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Wall extensibility during hypocotyl growth: A hypothesis to explain elastic‐induced wall loosening
Author(s) -
Edelmann Hans G.
Publication year - 1995
Publication title -
physiologia plantarum
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.351
H-Index - 146
eISSN - 1399-3054
pISSN - 0031-9317
DOI - 10.1111/j.1399-3054.1995.tb00841.x
Subject(s) - hypocotyl , turgor pressure , rheology , helianthus annuus , biophysics , shrinkage , sunflower , chemistry , horticulture , materials science , biology , composite material
The physico‐chemical nature of wall loosening of plants is still a matter of speculation. For a better understanding of the mechanistic principles in which polymer interactions may be affected during wall loosening, the rheological properties of sunflower ( Helianthus annuus L.) were investigated during white light (WL)‐ and auxin (IAA)induced growth changes. As rheological parameter, the capacity for elastic shrinkage of standard hypocotyl segments after release of turgor‐mediated wall stress by freezing/thawing was studied (relative reversible length). Segment length remaining after shrinkage relative to turgid length has been designated as relative irreversible length. The following results were obtained: Temporary growth inhibition of in planta growing hypocotyls by WL is characterized by a temporary increase in relative irreversible length and a complementary decrease of relative reversible length. Analogously, but with opposite effect, IAA‐induced growth of hypocotyl segments is characterized by a decrease in relative irreversible length and an increase in relative reversible length; i.e., an increased capacity to shrink elastically per standard length. The changes of the two wall‐rheological parameters follow similar principles in hypocotyls grown in planta and ex planta and independent of whether the growth rate was changed by either WL conditions or IAA concentration. As suggested earlier (Edelmann 1994) the results indicate that growth may be regulated by wall loosening mechanisms which initially result in elastic (reversible) wall extension. To render this extension irreversible, it must be fixed subsequently. The finding that loosened walls also become shorter in irreversible length per standard length once tensional stress is released is new. It represents pivotal evidence for an initially elastic‐induced wall loosening.