Vera Cesar

Changes in photosynthetic performance and antioxidative strategies during maturation of Norway maple (Acer platanoides L.) leaves

Different structural and functional changes take place during leaf development. Since some of them are highly connected to oxidative metabolism, regulation of reactive oxygen species (ROS) abundance is required. Most of the reactive oxygen species ROS in plant cells are produced in chloroplasts as a result of highly energetic reactions of photosynthesis. The aim of our study was to examine the changes in concentration of oxidative stress parameters (TBARS - thiobarbituric acid-reacting substances and protein carbonyls) as well as antioxidative strategies during development of maple (Acer platanoides L.) leaves in the light of their enhanced photosynthetic performance. We reveal that biogenesis of the photosynthetic apparatus during maple leaf maturation corresponded with oxidative damage of lipids, but not proteins. In addition, antioxidative responses in young leaves differed from that in older leaves. Young leaves had high values of non-photochemical quenching (NPQ) and catalase (CAT, EC 1.11.1.6) activity which declined during the maturation process. Developing leaves were characterized by an increase in TBARS level, the content of non-enzymatic antioxidants as well as ascorbate peroxidase activity (APX, EC 1.11.1.11), while the content of protein carbonyls decreased with leaf maturation. Fully developed leaves had the highest lipid peroxidation level accompanied by a maximum in ascorbic acid content and superoxide dismutase activity (SOD, EC1.15.1.1). These observations imply completely different antioxidative strategies during leaf maturation enabling them to perform their basic function.

Differential accumulation of plastid preprotein translocon components during spruce (Picea abies L. Karst.) needle development.

Abstract We demonstrate that basic components of the plastid protein-import apparatus originally found in pea, Toc34, Toc159, and Tic110, are also conserved in evolutionarily younger gymnosperms. We show that multiple isoforms of the preprotein receptor Toc34 differentially accumulate in various stages of needle development, while the amounts of Toc159 drastically decrease during chloroplast morphogenesis. Spruce Toc34 and Toc159 receptors are able to recognise and interact with the angiosperm precursor of the Rubisco small subunit. Young proplastids found in closed buds contain a highly elevated number of protein translocation complexes equipped with only two types of outer envelope receptors, Toc159 and a 30-kDa Toc34-related protein. Photosystem II (PSII) can already be assembled in a fully functional complex at this very early stage of needle development, suggesting that no additional receptor isoforms are needed for translocation of all necessary PSII components. We conclude that the accumulation of evolutionarily conserved plastid preprotein translocation components is differentially regulated during spruce needle development.

Biochemical and epigenetic changes in phytoplasma-recovered periwinkle after indole-3-butyric acid treatment.

Aim:  To elucidate the possible mechanism of phytoplasma elimination from periwinkle shoots caused by indole‐3‐butyric acid (IBA) treatment.

Response of Lemna minor L. to short-term cobalt exposure: The effect on photosynthetic electron transport chain and induction of oxidative damage

The effect of two concentrations of cobalt (Co(2+)) on photosynthetic activity and antioxidative response in Lemna minor L. were assessed 24, 48 and 72h after the start of the exposure. Higher concentration of cobalt (1mM) induced growth inhibition while lower concentration (0.01mM) increased photosynthetic pigments content. Analysis of chlorophyll a fluorescence transients revealed high sensitivity of photosystem II primary photochemistry to excess of Co(2+) especially at the higher concentration where decreased electron transport beyond primary quinone acceptor QA(-) and impaired function of oxygen evolving complex (OEC) was observed. Due to impairment of OEC, oxygen production was decreased at higher Co(2+) concentration. Activity of superoxide dismutase was mainly inhibited while lipid peroxidation increased, at both concentrations, indicating that cobalt-induced oxidative damage after short exposure and moreover, susceptibility of the membranes in the cell to cobalt toxicity. Results obtained in this study suggest possible application of used parameters as tools in assessment of early damage caused by metals.

