Chloroplast proteins of the Alb3/YidC/Oxa1p family are necessary for assembly of photosynthetic complexes in the thylakoid membranes. Alb3p in Arabidopsis thaliana is essential for posttranslational LHCII-integration into thylakoid membranes and participates in cotranslational assembly of D1. However, the pleiotropic defects of an Alb3p mutant, albino3, suggest additional functions for Alb3p. To obtain an impression of such potential further Alb3p activities from phenotypic manifestations, properties of mutants disturbed in thylakoid membrane protein transport or carotenoid biosynthesis were compared with the albino3 mutant. Specific defects observed in albino3 were similar to those in a carotenoid synthesis mutant. While this correlation did not provide tangible evidence for Alb3p being involved in the integration of carotenoids in photosynthetic complexes, it suggests a possible avenue for future investigations., M. Kugelmann, A. Fausser, F. Ossenbühl, A. Brennicke, and Obsahuje bibliografii
Phosphoenolpyruvate carboxylase (PEPC) was purified from leaves of four species of Alternanthera differing in their photosynthetic carbon metabolism: Alternanthera sessilis (C3), A. pungens (C4), A. ficoides and A. tenella (C3-C4 intermediates or C3-C4). The activity and properties of PEPC were examined at limiting (0.05 mM) or saturating (10 mM) bicarbonate concentrations. The Vmax as well as Km values (for Mg2+ or PEP) of PEPC from A. ficoides and A. tenella (C3-C4 intermediates) were in between those of C3 (A. sessilis) and C4 species (A. pungens). Similarly, the sensitivity of PEPC to malate (an inhibitor) or G-6-P (an activator) of A. ficoides and A. tenella (C3-C4) was also of intermediate status between those of C3 and C4 species of A. sessilis and A. pungens, respectively. In all the four species, the maximal activity (Vmax), affinity for PEP (Km), and the sensitivity to malate (KI) or G-6-P (KA) of PEPC were higher at 10 mM bicarbonate than at 0.05 mM bicarbonate. Again, the sensitivity to bicarbonate of PEPC from C3-C4 intermediates was in between those of C3- and C4-species. Thus the characteristics of PEPC of C3-C4 intermediate species of Alternanthera are intermediate between C3- and C4-type, in both their kinetic and regulatory properties. Bicarbonate could be an important modulator of PEPC, particularly in C4 plants. and Bhaskarrao Chinthapalli ... [et al.].
Leaves and other chlorophyllous tissues of plants often show transient or permanent anthocyanin coloration. The question of whether anthocyanins can function as effective light screens to modulate photosynthesis in plants was addressed by comparing photosynthetic responses in reddish-purple pods with those in green pods of the ornamental leguminous tree Bauhinia variegata. For these comparisons the actinic radiation employed was either red radiation (RR) which was poorly absorbed by anthocyanin or blue-green radiation (BGR) which was strongly absorbed by anthocyanin. Photon yields of photosystem 2 (PS2) photochemistry and photochemical chlorophyll fluorescence quenching coefficients (qp), measured over a range of photon flux densities (PFD) up to 1200 µmol m-2 s-1 at 23 °C and at five temperatures from 8 to 28 °C at a PFD of 260 µmol m-2 s-1, were almost identical in green pods irradiated with either RR or BGR and in purple pods irradiated with RR. However, qp values remained much higher in purple pods irradiated with BGR, e.g., 0.80 in BGR versus 0.29 in RR at a PFD of 1200 µmol m-2 s-1 at 23 °C, and 0.67 in BGR versus 0.28 in RR at a PFD of 260 µmol m-2 s-1 at 8 °C. The higher values of qp in BGR compared to RR indicated that photoabatement by anthocyanin allowed the first stable acceptor of PS2, QA, to be kept in a more oxidized state, thus decreasing the likelihood of photoinhibition. This was confirmed by demonstrating a lower susceptibility to photoinhibition in purple pods than in green pods in the sunlight, either naturally in pods on trees or in detached pods exposed to photoinhibitory conditions. We conclude that photoabatement by anthocyanin is a mechanism for allowing maintenance of higher oxidative levels of PS2 acceptor during episodes of high radiation stress, thereby minimizing photodamage to photosynthetic tissues. and R. M. Smillie, S. E. Hetherington.
Light is a limiting factor in plant establishment and growth in the understory of forests. In this paper, we assessed acclimation capacity of Siparuna guianensis, an early secondary successional species. We used seedlings and saplings in three regeneration areas with different irradiance regimes to determine the traits that confer photoplasticity. We examined whether these traits differ at different developmental stages. Anatomical characteristics, photochemical efficiency, photosynthetic capacity, and growth were analyzed. Multivariate component analysis revealed the formation of six clusters: three for seedlings (one for each regeneration area) and three for saplings (following the same pattern of seedlings, considering the area). Increased irradiance favored photosynthetic performance, independently of the developmental stage. The same trend was observed for most data on chlorophyll (Chl) a fluorescence and the ratios of net photosynthetic rate/intercellular CO2 concentration (PN/Ci) and PN/PPFD. No parameter indicated photoinhibition stress. The CO2- and light-response curve data indicated that seedlings were already acclimated to tolerate variation in irradiance. Anatomical adaptations, such as thickness of leaf blade and of adaxial cuticle, were observed in individuals growing in areas with higher irradiation. Thinning of spongy parenchyma and higher investment into a plant height were observed in seedlings, possibly due to the vertical stratification of CO2 and light in the understory; because light is a more limiting resource than CO2 in the lower stratum of the forest. Photoplasticity in S. guianensis is associated with a set of morphological, anatomical, photochemical, and biochemical traits, whereas biochemical performance is best acclimated to variation in irradiance. These traits differed in seedlings and saplings but they were modulated mainly by irradiance in both developmental stages., T. O. Vieira, M. S. O. Degli-Esposti, G. M. Souza, G. R. Rabelo, M. Da Cunha, A. P. Vitória., and Obsahuje bibliografii
We investigated photoacclimation of Dunaliella tertiolecta (Butcher) in irradiance (I) regimes simulating mixed layer conditions of turbid estuarine waters or lakes. D. tertiolecta was exposed to a range of fixed I regimes to establish baseline physiology-I relationships that were compared with subsequent photoacclimation to a simulated mixed layer. Measured indices of photoacclimation included cellular pigmentation, chlorophyll variable fluorescence, and effective photosystem 2 antenna size. While D. tertiolecta grown under fluctuating I maintained division rates comparable to cells grown at high I, the cells exhibited characteristics of photoacclimation consistent with cells grown under a stable regimes at irradiances considerably lower than the average I of the simulated mixed layer. and H. Havelková-Doušová, O. Prášil, M. J. Behrenfeld.
