Abbas H K, Paul R N, Riley R T, Tanaka T, Shier W T
Southern Weed Science Research Unit, ARS, USDA, Stoneville, MS 38776, USA.
Toxicon. 1998 Dec;36(12):1821-32. doi: 10.1016/s0041-0101(98)00091-9.
Ultrastructural effects of AAL-toxin TA from Alternaria alternata on black nightshade (Solanum, nigrum L.) leaf discs and correlation with biochemical measures of toxicity. In black nightshade (Solanum nigrum L.) leaf discs floating in solutions of AAL-toxin TA (0.01-200 microM) under continuous light at 25 degrees C, electrolyte leakage, chlorophyll loss, autolysis, and photobleaching were observed within 24 h. Electrolyte leakage, measured by the conductivity increase in the culture medium, began after 12 h with 200 microM AAL-toxin T(A), but was observed after 24 h with 0.01 to 50 microM AAL-toxin T(A), when it ranged from 25%) to 63% of total releasable electrolytes, respectively. After 48 h incubation, leakage ranged from 39% to 79% of total for 0.01 to 200 microM AAL-toxin T(A), respectively, while chlorophyll loss ranged from 5% to 32% of total, respectively. Ultrastructural examination of black night-shade leaf discs floating in 10 microM AAL-toxin TA under continuous light at 25 degrees C revealed cytological damage beginning at 30 h, consistent with the time electrolyte leakage and chlorophyll reduction were observed. After 30 h incubation chloroplast starch grains were enlarged in control leaf discs, but not in AAL-toxin T(A)-treated discs, and the thylakoids of treated tissue contained structural abnormalities. After 36-48 h incubation with 10 microM AAL-toxin T(A), all tissues were destroyed with only cell walls, starch grains, and thylakoid fragments remaining. Toxicity was light-dependent, because leaf discs incubated with AAL-toxin T(A) in darkness for up to 72 h showed little phytotoxic damage. Within 6 h of exposure to > or =0.5 microM toxin, phytosphingosine and sphinganine in black nightshade leaf discs increased markedly, and continued to increase up to 24 h exposure. Thus, phy siological and ultrastructural changes occurred in parallel with disruption of sphingolipid synthesis, consistent with the hypothesis that AAL-toxin T(A) causes phytotoxicity by interrupting sphingolipid biosynthesis, thereby damaging cellular membranes.
链格孢菌产生的AAL毒素TA对龙葵（Solanum nigrum L.）叶片圆片的超微结构影响及其与毒性生化指标的相关性。在25℃连续光照条件下，将龙葵叶片圆片漂浮于AAL毒素TA（0.01 - 200微摩尔）溶液中，24小时内观察到电解质渗漏、叶绿素损失、自溶和光漂白现象。通过培养基电导率增加来测量电解质渗漏，200微摩尔AAL毒素TA处理12小时后开始出现电解质渗漏，而0.01至50微摩尔AAL毒素TA处理24小时后才观察到电解质渗漏，此时电解质渗漏分别占可释放总电解质的25%至63%。孵育48小时后，0.01至200微摩尔AAL毒素TA处理的叶片圆片电解质渗漏分别占总量的39%至79%，叶绿素损失分别占总量的5%至32%。在25℃连续光照条件下，对漂浮于10微摩尔AAL毒素TA溶液中的龙葵叶片圆片进行超微结构检查，结果显示30小时开始出现细胞学损伤，这与观察到电解质渗漏和叶绿素减少的时间一致。孵育30小时后，对照叶片圆片中叶绿体淀粉粒增大，而经AAL毒素TA处理的叶片圆片中淀粉粒未增大，且处理组织的类囊体存在结构异常。用10微摩尔AAL毒素TA孵育36 - 48小时后，所有组织均被破坏，仅留下细胞壁、淀粉粒和类囊体片段。毒性具有光依赖性，因为在黑暗中用AAL毒素TA孵育龙葵叶片圆片长达72小时，几乎未观察到植物毒性损伤。在暴露于≥0.5微摩尔毒素的6小时内，龙葵叶片圆片中的植物鞘氨醇和鞘氨醇显著增加，并持续增加直至暴露24小时。因此，生理和超微结构变化与鞘脂合成的破坏同时发生，这与AAL毒素TA通过中断鞘脂生物合成从而破坏细胞膜导致植物毒性的假说一致。
