Chloroplast Fatty Acid Transformations in Nitrogen-Deficientand Senescent Tissues'
David W. NewmanBotany Department, Miami University, Oxford, Ohio
Received Jtunie 25, 1965.
SInitninary. The 1attv acids of plasti(ls fromii several types of miiineral-deficieint andseniescenit tissues were analvzed. Incorl)oration of acetate inlto long-chain fattv acids ofleaf tisssue and(l of plasti(ls fronmJ nitrogen-deficient and(l niormal plants was (leterminie(l.In general, the seniescenlt anid nitrogen-deficient cilloroplasts conitainedI a higiher ratio ofsaturates to unisaturates than (lid plastids fromi younlger tissues an(l from tissues grown onal complete niutrienit.
Nitrogen-deficient leaf tissue calnd plastids weri capable of ralidlly incorporating ace-tate inlto soonic of the fatty acids, esplecially palmitic ail(l oleic acids. However, the coiln-arative rate of -cetate incorl)oration inito linolenic acid in nitrogenl-deficient chlorophyll-
ouIs tissue was less thani in tisstie grown oni a complete nutrient. With the addi,tion otUDI'-glucose to a reictioni mixture conltaininiig ad(led cofactors for noncyclic photosvn-thetic phosphorylation the relati-ve incorporation of acetate inito liniolenate as comliparedto palmiiitate wvas inicrease(d in both the niitrogen-deficienit anld niormal leaf tissue. Thi swould in(licate that nlitrogenl-deficient tissues have the enlzvmllic systemns for forminig long-chaini fatty acids but that the reduced photosvnthesis limlits the amoulnt of precursors forhlie formiiationi of lipids, esl)ecially galactolipids. However, iothinig is knioxv-n about ther'ate of fatty aci(d (legra(latioln tundler these conditionxS.
Chloroplasts of leaf tisstue grown under condi-tionls favorable for photosvynthesis often con-ltainl pro-portionately more tilusaturated fatty acid materialthani do chloroplasts of leaves grownl uli(ler cond(litionistinfavorable for photosvynthesis (3). Eilvirollmen-talcon(ditionis which tenid to cauise a comparatively re-(duice(l amiiouint of uilnsa,tturated fatty aci(ds, especiallylinolenic, wvithin the chloroplast iliclu(le: (larkiness(4, 16, 17, 22), ironl-deficient niutrienit (14, 15), initro-gen-deficient ntutrient (22), and(I main-ganlese-(leficientnutrieint (2). Ill addlitioni, as chlorophvllous tissuesaage a redtuction inh the relative amlotuit of plasti(dtillisattirate(l fatty aci(d material occurs. Occasionally,wx e have inotice(d that this alpl)arelt redtcctioll ill 1111-saturate(l fatty aci(ds (loes nlOt occuir tinilder the above-niieIitiolie( coln(litionis. 11 owever, since the relation-slhi) between (levelol)melltal changes and(I fatty acidcoml)osition of chlorophyllous tissuies is niot wellunderstood, (diffictifties arise ini inlterl)retation of tllein formation. Il'rtlher it is not known why the (lar-k-treate(l, iniieral-deficielt, or senlescenit plastids conitaillrelatively less of the tinsaturates, eslpecially linolenate.
Two alplpro,aches were miiade: A ) a, limite(d survevwas nla(le of plasti(l fatty acids fromii chlorophvlloustissties of variouts ages anld B) the comparative ratesof acetate-2-C 4 incorporatioon inlto long-chaini fatty
Supported by National Scicence Foundation GrantGB-2717.
acids were (determinie(d. T'he survey consisted of de-termininig p)lasti(l fatty acidIs: A) of squiash and oatleaves sampled at various times dturing developiment,1B) of green and yellow decidtiouts tree leaves (ltlringthe tlime of auitumnlllal colorationi, and(1 C) of nlitrogen-leficienit s(qtiashi leaves a5. well as of squash leavesfromil plan)ts grownl on a comlplete mineral lntitrienit.Th'e rate of acetate-2-C'1 4 incorporation inlto thefatty acidls of nitrogen-dleficient an(ol normal plastidsfr-omil votigil alnd seniescent tissues was (leteriille(l.In somle procedures leaf discs were used, in otherlprocedures plastids wN-ere stispenided in a reaction milix-ttire colntaininig a complete set of cofactors for nioni-cyclic photosynitlhetic phosphorvlation.
