两种杂交杨叶绿素荧光特性及光能利用

比较研究了伊犁地区两种杂交杨伊犁杨1号(Populus deltaids‘cv-64’ (P64))和伊犁杨小叶杨(P. simonii canaden×P. russkii-9(Jia))对太阳辐射光能的利用和耗散特性。两种杂交杨光合速率(P_n)的日变化均呈现双峰型, 高光量子通量密度(PFD)阶段P_n达到20.1%的差距; 实际最大光化学猝灭ΦPSII日变化均呈“U”型, 于16:30时, P64的ΦPSII达到最低值, 而Jia的值于14:30时达到最低(Jia>P64); 光合系统的闭合程度(L)在14:30时均出现一个短暂回落, 全天平均闭合程度无显著差异(p>0.05)。非光化学猝灭系数(NPQ)在16:30同时达到最大值(Jia>P64), 两者NPQ全天相差31.7%。叶片转化吸收太阳能热能耗散(E.D)和光化学反应转化的光能量(E.P)进行估算表明: 在PFD较低的环境条件下, 两种杂交杨将吸收的光能50%以上用于光化学猝灭; 在PFD较高的环境条件下, P64的E.P值比例大于Jia, 两者全天的E.P值没有太大的差异, P64的E.D值显著大于Jia的E.D值(p>0.01), 而P64的E.D值占全天转化能量的比例小于Jia。P64和Jia的E.P达到最大的估算值时, 其E.D也达到了最大。分析结果表明: 两种杂交杨对高光能形成不同的适应机制, P64利用更多的太阳能进行光化学猝灭反应, 而Jia利用更多的太阳能进行非光化学猝灭反应, 减缓强太阳辐射伤害; 两种杂交杨用于光化学能量分配的比例P64大于Jia, 而P_n值在强辐射阶段和全天平均值、累积值均出现Jia>P64。结果证明, 仅通过杂交杨本身叶绿体对光的荧光特性反应计算接收到的光能中有多少能量被利用与实际植物光合速率的转化的干物质存在一定的差异, 两种杂交杨光化学实际固定碳和转化光能的多少的内在关系需进一步的研究。     

4种木本植物叶片的光合电子传递和吸收光能分配特性对光强的适应

以气体交换和叶绿素荧光测定相结合的方法研究了亚热带自然林乔木荷树、黧蒴和林下灌木九节、罗伞幼苗的光合电子传递及激发能利用的分配对生长光强的适应特性。4种植物生长于100%、36%和16%的自然光下8个月,叶片的光化学速率和热能耗散速率随光强增大而提高,热能耗散占总的光能吸收的比例也因光强不同而改变,16%光下的相对热耗散率约为40%～45%,100%自然光下增大至50%～75%。叶片总的非环式电子流速率及其分配到光呼吸的比例在100%光强下最高。乔木和灌木的电子传递和光能分配特性在16%光下相似,在100%光下差别较明显。除灌木种有较高的热耗散比例之外,其余的参数皆比乔木的低。结果表明乔木与灌木皆可通过提高激发能热耗散比例和提高光合电子传递向光呼吸的比例来适应于高光强条件。     

Recombination in an isochromosome preferentially occurs between cis isochromatids

An isochromosome has identical arms attached to the same centromere. At the pachytene stage of meiosis, it has four isochromatids and recombination can occur either between cis isochromatids (attached to the same half-centromere) or trans isochromatids (attached to different half-centromeres). Normally such recombination cannot be detected because all four chromatids are homogenetic (arose from misdivision of a centromere to which genetically identical sister chromatids were attached). We isolated an isochromosome of wheat that is heterogenetic for the distal 64% of the long arm. The heterogenetic isochromosome was recovered from the progeny of a cross between Triticum aestivum cv. Chinese Spring containing an isochromosome for the long arm of chromosome 5B (i5BL) and a disomic substitution line of Triticum turgidum ssp. dicoccoides chromosome 5B in Chinese Spring wheat. New recombinants were produced when the two arms of i5BLrec paired at metaphase I of meiosis. Only trans isochromatid exchanges led to some homozygous loci in i5BLrec, whereas exchanges between cis isochromatids resulted in heterozygosity at all loci similar to the parental type. There was an average frequency of 0.87 chiasmata per pollen mother cell for the heterogenetic i5BL, which will result in 0.44 cis and 0.44 trans isochromatid exchanges, assuming that both are occurring at the same frequency. The average crossover frequency based on recombination between trans isochromatid exchange detected by restriction fragment length polymorphism analysis in 98 plants was 0.29. This observed value is significantly lower (P<0.01) than the value of 0.44 as expected from chiasmata counts. Our study provides the first experimental evidence that crossovers preferentially occur between cis isochromatids rather than trans isochromatids.     

