Physiological characterization of ‘stay green’ wheat cultivars during the grain filling stage under field growing conditions

Rye (Secale cereale L.) chromosome arm 1RS could delay leaf senescence, and change in H₂O₂ content is a useful index for weighing the ability to delay the senescence. Two wheat cultivars, Chuannong12 (CN12) and Chuannong 18 (CN18), harboring the wheat–rye 1BL/1RS translocated chromosome were investigated for H₂O₂ change and physiological index after flowering under field conditions, and MY11, the agronomical parent of both CN12 and CN18, was used as the control. A combined change in the peak value of CdSe/ZnS quantum dot (QD) fluorescence and morphological observation indicated that the H₂O₂ contents in CN12 and CN18 were generally lower than that in MY11. They both had higher values for net photosynthetic rate (P _n), stomatal conductance (G _s), F_\textv /F_\textm^￠ F_{\text{v}} /F_{\text{m}}^{\prime } F_\textv^￠ /F_\textm^￠ F_{\text{v}}^{\prime } /F_{\text{m}}^{\prime } , and photochemical quenching of PSII (qP) than MY11 only in the late measurement stage. Some small differences were also observed, such as CN12 and CN18 wheat cultivars having higher and longer photosynthetic competence than MY11 during the grain filling stage, which perhaps resulted from a mechanism for removing oxidative species, especially H₂O₂.     

Photosynthetic Potential and its Association with Lipid Peroxidation in Response to High Temperature at Different Leaf Ages in Maize

High temperature generally constrains plant growth and photosynthesis in many regions of the world; however, little is known about how photosynthesis responds to high temperature with regard to different leaf ages. The synchronous changes in gas exchange and chlorophyll fluorescence at three leaf age levels (just fully expanded, mature, and older leaves) of maize (Zea mays L.) were determined at three temperatures (30°C as a control and 36 and 42°C as the higher temperatures). High temperature significantly decreased the net CO₂ assimilation rate (A), stomatal conductance (g _s), maximal efficiency of photosystem II (PSII) photochemistry (F _v/F _m), efficiency of excitation energy capture by open PSII reaction centers ( F^￠_\textv /F^￠_\textm F^{\prime}_{\text{v}} /F^{\prime}_{\text{m}} ), photochemical quenching of variable chlorophyll fluorescence (q _P), and the electron transport rate (ETR), whereas minimal fluorescence yield (F ₀) and nonphotochemical quenching of variable chlorophyll fluorescence (q _N) were increased. The youngest fully expanded leaves had higher A, ETR, and q _P compared with older leaves. Higher temperature with old leaves led to significant malondialdehyde (MDA) accumulation, a proxy for lipid peroxidation damage from active oxygen species (AOS). MDA content was significantly negatively correlated with A, F _v/F _m, F^￠_\textv /F^￠_\textm F^{\prime}_{\text{v}} /F^{\prime}_{\text{m}} , and q _P. Thus, the results suggest that photosynthetic potentials, including stomatal regulation and PSII activity, may be restricted at high temperature, together with increasing cell peroxidation, which may be closely associated with leaf age.     

Expression,subcellular localization,and <Emphasis Type="Italic">cis</Emphasis>-regulatory structure of duplicated phytoene synthase genes in melon (<Emphasis Type="Italic">Cucumis melo</Emphasis> L.)

The emission of molecular iodine (I₂) from the stipe, the meristematic area and the distal blade of the brown macroalga Laminaria digitata (Hudson) Lamouroux (Phaeophyceae) was monitored under low light and dark conditions. Photosynthetic parameters were determined to investigate both the extent of stress experienced by different thallus parts and the effects of emersion on photosynthesis. Immediately after air exposure, intense I₂ emission was detectable from all thallus parts. I₂ emission declined continuously over a period of 180 min following the initial burst, but was not affected by the light regime. The total number of mole of I₂ emitted by stipes was approximately 10 times higher than those emitted from other thallus parts. Initial I₂ emission rates (measured within 30 min of exposure to air) were highest for stipes (median values: 2,999 and 5,222 pmol g⁻¹ dw min⁻¹ in low light and dark, respectively) and lower, by one order of magnitude, for meristematic regions and distal blades. After exposure to air for between 60 and 180 min, I₂ emission rates of all thallus parts were reduced by 70–80%. Air exposure resulted in a decrease of the maximum photosystem II (PSII) efficiency (F _v/F _m) by 3%, and in a 25–55% increase of the effective PSII quantum efficiency ( \Updelta F/F^￠_\textm \Updelta F/F^{\prime}_{\text{m}} ); this was caused by a higher fraction of open reaction centres (q_P), whereas the efficiency of the latter in capturing energy ( F^￠_\textv /F^￠_\textm F^{\prime}_{\text{v}} /F^{\prime}_{\text{m}} ) remained constant. The results indicate the presence of an iodine pool which is easily volatilised and depleted due to air exposure, even under apparently low stress conditions.     