Materials and Methods
1J1Iaot (liateria! (ad Pla)/sti Isol(itioni. Thliree (lif-fer-ent l)roce(llures w\,ere used in isolating chloroplasts:A ) Il'lastids released from about 85 , of squashC 'oi t,rbila iaxMiani D)uchesne, \var. Burpee's 1ilute
IHI ubbard ) or oat ( Ieiia sati.a oL. ) leaves wereisolated in the cold 1by differential centrifutgation.'I'he plasti(ld were release(d with a W\aring blendorin 2 X volutme of cold 0.35 ii NaCl theni filteredIthrouglh 3 layers of cheesecloth. The fraction sedi-mentinig between 200 and 1000 X g was collected,washed, anid recentrifuged. The fraction sedimentingbetween 200 and 1000 X g was againi collected andtised as the lplastid fraction. Isopropanol was ad(led
to the sediment and the mixture boiled for 2 minutes(9). After cooling the mixture was stored underniitrogen in the cold. B) The plastids from leavesof yellowwood ( Cladrastis lutte(a Koch), Ginikgobiloba L., sugar maple (Acer saccharumt Marsh), anidred oak (Quiercuts borealis Michx.) were releasedin 2 X volume of cold 0.35 M NaCI. About 85 gof leaf material was used. The homiiogeniate wasfiltered through 4 layers of cheesecloth without press-ing and the filtrate was cenitrifuged at 1000 X g forI minlutes. The sediment was resuspended in a smallvolume (ca. 40 ml) of cold 0.4 AI sucrose. 0.01 MdrTris HCl buffer (23) and recentrifuged at 150 X g.The supernatant fraction, containing the plastids, wascarefully collected, added to 200 ml of isopropanol.and the mixture boiled for 2 minutes. The mixturewas stored overnight under nitrogen in the cold.The above procedure was found suitable for recoveryof comparatively clean plastid isolates of the treeleaves, whereas the first-mentioned procedure wassuitable for isolatinig plastids from squash and oatleaves but not for isolating plastids from the treeleaves. The heavy cuticle and more generallv stiffcharacter of the tree leaves made the release ofwhole plastids more difficult. C) Lettuce (Lactucasativa L.. var. Burpee's Ruby Red) plastids wereisolated in 0.5 M sucrose containinlg 0.1 M NaCl, 0.04 Msodituml ascorbate, 0.01 M potassium phosphate buffer(pH 7.2), anld 0.01 m EDTA (21). These plastidswere used for acetate incorporation studies.