The dark-adapted cells of the green alga Spongiochloris sp. were exposed to "white light" of 1000 µmol(photon) m-2 s-1 for 2 h and then dark adapted for 1.5 h. Changes of photochemical activities during photoadaptation were followed by measurement of chlorophyll (Chl) fluorescence kinetics, 77 K emission spectra, photosynthetic oxygen evolution, and pigment composition. We observed a build-up of slowly-relaxing non-photochemical quenching which led to a decrease of the Fv/Fm parameter and the connectivity. In contrast to the depression of Fv/Fm (35 %) and the rise of non-photochemical quenching (∼ 1.6), we observed an increase in effective absorption cross-section (20 %), Hill reaction (30 %), photosynthetic oxygen evolution (80 %), and electron transport rate estimated from the Chl fluorescence analysis (80 %). We showed an inconsistency in the presently used interpretation schemes, and ascribe the discrepancy between the increase of effective absorption cross-section and the photosynthetic activities on one side and the effective non-photochemical quenching on the other side to the build-up of a quenching mechanism which dissipates energy in closed reaction centres. Such a type of quenching changes the ratio between thermal dissipation and fluorescence without any effect on photochemical yield. In this case the Fv/Fm ratio cannot be used as a measure of the maximum photochemical yield of PS2. and M. Koblížek ... [et al.].
Net photosynthetic rate (PN) in the mother leaves was higher in the drought tolerant (DT) clones of tea (Camellia sinensis) while liberation of the fixed 14C in light from the mother leaves was higher in the drought susceptible (DS) clones. The DT clones translocated more photosynthates to the crop shoots (three leaves and a bud) from the mother leaf than the DS clones. Concentrations of RuBP carboxylase (RuBPC) or oxygenase (RuBPO) had no relationship with the drought tolerant nature of tea clones but their ratio correlated with the same. DT tea clones had higher catalase activity that could scavenge the hydrogen peroxide formed in the photorespiratory pathway and thereby reduced photorespiration rate (PR). The ratio of RuBPC/RuBPO had a positive correlation with PN and catalase activity. Negative correlation between RuBPC/RuBPO and PR and between catalase activity and RuBPO activity was established. and P. R. Jeyaramraja ... [et al.].
In order to maximize yield, Spathiphyllum, an ornamental plant, was cultured in vitro in novel culture vessels termed Vitron. The best growth was obtained by culturing plantlets on sugar-free liquid medium under CO2 enrichment (3 000 µmol mol-1 24 h-1 d-1) at a low photon flux density (PPFD of 45 µmol m-2 s-1), suggesting that the novel Vitron culture system is suitable for the photoautotrophic micropropagation of Spathiphyllum. and J. A. Teixeira da Silva, D. D. T. Giang, M. Tanaka.
There are several types of quenching coefficients currently in use which describe the decrease of the chlorophyll fluorescence: the photochemical quenching coefficients qP and q(P)rel and the non-photochemical quenching coefficients qN, q(N)rel, and NPQ. These five coefficients were calculated for a broad variety of cases of the fluorescence signals in a normal, realistic range and for determining the limits in a range with extremely low and high fluorescence values. The calculations showed that the quenching coefficients currently in use are not only numbers between 0 and 1 as one would expect when taking them as a relative measure of the quenching process. Most quenching coefficients must be regarded and interpreted carefully separated from each other. Each photochemical quenching coefficient and each non-photochemical quenching coefficient describe the same fluorescence signal in a different way. Only the relative quenching coefficients q(P)rel and q(N)rel match together and can be used to demonstrate a shift of the energy de-excitation from the photochemical to the non-photochemical route.
The measurement of variable chlorophyll (Chl) a fluorescence is widely used as a convenient and versatile tool in photosynthesis research. In many applications empirical correlations and simplified models of Chl a fluorescence are used with success. Nevertheless, variable Chl a fluorescence provides only indirect and complex image of processes occurring within photosynthetic membranes and such simplifications have only limited validity. In this review we elucidate some controversial and still unresolved questions about the origin and interpretation of the variable Chl a fluorescence induction and the proper use of variable Chl a fluorescence for studies of photochemical events in photosystem 2 (PS2). Although the major part of variable Chl a fluorescence reflects the photochemical closure of the PS2 reaction centers (RCs) and can be considered as a function of the redox state of the primary acceptor QA, up to 50 % of the change in the Chl a fluorescence yield can be of secondary, nonphotochemical origin. We review the possible sources of the inherent heterogeneity in the origin of variable Chl a fluorescence. We also comment on the practical implications this bears for the use of variable Chl a fluorescence. and G. Samson, O. Prášil, B. Yaakoubd.