Burke John J
United States Department of Agriculture, Plant Stress and Germplasm Development Unit, Lubbock, Texas 79415, USA.
Plant Physiol. 2007 Jan;143(1):108-21. doi: 10.1104/pp.106.087783. Epub 2006 Oct 27.
Water-deficit stresses preferentially reduce shoot growth, thereby disrupting the flow of carbohydrates from source leaves to the developing sinks. Here, we use a novel stress bioassay to dissect responses of field and greenhouse-grown cotton (Gossypium hirsutum) source leaves to water-deficit stresses. Fifth main stem leaf samples were harvested at sunrise and subjected to a prolonged elevated respiratory demand in the dark. Sucrose levels are lower in nonstressed cotton at sunrise compared to water-deficit stressed cotton, potentially predisposing the nonstressed tissue to succumb more rapidly. Tissue death was determined initially using the cell viability stain 2,3,5-triphenyltetrazolium chloride, but was determined in subsequent experiments by monitoring the decline in chlorophyll fluorescence yield. Fluorescence yield measurements were obtained within minutes of harvesting and individual samples were monitored over the time course of the treatment. Analyses of the time course and magnitude of chlorophyll fluorescence yield decline in samples from irrigated and dryland plots permitted the detection of stress responses within 24 h of the cessation of irrigation. The rate of fluorescence yield decline during the elevated respiratory demand treatment slowed as the water-deficit stress increased. Upon irrigation, the source leaves of the water-stressed plants recovered to prestress values within 4 d. Well-watered cotton overexpressing heat shock protein 101 had identical rates of fluorescence yield decline as nontransgenic cotton. These results suggest that the delayed decline in fluorescence yield of water-stressed tissue exposed to prolonged elevated respiratory demand can be used as a sensitive indicator of water-deficit stress responses.
水分亏缺胁迫优先降低地上部生长，从而破坏碳水化合物从源叶向发育中的库的流动。在此，我们使用一种新型胁迫生物测定法来剖析田间和温室种植的棉花（陆地棉）源叶对水分亏缺胁迫的响应。在日出时采集第五主茎叶样本，并在黑暗中使其呼吸需求长期升高。与水分亏缺胁迫的棉花相比，日出时未受胁迫的棉花中蔗糖水平较低，这可能使未受胁迫的组织更容易更快地死亡。最初使用细胞活力染料2,3,5 - 三苯基氯化四氮唑来确定组织死亡，但在后续实验中通过监测叶绿素荧光产量的下降来确定。在收获后几分钟内获得荧光产量测量值，并在处理的时间过程中对单个样本进行监测。对灌溉地块和旱地地块样本中叶绿素荧光产量下降的时间进程和幅度进行分析，使得能够在灌溉停止后24小时内检测到胁迫响应。随着水分亏缺胁迫增加，在呼吸需求升高处理期间荧光产量下降速率减缓。灌溉后，水分胁迫植物的源叶在4天内恢复到胁迫前的值。过量表达热激蛋白101的充分浇水棉花与非转基因棉花具有相同的荧光产量下降速率。这些结果表明，暴露于长期升高的呼吸需求下的水分胁迫组织中荧光产量的延迟下降可作为水分亏缺胁迫响应的敏感指标。