Reactioni. Alixttures. Two reactioln miiixtures wereuised in the studies inivolvinig the incorporationi of ace-tate-2-C'1 into fatty acids: A) Squash leaf discs werereacted in 250 mil flasks in a water batlh mainitainledat 20.30. Each flask conitaine(l 10 ml of 0.2 AI phos-phate buffer (pH 7.4), 300 unimoles of sodiumii bicar-bonate, 1 mil of aqtueotus acetate-2-C' 4 ( 10 Ac/11l:specific activity, 20 miic/immlole), anid 50 leaf discs 1cnm in diamiieter. Prior to placing the flasks in thewater bath the contents of each flask were aspiratedto cause inifiltration of the reaction ilmixtture inlto theleaf discs. Otherwise, very little inlcorporation wasobtained. Some flasks were exposed to 1300 ft-cinitensity inicandescenit light, others were imiainitainedin the dark durilng the reactioln time, 30 miniutes to30 hours. At the enid of the reaction timiie. the leafdiscs were rinsed with distilled waiter, boiled for 4 mini-utes in 150 ml of chloroform-methanol (2: 1, v/v),stored under nitrogen for 12 hours, and finially re-extracted while grilnding. B) Lettuce chloroplastswere reacted for 1 to 2 hours in 15 ml capacity, rec-tangular Warburg flasks at 20.30. The ireactionmixture contained the following constituenits in,umoles: ADP, 6.6 in 0.1 M phosphate buffer (p1i6.8); *NADP, 9.9; CoA, 0.63; Mg504, 7.92;NaHCO1, 95: the mixture also conitained phosplhatebuffer, 0.3 M pH 8.2; sodium acetate-2-C'4, 2 ,uc (spe-cific activity. 20 mc/mmole) ; chloroplasts. 2 mgchilorophyll per flask for most of the flasks.The total volumiie was 3.7 ml. Soome flaskswere illuminiated (1300 ft-c) ; others were maintained
in the dark. Following the incubationi. 0.2 ml of0.1 N KOH was added to each flask and the contenitsallowed to stand for 2 minutes. Then 1.0 ml of 5N H2SO4 and 25 ml of c1hloroform-methanol (2:1.v/v) were added to each flask and the contenits boiledfor 3 minutes (20).
G(s Chlroinatography. The plastids or leaf discswere exhaustively extracted either with isopropanol-chloroformi mixtures or with methaniol-chloroformmixtures. The extract was passed several timesthrough a layer of water containling smiiall amounitsof Ho SO,. The washed extract was evaporated(600, NT), taken up in 4 ml methanolic HCl (2.5 %.v/w), and refluxed for 2 hours. The procedure ofKates (10) was followed in order to prepare themethyl esters for gas chromatography. The fatty acidmethyl esters were chromatographed in a 10-footcolumn of 15 % DEGS on HMDS-treated Chromo-sorb \V operated isothermally at 185°. The thermalconductivity detector was calibrated usinig purified,standard conmpounds. Samples were furtFher chro-matographed in Apiezon L onl Chromosorb W as anaid in identification.
CoIl1ntintg. The separated compounds were col-lected in cooled U-tubes conitaining hexanie-saturatedglass wvool; the contenlts of each collector were rinisedinto 20 ml liquid-scinitillatioln counitinig vials. the sol-venit evaporatedl, aiid( a dimiethyl-POPOP PP(P)liqui(l scintillator added. Tlhe counting efficiencywas about 57 % for C14.
Results
Fatty ticids of Agbing Oat atid 5q(slih Plasti(ls.Plastidls were isolated from first-node squash andoat leaves over a 4-week period (fig 1). The ratio
0.22[C0
0.201
SAT.UNSAT 0.18_
0.16- 00
0.141
0.12
2 3 4WK
FIG. 1. Ratios of saturated to unsaturated fatty acidmaterial of squash (solid line) and oat (brokeni line) leafplastids isolated at various stages of leaf development.The oat leaves used for each harvest represented newvgrowth sinlce the last harvest. The first harvest wvasmade 13 days after planting. The plants were grown ona 20-hour photoperiod in a plant-growth room maintainedat about 280 during the light period anid at about 210during the dark period.
of sa-turated to unsaturated fatty acid miiaterial inthe squash plastids increased with increasing age ofthe tissue. This is in agreement with previously-obtained results (14). However, the ratio of satur-ated to unsaturated fatty acid material in the oatplasti(ls declined duiring the several weeks of growtlh.
