The effects of carbon dioxide concentration on oxygen evolution and fluorescence transients in synchronous cultures of Chlorella pyrenoidosa

1. 1. The steady-state fluorescence yield of Chlorella pyrenoidosa is strongly affected by CO₂ concentration: the yield is approximately 2-fold higher in the presence than in the absence of CO₂. During induction, in the presence of saturating CO₂, accelerating oxygen evolution is paralleled by rising fluorescence (M₂-P₃ transient); in the absence of CO₂, fluorescence yield remains at the low M₂ level.

2. 2. Both illumination and CO₂ content are important in determining the steady-state fluorescence yield: at lower illuminations, lower concentrations of CO₂ are required to obtain a maximum fluorescence yield.

3. 3. The slow fluorescence transients are not affected directly by pH but only indirectly through the CO₂ concentration.

4. 4. The CO₂-dependent fluorescence rise (M₂-P₃ transient) is most readily observed in cells harvested early in the light period of a synchronous culture, but it can also be elicited in cells harvested during the dark period.

5. 5. Addition of 3-(3,4-dichlorophenyl)-1, 1-dimethylurea (DCMU) to CO₂-deprived cells raises the fluorescence yield approximately 4-fold, that is to the same high level as cells supplied with CO₂ and DCMU.

6. 6. The effects of CO₂ provide a new example of a marked parallelism between photosynthetic electron transport and fluorescence. To explain such parallelism, it seems necessary to postulate large changes in the de-excitation processes within Photosystem II units or in the distribution of excitation between Photosystems I and II.

Inorganic carbon uptake kinetics of the stream macrophyte Callitriche cophocarpa Sendt.

Photosynthetic carbon uptake of Callitriche cophocarpa Sendt. was examined in plants collected from six Danish streams and in plants grown under variable inorganic carbon conditions in the laboratory. Both field and laboratory plants showed a low affinity for inorganic carbon (CO₂ compensation points ranging from 0.7 to 22 μM, and K_0.5(CO₂) from 51 to 121 μM), consistent with C-3 photosynthesis and use of CO₂ alone. Variation in inorganic carbon uptake characteristics was low in both groups of plants. Only in laboratory-grown plants was a coupling found between carbon uptake and the inorganic carbon regime of the medium. The carbon extraction capacity, expressed as a percentage of the initial amount of dissolved inorganic carbon (DIC) assimilated in PH-drift experiments, increased from −1.4 to 11.8% with declining external carbon availability, and the initial slope of the CO₂ response curve increased from 6.4 to 15.3 g⁻¹ h⁻¹ dm³. The plasticity of the inorganic carbon uptake system of C. cophocarpa was very low compared to the plasticity observed for submerged macrophytes with accessory carbon uptake systems (i.e. HCO₃⁻ use or C-4 photosynthesis), suggesting that the plasticity of the C-3 photosynthetic apparatus as such is restricted. The low carbon affinity of C. cophocarpa indicates that this species depends on CO₂ oversaturation for a sufficient supply of CO₂ for photosynthesis and growth.     

Physiological responses of the legume model Medicago truncatula cv. Jemalong to water deficit

In Medicago truncatula Gaertn. cv. Jemalong plants some mechanisms involved in drought resistance were analysed in response to a progressive water deficit imposed by suppression of soil irrigation. Withholding water supply until the soil had reached one-half of its maximum water content had no significant effect on leaf RWC, gas exchanges or chlorophyll fluorescence parameters. Under severe drought conditions, the plants resistance to water shortage involved mainly drought avoidance mechanisms through a decrease in stomatal conductance. The consequent decrease in the internal CO₂ concentration (C_i) should have limited the net CO₂ fixation (A). Since A decreased slightly more than C_i under severe water deficit, non-stomatal limitations of photosynthesis may have also occurred. Analysis of A/C_i curves showed reduced carboxylation efficiency due to limitations in RuBP regeneration and Rubisco activity, confirming the presence of non-stomatal limitations of photosynthesis. Drought tolerance mechanisms involving osmotic adjustment and an increase in cell membrane integrity were also present. Altogether, these mechanisms allowed M. truncatula cv. Jemalong plants to still maintain a quite elevated level of net CO₂ fixation rate under severe water deficit conditions. These results may contribute to identify useful physiological traits for breeding programs concerning drought adaptation in legumes.     

