Allelopathic mechanism of pyrogallol to Microcystis aeruginosa PCC7806 (Cyanobacteria): From views of gene expression and antioxidant system

Pyrogallol is a potent allelochemical on Microcystis aeruginosa, but its allelopathic mechanism is not fully known. In order to explore this mechanism, gene expressions for prx, mcyB, psbA, recA, grpE, fabZ under pyrogallol stress were studied, and activities of the main antioxidant enzymes were also measured. The results showed that expression of grpE and recA showed no significant change under pyrogallol stress, while psbA and mcyB were up-regulated at 4 mg L-1. Both prx and fabZ were up-regulated even under exposure to 1 mg L-1 pyrogallol concentration. The activities of superoxide dismutase (SOD) and catalase (CAT) were enhanced under pyrogallol stress. Levels of malodialdehyde (MDA) at 2 and 4 mg L-1 pyrogallol were significantly higher than those of the controls. It was concluded that oxidant damage is an important mechanism for the allelopathic effect of pyrogallol on M. aeruginosa. (c) 2009 Elsevier Ltd. All rights reserved.

水稻化感物质对土壤微生物的作用

本文主要目的是探讨水稻化感品种对土壤微生物的影响，为进一步阐明水稻化感品种与稻田微生物的生物化学关系奠定基础。在分离出两种水稻化感物质黄酮甙基础上，首先研究水稻化感物质对环境因子的响应情况。同时，探讨土壤中黄酮甙的降解动态和水稻组织及其释放到培养基质中的黄酮甙浓度情况，并用土壤薄层层析和生测实验研究黄酮甙在土壤中的迁移性。随后系统研究水稻化感品种幼苗、萌发液、根分泌物以及水稻化感物质黄酮甙对土壤微生物的作用。结果表明： 1、虽然化感物质释放程度和环境因子有关，但主要取决于水稻自身的化感特性。黄酮甙进入土壤10 h后消失，生成稳定的黄酮甙元，这种甙元是水稻真正的化感物质，因此，黄酮甙是水稻化感品种存储化感物质的形式，而不是真正起作用的物质。 2、水稻化感品种根际土壤中的微生物数量受到显著的抑制作用，根际土壤微生物的群落结构和对照土壤相似，和水稻非化感品种根际土壤微生物的群落结构不同。 3、向土壤中施加萌发液和根系分泌物初期，土壤细菌、氨化细菌、放线菌数量表现为水稻非化感品种大于水稻化感品种。水稻化感品种土壤中的微生物生物量碳受到抑制，而真菌生物量受到促进。萌发液土壤中对照和水稻化感品种群落结构变化相似，根分泌物土壤中对照和水稻非化感品种群落结构变化相似。 4、施加低浓度黄酮甙土壤中的细菌、氨化细菌以及真菌数量均高于高浓度黄酮甙土壤中的数量，但是土壤中的放线菌和真菌生物量却表现为：随着土壤中黄酮甙浓度升高，受到的抑制作用增强。在添加浓度范围内，黄酮甙对土壤微生物群落结构产生不同影响。

Interactions between the bloom-forming dinoflagellates Prorocentrum donghaiense and Alexandrium tamarense in laboratory cultures

Interactions between Prorocentrum donghaiense and Alexandrium tamarens, two bloom-forming dinoflagellates, were investigated using bi-algal cultures. All R donghaiense died, but A. tamarense was hardly affected by the end of the experiment when the initial cell density was set at 1.0 X 10(4) cells mL(-1) for P. donghaiense and 0.28 x 10(4) cells mL(-1) for A. tamarense. However, significant growth suppression occurred in either species when the initial cell density of P donghaiense increased to I. 0 X 105 Cells mL(-1) in the bi-algal culture, but no out-competement was observed. The simultaneous assay on the culture filtrates showed that P donghaiense filtrate prepared at a lower initial density (1.0 X 10(4) cells mL(-1)) stimulated growth of the co-cultured A. tanzarense (0.28 x 10(4) cells mL(-1)), but filtrate at a higher initial density (1.0 x 10(5) cells mL(-1)) depressed its growth. The filtrate of A. tamarense at a density of 0.28 x 10(4) cells mL(-1) killed all R donghaiense at a lower density (1.0 x 10(4) cells mL(-1)), but only exhibited an inhibitory effect on it at a higher density (1.0 x 10(5) cells mL(-1)). It is likely that these two species of microalgae interfere with each other mainly by releasing allelochemical substance(s) into the culture medium, and a direct cell-to-cell contact was not necessary for their mutual interaction. The allelopathic test further proved that A. tamarense could affect the growth of co-cultured P. donghaiense by producing allelochemical(s); moreover, A. tamarense culture filtrate at the stationary growth phase (SP) had a strongly inhibitory effect on P donghaiense compared to that at the exponential phase (EP). Results also demonstrated a dose-dependent relationship between the microalgal initial cell density and the degree of the allelopathic effect. The growth of R donghaiense and A. tamarense in the bi-algal cultures was simulated using a mathematical model to quantify the interaction. The estimated parameters from the model showed that the inhibition exerted by A. tamarense on P. donghaiense was about 17 and 8 times stronger than the inhibition P. donghaiense exerted on A. tamarense, when the initial cell density was set at 1.0 X 10(4) and 1.0 X 10(5) cells mL(-1) for P donghaiense, respectively. and 0.28 x 10(4) cells mL(-1) for A. tamarense in the bi-algal cultures. A. tamarense seems to have a survival strategy that is superior to that of P. donghaiense in bi-algal cultures under controlled laboratory conditions. (c) 2006 Elsevier B.V. All rights reserved.