The development of antenna complexes of barley (Hordeum vulgare cv. Akcent) under different light conditions as judged from the analysis of 77 K chlorophyll a fluorescence spectra

Using 77 K chlorophyll a (Chl a) fluorescence spectra in vivo, the development was studied of Photosystems II (PS II) and I (PS I) during greening of barley under intermittent light followed by continuous light at low (LI, 50 μmol m⁻² s⁻¹) and high (HI, 1000 μmol m⁻² s⁻¹) irradiances. The greening at HI intermittent light was accompanied with significantly reduced fluorescence intensity from Chl b excitation for both PS II (F685) and PS I (F743), in comparison with LI plants, indicating that assembly of light-harvesting complexes (LHC) of both photosystems was affected to a similar degree. During greening at continuous HI, a slower increase of emission from Chl b excitation in PS II as compared with PS I was observed, indicating a preferred reduction in the accumulation of LHC II. The following characteristics of 77 K Chl a fluorescence spectra documented the photoprotective function of an elevated content of carotenoids in HI leaves: (1) a pronounced suppression of Soret region of excitation spectra (410–450 nm) in comparison with the red region (670–690 nm) during the early stage of greening indicated a strongly reduced excitation energy transfer from carotenoids to the Chl a fluorescing forms within PS I and PS II; (2) changes in the shape of the excitation band of Chl b and carotenoids (460–490 nm) during greening under continuous light confirmed that the energy transfer from carotenoids to Chl a within PS II remained lower as compared with the LI plants. This revised version was published online in June 2006 with corrections to the Cover Date.     

Energy transfer in reconstituted peridinin-chlorophyll-protein complexes: ensemble and single-molecule spectroscopy studies

We combine ensemble and single-molecule spectroscopy to gain insight into the energy transfer between chlorophylls (Chls) in peridinin-chlorophyll-protein (PCP) complexes reconstituted with Chl a, Chl b, as well as both Chl a and Chl b. The main focus is the heterochlorophyllous system (Chl a/b-N-PCP), and reference information essential to interpret experimental observations is obtained from homochlorophyllous complexes. Energy transfer between Chls in Chl a/b-N-PCP takes place from Chl b to Chl a and also from Chl a to Chl b with comparable Förster energy transfer rates of 0.0324 and 0.0215 ps⁻¹, respectively. Monte Carlo simulations yield the ratio of 39:61 for the excitation distribution between Chl a and Chl b, which is larger than the equilibrium distribution of 34:66. An average Chl a/Chl b fluorescence intensity ratio of 66:34 is measured, however, for single Chl a/b-N-PCP complexes excited into the peridinin (Per) absorption. This difference is attributed to almost three times more efficient energy transfer from Per to Chl a than to Chl b. The results indicate also that due to bilateral energy transfer, the Chl system equilibrates only partially during the excited state lifetimes.     

Linear dichroism of microalgae,developing thylakoids and isolated pigment-protein complexes in stretched poly (vinyl alcohol) films at 77 K

A variety of unicellular algae, thylakoids from higher plants in different stages of maturity and isolated pigment-protein complexes were oriented in stretched polyvinyl alcohol films. Low temperature linear dichroism (LD) spectra of Chlorella pyrenoidosa and higher plant thylakoids in the films were very similar to those obtained after orientation of similar samples using magnetic or electric fields.Positive LD bands corresponding to Chl a (670) and (682) and negative bands due to Chl a (658) and Chl b (648) were resolved in spectra of the light harvesting Chl a/b protein. Chl b (648) and Chl a (658) and (670) were not seen in the LD spectrum of thylakoids from plants grown in intermittent light, the Chl b-less mutant of barley, Euglena gracilis or the cyanobacteria, Phormidium luridum and Anacystis nidulans, but did appear upon chloroplast maturation in Romaine lettuce and during the greening of etiolated and intermittent light plants. The highly oriented long wavelength Chl a (682) in the light-harvesting complex may represent residual PS II whose peak dichroism is centered at 681 nm. The PS I preparation had a Chl $\text{a}\text{b}$ ratio of approx. 6 and the LD spectrum was positive with a maximum at 690–694 nm and a band of lower amplitude at 652 nm. The minor LD band was not observed in PS I preparations from organisms that lack Chl b such as the cyanobacteria, intermittent light plants and the Chl b-less mutant of barley. We suggest that the 652 nm band is due to Chl b molecules associated with the antenna of PS I and are distinct from those on the light harvesting complex whose orientation is different. We also conclude that all the Chl a forms are oriented and that the long geometric axes of the pigment-protein complexes, as deduced from the configuration they assume in the stretched films, are axes that normally lie parallel to the plane of the native thylakoid.     

