Karl Grumbach

CHLOROPLAST PIGMENTS and THEIR BIOSYNTHESIS IN RELATION TO LIGHT INTENSITY

Abstract— Depending on the light intensity that they received during growth, radish seedlings altered not only the pigment and quinone composition of the thylakoid membrane but also the chloroplast ultrastructure. In strong light, sun chloroplasts of radish were very similar to those from sun leaves of beech trees, while those developed under under dim light possessed a typical shade chloroplast. Radish shade chloroplasts contained a higher chlorophyll content and a higher concentration of xanthophylls resulting in a lower xanthophyll to carotene ratio as compared to sun chloroplasts. Chloroplasts from radish grown in strong light showed a much higher activity in their terpenoid metabolism than plastids from shade plants. Chlorophylls and carotenoids which are involved in the absorption of light and the transfer of energy during photosynthesis were labeled by [3H]‐mevalonate to a much higher degree in plastids from sun leaves as compared to plastids from shade leaves. This shows that in strong light where pigments are continuously broken down and resynthesized in order to maintain photosynthesis, chlorophylls and carotenoids exhibit a much higher turnover rate than the pigments of shade plants.

Distribution of carotenoids in sub-cellular and sub-plastidic fractions of radish seedlings (Raphanus sativus) grown in the presence of bleaching herbicides

Abstract The intracellular and intraplastidic distribution of carotenoids has been investigated in radish seedlings grown in the presence of the herbicides amitrole and SAN 6706. Both herbicides caused bleaching and the plants became deficient in chlorophylls and the usual chloroplast cyclic carotenoids, but accumulated the acyclic carotenoid biosynthetic intermediates 15- cis -phytoene and all- trans -lycopene. In both the untreated and herbicide-treated plants all carotenoids, including phytoene and lycopene, were contained in the plastid. In all cases the normal cyclic carotenoids were located virtually exclusively in the thylakoid or prothylakoid fraction. In amitrole-treated plants, lycopene also was contained only in the thylakoid fraction, whereas phytoene, in these and in SAN 6706-treated plants, was detected in both the thylakoid fraction and an envelope preparation. Possible implications for the biosynthesis of the carotenoids are discussed.

Kinetic of Lipoquinone and Pigment Synthesis in Green Hordeum Seedlings during an Artificial Day-Night Rhythm with a Prolonged Dark Phase

Abstract The effect of a prolonged darkness (48 h) with a following re-illumination on the prenyllipid metabolism of chloroplasts is tested in green Hordeum seedlings. Continuous darkness induces thylakoid and prenyllipid breakdown and changes the remaining lipoquinone and carotenoid metabolism of chloroplasts to that of etioplasts. Re-illumination, in turn, reverses the effects of darkness and regenerates the photosynthetic apparatus within 24 hours by a continuous and specific synthesis of certain thylakoid prenyllipids. 1. The level of chlorophylls, vitamin K1 and that of the oxidized benzoquinone forms, plasto-quinone-9 and α-tocoquinone, decreases continuously in darkness. All these prenyllipids are re synthesized upon re-illumination, whereby a faster destruction rate in the dark (α-tocoquinone + plastoquinone-9 > vitamin K1 > chlorophylls) corresponds to a faster re-accumulation rate in the light. 2. The concentration of the reduced benzoquinones plastohvdroquinone-9 and α-tocopherol. which are preferentially deposited in the osmiophilic plastoglobuli, increases until 24 hours of darkness and decreases thereafter either continuously (plastohydroquinone-9) or exhibits another strong increase (α-tocopherol). Re-illumination results only in the accumulation of the oxidized quinone forms (mainly plastoquinone-9 and little α-tocoquinone) ; the level of plastohydroquinone remains, however, almost constant with a concomitant and steady decrease in the concentration of α-tocopherol. Darkness changes the main metabolite flow in benzoquinone synthesis via the formation of α-tocopherol (a trimethyl-, phythyl-(1,4-benzoquinone derivative) and light (re-illumination) via the production of plastoquinone-9 (a trimethyl, solanesyl-1.4-benzoquinone). 3. Carotenoids are enriched throughout the dark phase (mainly xanthophylls, little β-carotene) with a higher accumulation rate than after re-illumination, which yields again a higher portion of β-carotene. The correlation of prenyl chain synthesis (phytyl chain for chlorophylls and vitamin K1, solanesyl chain for plastoquinone-9) in the light with a reduced rate of carotenoid formation is discussed with respect to prenyl biosynthesis. 4. It is concluded that breakdown and re-synthesis of thylakoids and their prenyllipds, which are described here in a prolonged dark phase with following re-illumination, also occur during natural day-night growth of plants. The turnover of the thylakoid membranes and their lipids does, however, not get visible, since the decomposition in the night is recompensated by new synthesis during day. From the destruction rate one can calculate in a first approximation the biological half life time (τ 1/2) which gives values in the range of 7 to 2,5 days for all thylakoid prenyllipids

Herbicides which Inhibit Electron Transport or Produce Chlorosis and Their Effect on Chloroplast Development in Radish Seedlings II. Pigment Excitation, Chlorophyll Fluorescence and Pigment-Protein Complexes

