AUTHOR=He Jiali , Zhou Jiangtao , Wan Huixue , Zhuang Xiaolei , Li Huifeng , Qin Sijun , Lyu Deguo 

TITLE=Rootstock–Scion Interaction Affects Cadmium Accumulation and Tolerance of Malus

JOURNAL=Frontiers in Plant Science

VOLUME=11

YEAR=2020

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2020.01264

DOI=10.3389/fpls.2020.01264

ISSN=1664-462X

ABSTRACT=<p>To understand the roles of <italic>Malus</italic> rootstock, scion, and their interaction in Cd accumulation and tolerance, four scion/rootstock combinations consisting of the apple cultivars “Hanfu” (HF) and “Fuji” (FJ) grafted onto <italic>M. baccata</italic> (Mb) or <italic>M. micromalus</italic> “qingzhoulinqin” (Mm) rootstocks differing in relative Cd tolerance were exposed either to 0 µM or 50 µM CdCl<sub>2</sub> for 18 d. Cd accumulation and tolerance in grafted <italic>Malus</italic> plants varied within rootstock, scion, and rootstock–scion interaction. Cd-induced decreases in photosynthesis, photosynthetic pigment level, and biomass were lower for HF grafted onto Mb than those for HF grafted onto Mm. Reductions in growth and photosynthetic rate were always the lowest for HF/Mb. Cd concentration, bioconcentration factor (BCF), and translocation factor (<italic>T<sub>f</sub></italic>) were always comparatively higher in HF and FJ grafted onto rootstock Mm than in HF and FJ grafted on Mb, respectively. When HF and FJ were grafted onto the same rootstock, the root Cd concentrations were always higher in HF than FJ, whereas the shoot Cd concentrations displayed the opposite trend. The shoot Cd concentrations and <italic>T<sub>f</sub></italic> were lower for HF/Mb than the other scion/rootstock combinations. Rootstock, scion, and rootstock–scion interaction also affected subcellular Cd distribution. Immobilization of Cd in the root cell walls may be a primary Cd mobility and toxicity reduction strategy in <italic>Malus</italic>. The rootstock and scion also had statistically significant influences on ROS level and antioxidant activity. Cd induced more severe oxidative stress in HF and FJ grafted onto Mm than it did in HF and FJ grafted onto Mb. Compared with FJ, HF had lower foliar O<sub>2</sub><sup>-</sup>, root H<sub>2</sub>O<sub>2</sub>, and root and leaf MDA levels, but higher ROS-scavenging capacity. The rootstock, scion, and rootstock–scion interaction affected the mRNA transcript levels of several genes involved in Cd uptake, transport, and detoxification including <italic>HA7</italic>, <italic>FRO2-like</italic>, <italic>NRAMP1</italic>, <italic>NRAMP3</italic>, <italic>HMA4</italic>, <italic>MT2</italic>, <italic>NAS1</italic>, and <italic>ABCC1</italic>. Hence, the responses of grafted <italic>Malu</italic>s plants to Cd toxicity vary with rootstock, scion, and rootstock–scion interaction.</p>