerged macrophytes.

Effects of low and high irradiation levels on growth and PSII efficiency in Lemna minor L.

Plant growth and reproduction depend on light energy that drives photosynthesis. In the present study we compared growth characteristics, photosynthetic pigments content and photosystem II (PSII) performance in Lemna minor L. grown in two different irradiation regimes: low light (LL) – 50 μmolPHOTONS m-2 s-1 and high light (HL) – 500 μmolPHOTONS m-2 s-1. The main goal was to investigate the photosynthetic regulatory mechanisms that ensure adjustment to different light conditions and integrate these observations with the data on plant multiplication and biomass production. For this purpose, we measured chlorophyll (Chls) and carotenoid (Cars) contents and analyzed the energy fluxes through the PSII by saturation pulse method as well as by Chl a transient induction and JIP test. In a comparison of the effect of LL and HL on plant multiplication and fresh biomass, it was shown that the effect on growth was primarily attributed to the biomass reduction in LL while the effect on number of plants was much smaller. Total Chl and Cars contents were decreased in plants exposed to HL which indicated long-term acclimation response to the increased irradiance. Furthermore, the HL plants revealed better capability for the utilization of absorbed light in photosynthesis accompanied by photoprotective adjustment of certain number of PSII reaction centers from active to dissipative mode of functioning. In conclusion, our study showed that duckweed plants had great adjustment potential to different irradiation conditions, which might be of great importance not only under variable light availability but also when simultaneously challenged by some other environmental disturbance (e.g. different pollutants).

The half-life of the cytochrome bf complex in leaves of pea plants after transfer from moderately-high growth light to low light.

The content of cytochrome (cyt) bf complex is the main rate-limiting factor that determines light- and CO2-saturated photosynthetic capacity. A study of the half-life of the cyt f content in leaves was conducted whereby Pisum sativum L. plants, grown in moderately high light (HL), were transferred to low light (LL). The cyt f content in fully-expanded leaves decreased steadily over the 2 weeks after the HL-to-LL transfer, whereas control leaves in HL retained their high contents. The difference between the time courses of HL-to-LL plants and control HL plants represents the time course of loss of cyt f content, with a half-life of 1.7 days, which is >3-fold shorter than that reported for tobacco leaves at constant growth irradiance using an RNA interference approach (Hojka et al. 2014). After transfer to LL (16h photoperiod), pea plants were re-exposed to HL for 0, 1.5h or 5h during the otherwise LL photoperiod, but the cyt f content of fully-expanded leaves declined practically at the same rate regardless of whether HL was re-introduced for 0, 1.5h or 5h during each 16h LL photoperiod. It appears that fully-expanded leaves, having matured under HL, were unable to increase their cyt f content when re-introduced to HL. These findings are relevant to any attempts to maintain a high photosynthetic capacity when the growth irradiance is temporarily decreased by shading or overcast weather.

Influence of light and nitrogen on the photosynthetic efficiency in the C4 plant Miscanthus×giganteus.

There are numerous studies describing how growth conditions influence the efficiency of C4 photosynthesis. However, it remains unclear how changes in the biochemical capacity versus leaf anatomy drives this acclimation. Therefore, the aim of this study was to determine how growth light and nitrogen availability influence leaf anatomy, biochemistry and the efficiency of the CO2 concentrating mechanism in Miscanthus×giganteus. There was an increase in the mesophyll cell wall surface area but not cell well thickness in the high-light (HL) compared to the low-light (LL) grown plants suggesting a higher mesophyll conductance in the HL plants, which also had greater photosynthetic capacity. Additionally, the HL plants had greater surface area and thickness of bundle-sheath cell walls compared to LL plants, suggesting limited differences in bundle-sheath CO2 conductance because the increased area was offset by thicker cell walls. The gas exchange estimates of phosphoenolpyruvate carboxylase (PEPc) activity were significantly less than the in vitro PEPc activity, suggesting limited substrate availability in the leaf due to low mesophyll CO2 conductance. Finally, leakiness was similar across all growth conditions and generally did not change under the different measurement light conditions. However, differences in the stable isotope composition of leaf material did not correlate with leakiness indicating that dry matter isotope measurements are not a good proxy for leakiness. Taken together, these data suggest that the CO2 concentrating mechanism in Miscanthus is robust under low-light and limited nitrogen growth conditions, and that the observed changes in leaf anatomy and biochemistry likely help to maintain this efficiency.