A high-activity ATP translocator in mesophyll chloroplasts of Digitaria sanguinalis, a plant having the C-4 dicarboxylic acid pathway of photosynthesis

The effect of exogenous adenine nucleotides on CO₂ fixation and oxygen evolution was studied with mesophyll protoplast extracts of the C₄ plant Digitaria sanguinalis. Exogenous ATP was found to stimulate the rate of pyruvate and pyruvate + oxalacetate induced CO₂ fixation, as well as reverse the inhibition of CO₂ fixation by carbonyl cyanide m-chlorophenyl hydrazone and several electron transport inhibitors. The ATP-dependent stimulation of CO₂ fixation varied from 40 to 70 μmol CO₂ fixed/mg chlorophyll per h, suggesting that ATP was crossing the chloroplast membranes at rates of 80–140 μmol/mg chlorophyll per h, since 2 ATP are required for each CO₂ fixed. Fixation of CO₂ could also be induced in the dark by exogenous ATP, in which case ADP accumulated outside the chloroplasts. This suggests that external ATP is exchanging for internal ADP. In contrast, ADP and AMP were found not to traverse chloroplast membranes, on the basis that neither nucleotide inhibited CO₂ fixation or stimulated oxygen evolution that was limited by available ADP for phosphorylation. Further evidence that ATP can enter the chloroplasts was obtained by direct measurements of the increase in ATP in the chloroplasts due to addition of exogenous ATP in the dark. These studies yielded minimal rates of ATP uptake on the order of 30–40 μmol/mg chlorophyll per h. It is suggested that a membrane translocator exists that specifically transports ATP into the chloroplasts in exchange for ADP. The significance of these findings are considered with respect to the C₄ pathway of photosynthesis.     

The high-energy state of the thylakoid system as indicated by chlorophyll fluorescence and chloroplast shrinkage

Certain long-term fluorescence phenomena observed in intact leaves of higher plants and in isolated chloroplasts show a reverse relationship to light-induced absorbance changes at 535 nm (“chloroplast shrinkage”).

1. 1. In isolated chloroplasts with intact envelopes strong fluorescence quenching upon prolonged illumination with red light is accompanied by an absorbance increase. Both effects are reversed by uncoupling with cyclohexylammonium chloride.

2. 2. The fluorescence quenching is reversed in the dark with kinetics very similar to those of the dark decay of chloroplast shrinkage.

3. 3. In intact leaves under strong illumination with red light in CO₂-free air a low level of variable fluorescence and a strong shrinkage response are observed. Carbon dioxide was found to increase fluorescence and to inhibit shrinkage.

4. 4. Under nitrogen, CO₂ caused fluorescence quenching and shrinkage increase at low concentrations. At higher CO₂ levels fluorescence was increased and shrinkage decreased.

5. 5. In the presence of CO₂, the steady-state yield of fluorescence was lower under nitrogen than under air, whereas chloroplast shrinkage was stimulated in nitrogen and suppressed in air.

6. 6. These results demonstrate that the fluorescence yield does not only depend on the redox state of the quencher Q, but to a large degree also on the high-energy state of the thylakoid system associated with photophosphorylation.