Genetic effects of forest fragmentation in high-density Araucaria angustifolia populations in Southern Brazil

Araucaria angustifolia is an endangered tropical/subtropical coniferous of great interest for conservation due its economical, ecological, and social value. Only 3% of original Araucaria forests remain, which are generally confined to small forest fragments. Forest fragmentation can have serious consequences on genetic process in tree population, affecting long-term fitness and adaptability. To investigate the effects of forest fragmentation on genetic diversity and the structure of A. angustifolia populations, the genetic diversity of eight microsatellite loci was compared in four small fragmented populations (<22 ha), four tree groups (five to 11 trees) occurring in pastures and in three plots in a large continuous population. The clearest effect of fragmentation was the loss of rare alleles (p ≤ 0.05) in fragmented populations (19.4% to 47.2%) and intermediate frequency (0.05 < p ≤ 0.25) and rare alleles (p ≤ 0.05) in tree groups (19% to 86.1%) in comparison to continuous populations. Fragmented populations have significant higher fixation index ( [^(F)]_\textIS = 0.121 \widehat{F}_{\text{IS}} = 0.121 , P < 0.05) than continuous populations ( [^(F)]_\textIS = 0.083 \widehat{F}_{\text{IS}} = 0.083 , P < 0.05). High genetic differentiation was detected among tree groups ( [^(G)]_\textST^￠ = 0.258 \widehat{G}_{{{\text{ST}}}}^{\prime } = 0.258 , P < 0.01) and low among fragments ( [^(G)]_\textST^￠ = 0.031 \widehat{G}_{{{\text{ST}}}}^{\prime } = 0.031 , P < 0.05) and continuous populations ( [^(G)]_\textST^￠ = 0.026 \widehat{G}_{{{\text{ST}}}}^{\prime } = 0.026 , P < 0.05), showing a significant bottleneck effect in tree groups. Evidence that forest fragments have experienced a recent bottleneck was confirmed in at least two studied fragments. The implications of the results for conservation of the fragmented A. angustifolia populations are discussed.     

Chloroplast DNA phylogeography of Betula maximowicziana, a long-lived pioneer tree species and noble hardwood in Japan

Betula maximowicziana is an ecologically and economically important tree species in Japan. In order to examine the phylogeographical pattern of the species in detail, maternally inherited chloroplast (cp) DNA variations of 25 natural populations of Betula maximowicziana and a total of 12 populations of three related species were evaluated by PCR-RFLP analysis. Two main haplotypic groups of B. maximowicziana populations (northern and southern) were detected, with the main boundary passing through the Tohoku region in northeastern Japan; in addition there was high genetic differentiation among the 25 populations studied (G _ST = 0.950, G_\textST^￠ = 0. 9 7 7 G_{\text{ST}}^{\prime } = 0. 9 7 7 ). The phylogeographical pattern exhibited by B. maximowicziana was much more similar to that of alpine plants than to that of beech and oak. Comparison of the patterns of genetic structure obtained from the cpDNA with previously and newly acquired data on bi-parentally inherited nuclear DNA indicates that the nuclear genome was transferred via pollen from the northern haplotypic group to the southern group more frequently than it moved in the opposite direction. Although common haplotypes were detected among B. maximowicziana and the two related species examined, these haplotypes were not shared sympatrically, suggesting very rare hybridization among the species currently occurring in their natural populations.     

