Uptake of Inorganic Carbon by Isolated Chloroplasts of the Unicellular Green Alga Chlorella ellipsoidea

Chloroplasts, isolated from protoplasts of the green alga, Chlorella ellipsoidea, were estimated to be 99% intact by the ferricyanide-reduction assay, and gave CO₂ and PGA-dependent rates of O₂ evolution of 64.5 to 150 micromoles per milligram of chlorophyll per hour, that is 30 to 70% of the photosynthetic activity of the parent cells. Intact chloroplasts showed no carbonic anhydrase activity, but it was detected in preparations of ruptured organelles. Rates of photosynthesis, measured in a closed system at pH 7.5, were twice the calculated rate of CO₂ supply from the uncatalyzed dehydration of HCO₃⁻ indicating a direct uptake of bicarbonate by the intact chloroplasts. Mass spectrometric measurements of CO₂ depletion from the medium on the illumination of chloroplasts indicate the lack of an active CO₂ transport across the chloroplast envelope.     

低渗膨胀对菠菜完整叶绿体光合作用的影响

菠菜离体完整叶绿体需要合适的介质渗透压（约０．９ＭＰａ）以保持其较高的光合作用速率。当渗透压因降低介质中山梨醇浓度（从０．３３ｍｏｌ／Ｌ至０．１７ｍｏｌ／Ｌ）而降低时,叶绿体的完整率保持不变。低于临界渗透压（约０．５ＭＰａ）,叶绿体被膜就发生破裂．并丧失ＣＯ２同化能力。在轻度低渗条件下,虽然叶绿体被膜未破,但依赖ＣＯ２的放氧速率已受抑制。渗透压在０．９ＭＰａ与０．５ＭＰａ之间,叶绿体依赖ＰＧＡ的放氧抑制,可由加入山梨醇至正常浓度（０．３３ｍｏｌ／Ｌ）而解除。膨涨叶绿体的ＡＴＰ合成水平与正常叶绿体相同,而ＮＡＤＰＨ形成速率则明显降低。利用能透过被膜的不同电子受体ＮＣ２、ＰＧＡ和ＯＡＡ发现,在膨胀叶绿体中,ＮＯ２的还原不受形响,而ＰＧＡ及ＯＡＡ的还原明显被抑制。我们推测,低渗膨胀叶绿体中光合作用的抑制,至少有一个原因是Ｆｄ－ＮＡＤＰ氧化还原酶作用的受阻。     

Division of Chloroplasts in a Green Alga, Pediastrum duplex

The division of chloroplasts in a green alga, Pediastrum duplex,was studied by electron microscopy. Cells were treated for observationwith the freeze-substitution method. Fibrils, or fibrous belts,which we had observed previously at the dividing constrictionsof chloroplasts in Trebouxia potteri were not visible in Pediastrum,even though the method of preparation was the same for bothsets of samples. Microtubules (MTs) and the septum seem notto participate directly in the division of the single chloroplastin Pediastrum cells. Many thin fibrils, 7–20 nm in diameter,attached to, or protruding from, the surface of the dividingconstriction were seen. These fibres were less densely distributedat the constrictions of non-dividing chloroplasts. It is suggestedthat these fibrils are involved in the divison of chloroplastsin Pediastrum duplex. Cell wall, chloroplast division, freeze-substitution, intermediate fibres, Pediastrum duplex, transmission electron microscopy     

Division of Chloroplasts in a Green Alga, Trebouxia potteri

The division of chloroplasts in Trebouxia potteri was studiedby electron microscopy. At the beginning of chloroplast division,vesicles with fine fibrils (FVs) and ER attach to the isthmusof the chloroplast. Then, filaments appear around the isthmusparallel to the direction of constriction and seem to contractin order to decrease the diameter of the isthmus. It is suggestedthat the FVs are involved in the formation of the filamentsand that the ER is involved in the contraction of the filaments.At the final stages of the division of the chloroplast, thefilaments decompose. FVs are partially surrounded and decomposedby lysosomal sheets. For the next cycle of division of the chloroplast,the recovery of substances from decomposed filaments by functionalFVs seems a realistic possibility. chloroplast division, division apparatus, division cycle, transmission electron microscopy, Trebouxia potteri.     

Division of Chloroplasts in a Green Alga, Trebouxia potteri

The division of chloroplasts in Trebouxia potteri was studiedby electron microscopy. At the beginning of chloroplast division,vesicles with fine fibrils (FVs) and ER attach to the isthmusof the chloroplast. Then, filaments appear around the isthmusparallel to the direction of constriction and seem to contractin order to decrease the diameter of the isthmus. It is suggestedthat the FVs are involved in the formation of the filamentsand that the ER is involved in the contraction of the filaments.At the final stages of the division of the chloroplast, thefilaments decompose. FVs are partially surrounded and decomposedby lysosomal sheets. For the next cycle of division of the chloroplast,the recovery of substances from decomposed filaments by functionalFVs seems a realistic possibility. chloroplast division, division apparatus, division cycle, transmission electron microscopy, Trebouxia potteri     

