IntroductionSilver nanoparticles (AgNPs) are widely used among other nanoparticles in many industries within a wide range of consumer products because of their antibacterial and biocidal properties (Thuesombat et al., 2014). In recent years, the significant increase in the consumption of nanoparticles has caused environmental, health, and safety concerns regarding their potential effects (Ma et al., 2010;Pokhrel and Dubey, 2013). Nanoparticles could uncertainly spread to the environment. However, the interaction between AgNPs and plant systems is still not well known (Patlolla et al., 2012;Song et al., 2013).AgNPs are known to be absorbed by plants and could interact with intracellular parts causing water imbalances, cell damage, and decreases in photosynthesis (Kumari et al., 2009;Qian et al., 2013). They are also reported to have genotoxic effects on plant cells, inducing chromosomal aberrations and micronucleus induction (Patlolla et al., 2012). However, the impacts of nanoparticles on plants can vary according to the nanoparticle concentration, size, chemical properties, and plant species (Ma et al., 2010;Thuesombat et al., 2014).Nanotoxicity could lead to oxidative stress and previous studies indicate that AgNPs could induce toxicity due to their effect on reactive oxygen species (ROS) formation (Qian et al., 2013;McShan et al., 2014). The imbalance of ROS production and antioxidant activity can cause oxidative damage, and plants cope with this oxidative damage by their antioxidant defense mechanism (Saed-Moucheshi et al., 2014). Previously, studies on the genotoxicity of nanoparticles have used cell viability, chromosome aberration, or micronucleus assays to identify the genotoxic effect, and comet analysis for detecting the DNA damage in different plant species (Kumari et al., 2009;Kumari et al., 2011;Patlolla et al., 2012;Ghosh et al., 2012). However, these methods are very restricted for identifying the genotoxic effects of nanoparticles at the DNA level. DNA-based techniques are sensitive and selective assays that help to determine the genotoxic effects of environmental pollutants on DNA. One of these methods used for these aims is the intersimple sequence repeat (ISSR)-PCR assay. ISSR-PCR uses as primer microsatellite repeats (Zietkiewicz et al., 1994). The ISSR-PCR method is more sensitive than the random amplified polymorphic DNA assay (RAPD) (Correia et al., 2014;Bajpai et al., 2015), because of the exhibiting specificity of the sequence-tagged-site markers and high ratio of reproducibility potential owing to the use of longer primers (16-25 bp).

Putrescine is reported to be necessary for cold acclimation under low-temperature stress. In this study, the effect of low-temperature on some physiological and biochemical parameters has been investigated using the green algae Chlamydomonas reinhardtii. The lipid peroxidation rate, amount of Rubisco protein, activities of antioxidant enzymes and gene expression of polyamine biosynthesis (odc2, and spd1), heat shock proteins (hsp70c, hsp90a, and hsp90c), and PSII repair mechanisms (psba, rep27, and tba1) were determined to understand the low-temperature response. Exogenous putrescine application significantly increased Rubisco protein concentration and catalase enzyme activities under low-temperature stress. Moreover, real-time RT-PCR results and gene expression analysis showed that polyamine metabolism induced gene expression at low-temperatures in the first 24 h. In the same way, the gene expression of heat shock proteins (hsp70c, hsp90a, and hsp90c) decreased under low-temperature treatment for 72 h; however, application of putrescine enhanced the gene expression in the first 24 h. The results obtained indicated that molecular response in the first 24 h could be important for cold acclimation. The psba and tba1 expressions were reduced under low-temperatures depending on the exposure time. In contrast, the exogenous putrescine enhanced the expression level of the psba response to low-temperature at 24 and 72 h. The results obtained in this study indicate that putrescine could play a role in the PS II repair mechanisms under low-temperature stress.