DECARBOXYLATION STUDIES OF GLUTAMATE, GLUTAMINE, AND ASPARTATE FROM BRAIN LABELLED WITH [1-14C] ACETATE, l-[U-14C]-ASPARTATE, AND l-[U-14C]GLUTAMATE

Studies in vivo and in vitro of the distribution of label in C-1 of glutamate and glutamine and C-4 of aspartate in the free amino acids of brain were carried out. [1-¹⁴C]-Acetate was used both in vivo and in vitro and l -[U-¹⁴C]aspartate and l -[U-¹⁴C]glutamate were used in vitro.

• 1 The results obtained with labelled acetate and aspartate suggest that CO₂ and a 3-carbon acid may exchange at different rates on a CO_a-fixing enzyme.
• 2 The apparent cycling times of both glutamate and glutamine show fast components measured in minutes and slow components measured in hours.
• 3 With [1-¹⁴C]acetate in vitro glutamine is more rapidly labelled in C-1 than is glutamate at early time points; the curves cross over at about 7 min.
• 4 The results support and extend the concept of metabolic compartmentation of amino acid metabolism in brain.

     

Decarboxylation and Transport of Auxin in Segments of Sunflower and Cabbage Roots. II. A Chromatographic Study Using IAA-1-14C and IAA-5-3H

The polar movement of IAA has been examined in 5-mm root segments of Brassica oleracea and Helianthus annum. The movement was studied partly with IAA-1-¹⁴C and partly with IAA-5-³H. In both plants a slight acropetal flux of ¹⁴C and IAA-³H was found through the segments. The recovered radioactivity in the agar receiver blocks and in the receiver end of the segments increased as a function of time. A large portion of the applied IAA was converted on the cut surfaces and in the tissues of the segments. Chromatographic analysis indicated different destruction products when estimated by scintillation counting and by spraying with in-dole reagent (DMCA). Chromatograms run in isopropanol: ammonia: water, 8:1:1, yielded three different substances, one spot near the starting line and one near the front, neither of which has been identified. Finally there was a spot with R_f 0.4–0.6, probably representing IAA.     

STUDIES WITH MURINE LPC-1 PLASMACYTOMA USING [6-14C]ARGININE

[6-¹⁴C]Arginine ([6-¹⁴C]Arg) was used as an in vivo pulse label to study BALB/c murine LPC-1 plasmacytoma synthesis and secretion of its tumour-associated M component (IgG2a, k). With this isotope, an eight- to ten-fold enhancement in the labelling of the γ globulin region and ten-fold reduction in the albumin labelling were observed. Production and secretion of the M component was detected (within 30 min) after cell transfer. Only mice which received tumour cells showed significant labelling in the γ globulin region 24 hr after isotope injection. The labelling behaviour of the tumour M component correlated with the administered cell dose. The peak heights of radioactivity in the γ region increased with increments in cell number. When the percentage radioactivity diverted into M component was plotted as a function of cell dose, a linear relationship was noted. This study demonstrates the feasibility of using [6-¹⁴C]Arg as a tool to follow the newly synthesized tumour-associated protein, and provides a means of estimating tumour cell number.     

THE BIOSYNTHESIS OF CHOLESTEROL AND OTHER STEROLS BY BRAIN TISSUE: DISTRIBUTION IN SUBCELLULAR FRACTIONS AS A FUNCTION OF TIME AFTER INJECTION OF [2-14C]MEVALONIC ACID, SODIUM [2-14C]ACETATE AND [U-14C]GLUCOSE INTO 15-DAY-OLD RATS

The distribution of [¹⁴C]-labelled material into subcellular fractions of 15-day-old rat brain was studied at 2 and 24 h following intraperitoneal and intracerebral injection of [2-¹⁴C]sodium acetate, [U-¹⁴C]glucose and [2-¹⁴C]mevalonic acid respectively. The total quantity of labelled isoprenoids in the brain was, except for glucose, greater when the precursor was administered intracerebrally. The intraperitoneal route was more advantageous in the case of [U-¹⁴C]glucose. The subcellular distribution of both labelled total isoprenoid material and sterol was distinct for each labelled precursor. Intracerebrally injected [U-¹⁴C]glucose at both time periods studied suggested no dominance of labelling in any fraction. After intraperitoneal injection of [U-¹⁴C]glucose the microsomes were more prominently labelled. Both methods of administration of sodium [2-¹⁴C]acetate resulted in heavy labelling of the myelin fraction after 24 h. The total labelled isoprenoids resided mainly in the microsomes 24 h after injection of [2-¹⁴C]mevalonic acid. Labelled sterol was found to be localized more in the myelin and microsomal fractions for all three precursors than was the labelled total isoprenoids. Depending on the type of experiment to be conducted, each of these precursors can give different results, which must be interpreted accordingly.     

