Nanoparticles have been recognized as an abiotic stress factor in the last decade. Although they are extensively used in nanotechnology, the possible effects of nanoparticles on plants are still unclear. Therefore the aim of the present study was to determine the dose dependent effects of 13 nm-sized aluminum oxide nanoparticles (Al₂O₃ NPs) on wheat roots correlating with programmed cell death related characteristics. Exposure to different concentrations of Al₂O₃ NPs (5, 25 and 50 mg ml^–1) decreased the mitotic indices dose dependently and caused chromosomal abnormalities such as c-mitosis, monopolar metaphase and stickiness after 96 h. Loss of plasma membrane integrity and irregular microtubule aggregations were determined. Nuclear deformations and TUNEL positive reactions indicating programmed cell death were also observed. Al₂O₃ NP-induced caspase 3, 8 and 9-like activities which control programmed cell death were observed in all concentrations. According to our results Al₂O₃ NPs induced programmed cell death in wheat roots after 96 h.

To assess the alternative responses to aluminum toxicity, maize (Zea mays L. cv Karadeniz yıldızı) roots were exposed to different concentrations of AlCl3 (150, 300 and 450 μM). Aluminum reduced the root elongation by 39.6% in 150 μM, 44.1% in 300 μM, 50.1% in 450 μM AlCl3 after 96 h period. To correlate the root elongation with the alternative stress responses including aluminum accumulation, lipid peroxidation, mitotic abnormalities, reduction of starch content, intracellular Ca2+ accumulation, callose formation, lignin deposition and peroxidase activity, cytochemical and biochemical tests were performed. The results indicated that aluminum accumulation and lipid peroxidation were observed more densely on the root cap and the outer cortex cells. In addition to morphological deformations, cytochemical analysis displayed cellular deformations. Furthermore, mitotic abnormalities were observed such as c-mitosis, micronuclei, bi- and trinucleated cells in aluminum treated root tips. Aluminum treatment induced starch reduction, callose formation, lignin accumulation and intracellular Ca2+ increase. Moreover, the peroxidase activity increased significantly by 3, 4.4 and 7.7 times higher than in that of control after 96 h, respectively. In conclusion, aluminum is significantly stressful in maize culminating in morphological and cellular alterations.

Salicylic acid (SA) is one of the endogenous plant growth regulators that modulate various metabolic and physiological events. To evaluate the exogenous SA-induced germination, biochemical and developmental alterations, different concentrations (10, 100, 500 and 1000 µM) of SA were applied to rye (Secale cerealeL.) seeds in hydroponic culture conditions for 15 days. The observations revealed that seed germination and root elongation were stimulated in 10 µM SA treatment, however they were inhibited in higher concentrations (100 and 500 µM) of SA. Furthermore, there was no germination in 1000 µM SA. The analysis of antioxidant enzymes revealed that although superoxide dismutase activity increased, catalase activity decreased in comparison to control. Besides, lipid peroxidation and peroxidase activity increased in 10 µM SA, whereas they decreased in higher concentrations. Similarly total chlorophyll content increased in 10 µM SA, but it decreased in 100 and 500 µM SA treatments. Moreover anthocyanins and carotenoids increased after SA treatment. In conclusion, exogenous SA application causes developmental and biochemical alterations in rye.

Aluminum (Al) toxicity is one of the major abiotic stress factors that decreases crop yield in acidic soils. Al inhibits the root growth and development due to cellular toxicity including nucleus, chromosome and DNA alterations. Although some Al-induced programmed cell death (PCD) features were identified, there are limited comparative and time-dependent studies. The aim of this study is to compare the Al-induced time-dependent DNA fragmentation, the most widely evaluated criterion for PCD in six agronomic plant (maize, wheat, triticale, rye, barley and oat) roots concerning their Al tolerance. Roots were exposed to 100 μM AlCl₃ solution (pH 4.5) for different times (½, 1, 2, 3, 4, 5, 6, 7, 8 h). All genomic DNA was isolated from control and AlCl₃ treated roots. Isolated DNA samples were analyzed by electrophoretically and DNA fragmentation was observed in triticale, rye, barley and oat roots, but not in maize and wheat. The obtained DNA fragmentation shows that wheat and maize are more tolerant than triticale, rye, barley and oat in which the PCD is active as early as ½ h after Al induction. The results obtained can provide a better understanding into the Al induced PCD and Al tolerance in plants.