Leaf gas exchange, chlorophyll fluorescence and growth responses of Genipa americana seedlings to soil flooding

Effects of soil flooding on photosynthesis and growth of Genipa americana L. seedlings, a neotropical fruit-tree species used in gallery forest restoration programs, were studied under glasshouse conditions. Despite the high survival rate and wide distribution in flood-prone habitats of the neotropics, previous studies demonstrated that growth of G. americana is reduced under soil flooding. Using leaf gas exchange and chlorophyll fluorescence measurements, we tested the hypothesis that stomatal limitation of photosynthesis is the main factor that reduces carbon uptake and growth rates of G. americana seedlings. Throughout a 63-day flooding period, the survival rates were 100%. The maximum values of the net photosynthetic rate (A) and stomatal conductance to water vapor (g_s) of control seedlings were 9.86 μmol CO₂ m⁻² s⁻¹ and 0.525 mol H₂O m⁻² s⁻¹, respectively. The earliest effects of flooding were significant decreases in g_s and A, development of hypertrophied lenticels and decrease in the dry weight of roots. A strong effect of the leaf-to-air vapor pressure deficit (LAVPD) on g_s and A were observed that was enhanced under flooded conditions. Between 14 and 63 days after flooding, significant reductions in g_s (31.7% of control) and A (52.9% of control) were observed followed by significant increments in non-photochemical quenching (q_N) (187.5% of control). During the same period, there were no differences among treatments for the ratio between variable to initial fluorescence (F_v/F₀), the maximum quantum efficiency of the photosystem II (F_v/F_m) and photochemical quenching (q_P), indicating that there was no damage to the photosynthetic apparatus. Based on the results, we conclude that decreases in stomatal opening and stomatal limitation of photosynthesis, followed by decrease in individual leaf area are the main causes of reductions in carbon uptake and whole plant biomass of flooded seedlings.     

Cell wall glycanases and their activity against the hemicelluloses from pine hypocotyls

O₂ evolution and chlorophyll a fluorescence emission have been monitored in intact cells of the cyanobacterium Anacystic nidulans 1402–1 to stdy the influence of carbon and nitrogen assimilation on the operation of the photosynthetic apparatus. The pattern of fluorescence induction in dark-adapted cyanobacterial cells was different from that of higher plants. Cyanobacteria undergo large, rapid state transitions upon illumination, which lead to marked changes in the fluorescence yield, complicating the estimation of quenching coefficients. The Kautsky effect was not evident, although it could be masked by a state II–state I transition, upon illumination with actinic light. The use of inhibitors of carbon assimilation such as D,L-glyceraldehyde or iodoacetamide allowed us to relate changes in variable fluorescence to active CO₂ fixation. Ammonium, but not nitrate, induced non-photochemical fluorescence quenching, in agreement with a previous report on green algae, indicative of an ammonium-induced state I transition.     

Sites of function of manganese within photosystem II. Roles in O2 evolution and system II

The Mn content of spinach chloroplasts has been decreased by growth deficiency, extraction and by ageing at 35°. We studied the effect of subnormal Mn content upon the chloroplasts capacity to evolve O₂ and to photooxidize electron donors other than water via Photosystem II. We observed the following:

1. 1. In fresh chloroplasts ascorbate and other reducing agents, if present in sufficient concentration, fully replace water as the System II oxidant and can sustain maximum rates of 1000–1200 equiv/chlorophyll per h.

2. 2. None of the studied donors proved entirely specific for System II; to a variable extent all could react with the oxidant of System I. We therefore considered only the 3-(3,4-dichlorophenyl)-1,1-dimethylurea-(DCMU)-sensitive fraction of the observed rates as pertinent.

3. 3. Normal fresh chloroplasts contained 3 Mn/200 chlorophylls_II and showed flash yields of approx. 1 O₂/1600 chlorophylls. This indicates that each System II trapping and O₂-evolving center contains three Mn atoms.

4. 4. O₂ evolution capacity is abolished when about 2/3 of the total Mn pool is removed by way of Tris or hydroxylamine extraction, i.e. upon removal of two of the three Mn atoms normally present per reaction center. Between the limits of 1 Mn per trap and 3 Mn per trap O₂ evolution capacity is linear with Mn content.

5. 5. Mn removal affects the rates of O₂ evolution in strong light and in weak light (quantum yield) in the same fashion. This indicates that complete O₂ reaction centers are inactivated.

