Arbuscular mycorrhizal inhibition of growth in barley cannot be attributed to extent of colonization, fungal phosphorus uptake or effects on expression of plant phosphate transporter genes

Abstract

Summary• Here, we used phosphorus-32 ( 32 P) labelling in compartmented pots combined with quantitative real-time polymerase chain reaction (PCR) analysis of phosphate (Pi) transporter gene expression to investigate regulation of Pi uptake pathways in barley (Hordeum vulgare), an arbuscular mycorrhizal (AM) plant that does not show strong positive growth responses to colonization.• Barley was colonized well by Glomus intraradices and poorly by Glomus geosporum, but both fungi induced significant and similar growth depressions compared with nonmycorrhizal controls. The lack of correlation between per cent colonization and extent of growth depression suggests that the latter is not related to carbon drain to the fungus • The contribution of the AM Pi uptake pathway for the two fungi was, in general, related to per cent colonization and expression of the AM-inducible Pi transporter gene, HvPT8, but not to plant responsiveness. Glomus intraradices contributed 48% of total plant P whereas G. geosporum contributed very little.• The growth depression in plants where the AM uptake pathway was functional suggests that the contribution of the direct Pi uptake pathway via root hairs and epidermis was decreased. This decrease was not correlated with downregulation of the epidermal-expressed Pi transporter genes, HvPT1 and HvPT2. We hypothesize post-transcriptional or post-translational control of this transport process by AM colonization.

Ecological relevance of strigolactones in nutrient uptake and other abiotic stresses, and in plant-microbe interactions below-ground

“…In general, AM symbiosis positively affects plant development and plant fitness, especially under unfavourable conditions. However, neutral or even negative effects on plant growth, attributed to P deprivation and an excessive carbon use by the AM fungus, have also been described (Grace et al 2009;Li et al 2008;Smith and Smith 2012). The negative plant response to AM colonisation has been proposed to be associated with the reduced P absorption capacity by the 'direct pathway' induced by the symbiosis and to a lower P uptake capacity by the AM fungus through the 'AM pathway' (Smith and Smith 2012).…”

“…Nowadays, due to the public concern about the side effects of these chemicals, there is increasing interest in finding alternatives for more environmentally friendly agriculture. AM symbiosis generally improves the growth of its host plant by facilitating water and mineral nutrient uptake, particularly under stress conditions, although negative effects have also been described, especially in cereals (Grace et al 2009;Li et al 2008). Moreover, AM fungi are widely distributed and can colonise most agricultural and horticultural crop species.…”

Effectiveness of native arbuscular mycorrhizal consortia on the growth of Agave inaequidens

“…On the other hand,the lack of a positive effect may be due to the species composition of the native consortia or to the inoculation of a particular AMF species, as well as the response with each host (Khade and Rodrigues, 2008;Camprubi et al, 2011). Smith and Smith (2012) suggest that the little or no effect of AMF on plant growth is due to a deficiency of phosphorus in the plants, owing to a reduction in the levels of uptake by the roots, which cannot be sufficiently offset by the low colonization percentage of the roots (Grace et al, 2009). This could be happening in the treatment without inoculation, where the lowest growth of agaves was observed.…”

Effects of arbuscular mycorrhizal fungi and Rhizobium on ion content and root characteristics of green bean and maize under intercropping

“…Fungi showed high solubilization of P with reduction in the pH of the medium. The reduction in the soil pH, increase in available P and organic carbon was greater in inoculated by fungi as compared to non-inoculated which may be attributed to ability of such microorganisms to excrete organic acids, thereby decrease the pH and increase the concentration of phosphorus in soil by mechanisms involving chelation and exchange reactions (Reyes et al, 2006).There are many reports stating that P absorption and availability would be increased in mycorrhizally inoculated plants (Martin et al, 2012;Grace et al, 2009). AMF colonization can significantly promote plant P uptake from the soil, so that other functions are often inextricably linked with the improvement of P nutrition status (Cozzolino et al, 2010).…”