提出问题：However, the effect of light-dark on the interactions between the two tropisms remains unclear.

结果1-光暗条件：Here, by developing a method that makes it possible to mimic natural conditions more closely than the conventional lab conditions, we show that hydrotropism is higher in wild-type Arabidopsis seedlings whose shoots are illuminated but whose roots are grown in the dark compared with seedlings that are fully exposed to light.

结果2-淀粉体：Root gravitropism is substantially decreased because of the reduction of amyloplast content in the root tip with decreased gene expression in PGM1 (a key starch biosynthesis gene), which may contribute to enhanced root hydrotropism under darkness. Furthermore, the starch-deficient mutant pgm1-1 exhibits greater hydrotropism compared with wild-type.

结论：Our results suggest that amyloplast response and starch reduction occur under light-dark modulation, followed by decreased gravitropism and enhanced hydrotropism in Arabidopsis root.