6. 6. With Mn removal the capacity for donor (ascorbate or p-phenylenediamine) photooxidation in strong light declines in a very similar fashion as the O₂ evolving capacity. However, after removal of 2/3 of the Mn pool (by Tris or hydroxylamine extraction) 15–20% of the maximum rate remains (100–250 equiv/chlorophyll per h) as previously noticed by other workers. Secondly, the rate in weak light (quantum yield) of these photooxidations remains unaffected by Mn removal. This shows that for donor photooxidation the larger of the two Mn pools is not essential.

7. 7. Complete removal of Mn (< 1 Mn/4000 chlorophylls) led to 90–95% loss of donor photooxidation in strong light.

8. 8. Removal of 2/3 of the Mn left a low fluorescence yield (variable fraction = 0) which could be fully restored by adding DCMU. After complete removal of Mn (< 1 Mn/4000 chlorophylls) DCMU enhanced the yield of the variable fluorescence to only 1/2 the maximum level but the full maximum could be restored by chemical reduction. This indicates that fluorescence quencher of System II, Q, is not affected by Mn removal.

9. 9. Of the three Mn associated with each trapping center, one is linked more closely to the center than the other two. While all three are essential for O₂ evolution, artificial donors can enter with various rate constants at several loci on the oxidant side of System II.

Dark reduction of QA in intact barley leaves as an effect of lowered CO2 concentration monitored by chlorophyll a luminescence and chlorophyll a F0 dark fluorescence

When the CO₂ concentration in the atmosphere above an intact barley leaf was lowered in the dark after illumination, chlorophyll a luminescence and chlorophyll a dark fluorescence were stimulated. The stimulation was induced by lowered levels of CO₂ in a wide concentration range including concentrations well above that saturating photosynthesis. The stimulation of luminescence by lowered CO₂ concentrations was more pronounced after far-red excitation than after white light excitation. The difference in response to lowered CO₂ concentrations after white/far-red excitation was less pronounced for fluorescence than for luminescence. Stimulation of luminescence was more pronounced when the CO₂ concentration was lowered in an O₂-containing atmosphere than under anaerobic conditions. It is concluded that lowering of the CO₂ concentration in the dark after illumination causes a partial reduction of the primary Photosystem II acceptor Q_A.     

Activation of CO2 fixation in isolated spinach chloroplasts

1. 1. The effect of the Mg²⁺ concentration on the CO₂ fixation activity in situ in isolated and intact spinach chloroplasts upon suspension in hypotonic medium was examined. CO₂ fixation in the dark was activated 25–100 fold by 20 mM Mg²⁺ in the presence of added ATP plus either ribulose 5-phosphate or ribose 5-phosphate. 20 mM Mg²⁺-stimulated fixation only 2–3 fold in the presence of the substrate of fixation, ribulose 1,5-diphosphate. The highest Mg²⁺-stimulated rate of fixation in the dark observed with chloroplasts was 480 μmoles CO₂ fixed per mg chlorophyll per h.

2. 2. The concentration of bicarbonate at half of the maximal velocity (apparent K_m) during the Mg²⁺-stimulated fixation of CO₂ was 0.4 mM in the presence of ATP plus ribose 5-phosphate and 0.6 mM with ribulose 1,5-diphosphate.

3. 3. Dithioerythritol or light enhanced Mg²⁺-stimulated CO₂ fixation 1–3 fold in the presence of ATP plus ribose 5-phosphate but not ribulose 1,5-diphosphate.

4. 4. These results indicate that Mg²⁺ fluxes in the stroma of the chloroplast could control the activity of the phosphoribulokinase with a lesser effect on the ribulosediphosphate carboxylase. An increase in Mg²⁺ of 6–10 mM in the stroma region of the chloroplast would be enough to activate CO₂ fixation during photosynthesis.

