In this field experiment, the effect of potassium silicate (PS) on the physiological and biochemical responses of Damask rose was investigated under the water deficit stress. The treatments were four levels of irrigation water application including 100, 75, 50 and 25% plant water requirement (PWR) and potassium silicate at three rates (0, i.e., just pure water, 0.2 and 0.4%), once (in spring or summer) or twice (once in spring and once in summer) during the plant growth. The results showed that with irrigation of 75% of plant water requirement significantly reduced the concentration of chlorophyll a (Chl a, 170%), chlorophyll b (Chl b, 163%) and carotenoids (91%), the leaf relative water content (RWC, 14.8%) and the total flower yield (20%) as compared to control. The elevated malondialdehyde (MDA) content and ion leakage, as two indicators of oxidative damage, were observed in the plants subjected to the water deficit stress. In response to oxidative stress induced by water deficit stress, the leaf catalase (CAT, 59.5%) activity and concentration of proline (64.8%) as compared to control increased. The foliar-applied Si at two rates of 0.2 and 0.4% in spring and summer resulted in a higher concentration of Chl a (57.3% and 61.7%), Chl b (31% and 24.6%) and carotenoid content as compared to control, respectively. The increased concentration of proline and higher activity of CAT in the plants supplied with Si led to the higher leaf RWC and less intensity of oxidative damage, namely ion leakage and MDA content. According to the results, with the potassium silicate spraying in 0.2 or 0.4% both in spring and summer at the irrigation level equal to 50% of the PWR, the optimum flower yield was achieved.
Physiological and biochemical responses of five nerica rice varieties (Oryza sativa L.) to water deficit at vegetative and reproductive stage