CONVERSION OF [1-14C]PALMITIC ACID TO [1-14C]HEXADECANOL BY DEVELOPING RAT BRAIN CELL-FREE PREPARATIONS

—The conversion of [l-¹⁴C]palmitic acid to [1-¹⁴C]hexadecanol has been demonstrated with a cell-free system from developing rat brain. ATP, Coenzyme A and Mg²⁺ were required for the activity. Fatty aldehyde was found to be an intermediate in this reaction. The conversion of fatty acid to fatty alcohol was mainly localized in the microsomal fraction and the formation of hexadecanol showed absolute specificity towards NADPH while fatty aldehyde was formed even in the absence of exogenous reduced pyridine nucleotides. The brain microsomes showed maximal activity with stearic acid and the activities with palmitic and oleic acids were 65% and 38% respectively of that with stearic acid. This enzymic reduction increased with age and showed a maximum in the 15-day old rat brain.     

Devenir de la putrescine-1,4-14C chez Glycine max

Fate of Putrescine-1,4-¹⁴C in Glycine max Putrescine-1,4-¹⁴C was supplied to young decotylized Glycine max (L.) Merr. cv. Chippewa plants growing under aseptic conditions on a liquid medium with nitrogen supplied either as ammonium chloride or nitrates. Whatever the source of nitrogen the diamine was quickly transformed to γ-aminobutyric acid, succinic acid and malic acid; only a very minor part was utilized for the synthesis of polyamines. In the presence of ammonium chloride the putrescine catabolism may be slower than in the presence of nitrates. The results are explained by a weak isotopic dilution or by a diamine oxidase activity lower in “ammonium” plants than in “nitrate” plants; the two causes might co-exist. The possibility of a diamine compartmentation has to be considered.     

Effect of kinetin and abscisic acid on the distribution of 2-amino (1-14C) isobutyric acid in leaves of Zea mays

2-Amino (1-¹⁴C) isobutyric acid (AIB) was applied to the leaf tips of thirteen-day-old primary leaves of Zea mays L. cv. Goldprinz. Simultaneously, the leaves were treated in the basal region with solutions of kinetin (KN), abscisic acid (ABA) and mixtures of both hormones. The distribution of the radioactive material was determined after 72 h. Treatment with KN caused an accumulation of radioactive material at the point of application (KN spot). In comparison to controls, the leaf zones between the KN spot and the leaf tip contained lower amounts of radioactive material. Treatment with ABA caused a pattern of distribution opposite to that induced by KN. The ABA point of application (ABA spot) was depleted of radioactive material, whereas the leaf area between the ABA spot and the leaf tip showed enhanched levels of radioactive AIB. The effect of ABA was reduced by application of ABA and KN in equimolar amounts. The results are discussed in relation to the possible role of ABA in hormone-directed transport processes.     

SIMULTANEOUS INCORPORATION OF ORALLY ADMINISTERED [9, 10-3H2]OLEIC AND [1-14C]LINOLEIC ACIDS INTO LIPIDS OF THE ADULT RAT BRAIN

—The incorporation of an orally administered mixture of [9,10-³H₂joleic acid and [1-¹⁴C]linoleic acid into the brain and spinal cord lipids was maximal after 24 h compared with 4 h for extraneural tissue. In the latter, both acids were utilized equally well for triglyceride biosynthesis, but linoleate entered phosphatidylcholine more rapidly than oleate. Oleic acid was preferentially incorporated into newly synthesized cholesterol esters although 4 h after dosing most cholesterol esters present in serum were formed preferentially from linoleate presumably by the action of lecithin-cholesterol acyl transferase. In neural tissue, a considerable amount of [1-¹⁴C]linoleate was metabolized to higher polyunsaturated fatty acids, whereas in the case of oleate, 90 per cent of the tritium activity remained in monoenic acids at all time periods studied. Both acids were initially incorporated most rapidly into the lecithin fraction of brain and spinal cord, but after 7 days diacyl phosphatidylethanolamine had the highest specific activity. These data are consistent with the view that the uptake of labelled fatty acids by the brain takes place principally as free acids but that some uptake of esterified forms, probably largely as phosphatidylcholine, also occurs. The low linoleate content of the brain and probably also of cerebrospinal fluid cannot be explained on the basis of a selective restriction on the uptake of this lipid from plasma.     

