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Carbonic anhydrases (CAs) catalyse reversible interconversion of CO2 and water into bicarbonate and protons and regulate concentration of CO2 around photosynthetic enzymes. In higher plants the CAs are divided into three distinct classes α, β and γ, with members off each of them being involved in CO2 uptake, fixation or recycling. The most abundant group is βCAs. In C4 plants they are localized in the cytosol of mesophyll cells and catalyse first step of carbon concentration pathway. C3 plants contain orthologues genes encoding βCAs's, however their functions are unknown. Given the importance of βCAs in the present study we analysed the effect of carbonic ions, selected orthologues βCAs's gene expression and βCAs enzymatic activity on Arabidopsis photosynthesis, growth and cell death in different light conditions. Plants fertilised with 0.5-3mM sodium bicarbonate had a significantly increased number of leaves, improved fresh and dry weight and reduced cell death (cellular ion leakage). This effect was dependent on provided photon flux density and photoperiod. Higher content of carbonic ions also stimulated photoprotective mechanisms such as non-photochemical quenching and foliar content of photoprotective pigments (neoxanthin, violaxanthin and carotenes). Function of various βCAs genes examined in null βcas mutants showed to be complementary and additive, and confirm results of fertilizing experiments. Taken together, regulation of βCAs gene expression and enzymatic activities are important for optimal plant growth and probably can be one of the factor influencing a switch between C3 and C4 photosynthesis mode in variable light conditions. Therefore, biotechnological amelioration of βCAs activity in economically important plants and their fertilisation with carbonic ions may lead to improved photosynthetic efficiency and further crop productivity.

Zeaxanthin epoxidase (ZE, E.C. 1.14.13.90), an enzyme belonging to the lipocalin superfamily, catalyses the conversion of zeaxanthin to antheraxanthin and violaxanthin. These reactions are part of the xanthophyll biosynthetic pathway and the xanthophyll cycle. The role of carotenoids in the dissipation of excessive light energy has been widely studied using mutants with a disabled carotenoid biosynthetic pathway. In this paper, the transgenic line MaZEP7 with partially disabled ZE activity is described and compared with wild-type plants and npq2 mutant lacking active ZE. We examined the presence and the abundance of aba1 transcripts, measured pigment composition, xanthophyll cycle functioning and chlorophyll fluorescence in all three lines. The MaZEP7 line contains additional copies of the aba1 gene introduced by agroinfiltration, but no enhanced aba1 transcript level was observed. In addition, ZE activity in MaZEP7 was impaired, resulting in an altered xanthophyll profile. In dark-adapted plants, violaxanthin and neoxanthin levels were lower than in wild-type plants, whereas antheraxanthin and zeaxanthin levels were considerably higher. The presence of lutein epoxide was also observed. Violaxanthin levels changed only minimally during light exposition, whereas antheraxanthin was converted to zeaxanthin and there was no epoxidation during the course of the experiment indicating disturbed xanthophyll cycle functioning. The amounts of carotenoids and chlorophylls on a dry weight basis and chl a/chl b ratio were similar in all lines. The presence of epoxidated pigments in MaZEP7 plants indicates that epoxidation occurs, but it is likely very slow. Chlorophyll fluorescence measurements showed that the dependence of electron transport rates on light intensity for the MaZEP7 line resembled the npq2 mutant. Kinetic measurements showed that the MaZEP7 line exhibited very rapid induction and a high steady-state value of non-photochemical quenching.

Summary The content and relative variations of individual carotenoids during the leaflet development stages (I, II, III, A and P) of six species of Ceratozamia (Cycads) were investigated. There is an unusual, transitory and marked presence of six red stroma keto-carotenoids in the first development stages, while the thylakoidal carotenoids showed a low concentration during the same period. As no official A 1 cm 1 % coefficients were available, it was necessary to calculate these for the following stroma carotenoids: semi- β -carotenone (major component), triphasiaxanthin, ceratoxanthin, ceratozamiaxanthin, kuesteriaxanthin and ceratoxanthone. The stroma keto-carotenoids, which reached the highest content in the first development stage (average of 78% of total carotenoids), were always present in the five species: C. fuscoviridis, C. robusta, C. spinosa, C. kuesteriana and C. hildae, but never in C. mexicana. From stage II, the stroma keto-carotenoids decreased and finally disappeared in the green adult leaflets. The thylakoidal carotenoids showed a minimum at stage III, and then increased to a maximum in the perennial leaflets. Among these, β -carotene showed an anomalous and characteristic behaviour, being a minor component during leaflet development (from stage I to A). In stage P it was markedly exceeded not only by lutein but also by α -carotene, neoxanthin and violaxanthin, and in C. robusta also by lutein-5,6-epoxide. Additionally, the α / β ratio in these species is unusual: it increased from 0.3–0.5 to 1.5–3.0 during leaflet development. Moreover, antheraxanthin amounts are very small, while zeaxanthin was present only in the evergreen leaflets of C. mexicana in small quantities. Lutein-5,6-epoxide represented more than 5% of thylakoidal carotenoids in the leaflets of all the species. A revision of the taxonomic rank of C. fuscoviridis is recommended.