Degradation of chloroplast DNA during natural senescence of maple leaves.

The fate of chloroplast DNA (cpDNA) during plastid development and conversion between various plastid types is still not very well understood. This is especially true for the cpDNA found in plastids of naturally senescing leaves. Here, we describe changes in plastid nucleoid structure accompanied with cpDNA degradation occurring during natural senescence of the free-growing deciduous woody species Acer pseudoplatanus L. Natural senescence was investigated using three types of senescing leaves: green (G), yellow-green (YG) and yellow (Y). The extent of senescence was evaluated at the level of photosynthetic pigment degradation, accumulation of starch and plastid ultrastructure. Determination of cpDNA amount was carried out by in planta visualization with 4,6-diamidino-2-phenylindole, by Southern hybridization, and by dot-blot using an rbcL gene probe. During natural senescence, plastid nucleoids undergo structural rearrangements accompanied by an almost complete loss of cpDNA. Furthermore, senescence-associated protein components exhibiting strong binding to an ∼10kbp rbcL-containg cpDNA fragment were identified. This interaction might be important for rbcL expression and Rubisco degradation during the course of natural senescence in trees.

Endogenous Auxin Profile in the Christmas Rose (Helleborus niger L.) Flower and Fruit: Free and Amide Conjugated IAA

The reproductive development of the Christmas rose (Helleborus niger L.) is characterized by an uncommon feature in the world of flowering plants: after fertilization the white perianth becomes green and photosynthetically active and persists during fruit development. In the flowers in which fertilization was prevented by emasculation (unfertilized) or entire reproductive organs were removed (depistillated), the elongation of the peduncle was reduced by 20–30%, and vascular development, particularly lignin deposition in sclerenchyma, was arrested. Chlorophyll accumulation in sepals and their photosynthetic efficacy were up to 80% lower in comparison to fertilized flowers. Endogenous auxins were investigated in floral and fruit tissues and their potential roles in these processes are discussed. Analytical data of free indole-3-acetic acid, indole-3-ethanol (IEt), and seven amino acid conjugates were afforded by LC-MS/MS in floral tissues of fertilized as well as unfertilized and depistillated flowers. Among amino acid conjugates, novel ones with Val, Gly, and Phe were identified and quantified in the anthers, and in the fruit during development. Reproductive organs before fertilization followed by developing fruit at post-anthesis were the main source of auxin. Tissues of unfertilized and depistillated flowers accumulated significantly lower levels of auxin. Upon depistillation, auxin content in the peduncle and sepal was decreased to 4 and 45%, respectively, in comparison to fruit-bearing flowers. This study suggests that auxin arising in developing fruit may participate, in part, in the coordination of the Christmas rose peduncle elongation and its vascular development.

TROL-FNR interaction reveals alternative pathways of electron partitioning in photosynthesis

In photosynthesis, final electron transfer from ferredoxin to NADP+ is accomplished by the flavo enzyme ferredoxin:NADP+ oxidoreductase (FNR). FNR is recruited to thylakoid membranes via integral membrane thylakoid rhodanase-like protein TROL. We address the fate of electrons downstream of photosystem I when TROL is absent. We have employed electron paramagnetic resonance (EPR) spectroscopy to study free radical formation and electron partitioning in TROL-depleted chloroplasts. DMPO was used to detect superoxide anion (O2.−) formation, while the generation of other free radicals was monitored by Tiron. Chloroplasts from trol plants pre-acclimated to different light conditions consistently exhibited diminished O2.− accumulation. Generation of other radical forms was elevated in trol chloroplasts in all tested conditions, except for the plants pre-acclimated to high-light. Remarkably, dark- and growth light-acclimated trol chloroplasts were resilient to O2.− generation induced by methyl-viologen. We propose that the dynamic binding and release of FNR from TROL can control the flow of photosynthetic electrons prior to activation of the pseudo-cyclic electron transfer pathway.

