Inducing Gravitropic Curvature of Primary Roots of Zea mays cv Ageotropic

Abstract

Primary roots of the mutant 'Ageotropic' cultivar of Zea mays are nonresponsive to gravity. Their root caps secrete little or no mucilage and touch the root only at the extreme apex. A gap separates the cap and root at the periphery of the cap. Applying mucilage from normal roots or substances with a consistency similar to that of mucilage to tips of mutant roots causes these roots to become strongly graviresponsive. Gravicurvature stops when these substances are removed. Caps of some mutants secrete small amounts of mucilage and are graviresponsive. These results indicate that (a) the lack of graviresponsiveness in the mutant results from disrupting the transport pathway between the cap and root, (b) movement of the growth-modifying signal from the cap to the root occurs via an apoplastic pathway, and (c) gravity (18). This indicates that the lesion for gravitropism is downstream from gravity-detection, perhaps in transmitting the signal from the cap to the root. We studied this by examining the nature of the cap/root interface of mutant roots. MATERIALS AND METHODSAlmost all models for root gravitropism involve a similar sequence of events. Detection of gravity occurs in the root cap and probably involves sedimentation of amyloplasts in columella cells (2,5,15). This change in cellular structure somehow generates a chemical and/or electrical signal in the cap (2,4,5). This signal moves from the root cap to the elongating zone of the root, which is 2 to 6 mm behind the cap. There, the signal preferentially inhibits cellular elongation along the lower side of the root, thus causing the root to curve down (4,5,15).Although we cannot identify the gravitropic signal, much evidence indicates that it moves from the cap to the root before gravicurvature. For example, decapped roots are nonresponsive to gravity (7,23,24), and removing half of the cap of vertically oriented roots induces curvature toward the remaining half-cap (6). Inserting barriers into one side of a root between the root cap and elongating zone causes curvature away from the barrier (26). Taken together, these results suggest that root gravitropism involves movement of a growth-modifying signal from the root cap to the root.The objective of this research was to use mutants to characterize the pathway by which the gravitropic signal moves from the root cap to the root in primary roots of Zea mays.'

Comparative analyses of three legume species reveals conserved and unique root extracellular proteins

“…Proteins have been demonstrated to be important high molecular weight compounds released by different plant species, even under axenic conditions . Maize roots can exudate large amounts of mucilage . In comparison, the amount of mucilage released by the three legumes studied here is less than that of maize, as observed in our previous experiments .…”

Immunocytochemical localization of indole‐3‐acetic acid in primary roots of Zea mays

“…(2) Removing mueilage from a root renders the root nonresponse to gravity (Moore & McClelen 1989), and applying mucilage to agravitropic roots of corn restores its responses to gravity (Miller & Moore 1990;Moore, Evans & Fondren 1990).…”

The Role of DNA in the Extracellular Environment: A Focus on NETs, RETs and Biofilms

“…This putative function could resemble the wellknown extracellular digestive activity before substrate absorption in fungi, during organic matter decomposition processes (Jennings, 1995;Cole, 1996). Many other roles were associated with the root mucilage, such as: lubricant protecting the root tips while growing into the soil (Greenland, 1979); carrier of gravitropic signals from the root cap to the root tip (Moore et al, 1990); protection of roots from the toxicity of ions such as copper, cadmium, boron, lead, mercury, iron, arsenic, aluminum (Mench et al, 1987;Hawes et al, 2016), or as carbon source for soil microbes (Knee et al, 2001).…”