Summary Plants of three Lycopersicon genotypes, the chilling-sensitive cultivated tomato, L. esculentum cv. Abunda, and two relatively chilling-tolerant lines of L. peruvianum (LA 2172 and LA 385) were grown at 20–27°C (control plants) and subjected to a temperature shift to 10° under 300 µmol photons m−2 s−1 (12-h light periods). Two weeks after the temperature shift, the effects of chilling and light stress on photosynthetic pigment composition, xanthophyll cycle activity and non-photochemical chlorophyll fluorescence quenching were studied. In leaves of all three genotypes, the chilling treatment caused substantial increases in contents of xanthophyll cycle pigments (sum of viola-, anthera- and zeaxanthin), lutein and neoxanthin, based on chlorophyll. In the chilling-treated plants, particularly in L. esculentum and L. peruvianum LA 385, higher fractions of zeaxanthin and antheraxanthin and higher zeaxanthin/chlorophyll ratios were built up in excessive light at temperatures between 0° and 40 °C. The chilling-treated plants exhibited increased non-photochemical quenching, indicating enhanced thermal dissipation of excessively absorbed light energy. The data show that leaves of the chilling-sensitive tomato as well as of its less sensitive relatives, which have developed at warm temperatures, are capable of responding to a shift to conditions of chilling and excessive light by acclimating the thylakoid membrane with respect to pigment content and xanthophyll cycle activity. The enhanced thermal energy conversion associated with increased zeaxanthin (and antheraxanthin) levels is assumed to provide protection of the leaves from severe photodestruction during events of light stress at low temperatures.

Summary The changes to the carotenoid composition and photosynthetic activity induced by chilling in the light were examined under controlled environment in the third leaf of a chilling-tolerant genotype ( Z7 ) and a chilling-sensitive genotype ( Penjalinan ) of Zea mays L. In control plants, grown at 24/22 °C (day/night) under a photon flux density of 500 μmol · m −2 · s −1 and a photoperiod of 12 h, the rate of CO 2 assimilation and the carotenoid composition did not differ significantly in the two genotypes. However, the chilling-tolerant genotype was able to maintain a higher photosynthetic capacity than the chilling-sensitive genotype when the plants were chilled for 5 days at 10/8 °C (day/night). The stress led to a reduction in the maximum quantum efficiency of photosystem II (PSII) photochemistry, as judged by the decrease in the ratio of variable to maximum chlorophyll a fluorescence (F v /F m ), but no significant differences appeared between the two genotypes. The maximum quantum efficiency of PS II photochemistry recovered faster from chilling than the rate of CO 2 assimilation on transfer of the chilled plants to 24 °C for 5 days. The rate of recovery was similar in the two genotypes. During the stress, there was a decrease in the chlorophyll a content which was accompanied by a decrease in the s-carotene content and an increase in the content of the carotenoids of the xanthophyll cycle. Opposite reactions occurred during recovery. The contents of lutein and neoxanthin were hardly affected by the temperature changes. The most important impact of chilling was a large and reversible de-epoxidation of violaxanthin to zeaxanthin in the xanthophyll cycle which was more pronounced in the chilling-sensitive genotype than in the chilling-tolerant genotype. Short-term (minutes to hours) exposure of plants or leaf segments to various temperature and light stress conditions revealed that the temperature- and light-dependent changes in the maximum quantum efficiency of PS II photochemistry and the degree of violaxanthin de-epoxidation were generally similar for the two genotypes. The results indicate that it is unlikely that the content and composition of carotenoids and the operation of the xanthophyll cycle are major factors in determining the better ability of chilling-tolerant genotypes, as compared to chilling-sensitive ones, to cope with low temperature-induced reductions in photosynthesis.