Characteristics of Root-to-Shoot Transport of Cytokinin 6-Benzylaminopurine in Intact Seedlings of Citrus aurantium

Transport of the cytokinin 6-benzylaminopurine-8-¹⁴C in the root and shoot of intact Citrus aurantium L. seedlings was studied by “replacing” the 0.5 cm root tip with the uptake solution. The cytokinin was transported basipetally in the root and was distributed in an acropetal direction in the stem and into the leaves. Kinetic analysis of the transport for periods of up to 96 h revealed a characteristic advancing front of the label along the axis of the seedling. The estimated velocity of transport of 6-benzylamino-purine-8-¹⁴C in various regions of the intact root was 2.6 to 5.1 mm/h. The transport of 6-benzylaminopurine was predominantly in the transpiration stream, in stelar tissues of the root. Conditions of high transpiration favored enhanced transport to the shoot and an overall greater accumulation of the label. The total accumulation of 6-benzylaminopurine in roots of intact seedlings after 48 h of transport was 354% of that in roots of shoot-less seedlings. Root girdling and treatment of the root with KCN did not reduce the basipetal transport of the label in the root and into the shoot. Radiochromalogram scanning of root extracts and analysis of the ethanol insoluble-NaOH soluble fraction revealed considerable metabolic changes in the translocated cytokinin. Only 51% of the radioactivity remained in the original 6-benzylaminopurine peak after 24 h of incubation. Two other, unidentified, metabolites were detected. It is suggested that all the factors that affect the ascent of sap are involved in the long-distance transport of cytokinins, and that the rate and mode of transport of cytokinins from the root system to the shoot may be a major factor in the expression of their physiological activity.     

Chlorophyll turnover in etiolated greening barley transferred to darkness: Isotopic (1-14C glutamic acid) evidence of dark chlorophyll synthesis in the absence of chlorophyll accumulation

Synthesis of chlorophyll was initiated in 5- to 6-day-old dark-grown barley (Hordeum vulgare L. cv. Clipper)seedlings by exposing them to light in the presence of 1-¹⁴ C glutamic acid supplied via the roots.The plants were then returned to darkness. At the end of light treatment (_T) and after 7 or 18 h dark treatment chlorophylls a and b were extracted, quantified (μgleaf¹). purified by HPLC to their magnesium-free derivatives (pheophytin a and b) and their molar radioactivities determined. After 2 h exposure to light followed by 6 h illumination in the presence of 1-¹⁴ C glutamic acid, seedlings had accumulated 4-7 nmol chlorophyll leaf¹ and had incorporated between 900-1 350 Bq (g fresh weight)¹ of radioactive label into the chlorophyll pool. When seedlings were transferred to darkness, label continued to be incorporated and after 18 h the radioactivity of the chlorophyll pool had increased by 300-700 Bq (g fresh weight)¹. Net chlorophyll content, however, remained constant during dark treatment. The increase in radioactivity of the chlorophyll pool in darkness represented the difference between a net increase of label incorporated into chlorophyll a and a small loss of label from chlorophyll b. The absence of measurable radioactivity in the phytol moiety of labelled chlorophyll a, extracted at the endof dark treatment, demonstrated thatincorporation of label was into the tetrapyrrole moiely of chlorophyll and not into the phytol chain. Light-independent incorporation of 1-¹⁴ C glutamic acid into chlorophyll of greening barley seedlings transferred to darkness indicates that chlorophyll synthesis continues when light is withheld. We interpret the net gain in radioactivity of chlorophyll in darkness, in the absence of a net gain in chlorophyll content, to chlorophyll turnover i.e. to simultaneous synthesis and breakdown of chlorophyll when etiolated greening barley seedlings are transferred to darkness.     

