Root Exudation in Relation to Supply of Phosphorus and Its Possible Relevance to Mycorrhizal Formation

Ratnayake, M.P.K.; Leonard, Robert T.; Menge, J. A.

doi:10.1111/j.1469-8137.1978.tb01627.x

Cited by 298 publications

(149 citation statements)

References 23 publications

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“…from cortical cells and subsequent transport into the xylem. This idea is consistent with reports that P deficiency increases solute leakage into the external medium (9,22). However, P nutrition did not greatly alter the electrical conductivity of collected exudate, which itself displayed hysteresis even when volume flow did not (Fig.…”

Section: Resultssupporting

confidence: 82%

Hydraulic Conductance as a Factor Limiting Leaf Expansion of Phosphorus-Deficient Cotton Plants

Radin¹,

Eidenbock²

1984

Plant Physiol.

221

115

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ABSITRACT Suboptimnal levels of phospborus (P) strongly inhibited leaf expansion in young cotton (Gousypium hirstum L.) plants during the daytime, but had little effect at night. The effect of P was primarily on cell expansion. Compaed to plants grown on high P, plants grown on low P had lower leaf water potentials and transpiration rates, and greater diurnal fluctuations in leaf water potential. Hydraulic conductances of excised root systems and of intact transpiring plants were determined from curves relating water flow rate per unit root length to the pressue differential across the roots. Both techniques showed that low P significantly decreased root hydraulic conductance. The effects of P nutrtion on hydraulic conductance preceded effects on leaf area. Differences in total root length, shoot dry weight, and root dry weight all occurred well after the onset of differences in kaf expansion. The data strongly inicate that low P limits leaf expansion by decreasing the hydraulic conductance of the root system.In dicotyledonous plants, growth on suboptimal levels of N is characterized by a specific inhibition of leaf expansion (18)(19)(20). Low N decreases plant hydraulic conductance, thereby lowering the leaf O.' during the daytime when transpiration generates large fluxes of water (18,19). This increased water deficit, in turn, inhibits leaf expansion (18,19). One consequence of this alteration is an increased root: shoot ratio (21). Low P also decreases hydraulic conductance (17, 23) and increases the root:shoot ratio (4, 13). These parallels between effects of N and of P suggest that hydraulic conductance may limit growth in Pdeficient plants as it does in N-deficient plants. Here we present evidence that effects of P nutrition on hydraulic conductance determine its effects on growth of cotton plants.MATERIALS AND METHODS Plant Growth Conditions. Cotton (Gossypium hirsutum L. cv Deltapine 70) plants were grown in a growth chamber. In early experiments, plants were grown in 14-L pots containing sand.The pots were watered three times weekly with a modified halfstrength Hoagland solution containing either 0.5 mM Pi as KH2PO4 (normal P) or 0.5, 0.25, 0.125, 0.0625, or 0 x normal P levels. In later experiments, plants were grown in liquid nutrient solution. Seeds Cell size in the upper epidermis of a leaf was determined by spraying an acrylic resin on the surface, peeling it offafter drying, and using its negative image of the surface for cell counts under a microscope (20

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Section: Resultssupporting

confidence: 82%

Hydraulic Conductance as a Factor Limiting Leaf Expansion of Phosphorus-Deficient Cotton Plants

Radin¹,

Eidenbock²

1984

Plant Physiol.

221

115

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“…Increased levels of PEPC in Pi-limited plants has been linked to enhanced synthesis and excretion of organic acids that increase Pi concentration in the soil solution (reviewed in Plaxton and Tran 2011). Interestingly, a decrease in phospholipid levels in phosphatestarved roots has been correlated with an increase in permeability of root membranes (Ratnayake et al 1978). As this led to a greater leakage of amino acids and reducing sugars and increased mycorrhizal infection, Graham et al (1981) proposed a membrane-mediated decrease in root exudation might be responsible for Pi inhibition of mycorrhiza formation.…”

Section: Am-responsive Proteins As Related To Interface Biogenesis Anmentioning

confidence: 99%

The plasma membrane proteome of Medicago truncatula roots as modified by arbuscular mycorrhizal symbiosis

Aloui¹,

Recorbet²,

Lemaître‐Guillier³

et al. 2017

Mycorrhiza

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In arbuscular mycorrhizal (AM) roots, the plasma membrane (PM) of the host plant is involved in all developmental stages of the symbiotic interaction, from initial recognition to intracellular accommodation of intra-radical hyphae and arbuscules. Although the role of the PM as the agent for cellular morphogenesis and nutrient exchange is especially accentuated in endosymbiosis, very little is known regarding the PM protein composition of mycorrhizal roots. To obtain a global overview at the proteome level of the host PM proteins as modified by symbiosis, we performed a comparative protein profiling of PM fractions from Medicago truncatula roots either inoculated or not with the AM fungus Rhizophagus irregularis. PM proteins were isolated from root microsomes using an optimized discontinuous sucrose gradient; their subsequent analysis by liquid chromatography followed by mass spectrometry (MS) identified 674 proteins. Cross-species sequence homology searches combined with MS-based quantification clearly confirmed enrichment in PM-associated proteins and depletion of major microsomal contaminants. Changes in protein amounts between the PM proteomes of mycorrhizal and non-mycorrhizal roots were monitored further by spectral counting. This workflow identified a set of 82 mycorrhiza-responsive proteins that provided insights into the plant PM response to mycorrhizal symbiosis. Among them, the association of one third of the mycorrhiza-responsive proteins with detergent-resistant membranes pointed at partitioning to PM microdomains. The PM-associated proteins responsive to mycorrhization also supported host plant control of sugar uptake to limit fungal colonization, and lipid turnover events in the PM fraction of symbiotic roots. Because of the depletion upon symbiosis of proteins mediating the replacement of phospholipids by phosphorus-free lipids in the plasmalemma, we propose a role of phosphate nutrition in the PM composition of mycorrhizal roots.

