Abstract
To obtain new insights into the mechanisms of the positive effects of exogenous melatonin applications to cucumber seedlings during chilling, we investigated its role in regulating photosynthesis, the transcription level of csZat12 and the metabolism of polyamines (PAs) and of abscisic acid (ABA). The negative effects of chilling were clearly alleviated in cucumber seedlings by irrigation with 200 μM melatonin solution. This was evidenced by alleviation of the decline in net photosynthesis rate and also in electrolyte leakage in chilled plants. The reasons for this can be explained as follows. First, melatonin up-regulates CsZat12, an important stress-related gene. Second, melatonin increases the content of putrescine (Put) and spermidine (Spd) and stabilized spermine (Spm) by altering the activity of the PA metabolic enzymes. And, third, ABA is also involved in these effects as melatonin modulated the expression of the key ABA biosynthesis genes (CsNCED1 and CsNCED2) and also the key ABA catabolism genes (CsCYP707A1 and CsCYP707A2). This study provides new evidence suggesting melatonin mitigates chilling stress in cucumber by up-regulating the expression of CsZat12 and by modulating the metabolism of PAs and ABA.
Highlights
Cucumber is an important salad crop in several countries and must be grown year-round to meet market demand
We studied the transcript level of Zat[12]; this gene is known to be important in relation to stress and involved in Put synthesis through up-regulating ADC1&ADC2, and responses to spermine[22]
The degree of membrane damage can be indicated by measuring the electrolyte leakage rate, because electrolyte leakage reflects membrane integrity[29]
Summary
Cucumber is an important salad crop in several countries and must be grown year-round to meet market demand. Reduced enzyme activity together with membrane damage leads to dysfunction of a number of biochemical reactions and physiological functions, including photosynthesis[1] Exogenous substrates such as melatonin have been used widely to help plants cope better with environmental stresses - including chilling stress[6]. PAs are small aliphatic amines; the three most common ones found in plants are diamine putrescine (Put), triamine spermidine (Spd) and tetramine spermine (Spm)[16] Owing to their positive charge at physiological values of pH, these PAs help to preserve the structure of nucleic acids and proteins, to maintain the integrity of membranes and to sustain enzyme activity.
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