Photosynthetic activity of vascular bundles in Plantago media leaves

Photosynthetic processes in the leaf lamina and midribs of Plantago media were investigated using plants grown in high light (HL) or low light (LL) conditions. The fluorescence parameters, which indicate photochemical/photosynthetic activity, were different in HL and LL grown plants, but no major differences between lamina and midribs were found. An OJIP test (chlorophyll a fluorescence transient induction) of LL grown plants, indicative of the chloroplast electron transport chain, also showed both tissues to be similar. In HL plants, a partial blockage of electron flow between QA (the primary plastoquinone electron acceptor of PSII) and QB (the secondary plastoquinone acceptor of PSII) was found, and this was less visible in midribs. The effective dissipation of quantum energy per reaction center (DI0/RC) was similar in both tissues of HL grown plants, while in the midribs of LL leaves, this process seemed to be less effective. Measurements of 13C discrimination showed that the midrib tissues of LL and HL leaves effectively used β-carboxylation products to accumulate their biomass. Thus, the well protected activity of electron transport in midribs with their limited capacity to fix CO2 from the air may indicate the involvement of this tissue in β-carboxylation, transport or signaling. Carbon accumulated in roots showed a lower 13C discrimination value (more negative) than the values observed in lamina. This could indicate that roots are supplied with assimilates mostly during the light phase of the day cycle with intensive C3 photosynthesis.

Light acclimation at the end of the growing season in two broadleaved oak species

The ability of plants to increase their net CO2 assimilation rate in response to increased irradiance is due to morphological and physiological changes, which might be related to their shade tolerance and leaf ontogeny, but few studies have considered morphology and physiology. Two sympatric oak species (the shade-tolerant Q. petraea and the comparatively shade-intolerant Q. pyrenaica) were grown in hydroponic solution in low-light (LL) and high-light (HL) conditions. 5 months after leaf expansion under these conditions, half of the LL plants were transferred to high light (TLH). Transfer of Q. pyrenaica, from low- to high light led to photoinhibition and after 21 days in higher light there was little acclimation of the maximum rate of carboxylation (VCmax) or the maximum rate of electron transport (Jmax). Q. pyrenaica TLH plants showed lower stomatal conductance at all times compared to plants growing in LL. Stomatal closure was the main limitation to photosynthesis after transfer in Q. pyrenaica. The increase in evaporative demand upon TLH did not affect hydraulic conductivity of Q. pyrenaica. In contrast, the more shade-tolerant Q. petraea showed a greater degree of acclimation of gas exchange in TLH than Q. pyrenaica and two weeks after transfer gas-exchange rates were as high as in LL plants. In Q. petraea, the most important changes occurred at the level of leaf biochemistry with significant increase in VCmax that decreased the Jmax/VCmax ratio below values recorded in HL plants. However, this potential increase in photosynthesis was at least partially hamstrung by a decrease in internal conductance, which highlights the importance of internal conductance in acclimation to higher light in mature leaves. Neither oak species reached the photosynthetic rates of HL plants; however a trend towards leaf acclimation was observed in Q. petraea while the transfer was harmful to the leaves of Q. pyrenaica developed in the shade.

Distinct responses of the mitochondrial respiratory chain to long‐ and short‐term high‐light environments in Arabidopsis thaliana

In order to ensure the cooperative function with the photosynthetic system, the mitochondrial respiratory chain needs to flexibly acclimate to a fluctuating light environment. The non-phosphorylating alternative oxidase (AOX) is a notable respiratory component that may support a cellular redox homeostasis under high-light (HL) conditions. Here we report the distinct acclimatory manner of the respiratory chain to long- and short-term HL conditions and the crucial function of AOX in Arabidopsis thaliana leaves. Plants grown under HL conditions (HL plants) possessed a larger ubiquinone (UQ) pool and a higher amount of cytochrome c oxidase than plants grown under low light conditions (LL plants). These responses in HL plants may be functional for efficient ATP production and sustain the fast plant growth. When LL plants were exposed to short-term HL stress (sHL), the UQ reduction level was transiently elevated. In the wild-type plant, the UQ pool was re-oxidized concomitantly with an up-regulation of AOX. On the other hand, the UQ reduction level of the AOX-deficient aox1a mutant remained high. Furthermore, the plastoquinone pool was also more reduced in the aox1a mutant under such conditions. These results suggest that AOX plays an important role in rapid acclimation of the respiratory chain to sHL, which may support efficient photosynthetic performance.