Seasonal physiological plasticity and recovery capacity after summer stress in Mediterranean scrub communities

Under natural conditions the overlapping of multiple stressors may initiate coordinated ecophysiological responses in Mediterranean species. Seasonal plasticity may enable plants to better cope with adverse environmental conditions and/or resource variability. In this article, we study the seasonal responses of 12 woody species in two sites of differing water availability, in a Mediterranean-type climate. Plants were measured for water potential, photochemical efficiency, photosynthetic pigments and leaf proline content throughout the year. The results revealed that species presented different ecophysiological strategies, even when sharing the same area. In the xerophytic site, some species suffered severe water stress (−12 MPa and F _v/F _m lower than 0.3), while others exhibited optimal values of F _v/F _m and only moderate water stress. All the plants recovered after the first autumn rains. In the hygrophytic site, some sclerophyll species did not exhibit signs of water stress, but did suffer photoinhibition in clear winter days. A plasticity index was calculated to provide an integrated value of species plasticity. In summer, plasticity was higher in the xerophytic site, while in winter it was higher in the hygrophytic site. Ordination analysis of the physiological traits supports the traditional gradient of Mediterranean strategies from drought semideciduous to evergreen sclerophyll species, although spiny legume species formed an independent functional group. The functional responses of species clearly differ among plant communities according to the prevailing site stressors, but no unique pattern emerges. Species combine traits in broader strategies according to previous evolutionary story exhibiting a certain amount of trade among traits, each contributing to alleviate a part of the plant stress.     

The genetic structure of <Emphasis Type="Italic">Quercus crispula</Emphasis> in northeastern Japan as revealed by nuclear simple sequence repeat loci

Previous studies have reached different discussions about the genetic variation and genetic structure of Quercus crispula populations in northeastern Japan. This is a common oak species in Eastern Asia. Some studies have suggested that the populations in northeastern Japan were derived from those remaining in the southwest after the last glacial maximum (LGM), whilst other studies have found evidence that populations persisted in northeastern Japan during the LGM. Using seven highly polymorphic nuclear simple sequence repeat loci, we investigated the genetic structure of 16 Q. crispula populations along a latitudinal gradient in northeastern Japan (northern Honshu and Hokkaido), spanning about half of the species’ biogeographic range in the country. Although the level of population differentiation was low (F _ST = 0.021; G^￠_\textST G^{\prime}_{\text{ST}}  = 0.090), two geographically differentiated clusters were detected by STRUCTURE analysis. The first cluster included most of the populations in Hokkaido, and may indicate continued survival throughout past glacial periods. We found a significant decrease in allelic richness with latitude, so the second cluster may represent an expansion of the lineage from Honshu during the post-glacial period. These results should enhance our understanding of historical north–south migrations of this species in northeastern Japan.     

Effects of low night temperature on pigments,chl <Emphasis Type="Italic">a</Emphasis> fluorescence and energy allocation in two bitter gourd (<Emphasis Type="Italic">Momordica charantia</Emphasis> L.) genotypes

Using two different inbred lines of Momordica charantia (bitter gourd), Y-106-5 and Z-1-4, the cell membrane stability, leaf water potential, pigment contents and the chlorophyll a fluorescence were investigated with different low night temperature (LNT) treatments over a 7 day time period and the sequent a 7 day recovery. Under LNT treatments, electrolyte leakage increased in both inbred lines and it increased more significantly in Y-106-5 plants than that in Z-1-4. The content of Chl b and total Chl decreased, while the Chl a/b ratio increased in stressed plants of the two lines. Almost all LNT treatments induced little change in Chl a content in Z-1-4 whereas obvious decreases in 5 and 8°C treated Y-106-5 plants were observed. Chilling changed the water status of plants and induced decreases of leaf water potential (LWP) in 5 and 8°C treated plants. LNT treatments also resulted in changes in the chlorophyll fluorescence parameters in bitter gourd leaves. The potential PSII activity (F _v/F _o) was reduced obviously by LNT stress and showed more sensitive to LNT than the maximum quantum efficiency of PSII primary photochemistry (F _v/F _m). The efficiency of open PSII centers exhibited a slight decrease whereas the photochemical quenching efficient (q _P) was affected more seriously by LNT stress in both two inbred lines. The allocation of energy was rearranged by LNT stress. The light fraction used for PSII photochemistry (P) was reduced, while that used for heat dissipation (D) and the third fraction of absorbed light defines excess energy (E) increased due to the chilling stress. The impacts of LNT stress on bitter gourd generally increased with the number of LNT chilling and the severe night chilling. Plants were little affected by 12°C night chilling and the most acute damage was found in 5°C night chilling treatments. A 7 day recovery mitigated the adverse effects of LNT for both lines and almost all LNT treated plants restored to control levels except 5°C night chilling treated Y-106-5 plants. The two lines have a variance in tolerance to LNT stress and display obvious differences of phenotypes under extreme conditions.     

