Inhibition of photosynthetic electron transport and formation of inactive chlorophyll in winter stressed Pinus silvestris

Kinetics of fluorescence at room temperature, electron transport and photooxidation of P700 and cytochrome f have been studied in chloroplasts isolated from active and winter stressed Pinus silvestris. The winter stress induced block in the electron transport chain between the two photosystems is close to the site of plastoquinone, since winter stress and DCMU caused the same type of inhibition of the reoxidation of the primary electron acceptor Q of photosystem II. No winter inhibition of the electron transport between cytochrome f and P700 was observed. Time course studies of P700 photooxidation in chloroplasts of active and winter stressed pine have shown that the photosynthetic unit size must be about equal in the two types of chloroplasts. An apparent increase of the photosynthetic unit size was induced by winter stress, as revealed by the high chlorophyll/P700 ratio of winter stressed pine. The phenomenon is explained by the formation of photosynthetically inactive chlorophyll. Low-temperature fluorescence emission spectra were recorded when either chlorophyll a (433 nm) or chlorophyll b (477 nm) were preferentially excited. Winter stress induced the formation of a chlorophyll a fraction emitting at 673 nm. This chlorophyll is most likely derived from the chlorophyll a antennae of the two photosystems, and it probably contributes to the photosynthetically inactive pool of chlorophyll in winter stressed pine. The light harvesting chlorophyll a/b complex is relatively resistant to winter stress.     

Phycochromes b and d: their occurrence in some phycoerythrocyanin-containing blue-green algae (cyanobacteria)

Abstract
Phycochromes b and d, two types of photoreversibly photochromic pigments previously extracted from the blue-green alga Tolypothrix distorta , which contains phycoerythrocyanin, have now been found in three Anabaena strains also containing phycoerythrocyanin. Tests for the presence of phycochromes b and d in a number of blue-green algae lacking phycoerythrocyanin have been negative. The possibility that phycochrome b-type absorbance changes are due to changes in the α-subunit of phycoerythrocyanin is discussed.     

Some effects of humidity on the light reaction of photosynthesis in the lichens Cladonia impexa and Collema flaccidium

Luminescence and fluorescence were measured at different relative humidities in the lichen Cladonia impexa Harm. Both parameters showed a constant value at relative humidities lower than 80%: thereafter they increased. Low relative humidity was found to decrease energy transfer from chlorophyll b to chlorophyll a. inhibit electron transport, lower electron holding capacity on the reduced side of photosystem two and impair far-red-induced afterglow, reflecting photophosphorylation. In Collema flaccidium Ach. Ach. energy transfer from the accessory pigments phycocyanin and phycoerythrin to chlorophyll a was only possible at high relative humidity. The results are interpreted as due to conformational changes caused by changed water content in the lichen.     

Decarboxylation and Transport of Auxin in Segments of Sunflower and Cabbage Roots. II. A Chromatographic Study Using IAA-1-14C and IAA-5-3H

The polar movement of IAA has been examined in 5-mm root segments of Brassica oleracea and Helianthus annum. The movement was studied partly with IAA-1-¹⁴C and partly with IAA-5-³H. In both plants a slight acropetal flux of ¹⁴C and IAA-³H was found through the segments. The recovered radioactivity in the agar receiver blocks and in the receiver end of the segments increased as a function of time. A large portion of the applied IAA was converted on the cut surfaces and in the tissues of the segments. Chromatographic analysis indicated different destruction products when estimated by scintillation counting and by spraying with in-dole reagent (DMCA). Chromatograms run in isopropanol: ammonia: water, 8:1:1, yielded three different substances, one spot near the starting line and one near the front, neither of which has been identified. Finally there was a spot with R_f 0.4–0.6, probably representing IAA.     

1:1 Distribution between Induced Mutants and Phenocopies

BY ultraviolet irradiation of germiings of the multicellular alga Ulva mutabilis Føyn, it is possible to obtain chimaeric plants which consist of two morphologically different parts of different genetic constitution, one part wild type and the other mutant^{1, 2}. Other plants found have been identical in appearance to the chimaeras, though the morphologically different parts were both genetically wild type. They should be considered phenocopies of the genetic chimaeras. Surprisingly, the genetical chimaeras and their phenocopies were found in equal numbers. This observation and the previous one that only complete mutations are found after ultraviolet irradiation of Ulva cells¹, can be explained if only one of the two strands in the DNA molecule is genetically conserved.     

The State of Protochlorophyll and Chlorophyll in Corn Roots

The protochlorophyll(ide) present in primary roots of dark-grown corn (Zea mays) seedlings has an in vivo absorption maximum at 634 nm. Red light converts the pigment to chlorophyll(ide) a with an absorption maximum at 675 nm.     

