土壤H2S调控苹果根系死亡与更新的分子生理机制

Roots are the foundations of plant standing, soils are the sites of root survival. Regulators produced in soil are essential for root development and plant growth. Soil hydrogen sulfide (H2S) is not only a toxin, but also a new type gaseous signal molecule with regulating function. This project is to clarify the correlation between soil H2S concentration and the death and renewal of apple roots by investigating H2S production in the root-zone soil of orchards and potted apple trees and analyzing the sensitivity of new roots (absorbing roots and extensive roots) to H2S concentration. And then, the soil H2S concentration will been regulated by alternating droughts and floods, applying organic fertilizer with different maturity and applying H2S donors and scavengers using young apple trees planted in root chamber underground, potted Malus hupehensis seedling and transgenic plants with apoptotic gene of M. hupehensis. Under the different soil H2S concentration in root-zone, we will examine the characteristics of root cell death and metabolism associated with death by detecting root caspases-like and vacuolar processing enzyme (VPE) activity mitochondrial permeability and apoptosis rate, analyzing the expression of promoting apoptosis gene MhVPE and anti-apoptosis gene MhBAG, and investigating the death and renewal of new roots. By analyzing the relationship between them, the regulation mechanism of soil H2S to root death and regeneration will been revealed from the level of apoptosis and gene expression. This will provide the theoretical guidance for the soil management and root regulation in apple orchard.

根系是植物立地之本，土壤是根系生存之地，来自土壤的调节因子对根系发育和植株生长至关重要；土壤硫化氢（H2S）既是一种毒素，也是一种具有调节功能的新型气体信号分子。本项目在调查果园和盆栽苹果根区土壤H2S产生规律、分析苹果新根（吸收根和延长根）对H2S浓度敏感性的基础上，明确土壤H2S浓度与根系死亡更新的相关性；并且，选择苹果幼树、平邑甜茶幼苗及转入促/抗凋亡基因的材料，借助根窖和盆栽体系，通过旱涝交替、施用腐熟度不同的有机肥及H2S供体和清除剂改变土壤H2S浓度，检测不同H2S浓度下根系类Caspase与液泡加工酶活性、线粒体通透性、细胞凋亡率、促凋亡基因MhVPE和抗凋亡基因MhBAG等的表达，同时调查新根死亡与更新情况，解析它们之间的关系，进而从细胞凋亡和基因表达层面揭示土壤H2S调控根系死亡与更新的机制，为果园土壤管理和苹果根系调控提供深层次理论依据。

硫化氢（H2S）对根系发育和植株生长是一种“双刃剑”。摸清苹果根区土壤H2S生成特点和分布规律，明确根系死亡与更新对不同浓度H2S的反应，阐明H2S对根系的影响及对胁迫伤害的缓解作用和机制，对于果园土壤管理和苹果根系调控有重要价值。. 本项目调查了苹果根区土壤H2S及苹果砧木（平邑甜茶）根系等器官内源H2S生成规律，探讨了有机肥和生物炭对土壤H2S的影响，分析了苹果幼树和砧木对外源H2S的反应，研究了土壤淹水和盐胁迫下平邑甜茶内源H2S生成特点以及外源H2S对胁迫伤害的缓解作用，还从硫代谢、MYB等转录因子、MhVPE等细胞凋亡相关基因、miRNA和根系离子流及其相关基因等多方面，探讨了H2S调控根系死亡与更新以及缓解淹水和盐胁迫的机制。. 结果表明，H2S主要分布在土壤中上层，粘土H2S浓度最高，砂土H2S浓度最低。较高浓度（大于1.0 mmol·L-1）硫化氢抑制平邑甜茶根系生长发育，加剧土壤淹水、氯化钠和碱性混合盐的胁迫伤害，甚至杀死植株，但其在适宜低浓度下（0.02-0.1 mmol∙L-1）能够不同程度地促进根系生长，缓解土壤淹水、氯化钠和碱性盐胁迫对根系的伤害。在盐胁迫下，H2S能够降低根系对Na+的吸收，维持细胞Na+/K+的稳态，提高根系抗氧化酶活性，维持细胞氧化还原平衡，调节MhVPEγ和MhNCED3基因表达，降低盐胁迫导致的根系细胞死亡。H2S预处理可以特异性地诱导mhp-miR408a表达下调，并上调mhp-miR477a和mhp-miR827；H2S还通过调节mhp-miR159c和mhp-miR169及其靶基因的表达，改善碱性盐胁迫下的根系结构，显示miRNA介导的调控网络参与H2S缓解平邑甜茶盐胁迫伤害过程。. 项目执行期间发表18篇论文，获1项国家授权专利，培养3名博士和4名硕士研究生。