Effects of gamma-ray irradiation on metabolic changes in potato tubers in response to cutting

Potato tubers were subjected to cobalt-60 gamma-ray irradiationand stored at room temperature for from 10 days to 4 months.Effects of this irradiation on metabolic changes in potato tubersin response to cutting were investigated. The quantities ofpolyphenols, such as chlorogenic acid and isochlorogenic acid,in the tissue increased as compared with the non-irradiatedsample. Although the polyphenol content and activities of o-diphenoloxidase, peroxidase and phenylalanine ammonialyase increasedafter cutting, increases were lower in the irradiated sample.On the other hand, in the dose range between 5,000 and 12,400rad, the irradiated sample showed a larger defense action againstinfection by the black rot fungus, Ceratocystis fimbriata thandid the non-irradiated sample. (Received April 16, 1968; )     

DISTRIBUTION OF QUINONES IN SOME PHOTOSYNTHETIC BACTERIA AND ALGAE

The distribution and the concentration of quinones in 5 speciesof photosynthetic bacteria and 4 species of algae were investigated.The Athiorhodaceae, except for Rhodospirillum rubrum, containedubiquinone as the major quinone component. Rhodospirillum rubrumcontained two kinds of quinones, i.e. ubiquinone and rhodoquinone.Chromatium, strain D contained two kinds of quinones, i. e.ubiquinone and vitamin K₂. The green sulfur bacterium, Chloropseudomonasethylicum, contained vitamin K₂ and a Chlorobium quinone-likesubstance. The marine algae tested, Porphyra yezoensis, Porphyra sp. andHizikia fusiforme, contained vitamin K₁, plastoquinone A, -tocopherylquinoneand ubiquinone. In Chondrus ocellatus, the presence of a ubichromenol-likesubstance was detected instead of ubiquinone. Other types ofplastoquinone and tocopherylquinone were not found in thesealgae. In the thalli of Porphyra sp., vitamin K₁, plastoquinoneA and -tocopherylquinone were found to be localized in chloroplasts. ¹Present address: Department of Biophysics and Physical Biochemistry,Johnson Research Foundation, University of Pennsylvania, Philadelphia,Pennsylvania, U.S.A.     

CHANGES IN CONTENTS OF CARBOHYDRATE AND FATTY ACID IN THE CELLS OF CHLORELLA PROTOTHECOIDES DURING THE PROCESSES OF DE- AND RE-GENERATION OF CHLOROPLASTS

1. Previous work has demonstrated that when cells of Chlorellaprotothecoides are grown mixotrophically under illuminationin a medium rich in nitrogen source (urea) and poor in glucose,normal green cells are obtained, while in a medium rich in glucoseand poor in the nitrogen source, strongly bleached cells containingapparently no discernible chloroplast structures — called"glucose-bleached" cells — are produced either in thelight or in darkness. When the green cells are incubated ina glucose-enriched mineral medium without added nitrogen source,they are fairly rapidly bleached with concomitant degenerationof chloroplast structures (" bleaching "). When, on the otherhand, the "glucose-bleached" cells are transferred in a nitrogen-enrichedmedium without added glucose under illumination, they turn greenwith regeneration of chloroplasts (" greening "). In the presentstudy changes in contents of carbohydrate and fatty acid inalgal cells were followed during these processes of "bleaching"and "greening.".
2. During the process of "bleaching", the quantityof glucose existingin the insoluble carbohydrate fraction ofalgal cells increasedrapidly and markedly. A considerable increasewas also observedin the contents of cells in oleic, linoleicand palmitic acids.It was noted, however, that linolenic aciddecreased in quantityduring the most active phase of cell bleaching.
3. During the process of "greening", the glucose in the insolublecarbohydrate fraction rapidly decreased, suggesting that itis utilized, as carbon and energy sources, for the chloroplastregeneration. Linolenic acid was found to be synthesized inparallel with formation of chlorophyll. A peculiar pattern ofchange in contents was observed with oleic and palmitic acids,which was interpreted as being related with the process of cellulardivision occurring incidentally during the process of greening.

