The composition of the lipid globules of Ilex aquifolium leaves and its variability with the age of the leaf and with season

The cytoplasmatic globules of Ilex aquifolium L. mainly consist of fatty acid esters of the triterpenoid alcohols α and β-amyrin. In very young leaves these are practically only palmitates. With increasing leaf age, increasing amounts of saturated and unsaturated C18 acids were found with comparatively high amounts of linoleic and linolenic acid in leaves of one year and older. Some accumulation of the triterpene precursor squalene was also observed with increasing age of the leaves. In addition to age effects, seasonal changes occur too. Independent of the age of the leaf, an increase in palmitic acid and a decrease in linoleic and especially linolenic acid was observed in the winter in mature leaves.     

Biosynthese de l'acide linolenique dans la feuille de pois

During the development of pea seedlings in complete darkness or under a short-day photoperiod, the capacity of linolenic acid biosynthesis reaches a maximum about 7 days after germination. At all stages of development the light markedly and specifically increases the incorporation of 1-¹⁴C-acetate into the linolenic acid, causing a 20-fold increase in the labelling at the maximum as compared with dark incubation. The evolution of the capacity of linolenic acid biosynthesis in leaves follows strictly the ability to produce chlorophyll under light. First analysis shows that the linolenic acid biosynthesis observed occurs specifically into the galactolipids.     

Fatty Acid Levels in Apple Leaves of Different Age as Affected by Temperature

Relative electrical conductivity (RC) values and Tally acid levels were measured on apple leaves of different ages exposed to 0 and 20°C. RC values were measured at—3°C and high RC values indicate frost-sensitive tissue. A prolonged period at 0°C gave an increased RC value of the leaves, which indicates damage. At 20°C the RC values were lower in older leaves than in young leaves. The fatty acids level as well as the degree of saturation were different at different ages of the leaves. Young leaves showed a higher fatty acid level in plants held at 20°C than in plants at 0°C. The older leaves maintained the same level after 12 days at 20°C as after 3 days at 20°C. The fatty acid level decreased at 0°C. The linolenic acid level followed the same trend as total fatty acids, indicating that synthesis and degradation of linolenic acid can occur in the same plant depending on the age of the leaf and on the temperature. Cold resistance and linolenic acid levels were correlated in both old and young leaves at 20°C and in older leaves at 0°C. There was no correlation between cold resistance and levels of linotenic acid levels in young leaves at 0°C. Two hiosynthetic pathways for linolenic acid synthesis are discussed.     

Metabolism of linolenic acid in a cold sensitive (Penjamo 62) and a cold resistant (Miranovskaja 808) wheat cultivar

Formation of linolenic acid in vivo from various precursors [1-¹⁴C]-2:0, -12:0, -16: 0, -18:0, -18:1, 18:2 in the cold resistant wheat cultivar Miranovskaja 808 and cold sensitive wheat cultivar Penjamo 62 was investigated at three different temperatures (+25, +5, and ?6 °C). Both cultivars converted the offered precursors to linolenic acid only very slowly. Decreasing the experimental temperature brought about an increase formation of linolenic acid, however, Miranovskaja 808 being more successful than Penjamo 62. Comparison of the specific activities of linolenic acid at the “time of equal level of tissue labeling” revealed that Miranovskaja 808 formed 2 to 10 times faster linolenic acid from various precursors upon exposure to cold than Penjamo 62. Considering the low rate of formation of linolenic acid in leaves it appears probable that even the cold resistant cultivars are unable to increase the proportion of linolenic acid in their membranes fast enough to prevent the thermotropic phase transition from liquid crystalline to solid gel state at beginning of the onset of cold. It is suggested that rapid accumulation of hitherto unknown cryoprotective substance (s) of lipidic nature precedes the accumulation of linolenic acid upon exposure of the seedlings to chilling temperatures.     