Fatty Acids of Sentescent Tree-Leaf Plastids.Fatty acids of plastids which were isolated fromii de-ciduous tree leaves collected during the transitionl)eriod at the timiie of autumnal coloration wereanialyzed (table I). Separate batches of compar-atively greeln and of yellow leaves were collected atthe samiie time and fromii the same tree of each par-ticular species sampled. There was variation in thetotal amiiount of plastid material released per uilit leafmiiaterial. In all 3 species the plastids of vellowleaves contained a lower percentage of linolenic acidtlhani did the plastids of corresponding greeni leaves.Since linolenic acid is commonly the miiost abundantunsaturated fatty acid within the plastid, the yellowleaves had a higher ratio of saturated to unsaturatedfatty acids.
Effects of ANitrogen-Deficiency oil ChloroplastFatty Acid Comiposition. Since nitrogen supply af-fects the synthesis of RNA, it was thought that per-haps by withhol(dinig nitrogen the synthesis of RNAwould be reduced and the rate of leaf tissue agingwould be accelerated. Generally, the nlitrogen-de-ficient plastids contained a higher percentage ofpalmitic acid (table II). The nitrogeni-deficienltplastids from the first- and second-node leaves of thefirst harvest, prior to adding niitrogeni to the iiti-trienit, containe(I relatively less linoleinic acid andhence the ratio of satturated to uinsaturated fattvacids wvas higher in these plastids. After the addi-tionl of nlitrogen-conltaininlg nutrienit to these niitro-gren-deficient plalnts, the first- alnd seconid-niode plas-tids still containied relatively less linolenic acidl.However, the plastids isolated from the sixthl-iodeleaves of these planits containled about the same per-centage of linoleniic acid as did the plastids of plantsmiaintained on complete nutrient for the full period.'Fhe sixth-node leaves developed after niitrogen wasprovided to the niitrogen-deficient plants.
Table I. Fatt, Acid Comitposition of Deciduouts 7rec-Lcaf PlastidsFree fatty acids were separated from esterified fatty acids after the addition cf 1 % aqueous sodiunm carbounate to
the fatty acid mixture dissolved in diethyl ether-petroleum ether-95 % aqueous ethanol (70: 70: 25, v/v). The non-polar layer was washed with 1 % aqueous sodium carbonate and then with water. The combinied aqueous layerwas acidifie(d and the fatty acids extracted.
C12 C14 C16 C18
2.1 5.9 13.5 2.0
... 3.5 16.8 4.2
9.9 4.3 20.2 7.8
8.5 70.1 21.4
10.() 9.1 23.9 4.3
23.3 14.7 44.1 17.6
12.8 19.2 17.2 6.4
10.1 9.3 24.9 4.1
3.6 6.6 18.2 3.6
6 5 7.7 70.9 9.2
2.5 7.9 31.2 2.3
3.9 13.5 21.3 3.1
25 3.8 22.7 5.4
0.4 1.8 29.9 4.4
('20 C15* C17 C19Mole /c
.... ... 4.7
1.4 ... 4.8 4.3
3.3 .2 ......
C16: 1 C18: I C18: 2 C18: 3Total
,,nmoles/25 g**
Satuirated /unisaturated
imiaterial
... ... /.7 64.1 13.5 0.39
.7~i 8.8 2.3 48.4 3.1 0.54
1.8 14.5 4.9 28.0 1.5 1.03
0.1
~~~~~~~.......0.(.... 8.9 4.0 34.i' 0.6 0.'92
........ ... ... 0.03..
4.7 7.9 7.5 2.0
1.6 4.4 2.7
.. 3.1
1.3 9.5 4.6 7.0 4.6 3.47
4.4 11.6 5.8 21.1 2.2 1.33
1.8 6.0 7.9 49.1 2.1 0.54
3.1 2.7 ... ...... ... 0.3
2.6 0.7 2.3 6.4 5.7 38.4 2.1 0.90
.... ... 1.1
0.3 4.1 ......
... 1.1 ......
* The identification of odd-numbered fatty acids was based
1.9 6.7 7.4 41.1 1.3 0.75
2.6 7.8 7.6 43.2 2.0 0.64
2.9 10.2 9.1 40.1 0.3 0.60
only on retention volume. These compounds may behydrocarbons.
