A Strategy for the Proliferation of Ulva prolifera, Main Causative Species of Green Tides, with Formation of Sporangia by Fragmentation

Ulva prolifera, a common green seaweed, is one of the causative species of green tides that occurred frequently along the shores of Qingdao in 2008 and had detrimental effects on the preparations for the 2008 Beijing Olympic Games sailing competition, since more than 30 percent of the area of the games was invaded. In view of the rapid accumulation of the vast biomass of floating U. prolifera in green tides, we investigated the formation of sporangia in disks of different diameters excised from U. prolifera, changes of the photosynthetic properties of cells during sporangia formation, and development of spores. The results suggested that disks less than 1.00 mm in diameter were optimal for the formation of sporangia, but there was a small amount of spore release in these. The highest percentage of area of spore release occurred in disks that were 2.50 mm in diameter. In contrast, sporangia were formed only at the cut edges of larger disks (3.00 mm, 3.50 mm, and 4.00 mm in diameter). Additionally, the majority of spores liberated from the disks appeared vigorous and developed successfully into new individuals. These results implied that fragments of the appropriate size from the U. prolifera thalli broken by a variety of factors via producing spores gave rise to the rapid proliferation of the seaweed under field conditions, which may be one of the most important factors to the rapid accumulation of the vast biomass of U. prolifera in the green tide that occurred in Qingdao, 2008

Modeling of chlorophyll a fluorescence kinetics in plant cells. Derivation of a descriptive algorithm.

In this chapter, we present the model and simulation of light-driven chlorophyll fluorescence induction in 10–20 min dark-adapted intact leaves and thylakoids. The algorithm for it has been derived from analyses of fluorescence kinetics upon excitation with single- (STF), twin- (TTF) and repetitive STF excitations. These analyses have led to definition and formulation of rate equations that describe the sequence of electron transfer steps associated with the oxidation of the oxygen evolving complex (OEC) and the reduction of the primary plastoquinone acceptor QA of photosystem II (PS II) in multi turnover excitation (MTF). The model considers heterogeneity in reaction centers (RCs) associated with the S-states of the OEC and incorporates the presence of a 20–35% fraction of QB nonreducing RCs that probably is identical with the S0 fraction. The fluorescence induction algorithm (FIA) considers a photochemical O—J—D, a photo-electrochemical J—I and an I—P component (phase), which probably is associated with a photoelectric interaction between PS I and PS II. The photochemical phase incorporates the kinetics associated with the double reduction of the acceptor pair of pheophytin (Phe) and plastoquinone QA[PheQA] in QBnonreducing RCs and the associated doubling of the variable fluorescence, in agreement with the three-state trapping model (TSTM) of PS II. Application of and results with the algorithm are illustrated for a variety of MTF-induced OJDIP curves, measured in dark-adapted leaves and thylakoids under various light and dark conditions

On the polyphasic quenching kinetics of chlorophyll a fluorescence in algae after light pulses of variable length

This study reports on kinetics of the fluorescence decay in a suspension of the alga Scenedesmus quadricauda after actinic illumination. These are monitored as the variable fluorescence signal in the dark following light pulses of variable intensity and duration. The decay reflects the restoration of chlorophyll fluorescence quenching of the photosystem II (PSII) antennas and shows a polyphasic pattern which suggests the involvement of different processes. The overall quenching curve after a fluorescence-saturating pulse (SP) of 250-ms duration, commonly used in pulse amplitude modulation applications as the tool for estimating the maximal fluorescence (Fm), has been termed P–O, in which P and O have the same meaning as used in the OJIP induction curve in the light. Deconvolution of this signal shows at least three distinguishable exponential phases with reciprocal rate constants of the order of 10, 102, and 103 ms. The size of the long ([103 ms) and moderate (*102 ms) lasting components relative to the complete quenching signal after an SP increases with the duration of the actinic pulse concomitantly with an increase in the reciprocal rate constants of the fast (*10 ms) and moderate quenching phases. Fluorescence responses upon single turnover flashes of 30-ls duration (STFs) given at discrete times during the P– O quenching were used as tools for identifying the quencher involved in the P–O quenching phase preceding the STF excitation. Results are difficult to interpret in terms of a single-hit two-state trapping mechanism with distinguishable quenching properties of open and closed reaction centers only. They give support for an earlier hypothesis on a double-hit three-state trapping mechanism in which the so-called semi-closed reaction centers of PSII are considered. In these trapping-competent centers the single reduced acceptor pair [PheQA]1-, depending on the size of photoelectrochemically induced pH effects on the QBbinding site, functions as an efficient fluorescence quencher

