The sowing date changed the temperature and light conditions in the field modified the cadmium content of brown rice (Oryza sativa L.) by regulating the expression of Cd-related genes

Cadmium (Cd) contamination in rice is a potential health hazard when ingested through the food chain worldwide. Reducing the Cd content in rice through agronomic measures is an effective way to reduce the risk of Cd contamination to human health. In order to clarify the correlation between temperature and light conditions and Cd accumulation (Cd-A) and Cd content of brown rice (CdBR) during the field growth period (FGP) of rice, consequently provide a theoretical basis for the selection of sowing date (SD) for "Low-Cd-Rice" production, field experiment with different SDs was carried out by using two rice varieties with different Cd accumulation characteristics (Luliangyou 996, V1, a high Cd accumulation variety; Zhuliangyou 819, V2, a low Cd accumulation variety). The results showed that the temperature and light factors such as mean soil temperature (ST), mean air temperature (AT), soil accumulation temperature (SAT), air accumulation temperature (AAT), ultraviolet radiation accumulation (UR), photosynthetic radiation accumulation (PR), light intensity accumulation (I) and sunshine hours accumulation (SH) varied to different degrees under different SDs; The difference in CdBR in two varieties could be up to 2.82 and 8.48 times respectively among SDs, with the CdBR of S4 and S5 of V2 being lower than the national standard of 0.2 mg/kg. The relative expression of OsIRT1 in the root system was significantly positively correlated with ST, SAT, AT, AAT, and SH, while OsNramp5, OsNramp1, and OsHMA3 showed significant negative correlations with ST, SAT, AT, AAT, and SH in relative expression in the root system; OsIRT1 expressed in the roots of V1 was significantly negatively correlated with CdBR, while OsHMA3 expression was significantly positively correlated with CdBR; OsLCD, OsNramp1, and OsHMA3 expression in the roots of V2 were significantly positively correlated with Cd-A and CdBR, while OsIRT1 in the roots of V2 and OsLCT1 in the leaves were significantly negatively correlated with Cd-A; The expression of OsNramp5 in roots was significantly negatively correlated with Cd-A and CdBR in both V1 and V2. Bias correlation analysis showed that ST, SAT, AT, and AAT were significantly negatively correlated with both Cd-A and CdBR; SH was significantly negatively correlated with CdBR in V1. Summarily, the temperature and light conditions during the FGP of rice and their regulation of the expression levels of related genes could be changed by sowing selection, so as to achieve safe production of rice under Cd-contaminated fields.