David W. Newman

Lipids of proplastids and nitrogen-deficient chloroplasts☆

Abstract The influence of darkness and a nitrogen-deficient nutrient medium, conditions which would reduce the photosynthetic rate, on the plastid lipids was studied. The galactolipids and associated fatty acids, mainly linolenic, were present in relatively less concentration in dark-treated and nitrogen-deficient plastids. Increased exposure to light caused an increase in monogalactosyl glyceride 1 and digalactosyl glyceride. Younger tissues were obviously more severely affected by nitrogen deficiency.

Galactosyl transferase activity of chloroplast envelopes from senescent soybean cotyledons

Abstract During the senescence of photosynthetic tissues, the level of chloroplast galactolipids markedly declines. The final assembly of these lipids occurs in the plastid envelope. An investigation was made to determine the activity of plastid envelope UDP-galactose-diglyceride galactosyl transferase (galactosyl transferase), which makes this final assembly, in envelopes from greening and senescing soybean cotyledons. When the tissue greened there was an increase in the galactosyl transferase activity. As the tissue senesced there was a decline of the activity of this enzyme as well as a decrease in cotyledon chlorophyll, nucleic acid, protein, mono- and di-galactosyl diacylglycerols, phosphatidyl glycerol, phosphatidyl ethanolamine and phosphatidyl choline levels. It is suggested that the decreased plastid envelope galactosyl transferase activity in senescent tissue may explain, at least in part, the decreased levels of mono- and digalactosyl diacylglycerols in these tissues.

Quantitative Changes in the Chloroplast Thylakoid Polypeptide Complement During Senescence

Summary Chloroplast thylakoid polypeptides from mature, senescent, and re-greened soybean cotyledons were examined using SDS-PAGE. Twenty polypeptide bands were spectrophotometrically observed; ten additional bands were usually observed visually. Eleven of these polypeptides, representing over 85% of the total thylakoid protein, were quantified on both a relative and (to a first approximation) an absolute abundance basis. The polypeptides quantified generally fell into one of two classes: group I polypeptides decrease rapidly during senescence, group II polypeptides decrease much more slowly. Additionally an anomalous polypeptide (M.W. 62.6 kD) was observed which increased in abundance through senescence and disappeared during re-greening. The possible nature of this anomalous polypeptide as well as possible mechanisms for the differential decrease of the other thylakoid polypeptides are discussed.

Quantitative changes of fatty acids in soybean cotyledons during senescence and regreening

Abstract The quantity of total fatty acids in soybean cotyledons during aging, senescence and regreening has been studied. The greatest change in the fatty acid profile during the initial greening of the cotyledons (4–7 days after germination) was a 130% increase in the content of linolenate. Linoleate, as in the case of the other fatty acids, declined in the first 4 days and then increased by 7 days. Following the 10th day after germination, the quantity of palmitate, linoleate, and linolenate decreased continuously through senescence to 20–28% of the maximum quantity of each. When the cotyledons were regreened by removal of the epicotyl 15 or 16 days after germination, linolenate was present in quantities substantially higher than in the senescing cotyledon. On the 22nd day after germination, the quantity of linolenate in regreened tissue was 140% greater than that in senescing tissue of the same age. By contrast, the quantity of linoleate was only 30–40% greater in regreening tissue and the quantity of most of the other fatty acids was similar in both tissues. Similar changes in the quantity of chloroplast fatty acids were observed during this period. Removal of the epicotyl resulted in a higher level of chloroplast linolenate. During aging, the total chlorophyll and the number of chloroplasts reached a maximum on the 10th day and decreased rapidly during senescence. The amount of chlorophyll per chloroplast remained relatively constant during this period whereas the quantity of linolenate per chloroplast decreased during senescence. It is suggested that major structural changes observed in chloroplast membranes may be related to changes in fatty acid composition, but are not dependent on changes in chlorophyll concentration.

Some factors which influence fatty acid accumulation in leaves

Abstract The effect of age, flowering and nitrogen deficiency on the fatty acid composition of lettuce leaves has been investigated. Nitrogen deficiency increases the ratio of saturated to unsaturated acids as well as decreasing the total amount present. Aging shows a more marked effect in the flowering shoots where the older leaves contain a higher proportion of saturated acids but lower overall totals. Squash leaf discs showed a higher incorporation of acetate-2- 14 C into linolenate in the presence of UDPG than in its absence, in both normal and nitrogen-deficient plants. UDPG- 14 C was incorporated into two unidentified lipid components in lettuce leaves. 8-Azaguanine and actinomycin- d , as expected, both inhibited acetate- 14 C incorporation into lipids in lettuce leaf.

