Richard T. Wang

ACTION SPECTRA FOR PHOTOREACTIONS I AND II OF PHOTOSYNTHESIS IN THE BLUE‐GREEN ALGA ANACYSTIS NIDULANS

Abstract— Action spectra for photoreactions I and II of photosynthesis were obtained for Anacystis nidulans and three of its variants which had altered chlorophyll/phycocyanin ratios. The spectra are properly scaled to each other. They provide information on contributions of phycocyanin and chlorophyll to initial absorption and final distribution of excitation energy to reaction centers I and II. In normally pigmented cells the light harvesting pigments for photoreaction I include about 40% of the phycocyanin and 84% of the chlorophyll. Both in normal cells and in cells with altered pigmentation excitation energy from phycocyanin is delivered to photoreaction II via a small number of chlorophylls. In response to alterations in chlorophyll/phycocyanin ratio Action I spectra showed large variations whereas Action II spectra were essentially invariant. The result is taken to mean that alteration in chlorophyll components in Anacystis is attended by a special restriction: there are only small changes in amount of chlorophyll accessible to photoreaction II in the face of large changes in amount committed to photoreaction I.

ON SPECTRAL CONTROL OF PIGMENTATION IN ANACYSTIS NIDULANS (CYANOPHYCEAE)1,2

Growth of Anacystis nidulans (Richt.) Drouet & Daily in wavelengths of light predominantly absorbed by chlorophyll a causes a dramatic lowering in chlorophyll content and in the chlorophylllphycocyanin ratio. A limit to the effect is reached in far red (680 nm) light where the ratio chlorophylllphycobilinogen falls to <0.3. A special water bath for culture tubes was illuminated by tungsten‐halogen lamps through far red (>650 nm)filters; it gave the same extreme pigment ratio together with a high specific growth rate of 2.5 day‐1. Compared with normally pigmented cells there are three features which accompany the low‐chlorophyll condition of far red light. At 677 nm relative quantum efficiency increases but action decreases. Synthesis of total pigment and total cell material in far red light also decreases. These observations suggest that the low chlorophyll response to far red light reflects an incompetence rather than an adaptation.

Effects of water-soluble components of petroleum oils and aromatic hydrocarbons on Barnacle larvae

The effects of the water-soluble fractions (WSF) of petroleum oils and of solutions of aromatics on embryos and nauplii of barnacles (Chthamalus fragilis and Balanus amphitrite niveus) were investigated. The oils tested were S. Louisiana, Alaska, Kuwait, Venezuela crudes, Diesel fuel, Bunker C, No. 2 fuel and crankcase oils. Eighteen aromatic hydrocarbons occurring in petroleum oils were also tested. Observations were made on development and hatching of embryos, and the activity, phototaxis and survival of larvae. Acute experiments (1 h duration) were carried out in glass tubes illuminated above, and larvae remaining on the bottom were separated from those actively swimming. Concentrations at which half the larvae occurred in the bottom fraction were determined. Oils were toxic in the series used: crank case > No. 2 fuel oil > Bunker C > Diesel > Venezuela > Kuwait > Alaska > S. Louisiana (in terms of percentages of WSF). Relative toxicities of the aromatics (in terms of percentages of saturated solutions) are given. Embryonic development and larval activity were adversely affected by No. 2 fuel oil at a concentration of 3 ppm and larval activity by naphthalene at the same level.

On the State 1-State 2 phenomenon in photosynthesis

Abstract The State 1-State 2 phenomenon of photosynthesis was studied in Chlorella by measuring the flash yield (Y) and the modulated rate ( v ) of oxygen evolution induced by weak modulated 650-nm light. From light intensity curves, intensities of 650 and 710 nm background and preilluminations were chosen to give maximum values of Y and v . Following long preilluminations in 710 nm (State 1) or in 650 nm (State 2), Y and v were measured in background light of chosen wavelength. The resulting plots of v vs Y show a discontinuity between State 1 and State 2. They confirm the predictions of Bonaventura and Myers [(1969) Biochim. Biophys. Acta 189, 366–383] and are consistent with changes in α (fraction of absorbed light captured by System II) as explanation of the State 1–State 2 phenomenon. When the intensity of 710 nm preillumination was too low, the characteristics of State 1 were not fully developed and the results then were similar to those of Delrieu [(1972) Biochim. Biophys. Acta 256, 293–299].

SIMULTANEOUS MEASUREMENT OF ACTION SPECTRA FOR PHOTOREACTIONS I AND II OF PHOTOSYNTHESIS

Abstract— We have devised a method of obtaining simultaneous action spectra for photoreactions I and II by analysis of direct and indirect effects involved in enhancement. The method requires previous determination of the neutral wavelength which gives maximum quantum yield by virtue of equal fractions of open reaction centers (p and q) for each photoreaction. A sufficient intensity of the neutral wavelength is used as a constant background. Upon addition of a weak modulated measuring light of intensity Im and wavelength λm two amperometric signals are obtained for rate of oxygen evolution. A modulated signal (AC¯) isolates the direct effect of Im and gives action of photoreaction II as AC/Im. An increment in total rate (ΔDC) also includes an indirect effect of Im in perturbing reaction center conditions (p and q). From analysis of interaction of the two photoreactions, action for photoreaction I can be estimated as (2 ΔDC‐AC)/Im. The method is applicable to whole cells, properly scales the two action spectra to each other, and removes contribution of the State 1‐State 2 phenomena. Action spectra were obtained for Chlorella.