Photosynthetic Nitrite Reduction as Influenced by the Internal Inorganic Carbon Pool in Air-Grown Cells of Synechococcus UTEX 625

Photosynthetic reduction of NO2- was studied in air-grown cells of a cyanobacterium, Synechococcus UTEX 625. Addition of NO2- resulted in significant amounts of chlorophyll a fluorescence quenching both in the absence and presence of CO2, fixation inhibitors, glycolaldehyde or iodoacetamide. The degree of NO2- quenching was insensitive to the O2 concentration in the medium. Addition of 100 [mu]M inorganic carbon in the presence of glycolaldehyde and O2, leading to formation of the carbon pool within the cells, resulted in pronounced fluorescence quenching. Removal of O2 from the medium restored the fluorescence yield completely, and the subsequent addition of NO2- quenched 36% of the variable fluorescence. From the response to added 3-(3,4-dichlorophenyl)-1,1-dimethylurea, the quenching by NO2- appeared to be photochemical quenching, and nonphotochemical quenching did not seem to be present. The reduction of NO2- observed on its addition to inorganic carbon-depleted cells remained uninfluenced by O2 or glycolaldehyde. The internal inorganic carbon pool in the cells stimulated NO2- reduction, both in the presence and absence of O2, by 4.8-fold. An increase in NO2- reduction by 0.5-fold was also observed in the presence of O2 during simultaneous assimilation of carbon and nitrogen in inorganic carbon-depleted cells. Contrary to this, under anaerobiosis, NO2- reduction was suppressed when carbon and nitrogen assimilation occurred together.     

铅污染对烤烟光合特性、产量及其品质的影响

为研究土壤中Pb污染对烤烟(Nicotiana tabacum)叶片光合特性、烟叶品质及其产量的影响,对烤烟主栽品种‘云烟85’进行了盆栽条件下的Pb污染实验,实验浓度为0、150、300、450、600、750和1 000 mg·kg^-1(以纯Pb²⁺计),分别于团棵期、现蕾期和采收期测定叶片光合特性的变化,并在采收期测定烟叶产量和烤后烟叶的品质变化。结果表明:在3个生育时期,Pb污染下供试烤烟品种叶片净光合速率(P_n)和气孔导度(G_s)均随Pb浓度的升高而下降,而胞间CO₂浓度(C_i)随Pb浓度的升高先增加后下降;PSⅡ活性(F_v/F_o)、最大光能转换效率(F_v/F_m)、光化学猝灭系数(q_P)、非光化学猝灭系数(NPQ)、电子传递的量子产率(Ф_PSⅡ)、表观电子传递速率(ETR)和烟叶产量均随Pb浓度的升高而下降,不利于烟叶充分地利用捕光色素所吸收的光能,降低其光能利用效率,从而降低了光合速率;烤烟烟叶品质指标糖/碱比和氮/碱比升高,糖/碱比和氮/碱比分别为9.52~11.96和1.05~1.23,分别大于7(优质烟叶标准)和1(优质烟叶标准),不利于烟叶香吃味的形成。     

Cadmium effect on the growth, photosynthesis, ultrastructure and phytochelatin content of green microalga Scenedesmus armatus: A study at low and elevated CO2 concentration