Physiology and biochemistry of leaf bleaching in prematurely aging maple (Acer saccharinum L.) trees. II. Functional and molecular adjustment of PSII

Physiology and biochemistry of leaf bleaching in prematurely aging maple (Acer saccharinum L.) trees. II. Functional and molecular adjustment of PSII In the present study we aimed to investigate physiological and molecular mechanisms of photosynthetic performance decline in prematurely aged bleached leaves of silver maple (Acer saccharinum L.) trees. We used in vivo chlorophyll a fluorescence measurement to analyze changes in PSII photochemistry, relative abundance of photosynthetic proteins (D1, LHCII, Cytf and Rubisco LSU), relations between chlorophylls and their precursor protochlorophyllide as well as elemental composition of the leaves. Decreases in Al, Cr, Cu, Fe, K, Zn and an increase in S concentrations were found in bleached leaves in comparison to healthy green ones. The bleached leaves were visually expressing symptoms characteristic of Fe deficiency. Further, they had considerably decreased chlorophyll contents and protochlorophyllide contents, overall photosynthetic activity and relative abundance of major photosynthetic proteins. All the results indicate that modifications in the molecular organization of photosynthetic electron-transport chain components in bleached leaves led to functional adaptation of the PSII achieved by modifications of some reaction centres (RCs), turning them from active to dissipative. This provided efficient adaptation of bleached leaves to high-light induced oxidative damage during summer.

Functioning of the photosynthetic apparatus under low and high light conditions in chlorotic spruce needles as evaluated by in vivo chlorophyll fluorescence

The photosynthetic apparatus rapidly responds to the environmental influences. In vivo chlorophyll fluorescence was applied for the evaluation of photosystem II (PSII) and electron-transport chain functioning and for determination of photochemical and nonphotochemical quenching in chlorotic spruce needles exposed to urban pollution. More injured needles had lower content of chloroplast pigments and changed chloroplast ultrastructure, in comparison with less injured needles. The maximum PSII efficiency was measured in dark-adapted samples, whereas other parameters were measured under low and high light conditions (125 and 1400 µmol photons/(m2s), respectively). The PSII efficiency and relative electron transport rate (rel. ETR) were lowered at both irradiance levels while the photochemical quenching was significantly lower only in high light. Nonphotochemical quenching coefficients (qN) values were higher at both light levels in more injured needles, however, the difference was insignificant. High nonphotochemical quenching in both needle groups probably made possible the photosynthetic apparatus to function at the high light level. Our results suggested that the lowering of the chlorophyll content could be considered as a protecting event rather than just the consequence of the stress.

Differential accumulation of photosynthetic proteins regulates diurnal photochemical adjustments of PSII in common fig (Ficus carica L.) leaves

Molecular processes involved in photosystem II adaptation of woody species to diurnal changes in light and temperature conditions are still not well understood. Regarding this, here we investigated differences between young and mature leaves of common fig (Ficus carica L.) in photosynthetic performance as well as accumulation of the main photosynthetic proteins: light harvesting complex II, D1 protein and Rubisco large subunit. Investigated leaf types revealed different adjustment mechanisms to keep effective photosynthesis. Rather stable diurnal accumulation of light harvesting complex II in mature leaves enabled efficient excitation energy utilization (negative L-band) what triggered faster D1 protein degradation at high light. However, after photoinhibition, greater accumulation of D1 during the night enabled them faster recovery. So, the most photosynthetic parameters, as the maximum quantum yield for primary photochemistry, electron transport and overall photosynthetic efficiency in mature leaves successfully restored to their initial values at 1a.m. Reduced connectivity of light harvesting complexes II to its reaction centers (positive L-band) in young leaves increased dissipation of excess light causing less pressure to D1 and its slower degradation. Decreased electron transport in young leaves, due to reduced transfer beyond primary acceptor QA- most probably additionally induced degradation of Rubisco large subunit what consequently led to the stronger decrease of overall photosynthetic efficiency in young leaves at noon.