Transport and Distribution of 14CO2 Assimilate in Lolium perenne in Response to Varying Nitrogen Supply to Halves of a Divided Root System

The movement of ¹⁴C assimilate from shoots to roots and its subsequent metabolism in the root of Lolium perenne L. was studied using variable N nutrition supplied to halves of a divided root system. Half of the N-deficient root system was supplied with either high NO₃-N or high NH₄-N for 16 hours or 6 days before ¹⁴CO₂ labeling of the shoots. The distribution of ¹⁴C in sugars, ethanol-soluble nitrogen and organic acids in roots appeared to be related to the N content of the tissue. Supply of high NO₃-N for 6 days resulted in significant internal translocation of N into the low N supplied root half. Both root halves also had similar patterns of ¹⁴C distribution among soluble and insoluble metabolites. However, NH₄-N supply for 6 days did not result in a significant increase of N in the low N supplied roots, thus only the high NH₄-N supplied roots displayed stimulated sugar metabolism, similar to that in both root halves in the high NO₃-N supply treatment. Percent transport of ₁₄C assimilates from shoot to root was influenced by form and level of N supplied to root halves. Root halves supplied with either high N source for 6 days accumulated greater amounts of ¹⁴C assimilate than the corresponding low N root half. However NH₄-N supply appeared to make roots stronger sinks since NH₄ supply resulted in significantly greater ¹⁴C accumulation in both the high NH₄ supplied and the low N root halves than did NO₃-N supply in corresponding root halves. The data suggest that factors other than root metabolism, such as N mediated metabolism in the shoot, may also influence the percent transport of assimilates to the root. Internal distribution of the incoming assimilate within the root system could be regulated by the metabolic activity or assimilate demand of the roots.     

Studies on Cassava, Manihot utilissima. II. Biosynthesis of Asparagine-14C from 14C-labelled Hydrogen Cyanide and its Relations with Cyanogenesis

Seeds and seedlings of Manihot utilissima were analysed for cyanogenic glycosides und free amino acids, with special reference to valine and isoleucine which serve as precursors of the aglycone moieties of linamarin and lotaustralin. Seeds contained traces of valine and isoleucine but no glycosides, whereas seedlings contained high concentrations of these amino acids and glycosides. Illumination of seedlings led to a steep increase in the concentration of glycosides followed by a decrease without excretion of detectable HCN. Seeds accumulated asparagine, while seedlings accumulated both asparagine and glutamine in the storage and transport of nitrogen. Seedlings incorporated 13.2 per cent of label from valine-¹⁴C(U) and 2.4 per cent of label from isoleucine-¹⁴C(U)into linamarin and lotaustralin, respectively. In both cases, appreciable amounts of label were also incorporated into asparagine. 49 per cent of label from H¹⁴CN was incorporated inio asparagine in which ca. 98 per cent of total radioactivity was located in the amide-carbon atom. The different patterns of labelling which occurred during the assimilation of H¹⁴CN and ¹⁴CO₂ showed that cyanide metabolism did not proceed via CO₂, and that M. utilissima contains an efficient enzyme-system which catalyses the conversion on high concentrations of HCN into asparagine, which subsequently enters different metabolic pools involved with respiration, protein and carbohydrate syntheses. Cyanogenesis in M. utilissima appears lo be directly influenced by available pools of valine and isoleucine, and the metabolism of HCN released from linamarin and lotaustralin by the action of linamarase may be directly related to respiratory and synthetic processes by way of the incorporation of HCN as a unit into asparagine.     

Allocation and residence time of photosynthetic products in a boreal forest using a low-level 14C pulse-chase labeling technique

Much of our understanding about how carbon (C) is allocated in plants comes from radiocarbon (¹⁴C) pulse‐chase labeling experiments. However, the large amounts of ¹⁴C required for decay‐counting mean that these studies have been restricted for the most part to mesocosm or controlled laboratory experiments. Using the enhanced sensitivity for ¹⁴C detection available with accelerator mass spectrometry (AMS), we tested the utility of a low‐level ¹⁴C pulse‐chase labeling technique for quantifying C allocation patterns and the contributions of different plant components to total ecosystem respiration in a black spruce forest stand in central Manitoba, Canada. All aspects of the field experiment used ¹⁴C at levels well below regulated health standards, without significantly altering atmospheric CO₂ concentrations. Over 30 days following the label application in late summer (August and September), we monitored the temporal and spatial allocation patterns of labeled photosynthetic products by measuring the amount and ¹⁴C content of CO₂ respired from different ecosystem components. The mean residence times (MRT) for labeled photosynthetic products to be respired in the understory (feather mosses), canopy (black spruce), and rhizosphere (black spruce roots and associated microbes) were <1, 6, and 15 days, respectively. Respiration from the canopy and understory showed significantly greater influence of labeled photosynthates than excised root and intact rhizosphere respiration. After 30 days,∼65% of the label assimilated had been respired by the canopy,∼20% by the rhizosphere, and∼9% by the understory, with∼6% unaccounted for and perhaps remaining in tissues. Maximum ¹⁴C values in root and rhizosphere respiration were reached 4 days after label application. The label was still detectable in root, rhizosphere and canopy respiration after 30 days; these levels of remaining label would not have been detectible had a ¹³C label been applied. Our results support previous studies indicating that a substantial portion of the C fueling rhizosphere respiration in the growing season may be derived from stored C pools rather than recent photosynthetic products.     