Fluoride inhibition of photosystem II and the effect of removal of the PsbQ subunit

Photosystem II (PSII), the light-absorbing complex of photosynthesis that evolves oxygen, requires chloride for activation of the oxygen evolving complex (OEC). In this study, fluoride was characterized as an inhibitor of Cl⁻-activated oxygen evolution in higher plant PSII. It was confirmed to be primarily a competitive inhibitor in intact PSII, with Cl⁻-competitive inhibition constant K_i = 2 mM and uncompetitive inhibition constant \textK_\texti^￠ {\text{K}}_{\text{i}}^{\prime }  = 79 mM. A pH dependence study showed that fluoride inhibition was more pronounced at lower pH values. In order to determine the location of the fluoride effect, PSII preparations lacking various amounts of the PsbQ subunit were prepared. The competitive F⁻ inhibition constant and the Michaelis constant for Cl⁻ activation increased with loss of the PsbQ subunit, while the uncompetitive F⁻ inhibition constant was relatively insensitive to loss of PsbQ. The S₂ state EPR signals from PSII lacking PsbQ responded to Ca²⁺ and Cl⁻ removal and to F⁻ treatment similar to intact PSII, with enhancement of the g = 4.1 signal and suppression of the multiline signal, but the effects were more pronounced in PSII lacking PsbQ. Together, these results support the interpretation that the PsbQ subunit has a role in retaining anions within the OEC.     

Ecophysiological responses of nine floodplain meadow species to changing hydrological conditions

Here, we investigated how species from different floodplain meadow plant communities differ in their ecophysiological responses to an abrupt change in hydrological conditions. We simulated two contrasting hydrological scenarios for 5 weeks under controlled conditions: the waterlogging of a mesophilic species mixture (flooding scenario) and the drying of a hygrophilic species mixture (drying scenario). The mesophilic mixture was composed of three characteristic species of dry habitats (dry species) and three indifferent species with regard to the hydrological conditions; the hygrophilic mixture was composed of three characteristic species of wet habitats (wet species) and the same three indifferent species. The flooding scenario induced a significant decrease in photochemical efficiency (F _v/F _m) of all species for at least one day, and four of these species did not readjust their F _v/F _m at the end of the experiment. The F _v/F _m of four species was significantly reduced by the drying scenario, but was readjusted within the time of the experiment. Significant leaf plastic responses were mainly detected under the drying scenario, through increasing specific leaf area (SLA) and decreasing leaf dry matter content (LDMC) for two indifferent species, and through decreasing SLA and increasing LDMC for two wet species. Finally, the flooding scenario significantly decreased the aboveground biomass of one dry species, but increased the aboveground biomass of the three indifferent species, suggesting an acclimation response to waterlogging through increasing shoot/root ratio. Since the dry species did not show ecophysiological acclimation to changing hydrological conditions (in contrast to the wet species and the indifferent species), this study demonstrated that mesophilic meadow communities should be particularly affected by a change from dry to wet conditions. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Analysis of the activation mechanism of <Emphasis Type="Italic">Pseudomonas stutzeri</Emphasis> cytochrome <Emphasis Type="Italic">c</Emphasis> peroxidase through an electron transfer chain

