Objectives The accumulation of cadmium (Cd) in rice is influenced by both the cultivar’s Cd tolerance characteristics and environmental factors. While light duration significantly impacts plant growth, its precise effect on Cd accumulation remains elusive. Therefore, we conducted an investigation into rice growth and Cd accumulation under varying light durations, aiming to provide insights into regulating Cd accumulation in rice.

Methods A hydroponic experiment was carried out using two rice varieties known for high Cd accumulation, ‘Yuzhenxiang’ (YZX) and ‘Xiangwanxian 12’ (XWX12), along with ‘Shaoxiang 100’ (SX100), which lacks the major Cd uptake gene Nramp5 and thus exhibits Cd exclusion. In Hoagland nutrient solution, 1 μmol/L Cd was added to simulate Cd stress conditions. Rice seedlings were grown in this Cd-stress solution and subjected to two light treatments: 12 hours of light followed by 12 hours of darkness (12 h) or 16 hours of light followed by 8 hours of darkness (16 h). At the tillering stage, rice plants were harvested to measure plant height, root biomass, and Cd content in different tissues. Additionally, Cd distribution in subcellular fractions and the expression levels of key genes involved in Cd uptake and transport were analyzed.

Results Compared to the 12 h light treatment, the 16 h treatment significantly increased the SPAD values of all rice varieties, increased the plant height of XWX12 and SX100 but decreased it in YZX, and reduced the root volume and root dry weight of all three varieties. Furthermore, the 16 h treatment enhanced Cd contents in both the shoots and roots of all rice varieties. At the subcellular level, the Cd content in the cell wall and organelles of YZX under 16 h was significantly increased, while the Cd content in the soluble fraction was significantly decreased. In contrast, the Cd contents in all three subcellular fractions of XWX12 and SX100 were significantly increased. Under the 16 h treatment, the expression level of the Cd uptake gene OsNramp5 in the shoots of YZX was up-regulated, but down-regulated in XWX12. The expression of the vacuolar Cd sequestration gene OsHMA3 was up-regulated in YZX and SX100, but down-regulated in XWX12.

Conclusions Extended light duration significantly inhibits the growth and development of rice seedlings under Cd stress and increases their Cd accumulation, regardless of the cultivar’s Cd accumulation characteristics. The differences in Cd distribution among subcellular components are regulated by Cd uptake and transport genes. Further research is needed to investigate the reasons for the differential expression of the same gene related to Cd uptake and transport in different rice varieties.