Exogenous Silicon Modulates Growth, Physio-Chemicals and Antioxidants in Barley (Hordeum vulgare L.) Exposed to Different Temperature Regimes

The exogenous application of silicon (Si) is reported to enhance tolerance of plants against various environmental stresses. Therefore, the present study was carried out to examine the influence of foliar applied Si (1.5 mM) on growth, physiochemical processes and antioxidant defense system of barley plants (cvs. Jow-83 and B-12026) under different regimes of temperature (20 °C (control), 25 °C, 30 °C, and 35 °C). High temperature (HT) regimes caused a significant (P < 0.001) decline in shoot (68% and 84%) and root (44% and 77%) dry masses, leaf area (66% and 81%), chlorophyll (Chl) a (11% and 70%), Chl b (69% and 71%), carotenoids (60% and 62%), anthocyanins (56%), total soluble proteins (62%) and phenolics (36% and 50%) contents in both cvs. Jow-83 and B-12026, respectively. A significant (P < 0.001) increase in superoxide dismutase (205% and 133%), peroxidase (128% and 88%) and catalase (127% and 87%) activities was recorded in stressed plants of both cultivars, respectively. Moreover, HT stress markedly (P < 0.001) increased hydrogen peroxide (H2O2) (54% and 75%) and malondialdehyde (MDA) (52% and 149%) levels in both cultivars that activated the oxidative stress. But, plants treated with Si showed better growth and had higher total soluble proteins (18% and 12%), anthocyanins (74% and 39%), flavonoids (31% and 27%) and phenolics (39% and 19%) as well as the activities of SOD (43% and 29%), POD (46% and 40%) and CAT (24% and 63%) enzymes. Application of Si reduced HT-mediated oxidative stress by decreasing the concentration of MDA (39% and 49%) and H2O2 (14% and 56%) and increased shoot (49% and 46%) and root (40% and 34%) dry masses, Chl a (10% and 86%), Chl b (82% and 81%), and carotenoids (53% and 33%) in both barley cultivars. Plants of cv. Jow-83 showed more tolerance to temperature regimes than that of cv. B-12026 as evident from higher plant dry masses. Thus, our findings exhibited that foliar-applied Si is an efficient strategy that can be used to enhance the tolerance of barley plants to HT stress.