Diets of giants: the nutritional value of sauropod diet during the Mesozoic

A major uncertainty in estimating energy budgets and population densities of extinct animals is the carrying capacity of their ecosystems, constrained by net primary productivity (NPP) and its digestible energy content. The hypothesis that increases in NPP due to elevated atmospheric CO₂ contributed to the unparalleled size of the sauropods has recently been rejected, based on modern studies on herbivorous insects that imply a general, negative correlation of diet quality and increasing CO₂. However, the nutritional value of plants grown under elevated CO₂ levels might be very different for vertebrate megaherbivores than for insects. Here we show plant species‐specific responses in metabolizable energy and nitrogen content, equivalent to a two‐fold variation in daily food intake estimates for a typical sauropod, for dinosaur food plant analogues grown under CO₂ concentrations spanning estimates for Mesozoic atmospheric concentrations. Our results potentially rebut the hypothesis that constraints on sauropod diet quality were driven by Mesozoic CO₂ concentration.     

On the Possibilities of Averaging the Seasonal Pattern in Kjeldahl Nitrogen in a Group of Water Bodies

It is shown that the seasonal change of Kjeldahl nitrogen in several ponds and several years shows an average seasonal change which is statistically significant on a month-to-month basis although not apparent at first sight. The relative deviation of Kjeldahl nitrogen values in individual months and individual ponds from seasonal averages of individual ponds is closer to lognormal than to normal distribution. The seasonal curve based on average values of relative deviations in individual months and ponds from the seasonal averages of individual ponds shows the lowest variation of average monthly values and is therefore most adequate to a comparison of the seasonal pattern of two or more groups of water bodies.     

慈竹无性系种群能值特点及其影响能值计测因素的研究

 本文引用Harper(1977)的构件结构理论,从构件结构单位、无性系分株和无性系三个层次,对四川南充市郊慈竹无性系种群的能值特点及其影响能值的计测因素进行了定量研究。研究结果表明：慈竹无性系种群中,各构件单位的去灰分热值(AFCV)分别为：根15349.42J／g、根茎16372.92J／g、秆17106.06J／g、枝18111.99J／g和叶19451.90J／g;慈竹无性系分株的AFCV(J／g)随龄级增大而递增;慈竹无性系水平上的AFCV为：Ⅰ龄占16.47%、Ⅱ龄占25.76%、Ⅲ龄占36.32%、Ⅳ龄为13.08%及Ⅴ龄为8.37%。用恒容燃烧法测定热值时,其能值变化与氧分压密切相关。用经验公式计算的能值较作图法高;用AFCV表示能值较总干重热值(GCV)准确。     

饵料蛋白质水平对德国小蠊营养效应及氮代谢的影响

【目的】本研究旨在探究饵料蛋白质水平对德国小蠊Blattella germanica营养利用及氮代谢的影响,为蟑螂毒饵的研发提供新思路。【方法】采用标准重量分析法评估了取食4种不同蛋白质水平(5%, 25%, 45%和65%)饵料的德国小蠊雄成虫营养效率指数和氮利用率;利用分光光度法测定了取食不同蛋白水平饵料的德国小蠊雄成虫体内黄嘌呤氧化酶(xanthine oxidase, XOD)、谷草转氨酶(glutamic oxaloacetic transaminase, GOT)、谷丙转氨酶(glutamic pyruvic transaminase, GPT)活性及尿酸含量。【结果】取食65%蛋白质饵料组的德国小蠊雄成虫的相对取食量最高,而取食45%蛋白质饵料组的雄成虫食物利用率、食物转化率及相对生长率均显著高于取食5%和65%蛋白质饵料组的雄成虫。且德国小蠊雄成虫体内氮、粪便氮、氮消耗速率、氮排泄率、氮生成率、氮同化效率、黄嘌呤氧化酶活性和尿酸含量均随饵料蛋白质水平的提高而提高,但65%蛋白质饵料组氮利用率最低,45%蛋白质饵料组谷草转氨酶活性最高,25%和45%蛋白质饵料组谷丙转氨酶活性显著高于5%和65%蛋白质饵料组。【结论】适量蛋白质饵料有利于德国小蠊对食物及氮的利用,而高蛋白质含量条件下德国小蠊谷草转氨酶和谷丙转氨酶活性下降,说明高蛋白不利于德国小蠊利用食物,且增加其代谢负担。     