Effect of Low Temperature upon Lipid and Fatty Acid Composition of Roots and Leaves of Winter Rape Plants

When winter rape plants were transferred from favourable temperature conditions (25/20°C day/night temperature) to 5°C, the frost resistance of the leaves was increased whereas the frost tolerance of the roots remained unaffected. This permitted an analysis of the changes in lipid and fatty acid composition both as related to functioning of the plant at low temperature alone (roots) and as related to adaptation to freezing and functioning at low temperature (leaves). — Transfer of the plants to 5°C lead to an increase in the level of linolenic acid in roots and leaves. This increase was most evident in the phosphatidyl choline and ethanolamine fractions of the leaves, and in the neutral lipids and in an unidentified phospholipid from the roots. It was concluded that upon transfer of the plants to 5°C a general and non-specific increase in linolenic acid level contributed to functioning of the rape plants at low temperature; and that parallel but minor increases in linolenic acid level of digalactosyl diglyceride, phosphatidyl inositol and the unknown phospholipid in roots and leaves could only contribute to low-temperature functioning in specific membrane enzyme locations. Combined adaptation of the leaves to freezing tolerance and low-temperature functioning was correlated with a higher level of phosphatidyl choline and ethanolamine, predominantly esterified with linolenic acid.     

Fatty acid synthesis by slices from developing leaves

Fatty acid synthesis was studied in successive leaf sections from the base to the tip of developing barley (Hordeum vulgare L.), maize (Zea mays L.), rye grass (Lolium perenne L.) and wheat (Triticum aestivium L.) leaves. The basal regions of the leaves had the lowest rates of fatty acid synthesis and accumulated small amounts of very long chain fatty acids. Fatty acid synthesis was highest in the middle leaf sections in all four plants. Linolenic acid synthesis from [1-¹⁴C]acetate was highest in the distal leaf sections of rye grass. The labelling of the fatty acids of individual lipids of rye grass was examined and it was found that [¹⁴C]linolenic acid was highest in the galactolipids. Synthesis of this acid in the galactolipids was most active in leaf segment C. Only traces of [¹⁴C]linolenic acid were ever found in phosphatidylcholine and it is concluded that this phospholipid cannot serve as a substrate for linoleic acid desaturation in rye grass. The synthesis of fatty acids was sensitive to arsenite, fluoride and the herbicide EPTC. The latter was only inhibitory towards those leaf segments which made very long chain fatty acids. Formation of fatty acids from [1-¹⁴C]acetate was also studied in chloroplasts prepared from successive leaf sections of rye grass. Chloroplasts isolated from the middle leaf sections had the highest activity. Palmitic and oleic acids were the main fatty acid products in all chloroplast preparations. Linolenic acid synthesis was highest in chlorplasts isolated from the distal leaf sections of rye grass.     

Expression of a gene for plastid ω-3 fatty acid desaturase and changes in lipid and fatty acid compositions in light- and dark- grown wheat leaves

The leaves of monocotyledonous plants create a developmental sequence of cells and plastids from the base to the apical portion. We investigated fatty-acid and lipid compositions in successive leaf sections of light- and dark-grown wheat (Triticum aestivum L. cv. Chihoku) seedlings. The most notable change in the fatty acid composition was the increase of linolenic acid (18:3) with maturation of leaf cells, which occurred both in light- and dark-grown leaf tissues. In light-grown leaves, the increase of 18:3 with maturation was mainly attributed to the increase of monogalactosyldiacylglycerol (MGD) and also to the increase of the 18:3 level of MGD. In dark-grown leaves, the increase of 18:3 in the leaf apex was caused by the increase of the levels of MGD and digalactosyldiacylglycerol (DGD) and also by the increase of the 18:3 levels of within these two lipids. Since MGD and DGD are mainly found in plastid membranes, these findings indicate that both the synthesis of galactolipids and the formation of 18:3 these lipids take place during plastid development. The plastid ω-3 fatty acid desaturase is responsible for the formation of 18:3 in plastid membrane lipids. To investigate the regulation of desaturation, we isolated a gene for wheat plastid ω-3 fatty acid desaturase (TaFAD7). The mRNA level of TaFAD7 in light-grown leaves was much higher than that in dark-grown leaves. During the greening of etiolated leaves the level of TaFAD7 mRNA increased significantly, accompanied by an increase of the 18:3 level of total fatty acids. On the other hand, the levels of TaFAD7 mRNA were almost the same in all the leaf sections of both light- and dark-grown leaf tissues. These results suggest that the effect of the expression of the TaFAD7 gene on the increase of the 18:3 level is different between the leaf development under continuous light- or dark-conditions and the light-induced greening process of etiolated leaves. The increase of 18:3 content of MGD (or MGD and DGD) with maturation is apparently regulated not solely by the level of TaFAD7 mRNA.     

