Photoperiodic control of seasonal plant growth is mediated by ABA, acting on cell-cell communication

About 2 weeks ago, these GEITP pages described how a plant receives a signal that “it is getting stressed by dehydration (drought).” The root-derived CLE25 peptide moves from the roots to the leaves, where it induces (leaf) stomatal closure by modulating abscissic acid (ABA) accumulation –– thereby enhancing resistance to dehydration stress. Herein, the “gene-environment interactions” topic again involves ABA: perennial plants living in temperate zones must respond to colder temperatures by going into a state of dormancy, which prevents growth during wintertime. Release from dormancy in the spring then enables reinitiation of growth, when favorable conditions return.

Thus, shorter photoperiods –– as winter approaches –– induce growth cessation, formation of a bud that encloses the arrested leaf primordia, shoot apical meristem (plant tissue loccated mostly at the growing tips of roots and shoots and in the cambium –– consisting of actively dividing cells that form new tissue), and bud dormancy. However, longer photoperiods alone cannot promote growth in dormant buds. Instead, prolonged exposure to low temperatures is required to release dormancy. Authors [see attached particle] demonstrate that blockage of symplastic communication (the plant’s symplast is the inner side of the plasma membrane in which water and low-molecular-weight solutes can freely diffuse), mediated by the action of ABA, is part of the photoperiodically-controlled dormancy mechanism in aspen trees.

Photoperiodic regulation of dormancy is mechanistically distinct from autumnal growth cessation. Dormancy sets in when symplastic intercellular communication through plasmodesmata (narrow threads of cytoplasm that pass through the cell walls of adjacent plant cells, thereby allowing communication between them) become blocked by a process dependent on the phytohormone ABA. This communication blockage prevents growth-promoting signals from accessing the meristem. Therefore, precocious growth is not allowed during dormancy. Dormancy (the phenotypic response), which supports robust survival of the aspen tree in winter, is due to loss of access to growth-promoting signals (the environmental stimulus).

Science 13 Apr 2o18; 360: 212–215

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