Fluorescence Induction in Chloroplasts Isolated from the Green Alga, Bryopsis maxima IV. The I-D Dip

Fluorescence induction of intact Bryopsis chloroplasts whichpreviously had been illuminated in the presence of dithionitethen kept in the dark prior to measurement showed marked quenchingfrom an intermediary peak I to a lower level D before a secondaryrise to a peak P. A small hump (H), related to the membranepotential formed across the thylakoid membranes, overlappedD. The maximum extent of quenching—the I-D dip—wasattained in chloroplasts which had been illuminated for 1 secprior to dark incubation for 1 min. This illumination causedthe complete reduction of secondary electron acceptors and thepartial reduction of Q, the primary electron acceptor of photosystemII. Chloroplasts developed the capacity for transient photooxidationof cytochrome f during subsequent dark incubation, indicatingthat there was dark oxidation of electron acceptors of photosystemI which had been reduced by the illumination. A close correlationwas found between the I-D dip and the transient photooxidationof cytochrome f with respect to the kinetics of light inducedchanges as well as dark restoration after the illumination.Inhibitor studies showed that the dip decreased when the poolsize of photosystem I acceptors was reduced. Our results showthat the I-D dip and the transient photooxidation of cytochromef depend upon a common acceptor pool of photosystem I. We concludedthat the I-D dip is due to the oxidation of Q by photosystemI with a limited electron acceptor pool. (Received September 12, 1980; Accepted November 14, 1980)     

The Effect of Deleterious Concentrations of Mercury on the Photosynthesis and Growth of Chlorella pyrenoidosa

The effect of mercury ions on the photosynthesis and growth of Chlorella pyrenoidosa in a balanced medium has been studied and compared with the effect of copper. In many ways Hg treated algae behave like algae treated with Cu in concentrations of the same molarity, but important deviations occur. Hg acts at a lower and in a more narrow range of concentrations than does Cu due to a more specific binding. The depressing effect of Hg is not counteracted by other cations such as potassium and sodium, and iron has only a slight effect. Cell division is stopped after Hg addition and there is no accumulation of assimilation products. On the contrary the cells become pale yellow. Preliminary studies indicate a light-independent leakage in the cytoplasmatic membrane leading to an outflow of potassium ions. This is the primary action of both Hg and Cu poisoning, but the leakage does not seem to be correlated with the decrease of photosynthesis. After a lapse of time — dependent on the mercury/cell concentration ratio — a detoxication takes place probably due to the binding of Hg to “insensitive sites” in the cells. Probable mechanisms for the action of Hg on photosynthesis and growth are discussed.     

草酰乙酸和苹果酸对菠菜叶片和完整叶绿体光合作用的影响

观测了OAA和MA对菠菜叶片和完整叶绿体光合作用的影响.结果显示,当叶片切块在20μmol/L的OAA存在时,其叶片的光合放氧速率增加了89%,经OAA处理的离体完整叶绿体的光合放氧速率增加了72%;当反应体系中存在有较高浓度的NaHCO3时,OAA的作用不明显.叶片经20 μmol/L的MA处理后,叶片光合放氧速率比对照高127%.用CO2分析仪观测了处理后叶片的净光合速率(Pn),结果显示,OAA和MA处理后的叶片Pn值分别是对照的117%和111%.对在C3植物中建立C4微循环系统来提高光合作用效率的可能性进行了讨论.     

The Effect of Chromium on the Photosynthesis and Growth of Diatoms and Green Algae

The effect of hexavalent chromium ions on the photosynthesis and growth of the diatom Nitzschia palea and the green alga Chlorella pyrenoidosa has been studied and compared with the effect of Cu and Hg. The effect of chromium is very similar to that of Cu and Hg, but it is more than one hundred times less toxic for the algae than copper. The toxicity of chromium is not counteracted by adding Fe to the culture solution. The problems regarding cleaning glass-ware in dichromate-sulphuric acid are discussed and it is strongly recommended to use other cleaning agents.     

The Effect of Toxic Doses of Copper upon Respiration, Photosynthesis and Growth of Chlorella vulgaris

When cells of Chlorella vulgaris absorb copper under anaerobic conditions, subsequent respiration, photosynthesis and growth of the cells are all severely inhibited. This does not occur when the metal is absorbed under aerobic conditions. When, after aerobic absorption of copper, the cells are exposed to a period of anaerobiosis, respiratory inhibition is as profound as when the uptake is anaerobic. In this case, however, respiration must eventually recover, for growth is not affected so severely as it is when copper is taken up under anaerobic conditions. It is concluded that the extra copper absorbed under anaerobic conditions is directly or indirectly responsible for the greatly increased toxicity to growth, and that this copper is bound to sites not normally available under aerobic conditions. Some aspects of the apparently unique toxic effect of copper suggest that these extra sites are sulphydryl groups.     

