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Abstract

Growth and photosynthetic characteristics, inducibility of the CAM pathway and the functioning of the antioxidant defense system were investigated in Rosularia elymaitica (Crassulaceae) under drought and UV stresses. Drought did not substantially affect the growth of the plants, but it significantly reduced leaf thickness as well as osmotic potential, water potential and relative water content. In contrast, UV radiation treatment affected neither growth nor the water relations of leaves. Water limitation for 12 days caused a significant increase in nighttime PEPC and NAD-MDH activity and an increase in Δtitratable acidity relative to well-watered plants. The nighttime CO2 net assimilation rate increased significantly in drought-stressed plants but was still negative, resembling a C3-like pattern of gas exchange. Twenty days of UV treatment, increased Δtitratable acidity slightly and increased only daytime PEPC activity, and did not affect other parameters of carbon metabolism. As judged by maintenance of membrane integrity and stable amounts of H2O2 under UV stress, the antioxidant defense system effectively protected the plants against UV radiation. In contrast, oxidative stress occurred under severe drought stress (20 days of withholding water). Except for higher daytime APX activity in the UV-treated plants, enzyme activity in the control and in the drought- and UV-stressed plants did not show any diurnal fluctuation during 24 h. Temporal changes in Δtitratable acidity and ΔPEPC activity coincided closely with those of antioxidant enzymes; both started to increase after 12 days of drought stress. These results indicate that drought stress but not UV radiation induced the CAM-cycling pathway in R. elymaitica.

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Authors and Affiliations

Ghader Habibi
Roghieh Hajiboland
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Abstract

Since silver nanoparticles (AgNPs) are used as nanofungicides and nanopesticides in agriculture, the toxicity of AgNPs as well as AgNO3 must be determined. Besides this, we evaluated the combined effects of salicylic acid (SA) and nitric oxide (NO) on responses of Phlomis tuberosa plants to Ag-induced stress. The results of growth parameters together with measurement of malondialdehyde (MDA) indicated that exposure to 1000 mg L–1 of AgNPs or AgNO3 exerted more toxicity, which was closely associated with the over– accumulation of ROS and the reduction of photochemical functioning. However, SNP (NO) and SA addition successfully alleviated adverse impact of AgNPs on Phlomis seedlings. Maximum amelioration of Ag-induced stress was found by combined treatments of SA+NO. Phlomis plants primed with SA+NO exhibited higher synthesis of chlorophyll b and carotenoid pigments to ameliorate AgNP-induced adverse effects on chlorophyll fluorescence parameters. SA+NO led to high levels of proline under both AgNPs and AgNO3 treatments. A further increase in antioxidants (phenolic compounds) was observed in NO-primed plants under AgNPs- induced stress, which was attendant with the high level of CAT and APX activities. Increase in total Ag translocation into shoot organs and cell survival were also enhanced by SA+NO under AgNPs stress. We concluded that SA+NO mitigated the inhibitory effects of AgNPs stress on the photosynthetic apparatus by increasing the phenolic compounds and carotenoids as well as by regulating accumulation of Ag, ROS and antioxidants. The present findings provide important knowledge to design strategies that minimize the negative impact of AgNPs and AgNO3 on crops.
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Authors and Affiliations

Elham Ghasemifar
1
Ghader Habibi
1
Golamreza Bakhshi-Khaniki
1

  1. Department of Biology, Payame Noor University (PNU), PO BOX 19395-3697 Tehran, Iran
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Abstract

Since plant responses to selenium nanoparticles (nSe) had not been clarified, this study was carried out to evaluate the effects of nSe (10 and 100 μM) on photosynthesis performance, ion homeostasis, antioxidant system, and phenylpropanoids in strawberry exposed to salt stress. Inductively Coupled Plasma-Mass Spectroscopy analyses indicated that foliar-applied nSe can be taken up by leaves and trans-located to roots. Salinity led to an increase in Na concentration and reductions in Ca and K contents which were relieved by the nSe applications. Moreover, the nSe treatment at 10 μM alleviated the NaCl-induced lesion to PSII functioning, contributing to improvement in water-splitting complex (Fv/Fo) under salinity. The exposure to nSe at a concentration of 100 µM exhibited a moderate stress, determined by the increases in hydrogen peroxide (H2O2) and lipid peroxidation rate (membrane integrity index). The nSe10 treatment increased catalase activity and phenylpropanoid derivatives contents (salicylic acid, catechin, and caffeic acid) and decreased the content of oxidants under salinity condition. Consequently, nSe utilization at a suitable dose can be an effective method to alleviate signs of salt stress via improvements in photosynthesis, ion hemostasis, photosynthesis performance, salicylic acid (a vital signaling defensive hormone), and antioxidant machinery.

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Authors and Affiliations

Reza Soleymanzadeh
Alireza Iranbakhsh
Ghader Habibi
Zahra Oraghi Ardebili

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