Summary In primary leaves of dark grown bean seedlings ( Phaseolus coccineus L.) the transformation of etioplasts to chloroplasts upon illumination (1-120 h continuous light) was studied by recording the alterations of the emision peaks of laser-induced chlorophyll fluorescence spectra and corresponding induction kinetics using a diode array spectrophotometer. In addition, pigment-protein complexes solubilized from isolated plastids of different developmental stages were separated by nondenaturating Deriphat polyacrylamide gel electrophoresis. Chlorophyll fluorescence spectra (77K) of the green pigment-protein complexes were measured directly on the gels. Subsequently, the complexes were extracted by electroelution and their pigment composition analyzed by HPLC. It was found that in leaves in the early light-dependent developmental phase (after about 1 h) a fluorescence maximum at 688 nm appeared that was followed (after several hours) by an additional peak emision at 742 nm. When analyzing 77K fluorescence spectra of leaves an increasing intensity of fluorescence between 735 nm and 739 nm was also found after a prolonged illumination period. In protein complexes, which were isolated from dark-grown leaves and separated on gels, no appreciable amounts of chlorophyll were visible. However, if 12-h illuminated leaves had been used, two green protein bands were detectable asigned to PS I and PS II by their 77K fluorescence. From fully developed leaves (120 h light) eight green bands were finally detected and classified as derivatives of PS I or PS II. PS I complexes exhibited a Chl a : Chl b ratio of about 10: 1, whereas PS II complexes had a ratio of 2: 1. s-carotene was mainly localized in PS I complexes, whereas lutein, neoxanthin and violaxanthin were especially found in PS II complexes. It is concluded that during the light-dependent arrangement of etioplasts to chloroplasts the asembly of PS II units and the insertion of pigments therein preceeds the asembly of PS I.

Summary The effect of high light stress and salt stress, individually and in combination, was investigated in the leaves of Sorghum bicolor (1.). High light treatment at 5°C and 20°C caused an increase in zeaxanthin and a decrease in violaxanthin contents. Decreases in β-carotene were also observed, which was followed by increased formation of 5,6-epoxide-β-carotene. Violaxanthin + antheraxanthin + zeaxanthin (total) was not the same in control and stressed plants. Salt stress (no photoinhibition) also resulted in the formation of zeaxanthin but it was significantly less than that observed in the high light stressed plants. Neoxanthin content showed a slight decrease, while 5,6-epoxide lutein increased under salt stress. Changes in the xanthophyll cycle (violaxanthin + antheraxanthin + zeaxanthin) were reversed during recovery after photoinhibition. The CO2 assimilation rate and fluorescence Fv/Fm ratio were measured in intact leaves and isolated chloroplasts, respectively, from control and stressed plants. Formation of zeaxanthin and degradation of β-carotene are apparently involved in protection against photoinhibition.

Summary The fate of chloroplast pigments during senescence of detached primary leaves of Hordeum vulgare L. and Avena sativum L. has been studied. In both species, the carotenoids were lost at a much slower rate than the chlorophylls, with chlorophyll a being lost at a slightly faster rate than chlorophyll b. A detailed examination of the pattern of carotenoid destruction by high performance liquid chromatography revealed, however, that different processes were taking place in the two species. In H. vulgare , β-carotene levels were reduced to approximately 40 % of their original levels whereas the xanthophylls (lutein, violaxanthin and neoxanthin) were reduced to between 8 % and 16 % of their original levels. Violaxanthin and neoxanthin were particularly susceptible to the oxidative processes involved in senescence. In A. sativum lutein was the most stable carotenoid and both neoxanthin and β-carotene were readily destroyed. In both species quite high levels of xanthophyll acyl esters, accounting for up to 60 % of total carotenoid, were detected in the leaves, especially in the late stages of senescence. Plastoglobuli isolated from H. vulgare contained equivalent amounts of unesterified lutein and β-carotene together with small amounts of xanthophyll acyl esters. Chlorophylls were present in only trace amounts in the plastoglobuli. Similar patterns of pigment destruction were seen in detached leaves and intact seedlings.

In addition to the usual complement of carotenoids found in the plant leaf tissues, lettuce (Lactuca sativa), unusually, possesses large amounts of the diol lactucaxanthin. This carotenoid possesses two epsilon-end-groups and its presence provides a good model in which to study the effects of the substituted triethylamine compound 2-(4-methylphenoxy)triethylamine (MPTA) on the cyclisation of beta- and epsilon-end-groups during the biosynthesis of carotenoids. Treatment with 10 or 20microM MPTA significantly reduced levels of both beta-carotene and neoxanthin (up to 18-fold), whilst levels of violaxanthin and lutein were less affected (4-fold reduction). In contrast, levels of lactucaxanthin were not reduced even at the highest inhibitor concentration, and at 10microM MPTA levels of this xanthophyll doubled. The pigment stoichiometry of the bulk light-harvesting complex (LHCIIb) isolated from treated plants shows that lactucaxanthin successfully substituted for lutein and neoxanthin in two of the xanthophyll binding sites, namely L2 and N1. Inhibition of cyclisation was accompanied by the accumulation of lycopene and trace amounts of delta-carotene and a number of oxygenated derivatives of these precursors. Two forms of mono-hydroxy lycopene were identified together with mono-epoxy delta-carotene.

