Lipid composition of envelopes,prolamellar bodies and other plastid membranes in etiolated,green and greening wheat leaves

Summary Comparative studies of lipid composition were made on prolamellar bodies, envelopes and other plastid membranes separately extracted from etiolated, green or greening (intermittent or continuous light) wheat (Triticum sativum L.) leaves. The different membrane fractions were examined by electron microscopy.The major lipid was digalactosyldiglyceride in the envelopes and prolamellar bodies and monogalactosyldiglyceride in stroma lamellae and grana. Phosphatidylcholine represented 60% of total phospholipids in the envelopes, 30% in prolamellar bodies and 14% in grana. All types of envelopes had the same lipid proportions.For all lipids the lowest fatty acid unsaturation was always found in the envelope membranes. The relative amount of {ie193-1} acid in the phosphatidylglycerol of envelopes increased from 4% (etioplasts) to an average of 15% (etiochloroplasts and chloroplasts).Abbreviations DGDG digalactosyldiglyceride - MGDG monogalactosyldiglyceride - PC phosphatidylcholine - PE phosphatidylethanolamine - PG phosphatidylglycerol - PI phosphatidylinositol - PS phosphatidylserine - SL sulfolipid     

The effect of low oxygen concentration on the acyl-lipid and fatty-acid composition of the C4 plant Amaranthus paniculatus L.

Acyl lipids and their constituent fatty acids were studied in leaves, chloroplasts and bundle-sheath strands of the C₄ plant Amaranthus paniculatus L. grown under normal and 4%-oxygen-containing atmospheres. In all fractions the major lipids were found to be monogalactosyldiacylglycerol, digalactosyldiacylglycerol, sulphoquinovo-syldiacylglycerol and phosphatidylglycerol. Significant quantities of phosphatidylcholine and phosphatidylethanolamine were restricted to leaves and bundle-sheath strands. All lipids, except phosphatidylglycerol where 3-trans-hexadecenoic acid was also present, contained palmitic acid, stearic acid, oleic acid, linoleic acid and linolenic acid. On a chlorophyll basis and compared with whole leaves, the amounts of phosphatidylcholine and phosphatidylethanolamine in bundle-sheath strands were considerably reduced. Three weeks after the change from a normal to a 4% atmospheric O₂ level, the galactolipid content, particularly in the bundlesheath strands, was enhanced. There were no significant differences in the degrees of saturationunsaturation of total acyl lipid for the plants grown in the low oxygen and normal atmospheres, although under 4% O₂ the phosphatidylglycerol contained an increased proportion of 3-trans-hexadecenoic acid at the expense of palmitic acid.Abbreviations DGDG digalactosyldiacylglycerol - MGDG monogalactosyldiacylglycerol - PC phosphatidylcholine - PE phosphatidylethanolamine - PG phosphatidylglycerol - SQDG sulphquinovosyldiacylglycerol     

Plastid differentiation, acyl lipid, and Fatty Acid changes in developing green maize leaves

Plastid differentiation, acyl lipid, and fatty acid composition have been followed in successive 2-cm sections from the base (youngest tissue) to the tip (oldest tissue) of green Zea mays (maize) leaves grown under a normal diurnal light regime. Although the youngest cells (0-4 cm from the leaf base) had only proplastids with one or two grana, they contained chlorophylls a and b, monogalactosyldiglyceride, digalactosyldiglyceride, sulfolipid, phosphatidylcholine, phosphatidylethanolamine, and phosphatidylglycerol. In the more mature sections, the plastids increased in size 5-fold, and differentiation into mesophyll and bundle-shealth chloroplasts had occurred. Concomitantly, the levels of all the lipids increased with the exception of phosphatidylcholine and phosphatidylethanolamine which decreased. With increasing cell maturity, the percentage of linolenic acid increased in all the individual acyl lipids, but palmitic acid remained constant in phosphatidylcholine, phosphatidylethanolamine, and sulfolipid. The Δ^3t-hexadecenoic acid was only detectable in the phosphatidylglycerol of the most mature maize tissue.     