Studies on the interaction of the food colorant tartrazine with double stranded deoxyribonucleic acid

Interaction of the food additive tartrazine with double-stranded DNA was studied by spectroscopic and calorimetric techniques. Absorbance studies revealed that tartrazine exhibited hypochromism in the presence of DNA without any bathochromic effects. Minor groove displacement assay of DAPI and Hoechst 33258 suggested that tartrazine binds in the minor groove of DNA. The complexation was predominantly entropy driven with a smaller but favorable enthalpic contribution to the standard molar Gibbs energy. The equilibrium constant was evaluated to be (3.68?±?.08)?×?10⁴?M^?1 at 298.15?K. The negative standard molar heat capacity value along with an enthalpy–entropy compensation phenomenon proposed the involvement of dominant hydrophobic forces in the binding process. Tartrazine enhanced the thermal stability of DNA by 7.53?K under saturation conditions.     

Autumnal mixing in Mahoney Lake,British Columbia

Salinity, water temperature and meteorlogical measurements were made over a 5 month period (June–Oct.) at Mahoney Lake, British Columbia to study autumnal mixing. The measurements were made during a time when the lake had been well stratified by a much larger than average runoff the previous spring. The potential energy of stratification decreased from 50 to 24 MJ, in the top 8 m of the water column, from mid August to mid October. Analysis of the energy available from wind shear on the water surface and from penetrative convection during the autumn cooling period was made. Winds were found to be weak (av. 2.17 m s ^–1) at Mahoney Lake, and their average contribution to mixing energy during the study period was less than 30%. Penetrative convection from thermals descending from the cool surface contributed an average of 2.21 J m^–2 d^–1 to mixing which represented 72 % of the energy available. An efficiency factor of 0.20 for the penetrative convection energy, larger than values previously reported in the literature, was found to fit the measured loss of potential energy of stratification during the period.     

The primary structure of Bacillus cereus neutral proteinase and comparison with thermolysin and Bacillus subtilis neutral proteinase

The complete amino-acid sequence of a neutral proteinase, produced by Bacillus cereus, was determined by protein sequencing. The neutral proteinase consists of 317 amino-acid residues. The primary structure is 70% homologous to thermolysin, a thermostable neutral proteinase and 45% homologous to Bacillus subtilis neutral proteinase. The zinc-binding site and the hydrophobic pocket of the active site are highly similar in all three proteinases. B. cereus neutral proteinase which is 20 degrees C less thermostable (60 degrees C) than thermolysin (80 degrees C) shows only minor differences in calcium binding sites and salt bridges compared to thermolysin (known from its X-ray diffraction analysis), whereas B. subtilis neutral proteinase (50 degrees C) differs considerably. Therefore it was assumed that the difference in thermostability between B. cereus neutral proteinase and thermolysin is not caused by different metal binding properties, or differences in the active site, but by changes within the rest of the molecule. Calculation of secondary structure potentials according to Chou & Fasman, hydrophobicity and bulkiness of the different structural elements and preferred cold----hot amino-acid residue exchanges indicated, that the thermostability of thermolysin compared to B. cereus neutral proteinase is caused by small effects contributed by numerous amino-acid exchanges distributed over the whole molecule, resulting in increased hydrophobicity of beta-pleated sheet and higher bulkiness of alpha-helical regions.     

Sieve-Element Plastids,Nuclear Crystals and Phloem Proteins in the Zingiberales

The sieve-element characters of 40 species from all families making up the monocotyledon order Zingiberales have been studied by transmission electron microscopy. While phloem-proteins are a typical component of all eight families, the Zingiberaceae are characterized by nondispersive protein bodies derived from nuclear crystals. The sieve-element plastids are of the form-P2cs, i.e. contain cuneate protein crystals (as typical of all monocotyledons) and starch grains, those of the family Musaceae have protein filaments in addition (form-P2cfs). The exclusiveness of the form-P2c(f)s plastids contributed to the homogeneity of the order and its distinctness among other monocotyledon taxa. When diameters of the sieve-element plastids from leaf phloem are compared, in the “banana group” the family averages of the Strelitziaceae and the Lowiaceae have, respectively, maximum and minimum values and are clearly different from those in the Musaceae, the family in which they have been included previously. In the “ginger group”, the family averages of the Zingiberaceae, Costaceae, and Marantaceae are close to the order average, with only Cannaceae having minimum values. A comparison of species averages, however, reduces the size differences between families: the value for Ravenala (Strelitziaceae) is close to those of the five Musaceae tested, and that of Globba (Zingiberaceae) even slightly lower than the species average of Canna.     