Lipid Composition of Zea mays Seedlings and Water Stress-Induced Changes

The imposition of a polyethylene glycol-induced osmotic stressof –1.5 MPa for 48 h on 28 d old Zea mays (cv. Style Pak)seedlings resulted in a 44% decreased stem dry weight and increasedtriglyceride levels in stem and leaf tissues; increased sterylester levels also occurred in stems. The magnitude of theseincreases was such that, on a dry weight basis, there were increasedtotal triglyceride and steryl ester levels in the seedlingsafter the 48 h applied stress. In stems the increased triglyceridelevel was evident in all of the component fatty acids examined,whereas in leaves it was associated mainly with one fatty acidcomponent, viz. linolenic acid (C18: 3). Changes in sterol levels were small but significant and largelyrestricted to the stem. Proline levels of all three tissuesincreased in response to water-stressing the seedlings and thegreatest increase also occurred in the stem tissues.     

Lipid biosynthesis in relation to chloroplast development in barley

During greening of detached leaves from dark-grown barley seedlings, the linolenic acid content of the lipids increases in the early stages of the formation of the chloroplast lamellar system. Primarily the fraction containing monogalactosyl diglyceride is enriched with linolenic acid. Incorporation of (14)C-labeled acetate into the leaf lipids of detached whole leaves is low, but increases 10- to 20-fold during greening. Increasing percentages of label appear in linolenic acid during the first 15 hr of greening, whereafter they remain constant. A constant, relatively high amount of acetate is incorporated into lipids when slices of leaves at various stages of greening are incubated by submersion in acetate solution, a treatment that blocks further chlorophyll synthesis during incubation. At the initial greening stages 75% of the label is channeled into steroids and other unsaponifiable lipids, but in advanced stages of chloroplast development 75% of the incorporated acetate is built into phospho-, sulfo- and galacto-lipids, and only 25% is channeled into unsaponifiable lipids. Experimental variation of the physiological conditions of the tissue during incubation resulted in differences in the amount of label found in the various phospho- and galacto-lipids. The amounts of labeling of the individual fatty acids in the lipid classes studied differ markedly and could be changed by varying the conditions of incubation. Labeling of linolenic acid was found to be highest in the monogalactosyl diglyceride fraction at all stages of greening.     

外源胆固醇对水稻幼苗膜脂组成及抗冷力的影响

分析了水稻幼苗低温胁迫前后膜脂和膜脂脂肪酸含量变化。结果表明,经胆固醇处理的幼苗叶和根细胞膜脂中LPC、PS和PG含量比对照下降少,PA含量增加也较少。胆固醇处理的幼苗叶和根棕榈酸(16:0)增加量和亚麻酸(18:3)与IUFA减少量均明显比对照少。试验结果证明,水稻幼苗叶片和根系的抗冷力与PA含量和脂肪酸不饱和程度变化有密切关系。外源胆固醇处理水稻幼苗能阻止低温对膜脂的破坏作用,提高幼苗抗低温胁迫能力。     

Changes in Composition of Non-polar Lipids of the Axis and Root of Germinating Soybeans

Soybean seedlings were grown at 28°C under dark or light conditions for 12 days. Non-polar lipids (NPL) were separated by silicic acid column chromatography from total lipids in epicotyl containing young leaves, hypocotyl and root. The glyceride (TG, DG, and MG), free fatty acid (FFA) and sterol lipid (SE) components in NPL were analyzed mainly by thin-layer and gas-liquid chromatographies (TLC and GLC).

During germination, the amounts of polar lipids (PL) markedly increased in the tissues of soybean seedlings, especially in light-grown seedlings, whereas these of NPL increased slightly or maintained constant values. The features of the compositions and changing patterns of NPL in the tissues were more clarified in light-grown seedlings than in dark-grown ones. The pattern of change in fatty acid composition was similar in TG and 1,2-DG, which showed higher proportions of linoleic and linolenic acids, whereas FFA, 1,3-DG or MG had high proportions of saturated fatty acids. These results indicate that the compositions and changing patterns of NPL and their fatty acids in the tissues depend on the differences under two germinating conditions tested.     

Effect of toxaphene on carbon dioxide assimilation and translocation in avena secale

In susceptible oat, toxaphene inhibits photosynthetic electron flow and concomitant ATP synthesis. Although the rate of ¹⁴CO₂ assimilation is apparently not affected markedly there is an increase in dry weight of leaves contacting the pesticide. The labelling patterns in leaf sections exposed to ¹⁴CO₂ are similar for both toxaphene-treated and untreated seedlings. However, if given a period in darkness before extraction it is evident that assimilation products in leaf sections from toxaphene-treated leaves remain as small M, materials, including substantial amounts of sugars, whereas in untreated controls these were converted to polymeric materials. In toxaphene-treated seedlings the translocation of assimilation products to the roots is decreased and sucrose accumulates in the leaves.     