Phosphatidylglycerol and sulphoquinovosyldiacyl-glycerol in leaves and fruits of chilling-sensitive plants

The fatty acid composition of phosphatidylglycerol and sulphoquinovosyldiacylglycerol from the leaves and fruits of five chilling-sensitive plants has been analysed. The sum of the contents of hexadecanoic acid, octadecanoic acid and trans-3-hexadecenoic acid in the phosphatidylglycerols from the leaves and fruit tissue of each plant is very similar. The sum of the contents of hexadecanoic and octadecanoic acids in sulphoquinovosyldiacylglycerol also appears to be closely related in leaves and fruits from the same plant.     

Changes in the composition of membrane lipids in relation to differentiation in Aegle marmelos callus cultures

Changes in fatty acid, phospholipid and galactolipid contents during cellular and organ differentiation in Aegle marmelos have been described. Decrease in phosphatidylinositol content and presence of 3-trans-hexadecenoic acid in phosphatidylglycerol were related to greening and shoot buds differentiation. The galactolipids level, the monogalactosyl diglyceride/digalactosyl diglyceride ratio and the linolenic acid level (mainly in monogalactosyl diglyceride) increased with the degree of differentiation, indicating the possible biogenesis of functional chloroplasts.Abbreviations 2,4-D 2,4 dichlorophenoxyacetic acid - BA benzylaminopurine - DW dry weight - FW fresh weight - PC phosphatidylcholine - PE phosphatidylethanolamine - PI phosphatidylinositol - PG phosphatidylglycerol - PS phosphatidyl serine - MGDG monogalactosyl diglyceride - DGDG digalactosyl diglyceride - 16:0 palmatic acid - 18:0 stearic acid - 18:1 oleic acid - 18:2 linoleic acid - 18:3 linolenic acid - trans-16:1 3-trans-hexadecenoic acid     

Metabolism of Glycerolipids in Plastidial and Extraplastidial Membranes of Etiolated Wheat Leaves: In Vivo and In Vitro Studies

Etiolated wheat leaves were fed with [l-¹⁴C]-acetate and chaseexperiments were performed in the dark or under light. In bothconditions, in extraplastidial membranes, phosphatidylglycerol(PG) and phosphatidylcholine (PC) were fatty acid donors, PGand PC providing palmitate and oleate respectively. The labelof linoleate increased only in phosphatidylethanolamine (PE).In etioplasts, PG was also a palmitate donor but PC, ratherpoor in labelled oleate, was an oleate acceptor, contrary towhat was observed in chloroplasts. The galactolipids and sulfoquinovosyldiacylglycerol(SL) remained poorly labelled. When isolated etioplasts were labelled in vitro, during thefirst two hours they incorporated the same amount of [l-¹⁴C]-acetatein their phospholipids, whether they were in the presence orin the absence of extraplastidial membranes. Afterwards, theaddition of a mitochondrial fraction enhanced the label of PG,mainly in palmitate, then in oleate, and to some extent, andonly under light in palmitoleate and linoleate. The mitochondrialfraction might be regarded here as a supplier of labelled precursorto he etioplasts which rapidly accumulated radioactivity inpalmitoyl-PG. In PC of isolated etioplasts, only palmitate wasfairly labelled. The deficiency in labelled oleoyl-PC in plastidsof dark-grown plants and of linoleoyl-PC in extraplastidialmembranes might be the reason for the delay in the labellingof unsaturated galactolipids. ¹ (Received March 9, 1987; Accepted August 21, 1987)     

Iron-deficiency in pea leaves: Effect on lipid composition and synthesis

The lipid composition of chlorotic leaves of Pisum sativum L. cv. Kelvedon Wonder, developed under iron-deficiency was determined and compared to similar material developed under normal nutrient conditions. All lipid classes were affected by iron-deficiency but to different extents, and thylakoid lipids were more affected than non-thylakoid lipids. The most striking results concerned changes in the fatty acid content of the main polar lipids. The linolenic acid of the galactolipids decreased to the benefit of more saturated fatty acids, mainly linoleic acid. In phosphatidylglycerol, the proportion of Δ³- trans -hexadecenoic acid decreased. Using radioactive acetate, lipid synthesis was investigated. Desaturation leading to linoleic acid was less affected by iron-deficiency than desaturation leading to Δ³- trans -hexadecenoic and linolenic acids.     

