Transcriptomic insights into the allelopathic effects of the garlic allelochemical diallyl disulfide on tomato roots.

Garlic is an allelopathic crop that can alleviate the obstacles to continuous cropping of vegetable crops. Diallyl disulfide (DADS), one of the most important allelochemicals in garlic, promotes tomato root growth. Therefore, the global transcriptome profiles of DADS-treated tomato roots over time were investigated to reveal the potential growth-promoting mechanisms. We detected 1828, 1296 and 1190 differentially expressed genes (DEGs) in the 4, 24 and 48 h samples, respectively. Most DEGs involved in assimilatory sulfate reduction and glutathione metabolism were up-regulated after short-term (4 h) DADS treatment. In addition, increased activity of defensive enzymes and up-regulation of six peroxidase genes were observed, suggesting that DADS could induce tomato resistance. In plant-pathogen interactions, DEGs related to calcium signaling were primarily inhibited, while those encoding pathogenesis-related proteins were primarily up-regulated. Although plant hormone synthesis and signal transduction were both significantly affected by DADS, the expression trends of the genes in these two pathways were conflicting. This research provides comprehensive information concerning the changes in the tomato root transcriptome affected by DADS and may help direct further studies on DADS-responsive genes to enhance the current understanding of the mechanisms by which DADS alleviates the obstacles to continuous cropping.

Isolation, expression, and characterization of a hydroperoxide lyase gene from cucumber.

A full-length cDNA coding for hydroperoxide lyase (CsHPL) was isolated from cucumber fruits of No. 26 (Southern China type) and No.14-1 (Northern China type), which differed significantly in fruit flavor. The deduced amino acid sequences of CsHPL from both lines show the same and significant similarity to known plant HPLs and contain typical conserved domains of HPLs. The recombinant CsHPL was confirmed to have 9/13-HPL enzymatic activity. Gene expression levels of CsHPL were measured in different organs, especially in fruits of different development stages of both lines. The HPL activities of fruit were identified basing on the catalytic action of crude enzyme extracts incubating with 13-HPOD (13-hydroperoxy-(9Z,12E)-octadecadienoic acid) and 13-HPOD + 9-HPOD (9-hydroperoxy-(10E,12Z)-octadecadienoic acid), and volatile reaction products were analyzed by GC-MS (gas chromatography-mass spectrometry). CsHPL gene expression in No. 26 fruit occurred earlier than that of total HPL enzyme activity and 13-HPL enzyme activity, and that in No. 14-1 fruit was consistent with total HPL enzyme activity and 9-HPL enzyme activity. 13-HPL enzyme activities decreased significantly and the 9-HPL enzyme activities increased significantly with fruit ripening in both lines, which accounted for the higher content of C6 aldehydes at 0-6 day post-anthesis (dpa) and higher content of C9 aldehydes at 9-12 dpa.

[Allelopathy of garlic root exudates on different receiver vegetables].

By the method of tissue culture under sterilized condition, this paper studied the allelopathy of garlic root exudates on lettuce, hot pepper, radish, cucumber, Chinese cabbage, and tomato. The results showed that garlic root exudates had no evident effects on the germination rate, germination index, shoot height, and protective enzyme system of test crops, but significantly increased the root length, aboveground fresh mass, and root fresh mass of lettuce, with the RIs being +0.163, +0.106, +0.318, respectively. The exudates also increased the root length of Chinese cabbage, with a RI of +0.120. For other test crops, no significant difference was observed between the treatments and the control. Garlic root exudates significantly increased the chlorophyll content and root activity of the receiver vegetables. The strongest promotion effects were found on chlorophyll content in radish, with RI being +0.282, and on root activity of cucumber, with RI being +0.184. The exudates promoted the nutrient absorption of all the receiver vegetables.

[Relationships between soil nutrients and rhizospheric soil microbial communities and enzyme activities in a maize-capsicum intercropping system].

By using plastic sheet and nylon mesh to partition the root systems of maize and capsicum in a maize-capsicum intercropping system, this paper studied the relationships between soil biological factors and nutritive status in the intercropping system, with no partitioning and maize monoculture and capsicum monoculture as the control. The results showed that intercropping maize and capsicum had its high superiority. In the treatments of no partitioning and nylon mesh portioning in the intercropping system, soil enzyme activities, microbial individuals and nutrient contents were significantly higher, compared with those in the treatments of nylon mesh partitioning and monocultures. All kinds of soil available nutrients showed significant or very significant positive correlations with soil biological factors, except that soil available Mg was negatively correlated with soil fungi and catalase activity. Pathway analysis indicated that in the intercropping system, soil urease, catalase, protease, and bacteria were the main factors affecting the accumulation of soil organic matter, saccharase was the most important factor affecting soil alkali-hydrolyzable N, urease was the most important factor affecting soil available P, and bacteria largely determined soil available K. Soil alkaline phosphatase and fungi selectively affected the accumulation of soil organic matter and available N, P and K. There was a slight negative correlation between soil actinomycetes and soil nutrients, suggesting that actinomycetes had little effect on soil nutrient formation.