Protein Synthesis Initiated by Cell Fusion in Dictyostelium discoideum

D. discoideum has two alternative developmental pathways. If cells of two complement mating-type strains, NC4 and HM1, fuse sexually, a giant cell is produced which subsequently develops into a macrocyst, the sexual structure of this organism. However, if fusion fails to occur and cells are starved, a fruiting-body is produced instead of a macrocyst. In this paper, a two-dimensional polypeptide gel electrophoresis study showed that giant cells produce specific polypeptides which may possibly be involved in macrocyst development. Out of total 497 polypeptides which appeared in a giant cell during an incubation period of 13 hr, 92 were the specific for giant cells. Four of these polypeptides were appeared within only 1 hr after the cell fusion. The other 405 were non-specific polypeptides which appeared in both giant cells and NC4 or/and HM1 cells. However, the patterns and the rates of production of each polypeptide during the incubation period were different between these cells.     

Change in CO2 balance under a series of forestry activities in a cool-temperate mixed forest with dense undergrowth

To evaluate the effects on CO₂ exchange of clearcutting a mixed forest and replacing it with a plantation, 4.5 years of continuous eddy covariance measurements of CO₂ fluxes and soil respiration measurements were conducted in a conifer-broadleaf mixed forest in Hokkaido, Japan. The mixed forest was a weak carbon sink (net ecosystem exchange, −44 g C m⁻² yr⁻¹), and it became a large carbon source (569 g C m⁻² yr⁻¹) after clearcutting. However, the large emission in the harvest year rapidly decreased in the following 2 years (495 and 153 g C m⁻² yr⁻¹, respectively) as the gross primary production (GPP) increased, while the total ecosystem respiration (RE) remained relatively stable. The rapid increase in GPP was attributed to an increase in biomass and photosynthetic activity of Sasa dwarf bamboo, an understory species. Soil respiration increased in the 3 years following clearcutting, in the first year mainly owing to the change in the gap ratio of the forest, and in the following years because of increased root respiration by the bamboo. The ratio of soil respiration to RE increased from 44% in the forest to nearly 100% after clearcutting, and aboveground parts of the vegetation contributed little to the RE although the respiration chamber measurements showed heterogeneous soil condition after clearcutting.     

Differential anatomical responses to elevated CO2 in saplings of four hardwood species

To determine whether an elevated carbon dioxide concentration ([CO₂]) can induce changes in the wood structure and stem radial growth in forest trees, we investigated the anatomical features of conduit cells and cambial activity in 4‐year‐old saplings of four deciduous broadleaved tree species – two ring‐porous (Quercus mongolica and Kalopanax septemlobus) and two diffuse‐porous species (Betula maximowicziana and Acer mono) – grown for three growing seasons in a free‐air CO₂ enrichment system. Elevated [CO₂] had no effects on vessels, growth and physiological traits of Q. mongolica, whereas tree height, photosynthesis and vessel area tended to increase in K. septemlobus. No effects of [CO₂] on growth, physiological traits and vessels were seen in the two diffuse‐porous woods. Elevated [CO₂] increased larger vessels in all species, except B. maximowicziana and number of cambial cells in two ring‐porous species. Our results showed that the vessel anatomy and radial stem growth of Q. mongolica, B. maximowicziana and A. mono were not affected by elevated [CO₂], although vessel size frequency and cambial activity in Q. mongolica were altered. In contrast, changes in vessel anatomy and cambial activity were induced by elevated [CO₂] in K. septemlobus. The different responses to elevated [CO₂] suggest that the sensitivity of forest trees to CO₂ is species dependent.     

EFFECT OF ULTRAVIOLET LIGHT UPON VARIOUS PHYSIOLOGICAL ACTIVITIES OF CHLORELLA CELLS AT DIFFERENT STAGES IN THEIR LIFE CYCLE