Effect of growth temperature on the fatty acid composition of Mycobacterium phlei

In Mycobacterium phlei, fatty acid unsaturation increased with decreasing temperature. The 10-hexadecenoic acid content increased as the temperature was reduced from 35°C to 26–20°C. At lower temperatures tuberculostearic acid decreased while oleic and linoleic acids increased, the latter being found in M. phlei for the first time. Concomitantly palmitic acid content decreased, and the 6- and 9-hexadecenoic acids increased slightly on reducing the temperature from 35 to 10°C. Thus, down to 26–20°C palmitic acid was mainly replaced by 10-hexadecenoic acid. From this range down to 10°C, palmitic and tuberculostearic acids were replaced by oleic and linoleic acids. Consequently, fatty acid branching decreased and mean chain length increased, as the temperature was reduced. These observations support the view that regulation of membrane fatty acid composition is part of microbial temperature adaptation, and that themechanism behind the responses might be more complex than generally believed.Abbreviations ACP acyl carrier protein - FAS I (Type I) fatty acid synthetase I - FAS II (Type II) fatty acid synthetase II - MGLP methylglucose containing lipopolysaccharide - MMP methylmannose containning polysaccharide     

Etioplast Development in Dark-grown Leaves of Zea mays L

The ultrastructure of etioplasts and the acyl lipid and the fatty acid composition of sequential 2-centimeter sections cut from the base (youngest) to the top (oldest) of nonilluminated 5-day-old etiolated leaves of Zea mays L., and the acyl lipid and fatty acid composition of the etioplasts isolated from them have been investigated. There is a 2.5-fold increase in the size of the plastids from the base to the tip of the leaf, and an increase both in the size of the prolamellar body and in the length of lamellae attached to it. The etioplasts in the bundle sheath and mesophyll cells of the older, but not the younger leaf tissue, are morphologically distinct. The monogalactosyl and digalactosyldiglycerides, phosphatidylcholine, phosphatidylglycerol, and phosphatidylinositol were the only detectable acyl lipids in the isolated etioplast fractions. Together with phosphatidylethanolamine these were also the major acyl lipids in the whole leaf sections. With increasing age of the leaf tissue, increases occurred in two of the major plastid lipids, monogalactosyldiglyceride and phosphatidylglycerol, while the levels of essentially nonplastid lipids remained constant or declined slightly. The monogalactosyldiglyceride to digalactosyldiglyceride ratio increased from 0.4 to 1.1 in the tissue sections of increasing age and from 0.7 to 1.2 in the etioplasts isolated from them. Similarly, the galactolipid to phospholipid ratio increased from 0.8 to 1.4 in the tissue and from 0.5 to 4.5 in the isolated plastids. In the latter, the proportions of phosphatidylglycerol (as a per cent of total phospholipid) increased from 20 to 41% with increasing age of plastids.

Linolenic acid was the major fatty acid in the total lipid of each of the etioplast fractions, but it was only the major fatty acid in the total lipid of the oldest leaf tissue. Its proportion in both total lipid extracts and individual lipids increased with age. The trans Δ³ hexadecenoic acid was absent from all lipids. The protochlorophyllide content of the tissue increased with age. The results are discussed in relation to the use of illuminated etiolated leaves for studying chloroplast development.

     

Composition and positional distribution of fatty acids in polar lipids from Chlorella ellipsoidea differing in chilling susceptibility and frost hardiness

The composition and positional distribution of fatty acids in the polar lipids from 4 strains of Chlorella differing in chilling susceptibility and frost hardiness were analyzed by enzymatic hydrolysis and gas-liquid chromatography. Analysis of the polar lipids from chilling-sensitive, chilling-resistant and chilling-sensitive revertant strains of Chlorella ellipsoidea IAM C-102 showed that the sum of palmitic and trans -3-hexadecenoic acid in phosphatidylglycerol (PG) is about 60% for the sensitive strains and 53% for the resistant strain. The sum of dipalmitoyl and 1-palmitoyl-2-( trans -3-hexadecenoyl) PG as estimated from the positional distribution of their fatty acids, is about 10% in the case of each of the three strains. The contents of unsaturated fatty acids in phosphatidylcholine (PC) and phosphatidylethanolamine (PE) were higher in the resistant than in the sensitive strain. This suggests that unsaturation of fatty acids in not only PG but also PC and PE is involved in chilling sensitivity of Chlorella . On the other hand, lipid changes during the development of frost hardiness of C. ellipsoidea IAM C-27, a frost hardy strain, were examined. The results showed that fatty acids in most lipid classes are unsaturated in the hardening process but their degree of unsaturation is not greatly different from that of the chilling-resistant strain, suggesting that not only unsaturation of fatty acids in lipids but also other factors are necessary for the development of frost hardiness.     