Energy transfer pathways in the CP24 and CP26 antenna complexes of higher plant photosystem II: a comparative study

Antenna complexes are key components of plant photosynthesis, the process that converts sunlight, CO₂, and water into oxygen and sugars. We report the first (to our knowledge) femtosecond transient absorption study on the light-harvesting pigment-protein complexes CP26 (Lhcb5) and CP24 (Lhcb6) of Photosystem II. The complexes are excited at three different wavelengths in the chlorophyll (Chl) Qy region. Both complexes show a single subpicosecond Chl b to Chl a transfer process. In addition, a reduction in the population of the intermediate states (in the 660-670 nm range) as compared to light-harvesting complex II is correlated in CP26 to the absence of both Chls a604 and b605. However, Chl forms around 670 nm are still present in the Chl a Qy range, which undergoes relaxation with slow rates (10-15 ps). This reduction in intermediate-state amplitude CP24 shows a distinctive narrow band at 670 nm connected with Chls b and decaying to the low-energy Chl a states in 3-5 ps. This 670 nm band, which is fully populated in 0.6 ps together with the Chl a low-energy states, is proposed to originate from Chl 602 or 603. In this study, we monitored the energy flow within two minor complexes, and our results may help elucidate these structures in the future.     

Evidence that Isolated Developing Chloroplasts Are Capable of Synthesizing Chlorophyll b from 5-Aminolevulinic Acid

Developing chloroplasts isolated from cucumber (Cucumis sativus L. var Beit Alpha) cotyledons are capable of incorporating [¹⁴C]5-aminolevulinic acid into chlorophyll (Chl) b and Chl a when incubated under photosynthetic illumination. Thin layer chromatography and high pressure liquid chromatography were employed to analyze the pigments. The specific radioactivity in Chl a was over three times higher than that found in Chl b. Both Chl a and b synthesizing activities in organello decayed rapidly at approximately the same rate. We conclude that concomitant synthesis of Chl a/b-binding apoprotein is not required for Chl b synthesis.     

Formation of Chlorophyll-Protein Complexes during Greening 1. Distribution of Newly Synthesized Chlorophyll among Apoproteins

The relationship between the accumulation of Chl and the apoproteinsof the light-harvesting Chl a/b-protein complex of PS II (LHCII)during the greening of cucumber cotyledons was studied. LHCIIapoproteins were not detected in etiolated cotyledons. Uponillumination, Chl a was formed as a result of photoconversionof protochlorophyllide (Pchlide) which had accumulated in thedark. During the lag period that preceded the accumulation ofChl, a small amount of LHCII apoproteins appeared. The amountof LHCII apoproteins increased with increases in levels of Chlb, though somewhat more rapidly during the first 10 h of greening.Treatment with benzyladenine (BA) or levulinic acid (LA) wasused to vary the supply of Chl a for apoproteins by promotingor inhibiting the synthesis of Chl a, respectively. LA decreasedbut BA increased the rate of accumulation of Chl b and LHCIIapoproteins. Only small amounts of Chl b and LHCII apoproteinswere formed under intermittent illumination. However, in thepresence of chloramphenicol (CAP), which inhibits the synthesisof plastome-coded proteins including apoproteins of the P700-Chla-protein complex (CP1) and a Chl a-protein complex of PS II(CPa), we observed the accumulation of Chl b and LHCII apoproteins,both of which are of nuclear origin. During incubation in thedark after intermittent exposure to light, CAP alone allowedneither destruction nor accumulation of Chl b and LHCII apoproteins,but it did enhance the effect of CaCl₂ in inducing both Chlb and these apoproteins. These results can be explained by assumingthat apoproteins of CP1 and CPa have a higher affinity for Chla than do LHCII apoproteins. When the availability of Chl ais limited, these apoproteins compete with one another for Chla, with the resultant preferential formation of CP1 and CPa.However, when the supply of Chl a becomes large enough for saturationof apoproteins of CP1 and CPa, some of the Chl a is incorporatedinto LHCII apoproteins either directly or after conversion toChl b. Thus, the formation of different Chl-protein complexes(CPs) is regulated by the relative rates of synthesis of Chla and apoproteins and by differential affinities of the apoproteinsfor Chl a. ⁴Present address: Kyowa Hakko Co., Ltd., 4041, Ami-machi, Inashiki,Ibaraki, 300-03 Japan (Received September 14, 1989; Accepted April 26, 1990)     