1. Using Chlorella ellipsoidea as material, investigations weremade of the effects of ultraviolet irradiation upon variousactivities of cells at different developmental stages in theirlife cycle. Cell activities investigated were photosynthesis,respira tion, over-all growth, modes of synchronous growth andcell division as well as the formation of nucleic acids. Theu. v.- light applied was 30 µµW/cm²in intensityand 2537 Å in wavelength.
2. The most u. v.-sensitive wasthe over-all growth activity, andin this respect the irradiationapplied at the L₂-stage wasmore inhibitive than that givenat the D-stage. The next mostvulnerable was the photosyntheticactivity, the sensitivitybeing the same in the D- and L-cells.The most resistant towardu.v. was the endogenous respirationof D-cells followed by theirrespiration using exogenous glucoseas substrate. The L₂-cellsappeared to be unable to use exogenousglucose as substrateof respiration, but their endogenous respirationwas considerablystronger than that of D-cells, and its u. v.-sensitivitywasthe same as that of glucose respiration of D-cells.
3. WhenD-cells were u. v. irradiated immediately before the startofsynchronous culture, growth and cell division as well astheformation of DNA and RNA were retarded in proportion totheu. v.-dose applied. The division number (n) was normal (around4) at lower u.v.-doses (1-2 minute irradiation), but was reducedto a half (about 2) at a higher dose.
4. When, during the synchronousculture, 1-minute u.v.- irradiationwas applied at various stagesof the ripening phase, the divisionwas retarded, but the cells,after attaining an abnormally largesize, divided into about8. If the irradiation was given atthe L₄-stage, the divisionnumber was practically unmodified(n=4.5), although the divisionwas somewhat retarded comparedwith that of the control culture.When a 1-minute irradiationwas given at the L₂-stage, thereoccurred an apparent stimulationof DNA- and RNA-formation,a phenomenon which corresponds tothe production of a largernumber of daughter cells than itwas the case in control cultures.
5. Thus the cells which were moderately u.v.-irradiated at differentstages of synchronous culture were able to complete their lifecycle, but later a certain portion of irradiated cells becameunable to grow normally.

¹Present address: Department of Biochemistry, Dartmouth MedicalSchool, Hanover, New Hampshire, U.S.A. (Received March 6, 1961; )     

Studies on chlorophyllase of Chlorella protothecoides II. Formation of atypical chlorophyllide a

When chlorophyll a was incubated with a preparation of chlorophyllaseextracted with Triton X-100 from methanol-acetone powder ofChlorella protothecoides, the substrate was changed to chlorophyllidea, and subsequently to an atypical form of chlorophyllide a.The formation of an atypical form of chlorophyllide was notdetected in the reaction with chlorophyll b as substrate, norin the reaction with another preparation of chlorophyllase extractedfrom the algal cells. (Received August 18, 1969; )     

中国东北地区兴安落叶松林树干呼吸的研究

树干呼吸是森林碳平衡估计中的一个重要项目同时还能够显示树木的活力.对于如何准确估计森林树干呼吸释放CO2总量还存在争论.在本项研究中,2001～2002连续两年在一个33年生的兴安落叶松(Larix gmelini Rupr.)人工林内对树干呼吸进行了测定,同时测定了不同高度树干呼吸、呼吸的日变化、同龄落叶松林内不同个体的树干呼吸以及相关生长状态因子、水分因子和温度因子.结果显示:1)树干上部的呼吸速率在不同季节都高于下部呼吸速率,树干温度的差异能够一定程度上解释这种差异;2)树干呼吸有午间降低的现象,上午的测定结果树干温度与树干呼吸速率紧密相关,而下午则温度依赖性很小,土壤、空气、小枝木质部水势、叶片蒸腾速率和气孔导度都显示下午植物水分亏缺下午较上午严重,呼吸的这种上下午温度相关性的差异可能受这种水分亏缺的影响;3)在同龄林内,树木个体生长状态包括平均生长速率和树冠投影面积与树干呼吸速率有显著相关关系,而树干温度与之相关性很小.幂指数模型和S曲线模型能够产生较好的拟合效果;4)树干呼吸季节变化明显,7月份出现最大值,但同一月份的年间差异较大.自然指数模型能够较好地拟合温度与树干呼吸的季节变化规律.Q10值在2.22(2001年)和3.53(2002年)之间,与以往研究的结果相当.从以上结果可以看出,通过单一的Q10值估计森林树干呼吸总量会产生偏差,要想得到准确的估计,至少应该考虑生长状态的差异和水分状态的差异.     

