Abstract
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.
Highlights
Abiotic stresses, such as low temperature, as limiting factors affect plant production and plant distribution [1,2,3]
The concentration of three hormones, including auxin, cytokinin, and gibberellin, which are most involved in regulating growth and development of plant cells [6], were studied along with the well-known stress hormone, abscisic acid [46,47], to provide new insights into the role of these hormones in responding to long-term, lowtemperature stress
We found that the content of endogenous hormones, including ZT, abscisic acid (ABA), indole-3-acetic acid (IAA), and GA3, especially in the susceptible species, are influenced by low, nonfreezing temperatures to regulate downstream pathways related to stress responses (Figure 1)
Summary
Abiotic stresses, such as low temperature, as limiting factors affect plant production and plant distribution [1,2,3]. Low-temperature damage is more pronounced in tropical or subtropical plants. During low, nonfreezing temperatures, changes occur in the structure and metabolism of plant cells, which are more visible in tropical plants species. The change in membrane conformation that results in a decrease in membrane fluidity is one of the first structural changes related to low-temperature stress [5]. The alteration of membrane conformation can cause oxidative stress by rapidly inducing reactive oxygen species (ROS), and the concentration of cryoprotective compounds increases in the cytoplasmic matrix [2,6,7]. Plants use various mechanisms, including morphological and structural modifications, as well as biochemical mechanisms to modulate cellular homoeostasis to reduce low, nonfreezing temperature-induced damage [2,8,9]
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