| Allelopathic autotoxicity is an important factor to cause continuous cropping obstacle inmelon cultivation. In order to analyze the allelopathic autotoxicity effects of melon, melongermplasm 'New Silverlit' was used as experimental material in this research. the impacts ofplant aqueous extracts, root exudates and some organic acids allelochemicals on seedgermination percentages, growth of seedlings and changes in protective enzyme system ofmelon had been studied. Gene involved in allelopathy was analyzed by cDNA-AFLPtechnique for reveal its molecular mechanism.1The allelopathic autotoxicity effects of plant aqueous extracts and root exudates on themelonIn order to analyze the allelopathic autotoxicity effects of melon, the impacts of plantaqueous extracts and root exudates on seed germination percentages, growth of seedlings andchanges in protective enzyme system of melon had been studied. The results showed that thelow concentrations (0.01g/mL) of plant aqueous extracts promoted the melon seedgermination and seedling growth, high concentrations (≥0.03g/mL) inhibited. Correspondingchanges in cell membrane permeability and the protection of the enzyme activity occurred inthe process. Morphological indicators and protective enzyme system changes were basiccoordinated. Melon root exudates also showed promotion at low concentrations and inhibitionat high concentrations on seed germination and seedling growth. The impact of root exudateswas weaker than plant aqueous extracts. Changes of morphological indicators and protectiveenzyme system did not show significant difference.2The allelopathic effects of organic acids allelochemicals on the melonAllelopathic effects of seven organic acids allelochemicals, include malic acid, citric acid,hydroxybenzoic acid, cinnamic acid, ferulic acid, salicylic acid and coumaric acid, werestudied in this experiment. Seed germination percentages, growth condition and changes inprotective enzyme system of melon seedlings after treated by different concentrations ofseven organic acids allelochemicals had been measured. The results showed that the selectedorganic acids in the experimental with varying degrees of impact on melon seed germinationand seedling growth. The same organic acids in different concentrations had different effectson the melon. The overall performance showed promotion at low concentrations andinhibition at high concentrations on seed germination and seedling growth. The sameconcentration of different organic acids had different impacts on melon.Malic acid and citric acid promoted the melon seed germination percentage andgermination index, hydroxybenzoic acid showed an inhibitory effect, ferulic acid andcoumaric acid showed promotion at low concentrations and inhibition at high concentrations.Cinnamic acid inhibited the germination index. Salicylic acid showed promotion at low concentrations and inhibition at high concentrations on germination index. Malic acid, ferulicacid, salicylic acid and coumaric acid significantly inhibited the plant fresh weight. Citric acid,hydroxy benzoic acid and cinnamic acid showed promotion at low concentrations andinhibition at high concentrations on the plant fresh weight. Malic acid promoted radiclegrowth and inhibited hypocotyl growth. Hydroxy benzoic acid, citric acid, cinnamic acid andsalicylic acid showed inhibition of radicle growth and promotion at low concentrations andinhibition at high concentrations on hypocotyl growth. Coumaric acid and ferulic acid had asuppression on radicle and hypocotyl growth.Changes of protective enzyme system was relatively complex. For SOD, the activitydeclined constantly with the increase of the concentration after treated by hydroxy benzoicacid and salicylic. Citric acid, ferulic acid and coumaric acid showed promotion at lowconcentrations and inhibition at high concentrations on SOD activity. Cinnamic acid andmalic acid showed downward trend of SOD activity, which no apparent regularity. All organicacids allelochemicals in this experiment were significantly enhanced CAT activity. Theconcentrations of CAT activity peak were not same in different organic acids allelochemicals.The changes of POD activity had no obvious linear regularity. MDA content in melonseedlings body was lower than the control after treated by all seven kinds of organic acidtreatment.3Gene expression profiling in response to allelopathy in melonGene involved in allelopathy of melon germplasm 'New Silverlit' was analyzed by cDNA-AFLPtechnique. More than3600transcript-Derived Fragments (TDFs) were obtained by using82pairs ofprimers. Each pair of primers can amplified30-50bands and the size of these fragments between50~800bp.103TDFs were sequenced and75TDFs were effective sequence. These TDFs were classified intoseveral functional groups with Blast in GenBank. The TDFs included39(52%) upregulated,21(28%)downregulated,and15(20%) transiently expression genes.55TDFs, which showed higher homology toknown functional genes, conferred functions of signal transduction, energy metabolism, protein synthesis,ion transport, response to stress, transcriptional regulation.12had low identity with known sequences and8had no match sequence. |
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