The Onset of Gravisensitivity in the Embryonic Root of Flax

Abstract

Vertical orientation of emerging roots typically is the first response of plants to gravity. Although root gravitropism has been studied extensively, no conclusive data on the onset of gravisensing exist. We determined the inception of gravisensitivity in flax (Linum usitatissimum) roots by clinorotating germinating seeds after various periods of static orientation (gravistimulation) of imbibed seeds. Gravitropic competency was established about 8 h after imbibition, 11 h prior to germination. The time was determined based on 50% of the newly emerged roots curving in the direction of the gravity vector during static imbibition, despite subsequent clinorotation. The threshold value was affected by the orientation of the seeds. Upward orientation of the micropyle/radicle reduced the number of graviresponding roots to about one-half. Prolonged clinorotation weakened the graviresponse. Gravisensing was accompanied by the development of amyloplasts, but the actin cytoskeleton was not involved because imbibition in Latrunculin B did not affect the onset of gravisensitivity or germination, and the development of F-actin in untreated controls was observed only after the onset of gravisensitivity.

Effects of mechanostimulation on gravitropism and signal persistence in flax roots

“…3,42 Cress roots that were clinorotated vertically for 6 h showed auto-straightening, 42 similar to our data ( Fig. 1).…”

“…1 The physical process is then converted into a biochemical signal that elicits a growth response in the shoot and roots, where differential elongation on the top and bottom flank reestablishes the gravitropic set-point angle. The curvature is the final step in a series of complex processes 2,3 that include redistribution of auxin (the Cholodny-Went hypothesis), different sensitivities toward auxin and the ability of cells to retain wall plasticity. 4 While the detailed analysis of the gravitropic signal processing has made significant progress, signal retention or longevity received little attention.…”

Salt Modulates Gravity Signaling Pathway to Regulate Growth Direction of Primary Roots in Arabidopsis

“…4, A and B). This is consistent with the proposed role of columella cell amyloplasts in gravisensing (Takahashi et al, 2003;Ma and Hasenstein, 2005). However, our results indicate that salt-induced rapid degradation of amyloplasts, the proposed gravisensor, in the columella cells is not likely the main reason for a negative gravitropic response, because sos mutant roots exhibited profound negative gravitropic growth without apparent rapid digestion of amyloplasts (Fig.…”

“…First, amyloplasts are not detectable within the first several hours of imbibition and appear at the onset of gravisensing. This result suggests a role of amyloplasts in gravisensing (Ma and Hasenstein, 2005). Second, amyloplasts are a local carbohydrate reserve that can release sugar to protect root tips from stresses that inhibit photosynthesis.…”

Effect of Planting Depth and Orientation on Germination of Yam (Dioscorea) Minisett

“…The use of mechanical planter to plant yam sett requires a study of how variation of planting depth and orientation of minisett will affect germination since researcher has not come across much studies of this nature. Initial sprout development depends on successful seed germination, hypocotyl growth, and root emergence in the direction of gravity [12]. Seeds have a physiological ability to germinate and correctly orient themselves according to gravity, a process known as gravitropism [2].…”