Kinetics and efficiency of excitation energy transfer from chlorophylls,their heavy metal-substituted derivatives,and pheophytins to singlet oxygen

Time-resolved measurements of the singlet oxygen infrared (1269 nm) luminescence were used to follow the kinetics and efficiency of excitation energy transfer (EET) between chlorophyll (Chl) derivatives and oxygen in acetone. The studied pigments were Mg-Chl a and b and their heavy metal (Cu²⁺ and Zn²⁺)-substituted analogues, as well as pheophytin (Pheo) a and b. The efficiency of EET from chlorophyll to oxygen was highly dependent on the central ion in the pigment. Cu-Chl a and Cu-Chl b had the lowest efficiencies of singlet oxygen production, while Pheo a had a higher one, and Zn-Chl a had a similar one compared to Mg-Chl a. Also the side chain (position C-7, i.e. Chl a vs. Chl b) influenced the efficiency of singlet oxygen formation. In the case of square-planar complexes like Cu-Chl and Pheo, EET was more efficient in the Chl a derivatives than in those of Chl b; the opposite effect was observed in the case of the five- or six-coordinated Mg-Chl and Zn-Chl. As for the lifetime of the Chl triplet state, the most striking difference to Mg-Chl again was found in the case of Cu-Chls, which had much shorter lifetimes. Furthermore, the central ion in Chl affected the physical quenching of singlet oxygen: its efficiency was decreasing from Mg-Chl through Zn-Chl over Cu-Chl to Pheo. The results are discussed in the context of the oxidative stress accompanying heavy metal-induced stress in plants.     

Energy transfer in the peridinin-chlorophyll protein complex reconstituted with mixed chlorophyll sites

We use femtosecond transient absorption spectroscopy to study chlorophyll (Chl)-Chl energy transfer in the peridinin-chlorophyll protein (PCP) reconstituted with mixtures of either chlorophyll b (Chlb) and Chld or Chla and bacteriochlorophyll a (BChla). Analysis of absorption and transient absorption spectra demonstrated that reconstitution with chlorophyll mixtures produces a significant fraction of PCP complexes that contains a different Chl in each domain of the PCP monomer. The data also suggest that binding affinity of Chla is less than that of the other three Chl species. By exciting the Chl species lying at higher energy, we obtained energy transfer times of 40 ± 5 ps (Chlb-Chld) and 59 ± 3 ps (Chla-BChla). The experimental values match those obtained from the Förster equation, 36 and 50 ps, respectively, showing that energy transfer proceeds via the Förster mechanism. Excitation of peridinin in the PCP complex reconstituted with Chla/BChla mixture provided time constants of 2.6 and 0.4 ps for the peridinin-Chla and peridinin-BChla energy transfer, matching those obtained from studies of PCP complexes reconstituted with single chlorophyll species.     

