			Home About us Contact

Photosynthetic System (photosynthetic + system)

Distribution by Scientific Domains

Life Sciences	40%

Selected Abstracts

Enhanced Optical Properties of a Photosynthetic System Conjugated with Semiconductor Nanoparticles: The Role of Förster Transfer,

ADVANCED MATERIALS, Issue 22 2008
Alexander O. Govorov
The rate of optical generation of electron--hole pairs inside a photosynthetic system can be greatly increased through conjugation with nanoparticles. The enhancement stems from much larger optical absorption cross section of a semiconductor nanoparticle compared to a photosynthetic system. In the hybrid complex, excitons are transferred via the Förster mechanism to the photosynthetic system, where charge separation takes place. [source]

Drought stress effects on photosystem I content and photosystem II thermotolerance analyzed using Chl a fluorescence kinetics in barley varieties differing in their drought tolerance

PHYSIOLOGIA PLANTARUM, Issue 2 2009
Abdallah Oukarroum
Drought stress has multiple effects on the photosynthetic system. Here, we show that a decrease of the relative contribution of the I-P phase, ,VIP = ,VI = (FM,FI)/(FM, Fo), to the fluorescence transient OJIP is observed in 10 drought-stressed barley and 9 chickpea varieties. The extent of the I-P loss in the barley varieties depended on their drought tolerance. The relative loss of the I-P phase seems to be related to a loss of photosystem (PS) I reaction centers as determined by 820-nm transmission measurements. In the second part of this study, the interaction of drought and heat stress in two barley varieties (the drought tolerant variety A¨t Baha and the drought sensitive variety Lannaceur) was studied using a new approach. Heat stress was induced by exposing the plant leaves to temperatures of 25,45°C and the inactivation of the O2 -evolving complex (OEC) was followed measuring chlorophyll a (Chl a) fluorescence using a protocol consisting of two 5-ms pulses spaced 2.3 ms apart. In active reaction centers, the dark interval is long enough to allow the OEC to recover from the first pulse; whereas in heat-inactivated reaction centers it is not. In the latter category of reaction centers, no further fluorescence rise is induced by the second pulse. Lannaceur, under well-watered conditions, was more heat tolerant than Aït Baha. However, this difference was lost following drought stress. Drought stress considerably increased the thermostability of PS II of both varieties. [source]

Optimizing Hardwood Reforestation in Old Fields: The Effects of Treeshelters and Environmental Factors on Tree Seedling Growth and Physiology

RESTORATION ECOLOGY, Issue 2 2008
Etienne Laliberté
Abstract Strong competition for water is largely recognized as the main factor explaining the resistance of herbaceous old fields to tree invasion. Therefore, site preparation as well as chemical and mechanical vegetation control are recommended when establishing hardwood tree plantations on such sites, but those methods are sometimes socially or ecologically inappropriate. The main objective of this study was to analyze whether treeshelters could improve early tree growth in herbaceous old fields, when mulching alone is used to partially control herbaceous competition. Our results indicate that treeshelters can facilitate tree growth in those conditions but that this was not caused by an improvement of tree water relations. Rather, it appeared to be related to an optimization of light levels inside the shelter, where light intensity was low enough to lead to a photosynthetic system less costly to maintain due to a greater specific leaf area but high enough to have no adverse effects on photosynthetic rates. Although treeshelters increased tree growth when surrounding herbaceous vegetation was low (either height or standing biomass), allowing high light levels, they reduced growth when surrounding vegetation was high and blocked a substantial quantity of light. Therefore, environmental factors such as light availability need to be considered to optimize the success of hardwood plantations when treeshelters are used in recently abandoned agricultural fields. [source]

Dendrimers: A Mimic Natural Light-Harvesting System

CHEMISTRY - AN ASIAN JOURNAL, Issue 5 2010
Yi Zeng Dr.
Abstract In natural photosynthetic systems, a large array of chlorophyll molecules surrounds a single reaction center and channels the absorbed solar energy to the reaction center, ultimately resulting in ATP production. Dendrimers are well-defined tree-like macromolecules having numerous chain ends all emanating from a single core, which makes them an attractive candidate for light-harvesting applications. More importantly, their synthesis is controllable and the accurate positioning of chromophores can be achieved. Photoinduced electron transfer and energy transfer are main processes involved in photosynthesis. Studies on these processes in dendritic systems are important for the future application of dendrimers in optoelectronic devices. In this Focus Review we will discuss recent advances of light-harvesting dendrimers and emphasize the energy transfer and electron transfer characteristics in these systems. [source]