** 25 g of leaf material, wet weight.*** EFA, esterified fatty acids; FFA, free fattv acids fromii greeli or vellos leaf plastids.
Acetate-.2-C'4 In1Corporatiotn inlto tile Fatty Acidsof Noruzn,l and Nitrogen-Deficient Leaf Discs. Itcan be seen from table III that the cotyledon andleaf plastids fromli niitrogen-deficienit tissues had ahigher ratio of satutrated to unisaturated fatty acids.Anid, as woul(d he expected, the saiime was true forthe whole-leaf miiaterial (table IVT). Durinig a 1-
hour reaction period, the leaf discs froimi planitsgrown on complete nutrient incorporated more ace-tate-2-C14 into linolenic acid, as compared to incor-poration into palmnitic acid, than did the leaf discsfromii niitrogeni-deficielnt planits (table V) ; althouglthe nitrogen-deficient leaf discs were capable ofrelatively active inicorporationi as compared to the
Table II. Fatty Acid CouiLPositiont of Squa(lsh I'lastids Isolatcd from NitrogiCi-D)ficicn1lLeaves and fromn Leaves Grozn on Comitpletc Nutr;ient
The i)lallts were grown in vermiculite and leaves were collected at 27, 42, and 62 days after planitinig. After 27days, the niitrogen-deficient plants were irrigated with complete nutrienit.
Sample Node Harvest
Complete 1 1- N 1 1Complete 2 1- N 2 1Complete 1 2- N 1 2Complete 2 2- N 2 2Complete 6 2-- N ( 2Complete 6 3- N 6 3Complete 9 3- N 9 3
leaves of planits given com)plete nutrienit. The great-est amount of activity was found in plalmitic anidoleic acids. James (8) also found this.
In ani attempt to determine the rate of acetate-2-C14 ilncorporation into the various leaf fatty acids,leaf discs were allowed to remain with the acetate fordiffering l)eriods of timiie, following which the fattyacids were anialyzed (tables VI, VII ). T'he (lisesfronm leaves growni oni complete niutrielnt containedmuch more fatty acid material per unlit surface area.Conisequenitly, these leaf discs incorporated imiuclhmore acetate-2-C 4, for ani equivalenit specific activity, than did the nitrogen-deficienit leaf (liscs re-acted for a corresponidinig period of timiie. In the
discs fromii leaves grown oni a comiiplete niutrienit, thespecific activity of C14 in each fatty aci(d ilncrease(dwith increase(d time of reactioni. The ratio of specificactivitV of l)almitate to that of linolenate decreasedlwith inlcreased timiie of reactioni. However, the ratioof sp)ecific activ ity of l)almitate to that of lilnoleinateof the nitrogen-deficient leaf discs did nlot decreasesignificantl- with inicreased timiie of reactioni. It ap-pears as thouglh there Nx-as a comparatively ral)i(l ill-corl)oration in the nitrogen-deficient leaf discs, fol-lowed 1v either a decrease or onlly moderate increasein the specific activity.
Acctafte Incorporation itlto Isolated Lettuce-LeafC(iloroplasts. Results of the fatty acid analyses are
Table V. A1ceft tc Incorpor ationt ijnto prcdominant Fatty Acids of Sqnalsli Leaf I)isesfrom N'itroycnI-DeficieCnt PIlats and froiii P/omits Gro-zcit ott C'omiplete ANntrie'n1t
The leaf discs wvere reacted for 1 hour in 10 ml of phosphate buffer (0.2 -m, pH 7.4) containing 300 juiolessodium bicarboniate and 10 ,uc acetate-2-C'4.