Short-term experiments were carried out to examine the toxicity of cadmium chloride (CdCl₂) at a concentration of 93 μM (EC_50/24) to green microalga Scenedesmus armatus, cultured at low (0.1%) and elevated (2%) concentration of CO₂. Cadmium did not affect the viability of cells cultured for 24 h in both CO₂ variants but markedly inhibited the growth of algae. This inhibition was more pronounced in cultures aerated with 0.1% (about 50% of control) than with 2% CO₂ (about 75% of control) and did not change during 72 h of culture. Cadmium inhibited the rate of oxygen evolution (P_oxy.) (70% of control) of cells cultured at 0.1% CO₂ and had no effect on P_oxy. of cells cultured at 2% CO₂. The values of the chlorophyll fluorescence parameters, i.e. F_M (maximum fluorescence yield), F_V (variable fluorescence), F_V/F_M (maximum quantum yield of PSII), Φ_PSII (effective quantum yield of PSII) and qP (photochemical quenching) were reduced by cadmium treatment in algae grown at 0.1% CO₂ concentration, whereas F₀ (initial fluorescence yield) remained unaffected. In high-CO₂ grown cells only F_V was significantly reduced. Cd-treated cells synthesized several thiol-containing peptides identified by HPLC as a dimer (PC₂), a trimer (PC₃) and a tetramer (PC₄) of phytochelatins (PC_S). High-CO₂ grown cells produced significantly more PCs than low-CO₂ grown cells and their individual appearance depended on the time of exposure and CO₂ level. The ultrastructural analysis of low-CO₂ grown cells showed in chloroplasts an increased number of small starch grains visible around the pyrenoid. In the enhanced vacuome compartment, various types of vacuoles were clearly seen in Cd-treated cells. Vacuoles containing non-membranous, electron-opaque deposits of an undefined structure and myelin-like figures were especially observed. The results suggest that algae living in conditions of elevated CO₂ are better protected against cadmium than those at ordinary CO₂ level, and productive processes are less affected than the growth ones.     

Oxygen photoreduction and variable fluorescence during a dark-to-light transition in Chlorella pyrenoidosa

When dark-adapted (5 min in the dark) Chlorella cells were deposited on a bare platinum electrode, treated with DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea) and illuminated, O₂ was consumed after a lag time of about 250 ms. The comparison of the O₂ consumption kinetics with the fluorescence O-I-D-P-S transition (the fast change in chlorophyll fluorescence which occurs after the onset of illumination of dark-adapted algae and is over within 2 s) observed in untreated algae indicates that no O₂ is consumed during the fluorescence rise and that O₂ uptake is initiated approximately when the maximum level of fluorescence P is reached. Mass spectrometry measurements of O₂ exchange (using ¹⁸O₂) were performed during dark to light transition with DCMU-untreated Chlorella cells. Under these conditions, O₂ reduction began after a lag time (about 200–400 ms) and stopped after about 5 s of illumination. The above experiments clearly show that the reduction of O₂ starts nearly at the same time that the fluorescence P-S decline. On the other hand, we show that the reduction of CO₂ does not interfere in the fluorescence O-I-D-P-S transient. We found the same apparent affinity for O₂ (about 57 μM) for both the fluorescence P-S decline and the reduction of O₂. At least three consecutive short (2 μs) saturating flashes were required to affect the fluorescence transient significantly and also to induce a significant uptake of O₂. Moreover, parabenzoquinone, an artificial Photosystem I electron acceptor, inhibited both the fluorescence D-P rise and the 250 ms lag time observed in the reduction of O₂. We conclude from the above results that in the early stages of the illumination of dark-adapted algae, some Photosystem I electron acceptors are in an inactive form. In this form, the electron transport chain is unable to reduce either O₂ or CO₂. This would lead to the accumulation of electrons on the Photosystem II acceptors (principally Q⁻_A and the plastoquinone pool) and therefore explains the fluorescence D-P rise. The light activation, probably achieved through the reduction of at least two electron acceptors, first allows the reduction of O₂, and therefore explains the P-S fluorescence decline. By accepting electrons before the site of regulation and mediating rapid O₂ reduction, parabenzoquinone avoids the accumulation of electrons and therefore inhibits the D-P fluorescence rise.     