Fermentation of peptides and amino acids by a monensin-sensitive ruminal Peptostreptococcus.

A monensin-sensitive ruminal peptostreptococcus was able to grow rapidly (growth rate of 0.5/h) on an enzymatic hydrolysate of casein, but less than 23% of the amino acid nitrogen was ever utilized. When an acid hydrolysate was substituted for the enzymatic digest, more than 31% of the nitrogen was converted to ammonia and cell protein. Coculture experiments and synergisms with peptide-degrading strains of Bacteroides ruminicola and Streptococcus bovis indicated that the peptostreptococcus was unable to transport certain peptides or hydrolyze them extracellularly. Leucine, serine, phenylalanine, threonine, and glutamine were deaminated at rates of 349, 258, 102, 95, and 91 nmol/mg of protein per min, respectively. Deamination rates for some other amino acids were increased when the amino acids were provided as pairs of oxidized and reduced amino acids (Stickland reactions), but these rates were still less than 80 nmol/mg of protein per min. In continuous culture (dilution rate of 0.1/h), bacterial dry matter and ammonia production decreased dramatically at a pH of less than 6.0. When dilution rates were increased from 0.08 to 0.32/h (pH 7.0), ammonia production increased while production of bacterial dry matter and protein decreased. These rather peculiar kinetics resulted in a slightly negative estimate of maintenance energy and could not be explained by a change in fermentation products. Approximately 80% of the cell dry matter was protein. When corrections were made for cell composition, the yield of ATP was higher than the theoretical maximum value. It is possible that mechanisms other than substrate-level phosphorylation contributed to the energetics of growth.     

Fermentation of peptides and amino acids by a monensin-sensitive ruminal Peptostreptococcus

A monensin-sensitive ruminal peptostreptococcus was able to grow rapidly (growth rate of 0.5/h) on an enzymatic hydrolysate of casein, but less than 23% of the amino acid nitrogen was ever utilized. When an acid hydrolysate was substituted for the enzymatic digest, more than 31% of the nitrogen was converted to ammonia and cell protein. Coculture experiments and synergisms with peptide-degrading strains of Bacteroides ruminicola and Streptococcus bovis indicated that the peptostreptococcus was unable to transport certain peptides or hydrolyze them extracellularly. Leucine, serine, phenylalanine, threonine, and glutamine were deaminated at rates of 349, 258, 102, 95, and 91 nmol/mg of protein per min, respectively. Deamination rates for some other amino acids were increased when the amino acids were provided as pairs of oxidized and reduced amino acids (Stickland reactions), but these rates were still less than 80 nmol/mg of protein per min. In continuous culture (dilution rate of 0.1/h), bacterial dry matter and ammonia production decreased dramatically at a pH of less than 6.0. When dilution rates were increased from 0.08 to 0.32/h (pH 7.0), ammonia production increased while production of bacterial dry matter and protein decreased. These rather peculiar kinetics resulted in a slightly negative estimate of maintenance energy and could not be explained by a change in fermentation products. Approximately 80% of the cell dry matter was protein. When corrections were made for cell composition, the yield of ATP was higher than the theoretical maximum value. It is possible that mechanisms other than substrate-level phosphorylation contributed to the energetics of growth.     

Low temperature pre-treatment of domestic sewage in an anaerobic hybrid or an anaerobic filter reactor

The ability of pigs to use nitrogen and energy in Bermuda grass was evaluated in order to assess whether Bermuda grass harvested from spray fields could be fed to pigs as a means to recycle nitrogen. Digestibility of Bermuda grass incorporated into corn-soybean meal diets was evaluated in heavy finishing pigs and gestating sows. Results suggest that Bermuda grass digestibility is negative in animals not adapted to a high-fiber diet. Enzymes improve this digestibility, but even with enzymes, nitrogen digestibility was poor. Pigs fed a diet containing 10% Bermuda grass required a one week adaptation period for maximal digestion; following adaptation, pigs can digest approximately 40% of the energy in Bermuda grass but none of the nitrogen. Feeding Bermuda grass to pigs as a means of recycling nitrogen is thus not recommended.     

