Abstract
Greenhouse vegetable production (GVP) has grown rapidly and has become a major force for cucumber production in China. In highly intensive GVP systems, excessive fertilization results in soil acidification, increasing Cd accumulation and oxidative stress damage in vegetables as well as increasing health risk of vegetable consumers. Therefore, enhancing antioxidant capacity and activating the expression level of Cd transporter genes seem to be feasible solutions to promote plant resistance to Cd stress and to reduce accumulated Cd concentration. Here, we used transcriptomics to identify five cucumber transporter genes (CsNRAMP1, CsNRAMP4, CsHMA1, CsZIP1, and CsZIP8) in response to cadmium stress, which were involved in Cd transport activity in yeast. Ionomics, gene expression, and REDOX reaction level association analyses have shown that the transcript of CsNRAMP4 was positively correlated with Cd accumulation and antioxidant capacity of cucumber roots. The expression level of CsHMA1 was negatively correlated with Cd-induced antioxidant capacity. The overexpression of CsHMA1 significantly relieved Cd stress-induced antioxidant activities. In addition, shoots with high CsHMA2 expression remarkably presented Cd bioaccumulation. Grafting experiments confirmed that CsHMA1 contributed to the high antioxidant capacity of cucumber, while CsHMA2 was responsible for the transport of Cd from the roots to the shoots. Our study elucidated a novel regulatory mechanism for Cd transport and oxidative damage removal in horticultural melons and provided a perspective to regulate Cd transport artificially by modulating Cd accumulation and resistance in plants.
Highlights
Greenhouse vegetable production (GVP), a main part of vegetable production inChina, has grown rapidly
Our results showed that Cd accumulation in cucumber seedlings was positively cor related with oxidative stress indicators (Figure 1E,F), suggesting that the expression of Cd transporters might assist in the maintenance of REDOX reaction
This study demonstrated that five Cd-responsive transporters transcriptionally responded to Cd stress
Summary
Greenhouse vegetable production (GVP), a main part of vegetable production inChina, has grown rapidly. Greenhouse vegetable production (GVP), a main part of vegetable production in. In highly intensive GVP systems, excessive fertilization has resulted in heavy metal accumulation and soil acidification, which, in turn, has increased heavy metal accumulation in vegetables and has posed health risks to vegetable consumers [3,4]. Anecdotal evidence suggests that heavy metals in protected cultivated soil shows a significant accumulation trend, Antioxidants 2021, 10, 1973. Antioxidants 2021, 10, 1973 and the content of heavy metals was significantly higher than that in open cultivation soil [5]. Protected vegetable plots have become the type of vegetable plot with more serious accumulation of heavy metals after industrial and mining/sewage irrigation plots, which should be paid with attention. The Cd content in protected farmland was found to be the most serious, and the Cd contents in the south, north, and northwest of China were 41.7%, 54.5% and 11.1%, respectively, of the total Cd contamination of land [5]
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