Detelin Stefanov

Preservation of photosynthetic electron transport from senescence-induced inactivation in primary leaves after decapitation and defoliation of bean plants.

The comparative effects of decapitation and defoliation on the senescence-induced inactivation of photosynthetic activity in primary leaves of bean plants were investigated. Decapitation was performed during different phases of bean plant ontogenesis, immediately after the appearance of the 1st, 2nd, 3rd and 4th composite leaf. In addition, we examined a variant with primary leaves and stem with an apical bud, but without composite leaves, i.e. defoliated plants. Analyses of chlorophyll fluorescence, millisecond delayed fluorescence and absorption at 830nm in primary leaves were undertaken to investigate the alterations in photosystems II and I electron transport during the decapitation-induced delayed senescence in the non-detached leaves. Analysis of the OKJIP transients using the JIP-test (see [Strasser R, Srivastava A, Tsimilli-Michael M. Analysis of the chlorophyll a fluorescence transient. In: Papageorgiou G, Govindjee, editors. Chlorophyll a fluorescence: a signature of photosynthesis. The Netherlands: Kluwer Academic Publishers, 2004; pp. 321-362]) showed an increase in several biophysical parameters of photosystem II in decapitated plants, specifically, the density of active reaction centers on a chlorophyll basis, the yields of trapping and electron transport, and the performance index. We also observed a decrease in the absorbed light energy per reaction center. Such a decrease in light absorption could be a result of the photosystem II down regulation that appeared as an increase in Q(B)-non-reducing photosystem II centers. The effect was identical when all leaves except the primary leaves were removed. The variant with a preserved apical bud, the defoliated plant, showed values similar to those of decapitated plants with primary leaves only. The changes in the induction curves of the delayed fluorescence also indicated an acceleration of electron transport beyond photosystem II in the decapitated and in defoliated plants. In these plants, the photosystem I-driven electron transport was accelerated, and the size of the plastoquinone pool was enhanced. It was established that decapitation can retard the senescence of primary leaves, can expand leaf life span and can cause activation of both photosystems I and II electron transport. The decapitation procedure shows similarities to the process of defoliation. The overcompensation effect that is developed after defoliation could initially be manifested as an acceleration of the linear photosynthetic electron flow in the rest of the leaves.

Relationship between the degree of carotenoid depletion and function of the photosynthetic apparatus

Fluridone, an inhibitor of the carotenoid biosynthesis, was used to study the relationship between the degree of carotenoid depletion and the function of the photosynthetic apparatus. The data reveal that, at a small reduction of the carotenoid content (25% decrease of the total carotenoids), the PSII and PSI (oxidation of P700 by far-red light) photochemistry is not influenced, while the oxygen evolution is strongly inhibited. Further reduction of the total carotenoid content (more than 40%) leads to decrease of the chlorophyll content and inhibition of the functions of both photosystems as the effect on the photosynthetic oxygen evolution and primary photochemistry is stronger than the effect on P700 oxidation. The analysis of the oxygen production under continuous illumination and flash oxygen yields suggests that the inhibition of the oxygen evolution is caused mainly by the damage of PSIIalpha centers.

Effects of Grapevine Fanleaf and Stem Pitting Viruses on the Photosynthetic Activity of Grapevine Plants Grown in vitro

The effects of viral diseases on the photosynthetic activity of grapevine (Vitis rupestrisvar. Rupestris du Lot) leaves were investigated. The third and sixth leaves used for measurements were obtained from in vitrogrown healthy plants and plants affected by grapevine fanleaf and rupestris stem pitting viruses. The induction curves of prompt and delayed chlorophyll fluorescence, as well as the temperature characteristics of steady-state, prompt, and delayed emissions, were investigated. Age-dependent changes were found, which were related, on the one hand, to the acceleration of electron transport and the enhancement of thylakoid energization and, on the other hand, to a smaller extent of transmembrane ΔμH+in the younger sixth leaf compared to that in the third leaf. The infected plants characteristically showed faster electron transport, an elevated energetic efficiency of photosynthesis, and the suppression of CO2fixation owing to a presumable activation of the adenylate metabolism. An analysis of the thermograms of prompt and delayed fluorescence revealed the shifts in the position of the M1peak and a half-inhibition temperature T50towards a higher temperature in infected plants, which indicates a certain increase in the thermal tolerance of thylakoid membranes. The data suggest that the viral metabolism affects the functional activity and stability of thylakoid membranes.

Different effects of dark treatment on pigment composition and photosystem I and II activities in intact cotyledons and primary leaves of Cucurbita pepo (zucchini)

Darkness mediates different senescence-related responses depending on the targeting of dark treatment (whole plants or individual leaves) and the organs that perceive the signal (leaves or cotyledons). In this study, we presented data on the differential effects of 2-day dark treatment on progression of senescence in cotyledons and primary leaves of 14-day-old plants of Cucurbita pepo L. (zucchini). The lack of changes in chlorophyll a, chlorophyll b and carotenoid contents as well as in the PSI activity measured by the far-red induced alterations in the P700 oxidation levels and the quantum yield of electron transport from QA− to PSI end acceptors (

Fatty acid content during reconstitution of the photosynthetic apparatus in the air-dried leaves of Xerophyta scabrida after rehydration

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Local induction of senescence by darkness in Cucurbita pepo (zucchini) cotyledons or the primary leaf induces opposite effects in the adjacent illuminated organ

) indicated higher resistance of cotyledons to the applied dark stress compared to the primary leaves. In contrast to cotyledons, PSI activity in the primary leaves was significantly inhibited. Concerning the activity of PSII analyzed by the changes in the JIP-test parameters (the maximal efficiency of PSII photochemistry,

The Changes in Some Photosynthetic Characteristics of Transgenic Tobacco Plants, Resistant to Bacteria Pseudomonas Syringae pv. Tabaci

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