Enhancement of Drought Tolerance in Salvia coccinea Plants by Irradiation with Gamma and Laser Pre-Treatments

Abstract

Gamma-and laser-irradiated seeds were grown under drought stress conditions to evaluate the irradiation effects on growth, flowering and some physiological traits of Salvia coccinea plants grown in pots. Pre-sowing gammairradiation at 5, 10, 15, 20 and 25 k.rad or laser irradiation (He-Ne) for 5, 10, 15 and 20 min. exposure time were applied. Soil moisture levels were imposed by irrigating the plants with 100 (control), 80, 60 and 40% of field capacity (F.C.). Results indicated that laser-irradiation was less effective than gamma-irradiation on drought stress. Plants grown under high water stress (40 and 60% F.C.) resulted in significant decreases in all vegetative growth and flowering parameters tested. The decrease in plant growth and flowering quality induced by water deficit was associated with a reduction in leaf relative water content and increases in total phenols, proline and abscisic acid contents in plants. Under water stress, there were significant changes in the activities of the defensive enzymatic system in leaves. The activities of peroxidase and catalase in irradiated plants with gamma or laser were higher at 60% F.C. than in other water stress treatments. In general, it can be concluded that initiated resistance of Salvia coccinea plants under drought stress are enhanced after pre-sowing seed irradiation with gamma at 15-25 k.rad followed by laser for 10 min. exposure time. The most effective combination was gamma-radiation (15-25 k.rad) plus soil moisture content at 80% F.C. This combined treatment protects plants from the deleterious effects of drought. It can tolerate soil water deficit and consume less irrigation water by 30%.

Biophysical methods used to generate tolerance to drought stress in seeds and plants: a review

“…Hydrogen peroxide, tannin compounds, catalases (CATs), ascorbate peroxidases (APXs), glutathione (GSH) and ascorbate which plays an essential role in catalysing and dissociating hydrogen peroxide to protect the cells from oxidative damage (Fig. 3), and at the same time aiding the reduction of ROS (Feng et al, 2007;Qiu et al, 2018;El-Sallami et al, 2019;Wang et al, 2018;Rajabbeigi et al, 2013;Thomas and Puthur, 2017). As mentioned above, these antioxidant enzymes help to combat the adverse effects of ROS, however, the oxidative damage alone produces an inadequate response in the plant defence system (Qiu et al, 2008).…”

“…Conversely, Scarlet Sage (Salvia coccinea) seeds have been irradiated with He-Ne laser at 633 nm and at an intensity of 1 mW cm -2 with exposure times of 5, 10 and 20 min. These exposure times and intensities negatively affect plant size and the number of axillary buds (El-Sallami et al, 2019). This discovery emphasizes the need to find a window of values in which there could be a favourable response to drought tolerance, since other studies have shown that the effects of laser light can be positive, negative, or null, depending on the radiation parameters and the characteristics of the biological objects are highlighted by Hernández -Aguilar et al (2009b;.…”

“…The result is possible because the speed of plant emergence is accelerated (Hernández et al, 2006), generating plants with a greater height, allowing them to absorb more light, which favours an increase in Chl and carotenoid production (Pérez-Gálvez et al, 2020). Likewise, some authors have reported an increase in dry weight (Triticum aestivum L.) and root size of Triticum aestivum L., Salvia coccinea and Celosia argentea (Qiu et al, 2017;El-Sallami et al, 2019;Ali et al, 2020). Emergence speed is related to plant growth, some authors have noted in Salvia coccinea that this variable is negatively affected when water stress is applied in conjunction with laser treatment and positively in Triticum aestivum L. and Celosia argentea (Qiu et al, 2017;Ali et al, 2020).…”

“…Nonetheless, in some crops such as Celosia argentea, the increase in plant height may be associated with the stimulation of cell division (Metwally et al, 2013). In experiments with Salvia coccinea and Celosia argentea cultivars using laser treatment and axillary buds are decreased and increased, respectively (El-Sallami et al, 2019;Ali et al, 2020). This increase may happen since the He-Ne laser promotes the activation of phytochromes (Hernández-Aguilar et al, 2010) which trigger growth hormone production mechanisms thereby generating cell division (Dichio et al, 2004) and consequently the emergence of axillary buds.…”

“…This increase may happen since the He-Ne laser promotes the activation of phytochromes (Hernández-Aguilar et al, 2010) which trigger growth hormone production mechanisms thereby generating cell division (Dichio et al, 2004) and consequently the emergence of axillary buds. However, when they decrease in number, which may happen due to water stress which generates small plants with apical dominance in the axillary buds (Wilson, 2000;El-Sallami et al, 2019).…”