盐离子作用下组蛋白变体H2A.Z增强核小体结构的稳定性

真核生物染色质的基本结构组成单元是核小体,基因组DNA被压缩在染色质中,核小体的存在通常会抑制转录、复制、修复和重组等发生在DNA模板上的生物学过程。组蛋白变体H2A.Z可以调控染色质结构进而影响基因的转录过程,但其详细的调控机制仍未研究清楚。为了比较含有组蛋白变体H2A.Z的核小体和常规核小体在盐离子作用下的稳定性差异,本文采用Förster共振能量转移的方法检测氯化钠、氯化钾、氯化锰、氯化钙、氯化镁等离子对核小体的解聚影响。实验对Widom 601 DNA序列进行双荧光Cy3和Cy5标记,通过荧光信号值的变化来反映核小体的解聚变化。Förster共振能量转移检测结果显示:在氯化钠、氯化钾、氯化锰、氯化钙和氯化镁作用下,含有组蛋白变体H2A.Z的核小体解聚速度相比于常规核小体要慢,且氯化钙、氯化锰和氯化镁的影响更明显。电泳分析结果表明,在75℃条件下含有组蛋白变体H2A.Z的核小体的解聚速率明显低于常规核小体。采用荧光热漂移检测(fluorescence thermal shift analysis , FTS)进一步分析含有组蛋白变体H2A.Z核小体的稳定性,发现两类核小体的荧光信号均呈现2个明显的增长期,含有组蛋白变体H2A.Z核小体的第1个荧光信号增速期所对应的温度明显高于常规核小体,表明核小体中H2A.Z/H2B二聚体的解聚变性温度要高于常规的H2A/H2B二聚体,含有组蛋白变体H2A.Z核小体的热稳定性高。研究结果均表明,含有组蛋白变体H2A.Z的核小体的结构比常规核小体的结构稳定。     

Thermal heterogeneity,migration, and consequences for spawning potential of female bull trout in a river–reservoir system

The likelihood that fish will initiate spawning, spawn successfully, or skip spawning in a given year is conditioned in part on availability of energy reserves. We evaluated the consequences of spatial heterogeneity in thermal conditions on the energy accumulation and spawning potential of migratory bull trout (Salvelinus confluentus) in a regulated river–reservoir system. Based on existing data, we identified a portfolio of thermal exposures and migratory patterns and then estimated their influence on energy reserves of female bull trout with a bioenergetics model. Spawning by females was assumed to be possible if postspawning energy reserves equaled or exceeded 4 kJ/g. Given this assumption, results suggested up to 70% of the simulated fish could spawn each year. Fish that moved seasonally between a cold river segment and a warmer reservoir downstream had a greater growth rate and higher propensity to spawn in a given year (range: 40%–70%) compared with fish that resided solely in the cold river segment (25%–40%). On average, fish that spawned lost 30% of their energy content relative to their prespawn energy. In contrast, fish that skipped spawning accumulated, on average, 16% energy gains that could be used toward future gamete production. Skipped spawning occurred when water temperatures were relatively low or high, and if upstream migration occurred relatively late (mid‐July or later) or early (early‐May or earlier). Overall, our modeling effort suggests the configuration of thermal exposures, and the ability of bull trout to exploit this spatially and temporally variable thermal conditions can strongly influence energy reserves and likelihood of successful spawning.     

The severity of osteogenesis imperfecta: a comparison to the relative free energy differences of collagen model peptides

Molecular dynamics simulations were carried out to calculate free energy differences between the folded and unfolded states of wild type and mutant collagen model peptides. The calculated stability of the collagen models was compared with the severity of osteogenesis imperfecta. Free energy differences of Gly → Xaa (Xaa: Ser, Cys, Glu, and Asp) mutations between the wild type and the mutants at position 15 of the model peptide were 3.8, 4.2, 5.6, and 8.8 kcal/mol, respectively. The corresponding free energy differences of a second Gly mutation at the same position in different chains were, on average, 1.3, 1.5, 2.9, and 5.4 kcal/mol, respectively. Free energy simulations were also performed to estimate the relative stability between an oxidized form and a reduced form of the mutants containing two Cys residues, which indicated that the mutant of the collagen-like peptide containing an intramolecular disulfide bond was more stable than the mutant containing one Cys residue but less stable than the wild type. The calculated free energy differences between an oxidized and a reduced form of the mutants containing two Cys residues are 0.8 and 2.6 kcal/mol for the disulfide bonds between Chains A and B and between Chains A and C, respectively.     

