Stereochemistry of phytoene biosynthesis by isolated chloroplasts

The incorporation of [2-(14)C,(5R)-5-(3)H(1)]MVA* and [2-(14)C,5-(3)H(2)]MVA into geranylgeraniol and phytoene by a preparation of ;non-aqueous' bean leaf chloroplasts has been studied. In the formation of phytoene from two molecules of geranylgeranyl pyrophosphate, the loss of hydrogen is stereospecific, the hydrogen atom lost from C-1 of each molecule of geranylgeranyl pyrophosphate being that which was originally the pro-S hydrogen atom from C-5 of mevalonate. All the pro-R hydrogen atoms from C-5 of mevalonate are retained. These results with a cell-free system confirm and extend the observations made in previous work with tomato slices.     

The effect of gamma radiation on DNA methylation

The effect of 60Co gamma radiation on DNA methylation was studied in four cultured cell lines. In all cases a dose-dependent decrease in 5-methylcytosine was observed at 24, 48, and 72 h postexposure to 0.5-10 Gy. Nuclear DNA methyltransferase activity decreased while cytoplasmic activity increased in irradiated (10 Gy) V79A03 cells as compared to controls. No DNA demethylase activity was detected in the nuclei of control or irradiated V79A03 cells. Additionally, gamma radiation resulted in the differentiation of C-1300 N1E-115 cells, a mouse neuroblastoma line, in a dose- and time-dependent manner. These results are consistent with the hypothesis that (1) genes may be turned on following radiation via a mechanism involving hypomethylation of cytosine and (2) radiation-induced hypomethylation results from decreased intranuclear levels of DNA methyltransferase.     

The effect of salt concentration on the fluorescence parameters of isolated chloroplasts

The previously reported effect of salt concentration on the fluorescence and other photochemical activities of Photosystem II is interpreted in terms of a change in the radiationless transition and the trapping probabilities. This is confirmed by quantitative comparison of the fluorescence and the photochemical activity. As a by-product of this analysis a method is devised to estimate the background fluorescence.

We did not eliminate the possibility that the radiationless transition constant may include a contribution of energy transfer from Photosystem II to Photosystem I.     

The effect of gamma radiation on bacterial nodule formation

Summary Seeds ofTrifolium andTrigonella were planted after exposure to different dose rates 61.0, 75.8, 116.6 and 265.0 r/day from a radium tube for a period of seven days. The general effect was a tendency towards increase in the number of nodules and of lateral roots per plant, especially at a total dose of about 816 r.Colchicine treatment was found to have a similar effect.     

Lipid biosynthesis by isolated barley chloroplasts in relation to plastid development

The effect of seedling age and of the time of greening on the incorporation of 1-¹⁴C-acetate into lipids by isolated barley (Hordeum vulgare cultivar Svalöf's Bonus) plastids was examined. The fatty acid synthesizing capacity of plastids isolated from 5-day-old seedlings did not increase markedly from zero to 36 hours of greening nor was a light stimulation of fatty acid synthesis observed. However, an increasing capacity for fatty acid synthesis and an increasing light stimulation of this process with greening were attained by the plastids isolated from 7-, 9-, and 11-day-old seedlings.     

The effect of gamma radiation on recombination frequency in Caenorhabditis elegans

We have studied the effect of gamma radiation on recombination frequency for intervals across the cluster of linkage group I in Caenorhabditis elegans. Recombination frequency increased approximately twofold across the dpy-5-unc-13 interval after treatment with 2000 rads (1 rad = 10 mGy) of cobalt 60 gamma radiation. Several factors affecting the magnitude of the increase have been characterized. Recombination frequency increased more with higher doses of radiation. However, the increase in recombination frequency with increasing dose was accompanied by a reduced average number of progeny from radiation-treated individuals. The amount of the increase was affected by meiotic stage, age at the time of treatment (premeiotic), and radiation dose. The increase in recombination was detectable in the B brood and remained elevated for the remainder of egg production. X-chromosome nondisjunction was also increased by radiation treatment. A high frequency of the recombinant progeny produced with radiation treatment were sterile unlike their nonrecombinant siblings. When parameters affecting recombination frequency are held constant during treatment, chromosomal regions of high gene density on the meiotic map increased more (fourfold) than an adjacent region of low gene density (no increase). The greatest increase was across the dpy-14-unc-13 interval near the center of the gene cluster. These results may suggest that the physical length of DNA per map unit is greater within the cluster than outside.     

