Gravity induced changes in intracellular potentials in statocytes of cress roots

Abstract

Two glass microelectrodes were inserted from opposite sides of the root cap into statocytes of Lepidium sativum L. immersed in medium with or without cytochalasin D (CD). Intracellular potentials (Eis) of statocytes were measured with reference to an earthed electrode in the bathing solution. In the absence of CD, Ei values were -160 +/- 2 mV (n = 52) in vertical roots. During the recording of Eis, the roots were tilted from the vertical by 45 degrees so that in a tilted root one electrode was on the upper side and the other on the lower side; after 5 min the roots were returned to the vertical. At approximately 64 s after tilting (lasting 5-15 s) there was a transient lowering of Ei (more negative) by an average of 4.7 mV on both the upper and lower sides (n = 52). In some cases, this decrease in Ei was preceded by a transitory increase. Returning the roots to the vertical resulted in a response similar to that obtained by tilting. In roots treated with CD at a concentration of 3 (microM for 1 h, the initial Ei was -145 +/- 2 mV (n = 43), and the lowering of Ei on position change (tilting or returning) was smaller (2.0 mV) in some statocytes (n = 50) and higher (8.1 mV) in others (n = 14) compared to control roots (without and with DMSO). A higher concentration (10 microM) of CD and longer treatment (2 h) further reduced the decrease in Ei (1.1 mV) on position change (n = 26). The observed effects of CD support the hypothesis that statoliths in statocytes are anchored by actin filaments to the plasma membrane and/or to the cortical endoplasmic reticulum. Movement of statoliths during the first step of graviperception may lead to stress changes in actin filaments, affecting the transmembrane potential and also the Ei.

Lateral relocation of auxin efflux regulator PIN3 mediates tropism in Arabidopsis

“…Developmental requirements for PIN3, its localization, as well as the proposed biochemical function for PIN proteins make PIN3 a likely candidate for an efflux component of the lateral auxin transport system. The actin-dependent cycling and rapid relocalization of PIN3 in cells containing gravity-sensing statoliths 22 , taken together with previous findings supporting a direct role of the actin cytoskeleton in gravity perception 23,24 , imply a cellular mechanism for the regulation of asymmetric auxin distribution and differential growth. After a change of the gravity vector, actin-enmeshed statoliths 25 sediment, causing reorganization of the actin cytoskeleton.…”

Changes in Cytosolic pH within Arabidopsis Root Columella Cells Play a Key Role in the Early Signaling Pathway for Root Gravitropism

“…However, gravityinduced changes, if present, have so far remained undetected (Leagué et al, 1997), possibly because of their small size or location to specific cellular microdomains. Changes in root cap cell membrane potentials following gravistimulation have been reported in the literature (Behrens et al, 1985;Sievers et al, 1995). Following gravistimulation of Lepidium sativum roots, Behrens et al (1985) found a transient depolarization of statocytes on the lower side of the root, with repolarization occurring within 60 s to a membrane potential slightly more positive than the original resting potential.…”

“…Statocytes on the upper side showed a slow hyperpolarization following gravistimulation. Sievers et al (1995), also studying L. sativum roots, found that after gravistimulation there was a transient lowering of the membrane potential on both the upper and lower sides after 64 s. In some cases this was preceded by a transient increase. Although changes in membrane potential in response to gravistimulation are not entirely understood, they may play a role in the signaling as well.…”

“…Intracellular ionic currents in root cap cells during gravistimulation have been observed using microelectrodes and in vibrating probe studies (Behrens et al, 1985;Bjö rkman and Leopold, 1987;Sievers et al, 1995). In plant cells, the plasma membrane H ϩ -ATPase is primarily responsible for generating the membrane potential (Briskin, 1990;Assmann and Haubrick, 1996).…”

In Memoriam: Zygmunt Hejnowicz (1929–2016)

“…[26][27][28][29] Zygmunt initiated electrophysiological studies aimed at examination of correlation between electrical signals, i.e., ion fluxes, and different physiological processes. Kazimierz Trębacz recalls that technical difficulties were usually a big challenge but they were solved by Zygmunt's ingenious ideas.…”