Seeds of the ysl3-3 mutant accumulate less copper and soluble protein are smaller and lighter. Grains were collected from soil-grown plants that were fertilized bi-weekly with N–P–K. (A) ICP-MS analysis of copper concentration in seeds of the indicated plant lines. (B, C) Straight length and width, respectively, of grains collected from the indicated plant lines. Grains were dehusked and the straight length and width of randomly selected grains were measured using the WinSEEDLETM of STD4800 Scanner (Regent Instruments Inc., Canada, 2015). (D) A representative image of seeds pooled from at least three plants from each independent experiment (n = 3). (E, F) The weight of 1,000 dehusked grains and the concentration of soluble proteins in seeds, respectively, in the indicated plant lines. Presented values are arithmetic means ± S.E. (n = 3 pools of seeds from five plants per each line; a representative result from three independent experimental setups is shown). Seeds were pooled together from five plants per line. Levels not connected by same letter are significantly different (p < 0.05, Tukey–Kramer HSD test). When indicated (+Cu), plants were fertilized bi-weekly with 20 µM CuSO4.Wt, wild-type; ysl3, the ysl3-3 mutant; YSL3-1, YSL3-2, two transgenic lines of the ysl3-3 mutant expressing the YSL3 cDNA; DW, dry weight.