The molecular mechanism of injury and tolerance related to acid stress in higher plant

研究了酸性条件下植物对铝胁迫的响应。1)大麦根系经铝胁迫处理后，质膜H~+-ATPase活性降低。铝处理根膜上结合的Ca~(2+)量约为对照的一半，而铝处理根膜上有大量的Al与膜结合。2)铝胁迫增加了液泡膜上依赖于ATP和PPI的H~+泵的活性。3)以耐铝性不同的小麦品种为材料，研究了预载K~(++)的外流规律。降低pH可使两个品种的K~+流出增加，在pH为4.2时，敏感品种的K~+流出速率是耐性品种的两倍。胞外低pH可引起细胞质H^+浓度升高，进而引起质膜去极化，K^+和H^+外流可能对此有调节作用。在铝胁迫下，铝敏感品种的H^+泵和K^+通道活性的下降幅度似乎更大。4)铝胁迫下预培养的烟草细胞生长速度是对照细胞的3~7倍。磷饥饿处理后，细胞对铝的吸收能力增强。5)磷饥饿处理细胞后，45KD和21KD两种多肽的合成增加。试图寻找与这些多肽表达相关的基因(S)。利用差异杂交技术，选择合适的探针，构建文库，筛选出诱导耐铝的阳性克隆S。已分离到几个阳性克隆，目前正在进行进一步鉴定。

Responses of plant to aluminum(Al) stress in acidic condition were investigated.1) When barley roots were treated for Al stress, H^+-ATPase of plasma membrane decreased. The amount of Ca^<2+> associated with the membrane of the Al-treated sample was approximately half as large as that of the control, while substantial binding of Al to the membrane was observed in the membrane of Al-treated roots.2) The activities of ATP- and PPi-dependent H^+ -pump of tonoplast increased by Al stress. During this process, the increase of ABA and the amount of protein of both pumps were observed.3) With wheat varieties differing in Al tolerance, the efflux of pre-loaded K^+ was investigated. Lowring the pH in duced increasing K^+ efflux in both cultivars, and the rate of K^+ efflux of sensitive cultivar was twice as much as that of tolerant cultivar at pH 4.2. Extracellular low pH may cause an increase in cytoplasmic H^+ concentration followed by the depolarization of the plasma membrane, which may be adjusted by the efflux of K^+ and H^+. It seemed that the activities of H^+ -pump and K^+ channel decreased more in Al sensitive cultivar by Al stress.4) The tobacco cells pre-cultured in a medium deprivated of phosphate exhibited 3 to 7 fold higher growth than the control cells under Al stress. Absorption of Al followed by the decrease of cell growth was only observed in the cells of logarithmic phase.The capability of the cells excluding of absorbed Al increased by the treatment of phosphate starvation.5) During the treatment of cells for phosphate starvation followed by Al treatment, the synthesis of two polypeptides of 45KD and 21KD increased. The gene(s) related to the expression of these peptides were tried to find. cDNA library was constracted and positive clone(s) for the induction of Al tolerance were isolated with differential hybridization technique with proper probes. Several positive clones were isolated and further identification is now under the progress.