Interconversions of Chlorophylls a and b Synthesized from Exogenous Chlorophyllides a and b in Etiolated and Post-Etiolated Rye Seedlings

A comparative study of reciprocal conversions of chlorophylls a and b (Chl aand Chl b) in etiolated and post-etiolated rye seedlings (Secale cereale L.) was performed. The production of these pigments was initiated by infiltration of exogenous chlorophyllides a and b (Chlide a and b). It was shown that Chlide b, when infiltrated into etiolated rye seedlings, was esterified, producing Chl b. A major portion of Chl b (more than 80%) was transformed into Chl aduring long-term seedling dark exposure. The high rate of Chl b conversion into Chl a in the pool of pigments of exogenous origin was also observed during the lag-phase when there was no chlorophyll formation from endogenous precursors. The infiltration of Chlide a resulted in Chl a formation. The efficiency of its conversion into Chl b was low (about 1%) in the etiolated seedlings but increased during their greening. In the post-etiolated seedlings infiltrated with Chlide b, which were preliminary illuminated for 6–12 h, the Chl /Chl a ratio was almost similar in the pools of pigments synthesized from both exogenous and endogenous precursors. The rates of direct and reverse reactions responsible for the interconversion of Chl aand Chl b depended on the stage of the formation of the photosynthetic apparatus during greening of etiolated seedlings, when the particular structural components are formed in a definite sequence.     

Engineering of B800 bacteriochlorophyll binding site specificity in the Rhodobacter sphaeroides LH2 antenna

The light-harvesting 2 complex (LH2) of the purple phototrophic bacterium Rhodobacter sphaeroides is a highly efficient, light-harvesting antenna that allows growth under a wide-range of light intensities. In order to expand the spectral range of this antenna complex, we first used a series of competition assays to measure the capacity of the non-native pigments 3-acetyl chlorophyll (Chl) a, Chl?d, Chl?f or bacteriochlorophyll (BChl) b to replace native BChl?a in the B800 binding site of LH2. We then adjusted the B800 site and systematically assessed the binding of non-native pigments. We find that Arg_?10 of the LH2 β polypeptide plays a crucial role in binding specificity, by providing a hydrogen-bond to the 3-acetyl group of native and non-native pigments. Reconstituted LH2 complexes harbouring the series of (B)Chls were examined by transient absorption and steady-state fluorescence spectroscopies. Although slowed 10-fold to ~6?ps, energy transfer from Chl?a to B850 BChl?a remained highly efficient. We measured faster energy-transfer time constants for Chl?d (3.5?ps) and Chl?f (2.7?ps), which have red-shifted absorption maxima compared to Chl?a. BChl?b, red-shifted from the native BChl?a, gave extremely rapid (≤0.1?ps) transfer. These results show that modified LH2 complexes, combined with engineered (B)Chl biosynthesis pathways in vivo, have potential for retaining high efficiency whilst acquiring increased spectral range.     

Chloroplast biogenesis. XXIX. The occurrence of several novel chlorophyll a and b chromophores in higher plants

With the use of low temperature spectrofluorometry and matrix calculations it was demonstrated that the chlorophyll a pool of higher plants is made up of four different chlorophyll a chromophores. The latter were segregated by high pressure liquid chromatography on a silica column. They were designated Chl a (E432 F664), Chl a (E436 F670), Chl a (E443 F672) and Chl a (E446 F674), where E refers to the Soret excitation maximum and F to the fluorescence emission maximum at 77 K in ether. Likewise the Chl b pool was shown to consist of at least four different Chl b chromophores which were designated: Chl b (E465), Chl b (E470), Chl b (E475) and Chl b (E485). It was proposed that the various chlorophyll chromophores differed by the degree of oxidation of their side chains at the 2 and 4 positions of the macrocycle. It was also suggested that the chemical modifications at the 2 and 4 positions of the macrocycle may play an important role in positioning the different chlorophyll chromophores in the thylakoid membranes.     