The effect of gamma radiation on breaking of dormancy in Phycomyces spores

Dormant sporangiospores of Phycomyces blakesleeanus were activated by Cs-137 gamma rays. After a dose of about 300 krad, between 80 and 90% of the spores germinated normally. However, further development of the mycelium was inhibited. Even with dry spores a partial activation was obtained. Activation by gamma rays was not accompanied by an increase in trehalase activity.     

Lipid biosynthesis by chloroplasts isolated from developing Zea mays

Fatty acid biosynthesis by isolated plastids has been examined in relation to chloroplast development and differentiation in leaves of maize plants grown in light for 7 days. Biosynthesis of fatty acids from acetate by proplastids prepared from the basal regions of the leaf was low and mainly palmitate was synthesized. The greatly increased utilization of acetate for fatty acid biosynthesis as the plastids increased in size was due to an increased synthesis of oleate. The maximum synthesis of total fatty acids and monoenoic fatty acids was obtained in chloroplasts prepared from leaf tissue 6–8 cm from the base of the plant where granal formation was most active. Fully-developed chloroplasts prepared from distal regions of the leaf were less active in fatty acid biosynthesis. Maize chloroplasts failed to synthesize fatty acids when isolated by methods commonly used to prepare active spinach chloroplasts. The method of isolation which included a density gradient gave a high proportion of Class I chloroplasts from maize leaves and incorporated up to about 10% of the acetate used. Biosynthesis of unsaturated fatty acids, especially with chloroplasts prepared from the most mature tissue, was increased by the addition of both mitochondrial and microsomal fractions. Increases in polyunsaturated fatty acids were also obtained but the proportions in the newly-synthesized fatty acids were well below the endogenous levels. Monoenoic synthesis was greatly stimulated by increasing the pH in the range 7·0–8·0 and also the highest proportions of unsaturated fatty acids were obtained at short incubation times.     

Redox conditions specify the proteins synthesised by isolated chloroplasts and mitochondria

In chloroplasts and mitochondria isolated from pea leaves, ³⁵S-methionine incorporation reveals that different subsets of proteins are selected for synthesis in the presence of the external redox reagents ferricyanide, ascorbate, duroquinol, dithiothreitol and dithionite, and in the presence of different electron transport inhibitors in the light (in chloroplasts) or with respiratory substrates (in mitochondria). Redox state of specific electron carriers may therefore regulate expression of specific genes in chloroplasts and mitochondria. The results are consistent with the hypothesis that chloroplast and mitochondrial genomes encode proteins whose synthesis must be regulated by electron transport in photosynthesis and respiration.     

The effect of gamma radiation on the enzyme activity of collalitin during storage

A study was made of the effect of gamma-irradiation of collalitin samples with doses of 25 and 50 kGy on proteolytic and enzyme activity with respect to denaturated collagen. The enzyme properties were found to change upon storage for periods of 6 and 12 months at 15 degrees C under unsterile conditions. No significant changes in the molecular mass of the collalitin samples were revealed by the method of gell-chromatography after irradiation and storage.     