The Chlorophyll-Proteins of Soybean (Glycine max L. var. Wayne) Cotyledons')*

Summary The chlorophyll-proteins of chloroplasts isolated from soybean cotyledons were examined. Ten chlorophyll-proteins were observed and nine of these were characterized with respect to visible absorption spectra, relative mobility, relative % distribution, chlorophyll a/b ratio, and the presence or absence of room temperature fluorescence. Three P - 700 chlorophyll-a protein complexes (CP1, CP1a, and CP1b), including one previously unreported (CP1b), were resolved. CP1b has a visible absorption spectrum and room temperature fluorescence characteristics identical to that of CPla but possesses a higher mobility, migrating between CP1 and CP1a. Four light-harvesting chlorophyll a/b protein complexes (HCP0 - LHCP3) and two chlorophyll-a proteins (CPa1, CPa2; possible reaction centers for PS II) were observed. In general, the characteristics of these chlorophyll-proteins are very similar to those isolated from barley chloroplasts. Additionally, a simple method for extracting chlorophyll from polyacrylamide gel slices is described.

Metabolism of polar lipids in green and senescent squash leaves

Abstract The rates of turnover of the various moieties of the lipids of green leaf tissue and of senescent leaf tissue were determined with pulse labeling experiments.

Chloroplast lipid synthesis and mitochondrial cytochrome c oxidase activities in barley leaves

Abstract Some biochemical changes of the chloroplast lipids and of the cytochrome c oxidase activity of the mitochondria of barley leaf tissue of varying developmental stages, grown both in the light and in the dark, were investigated. Generally, the dark treatment reduced the incorporation of hexose into the galactolipids of the chloroplast. Isolated protoplasts were more affected than whole tissues. Also, acetate incorporation into whole leaf tissues was reduced by dark treatment. An investigation of acetate incorporation to the acyl groups of phosphatidylglycerol, a chloroplast lipid, and phosphatidylethanolamine, a non-chloroplast lipid, was made. Also, dark treatment reduced the activity of cytochrome c oxidase.

Fatty-acid metabolism in senescing and regreening soybean cotyledons

Changes in fatty-acid metabolism were studied in soybean (Glycine max Merr.) cotyledons during senescence as well as in cotyledons which had been caused to regreen by removal of the epicotyl from the seedling. The activities of the enzymes acetyl-CoA synthetase (EC 6.2.1.1) and fatty-acid synthetase in plastids isolated from the cotyledons decreased during senescence but increased in response to regreening. These changes in enzyme activities followed the same pattern as changes in the quantities of chlorophyll and polyunsaturated fatty acids in this tissue. The in-vivo incorporation of [14C]acetate into total fatty acids in the senescing and regreening cotyledons did not vary markedly with age. In addition, the quantity of label in fatty acids did not decrease for as much as 60 h after the removal of the substrate. During this 60-h period however, there was substantial redistribution of the label among the individual fatty acids. While the labelling pattern of the individual fatty acids did not vary significantly with respect to age in the senescing cotyledons, there was a substantial increase in the synthesis of labelled polyunsaturated fatty acids in the regreening tissue. Thus, the incorporation of [14C]acetate into fatty acids did not reflect the changes in the quantities of the individual fatty acids in senescing tissue as well as they did in regreening tissue.

Preferential Metabolism of Linoleic Acid by Five-Day-Old Barley Shoots

The degradation of exogenous radioactively labeled fatty acids by 5-day-old barley shoots was examined. [1-14C] Linoleic acid was observed to be degraded 7 times faster than [1-14C] oleic acid and 5 times faster than [1-14C] palmitic acid. The pathway of degradation was determined by identifying the water-soluble products and determined to be β-oxidation. During a 15 min incubation, the barley shoots took up 0.91 nmol/g fresh wt of linoleic acid, of which 0.16 nmol/g fresh wt was incorporated into glutamic acid, 0.07 nmol/g fresh wt into succinic acid and 0.002 nmol/g fresh wt into carbohydrates. By 30 min, additional TCA cycle intermediates, especially malic acid, were detected. Palmitic acid and oleic acid were broken down to the same products. The rates of uptake and the distribution of label into lipids were determined. The uptake of label by the tissue was similar for all 3 fatty acid substrates. Label from linoleic, oleic and palmitic acids was found to be incorporated into similar lipids, primarily phosphatidylcholine (PC), and the extent of incorporation was comparable. Although all 3 fatty acid substrates were broken down by β-oxidation, the reason for the more rapid degradation of linoleic acid was not established. It does not appear to be related to uptake of substrate or incorporation of label into lipids.