Dynamics of Photosystem II and Its Light Harvesting System in Response to Light Changes in the Halotolerant Alga Dunaliella salina

A photosystem two (PSII) core complex consisting of five major polypeptides (47, 40, 32, 30, and 10 kilodaltons) and a light harvesting chlorophyll a/b complex (LHC-2) have been isolated from the halotolerant alga Dunaliella salina. The chlorophyll and polypeptide composition of both complexes were compared in illuminated and dark-adapted cultures. Dark adaptation is accompanied by a decrease in the chlorophyll a to chlorophyll b (Chl a/Chl b) ratio of intact thylakoids without any change in total chlorophyll. These changes occur with a half-time of 3 hours and are reversed upon reillumination. Analyses of PSII enriched membrane fragments suggest that the decrease in the Chl a/Chl b is due partly to an increase in the Chl b content of LHC-2 and partly to changes in the relative levels of the two complexes. Apparently during dark adaptation there is: (a) a net synthesis of chlorophyll b, (b) removal of PSII core complexes resulting in a 2-fold drop in the PSII cores to LHC-2 chlorophyll ratio. These changes should dramatically increase the light harvesting capacity of the remaining PSII reaction centers. Presumably this adjustment of antenna size and composition is a physiological mechanism necessary for responding to shade conditions. Also detected, using ³²P, are light-induced phosphorylation of the LHC-2 (consistent with the ability to undergo State transitions) and of the 40 and 30 kilodalton subunits of the PSII core complex. These observations indicate that additional mechanisms may also exist to help optimize the interception of quanta during rapid changes in illumination conditions.     

Excitation relaxation dynamics and energy transfer in fucoxanthin–chlorophyll a/c-protein complexes,probed by time-resolved fluorescence

In algae, light-harvesting complexes contain specific chlorophylls (Chls) and keto-carotenoids; Chl a, Chl c, and fucoxanthin (Fx) in diatoms and brown algae; Chl a, Chl c, and peridinin in photosynthetic dinoflagellates; and Chl a, Chl b, and siphonaxanthin in green algae. The Fx–Chl a/c-protein (FCP) complex from the diatom Chaetoceros gracilis contains Chl c₁, Chl c₂, and the keto-carotenoid, Fx, as antenna pigments, in addition to Chl a. In the present study, we investigated energy transfer in the FCP complex associated with photosystem II (FCPII) of C. gracilis. For these investigations, we analyzed time-resolved fluorescence spectra, fluorescence rise and decay curves, and time-resolved fluorescence anisotropy data. Chl a exhibited different energy forms with fluorescence peaks ranging from 677 nm to 688 nm. Fx transferred excitation energy to lower-energy Chl a with a time constant of 300 fs. Chl c transferred excitation energy to Chl a with time constants of 500–600 fs (intra-complex transfer), 600–700 fs (intra-complex transfer), and 4–6 ps (inter-complex transfer). The latter process made a greater contribution to total Chl c-to-Chl a transfer in intact cells of C. gracilis than in the isolated FCPII complexes. The lower-energy Chl a received excitation energy from Fx and transferred the energy to higher-energy Chl a. This article is part of a Special Issue entitled: Photosynthesis Research for Sustainability: Keys to Produce Clean Energy.     

A study of molecular interactions in light-harvesting complexes LHCIIb, CP29, CP26 and CP24 by Stark effect spectroscopy

Electric field-induced absorption changes (electrochromism or Stark effect) of the light-harvesting PSII pigment-protein complexes LHCIIb, CP29, CP26 and CP24 were investigated. The results indicate the lack of strong intermolecular interactions in the chlorophyll a (Chl a) pools of all complexes. Characteristic features occur in the electronic spectrum of Chl b, which reflect the increased values of dipole moment and polarizability differences between the ground and excited states of interacting pigment systems. The strong Stark signal recorded for LHCIIb at 650-655 nm is much weaker in CP29, where it is replaced by a unique Stark band at 639 nm. Electrochromism of Chl b in CP26 and CP24 is significantly weaker but increased electrochromic parameters were also noticed for the Chl b transition at 650 nm. The spectra in the blue region are dominated by xanthophylls. The differences in Stark spectra of Chl b are linked to differences in pigment content and organization in individual complexes and point to the possibility of electron exchange interactions between energetically similar and closely spaced Chl b molecules.     

