Abstract
Melatonin has been demonstrated to play a variety of roles in plants. Of particular importance is its role as a potent antioxidative agent. In the present study, we generated melatonin-deficient tomato plants using virus-induced gene silencing (VIGS) approach and melatonin-rich tomato plants by foliar application of melatonin. These tomato plants were used to assess the effect of melatonin on chilling-induced oxidative stress and chilling-induced photosynthesis inhibition. We found that melatonin deficiency increased accumulation of reactive oxygen species (ROS) and aggravated lipid peroxidation in chilling-stressed tomato leaves, while exogenous application of melatonin had the opposite effect. Under chilling stress, melatonin-deficient tomato plants showed impaired antioxidant capacity as evidenced by lower activities of antioxidant enzymes and decreased rations of reduced glutathione (GSH)/oxidized glutathione (GSSG) and reduced ascorbate (AsA)/oxidized ascorbate (DHA), compared with melatonin-rich tomato plants. Furthermore, suppression of melatonin biosynthesis led to more photosynthesis inhibition under the chilling condition and compromised the capability of subsequent photosynthesis recovery in tomato plants. In addition, melatonin-deficient tomato plants displayed less activity of an important Calvin-Benson cycle enzyme sedoheptulose-1,7-bisphosphatase (SBPase) than melatonin-rich tomato plants under chilling stress. Collectively, our data indicate that melatonin is critical for antioxidant capacity and redox balance and is in favor of photosynthesis in tomato plants under chilling stress.
Highlights
Due to their sessile nature, plants are constantly challenged by a broad spectrum of environmental factors, including low temperature, heat, drought, salinity and heavy metal toxicity
To study how melatonin biosynthesis was in alerted in response to low temperatures and melatonin, we investigated theofexpression level of tryptophan decarboxylase (TDC)
The evidence that we presented includes: (1) reduced level of endogenous melatonin increased the accumulation of reactive oxygen species (ROS) and aggravated lipid peroxidation in chilling-stressed tomato leaves, while exogenous application of melatonin had the opposite effect; (2) under chilling stress, melatonin-deficient tomato plants showed less antioxidant capacity as evidenced by lower activities of antioxidant enzymes and decreased ratios of GSH/GSSG and AsA/DHA, compared with melatonin-rich tomato plants; (3) suppression of melatonin biosynthesis led to greater photosynthesis inhibition under chilling conditions and compromised the capability of photosynthesis recovery after chilling stress; (4) melatonin deficiency increased SBPase inactivation and retarded photosynthesis recovery; melatonin enrichment sustained higher SBPase activity and facilitated photosynthesis recovery in chilling-stressed tomato plants
Summary
Due to their sessile nature, plants are constantly challenged by a broad spectrum of environmental factors, including low temperature, heat, drought, salinity and heavy metal toxicity. Low temperatures are often defined as low but not freezing temperatures (0–15 ◦ C), which occur frequently in nature during the growth season of warm-climate crops. Low temperatures impair growth and development in crops, causing a considerable proportion of yield loss [1,2]. The primary consequence of low temperature stress is the excessive accumulation of reactive oxygen species (ROS), which consist of hydrogen peroxide (H2 O2 ), superoxide anion radicals (O2 – ), and hydroxyl radicals (OH), due to disrupted electron transport chain in chloroplasts [3,4]. Excessive accumulation of ROS is toxic to nucleic acids, proteins and lipids, which causes cellular dysfunction [4,5]. Over-produced ROS suppresses carbon fixation by inactivating the Calvin–Benson cycle enzymes, resulting in reduced photosynthesis [6,7]
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