Starch biosynthesis by AGP AGP ase, but not starch degradation by BAM BAM 1/3 and SEX SEX 1, is rate‐limiting for CO CO 2 2 ‐regulated stomatal movements under short‐day conditions

摘要

Starch in guard cells functions in osmoregulation during stomatal movements. Starch metabolism is controlled by the circadian clock. We investigated the role of starch metabolism in stomatal responses to CO 2 under different photoperiodic conditions. Guard cell starch levels correlate with low/high [ CO 2 ] exposure. Starch biosynthesis‐deficient AGP ase ( ADG 1 ) mutants but, unexpectedly, not the starch degradation‐deficient BAM 1, BAM 3, and SEX 1 mutants alone, are rate‐limiting for stomatal conductance responses to [ CO 2 ]‐shifts. Interestingly, AGP ase is rate‐limiting solely under short‐ but not long‐day conditions. These findings suggest a model of enhanced AGP ase activity in guard cells under short days such that starch biosynthesis becomes rate‐limiting for CO 2 ‐induced stomatal closing.