Photoperiod alters partitioning of newly-fixed 14C and reserve carbon into sorbitol, sucrose and starch in apple leaves, stems, and roots

Abstract

The experiment was designed to determine how photoperiod duration affected the partitioning of newly-fixed ¹⁴C and reserve carbon into sorbitol, sucrose, and starch in apple source leaves, young sink leaves, stems, and roots. Apple plants (Malus domestica Borkh. cv. Gala), 1-year-old, were grown in environmental growth chambers and received five different photoperiod treatments of 1, 4, 7, 10 and 14 h for 8 d. On the eighth day of the light treatments, plants were exposed to ¹⁴CO₂ for 15 min and harvested at 0, 2, 6, 12 and 24 h after labelling for carbohydrate and ¹⁴C-carbohydrate analyses. Sorbitol and starch concentrations in leaves, stems, and roots increased as photoperiod increased, and peaked near 10-h photoperiod. Sucrose concentrations, however, either did not change in mature leaves or decreased slightly in stems as photoperiod increased from 1 to 14 h. At 24 h after ¹⁴ CO₂ labelling, plants grown in longer photoperiods had less [¹⁴C]sucrose, [¹⁴C]sorbitol and ¹⁴C-total soluble fraction remaining in mature leaves, but more ¹⁴C activities in stems and roots than those grown in shorter photoperiods. We suggest that the increases in ¹⁴C-carbohydrates in stems and roots under longer photoperiods are due to increased carbon export from mature source leaves.