A biochemical difference between healthy bean leaves resistant and susceptible to the halo-blight disease caused by Pseudomonas phaseolicola

Substrate for an endogenous oxidation in homogenates of leaves of bean (Phaseolus vulgaris) was traced to two fractions of lipids, each representing less than 2% of the dry weight of leaves. The substrate lipids, tentatively identified as galactosyl diglycerides, yielded linolenic and linoleic acids on acid hydrolysis. Amounts of linolenic acid in total lipids in resistant and susceptible leaves were similar. Amounts of free linolenic acid in resistant leaves increased eightfold to 408.6 μg and in susceptible leaves fourfold to 130.6 μg/g fresh leaf after homogenization and incubation for 16 min at 4 °C. These quantities are sufficient to account during their lipoxidation for the previously reported oxygen uptakes in homogenates. Differences between resistant and susceptible leaves were traced to the activities of lipase systems which liberate linolenic acid from substrate lipids.     

Formation of 2-hexenal from linolenic acid by macerated Ginkgo leaves

The content of linolenic acid and its fat-soluble derivatives in Ginkgo leaves has been determined. By utilization of uniformly ¹⁴C-labelled linolenic acid it has been shown that the linolenic acid in Ginkgo leaves is converted into 2-hexenal when the leaves are macerated in the presence of air. The conversion of linolenic acid to 2-hexenal under the conditions of temperature and pH existing in the Ginkgo leaf requires the presence in the leaves of an enzyme or other catalyst. This is not lipoxidase but is a hexane-insoluble, water-soluble substance. A preparation of this substance strongly catalyzes the absorption of oxygen by linolenic acid in water at 20°.     

Some Effects of 1-Amino-2-Nitrocyclopentane-1-Carboxylic Acid on Flowering Plants

A study has been made of the effects on higher plants of i-amino-2-nitrocyclo-pentane-1-carboxylicacid (ANPCA), a metabolite of Aspergillus wentii Wehmer. ANPCAwas rapidly translocated to young tissues when injected intothe stems of pea seedlings, but when applied to the roots ofvery young seedlings only trace amounts entered the plants.In intact plants ANPCA produced loss of apical dominance andshorter internodes but was without effect on isolated stem orleaf sections. There was some reduction of cell extension inthe internodes of intact pea seedlings, but the main effectwas on cell numbers. ANPCA inhibited mitosis in root tips andapical buds, the degree of inhibition varying with the species.There appeared to be a block in the mitotic cycle between theend of DNA synthesis and prophase. Inhibition caused by ANPCAcould be reversed by L-leucine. Chlorophyll synthesis was inhibitedby ANPCA in newly formed tissue and in etiolated leaves transferredto the light. There was a considerable increase in the freeamino-acid pool and a decrease in gibberellin content due totreatment with ANPCA. It is suggested that the primary effectof ANPCA may be on protein or RNA synthesis.     

Can early wilting of old leaves account for much of the ABA accumulation in flooded pea plants?

When pea plants (Pisum sativum L.) were subjected to flooding,abscisic acid (ABA) content in shoots and roots increased upto 8-fold in the following days and stomatal conductance significantlydecreased. Although young leaves of flooded plants had a slightlyhigher water potential than those of the unflooded plants, oldleaves had lower water potential and lost turgor at the timewhen a substantial ABA increase was detected. In plants wherethe old leaves were clipped off, flooding did not cause anyABA increase during 7 d of the experimental period, except underconditions of higher transpiration demand, when the increasein ABA content was both delayed and small in scale (only I-fold).When intact plants were flooded and ABA was assayed separatelyin both old and young leaves, the ABA increase in old leavespreceded that in young leaves. Evidence here suggests that theflooding-induced ABA increase mainly results from the wiltingof old leaves. This suggests that young leaves may be protectedfrom wilting by ABA originating in old leaves under unfavourableenvironmental conditions. Key words: Waterlogging, soil flooding, ABA, leaf water relations, pea, Pisum sativum     