On the chlorophill a fluorescence yield in chloroplasts upon excitation with twin turnover flashes (TTF) and high frequency flash trains

Chlorophyll fluorescence is routinely taken as a quantifiable measure of the redox state of the primary quinone acceptor QA of PSII. The variable fluorescence in thylakoids increases in a single turnover flash (STF) from its low dark level F o towards a maximum F mSTF when QA becomes reduced. We found, using twin single turnover flashes (TTFs) that the fluorescence increase induced by the first twin-partner is followed by a 20¿30% increase when the second partner is applied within 20¿100 ¿s after the first one. The amplitude of the twin response shows a period-of-four oscillation associated with the 4-step oxidation of water in the Kok cycle (S states) and originates from two different trapped states with a life time of 0.2¿0.4 and 2¿5 ms, respectively. The oscillation is supplemented with a binary oscillation associated with the two-electron gate mechanism at the PSII acceptor side. The F(t) response in high frequency flash trains (1¿4 kHz) shows (i) in the first 3¿4 flashes a transient overshoot 20¿30% above the F mSTF = 3*F o level reached in the 1st flash with a partial decline towards a dip D in the next 2¿3 ms, independent of the flash frequency, and (ii) a frequency independent rise to F m = 5*F o in the 3¿60 ms time range. The initial overshoot is interpreted to be due to electron trapping in the S0 fraction with QB-nonreducing centers and the dip to the subsequent recovery accompanying the reoxidation of the double reduced acceptor pair in these RCs after trapping. The rise after the overshoot is, in agreement with earlier findings, interpreted to indicate a photo-electrochemical control of the chlorophyll fluorescence yield of PSII. It is anticipated that the double exciton and electron trapping property of PSII is advantageous for the plant. It serves to alleviate the depression of electron transport in single reduced QB-nonreducing RCs, associated with electrochemically coupled proton transport, by an increased electron trapping efficiency in these centers

Photochemical and photoelectrochemical quenching of chlorophyll fluorescence in photosystem II

This paper deals with kinetics and properties of variable fluorescence in leaves and thylakoids upon excitation with low intensity multi-turnover actinic light pulses corresponding with an excitation rate of about 10 Hz. These show a relatively small and amply documented rise in the sub-s time range towards the plateau level Fpl followed by a delayed and S-shaped rise towards a steady state level Fm which is between three and four fold the initial dark fluorescence level Fo. Properties of this retarded slow rise are i) rate of dark recovery is (1–6 s)- 1, ii) suppression by low concentration of protonophores, iii) responsiveness to complementary single turnover flash excitation with transient amplitude towards a level Fm which is between five and six fold the initial dark fluorescence level Fo and iv) in harmony with and quantitatively interpretable in terms of a release of photoelectrochemical quenching controlled by the trans-thylakoid proton pump powered by the light-driven Q cycle. Data show evidence for a sizeable fluorescence increase upon release of (photo) electrochemical quenching, defined as qPE. Release of qPE occurs independent of photochemical quenching defined here as qPP even under conditions at which qPP = 1. The term photochemical quenching, hitherto symbolized by qP, will require a new definition, because it incorporates in its present form a sizeable photoelectrochemical component. The same is likely to be true for definition and use of qN as an indicator of non photochemical quenchin