Seasonal and Experimentally Induced Changes in the Ultrastructure of Chloroplasts of Pinus silvestris

The ultrastructure of chloroplasts in mesophyll cells of Pinus silvesris was examined under the electron microscope. Secondary needles were regularly sampled from a tree in a natural stand for one year. Primary needles from one-year-old seedlings exposed to frost hardening and dehardening conditions in a controlled environment chamber were also studied. These seedlings were exposed to 8 or 55 W m^-2. All needles were put in fixative at the different sampling dates and stored in a refrigerator until they were prepared for electron microscopy at the end of the experimental period. During the summer the choroplasts were symmetrically shaped and heavily loaded with starch. The membrane systems were well developed and consisted of both grana and stroma thylakoids. In autumn and during early artificial frost hardening the starch content was reduced, the chloroplasts appeared amoeboid and membrane-free stroma regions were seen. Later the chloroplasts became swollen and aggregated in one part of the cell. Starch was lost and the chloroplasts aggregated earlier at 8 W m^-2 than at 55 W m^-2. During winter the stroma thylakoids were first reduced in number and later even the grana thylakoids were damaged, resulting in mostly disorganized single membranes. Also the chloroplast envelope disappeared. In spring and early summer the chloroplasts migrated to the proximity of the cell walls. The membrane systems were reorganized and starch accumulated. During the first days of artificial dehardening the photosynthetic membranes were severely damaged, especially at 55 W m^-2, but soon new membranes were formed. Starch accumulated earlier at 55 than at 8 W m^-2. The reported ultrastructural variations are discussed in relation to functional and biochemical fluctuations caused by the season or by artificial variations in the climate as demonstrated earlier.     

Action Spectra for in vivo and in vitro Conversions of Phycochrome b, a Reversibly Photochromic Pigment in a Blue-Green Alga, and Its Separation from Other Pigments

Phycochrome b, one of the reversibly photochromic pigments found in Tolypothrix distorta seems to exist in only two forms: P^b₅₀₀ and P^b₅₇₀. The pigment has been spectroscopically demonstrated in vivo. It has also been separated from other pigments. Two different methods for separation have been used: isoelectric focusing and gel filtration. Preparations of purified phycobilisomes contain phycochrome b. The in vivo and in vitro absorption difference spectra were determined as well as action spectra for the conversions in vitro and in vivo of P^b₅₀₀ to P^b₅₇₀ and vice versa. Transformation kinetics of phycochrome b show that the conversions in both directions are initially first-order reactions.     

Photosynthetic CO2 fixation in spinach chloroplasts inhibited by pine chloroplasts or extracts of pine chloroplasts

Chloroplasts isolated from pine needles were found to be inactive with respect to CO₂ fixation. Since it was suspected that pine needles may contain substances inhibitory to photosynthesis, studies were carried out using photosynthetically active isolated spinach chloroplasts and chloroplasts isolated from pine needles. When isolated pine chloroplasts were suspended in buffer and were added to isolated spinach chloroplasts they inhibited photosynthetic CO₂ fixation. When the pine chloroplasts were separated from the medium by centrifugation, the separated pine chloroplasts severely inhibited CO₂ fixation by isolated spinach chloroplasts, but the supernatant solution from the pine chloroplasts was not inhibitory. As little as 5% pine chloroplasts (based on chlorophyll content) produced 50% inhibition of CO₂ fixation by the spinach chloroplasts. Studies of fixation of ¹⁴C-labelled CO₂ by spinach chloroplasts were carried out in which after 5 min photosynthesis the pine chloroplasts were added. It was found that the subsequent inhibition of spinach CO₂ fixation was neither due to any effect on the rate of export of photosynthetic metabolites from the chloroplasts to the medium, nor to a direct effect on the RUBP carboxylase reaction. The principal effect was found to be an inhibition of the conversion of fructose-1,6-bisphosphate and sedoheptulose-1,7-bisphosphate to the respective monophosphates and inorganic phosphate. From this finding it was concluded that a principal effect of the inhibition by pine chloroplasts is probably an inhibition either directly or indirectly of the bisphosphatase enzymes in the spinach chloroplasts. Based on its distribution between organic and aqueous acidic or neutral solutions, the inhibitory factor of the pine chloroplasts must be lipophilic. Most of the factor could be transferred to an aqueous phase in a strongly alkaline solution. Following subsequent acidification of the aqueous phase the activity could be completely transferred back into the organic phase. This procedure allowed for separation of the inhibitory factor from most of the pigments and other lipophilic substances present in the pine chloroplasts and yielded a preparation which could be subsequently fractionated by thin layer chromatography. UV absorption was found in two fast moving spots and at the origin. The fastest running spot from the thin layer chromatography plate was found to be the one containing most of the inhibitory activity.     

The Devonian nekton revolution

Klug, C., Kröger, B., Kiessling, W., Mullins, G.L., Servais, T., Frýda, J., Korn, D. & Turner, S. 2009: The Devonian nekton revolution. Lethaia, 10.1111/j.1502‐3931.2009.00206.x Traditional analyses of Early Phanerozoic marine diversity at the genus level show an explosive radiation of marine life until the Late Ordovician, followed by a phase of erratic decline continuing until the end of the Palaeozoic, whereas a more recent analysis extends the duration of this early radiation into the Devonian. This catch‐all approach hides an evolutionary and ecological key event long after the Ordovician radiation: the rapid occupation of the free water column by animals during the Devonian. Here, we explore the timing of the occupation of the water column in the Palaeozoic and test the hypothesis that ecological escalation led to fundamental evolutionary changes in the mid‐Palaeozoic marine water column. According to our analyses, demersal and nektonic modes of life were probably initially driven by competition in the diversity‐saturated benthic habitats together with the availability of abundant planktonic food. Escalatory feedback then promoted the rapid rise of nekton in the Devonian as suggested by the sequence and tempo of water‐column occupation. □Devonian, diversity, ecology, food webs, nekton, plankton, radiation.