Ricinus communis L. plants were grown in nutrient solutions in which N was supplied as N03-or NH4', the solutions being maintained at pH 5.5. In N03--fed plants excess nutrient anion over cation uptake was equivalent to net OH-efflux, and the total charge from N03-and S042-reduction equated to the sum of organic anion accumulation plus net OHefflux. In NH4+-fed plants a large H+ eMux was recorded in close agreement with excess cation over anion uptake. This H + efMux equated to the sum of net cation (NH4+ minus SO42-) assimilation plus organic anion accumulation. In vivo nitrate reductase assays revealed that the roots may have the capacity to reduce just under half of the total NO3-that is taken up and reduced in NO3--fed plants. Organic anion concentration in these plants was much higher in the shoots than in the roots. In NH4+-fed plants absorbed NH4+ was almost exclusively assimilated in the roots. These plants were considerably lower in organic anions than NO3--fed plants, but had equal concentrations in shoots and roots. Xylem and phloem saps were collected from plants exposed to both N sources and analyzed for all major contributing ionic and nitrogenous compounds. The results obtained were used to assist in interpreting the ion uptake, assimilation, and accumulation data in terms of shoot/root pH regulation and cycling of nuttients.It is well recognized that the pH of plant cells and of organelles is under strict biochemical control, with pH restricted to a narrow physiological range (26,29,33 The accumulation or degradation of organic acid anions in response to differential rates of cation or anion uptake by plant roots from simple non nitrogen containing salts, e.g. K2SO4 or CaCl2 is a reflection of this process of intracellular pH regulation. Excess cation uptake is associated with a corresponding net release of H+ into the medium, and thus an increase in cellular OH-which induces organic acid anion accumulation, especially malate, equivalent to the excess uptake of cations. The reverse is the case when anion uptake is greater than cation uptake (14,18).The forms of N uptake and N assimilation are of especial importance in the formation of intracellular H + and OH -. In the case of cells supplied with NO3--N, the reduction of one NO3-results in the production of one OH-(21, 26).NO3-+ 8H+ + 8e > NH3 + 2H20 + OHThe same kind of reaction occurs when SO42-is reduced but is of less quantitative significance in charge transfer since much less S042-is assimilated than NO3-per unit of plant dry or fresh weight.S042-+ 8H+ + 8e-SH2 + 2H20 + 20H-When NH4 + is the N source, assimilation leads to H + production. NH4+ -* NH3 + H+This extreme difference in behavior between NO3-and NH4+ assimilation in intracellular OH-or H + production accounts for the well known observation that concentrations of organic acid anions are almost always higher in NO3 --than in NH4 + -fed plants (1,4,15). In the removal of H+ or OH-from the cell to the external medium associated with these two forms of N uptake and assimilation...
Effects of vesicular-arbuscular mycorrhizal (VAM) infection and P on root respiration and dry matter allocation were studied in Plantago major L. ssp. pleiosperma (Pilger). By applying P, the relative growth rate of non-VAM controls and plants colonized by Glomus fasciculatum (Thaxt. sensu Gerdemann) Gerdemann and Trappe was increased to a similar extent (55-67%). However, leaf area ratio was increased more and net assimilation rate per unit leaf area was increased less by VAM infection than by P addition. The lower net assimilation rate could be related to a 20 to 30% higher root respiration rate per unit leaf area of VAM plants. Root respiration per unit dry matter and specific net uptake rates of N and P were increased more by VAM infection than by P addition. Neither the contribution of the altemative respiratory path nor the relative growth rate could account for the differences in root respiration rate between VAM and non-VAM plants. It was estimated that increased fungal respiration (87%) and ion uptake rate (13%) contributed to the higher respiratory activity of VAM roots of P. major. photosynthesis or respiration, such as light intensity (3), P status (15), ontogeny of the host plant (24), and/or the presence of other symbionts (2, 4).To sort out confounding nutritional and ontogenetic effects of VAM infection, both split-root systems (11, 16) and Pfertilized controls with equal dry weight (2,14,21, 27) (11,16,18,22, 27). Hence, the objective of the present study was to analyze the effect of VAM infection on root respiration and dry matter allocation in VAM and non-VAM P. major plants having equal RGR.
Effects of vesicular-arbuscular mycorrhizal infection and phosphate on Plantago major ssp. pleiosperma in relation to internal cytokinin concentrations. -Physiol. Plant. 76: 211-215.Relations between cytokinin concentrations and effects of P and vesieular-arbuscular mycorrhizal (VAM) infection were investigated in Plantago major L. ssp. pleiosperma Pilger. Both mycorrhizal infection by Glomus fasciculatum (Thaxt. sensu Gerdemann) Gerdemann and Trappe and P addition increased the shoot to root ratio, specific leaf area (SLA), and P concentrations of shoot and roots, and decreased the percentage of dry matter in the shoot during the experiment. In general, P concentration in the shoot and roots of each treatment correlated positively with the shoot to root ratio and specific leaf area, and negatively with the pereentage of dry matter in the shoot. Cytokinin concentrations in the tissue of shoots and roots were determined using an enzyme-linked immunosorbent assay. Concentrations of zeatin and zeatinribosides in the free base and nucleotide fractions had increased more after P addition than in the case of mycorrhizal infection in both shoot and roots, whereas the P concentrations had increased less. It is suggested that zeatin and zeatin-ribosides are not the primary growth-substances involved in mediating VAM effects.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.