Native gibberellins and the metabolism of [14C]gibberellin A53 and of [17-13C, 17-3H2]gibberellin A20 in tassels of Zea mays

The native hormones from tassels of maize (Zea mays) were re-investigated. The previous identification by GC/SIM of GA₁, GA₈ and GA₂₉ in normal tassels was confirmed by full GC/MS scans at the correct Kovats retention indices. In tassels of dwarf-1 mutants, GA₄₄,^?GA₁₉, GA₁₇, GA₂₀ and the 16,17-dihydro, 7β,16α,17-trihydroxy derivative of ent-kaurenoic acid were identified by GC/MS. Gibberellin A₁ was not found in the mutant tassels. [¹⁴C]Gibberellin A₅₃ was fed to tassels of the dwarf-5 mutant. In the ethyl acetate-soluble acidic fraction from the feeds, [¹⁴C]GA₄₄ was identified by GC/MS; [¹⁴C]GA₁₉ and [¹⁴C]GA₂₉ were identified by GC/SIM. The GA₂₉ is probably a metabolite of the feeds because the dwarf-5 mutant is known to control the step copalyl pyrophosphate to ent-kaurene in the maize GA-biosynthetic pathway and because GA₂₉ was not identified in a control experiment. The n-butanol fractions obtained from the feeds were shown, by GC/MS, to contain [¹⁴C]GA₅₃ after hydrolysis, suggesting that conjugated [¹⁴C]GA₅₃ is a major metabolite from GA₅₃ feeds. [17-¹³C, 17-³H₂]Gibberellin A₂₀ was fed to normal, dwarf-1 and dwarf-5 tassels. In each case, analysis of the purified ethyl acetate-soluble acidic extracts by GC/MS led to the identification of [¹³C]GA₂₉ and unmetabolized [¹³C]GA₂₀ in which no ¹³C-isotope dilution was observed.     

dl-[2-14C]p-CHLOROPHENYLALANINE AS AN INHIBITOR OF TRYPTOPHAN 5-HYDROXYLASE

The distribution in vivo of dl -[2-¹⁴C]p-chlorophenylalanine (p-CP) in regions and subcellular fractions of the rat brain was determined. The half-lives of p-CP and its metabolite p-chlorophenylpyruvic acid (p-CPPA) in plasma and brain were correlated with the development of inhibition of cerebral tryptophan 5-hydroxylase (EC 1.99.1.4). There was active transamination in vivo of p-CP and p-CPPA in the brain. Transport of indolealkylamino acids into brain was impaired by p-CP. Inhibition of tryptophan 5-hydroxylase could not be reversed by administration of large doses of l -tryptophan, l -tyrosine, or l -phenylalanine. After administration of [2-¹⁴C]p-CP in vivo, appreciable radioactivity was bound to cerebral proteins, including those with tryptophan 5-hydroxylase activity, as well as to phenylalanine 4-hydroxylase (EC 1.99.1.2) purified from liver. Amino acid analysis of the acid hydrolysate of purified, radioactive hepatic phenylalanine 4-hydroxylase showed over 80 per cent of the radioactivity to be present as p-CP. Neither the inhibition in vivo nor in vitro of tryptophan 5-hydroxylase could be reversed by dialysis; in controls, dialysis resulted in marked loss of enzyme activity. After incubation for 5 min with p-CP in vitro, enzymic activity was inhibited 60 per cent. In vitro, p-CPPA labelled protein much more extensively than p-CP, yet inhibited the enzyme less. Some of the label from p-CPPA was removable by dialysis.     

Effect of Vanadium Pentoxide on the Incorporation of (2-14C)-Acetate into Fungal Lipids

Mycelia of Glomerella cingulata grown in the presence of vanadium pentoxide (V₂O₅), incorporated many times less (2-¹⁴C)-acetate into their lipids than mycelia of the same organism grown in the absence of V₂O₅. All neutral and polar lipid fractions investigated were affected. These data suggested that V₂O₅ depressed lipid biosynthesis in G. cingulata.     

