Integration of Cadmium Accumulation, Subcellular Distribution, and Physiological Responses to Understand Cadmium Tolerance in Apple Rootstocks

Abstract

Cadmium (Cd) is a nonessential and highly toxic element causing agricultural problems. However, little information is available about the variation in Cd tolerance among apple rootstocks and its underlying physiological regulation mechanisms. This study investigated Cd accumulation, subcellular distribution, and chemical forms as well as physiological changes among four apple rootstocks exposed to either 0 or 300 μM CdCl2. The results showed that variations in Cd tolerance existed among these rootstocks. Cd exposure caused decline in photosynthesis, chlorophyll and biomass in four apple rootstocks, which was less pronounced in M. baccata, indicating its higher Cd tolerance. This finding was corroborated with higher Cd tolerance indexes (TIs) of the whole plant in M. baccata than those in the other three apple rootstocks. Among the four apple rootstocks, M. baccata displayed the lowest Cd concentrations in roots, wood, and leaves, the smallest total Cd amounts as well as the lowest BCF. In apple rootstocks, it was found that to immobilize Cd in cell wall and soluble fraction (most likely in vacuole) and to convert it into pectate- or protein- integrated forms and undissolved Cd phosphate forms may be the primary strategies to reduce Cd mobility and toxicity. The physiological changes including ROS, carbohydrates and antioxidants were in line with the variations of Cd tolerance among four apple rootstocks. In comparison with the other three apple rootstocks, M. baccata had lower concentrations of ROS in roots and bark, H2O2 in roots and leaves and MDA in roots, wood and bark, but higher concentrations of soluble sugars in bark and starch in roots and leaves, and enhanced antioxidants. These results indicate that M. baccata are more tolerant to Cd stress than the other three apple rootstocks under the current experiment conditions, which is probably related to Cd accumulation, subcellular partitioning and chemical forms of Cd and well-coordinated antioxidant defense mechanisms.

Exogenous melatonin alleviates cadmium uptake and toxicity in apple rootstocks

“…Before harvest, gas exchange was measured for three mature leaves (leaf plastochron index range: 7-9) per plant in a CIRAS-2 photosynthesis system (PP Systems, Amesbury, MA, USA) as recommended by Zhou et al (2017).…”

“…These inconsistencies may be explained by the relative differences between herbaceous and woody plants in terms of Cd uptake and accumulation. In general, fruit trees have strong abilities to accumulate Cd in their roots and block its translocation to their aerial organs (Nada et al 2007, Zhou et al 2017). In the present study, melatonin-promoted HMA4…”

“…Fruit tree rootstocks are used in vegetative propagation and control HM uptake and translocation to the aerial organs (Podazza et al 2016). Previously, we evaluated Cd accumulation and tolerance among various apple rootstocks and established that M. baccata and M. micromalus "qingzhoulinqin" differed greatly in terms of Cd uptake and accumulation (Zhou et al 2017). To examine the potential roles of melatonin in Cd uptake, accumulation 5 and detoxification in M. baccata and M. micromalus "qingzhoulinqin", we exposed the rootstocks to either 0 or 30 μM Cd together with 0 or 100 μM melatonin for 20 d. We measured their growth characteristics, net root Cd 2+ flux, Cd accumulation, melatonin concentrations, ROS and antioxidants levels, and the key genes involved in Cd uptake, translocation, and detoxification.…”

In vitro acclimation to prolonged metallic stress is associated with modulation of antioxidant responses in a woody shrub Daphne jasminea

“…Studies on metal-tolerant and metal-sensitive plant genotypes, ecotypes and species revealed that tolerant variants often exhibit constitutively higher antioxidant activity and accumulation of antioxidative compounds (Giannakoula et al 2010;Martins et al 2013;Zhou et al 2017;Muszyńska et al 2018b;Ferrer et al 2018). In D. jasminea treated with HM, irrespectively of treatment duration, antioxidant machinery was significantly reorganized.…”

Isolation and expression analysis of cadmium‐induced genes from Cd/Mn hyperaccumulator Phytolacca americana in response to high Cd exposure

“…For instance, Cd is immobilised in the cell wall with pectate or sequestrated in vacuoles in undissolved forms, reducing Cd mobility and toxicity in apple rootstocks (Zhou et al . ). In Populus × canescens Cd is preferentially accumulated in the transport pathway accompanied by sulphur‐containing ligands, which can detoxify Cd (He et al .…”