Summary The effect of acclimation to high irradiance stress (HIS, 250 W m −2 ) in wheat leaves grown under three different irradiances was investigated by HPLC analyses of pigments, chlorophyll a fluorescence parameters and photochemical activities of chloroplasts. Significant loss of β-carotene was observed compared to the xanthophylls in all three types of seedlings exposed to HIS. However, the effect of HIS on neoxanthin and lutein contents was not significant. The loss of partial electron transport (Asc-DCPIP to MV, PS I activity) was less than the whole chain (H 2 O to MV) and PS II activity (H 2 O to DCPIP) suggesting that PS I is less susceptible to HIS compared to PS II. The percent of reductions in Fv/Fm and Φ PS II were less in plants grown under high irradiance (HI-1, 30 W m −2 and HI-2, 45 W m −2 ) compared to those grown under moderate irradiance (MI, 15 W m −2 ). On the other hand, the percent of NPQ increased more in the leaves of HI plants compared to the leaves of MI when exposed to HIS which suggests a more efficient non-radiative dissipation of excess excitation energy in HI plants compared to MI. These observations suggest that plants grown under relatively high irradiance are better adapted to HIS condition.

Summary The effects of high salinity (0-400 mmol/L NaCl) on photosystem II (PSII) photochemistry and photosynthetic pigment composition were investigated in the halophyte Artimisia anethifolia grown under outdoor conditions and exposed to full sunlight. High salinity resulted in an inhibition in plant growth and a significant accumulation of sodium and chloride in leaves. However, high salinity induced no effects on the actual PSII efficiency, the efficiency of excitation energy capture by open PSII reaction centres, photochemical quenching, and non-photochemical quenching at midday. High salinity also induced neither changes in the maximum efficiency of PSII photochemistry, the efficiency with which a trapped exciton can move an electron into the electron transport chain further than Q A and the quantum yield of electron transport beyond Q A , nor changes in absorption, trapping and electron transport fluxes per PSII reaction centre. No significant changes were observed in the levels of neoxanthin, lutein, β-carotene, violaxanthin, antheraxanthin, and zeaxanthin expressed on a total chlorophyll basis in salt-adapted plants. Our results suggest that Artimisia anethifolia showed high resistance not only to high salinity, but also to photoinhibition even if it was treated with high salinity as high as 400 mmol/L NaCl and exposed to full sunlight. The results indicate that tolerance of PSII to high salinity and photoinhibition can be viewed as an important strategy for Artimisia anethifolia , a halophyte plant, to grow in very high saline soil.

The response of C(4), C(3) and CAM species to naturally induced drought and their subsequent recovery are similar. However, there are differences in the degree of the pigment responses, which are related to the differences in the pigment composition of the species. During drought the decrease of the lutein, neoxanthin and chl b content indicates the reduction of the LHC-xanthophyll-proteins, while the considerably increased level of β-carotene, together with the elevated chl a/b ratio, reflect the increased amounts of chl a/β-carotene-pigment-proteins. Moreover, from the pigment data it is concluded that the species seem to possess during drought a higher proportion of pigment-proteins of PSI than pigment-proteins of PS II. These reactions to drought decrease gradually in the direction of C(4)-C(3)-CAM (succulence). The C(4)Festuca vaginata responds with a considerable change in its pigment composition, while this is moderate in CAM Sedum, and C(3)Achillea occupies an intermediate position.

Summary Photosynthetic pigments, in particular violaxanthin and neoxanthin were destroyed under a wide variety of oxidative conditions such as photooxidation, light induced cooxidation and enzymatic oxidation. The breakdown of these pigments was followed by the highly sensitive HPLC method. In contrast to earlier findings of Firn and Friend (Plants 103 , 1972), the plant growth substance, xanthoxin, was not formed under any of these conditions. Consequently, the breakdown of photosynthetic pigments induced by oxidative «stress» cannot be regarded as a major biosynthetic pathway for xanthoxin.