施氮和大气CO2浓度升高对小麦旗叶光合电子传递和分配的影响

采用开顶式气室盆栽培养小麦,设计2个大气CO₂浓度（正常：400 μmol·mol^-1;高：760 μmol·mol^-1）、2个氮素水平（0和200 mg·kg^-1土）的组合处理,通过测定小麦抽穗期旗叶氮素和叶绿素浓度、光合速率（P_n）-胞间CO₂浓度（C_i）响应曲线及荧光动力学参数,来测算小麦叶片光合电子传递速率等,研究了高大气CO₂浓度下施氮对小麦旗叶光合能量分配的影响.结果表明：与正常大气CO₂浓度相比,高大气CO₂浓度下小麦叶片氮浓度和叶绿素浓度降低,高氮处理的小麦叶片叶绿素a/b升高.施氮后小麦叶片PSⅡ最大光化学效率（F_v/F_m）、PSⅡ反应中心最大量子产额（F_v′/F_m′）、PSⅡ反应中心的开放比例（q_p）和PSⅡ反应中心实际光化学效率（Φ_PSⅡ）在大气CO₂浓度升高后无明显变化,虽然叶片非光化学猝灭系数（NPQ）显著降低,但PSⅡ总电子传递速率（J_F）无明显增加;不施氮处理的F_v′/F_m′、Φ_PSⅡ和NPQ在高大气CO₂浓度下显著降低,尽管F_v/F_m和q_P无明显变化,J_F仍显著下降.施氮后小麦叶片J_F增加,参与光化学反应的非环式电子流传递速率(J_C)明显升高.大气CO₂浓度升高使参与光呼吸的非环式电子流传递速率(J₀)、Rubisco氧化速率（V₀）、光合电子的光呼吸/光化学传递速率比（J₀/J_C）和Rubisco氧化/羧化比（V₀/V_C）降低,但使J_C和Rubisco羧化速率（V_C）增加.因此,高大气CO₂浓度下小麦叶片氮浓度和叶绿素浓度降低,而增施氮素使通过PSⅡ反应中心的电子流速率显著增加,促进了光合电子流向光化学方向的传递,使更多的电子进入Rubisco羧化过程,P_n显著升高.     

空气CO2增高条件下荔枝叶片光合作用和超氧自由基产率

研究结果表明,生长在77±5PaCO₂分压下30d的荔枝幼树,其光合速率较大气CO₂分压(39.3Pa)下的低23%,光下线粒体呼吸速率和不包含光下呼吸的CO₂补偿点亦略有降低.空气CO₂增高使叶片最大羧化速率(V_cmax)和最大电子传递速率(J_max)降低,表明大气增高CO₂分压下叶片的光系统I(PSI)能量水平较低,叶片超氧自由基产率亦降低39%,叶片感染荔枝霜疫霉病率则从生长在大气CO₂分压下的1.8%增至9.5%.可能较低光合和呼吸代谢诱致较低的超氧自由基产率,而使叶片易受病害侵染.叶片受病害侵染后表现为超氧自由基的激增.在全球大气CO₂分压增高趋势下须加强对荔枝霜疫霉病的控制.     

减氮运筹对甘薯光合作用和叶绿素荧光特性的影响

光合性能是决定作物产量形成的关键,氮肥的合理施用是调控作物光合特性和产量形成的重要措施.于2016—2017年开展盆栽试验,研究了减氮和施肥方式对甘薯叶片光合作用和叶绿素荧光特性的影响.试验以常规习惯基施氮肥100 kg·hm^-2为对照(FP),在常规施氮量的基础上减氮20%,同时设置3种氮肥运筹方式:100%基施(JS)、100%移栽后35 d追施(KS)、50%基施+50%移栽后35 d追施(FS).结果表明:与常规基施氮肥100 kg·hm^-2相比,减氮条件下氮肥全部基施显著降低了全生育期甘薯光合性能,但追施处理显著提高了块根膨大期净光合速率(P_n)、气孔导度(g_s)、胞间CO₂浓度(C_i)和叶绿素(Chl a+b)含量.不同处理下,P_n、g_s、C_i和Chl a+b均以50%基施+50%追施处理最高.减氮分施处理甘薯块根膨大期的PSⅡ实际光化学效率(Φ_PSⅡ)、光化学淬灭系数(q_P)、PSⅡ最大光化学效率(F_v/F_m)和PSⅡ潜在活性(F_v/F_o) 提高,而初始荧光(F_o)和非光化学淬灭系数(NPQ)则降低.氮肥分施通过提高PSⅡ的光化学效率和电子传递速率,降低光能的热耗散,提高了甘薯块根膨大期功能叶的光合速率.2个品种不同年际间表现相同.表明氮肥一次性基施或追施均不利于提高甘薯叶片光合性能.减氮20%水平下,50%基施+50%追施可减缓叶片早衰,延长叶片功能期,提高甘薯的光合生产能力和生物量,有利于产量形成.     

