有机酸类化感物质对甜瓜的化感效应

Allelopathic effects of organic acid allelochemicals on melon

以甜瓜种质"新银辉"为材料,用苹果酸、柠檬酸、对羟基苯甲酸、肉桂酸、阿魏酸、水杨酸和香豆酸等7种有机酸类化感物质处理甜瓜种子和幼苗,探讨其对甜瓜的化感效应及作用机理。结果表明:苹果酸可以促进甜瓜种子发芽和幼苗胚根生长,抑制植株鲜重增加和胚轴生长;柠檬酸促进发芽,对羟基苯甲酸和肉桂酸抑制发芽,但三者均抑制胚根生长,且对鲜重和胚轴生长表现为低促高抑效应,高浓度肉桂酸对种子发芽和胚轴生长的抑制效应最强,可能是甜瓜重要的化感物质;阿魏酸和香豆酸对发芽表现为低促高抑效应,抑制鲜重、胚根和胚轴生长;水杨酸对发芽和胚轴生长表现为低促高抑效应、抑制鲜重和胚根生长。7种有机酸处理后过氧化物酶活性均增强,有机酸类物质对甜瓜的化感效应可能和其体内的过氧化氢水平有较高的相关性;苹果酸、肉桂酸、对羟基苯甲酸和水杨酸处理后甜瓜幼苗体内超氧化物歧化酶的活性基本呈下降趋势,柠檬酸、阿魏酸和香豆酸则表现为低促高抑效应;过氧化物酶活性变化较复杂,但基本随处理浓度升高而上升;丙二醛含量大多低于对照。

Melon is an important horticultural crop worldwide. In recent years, melon cultivation has been significantly affected by increasingly serious continuous cropping problems. Allelopathy is an important factor in the continuous cropping problems of melon. Organic acids are allelochemicals that are commonly found in Cucurbitaceae crops. However, there have been no reports on the isolation and characterization of allelochemicals from melon. In this research, we analyzed the effects of seven organic acid allelochemicals on the melon germplasm ＇New Silverlit＇. We evaluated the allelopathic effects of malic acid, citric acid, hydroxybenzoic acid, cinnamic acid, ferulic acid, salicylic acid, and coumaric acid. Seeds and seedlings were treated with different concentrations of the seven organic acids and seed germination percentages, morphological indexes, and changes in protective enzyme systems of melon seedlings were determined. The results showed that the selected organic acids in the experiment affected seed germination and seedling growth to varying degrees. Different concentrations of the same organic acids had different effects. In general, lower concentrations of organic acids showed promoting effects, whereas higher concentrations inhibited seed germination and seedling growth. In some cases, the same concentration of different organic acids had different effects on the various germination and growth parameters. Malic acid and citric acid increased the seed germination percentage and germination index. Hydroxybenzoic acid resulted in decreased seed germination percentage and germination index, while ferulic acid and coumaric acid showed a promoting effect on these parameters at low concentrations and an inhibitory effect at high concentrations. Cinnamic acid inhibited seed germination. Salicylic acid promoted seed germination at low concentrations and inhibited it at high concentrations. Seedlings treated with malic acid, ferulic acid, salicylic acid, and coumaric acid showed significantly lower fresh weight compared with the control. Seedlings treated with low concentrations of citric acid, hydroxybenzoic acid, and cinnamic acid showed increased fresh weight compared with the control, but showed lower fresh weight than the control when treated with high concentrations of these organic acids. Malic acid promoted radicle growth but inhibited hypocotyl growth. Hydroxybenzoic acid, citric acid, cinnamic acid, and salicylic acid inhibited radicle growth at low concentrations and inhibited hypocotyl growth at high concentrations. Coumaric acid and ferulic acid inhibited radicle growth and hypocotyl growth. At high concentrations, cinnamic acid showed the strongest inhibitory effect on seed germination and hypocotyl growth among the tested organic acids, suggesting that it may be one of the main allelochemicals of melon. The changes in the protective enzyme system were relatively complex. The activity of superoxide dismutase （SOD） decreased with increasing concentrations of hydroxybenzoic acid and salicylic acid. SOD activity increased in response to low concentrations of citric acid, ferulic acid, and coumaric acid, but decreased in response to higher concentrations of these acids. Cinnamic acid and malic acid treatments tended to cause a decrease in SOD activity. All of the tested organic acids significantly enhanced catalase activity, but the trends in catalase activity differed among the various organic acids. Peroxidase activity did not show a particular trend in response to organic acids. The malondialdehyde contents in melon seedlings treated with the seven organic acids were lower than that in control seedlings. These experimental results partly reveal the allelopathic effect of seven organic acid allelochemicals on melon and the mechanisms involved in the response to these compounds.