An apparent increase in symplastic water contributes to greater turgor in mycorrhizal roots of droughted Rosa plants*

Abstract

SUMMARYUsing psychrometric pressure-volume analysis, root water relations following drought were characterized in Rosa hybrida L. plants colonized by the vesicular-arbuscular mycorrhizal fungus Glomus intraradices Schenck & Smith. Measurements were also made on uncolonized plants of similar size and adequate phosphorus nutrition. Under well-watered conditions mycorrhizal colonization resulted in lower solute concentrations in root symplasm, and hence lower root turgors. Following drought, however, mycorrhizal roots maintained greater turgor across a range of tissue hydration. This effect was apparently not due to increased osmotic adjustment (osmotic potentials at full turgor were similar in mycorrhizal and non-mycorrhizal roots after drought) or to altered elasticity but to an increased partitioning of water into the symplast. Symplast osmolality at full turgor was similar in mycorrhizal and non-mycorrhizal roots but, because of their higher symplastic water percentages, mycorrhizal roots contained a greater amount of osmotic (symplastic) solutes. Drought-induced changes in osmotic potential were observed only in mycorrhizal roots, where a 04 MPa decrease (relative to well-watered controls) brought the full turgor osmotic potential of mycorrhizal roots to the same level as that of non-mycorrhizal roots under either watering treatment.

Arbuscular mycorrhizae and soil/plant water relations

“…In terms of promoting gas exchange and drought resistance, the symbiosis can allow leaves to maintain more normal water balance (closer to responses of unstressed controls) and fix more carbon during drought stress (Augé et al 1987a;Duan et al 1996). During drought, mycorrhizal symbiosis can alter osmotic and elastic properties in leaves (Augé et al 1986(Augé et al , 1987bGoicoechea et al 1997b) and roots (Augé and Stodola 1990), and accumulation of key solutes in leaves (Augé et al 1987a) and roots (Augé et al 1992b). Mycorrhizal plants often show physiological responses linked to increased drought resistance: e.g., the ability to maintain stomatal opening and hence carbon gain to lower soil water potential (Ψ) (Augé et al 1987a;Osonubi 1994;Duan et al 1996) and leaf Ψ (Allen and Allen 1986;Augé et al 1986) or water content (θ).…”

Growth, phosphorus uptake, and water relations of safflower and wheat infected with an arbuscular mycorrhizal fungus

“…One school of thought proposes that any similar in size and P status. They attribute these improvement of plant water relations by mycorrhizal efTects not mediated by P to improved osmotic infection is only a secondary effect of enhanced adjustment (Auge, Schekel & Wample, 1986a; Auge phosphorus nutrition, whilst another proposes that & Stodola, 1990), improved stomatal control (Auge, mycorrhizal infection can facilitate significant Schekel & Wample, 1986ft), and higher water uptake rates per unit root length (Kothari, Marschner & George 1990). …”

Influence of the ectomycorrhizas formed by Tuber melanosporum Vitt. on hydraulic conductance and water relations of Quercus ilex L. seedlings

“…Most studies of the hydraulic conductance of mycorrhizal roots have been performed in young seedlings, two to ten months of age and one to nine months after mycorrhizal inoculation [7,8,13,19]. In turn, ectomycorrhizae have been mainly studied in high altitude and/or latitude forest trees [12,29,35].…”