STUDIES ON CHLOROPHYLLASE OF CHLORELLA PROTOTHECOIDESI. ENZYMATIC PHYTYLATION OF METHYL CHLOROPHYLLIDE

1. The relation between chlorophyll content and the hydrolyticactivity of chlorophyllase in Chlorella protothecoides was examined.An increase in the activity was parallel to that in chlorophyllcontent during the development of green colouration, or greeningcourse, in the bleached cells. The activity sharply declinedand a parallel disappearance of chlorophyll was also found duringbleaching of the green cells.
2. A partially purified water-solublepreparation of chlorophyllasewas obtained by n-butanol treatmentand fractionation with coldacetone. It showed high activityand hydrolyzed 2 mg chlorophylla per hr per mg protein.
3. Forseparation and identification of the pigments concernedin thechlorophyllase reaction, a new solvent system of paperchromatographywas introduced.
4. When methyl chlorophyllide a and phytol wereincubated withthe enzyme, two products were formed. By comparisonwith theRf values of isolated pure substances, one was identifiedaschorophyll a and the other as chlorophyllide a. This enzymedid not catalyze the phytylation of free chlorophyllide a, butit had the ability to attach phytol to methyl chlorophyllidea. The final step in the biosynthesis of chlorophyll a is brieflydiscussed.

¹ Contribution No. 158 from the Department of Biology, Facultyof Science, Kyushu University. Supported in part by a grant-in-aidfor Fundamental Scientific Research from the Ministry of Education.     

CHANGES IN HYDROGENASE ACTIVITY DURING THE SYNCHRONOUS GROWTH OF SCENEDESMUS OBLIQUUS D3

1. A fairly good synchronization of Scenedesmus cells was obtainedby transferring the cells grown in a medium containing a lowconcentration of iron into a medium containing relatively highconcentration of iron.
2. During the synchronous culture in themineral medium, a goodparallelism between the average cellvolume and hydrogenaseactivity was observed.
3. Effect of glucoseon the development of the hydrogenase activitywas variabledepending on the stage of algal growth.
4. Iron is essentialfor the development of the hydrogenase activityand glucosesupplementary.

¹On leave from Laboratory of Applied Botany, Faculty of Agriculture,Kyoto University, Kyoto.     

Inhibition of Photosystem II in the Green Alga Ankistrodesmus falcatus by Copper

Copper strongly inhibited 2,6-dichloroindophenol (DCIP) photoreduction in the broken cells of the green alga Ankistrodesmus falcatus (C303), and the activity lost could not be restored by adding 1,5-diphenylearbazide (DPC). Inactivation of the DCIP Hill reaction reached 45% after incubation with 10 μM cupric sulfate for 20 min. In the same time, copper (13 μg/mg chlorophyll) was bound to the broken cells. Addition of 10 mM KCl reduced copper binding by about 53%. Fluorescence intensity at room temperature decreased upon addition of cupric sulfate and was partially restored by adding 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), These results suggest that copper inactivates electron transport between the oxidizing side of the reaction center of photosystem II and the electron-donating site of DPC. Further, the effect of light intensity shows that copper mostly affected the reaction rate of the dark step and had less inhibitory effect on the quantum efficiency of the primary reaction of electron transport in photosystem II.     

中国东北地区兴安落叶松林树干呼吸的研究

树干呼吸是森林碳平衡估计中的一个重要项目同时还能够显示树木的活力。对于如何准确估计森林树干呼吸释放CO2总量还存在争论。在本项研究中,2001、2002连续两年在一个33年生的兴安落叶松(Larix gmelini Rupr.)人工林内对树干呼吸进行了测定,同时测定了不同高度树干呼吸、呼吸的日变化、同龄落叶松林内不同个体的树干呼吸以及相关生长状态因子、水分因子和温度因子。结果显示：1)树干上部的呼吸速率在不同季节都高于下部呼吸速率,树下温度的差异能够一定程度上解释这种差异;2)树干呼吸有午间降低的现象,上午的测定结果树干温度与树干呼吸速率紧密相关,而下午则温度依赖性很小,土壤、空气、小枝木质部水势、叶片蒸腾速率和气孔导度都显示下午植物水分亏缺下午较上午严重,呼吸的这种上下午温度相关性的差异可能受这种水分亏缺的影响;3)在同龄林内,树木个体生长状念包括平均生长速率和树冠投影面积与树干呼吸速率有显著相关关系,而树干温度与之相关性很小。幂指数模型和S曲线模型能够产生较好的拟合效果;4)树干呼吸季节变化明显,7月份出现最大值,但同一月份的年间差异较大。自然指数模型能够较好地拟合温度与树干呼吸的季节变化规律。Q10值在2．22(2001年)和3．53(2002年)之间,与以往研究的结果相当。从以上结果可以看出,通过单一的Q10值估计森林树干呼吸总量会产牛偏差,要想得到准确的估计,至少应该考虑生长状态的差异和水分状态的差异。