A simplified isolation of phosphatidylglycerol

A two-stage, thin-layer chromatographic technique for the unequivocal separation of phosphatidylglycerol (PG) from other leaf glycerolipids is described. The method takes advantage of the partitioning of PG into petroleum ether from acidified aquous methanol and of its high chromatographic mobility on acidified adsorbents. Although particularly suited to the analyses of fatty acids in PGs from diverse leaves, the technique may also be used preparatively. The high content of saturated fatty acids within the PG of C4, dicotyledenous plants but not of C4 grasses is confirmed. Hexadeca-trans-3-enoic acid was absent from the leaf PG of all of the orchid species analysed.     

The lipid composition of the non-photosynthetic diatom Nitzschia alba

The lipid composition of the non-photosynthetic marine diatom, Nitzschia alba, has been quantitatively determined. Triglycerides accounted for 20% of the cell dry weight and 87% of the total lipids. Smaller amounts of 1,2- and 1,3-diglycerides, free sterol (24-methylene cholesterol), hydrocarbons and an unknown component were the remaining neutral lipids detected. Phosphatidylsulfocholine (phosphatidyl S,S-dimethylmercaptoethanol), present in amounts of 0.8% of cell dry weight (35% of total polar lipids), was the major polar lipid component. Other phospholipids were lysophosphatidylsulfocholine, phosphatidylglycerol, phosphatidylinositol and cardiolipin, but both phosphatidylcholine and phosphatidylethanolamine were completely absent. Another novel sulfolipid, deoxyceramide sulfonic acid, as well as the sulfate ester of the free sterol, were also present. Considerable amounts of the four lipids often associated with photosynthetic organisms, mono- and di-galactosyl diglycerides, sulfoquinovosyl diglyceride and phosphatidylglycerol, were identified in N. alba. However, the fatty acid components of the glycosyl diglycerides did not show the high amounts of polyunsaturated acids (18 : 2, 18 : 3) normally found in photosynthesizing organisms. All polar lipids were found to be associated with various cell membrane fractions in N. alba.     

Combination and positional distribution of fatty acids in lipids from blue-green algae

The main glycerolipids (monogalactosyl-, digalactosyl-, sulphoquinovosyl diacylglycerol, phosphatidylglycerol) from five blue-green algae (Microcystis, Anabaena, Nostoc, Oscillatoria, Tolypothrix) were analyzed for fatty acid composition, occurrence of diglyceride species and positional distribution of fatty acids between thesn-1- andsn-2-position of glycerol. In contrast to eucaryotic plants biosynthetically closely related lipids (monogalactosyl-, digalactosyl-, trigalactosyl diacylglycerol) show nearly identical diglyceride moieties, whereas sulphoquinovosyl diacylglycerol and phosphatidylglycerol are separated from galactolipids by composition as well as occurrence of fatty acids. On the other hand the positional distribution of fatty acids in all lipids is controlled exclusively by chain length and not by degree of unsaturation with C₁₈-fatty acids at thesn-1- and C₁₆-fatty acids at thesn-2-position. These results show that in procaryotic organisms the diversity in diglyceride portions of lipids is reduced as compared to eucaryotic organisms, but nevertheless does exist.Abbreviations MGD, DGD, TGD, SQD monogalactosyl-, digalactosyl-, trigalactosyl-, sulphoquinovosyl diacylglycerol - PG phosphatidyl glycerol     

Effects of Substituted Pyridazinones (San 6706, San 9774, San 9785) on Glycerolipids and Their Associated Fatty Acids in the Leaves of Vicia faba and Hordeum vulgare

The fatty acids of the major glycerolipids from the leaves of Vicia faba and Hordeum vulgare plants treated with three different concentrations of pyridazinone derivatives were analyzed. These compounds showed multiple effects on the levels of lipids and pigments. At low concentrations, the primary effect of San 9785 was on the level of linolenic acid (18:3) in the galactolipids of V. faba, whereas the effect of San 6706 was primarily on the trans-Δ³-hexadecenoic acid (16:1) content in phosphatidylglycerol. At higher concentrations, the two compounds reduced the content of both fatty acids in the leaves. The results appear to indicate a differential effect of these herbicides on fatty acid accumulation and a difference in susceptibility of two fatty acids in the species examined. Electron microscopic studies revealed that two herbicides caused different abnormalities in V. faba chloroplast ultrastructure.     