Dietary linolenic acid in man--an overview

Small amounts of linolenic acid are ubiquitous in human food but only a few foodstuffs contain sizable amounts, namely some plant oils, butter and fish; in marine fish, linolenic acid is accomplished by eicosapaentaenoic acid, highly exceeding linolenic acid in quantity. Of the linolenic acid ingested, some is incorporated into phospholipids and cholesteryl esters, very little is elongated and eventually converted to prostaglandins; probably most linolenic acid is used as fuel. Polyunsaturated fatty acids of the (n-3)-series should no longer be considered to be similar with respect to their metabolic fate and their effects. In particular, results from experiments with "eskimo diets" may not be applied to considerations of linolenic acid. There may be a small dietary requirement for linolenic acid, possibly only for growing children; yet it is prudent to recommend diets which are not devoid of linolenic acid, especially in formula diets or parenteral nutrition. Some experiments suggest that high doses of linolenic acid exert untoward effects by inhibiting prostaglandin synthesis of the 1- and 2-series. The ratio between linoleic and linolenic acid in relevant experiments was such that only excessive use of linseed oil could produce them under conventional dietary conditions. Still it must be considered prudent to keep the linolenic acid content of foods well below that of linoleic acid.     

Enzymic formation of carbonyls from linoleic acid in leaves of Phaseolus vulgaris

Homogenization of Phaseolus vulgaris leaves at acid pH results in the evolution of hexanal, cis-3- and trans-2-hexenal. With cell-free extracts of leaves, linoleic and linolenic acids are enzymically converted to their hydroperoxides (predominantly the 13-hydroperoxide isomers) and to hexanal or hexenal respectively. Activity was highest in young, dark-green leaves and was stimulated by Triton X-100. Oleic acid is not a substrate for these reactions. Both 9- and 13-hydroperoxides were cleaved to carbonyl fragments and are proposed as intermediates in the formation of volatile aldehydes and non-volatile ω-oxoacids in P. vulgaris leaves. Properties of the enzyme systems are described.     

Effect of alternating magnetic field on the composition and level of lipids in radish seedlings

The effects of alternating magnetic field (AMF) with the frequency of 50 Hz on the dynamics of unfolding of cotyledon leaves, the composition and level of polar and neutral lipids and their component fatty acids (FA) were studied in 5-day-old radish seedlings (Raphanus sativus L. var. radicula D.L., cv. Rozovo-krasnyi s belym konchikom) grown in the light and in the dark. AMF weakened the inhibitory effect of light on unfolding of cotyledon leaves. In the light, the total content of lipids, as well as the level of polar and neutral lipids, in the seedlings in AMF was greater than in control material. In polar lipids, the total amount of glyco-and phospholipids increased; in neutral lipids, the level of triacylglycerols rose. The ratio between phospholipids and sterols (PhL/S) increased. In the dark, the total content of lipids and the level of neutral lipids in the seedlings in AMF were lower than in control material, and the ratio PhL/S decreased. In control material, there were no differences in the relative total content of unsaturated FA in the light and in the dark, whereas the level of linolenic acid was higher in the light than in the dark. AMF induced a decrease in the content of linolenic acid in the light and a rise in the dark; the level of erucic acid in the light decreased. The ratio between unsaturated and saturated FA decreased both in the light and in the dark. It was concluded that AMF with the frequency of 50 Hz was an adjusting agent considerably changing the content of lipids in the radish seedlings in the light and in the dark.     

Developmental change in c(6)-aldehyde formation by soybean leaves

Damage to plant leaves by wounding or freezing induces the production of large amounts of C₆-compounds. However, the control of formation of these compounds in leaves is not yet clear. In the current study, C₆-aldehyde formation by freeze-injured soybean leaves of different ages (based on the leaf positions on the plant) at stage R1 of plant development was investigated. The results demonstrate that C₆-aldehyde formation by the soybean (Glycine max L.) leaves changes as leaves develop. Younger leaves produce high levels of C₆-aldehydes, mainly composed of hexanal. Subsequently, as the leaves develop, the level of C₆-aldehyde formation decreases markedly, followed by an increase with a large shift from hexanal to hexenals. Lipoxygenase and lipolytic acyl hydrolase activity was reduced, and, in contrast, hydroperoxide lyase activity increased. There was little difference in lipoxygenase substrate specificity for linoleic acid and linolenic acid, but hydroperoxide lyase preferentially utilized 13-hydroperoxy-9,11,15-octadecatrienoic acid. In the in vivo lipoxygenase substrate pool, the linoleic acid level declined and the relative level of linolenic acid increased. The change in ratios of linolenic acid to linoleic acid showed a similar trend during soybean leaf development to that of hexenals to hexanal.