Biomedical subjects

Z G Cerovic

Publications and source records attributed to Z G Cerovic.

6 recordsLinked to original sources

PubMed2006

Relationships between optically assessed polyphenols and chlorophyll contents, and leaf mass per area ratio in woody plants: a signature of the carbon-nitrogen balance within leaves?

Chlorophyll (Chl) and epidermal polyphenol (EPhen) contents were estimated in vivo using two optical leaf-clips, SPAD-502 and Dualex, respectively. The area-based measurements were transformed into mass-based data by taking into account the leaf dry mass per area (LMA). Measurements were performed on forest trees and on saplings grown under controlled conditions. While LMA increased with irradiance along a vertical transect in a beech canopy or in saplings grown under different and increasing irradiance levels, mass-based EPhen (EPhen(m)) increased, whereas mass-based Chl (Chl(m)) decreased. This was a signature of a gradual switch of investment from protein into polyphenol production. A similar signature was obtained in saplings grown on nitrogen-deficient soil with respect to fertilized controls. However, nitrogen effects remained moderate compared to irradiance-induced effects. EPhen(m) and Chl(m) both declined with plant ageing-induced increases in LMA, under all tested growth conditions. This was a signature of an accumulation of dry matter that diluted Chl and EPhen. The described competition between Chl and EPhen in leaves fits well with the predictions of the Protein Competition Model (PCM), that is, that the total leaf mass-based polyphenols content (Phen(t)) is controlled by the competition between protein and polyphenol biosynthetic pathways and its metabolic regulation.

Carbon↗

PubMed2003

UV-induced blue-green and far-red fluorescence along wheat leaves: a potential signature of leaf ageing.

Under UV-excitation, leaves emit red (RF) and far-red (FRF) fluorescence from chlorophyll and blue-green fluorescence (BGF) from hydroxycinnamic acids. In this study, the aim was to develop a fluorescence signature of wheat leaf ageing after the emergence of the lamina. FRF and BGF were examined in the first three leaves of 2-week-old wheat plants. It was investigated how FRF and BGF vary as leaf and tissue aged by spectroscopic measurements, time-resolved BGF analysis and microscopic imaging of the leaf surface. It was found that FRF decreased with leaf and tissue ageing because of an accumulation of UV-absorbers in the epidermis. BGF also decreased, but without changes either in the shape of excitation and emission spectra or in the fluorescence lifetime. So, BGF emanated from the leaf surface, without changes in fluorophore composition during leaf ageing. The shape of the BGF spectrum indicates that ferulic acid bound to the cell wall is the main blue-green fluorophore. The effects of pH and solvents on BGF from intact leaves and ferulic acid in solution were similar, confirming the hydroxycinnamic acid origin of BGF. UV-fluorescence microscopic imaging of the surface of intact leaves showed that different epidermis cell types and sclerenchyma bands emitted BGF. The decreasing gradient of BGF from the base to the apex of the lamina could be related to the decrease in the surface of the fluorescent sclerenchyma bands. The significance of FRF and BGF as potential signatures of wheat lamina growth are discussed.

Apoptosis↗

PubMed2001

Photoinactivation of the photosynthetic electron transport chain by accumulation of over-saturating light pulses given to dark adapted pea leaves.

The effect of cumulative over-saturating pulses (OSP) of white light (1 s, >10 000 mumol photons m(-2) s(-1)), applied every 20 min on pea leaves, was investigated during a complete diurnal cycle of 24 h. In dark-adapted leaves, this treatment leads to a progressive decline of the optimum Photosystem II (PS II) quantum yield. Continuous low background light (except far-red light) had a protective effect against this OSP-induced photoinactivation. The lack of far-red effect could be due to its absorption mainly in PS I and not in PS II, but could be also due to the general low absorption in this wavelength region. The photoinactivation was enhanced in leaves that had been previously infiltrated with chloramphenicol. The quantum yield of CO(2) assimilation, but not its maximal capacity, was inhibited by the OSP treatment. The most spectacular effects observed, in addition to an irreversible quenching of Fm, was a strong inhibition of Q(A) (-) reoxidation revealed by a large increase in the Fs level and consequently by a decrease of DeltaF/Fm'. Under such conditions, we observed that the electron flow deduced from DeltaF/Fm' underestimated the real electron flow to CO(2). Time-resolved Chlorophyll a fluorescence measurements showed that the reduced capacity of Q(A) (-) reoxidation in OSP treated leaves was accompanied by the appearance of a 4.7 ns component attributed to PS II charge recombination. We suggest that a modification at the Q(B) site may influence the redox potential of Q(A)/Q(A) (-), facilitating the reversion of the primary charge separation. In addition, a 1.2 ns fluorescence component accumulated, which appeared to be responsible for the underestimation of PS II electron flow. The observed photoinactivation seemed to be different from the photoinhibition often described in the literature, which occurs under continuous light.