Samnple
CompleteC(omplete- N
NConipleteComplete
NN
Node Light*
33
28-108-104-54-5
+-
±
+
Cli: 1
2572573
5556378210772309943745259
cpnti
2680591
5587358111321169646284072
C18: 3
27893
523277
3308,;
718638
Total
87032166
16(638127843874974741496615474
Activity,palmiticlinolelnic
9.36.2
10.613.73.35.66.18.2
-11corp)oration in the lighit as opposed to inlcorl)oration in thle (lark.
Table VI. Liqlmt Ittcorporation of Acetate intOtt lFatt . Icids of Sqimaslit Leaf I)iscs front.'itrogctn -Dcfcicint Plants attd fromt Plants Grown ot (IIompletc 'utricnt
The inicubationi time varied from 30 miniiiutes to 30 hours.
C14 C16 C18 C16: 1 C18: 1 C18: 2Reaction.
time
30 m,in 3.5 9.25 hr 37 75
30 hr 80 20130 miii 17 22hlir 27 20
30 hr 37 61
Specific activity, cpm/nglmole8.5 9.6 44
25 192 209119 572 28631 123 10016 36 7349 167 130
7.384276122750
C18: 3 Activity,- - p-lalmitic
linolellic0.3 318.5 8.8
45 4.51.6 141.8 114.9 12
Table VII. Dark Imtcorporatiomt of Acetatc inlto Pa-tty Acids tf Sqtislst Lctf l)ises frotttNitrogenl-Deficientt Plants antd frontl Plattts Grownt ott Comtipletc NiVtmtrietmt
The reactioni time varied from 30 minutes to 30 hours.
IReactionSample time
Comnlete 30 mini 4.1
Complete 5 hr 20Complete 30 hlr 26- N 30 mnii 8.1- N 5Slr 33- N 30 lir 27
Table VIII. Fatty, Acid Coniipositioni antd Acetate Incorporation int the Light into FattyAcids of Nitrogen-Dcficient Plastids antd Plastids of Lettuce Leaves
Grotwn, oni Complete NutrientLeaf material was harvested 53 anid 64 days after planting. The plastids were reacted for 2 hours with acetate-
2-C' 4 and added cofactors.
C12 C14 C16 C18 C16: 1 C18: 1 C18: 2 C18: 3
Sample Harvest
Complete 1- N 1Completelowernodes 2- N lowernodes 2Completeuppernodes 2- N uppernodes 2
given in table VIII. Light incorporationi was about10 to 20 times that in the dark (not reported in thetable). The nitrogen-deficienit leaves displayed vis-ible s mptomiis of the deficiency-reduced size and(1marked inicrease in anthocyanini productioni. Lettucechloroplasts, in genieral, seemiied to have more linoleicacid anid a greater number of trace comlponielnts, nlotreported here, thani did sqtuash l)lastids. The iiitro-gen (leficienicy did niot seemii to lhave a marked ef-fect oni the ratio of saturated to unsatturate{d fattyacid miiaterial. These anialyses have been repeatedseveral times anld we have founid this to be true ineach case. However, the niitrogeni-deficient leavesdid conitain a higher percentage of palmiitic acid anida lower percentage, in general, of linlolenic acid. Thenitrogen-deficien,t plastids had a higher ratio ofsl)ecific activity in palmiiitic acid to specific activityin linolenic acid. Durinig the reaction period tllera(te of acetate inciorporation inito linioleniic acid, withrespect to the rate of incorporation into palmitic aci(l,Nvas niot as rapid in nitrogen-deficient plastids as inp)lastids isolated fromii leaves grown oln comiiplete lntu-trient.
Table IX. Acetate Incorporation in1to Fatty Acids ofNitrogen-Deficient Plastids and Plastids of Lettuce
Lea;ves Grown on Com1plete NutrientSome of the reaction mixtures contained UDP-glucose
(6.6 ,umoles per flask) in additioni to chloroplasts, acetate-2-C14, and added cofactors. Samples were reacted in thelight and in the dark.