The activation mechanism of Pseudomonas stutzeri cytochrome c peroxidase (CCP) was probed through the mediated electrochemical catalysis by its physiological electron donor, P. stutzeri cytochrome c-551. A comparative study was carried out, by performing assays with the enzyme in the resting oxidized state as well as in the mixed-valence activated form, using cyclic voltammetry and a pyrolytic graphite membrane electrode. In the presence of both the enzyme and hydrogen peroxide, the peak-like signal of cytochrome c-551 is converted into a sigmoidal wave form characteristic of an \textE_\textr \textC_\texti^￠ {\text{E}}_{\text{r}} {\text{C}}_{\text{i}}^{\prime } catalytic mechanism. An intermolecular electron transfer rate constant of (4 ± 1) × 10⁵ M⁻¹ s⁻¹ was estimated for both forms of the enzyme, as well as a similar Michaelis–Menten constant. These results show that neither the intermolecular electron transfer nor the catalytic activity is kinetically controlled by the activation mechanism of CCP in the case of the P. stutzeri enzyme. Direct enzyme catalysis using protein film voltammetry was unsuccessful for the analysis of the activation mechanism, since P. stutzeri CCP undergoes an undesirable interaction with the pyrolytic graphite surface. This interaction, previously reported for the Paracoccus pantotrophus CCP, induces the formation of a non-native conformation state of the electron-transferring haem, which has a redox potential 200 mV lower than that of the native state and maintains peroxidatic activity.     

Effects of an Experimental Increase of Temperature and Drought on the Photosynthetic Performance of Two Ericaceous Shrub Species Along a North–South European Gradient

Plant ecophysiological changes in response to climatic change may be different in northern and southern European countries because different abiotic factors constrain plant physiological activity. We studied the effects of experimental warming and drought on the photosynthetic performance of two ericaceous shrubs (Erica multiflora and Calluna vulgaris) along a European gradient of temperature and precipitation (UK, Denmark, The Netherlands, and Spain). At each site, a passive warming treatment was applied during the night throughout the whole year, whereas the drought treatment excluded rain events over 6–10 weeks during the growing season. We measured leaf gas exchange, chlorophyll a fluorescence, and leaf carbon isotope ratio (¹³C) during the growing seasons of 1999 and 2000. Leaf net photosynthetic rates clearly followed a gradient from northern to southern countries in agreement with the geographical gradient in water availability. Accordingly, there was a strong correlation between net photosynthetic rates and the accumulated rainfall over the growing season. Droughted plants showed lower leaf gas exchange rates than control plants in the four sites. Interestingly, although leaf photosynthetic rates decreased along the precipitation gradient and in response to drought treatment, droughted plants were able to maintain higher leaf photosynthetic rates than control plants in relation to the accumulated rainfall over the months previous to the measurements. Droughted plants also showed higher values of potential photochemical efficiency (F _v/F _m) in relation to controls, mainly at midday. The warming treatment did not affect significantly any of the studied instantaneous ecophysiological variables..     

Effects of Abscisic Acid Application on Photosynthesis and Photochemistry of Stylosanthes guianensis under Chilling Stress

In our previous study, it was found that abscisic acid (ABA) improved the chilling resistance of Stylosanthes guianensis. In order to determine the effects of ABA on photosynthesis and photochemistry of S. guianensis, an experiment was conducted under controlled condition to determine the effects of exogenous ABA on stomatal conductance (g_s), transpiration (E), photosynthetic rate (A) and chlorophyll a fluorescence of this pasture legume. The results showed that ABA treatment reduced A, g_s, and E under both chilling (8 °C) and control temperature (28 °C). A of the ABA treated plants returned to a high rate, while that of the water-treated plants remained low when plants were rewarmed after chilling treatment. ABA-treated plants had higher maximum photochemical efficiency (F_v/F_m), non-photochemical quenching (NPQ), quantum efficiency of PS II photochemistry (Φ_{ps ii}) than water-treated ones during chilling. Although the biomass of S. guianensis was reduced by ABA under control temperature, ABA-treated plants had higher biomass than water-treated ones after 7 days of recovery.     