On the O2 flash yields of two cyanophytes

Abstract We explored O 2 flash yield in two cyanophytes, Anacystis nidulans and Agmenellum quadruplicatum . On a rate-measuring electrode, a single flash gave a contour of O 2 evolution with a peak at about 10 ms which was maximum (100) for 680 nm background light. On 625 nm illumination the peak was smaller (62) but was followed by an increased tail of O 2 attributed to enhancement of the background. After a period of darkness, repetitive flashes (5 Hz) gave a highly damped initial oscillation in individual flash yields which finally reached steady state at 94% of the yield for 680 nm illumination. When O 2 of repetitive flashes was measured as an integrated flash yield the results was distinctive and similar to that for a continuous light 1 (680 nm). An apparent inhibition of respiration which persisted into the following dark period was taken as evidence for the Kok effect. With a concentration-measuring electrode, integrated flash yield vs. flash rate showed the same nonlinear behavior as O 2 rate vs. intensity of light 1. We draw three conclusions about the two cyanophytes. (a) The plastoquinone pool is substantially reduced in darkness. (b) Because of a high ratio of reaction centers, reaction center 1 / reaction center 2, for the two photoreactions, saturating flashes behave as light 1. (c) Because repetitive flashes are light 1, they also give a Kok effect which must be guarded against in measurements designed to count reaction centers.

Spontaneous pigment mutants of Anacystis nidulans selected by growth under far-red light

Under far-red (>650 nm) illumination Anacystis nidulans grows poorly and develops a low chlorophyll content. During continued culture over many generations there are increases in growth rate and in the chlorophyll/phycocyanin ratio, usually occurring in concomitant and stepwise fashion. From such selection cultures six clones have been established which differ from the parent in pigment content and show improved growth rate in far-red light. From the evidence at hand the six clones are presumed to be spontaneous mutants selected under the photosynthetically restrictive condition of far-red illumination.

ENERGY TRANSFER BETWEEN PHOTOSYNTHETIC UNITS ANALYZED BY FLASH OXYGEN YIELD vs. FLASH INTENSITY

Abstract— Relative yield of O2 (Y) was measured in Chlorella pyrenoidosa in response to varied intensity (l) of single 10μsec flashes on a constant low background of 710 nm light. Analysis is based on the proposition that the photochemical event leading to O2 evolution occurs at a reaction center or trap which requires a time much longer than the flash for regeneration by dark reactions. Hence O2, flash yield measures the number of traps ‘killed’ and allows treatment in terms of target theory. Data for Y vs. l were analyzed by computer fitting to four models. The first three models supposed that each unit (aggregate of light‐harvesting pigment molecules) contains one, two, and three traps, respectively, and allows no transfer of excitation energy out of the unit. The last model supposed only one trap per unit and a probability of transfer out of a unit with closed trap. Among the first three models, the data best fit the one with two traps per unit. A slightly better fit for two traps per unit was obtained by introducing a trapping efficiency less than unity. An equally good fit was also obtained with the model of the Joliots with a probability of 0.3 that excitation energy in a unit with closed trap is transferred to another unit. Uncertainties in analysis arose from the necessity of treating maximum flash yield as an estimated parameter and by the possible inhomogeneity in units and traps.

Studies on the Eyes of Bigeyes (Teleostei Priacanthidae) with Special Reference to the Tapetum Lucidum

Eyes of glasseyes (Priacanthidae) show conspicuous eyeshine and have a brilliant tapetum in the chorioid. The tapetum underlies the entire retina; it is composed of several rows of reflecting cells which contain stacks of flat crystals lying parallel to the retinal surface in the central fundus and obliquely towards the periphery. Reflexion is orange and specular; the reflexion spectrum is a broad band centred at about 630 nm. Processes of the pigment epithelium contain black pigment in some parts of the eye; pigment is especially dense in a horizontal central band and in the lower field, but is absent from the cell bases. The ultrastructure of the pigment epithelium and of the tapetum is described. The crystals and intervening cytoplasmic lamellae are organized as quarter-wavelength films to give maximal reflexion of long wavelengths (orange and red light) by constructive interference. Rods and cones are present; there is no retinomotor activity. The mechanism of reflexion, efficiency of the tapetum and role of the retinal pigment are discussed.

On the origins of 718 nm fluorescence from Porphyridium cruentum at 77 K.

Emission spectra and transient behavior of fluorescence in Porphyridium cruentum have been studied in search of the pathway of excitation energy from the phycobilisome to Photosystem I (PS I) of photosynthesis. For activating light at 436 nm, absorbed almost entirely by chlorophyll, fluorescence is dominated by the 718 nm band generally attributed to chlorophyll of PS I. Activating light at 550 nm, absorbed mostly by the phycobilisome, gives rise to the distinctive fluorescence band of PS II chlorophyll at 696 nm but also gives a large component at 718 nm. Analysis depends critically upon the source of emission at 718 nm under 550 nm activation: does it arise from PS I or PS IIC0 Ley and Butler (Ley, A.C. and Butler, W.L. (1976) Proc. Natl. Acad. Sci. U.S.A. 73, 3956-3960) have proposed that the 718 nm arises mostly from PS I, to which it is transferred by spillover from PS II. We suggest a different proposition: that under 550 nm activation most of the 718 emission arises from PS II. Analysis shows that this proposition provides an alternative explanation. Using the small change in fluorescence yield observed under 436 nm activation as a monitor of excitation in PS I, we provide evidence that under 550 activation most of the 718 nm fluorescence arises from PS II.