Sample Light UDP- Specific activity,glucose palmitic/linolenic
Some lettuce chloroplasts were reacted withUDP-glucose added (table IX). The addition ofUDP-glucose to the reaction mixture increased theincorporation of acetate into linolenate with respectto that into palmitate. The plastids grown oni coinl-plete nutrient h.ad a higher incorporationi of acetateinto linolen,ate, with respect to that into )almitate,thiail did the nitrogeni-deficienit plastids. The ratioof specific activities of palniitate to linoleniate of tllel)lastids grown oni complete niutrienit withonit UD)P-glucose added to the reaction mixture was about thesamiie as that of nitrogen-deficienit plastids with UDP-glucose added to the reaction miiixture.
Discussion
The syntlhesis of fatty acids inl higher-plaint chloro-phyllous tissues is associated with the chloroplast( 11 ). The synthesis appears to proceed by way of themlaloniyl CoA pathway (12). Acetate incorporationinto chloroplast fatty acids seems to depenid tiponlNADPH, ATP, and O; wlhereas ATP alone doesnot stimulate acetate incorporation into the chloro-plast fatty acids (21). Long-chain saturated fattyacids, such as palmitic and stearic, are formed fromlower-chain precursors by the addition of C2 units.Formation of tihe abundant long-chain unsaturatedfatty aci,ds, oleic, linoleic, and linolenic, does notoccur from a desaturation of the corresponding satu-rated fatty acid, stearic. The precursor(s) of oleic,linoleic, and linolenic acids may very well be C12or C14 acids. However, Chlorella is able to use pal-mitic and stearic acids as precursor for oleic acid(6). The synthesis of the unsaturated acids ap-
pears to be an oxidative desaturation coupled witlhchain lengthening (8, 19). It is important to notethat in green leaves, linolenic acid is apparentlysynthesized much more slowly than oleic acid (8).
lBeinsoin (1) hias si-gested that galactolipids mavy be
desaturated while absorbed in the quantasomlies of
the laniiellac structure. Perhaps oleic acid is syn-thesized rapidly and formled as the free acid or CoAester, hut the synthesis of linoleinic acid occnrs l)X
desatiraltion of oleic aci(l, l)y wa of liiioleic acid (5),011v a fter t1e acid is combinied w-ith an intermiediateor is esteri ied an(l l)ecomles a part of the galacto-lipid. 'T'he rate-limiting factor could be the abund-aiice of available hexose-conitainillo illtermne(liate.Nenfel(d and(I 1-hall (13) foundl that isolated spinaclhchloroplasts cotild catalvze the transfer of UDn --
galactose C' to ani endogenous acceptor. 'lTheyfounid some of their products to have similar clhro-matograp)hic mobilities to those of digalactosyl distear-in ani(l miono-galactosvl disteariln. owever. thenatural galactolipids often contain over 90 % linolenicacid ( 18).
It appears that often senescent plastids and mim-eral-deficient plastids may contain relativelv lesslinoleniic acid as compared to younger plastids or
plastids grown on conmplete mineral nlutrienit. Cer-tainly, sufficient information is not available to sug-gest that this reduction in linoleniic acid in chloro-phyllous tissues durilng senescenice is universal. Ap-parently the total and relative fattv acid content ofchlorophvllous tisstues may varx wvidely dependinigpl)ofl the coniditionis uniider hihll the tissue is growni.
Nitrogen-deficient plastids ofteni containi less linoleni-ate w'itl respect to palmitate as comiipared to plastidsgrown on1 complete nutitrienit. Sinice palliitic anidlinolenic acids are the most abundanit saturated andtinisaturated fatty acids withlin the plastid, the ratioof these 2 fatty acids mav be an index of the activitvof the 2 pathways for the synthesis of saturated all(l
unsaturated fatty acids.The nitrogen-deficient plastids are capable of
long-chain fatty acid synthesi s if )rovidledl vitlh ace-tate hut (1o not accumlutilate linolenic acid to the samiie
extent as do lplastids growvn onl comiiplete nutrienit.
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