Clotrimazole对菠菜叶绿体光合磷酸化和电子传递的抑制作用

10μmol/的clotrimazole不仅抑制光合磷酸化活力,而且抑制各种类型的电子传递,是一个典型的电子传递抑制剂。经过它对叶绿体放氧,荧光和毫秒延迟发光影响的比较研究表明:clotri—mazole在光合电子传递链上的作用部位在Q与PQ之间,即与DGMU的作用部位相同或相近。     

Isolation,Growth, Ultrastructure,and Metal Tolerance of the Green Alga,Chlamydomonas acidophila (Chlorophyta)

An acidophilic volvocine flagellate, Chlamydomonas acidophila (Volvocales) that was isolated from an acid lake, Katanuma, in Miyagi prefecture, Japan was studied for growth, ultrastructural characterization, and metal tolerance.

Chlamydomonas acidophila is obligately photoautotrophic, and did not grow in the cultures containing acetate or citrate even in the light. The optimum pH for growth was 3.5-4.5. To characterize metal tolerance, the toxic effects of Cd, Co, Cu, and Zn on this alga were also studied. Effective metal concentrations, which limited the growth by 50%, EC₅₀ were measured, after 72h of static exposure. EC₅₀s were 14.4 μM Cd²⁺, 81.3 μM Co²⁺, 141μM Cu²⁺, and 1.16 mM Zn²⁺ for 72 h of exposure. Thus, this alga had stronger tolerance to these metals than other species in the genus Chlamydomonas.     

Possible Effect of Magnetically Induced Water Structures on Photosynthetic Electron Transport Chains of a Green Alga Chlorella Vulgarts

The effect of different water structures induced by exposure to the two separate pole faces of a 0.297 ± 0.003 T magnet was observed for the activities of photosystems of Chlorella vulgaris. The results show that time-dependent variable water structures produced by two poles have different effects on the activities of the photosystems. One possible mechanism may be due to the selective partitioning of ions among and within the extra- and intracellular aqueous solutions, and failure of the water-oxidizing clock to strip electrons from the magnetically restructured water.     

Physiological and Biochemical Role of Brassinosteroids and Their Structure-Activity Relationship in the Green Alga Chlorella vulgaris Beijerinck (Chlorophyceae)

This paper studies the influence of the 7-oxalactone type of brassinosteroids (BRs) and 6-ketone upon the biological activity of the alga Chlorella vulgaris (Chlorophyceae). The results of the study indicate significant differences in the growth and metabolism of C. vulgaris cells caused by the different chemical structures of the BRs used. The most significant differences in the stimulation of the growth of the biomass and metabolites contained in it were caused by structural differences in the B ring of BRs. It was found that in C. vulgaris 7-oxalactone type of BRs [brassinolide (BL) and its derivatives] are more active than 6-ketone type of BRs [castasterone (CS) and its derivatives]. It was found that BRs used within the range of concentration of 10⁻¹² to 10⁻⁸ m stimulate two- to threefold the growth and division of C. vulgaris cells. The most stimulating influence upon the number of the algal cells and the phosphorus, chlorophyll, and monosaccharides contained in the alga, as well as the intensity of the photosynthesis, and sugar and glycolate excretion was demonstrated by BL at a concentration 10⁻⁸ m in the 36th h of cultivation. HomoCS was characterized by the lowest biological activity. In turn, after the 48th h an inhibition of the rate of growth and development of the alga takes place. In the range from 10⁻⁷ to 10⁻⁶ m the inhibition of growth and development of the alga was manifested by BRs. During the further toxic activity of BRs the cells of C. vulgaris undergo complete degradation. In turn, in concentrations lower than 10⁻¹² m, BRs do not exert any biologically significant influence upon C. vulgaris cells. On the basis of the study, the biological activity of BRs was arranged in the following order: BL > 24-epiBL > homoBL > CS > 24-epiCS > homoCS. Received July 21, 1997; accepted April 7, 1998     

Effects of Low Oxygen on Photosynthesis, Translocation and Growth in Green Pepper (Capsicum annuum)

Green pepper (Capsicum annuum cv. Bell Boy) plants were exposedin chambers to low (2%) oxygen and controlled carbon dioxideconcentrations. Vegetative and fruiting plants showed short-termincreases in net photosynthesis in low oxygen or elevated carbondioxide (up to 900 µl CO₂ l^–1). Photosynthesis ofyoung vegetative plants increased in low oxygen in the short-termbut there was no long-term benefit. Low oxygen enhancement ofphotosynthesis declined with time and after 10 d, leaf areaand root dry weight were less than in plants grown in normalair. Labelled assimilates were translocated from leaves to otherregions at similar rates in low oxygen and normal air. Low oxygenreduced respiratory losses from leaves and reduced the proportionof soluble carbohydrate converted to polysaccharide in all plantparts. Thus, low-oxygen environments decrease the utilisationof assimilates which then may lead to inhibition of photosynthesis. Capsicum annuum, photosynthesis, photorespiration, translocation, utilization of assimilates