Journal Article↗

PubMed2000

Light-induced changes of NADPH fluorescence in isolated chloroplasts: a spectral and fluorescence lifetime study.

Isolated chloroplasts show a light-induced reversible increase in blue-green fluorescence (BGF), which is only dependent on NADPH changes. In the present communication, we report a time-resolved and spectral analysis of this BGF in reconstituted chloroplasts and intact isolated chloroplasts, in the dark and under actinic illumination. From these measurements we deduced the contribution of the different forms of NADPH (free and bound to proteins) to the light-induced variation of BGF and conclude that this variation is due only to the redox change of the NADP pool. A simple model estimating the distribution of NADPH between the free and bound form was designed, that explains the differences measured for the BGF of reconstituted chloroplasts and intact chloroplasts. From the decay-associated spectra of the chloroplast BGF, we also deduced the participation of flavins to the green peak of chloroplast fluorescence emission spectrum, and the existence of excitation energy transfer from proteins to bound NADPH in chloroplasts. In addition, we re-examined the use of chloroplast BGF as a quantitative measure of NADPH concentration, and confirmed that chloroplast BGF can be used for non-destructive, continuous and probably quantitative monitoring of light-induced changes in NADP redox state.

Chloroplasts↗

PubMed2000

The effect of decreasing temperature up to chilling values on the in vivo F685/F735 chlorophyll fluorescence ratio in Phaseolus vulgaris and Pisum sativum: the role of the photosystem I contribution to the 735 nm fluorescence band.

The effect of leaf temperature (T), between 23 and 4 degrees C, on the chlorophyll (Chl) fluorescence spectral shape was investigated under moderate (200 microE m-2 s-1) and low (30-35 microE m-2 s-1) light intensities in Phaseolus vulgaris and Pisum sativum. With decreasing temperature, an increase in the fluorescence yield at both 685 and 735 nm was observed. A marked change occurred at the longer emission band resulting in a decrease in the Chl fluorescence ratio, F685/F735, with reducing T. Our fluorescence analysis suggests that this effect is due to a temperature-induced state 1-state 2 transition that decreases and increases photosystem II (PSII) and photosystem I (PSI) fluorescence, respectively. Time-resolved fluorescence life-time measurements support this interpretation. At a critical temperature (about 6 degrees C) and low light intensity a sudden decrease in fluorescence intensity was observed, with a larger effect at 685 than at 735 nm. This is probably linked to a modification of the thylakoid membranes, induced by chilling temperatures, which can alter the spill-over from PSII to PSI. The contribution of photosystem I to the long-wavelength Chl fluorescence band (735 nm) at room temperature was estimated by both time-resolved fluorescence lifetime and fluorescence yield measurements at 685 and 735 nm. We found that PSI contributes to the 735 nm fluorescence for about 40, 10 and 35% at the minimal (F0), maximal (Fm) and steady-state (Fs) levels, respectively. Therefore, PSI must be taken into account in the analysis of Chl fluorescence parameters that include the 735 nm band and to interpret the changes in the Chl fluorescence ratio that can be induced by different agents.

Chlorophyll↗

PubMed1987

Photosynthesis by intact isolated chloroplasts on solid support.

A new approach to measurements of photosynthesis by isolated chloroplasts has been devised. Intact isolated chloroplasts were trapped in the cavities of membrane filters. The thin layers of chloroplasts so obtained were assayed for O(2) evolution and CO(2) assimilation in leaf-chambers. Photosynthetic gas exchange could be demonstrated to take place either in a closed or a flow-through system. The chloroplasts were morphologically intact as shown by light or scanning electron microscopy and displayed stable rates of photosynthesis in the presence of phosphate and alkaline phosphatase. The methods described open the way to in vitro measurement of photosynthesis, by chloroplasts under conditions more closely resembling those in leaves.

Journal Article↗