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“…This procedure was repeated five times for pre-VAM harvest and three tiues for YAM harvest. membrane permeability were performed according to Ratnayake et al (12), with minor modifications. Briefly, 2-g samples of roots from each treatment were cut into 2-cm segments and incubated for 3 h in a 0.25 mm KCl solution labeled with 86Rb (100,000 cpm/ pmol K+) with the addition of 0.5 mm CaCl2.…”

Section: Methodsmentioning

confidence: 99%

“…Ratnayake et al (12) proposed that the mechanism of P control of VAM formation was associated with a membrane-mediated decrease in root exudation. They were able to correlate low P content of sudangrass and citrus roots with a decrease in phospholipid levels and a large increase in permeability of root membranes, which results in a greater net leakage of amino acids and sugars from the root.…”

mentioning

confidence: 99%

Membrane-Mediated Decrease in Root Exudation Responsible for Phorphorus Inhibition of Vesicular-Arbuscular Mycorrhiza Formation

Graham¹,

Leonard²,

Menge³

1981

Plant Physiol.

436

204

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The mechanism responsible for phosphorus inhibition of vesicular-arbuscular mycorrhiza formation in sudangrass (Sorghum vulgare Pers.) was investigated in a phosphorus-deficient sandy soil (0.5 micrograms phosphorus per gram soil) amended with increasing levels of phosphorus as superphosphate (0, 28, 56, 228 micrograms per gram soil). The root phosphorus content of 4-week-old plants was correlated with the amount of phosphorus added to the soil. Root exudation of amino acids and reducing sugars was greater for plants grown in phosphorus-deficient soil than for those grown in the phosphorus-treated soils. The increase in exudation corresponded with changes in membrane permeability of phosphorus-deflcient roots, as measured by K' (86Rb) efflux, rather than with changes in root content of reducing sugars and amino acids. The roots of phosphorus-deficient plants inoculated at 4 weeks with Glomusfascicuaww were 88% infected after 9 weeks as compared to less than 25% infection in phosphorus-sufficient roots; these differences were correlated with root exudation at the time of inoculation. For plants grown in phosphorusdeficient soil, infection by vesicular-arbuscular mycorrhizae increased root phosphorus which resulted in a decrease in root membrane permeability and exudation compared to nonmycorrhizal plants. It is proposed that, under low phosphorus nutrition, increased root membrane permeability leads to net loss of metaboiltes at sufficient levels to sustain the germination and growth of the mycorrhizal fungus during pre-and postinfection. Subsequently, mycorrhizal infection leads to improvement of root phosphorus nutrition and a reduction in membrane-mediated loss of root metabolites.During the past 20 years, there has been a growing appreciation of the importance of VAM' in the improvement of plant growth through increased uptake of phosphorus (P) and other mineral nutrients, especially in soils of low fertility (5, 9). As evidence has mounted for the role of VAM in the enhancement of P uptake from P-deficient soils, it has also been recognized that high soil P levels severely limit VAM infection (9, 10).Early work failed to distinguish whether P was inhibiting the activity of the mycorrhizal fungus in the soil or during the hostfungus interaction (10,16 of sudangrass inoculated with Glomusfasciculatus (Thaxt.) Gerd. and Trappe only became heavily infected if the host was not receiving adequate P from the other half of the root system. It is now clear that the P content of the host plant is the critical factor controlling the mycorrhizal symbiosis.Ratnayake et al. (12) proposed that the mechanism of P control of VAM formation was associated with a membrane-mediated decrease in root exudation. They were able to correlate low P content of sudangrass and citrus roots with a decrease in phospholipid levels and a large increase in permeability of root membranes, which results in a greater net leakage of amino acids and sugars from the root. They suggested that under P-sufficient conditions, metabolites requi...

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Root Exudation in Relation to Supply of Phosphorus and Its Possible Relevance to Mycorrhizal Formation

Cited by 298 publications

References 23 publications

Hydraulic Conductance as a Factor Limiting Leaf Expansion of Phosphorus-Deficient Cotton Plants

Hydraulic Conductance as a Factor Limiting Leaf Expansion of Phosphorus-Deficient Cotton Plants

The plasma membrane proteome of Medicago truncatula roots as modified by arbuscular mycorrhizal symbiosis

Membrane-Mediated Decrease in Root Exudation Responsible for Phorphorus Inhibition of Vesicular-Arbuscular Mycorrhiza Formation

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