Fungal endophytes associated with the mistletoe <Emphasis Type="Italic">Phoradendron perrottettii</Emphasis> and its host tree <Emphasis Type="Italic">Tapirira guianensis</Emphasis>

The endophytic mycobiota of leaves and stems of the mistletoe Phoradendron perrottettii and its host tree Tapirira guianensis, two physiologically connected plant species of the Brazilian savannah in southeastern Brazil, were investigated to evaluate host and organ recurrence among endophytes. Leaves and stems of P. perrottettii and leaves of T. guianensis were sampled in the dry and wet season. Stems of T. guianensis were also sampled in the wet season. Endophytes were isolated by an adapted trituration and particle filtration protocol. A total of 1,615 isolates representing 99 species and 20 sterile morphotypes were recovered; 64 morphospecies occurred as singletons. The number of isolates and species was higher in the wet season. Leaves of P. perrottettii were less densely colonized than other organs studied, but were the most species-rich. Conversely, stems of T. guianensis yielded more isolates but were less species-rich. Both plants were found to harbor similar but distinguishable endophytic assemblages. The Jaccard’s index of similarity between the fungal assemblages of both plants was 0.82, higher than found for other plants in similar habitats. The fungal species composition seemed to be influenced by the collection season and organ type, as demonstrated by multivariate correspondence analysis. Paraconiothyrium brasiliense, P. sporulosum and Verticillium leptobactrum were the dominant species in P. perrottettii. In leaves of T. guianensis, Pseudocercospora sp., Phomopsis sp. 1 and Lecanicillium psalliotae were the most frequent, while Stagonospora sp. 1 and Phomopsis sp. 1 were the dominant endophytes in its stems. The results indicated that some of the dominant endophytic taxa isolated in this study colonize different hosts and plant organs while others seem to exhibit a high degree of host or organ recurrence. This study represents the first evaluation of diversity of fungal endophytes in natural vegetation of the Brazilian savannah and contributes information about the distribution and possible specificity of endophytes in tropical dicotyledoneous plants.     

New potent biphalin analogues containing p-fluoro-L-phenylalanine at the 4,4' positions and non-hydrazine linkers

We report the synthesis and the biological evaluation of two new analogues of the potent dimeric opioid peptide biphalin. The performed modification is based on the replacement of two key structural elements of the native biphalin, namely: the hydrazine bridge which joins the two palindromic moieties and the phenylalanine residues at the 4,4′ positions of the backbone. The new analogues 9 and 10 contain 1,2-phenylenediamine and piperazine, respectively, in place of the hydrazidic linker and p-fluoro-l-phenylalanine residues at 4 and 4′ positions. Binding values are: K_\texti^m = 0.51 \textnM K_{\text{i}}^{\mu } = 0.51\,{\text{nM}} and K_\texti^d = 12.8 \textnM K_{\text{i}}^{\delta } = 12.8\,{\text{nM}} for compound 9, K_\texti^m = 0.09 \textnM K_{\text{i}}^{\mu } = 0.09\,{\text{nM}} and K_\texti^d = 0.11 \textnM K_{\text{i}}^{\delta } = 0.11\,{\text{nM}} for analogue 10.     

不同原生境的6种棕榈科植物叶片水力性状的对比研究

为揭示生长在湿润生境和季节性干旱生境棕榈科植物的水分生理生态适应的差异,在中国科学院华南植物园中选取3种原分布于湿润生境(SOMH)植物:澳洲轴榈(Licualaramsayi)、槟榔(Arecacatechu)和所罗门皱籽棕(Ptychosperma salomonense),以及3种原分布于季节性干旱生境(SODH)植物:大丝葵(Washingtonia robusta)、澳洲蒲葵(Livistona australis)和大蒲葵(L. saribus),对叶片和叶柄的结构与功能性状进行测定。结果表明,与SODH物种相比,3种SOMH植物的水力加权导管直径(Dh)、理论导水率(Kth)、膨压丧失点(TLP)、脆弱性指数(VI)和比叶面积(SLA)较高,而其叶脉密度(VD)较低。TLP、VI均与Kth呈显著正相关,说明水力效率和水力安全之间存在权衡关系。可见,SOMH棕榈的叶片水力效率高于SODH棕榈,但叶片水力安全低于SODH,这揭示了生长于不同生境棕榈科植物在水分生理生态策略上的差异。     