A comparison of the three isoforms of the light-harvesting complex II using transient absorption and time-resolved fluorescence measurements

In this article we report the characterization of the energy transfer process in the reconstituted isoforms of the plant light-harvesting complex II. Homotrimers of recombinant Lhcb1 and Lhcb2 and monomers of Lhcb3 were compared to native trimeric complexes. We used low-intensity femtosecond transient absorption (TA) and time-resolved fluorescence measurements at 77 K and at room temperature, respectively, to excite the complexes selectively in the chlorophyll b absorption band at 650 nm with 80 fs pulses and on the high-energy side of the chlorophyll a absorption band at 662 nm with 180 fs pulses. The subsequent kinetics was probed at 30–35 different wavelengths in the region from 635 to 700 nm. The rate constants for energy transfer were very similar, indicating that structurally the three isoforms are highly homologous and that probably none of them play a more significant role in light-harvesting and energy transfer. No signature has been found in the transient absorption measurements at 77 K for Lhcb3 which might suggest that this protein acts as a relative energy sink of the excitations in heterotrimers of Lhcb1/Lhcb2/Lhcb3. Minor differences in the amplitudes of some of the rate constants and in the absorption and fluorescence properties of some pigments were observed, which are ascribed to slight variations in the environment surrounding some of the chromophores depending on the isoform. The decay of the fluorescence was also similar for the three isoforms and multi-exponential, characterized by two major components in the ns regime and a minor one in the ps regime. In agreement with previous transient absorption measurements on native LHC II complexes, Chl b → Chl a energy transfer exhibited very fast channels but at the same time a slow component (ps). The Chls absorbing at around 660 nm exhibited both fast energy transfer which we ascribe to transfer from ‘red’ Chl b towards ‘red’ Chl a and slow transfer from ‘blue’ Chl a towards ‘red’ Chl a. The results are discussed in the context of the new available atomic models for LHC II.     

Migration of Electronic Energy from Chlorophyll b to Chlorophyll a in Solutions

Absorption, emission, and fluorescence excitation spectra of pure solutions of chlorophyll a (Chl a) and chlorophyll b (Chl b) in diethyl ether and of equimolecular mixed solutions of the two pigments, were determined at room temperature as functions of concentration (in the range from 5 × 10^-6 M to 4 × 10^-3 M) and of wavelength of the exciting light (in the regions 380-465 and 550-650 nm). The efficiency of energy transfer from Chl b to Chl a, derived from these data, was found to depend on the wavelength of exciting light. Furthermore, the transfer efficiency calculated from sensitization of Chl a fluorescence by Chl b was substantially smaller than that calculated from quenching of Chl b fluorescence by Chl a. Both these effects are tentatively explained as evidence of superposition of a “fast” energy transfer (taking place before the Boltzmann distribution of vibrational energy had been reached) upon the “delayed” transfer, which takes place after vibrational equilibration. The first-named mechanism is made possible by overlapping of the absorption bands of the two pigments; the second, by overlapping of the emission band of Chl b and the absorption band of Chl a. The first mechanism can lead to repeated transfer of excitation energy between pigment molecules, the second only to a one-time transfer from the donor to the acceptor. Both mechanisms could be of the same, second-order type, with the transfer rate proportional to r^-6. An alternative is for the fast mechanism to be of the first order, with the transfer rate proportional to r^-3, but spectroscopic evidence seems to make this alternative less probable.     

Chlorophyll b accumulation and grana formation in low intensities of red light

Abstract When dark grown leaves of wheat (Triticum aesivum L.) were given a brief irradiation, there was an immediate onset of chlorophyll (Chl) b synthesis in the dark. This synthesis led to a rather slow accumulation of Chl b, which ceased when the Chl b/Chl a ratio had reached a value of about 0.1. The Chl b synthesis occurred also when the seedlings were treated with the herbicide SAN 9789. Leaves grown under different intensities of red light accumulated Chl b and Chl a, resulting in a ratio Chl b/Chl a which depended on the light intensity. If the light intensity was low, Chl a accumulated to a level about ten times the level of PChlide of the dark grown leaves. This occurred without any increase in the Chl b/Chl a ratio. There was no difference between SAN 9789-treated seedlings and water controls in this respect. Above a certain threshold of irradiance, the Chl b/Chl a ratio in the control leaves increased rapidly with the irradiation intensity. The increase in Chl b/Chl a ratio coincided with formation of grana in the plastids. This increase was not found and grana formation was completely absent in the seedlings treated with SAN 9789. The possibility of two different stages in the Chl b synthesis is discussed.     