High light intensity protects photosynthetic apparatus of pea plants against exposure to lead

The electron transport rates and coupling factor activity in the chloroplasts; adenylate contents, rates of photosynthesis and respiration in the leaves as well as activity of isolated mitochondria were investigated in Pisum sativum L. leaves of plants grown under low or high light intensity and exposed after detachment to 5 mM Pb(NO 3) 2. The presence of Pb 2+ reduced rate of photosynthesis in the leaves from plants grown under the high light (HL) and low light (LL) conditions, whereas the respiration was enhanced in the leaves from HL plants. Mitochondria from Pb 2+ treated HL-leaves oxidized glycine at a higher rate than those isolated from LL leaves. ATP content in the Pb-treated leaves increased to a greater extend in the HL than LL grown plants. Similarly ATP synthase activity increased markedly when chloroplasts isolated from control and Pb-treated leaves of HL and LL grown plants were subjected to high intensity light. The presence of Pb ions was found inhibit ATP synthase activity only in chloroplasts from LL grown plants or those illuminated with low intensity light. Low light intensity during growth also lowered PSI electron transport rates and the Pb 2+ induced changes in photochemical activity of this photosystem were visible only in the chloroplasts isolated from LL grown plants. The activity of PSII was influenced by Pb ions on similar manner in both light conditions. This study demonstrates that leaves from plants grown under HL conditions were more resistant to lead toxicity than those obtained from the LL grown plants. The data indicate that light conditions during growth might play a role in regulation of photosynthetic and respiratory energy conservation in heavy metal stressed plants by increasing the flexibility of the stoichiometry of ATP to ADP production.

Low light grown duckweed plants are more protected against the toxicity induced by Zn and Cd

Duckweed ( Lemna minor L.) plants acclimated to three light regimes: 50 low light (LL), 300 medium light (ML) and 500 high light (HL) μmol m –2 s –1 photosynthetic photon flux density (PPFD) increased photoprotective potential according to irradiance status as shown by the two- to fourfold higher contents of xanthophyll cycle pigments (VAZ), total glutathione (GLU) and α-tocopherol. LL, ML and HL plants were then exposed to Cd or Zn for 9 d and illuminated at 300 μmol m –2 s –1. Both metals inhibited plant growth and caused the accumulation of phytochelatins, but phytochelatin synthesis did not result in glutathione depletion in the Zn treatments. An antioxidative response was observed with a large increase in total ascorbate (ASC), tocopherol and VAZ pigments. These mechanisms seemed to be able to partly alleviate the adverse effects of Zn but not of Cd. The damage caused by Cd led to the complete bleaching of chlorophylls (Chl) at the end of the experiment in HL and ML plants. The pattern of antioxidative response was different when comparing Cd and Zn treatments, with a much larger accumulation of ASC in Cd-treated plants, and GLU on Zn-treated plants. Paradoxically, LL plants that initially had a lower level of photoprotection, were much less affected by Cd or Zn. Thus, these plants showed very small or no reductions in photochemical efficiency, chlorophyll content and a lower ASC accumulation. Although we could not explain this paradoxical effect, we can conclude that other reasons related to the previously light grown conditions could be more determinant to explain heavy metal induced damage than the basal level of antioxidant content in Lemna plants.

The evolution of photosynthetic capacity and the antioxidant enzymatic system during acclimatization of micropropagated Calathea plants