施氮和供水对混播和单播白羊草叶片叶绿素荧光特性的影响

为明确干旱条件下混播和施氮对白羊草〔Bothriochloa ischaemum(Linn.)Keng〕叶片叶绿素荧光参数的影响,采用盆栽法并设置不同混播比例〔白羊草与柳枝稷(Panicum virgatum Linn.)混播比例分别为8:0、6:2、4:4和2:6〕、施氮水平(即不施氮和1kg干土施01g纯氮)和供水条件(即正常供水和干旱胁迫6d后复水),对白羊草叶片叶绿素荧光参数的变化进行比较分析;在此基础上,采用一般线性模型分析这3个因素及其交互作用对白羊草叶绿素荧光参数的影响效应.结果显示:正常供水条件下,各处理组白羊草的最大光化学效率(Fv/Fm)、实际光化学效率(ΦPSⅡ)、表观光合电子传递速率(ETR)、光化学淬灭系数(qP)和非光化学淬灭系数(NPQ)均无明显变化.干旱及复水条件下,不施氮处理组白羊草的Fv/Fm值在干旱胁迫6 d(即土壤相对含水量最低)时降至最低值,并在复水2 d后恢复至与正常供水条件下相近的水平,而施氮处理组的Fv/Fm值则一直保持与正常供水条件下相近的水平;不论施氮与否,各处理组白羊草的ΦPSⅡ、ETR、qP和NPQ值基本上均表现为在干旱胁迫6 d时达到最高值,并在复水2 d后恢复至正常供水条件下各参数值的90%以上.总体上看,混播白羊草的qP和ETR值均高于单播白羊草,而其NPQ值则低于后者.统计分析结果表明:混播比例、施氮水平和供水条件3个因素间的交互作用对白羊草的ΦPSⅡ、qP和ETR值无显著影响,施氮水平对NPQ值的单独作用、施氮水平和混播比例的交互作用对Fv/Fm值以及施氮水平和供水条件的交互作用对ETR值也无显著影响,但这3个因素的单独作用及两两因素间的交互作用对白羊草其余叶绿素荧光参数均有显著或极显著影响.研究结果表明:一定程度的干旱胁迫有利于提高白羊草叶片PSⅡ反应中心的开放程度、光合电子传递速率和热耗散过剩光能的能力;在干旱胁迫条件下,施氮有助于白羊草叶片维持PSⅡ反应中心的活性和光化学效率;并且,与柳枝稷适度混播可改善白羊草叶片的光合性能,提高其种间竞争适应性.     

Effects of thermal regime on energy and nitrogen budgets of an early juvenile Arctic charr, Salvelinus alpinus, from Lake Inari

The feed intake, growth, oxygen consumption and ammonia excretion of juvenile Arctic charr were measured over period of four weeks at different temperatures which were either constant (11.0, 14.4, 17.7 °C) or fluctuated daily (14.3 ± 1 °C). Maximum feed intake was estimated to occur at 14.3 °C, while oxygen consumption and nitrogen excretion were highest at the highest temperature, and growth rate was estimated to be highest at 13.9 °C. Feed conversion efficiency was estimated to be highest at 13.2 °C, where over 62.7% of ingested energy was allocated to growth. Metabolic rate accounted for 16–30% of ingested energy and nitrogen excretion was under 3% of ingested energy. The nitrogen budget was under similar thermal influences to the energy budget. Thermal fluctuation increased metabolic rate, but not feed intake, leading to a reduction in feed conversion efficiency under fluctuating temperature conditions.     

Effects of Light Stress on Oxygen Evolution and Photochemical Energy Storage of Hybrid Poplar Clones Determined by Photoacoustic Technique

The oxygen evolution, thermal dissipation, and photochemical energy storage of three hybrid poplar clones, namely the triploid clone B342, the diploid clone B11［( Populus alba×P. glandulosa)×(P.tomentosa×P.bolleana)］ , and the triploid clone B346 ［ (P.tomentosa×P. bolleana)×(P. alba×P.glandulosa )］, under light stress were studied using photoacoustics. The oxygen evolution signal and photochemical energy storage varied negatively with the pretreatment-PFD (photon flux density), whereas the thermal signal varied positively with the pretreatment-PFD. Photochemical energy storage was reallocated to PSⅡ more than to PSⅠ, while the photochemical energy storage in PSⅠ was more stable than that in PSⅡ when subjected to light stress. The inhibitors streptomycin (SM), dithiothreitol (DTT) and sodium fluoride (NaF) could all affect the oxygen evolution signal. Clones B11 and B342 were more resistant to light stress than clone B346.