Auxin transport and the regulation of petiole abscission in cotton (Gossypium hirsutum L.): A comparison of indol-3yl-acetic acid and phenylacetic acid

Distal applications of indol-3yl-acetic acid (IAA) to debladed cotyledonary petioles of cotton (Gossypium hirsutum L.) seedlings greatly delayed petiole abscission, but similar applications of phenylacetic acid (PAA) slightly accelerated abscission compared with untreated controls. Both compounds prevented abscission for at least 91 h when applied directly to the abscission zone at the base of the petiole. The contrasting effects of distal IAA and PAA on abscission were correlated with their polar transport behaviour-[1-¹⁴C]IAA underwent typical polar (basipetal) transport through isolated 30 mm petiole segments, but only a weak diffusive movement of [1-¹⁴C]PAA occurred.Removal of the shoot tip substantially delayed abscission of subtending debladed cotyledonary petioles. The promotive effect of the shoot tip on petiole abscission could be replaced in decapitated shoots by applications of either IAA or PAA to the cut surface of the stem. Following the application of [1-¹⁴C]IAA or [1-¹⁴C]PAA to the cut surface of decapitated shoots, only IAA was transported basipetally through the stem. Proximal applications of either compound stimulated the acropetal transport of [¹⁴C]sucrose applied to a subtending intact cotyledonary leaf and caused label to accumulate at the shoot tip. However, PAA was considerably less active than IAA in this response.It is concluded that whilst the inhibition of petiole abscission by distal auxin is mediated by effects of auxin in cells of the abscission zone itself, the promotion of abscission by the shoot tip (or by proximal exogenous auxin) is a remote effect which does not require basipetal auxin transport to the abscission zone. Possible mechanisms to explain this indirect effect of proximal auxin on abscission are discussed.     

Metabolism of DL-Tryptophan-3-14C by the Fruitlets of Citrus aurantifolia

Developing lime fruit [Citrus aurantifolia (Christm.) Swingle] was supplied with dl-tryptophan-3-¹⁴C in a special medium. An incubation period of six hours was sufficient for the radioactivity to reach an equilibrium between the fruit tissue and the incubation medium. Analyses of the fruit tissue and the medium for acidic and neutral metabolites of tryptophan indicated the existence of indolic products. The auxin indole-3-acetic acid (IAA) was identified among the products by dry column chromatography and biological assay. Other acidic metabolites included indolepyruvic acid and an unidentified material. Neutral metabolites included indolealdehyde, indoleacetaldehyde, and two unidentified compounds. Biological activity in the Avena curvature test was obtained from extracted compounds which corresponded to IAA and indolepyruvic acid in the acidic fraction and indoleacetaldehyde in the neutral fraction. Radioactive tryptophan was also found in both the acidic and the neutral fractions due to its amphoteric nature. The experiment demonstrated the conversion of tryptophan to its indolic metabolites, including indole-3-acetic acid, in this Citrus tissue.     

Reserve lipid accumulation and translocation of 14C in the photosynthetically active and senescent shoot parts of Dicranum elongatum

Lipid metabolism of the subarctic moss Dicranum elongatum was studied by feeding the moss with 2-¹⁴C-acetate and, after extraction of the lipids, counting the ¹⁴C-content of different lipid fractions immediately after feeding or after chase periods. Translocation of ¹⁴C after ¹⁴C-feeding was studied with autoradiography. Both low temperature (+6°C) and drought (at +23°C) resulted in increased incorporation of ¹⁴C into the neutral lipid (NL) fraction and decreased incorporation of ¹⁴C into the glycolipid (GL) fraction of the green shoot part of the moss. The distribution of radioactivity between the NL classes suggests that diacylglycerols (1, 2-DAG) and common triacylglycerols (cTAG) are turned into acetylenic triacylglycerols (aTAG), which are accumulated preferentially. The decrease in the radioactivity of the GL fraction was due to two unknown fractions, whereas ¹⁴C incorporation into the chloroplast membrane lipids, monogalactosyl diacylglycerol (MGDG) and digalactosyl diacylglycerol (DGDG), was very low throughout the experiments. The phospho-lipid (PL) fraction accounted for 48–63% of total lipid radioactivity at both low and high temperatures. 2-¹⁴C-acetate feeding to the senescent moss part resulted in vigorous ¹⁴C incorporation into the lipids, especially into the reserve TAGs. Electron microscopic examination showed the presence of plastids, which explains the capability of the senescent part of the moss for lipid synthesis. The fact that transport of ¹⁴C from 2-¹⁴C-acetate took place upwards and downwards in the moss shoot, together with the capability for lipid synthesis of the senescent moss part, supports the suggestion that the senescent moss part plays a role as an energy store.