The effects of an increased PPFD on photosynthesis, the functioning of the photosynthetic apparatus and the response of the antioxidant enzymatic system were studied during the ex vitro establishment of micropropagated Calathea ‘Maui Queen’ plantlets. Measured chlorophyll and carotenoids contents in ex vitro formed leaves were almost three times higher compared to the in vitro formed ones. At the end of the acclimatization, an inverse relation between PPFD and the chlorophyll (a+b)/carotenoids ratio was observed. During the first days after transplantation Calathea plants are not photosynthetically active, as is illustrated by the photosynthetic light response curves. With the appearance of new leaves, higher photosynthetic capacities were observed and light saturation point increased (days 17 and 25). Also the maximal photosynthetic efficiency enlarged as shown by the increased initial slope of the curves. F v/ F m decreased directly after transplantation of the micropropagated plantlets, afterwards a recovery was observed, but highest F v/ F m values were observed in low light (LL) plants. The photochemical quenching coefficient increased gradually during the first two weeks of the acclimatization. In high light (HL) plants, q P decreased directly after transfer, while this was not observed in LL and medium light (ML). During the acclimatization period to increasing light intensities significant changes in the activity of the antioxidant enzymatic system were observed. A decrease in superoxide dismutase (SOD) activity was measured during the first half of the acclimatization period followed by a recovery in ML and HL plants by day 35. Dehydroascorbate reductase (DHAR) activity decreased during acclimatization. At the end of the experimental period the lowest levels were measured in ML plants. Catalase (CAT) activity increased significantly during the first two weeks after transfer, a clear inverse relationship to PPFD was detected. The relation between the adquisition of full photosynthetic capacity and the activation of the enzymatic antioxidant system in the leaves of calathea plants during ex vitro acclimatization is discussed.

The effect of light intensities on the transcript level of proteins involved in photosynthesis in mustard plants

Summary The influence of light quantity on the steady-state levels of plastid encoded transcripts was examined during the development of primary leaves from mustard ( Sinapis alba ) plants. RbcL mRNA, petA mRNA, and psbA mRNA, which encode the large subunit (LSU) of Rubisco, Cyt f of the Cyt b6/f complex, and D1 protein of PS II were investigated in leaves grown under high-light (HL) or low-light (LL) conditions. Additionally, the nuclear encoded 25 S rRNA was quantified. As a proportion of total RNA, the levels of 25 S rRNA, rbcL mRNA, petA mRNA, and psbA mRNA did not differ substantially in the HL versus LL plants. During leaf ontogenesis, though, the proportion of psbA mRNA in total RNA increased drastically, in contrast to the other transcripts. The results calculated per unit fresh weight, dry weight, leaf area, and chlorophyll closely resembled each other and gave an idea of the absolute prevalence of the transcripts in the cell. The light regime had a remarkable influence on the absolute levels of 25 S rRNA, rbcL mRNA, and petA mRNA: Paralleling total RNA content, the amounts of the three transcripts per unit fresh weight at the beginning of leaf development were, in HL plants, more than twice the amounts found in LL plants. Furthermore, during leaf ontogenesis the decrease in total RNA, 25 S rRNA, rbcL mRNA, and petA mRNA was more pronounced in HL than in LL, while the psbA mRNA content per unit fresh weight was only slightly higher in HL than in LL leaves and did not decline significantly during HL and LL leaf ontogenesis. Comparison of the absolute levels of rbcL mRNA, petA mRNA, and psbA mRNA with the amounts of the corresponding proteins revealed that the prevalence of the transcripts contributes principally to the differences in the protein content in HL and LL leaves.

Intercropping Stokes Aster: Effect of Shade on Photosynthesis and Plant Morphology

Stokes aster [Stokesia laevis (Hill) E. Greene] is a potential new crop source of an epoxy acid but grows slowly and does not yield the first summer. It could be intercropped that year. To evaluate Stokes aster's response to intercrop shade, plants were grown under 1010 [high light (HL)], 320 [medium light (ML)], or 120 [low light (LL)] μmol m−2 s−1 photosynthetic photon flux density (PWD) for 50 d prior to measurements of photosynthetic rate, light compensation point, light saturation point, chlorophyll concentration, and morphology of whole plants. Near light saturation points, LL and ML plants had the highest net CO2 assimilation based on leaf area and ML plants were highest based on land area. High light plants were least efficient due to a vertical leaf orientation. As environment light intensity (LI) declined, plants had more chlorophyll per unit dry weight (DW), a higher chl b/chl a ratio, less leaf DW, less leaf area, and a lower root/shoot ratio. Light compensation points were 25, 55, and 185 μmol m−2 s−1 PPFD for LL, ML, and HL plants, respectively. Saturation points were between 400 and 800 μmol m−2 s−1 for LL plants and between 800 and 1500 μmol m−2 s−1 PPFD for ML and HL plants. In an intercrop, stokes aster should produce efficiently on a leaf area basis but less efficiently on a land area basis when grown under a LI of 120 μmol m−2 s−1 or less. Growth in full sun after the overstory crop is harvested would not be a problem for intercropped plants.