The study examined photosynthetic efficiency of two barley landraces (cvs. Arabi Abiad and Arabi Aswad) through a prompt fluorescence technique under influence of 14 different abiotic stress factors. The difference in the behavior of photosynthetic parameters under the same stress factor in-between cv. Arabi Abiad and cv. Arabi Aswad indicated different mechanisms of tolerance and strategies for the conversion of light energy into chemical energy for both the landraces. This study confirmed the suitability of some chlorophyll fluorescence parameters as reliable biomarkers for screening the plants at the level of photosynthetic apparatus.
The ameliorative effect of fulvic acid (0, 300, and 600 mg L −1 ) on photosystem II and antioxidant enzyme activity of the rapeseed (Brassica napus L.) plant under water stress (60, 100, and 140 mm evaporation from class A pan) was studied using split plots in a randomized complete block design with three replications. Results indicated that application of fulvic acid (FA) improved the maximum quantum efficiency of PSII (F v /F m ) and performance index (PI) of plants under both well-watered and limited-water conditions. The time span from F o to F m and the energy necessary for the closure of all reaction centers was significantly increased, but the size of the plastoquinone pool was reduced with increasing water stress levels. Plants treated with FA had higher peroxidase and catalase activities under all irrigation conditions. Activities of ascorbate peroxidase and superoxide dismutase in plants increased with increasing water stress. Malondialdehyde increased under severe water stress, but application of FA significantly decreased lipid peroxidation. Production of reactive oxygen species (ROS) is a common phenomenon in plants under stress. Under this condition, the balance between the production of ROS and the quenching activity of antioxidants is upset, often resulting in oxidative damage. In this study, application of FA significantly increased fluorescence of chlorophyll a, inhibiting ROS production and enhancing antioxidant enzymes activity that destroyed ROS. Thus, ROS in plant cells was reduced under water stress by application of FA and consequently lipid peroxidation was reduced. (http://creativecommons.org/licenses/by-nc-nd/4.0/). Keywords: Brassica napus Fluorescence Antioxidant enzyme Water stress Fulvic acidT H E C R O P J O U R N A L X X ( 2 0 1 5 ) X X X -X X X
Water is a limited resource and is likely to become even more restricted with climate change. The aim of this study was to evaluate the effect of humic acid (HA) applications on photosynthesis efficiency of rapeseed plants under different watering conditions. Water stress strongly increased electron transport flux, probability that trapped excitation can move an electron into the electron transport chain beyond Q A , and quantum yield of reduction of end electron acceptors at the PSI acceptor side. Application of HA decreased the values of these parameters to be similar to those of non-stress conditions. We found that, the application of HA improved plants net photosynthesis under water stress via increasing the rate of gas exchange and electron transport flux in plants.
The ameliorative effect of salicilic (SA) and silicon (Si) on photosystem II (PSII) activity of mung bean plant under salt stress (control, 3, 6, and 9 dS/m) was studied by chlorophyll a fluorescence measure ment. Results showed that Na + accumulation decreased, but K + accumulation increased in mung bean (Vigna radiata (L.) Wilczek) leaves by application of Si and especially SA, leading to improvement in PSII activity under salinity. Initial fluorescence (F 0 ) and energy necessary for the closure of all reaction cen tres (S m ) were increased with increasing salt levels. Exogenous foliar application of SA and Si decreased initial fluorescence (F 0 ) and increased photosynthesis relative vitality (PI). Maximum fluorescence (F m ), variable flu orescence (F v ), the activity of the water splitting complex on the donor side of the PSII (proportional to F v /F 0 ) and the average redox state of Q A in the time span from 0 to T fm (S m /T fm ) were also enhanced by foliar appli cation of SA. Exogenous application of SA improved maximum quantum efficiency of PSII (F v /F m ) and per formance index (PI) under both saline and non saline conditions. Increasing in the size of the plastoquinone pool (Area) was much greater for SA than that for Si treated plants. It was concluded that foliar application of Si and SA in particular could play a key role in salt stress tolerance of mung bean plants.Abbreviations: Area-the area above the fluorescence induction curve between F 0 and F m ; F 0 -initial fluorescence; F m -maxi mum fluorescence; F v -variable fluorescence; PI-performance index; PSII-photosystem II; SA-salicylic acid; Si-silicon; S m -energy necessary for the closure of all reaction centres; T fm -the time span from 0 to F m .
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