不同光照强度下谢君魔芋的光合作用及能量分配特征

为了探讨喜阴植物谢君魔芋(Amorphophallus xiei)对不同光强的适应策略,测量和分析了不同透光率(高光,透光率100%;中光,透光率32.6%;低光,透光率5.98%)下谢君魔芋对光、CO₂、光斑的响应特征及响应过程中叶绿素a荧光和能量分配特征.结果表明: 随着生长光强的增大,谢君魔芋最大净光合速率(P_max)、暗呼吸速率、表观量子产额、羧化效率显著降低,光补偿点、CO₂补偿点显著升高.中光处理的谢君魔芋对光合诱导的响应更迅速(P<0.05);随着生长光强的增加,暗适应初始气孔导度(g_s-i)显著升高;完成光合诱导中最大净光合速率30%(t_30%P)、50%(t_50%P)和90%(t_90%P)所需的时间与g_s-i呈负相关.高光处理的植株PSⅡ实际光化学效率(ΔF/F_m′)、光化学猝灭(q_P)和电子传递速率(ETR)较高,且在光合诱导过程中所对应的非光化学猝灭(NPQ)值相对较高,而低光处理具有较高的反应中心激发能捕获效率(F_v′/F_m′).高光处理非光化学耗散途径比例(Ф_NPQ)较低,而低光处理Ф_NPQ则相对较高.表明喜阴植物谢君魔芋在中低光下生长时受到高光胁迫能够启动快速耗散机制来保护自身光合机构,长期处于高光环境则采用增加热耗散成本和形成淬灭复合物的策略在一定程度上应对高光胁迫,这可能是其不能很好适应高光环境的原因之一.     

γ-氨基丁酸（GABA）对低氧胁迫下甜瓜幼苗光合作用和叶绿素荧光参数的影响

采用营养液水培方法,研究了低氧胁迫下外源γ-氨基丁酸（GABA）对甜瓜幼苗光合色素含量、光合作用及叶绿素荧光参数的影响.结果表明：低氧胁迫导致甜瓜幼苗光合色素含量显著下降,光合作用降低;外源GABA能显著提高正常通气和低氧胁迫下甜瓜幼苗的光合色素含量、净光合速率、气孔导度、胞间CO₂浓度、CO₂羧化效率、最大光化学效率、光化学猝灭系数、表观光合电子传递速率和PSⅡ光合电子传递量子效率,而气孔限制值、初始荧光和非光化学猝灭系数显著降低,GABA在低氧胁迫下的提高效果更明显;同时添加GABA和GABA转氨酶抑制剂γ-乙烯基-γ-氨基丁酸（VGB）处理显著降低了低氧胁迫下GABA对甜瓜幼苗光合特性的缓解效果.     

Chlorophyll a Fluorescence Yield as a Monitor of Both Active CO(2) and HCO(3) Transport by the Cyanobacterium Synechococcus UTEX 625

Simultaneous measurements have been made of inorganic carbon accumulation (by mass spectrometry) and chlorophyll a fluorescence yield of the cyanobacterium Synechococcus UTEX 625. The accumulation of inorganic carbon by the cells was accompanied by a substantial quenching of chlorophyll a fluorescence. The quenching occurred even when CO₂ fixation was inhibited by iodoacetamide and whether the accumulation of inorganic carbon resulted from either active CO₂ or HCO₃⁻ transport. Measurement of chlorophyll a fluorescence yield of cyanobacteria may prove to be a rapid and convenient means of screening for mutants of inorganic carbon accumulation.