Abstract DCMU, bentazon, amitrole and SAN 6706 affected the formation of the pigment-protein complexes and caused drastic alterations in the absorption of light and in the transfer of the absorbed energy in the antennae systems. Bentazon and DCMU, photosystem II inhibitors, did not change the pigment absorption and fluorescence excitation spectra. After application of both herbicides the long wavelength fluorescence emission band at 740 nm was reduced similar as in young developing leaves. Although DCMU and bentazon inhibit the photosynthetic electron transport at the same site, bentazon mainly suppressed the formation of the photosystem I complexes CP 1 a and CP 1 while DCMU mainly reduced the photosystem II complex CPa. Bentazon specifically enhanced the formation of LHCP3. This may be important for the increased grana stacking in plastids from bentazon treated plants. The bleaching herbicides amitrole and SAN 6706 inhibited the formation of carotenoids leading to an accumulation of lycopene, phytofluene and phytoene, while the accumulation of chlorophylls was suppressed. This bleaching effect was most pronounced during growth under higher intensities of light. In weak light (100 lux) amitrole reduced the long wavelength fluorescence maximum but the fluorescence excitation was not affected. With amitrole at 2000 lux and SAN 6706 at 100 lux the long wavelength emission band was further decreased and the fluorescence excitation spectra point to a less efficient energy transfer to chlorophyll a. The fluorescence spectra changed due to herbicide treatment resembled those of not yet fully developed leaves. In contrast to the photosystem II herbicides the bleaching herbicides amitrole and SAN 6706 had a similar effect on the formation of pigment-protein complexes. After growth at 2000 lux both herbicides suppressed the formation of the photosystem I complex CP 1 a and the photosystem II complex CPa. At 100 lux only the formation of CPla was affected. Except for DCMU all herbicides assayed primarily changed the formation of photosystem I.

Effect of phytochrome on the biosynthesis of acyclic and cyclic carotenoids in higher plants

Radish plants were grown in the presence of three different herbicides that interfere with the formation of the normal range of cyclic carotenoids, leading to an accumulation of acyclic biosynthetic intermediates, mainly phytoene (SAN 6706 and amitrole) and zeta‐carotene (3852). Plants were then irradiated by four different light programs in order to gain more insight into the first steps of carotenoid biosynthesis and their control by light and phytochrome. In all cases, herbicide‐treated and control, carotenoid biosynthesis was greatly enhanced by red light consistent with an effect of phytochrome on the early steps of the pathway. However, similar enhancement was also obtained after treatment with far‐red light. Indeed with SAN 6706‐treated plants synthesis of phytoene was stimulated to a much greater extent by far‐red light given alone, than by red light. The involvement of phytochrome in the regulation of carotenoid biosynthesis appears not to be as simple as previously supposed.

Photosynthese und Symbiose

Symbiosen gibt es zwischen Pflanzen, aber auch zwischen Tieren und Pflanzen. Auch innerhalb einer Zelle findet man symbioseahnliche Wechselwirkungen zwischen den einzelnen Organellen.

Mechanismus der Photosynthese

Ohne Licht kann eine Pflanze keine Photosynthese betreiben. Die Pflanze nimmt Lichtenergie auf, indem die Chlorophylle und Carotinoide Licht absorbieren. Diese absorbierte Energie wird in den Antennen („Lichtsammeifallen“) weitergeleitet und letztlich auf die Reaktionszentren ubertragen, die dann einen Elektronentransport in Gang setzen. Beim Elektronentransport der Photosynthese wird aus Wasser Sauerstoff freigesetzt und das Reduktionsaquivalent NADPH/H+ gebildet. Gleichzeitig werden Energieaquivalente (ATP) Liber die Photophosphorylierung synthetisiert. Die Prozesse der Lichtabsorption, der Energieubertragung in den Antennen, des Elektronentransportes und der Photophosphorylierung fast man als Primarprozesse der Photosynthese oder unter dem Namen Lichtreaktion zusammen.

Bedeutung der Photosynthese

Nach heutigem Erkenntnisstand ist unser Milchstrasensystem 8 bis 16 Milliarden Jahre alt. Vor etwa 5 Milliarden Jahren sollen unser Sonnensystem und vor 4,6 Milliarden Jahren die einzelnen Planeten enstanden sein. Die meisten Wissenschaftler nehmen heute an, das der Entwicklung von Lebewesen, der biologischen Evolution, eine chemische Evolution vorausgegangen ist, bei der, ausgehend von chemischen Reaktionen der Uratmosphare, immer komplexere organische Verbindungen entstanden sind.

Photosynthese und anthropogene Faktoren

Mit dem Einsetzen der Industrialisierung in diesem Jahrhundert hat die Umweltverschmutzung stark zugenommen. Bis zum Jahr 2000 rechnet man damit, das 15–20% der heute vorhandenen Tier- und Pflanzenarten ausgestorben sind. Umweltverschmutzung hat schon zu einer sichtbaren Selektion resistenter Pflanzenarten, wie z.B. zu einer nitrophilen Ersatzgesellschaft an Flussen gefuhrt.

Entstehung der Photosynthese-Aktivität im Licht

Eine Pflanze, die im Dunkeln angezogen wurde, kann bei Belichtung nicht sofort Photosynthese betreiben. Die Photosynthese setzt erst nach 1–2 h Belichtung ein, da die Pflanze erst die fur die Photosynthese erforderlichen Einzelkomponenten synthetisieren und diese dann in die Thylakoide einbauen mus. Eine wichtige Voraussetzung fur die Entstehung der Photosynthese-Aktivitat im Licht ist die Biosynthese der Chlorophylle, die man schon als Ergrunung der Pflanze mit blosem Auge verfolgen kann. Nicht nur im Dunkeln angezogene Pflanzen sondern auch wachsende grune Gewebe bilden standig neue Chioroplasten und damit neue Photosynthese-Einheiten.