Influence of salt concentration and temperature on the fatty acid compositions of Ectothiorhodospira and other halophilic phototrophic purple bacteria

Influences of the salt concentration on the fatty acid composition of Ectothiorhodospira species and other phototrophic purple bacteria have been analysed. Major fatty acids in bacteria of the genera Rhodobacter, Rhodopseudomonas, Chromatium, and Ectothiorhodospira were straight chain saturated and monounsaturated C-16 and C-18 fatty acids. Salt-dependent responses of all investigated bacteria revealed relations to their salt optima. Minimum values of C-16 and saturated fatty acids and maximum values of C-18 and unsaturated fatty acids were found at or close to the salt optima. Responses of Ectothiorhodospira mobilis upon changes in salinity were nearly identical, whether cells were grown in batch culture or in continuous culture with identical dilution rates at all salt concentrations. With increasing temperature, the fatty acid composition of Ectothiorhodospira mobilis and Ectothiorhodospira halophila strains showed decreasing portions of C-18 and of unsaturated fatty acids, while the contents of C-16 and saturated fatty acids increased. The results are discussed with respect to bilayer stabilisation and membrane fluidity.Abbreviations PC phosphatidylcholine - PG phosphatidylglycerol - CL cardiolipin - PE phosphatidylethanolamine     

Introduction of the cDNA for shape Arabidopsis glycerol-3-phosphate acyltransferase (GPAT) confers unsaturation of fatty acids and chilling tolerance of photosynthesis on rice

The chilling sensitivity of several plant species is closely correlated with the levels of unsaturation of fatty acids in the phosphatidylglycerol (PG) of chloroplast membranes. Plants with a high proportion of unsaturated fatty acids, such as Arabidopsis thaliana, are resistant to chilling, whereas species like squash with only a low proportion are rather sensitive to chilling. The glycerol-3-phosphate O-acyltransferase (GPAT) enzyme of chloroplasts plays an important role in determining the levels of PG fatty acid desaturation.A cDNA for oleate-selective GPAT of Arabidopsis under the control of a maize Ubiquitin promoter was introduced into rice (Oryza sativa L.) using the Agrobacterium-mediated gene transfer method. The levels of unsaturated fatty acids in the phosphatidylglycerol of transformed rice leaves were found to be 28% higher than that of untransformed controls. The net photosynthetic rate of leaves of transformed rice plants was 20% higher than that of the wild type at 17°C. Thus, introduction of cDNA for the Arabidopsis GPAT causes greater unsaturation of fatty acids and confers chilling tolerance of photosynthesis on rice.     

An increase in unsaturation of fatty acids in phosphatidylglycerol from leaves improves the rates of photosynthesis and growth at low temperatures in transgenic rice seedlings

The level of cis-unsaturated fatty acids in phosphatidylglycerol (PG) from rice leaves was genetically altered from 19.3% in the wild-type to 29.4 and 32.0% in T1 plants segregated with cDNAs for glycerol-3-phosphate acyltransferase of chloroplasts (GPAT; EC 2.3.1.15) from Arabidopsis (+AGPAT plant) and spinach (+SGPAT plant), respectively; and to 21.4% in a non-transformant segregated from +SGPAT plants (-SGPAT plant). In all these plants, O2 evolution from leaves was similar at 25 degrees C and was impaired to a similar extent at 5 and 11 degrees C. However, in parallel with the levels of cis-unsaturated fatty acids in PG, +AGPAT and +SGPAT plants showed less impaired rates of O(2) evolution from leaves than the wild-type and -SGPAT plants at 14 and 17 degrees C. In agreement with this, the fresh weight of 14-day-old seedlings increased to 571 + or - 18, 591 + or - 23, 687 + or - 32 and 705 + or - 31 mg in the wild-type, -SGPAT, +AGPAT and +SGPAT plants, respectively, after 6 weeks at 17/14 degrees C (day/night). These results demonstrate the practical importance of the present technology with GPAT in improvement of the chilling sensitivity of crops.     