Effects of nitrate on intracellular nitrite and growth of Microcystis aeruginosa

Although nitrate is a macronutrient and can serve as good nitrogen source for many species of phytoplankton, high nitrate concentrations do not benefit the growth of phytoplankton. We hypothesise that algae cultured under high nitrate concentrations can accumulate intracellular nitrite, which is produced by nitrate reductase (NR) and can inhibit the growth of algae. To assess the validity of this hypothesis, Microcystis aeruginosa was grown under different nitrate concentrations from 3.57 to 21.43 mM in low CO₂ and high CO₂ conditions for 15 days. We observed that, with increasing nitrate concentrations, the intracellular nitrite concentrations of the alga increased and the growth rates and photosynthesis declined. When grown under high CO₂ conditions, M. aeruginosa showed lower intracellular nitrite concentrations and higher growth rates and \textP_\textm^\textchla {\text{P}}_{\text{m}}^{{\text{chl}}a} , \textR_\textd^\textchla {\text{R}}_{\text{d}}^{{\text{chl}}a} , α^chla than under low CO₂ conditions. These results suggest that the accumulation of intracellular nitrite could be the cause of inhibition of algal growth under high nitrate concentrations.     

Susceptibility to photoinhibition in seedlings of six tropical fruit tree species native to Malaysia following transplantation to a degraded land

To investigate the adaptive capacity to a strong light environment when planted on degraded land, we examined photosynthetic properties in relation to photoinhibition for the sun-leaves of six tropical fruit tree species native to Malaysia before and after transplanting. The six species were: Bouea macrophylla (Bm), Callerya atropurpurea (Ca), Canarium pilosum (Cp), Cynometra cauliflora (Cc), Morinda citrifolia (Mc) and Syzygium sp. (Ssp), which produce edible fruit for endemic animals and birds, and are candidates for corridor plantations. Based on the measurements performed before transplanting, the degree of chronic photoinhibition indicated by the decrease in pre-dawn F _v/F _m was well associated with an accumulation of excessive excitation energy in PSII indicated by a decrease in photochemical quenching (qP). Among the species, Ca and Mc showed lower degrees of photoinhibition with higher qP. Higher electron transport rates (ETR) were observed with higher qP whereas there was no significant relationship between regulatory thermal dissipation (indicated by ) and qP. Energy dissipation via electron transport was suggested to be important in keeping qP high and preventing photoinhibition when compared among species. Cc and Bm showed lower ETR and higher susceptibility to photoinhibition before and after transplanting. New Cp and Mc leaves developed after transplanting showed increased area-based leaf nitrogen content (N _area) and stomatal conductance (gs) compared with those before transplanting resulting in higher light-saturated net photosynthetic rates (A _max) and ETR, and contributing to mitigate photoinhibition. In contrast to these species, Ca achieved high A _max with a water conservative manner (indicated by its relatively lower gs), where the higher carboxylation efficiency accompanied with the higher N _area allowed them to maintain relatively high A _max and ETR at lower intercellular CO₂ concentration.     

Photoinhibition of photosynthesis in Minquartia guianensis and Swietenia macrophylla inferred by monitoring the initial fluorescence

We assessed the effect of the exposure to full sunlight (5, 35, and 120 min, i.e. T₅, T₃₅, and T₁₂₀) on fluorescence parameters of two young tropical trees, Swietenia macrophylla, a gap-demanding species, and Minquartia guianensis, a shade tolerant species. Fluorescence parameters (F₀, F_m, F_v/F_m) were recorded before treatments and after the transition to low irradiance (LI). Recovery from photoinhibition (measured as F_v/F_m) was monitored for 24 h at LI. In Swietenia, an almost complete restoration of the F_v/F_m values occurred in T₅ and T₃₅ plants, when a rise in F₀ was observed after the transition to LI. This was inferred as indicative of dynamic photoinhibition. T₁₂₀ led to a decline in F₀ in Minquartia, but not in Swietenia. The plants of both species were unable to recovery from photoinhibition after 24 h at LI, when F₀ declined or remained unchanged. This was interpreted as indicative of chronic photoinhibition. Compared with Swietenia, Minquartia was more susceptible to photoinhibition, as indicated by lower F_v/F_m values.