(Received September 24, 1966; )     

RIBONUCLEIC ACIDS IN SOLUBLE CYTOPLASM OF GERMINATING BEAN

From 1.5 day-old bean germ-axes and cotyledons were preparedmicrosomal (Ms) and 78,400 /g supernatant (Sp) RNA's by phenolextraction. Sp-RNA from germ-axes differed considerably fromMs.RNA from either tissue with respect of quantitative nucleotidecomposition; the former being very similar to yeast s.RNA. Sp-RNAfrom cotyledons gave an intermediate nucleotide pattern betweenthose of Ms-RNA's and of Sp.RNA of germ-axes. Accepting abilityfor ¹⁴C-leucine in the presnece of added ATP, MgCl₂ and "activatingenzyme" was the highest in Sp-RNA from germ-axes, followed bySp-RNA from cotyledons. Ms.RNA's could hardly function as acceptorfor activated leucine. The capacity of leucine incorporationof cotyledonous Sp-RNA agreed well with that predicted fromits s-RNA level evaluated from the observed nucleotide compositionon the assumption that the Sp.RNA consisted of active RNA ofyeast s-RNA type and inactive RNA of Ms.RNA type. The resultswere discussed along the line of a hypothesis on the presenceof "transportable RNA" in germinating bean seed tissues. (Received July 19, 1960; )     

Further studies on the metabolism of glucose in the process of "glucose-bleaching" of Chlorella protothecoides

Previous studies have demonstrated that when cells of Chlorellaprotothecoides are incubated in a medium containing glucosebut no nitrogen source, they are profoundly bleached with degenerationof chloroplast structure and photosynthetic activity. When anitrogen source (urea) is added to the glucose medium, bleachingof algal cells is greatly suppressed. In this work the metabolismof glucose in the process of glucose-induced bleaching was studiedusing ¹⁴C-glucose as tracer. Changes in algal cell activityfor ¹⁴CO₂-evolution and ¹⁴C-incorporation into various cellularsubstances from ¹⁴C-glucose were followed. Most conspicuouswere increases in cellular activities for assimilating ¹⁴C-glucoseinto lipids (fatty acids) and glucose polymer. When urea wasadded to the glucose medium, the incorporation of ¹⁴C by algalcells into fatty acids was greatly reduced, while the assimilationof ¹⁴C into glucose polymer was increased. These and previous observations suggest that the formation oflarge amounts of lipids (fatty acids) probably is causally relatedto the induction of algal cell bleaching. (Received March 5, 1969; )     

Light-induced absorbance changes at 475-515 nm, and electron flow close to photosystem II in Tris-washed chloroplast fragments

Rapid, reversible light-induced absorbance changes at 475 and515 nm in chloroplast fragments were diminished by washing thefragments with Tris. These diminished absorbance changes wererestoredby the donation of electrons to photosystem II by hydrogen peroxide (Received November 17, 1970; )     

STUDIES ON PHOTOPHOSPHORYLATION: I. TWO-STEP EXCITATION KINETICS OF PHOTOPHOSPHORYLATION

Based on the observations on the time lag and the low efficiencyof photophosphorylation at low light intensities, a ‘two-stepexcitation kinetics’ of photophosphorylation of chloroplastswas developed, which could explain some of the hitherto unexplainedfacts concerning photophosphorylation. By analyses of the experimental results along the line of thetheory, it was inferred that the assumed substance (X) responsiblefor ATP formation occurs in a relatively large quantity of about1 mole/5–20 moles of chlorophyll. It was concluded thatthe high energy intermediate (X^**) of ATP formation which wasassumed to accumulate on pre-illuminating the chloroplasts (inthe absence of ADP and Pi) does not represent a side pool ofextra energy, but a substantial intermediate in the normal courseof ATP formation. Alternative possibilities for the explanation of the experimentalfacts were also discussed. ¹This paper is submitted to the University of Tokyo to fulfilla part of the requirements for the doctorate of H. SAKURAI.