Low temperature is a major limiting factor for the growth and reproduction of some plant species, such as tomato. So far, few studies have been conducted on the effects of low temperature, and the mechanisms of plants’ response to this type of stress is not fully clear. In the current study, the effects of low, nonfreezing temperature (10 °C for three days) on the hormone content, antioxidant activity, and expression patterns of cold-related genes in the leaves of cold-tolerant species (Solanum habrochaites Accession ‘LA1777′) and cold-susceptible species (Solanum lycopersicum cultivar ‘Moneymaker’) were investigated. Low temperature increased the abscisic acid (ABA) content in both tomato species, while the content of zeatin-type cytokinins (ZT) increased in the cold-tolerant species. However, the content of indole-3-acetic acid (IAA) and gibberellic acid (GA) reduced in response to low temperature in susceptible species. Accordingly, cytokinin (CK) is identified as an important hormone associated with low-temperature stress in tomato. In addition, our results indicate that the C-repeat/DRE binding factor 1 (CBF1) gene is less induced in response to low temperature in tomato, although transcription of the inducer of CBF expression 1 (ICE1) gene was upregulated under low temperature in both tomato species. It seems that ICE1 may modulate cold-regulated (COR) genes in a CBF-independent way. In addition, in response to low temperature, the malondialdehyde (MDA) level and membrane stability index (MSI) increased in the susceptible species, indicating that low temperature induces oxidative stress. Additionally, we found that glutathione peroxidase is highly involved in reactive oxygen species (ROS) scavenging induced by low temperature, and antioxidants are more induced in tolerant species. Overall, our results suggest that sub-optimal temperatures promote oxidative stress in tomato and CK is introduced as a factor related to the response to low temperature that requires deeper attention in future breeding programs of tomato.
Salicylic acid (SA), a plant phenolic compound and calcium chloride have a great role on crop plants against biotic and abiotic stresses. This experiment was conducted to study the effects of foliar application of salicylic acid (S1=0, S2=50, S3=100 and S4=150 ppm) and calcium chloride (C1=0, C2=1.5 and C3=3 g/L) on cotton. The results showed that, salicylic acid increased the percentage of oil and nitrogen in seeds as well as the amount of chlorophyll content in the leaves, and this increased continued until S4=150ppm. Calcium chloride had no significant effect on them. The interaction between calcium chloride and salicylic acid had significant effect on the lint and grain yield in cotton and increased them. Biological yield, weight of seed per boll, weight of cotton per boll and number of boll per plant also affected by the interantion between of these two treatments. In thsese traits, although salicylic acid until S4 increased them, but the main effect of calcium chloride was up to C2. It was found unlike salicylic acid, which affectd on yield, yield components, photosynthesis piments and the content of mineral elements in seeds until S4, calcium chloride had a major effect on yield and yield components and this effect was until the level of C2.
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