Abstract
Cinnamic acid (CA), which is a well-known major autotoxin secreted by the roots in cucumber continuous cropping, has been proven to exhibit inhibitory regulation of plant morphogenesis and development. Melatonin (MT) has been recently demonstrated to play important roles in alleviating plant abiotic stresses. To investigate whether MT supplementation could improve cucumber seedling growth under CA stress, we treated cucumber seeds and seedlings with/without MT under CA- or non-stress conditions, and then tested their effects on cucumber seedling growth, morphology, nutrient element content, and plant hormone. Overall, 10 μM MT best rescued cucumber seedling growth under 0.4 mM CA stress. MT was found to alleviate CA-stressed seedling growth by increasing the growth rates of cotyledons and leaves and by stimulating lateral root growth. Additionally, MT increased the allocation of newly gained dry weight in roots and improved the tolerance of cucumber seedlings to CA stress by altering the nutrient elements and hormone contents of the whole plant. These results strongly suggest that the application of MT can effectively improve cucumber seedling tolerance to CA stress through the perception and integration of morphology, nutrient element content and plant hormone signaling crosstalk.
Highlights
Cucumber (Cucumis sativus L.) is a worldwide cultivated crop and China accounts for about 77% of the global production (FAO, 2016)
The growth rate of root dry weight was not influenced by Cinnamic acid (CA) under non-MT (0 μM) conditions, but was significantly higher at 1 and 10 μM MT than at 0 μM MT under non-CA (0 mM) conditions
The present study provides evidence that the exogenous application of MT is a potential solution for improving cucumber seedling growth under CA-stress by regulating the morphological growth, and the contents of nutrient elements and endogenous hormones
Summary
Cucumber (Cucumis sativus L.) is a worldwide cultivated crop and China accounts for about 77% of the global production (FAO, 2016). The intensive cultivation applied in the production systems in China leads to affect negatively the plant growth through a phenomenon of autotoxicity (Bennett et al, 2012). Qiao (2013) found that CA at 0.25 mM determined a growth inhibition on cucumber seeds by reducing the germination efficiency and affecting the further development of seedlings (reduction of growth rate of roots and less lateral roots). This was found to be correlated to several CA-induced negative impacts such as, decreased ion uptake and transport, disruption antioxidant system, and imbalanced hormonal regulation. It has been proved that CA can affect the chlorophyll content in leaves and decreases photosynthetic rate (Baziramakenga et al, 1995)
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