Life at elevated CO2 modifies the cell composition of Chromera velia

We investigated the response to high CO2 of Chromera velia, a photosynthetic relative of apicomplexan parasites that is possibly involved in symbiotic associations with scleractinian corals. The inorganic C content in the proximity of the symbiotic algal cells within the tissues of scleractinians is disputed. According to some authors, it is very high. A higher C content in the endodermal tissues of scleractinians than in the external environment may have favoured the constitution of symbiosis with organisms such as Symbiodinium and Chromera that have a type II Rubisco, which is intrinsically ill suited to low CO2 environments. We thus cultured C. velia at the very high inorganic C estimated by some authors and assessed its growth and photosynthetic performance. We also evaluated whether these conditions affected C allocation and elemental stoichiometry in C. velia cells by state-of-the-art Fourier transform infrared spectroscopy and total reflection X-ray fluorescence spectrometry in combination with more traditional biochemical and physiological techniques. Our results demonstrated that C. velia was capable of coping with very high CO2, which even stimulated biomass production and increased N, P, Mn, Fe and Zn use efficiency. Growth at elevated CO2 changed the stoichiometric relationships among elements in C. velia cells, but had no effect on the relative abundance of the main organic pools. The high CO2 in the animal tissue surrounding the photosynthetic cells may therefore facilitate C. velia life in symbiosis

The phycobilisomes of Synechococcus sp. are constructed to minimize nitrogen use in nitrogen-limited cells and to maximize energy capture in energy-limited cells

Synechococcus sp. UTEX LB2380 is a coastal strain of a cosmopolitan cyanobacterial genus. In coastal waters, N and light availability are highly variable and their interplay may influence C allocation and photosynthetic performance. In this paper, we compared the impact of nitrogen (N) limitation and energy (light, E) limitation on phycobilisome composition and photosynthesis, in the presence of either NO3- or NH4+. Our hypothesis was that the phycobilisome composition would be influenced by the factor limiting growth. Our results show that N-limited cells adjusted their phycobilisome antenna to minimize N utilization, whereas E-limited cells had a phycobilisome composition tailored to alleviate E deficiency. The N-source was relevant for the pigment composition, under both limitations. When N limited growth, excess energy management may become important to decrease the risk of photoinhibition and oxidative stress; when the sink of electrons constituted by NO3- reduction was not present, the cells tended to decrease their phycobiliprotein content, possibly in order to minimize the size of PSII antennas and decrease excitation. When energy was limiting, the energy saved for N assimilation in NH4+-grown cells was invested in antenna pigments to allow for a higher energy input

The chlorophyll a fluorescence induction pattern in chloroplasts upon repetitive single turnover excitations: Accumulation and function of QB-nonreducing centers

The increase of chlorophyll fluorescence yield in chloroplasts in a 12.5 Hz train of saturating single turnover flashes and the kinetics of fluorescence yield decay after the last flash have been analyzed. The approximate twofold increase in Fm relative to Fo, reached after 30-40 flashes, is associated with a proportional change in the slow (1-20 s) component of the multiphasic decay. This component reflects the accumulation of a sizeable fraction of QB-nonreducing centers. It is hypothesized that the generation of these centers occurs in association with proton transport across the thylakoid membrane. The data are quantitatively consistent with a model in which the fluorescence quenching of QB-nonreducing centers is reversibly released after second excitation and electron trapping on the acceptor side of Photosystem I

In search of a physiological basis for covariations in light-limited and light-saturated photosynthesis

The photosynthesis-irradiance (PE) relationship links indices of phytoplankton biomass (e.g. chl) to rates of primary production. The PE curve can be characterized by two variables: the light-limited slope (alpha(b)) and the light-saturated rate (P-max(b)) of photosynthesis. Variability in PE curves can be separated into two categories: that associated with changes in the light saturation index, E-k (=P-max(b)/alpha(b)) and that associated with parallel changes in alpha(b)and P-max(b) (i.e. no change in E-k). The former group we refer to as ``E-k-dependent'' variability, and it results predominantly from photoacclimation (i.e. physiological adjustments in response to changing light). The latter group we refer to as ``E-k-independent'' variability, and its physiological basis is unknown. Here, we provide the first review of the sporadic field and laboratory reports of E-k-independent variability, and then from a stepwise analysis of potential mechanisms we propose that this important yet largely neglected phenomenon results from growth rate-dependent variability in the metabolic processing of photosynthetically generated reductants (and generally not from changes in the oxygen-evolving PSII complexes). Specifically, we suggest that as growth rates decrease (e.g. due to nutrient stress), reductants are increasingly used for simple ATP generation through a fast (<1s) respiratory pathway that skips the carbon reduction cycle altogether and is undetected by standard PE methodologies. The proposed mechanism is consistent with the field and laboratory data and involves a simple new ``twist'' on established metabolic pathways. Our conclusions emphasize that simple reductants, not reduced carbon compounds, are the central currency of photoautotrophs