Chlorophyll-protein complexes of a Codium species,including a light-harvesting siphonaxanthin-Chlorophylla ab-protein complex,an evolutionary relic of some Chlorophyta

Eight chlorophyll-protein complexes were isolated from thylakoid membranes of a Codium species, a marine green alga, by mild SDS-polyacrylamide gel electrophoresis. CP 1a¹, CP 1a², CP 1a³ and CP 1a⁴ were partially dissociated Photosystem (PS) I complexes, which in addition to the core reaction centre complex, CP 1, possessed PS I light-harvesting complexes containing chlorophyll (Chl) a, Chl b and siphonaxanthin. LHCP¹ and LHCP³ are orange-brown green chlorophyll $\text{a}\text{b-}\text{proteins}$ ($\text{Chl}\text{a}\text{Chl}\text{b}$ ratios of 0.66) that contain siphonaxanthin and its esterified form, siphonein. CP a and CP 1, the core reaction centre complexes of PS II and PS I, respectively, had similar spectral properties to those isolated from other algae or higher plants. These P-680- or P-700-Chl a-proteins are universally distributed among algae and terrestrial plants; they appear to be highly conserved and have undergone little evolutionary adaptation. Siphonaxanthin and siphonein which are present in the Codium light-harvesting complexes of PS II and PS I are responsible for enhanced absorption in the green region (518 and 538 nm). Efficient energy transfer from both xanthophylls and Chl b to only Chl a in Codium light-harvesting complexes, which have identical fluorescence emission spectra at 77 K to those of the lutein-Chl $\text{a}\text{b-}\text{proteins}$ ($\text{Chl}\text{a}\text{Chl}\text{b}$ ratios of 1.2) of most green algae and all higher plants, proved that the molecular arrangement of these light-harvesting pigments was maintained in the isolated Codium complexes. The siphonaxanthin-Chl $\text{a}\text{b-}\text{proteins}$ allow enhanced absorption of blue-green and green light, the predominant light available in deep ocean waters or shaded subtidal marine habitats. Since there is a variable distribution of lutein, siphonaxanthin and siphonein in marine green algae and siphonaxanthin is found in very ancient algae, these novel siphonein-siphonaxanthin-Chl $\text{a}\text{b-}\text{proteins}$ may be ancient light-harvesting complexes which were evolved in deep water algae.     

Use of the atLEAF+ chlorophyll meter for a nondestructive estimate of chlorophyll content

At present, chlorophyll meters are widely used for a quick and nondestructive estimate of chlorophyll (Chl) contents in plant leaves. Chl meters allow to estimate the Chl content in relative units - the Chl index (CI). However, using such meters, one can face a problem of converting CI into absolute values of the pigment content and comparing data acquired with different devices and for different plant species. Many Chl meters (SPAD-502, CL-01, CCM-200) demonstrated a high degree of correlation between the CI and the absolute pigment content. A number of formulas have been deduced for different plant species to convert the CI into the absolute value of the photosynthetic pigment content. However, such data have not been yet acquired for the atLEAF+ Chl meter. The purpose of the present study was to assess the applicability of the atLEAF+ Chl meter for estimating the Chl content. A significant species-specific exponential relationships between the atLEAF value (corresponding to CI) and extractable Chl a, Chl b, Chl (a+b) for Calamus dioicus and Cleistanthus sp. were shown. The correlations between the atLEAF values and the content of Chl a, Chl b, and Chl (a+b) per unit of leaf area was stronger than that per unit of dry leaf mass. The atLEAF value- Chl b correlation was weaker than that of atLEAF value-Chl a and atLEAF value-Chl (a+b) correlations. The influence of light conditions (Chl a/b ratio) on the atLEAF value has been also shown. The obtained results indicated that the atLEAF+ Chl meter is a cheap and convenient tool for a quick nondestructive estimate of the Chl content, if properly calibrated, and can be used for this purpose along with other Chl meters.