The effect of air ions on light-induced swelling and dark-induced shrinking of isolated chloroplasts

Experiments were conducted to determine the effects of gaseous ions on isolated chloroplasts maintained in a physiologically active state. Chloroplasts shrink when stored in the dark for 48 hr at 4°C and swell again when illuminated. The rates of swelling and shrinking (s-s) determined by the light-scattering method are increased by exposure to air ions of either charge. If chloroplasts are preilluminated for 30 min, the rate of shrinking of air-ion-treated chloroplasts is increased. When the chloroplasts are illuminated again, the rate of swelling of airion-treated chloroplasts is lower than that of controls. If 2.5 mM of ATP is added to the system upon the reillumination,the swelling rate of ion-treated chloroplasts is markedly increased. However, ADP,p-nitrophenyl phosphate and inorganic phosphates are shown without effect. Prolonged illumination (5,000 ft-c for 48 hr) or the addition of NaF inhibits the s-s phenomenon. Exposure of the chloroplasts in the presence of ATP to unipolar ionized air of either charge at 4°C in the dark increases their s-s and ATPase activities. These data suggest that air ions stimulate ATP metabolism of isolated chloroplasts.

---

Zusammenfassung Es wurden Versuche durchgeführt,um die Wirkungen von Gasionen auf isolierte Chloroplasten zu bestimmen,die in einem physiologisch aktiven Zustand gehalten wurden. Chloroplasten schrumpfen, wenn sie für 48 Std.bei 4°C im Dunkeln gehalten werden, und schwellen bei Belichtung wieder an. Das Ausmass des Schwellens und Schrumpfens (s-s), das durch die unterschiedliche Belichtung bestimmt wurde, nimmt unter der Einwirkung von Luftionen beider Ladungen zu.Wenn Chloroplasten 30 Min. lang vorher beleuchtet werden, wächst das Ausmass des Schrumpfens der mit Luftionen behandelten Chloroplasten an. Wenn die Chloroplasten dann wieder beleuchtet werden, ist das Ausmass des Schwellens der mit Luftionen behandelten Chloroplasten geringer als das der Kontrollgruppe.Wenn 2,5 mM ATP dem System zusätzlich zur Wiederbelichtung verabfolgt werden, nimmt das Ausmass des Schwellens der mit Ionen behandelten Chloroplasten stark ab. ADP, p-nitrophenyl-Phosphate und anorganische Phosphate zeigen keine Wirkung. Eine verlängerte Belichtung (50.000 1x für 48 hr)oder der Zusatz von NaF hemmen das s-s-Phänomen.Setzt man Chloroplasten mit ATP bei 4°C im Dunkeln unipolar ionisierter Luft aus, so wächst das s-s und die ATPase-Aktivität.Diese Ergebnisse lassen vermuten, dass Luftionen den ATP-Stoffwechsel isolierter Chloroplasten anregen.

---

Resume On a effectué des essais tendant à déterminer les effets d'ions gazeux sur des chloroplastes isolés, mais maintenus dans un état physiologique actif.Les chloroplastes se ratatinent après avoir été maintenus 48 hr dans l'obscurité par 4°C et gonflent à nouveau après avoir été remis à la lumière. L'importance du ratatinement et du gonflement (s-s) déterminée par les fluctuations de l'éclairement augmente sous l'influence d'ions de l'air des deux signes. Si les chloroplastes sont éclairés durant 30 min auparavant,l'importance du ratatinement de ceux qui sont traités par des ions augmente. Lorsque les chloroplastes sont à nouveau éclairés, l'ampleur du gonflement de ceux qui sont traités est moindre que celle du groupe de contrôle.Si l'on ajoute au système, en plus de l'éclairement, 2,5 mM ATP l'importance du gonflement des chloroplastes traités à l'air ionisé diminue fortement. ADP, des p-nitrophénylphosphates et des phosphates inorganiques ne montrent aucun effet. Un éclairement prolongé (50.000 1x pour 48 hr) ou l'adjonction de NaF ralentissent le phénomène. Expose-t-on des chloroplastes avec de l'ATP dans l'obscurité par 4°C à de l'air ionisé unipolairement, on constate une augmentation des activités s-s et ATP.Ces constatations laissent supposer que les ions de l'air activent le métabolisme ATP de chloroplastes isolés.