Genomic and biochemical analysis of lipid biosynthesis in the unicellular rhodophyte Cyanidioschyzon merolae: lack of a plastidic desaturation pathway results in the coupled pathway of galactolipid synthesis

The acyl lipids making up the plastid membranes in plants and algae are highly enriched in polyunsaturated fatty acids and are synthesized by two distinct pathways, known as the prokaryotic and eukaryotic pathways, which are located within the plastids and the endoplasmic reticulum, respectively. Here we report the results of biochemical as well as genomic analyses of lipids and fatty acids in the unicellular rhodophyte Cyanidioschyzon merolae. All of the glycerolipids usually found in photosynthetic algae were found, such as mono- and digalactosyl diacylglycerol, sulfolipid, phosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, and phosphatidylinositol. However, the fatty acid composition was extremely simple. Only palmitic, stearic, oleic, and linoleic acids were found as major acids. In addition, 3-trans-hexadecanoic acid was found as a very minor component in phosphatidylglycerol. Unlike the case for most other photosynthetic eukaryotes, polyenoic fatty acids having three or more double bonds were not detected. These results suggest that polyunsaturated fatty acids are not necessary for photosynthesis in eukaryotes. Genomic analysis suggested that C. merolae lacks acyl lipid desaturases of cyanobacterial origin as well as stearoyl acyl carrier protein desaturase, both of which are major desaturases in plants and green algae. The results of labeling experiments with radioactive acetate showed that the desaturation leading to linoleic acid synthesis occurs on phosphatidylcholine located outside the plastids. Monogalactosyl diacylglycerol is therefore synthesized by the coupled pathway, using plastid-derived palmitic acid and endoplasmic reticulum-derived linoleic acid. These results highlight essential differences in lipid biosynthetic pathways between the red algae and the green lineage, which includes plants and green algae.     

Relationships of leaf Fatty acids to cold hardening of citrus seedlings

Three cultivars of citrus with different sensitivities to freezing temperatures (citron, Citrus medica L.; rough lemon, C. limon Burm. F; sour orange, C. aurantium L.) were cold hardened for 4 weeks. Lipids from leaves of hardened and control seedlings were fractionated and analyzed for fatty acids. The absolute amount of triglycerides and phospholipids increased in the leaves upon hardening. With hardening, total linoleic acid also increased 141% in citron, 210% in rough lemon, and 233% in sour orange. Specific increases in linoleic acid were found in triglycerides, in the four phospholipids (phosphatidylcholine, phosphatidylethanolamine, phosphatidylinositol, phosphatidylglycerol), and in neutral lipids more polar than triglycerides. Trans-3-hexadecenoic acid was found only in phosphatidylglycerol.     

Compositions and Positional Distributions of Fatty Acids in Phospholipids from Leaves of Chilling-Sensitive and Chilling-Resistant Plants

The compositions and positional distributions of fatty acidsin the major leaf phospholipids of phosphatidylglycerol, phosphatidylcholineand phosphatidylethanolamine were analyzed by gas-liquid chromatographyand enzymic hydrolysis, and chilling-sensitive and chilling-resistantplants were comparcd with respect to the relative contents ofpalmitic and trans-³-hexadecenoic acids in the separated phospholipids.A distinct difference between these plants was found in thefatty acid compositions of phosphatidylglycerol, in which thesum of palmitic and trans-³-hexadecenoic acids ranged from 60to 78% of the total fatty acids in 8 species of chilling-sensitiveplants, and from 50 to 57% in 11 species of chilling-resistantplants. The only exception among the chilling sensitive plantsin this respect was the tomato, in which the sum of palmiticand trans-³-hexadecenic acids in phosphatidylglycerol amountedto 54%. The fatty acid compositions and the positional distributionsof fatty acids in phosphatidylglycerol suggest that the occurrenceof high proportions of dipalmitoyl and 1-palmitoyl-2-(trans-³-hexadecenoyl)species in this lipid is correlated with the susceptibilityto chilling of the leaves of higher plants. In the compositionsand positional distributions of fatty acids in phosphatidylcholineand phosphatidylethanolamine, no difference was found betweenthe chilling-sensitive and chilling-resistant plants. ¹ Present address: Department of Biology, Faculty of Science,Universityof Tokyo, Hongo, Bunkyo-ku, Tokyo 113, Japan. (Received May 21, 1982; Accepted June 25, 1982)