The purpose of this study was to illuminate the effects of fulvic acid in plants’ stress signaling pathway. 2.0 mg/l fulvic acid was sprayed on soybean leaves for 3 days at 12 h intervals, followed by treatment of 150 mM NaCl or exposed to heat stress at 35°C for 2 h over 2 days. Pre-treatment with fulvic acid increased the relative water content (RWC), antioxidant enzyme, isoenzyme activities (SOD, APX, GST), as well as alleviated the stress-induced oxidative damage by decreasing the levels of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA). In addition, the application of fulvic acid under salt stress induced rubisco expression only at 12 h, while it induced the expression of cytochrome c oxidase at 6 h and 12 h. On the other hand, fulvic acid under heat stress induced significant expression of both rubisco and cytochrome c oxidase at 6 h and 12 h. However, under high salinity conditions, fulvic acid suppressed the transcript levels of Hsp70, while it induced increases in Hsp70 levels under heat treatment at 6 h. As a result, in this study, fulvic acid played the role of a regulator and stimulant in stress response of soybean leaves.

This study aimed to determine the effects of titanium dioxide nanoparticle (TiO₂NP) pretreatment on seeds of different safflower cultivars (Balci, Dinçer) under salt and heat stresses. The apparent effects on stress markers (malondialdehyde (MDA), hydrogen peroxide (H₂O₂) and superoxide radical (O₂ ^•⁻) content), as well as changes in germination and physiological parameters (radicle and plumula weight and length measurements), were investigated. TiO₂NP pretreatment caused an increase in radicle length and plumula fresh weight for the Balci cultivar under salinity. Furthermore, plumula dry weight was alleviated with TiO₂NP pretreatment for both cultivars. TiO₂NP pretreatment improved plumula dry and fresh weights for both cultivars under heat stress. In addition, MDA content decreased for both cultivars under heat stress but only for Balci under salt stress. The amount of O₂ ^•⁻ radicals positively affected only the radicle for both cultivars under heat stress. This study is the first to document the alleviation of salt stress damage for the Balci safflower cultivar, and protection for both Balci and Dinçer cultivars under heat stress, using 200 ppm TiO₂NP pretreatment.

In the present study, the effect of ascorbic acid (5 mM) on some physiological parameters and three hormones (auxin, abscisic acid, salicylic acid) was determined under heat stress (40 °C) in maize tolerant cv. (MAY 69) and sensitive cv. SHEMAL (SH) at 0 h, 4 h and 8 h. Heat stress reduced total chlorophyll content (CHL), relative water content (RWC) and stomatal conductance (gs) in SH but did not lead to changes in MAY 69 at 4 h and 8 h. However, pretreatment with ascorbic acid increased (CHL), (RWC) and (gs) in SH under heat stress while it reduced MDA content significantly in both cv. We also observed that heat stress led to a reduction in SA level but increased ABA and IAA levels in SH, whereas it increased SA and IAA levels but did not change ABA level in MAY 69 at 4 h. Furthermore, in SH, ASC application under heat stress increased SA level and decreased IAA and ABA levels at 4 h, but it had no effect on SA and ABA at 8 h.

In this paper, we describe the alleviated effects of alpha-tocopherol (α-T) on oxidative damage and its possible role as a signal transmitter in plants during salt stress. The results show that exogenously applied α-T under salt stress increased root length and weight, but reduced hydrogen peroxide (H2O2), superoxide anion radical (O2.—) and malondialdehyde (MDA) content in soybean roots. The proline content was reduced by α-T treatment. Interestingly, endogenous auxin (IAA) level was significantly increased after α-T application as compared to salt stress alone. Moreover, α-T reduced significantly superoxide dismutase (SOD) enzyme and isoenzyme activity but upregulated peroxidase (POX) 2, 3 and glutathione-s-transferase (GST) 1, 3 isoenzyme expression. However, ascorbate peroxidase (APX) enzyme activity was not affected at all. Consequently, the results show that α-T serves as a signal molecule under salinity from leaves to roots by increasing remarkably endogenous IAA levels and increasing partially antioxidant activity in roots.