缺锌胁迫下锌在苹果砧木根系质外体累积的生理机制

Apple tree is sensitive to zinc deficiency. Studies showed that most of zinc sequestrated in apoplast and caused zinc-deficiency in aerial parts. However, the specific mechanism of zinc accumulation in root apoplast is still not clear. In this study, with the common rootstock “Malus hupehensis Rehd.” tissue culture seedlings as materials, the synchrotron radiation X-ray fluorescence (SRXRF), XAS, Zinpyr-1 fluorescent probe and NMT techniques are used to define the distribution and accumulation characters of zinc in roots of zinc-deficient apple trees rootstock; in addition, the changes of apoplast pH and electric charge distribution on cell wall of root will be measured to clarify the changes of environment of apoplast under zinc deficiency. Our study is aimed to reveal the physiological mechanism of the zinc accumulation in root apoplast of apple rootstock under zinc deficiency. What’s more, this research can provide a theoretical support for the further reuse of accumulated zinc in roots as well as a better guide to prevent the occurence of zinc deficiency and clarify the zinc deficiency tolerance mechanism in field.

苹果树对缺锌敏感。前期研究表明，缺锌胁迫下大量锌在细胞壁等质外体中累积而不能有效运转利用，最终导致地上部因可利用锌不足而产生缺锌症状，然而，导致缺锌胁迫下锌在苹果树根系质外体中累积的生理机制尚不清楚。本研究采用Zinpyr-1荧光探针、XAS、NMT和质外体pH原位分析等技术，以缺锌敏感的苹果砧木“平邑甜茶（Malus hupehensis Rehd.)”组培苗为试材，研究缺锌胁迫下锌在根系质外体中累积的主要分子形态及其时、空变化规律；同步研究质外体pH和细胞壁负电荷、细胞壁组分等质外体环境因素对缺锌胁迫的响应，以阐明缺锌胁迫下锌在苹果树根系质外体累积的生理机制，完善苹果根系锌累积与再活化机理，同时为筛选累积锌的活化调控技术、预防和矫治苹果缺锌小叶病提供理论依据。

以平邑甜茶幼苗为材料，研究了缺锌胁迫下，锌在根系累积的生理机制以及根系质膜H+-ATPase和质外体pH对缺锌的响应机制。①对植株各器官锌含量进行测定结果表明，缺锌胁迫处理和正常处理锌含量都是表现为：根﹥茎﹥叶。随着缺锌胁迫时间的延长，缺锌胁迫初期锌根系含量较大幅度迅速下降，而在缺锌胁迫后期根系中锌含量减少幅度变小，根系中锌积累量有相同的变化趋势。②提取平邑甜茶幼苗根系细胞膜，测定H+-ATPase水解活性及动力学特征参数。发现缺锌胁迫下根系质膜H+-ATPase活性降低，ATP含量下降，从而影响了各种代谢活动的正常进行。③测定细胞质膜内外pH梯度，ATP含量，质膜H+流速以及质外体pH。发现缺锌胁迫降低根系的H+泵出质膜能力，造成pH梯度和根系内的ATP含量低于对照。对于H+流速，缺锌和对照均表现为外排趋势，但缺锌外排量降低显著，另外缺锌胁迫时，平邑甜茶根系质外体pH升高。缺锌胁迫下根系细胞壁各组分含量高于对照，并且随缺锌时间延长，果胶含量逐渐增加，果胶甲酯酶活性明显提高，使得细胞壁结合更多的锌离子，增加对锌离子的吸附能力。