Premium
Mannitol inhibits growth of intact cucumber but not pea seedlings by mechanically collapsing the root pressure
Author(s) -
STAHLBERG R.,
COSGROVE D. J.
Publication year - 1997
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1046/j.1365-3040.1997.d01-141.x
Subject(s) - mannitol , hypocotyl , epicotyl , xylem , osmotic pressure , horticulture , apoplast , incubation , chemistry , botany , biology , cell wall , biochemistry
The positive xylem pressure ( P x ) in cucumber hypocotyls is a direct extension of root pressure and therefore depends on the root environment. Solutions of the electrolyte KCl (0.10 osm) reduced the hypocotyl P x transiently (biphasic response), while the P x reduction by mannitol solutions was sustained. The amplitudes of the induced P x reduction depended directly, and the degree of P x restoration after stress release depended indirectly, on the size of the initial positive P x , indicating that mannitol released the root pressure by a mechanical rather than osmotic mechanism. Mannitol treatment and other means of root pressure reduction revealed two separate growth responses in the affected cucumber hypocotyls. Only steep P x drops (following root excision or root pressure release in mannitol) directly cause a rapid, transient drop in growth rate (GR). Both rapid and slow (after root incubation in KCN or NEM) decreases in root pressure, however, led to a sustained growth inhibition of cucumber hypocotyls after about 30 min. This delay characterizes the growth response as an indirect consequence of the P x change. Pea seedlings, which lacked root pressure and had a negative P x throughout, showed extremely small changes in epicotyl P x and GR after root incubation in mannitol. It is apparent that the higher sensitivity of cucumber growth to mannitol depended on the presence and release of root pressure.