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The involvement of ethylene in root architectural responses to phosphorus availability was investigated in common bean (Phaseolus vulgaris L.) plants grown with sufficient and deficient phosphorus. Although phosphorus deficiency reduced root mass and lateral root number, main root length was unchanged by phosphorus treatment. This resulted in decreased lateral root density in phosphorus-deficient plants. The possible involvement of ethylene in growth responses to phosphorus deficiency was investigated by inhibiting endogenous ethylene production with amino-ethoxyvinylglycine (AVG) and aerating the root system with various concentrations of ethylene. Phosphorus deficiency doubled the root-to-shoot ratio, an effect which was suppressed by AVG and partially restored by exogenous ethylene. AVG increased lateral root density in phosphorus- deficient plants but reduced it in phosphorus-sufficient plants. These responses could be reversed by exogenous ethylene, suggesting ethylene involvement in the regulation of main root extension and lateral root spacing. Phosphorus-deficient roots produced twice as much ethylene per g dry matter as phosphorus-sufficient roots. Enhanced ethylene production and altered ethylene sensitivity in phosphorus-deficient plants may be responsible for root responses to phosphorus deficiency. [ABSTRACT FROM AUTHOR]

Low phosphorus availability stimulates root hair clongation in many plants, which may have adaptive significance in soil phosphorus acquisition. We investigated the effect of low phosphorus on the elongation of Arabidopsis thaliana root hairs. Arabidopsis thaliana plants were grown in plant culture containing high (1000 munol m-3) or low (1 mmolm-3) phosphorus concentrations, and root hair clongation was analysed by image analysis. After 15 d of growth, low-phosphorus plants developed root hairs averaging 0.9mm in length while high-phosphorus plants of the same age developed root hairs averaging 0.3 mm in length. Increased root hair length in low-phosphorus plants was a result of both increased growth duration and increased growth rate. Root hair length decreased logarithmically in response to increasing phosphorus concentration. Local changes in phosphorus availability influenced root hair growth regardless of the phosphorus status of the plant. Low phosphorus stimulated root hair elongation in the hairless axr2 mutant, exogenously applied IAA stimulated root hair elongation in wild-type high-phosphorus plants and the auxin antagonist CMPA inhibited root hair clongation in low-phosphorus plants. These results indicate that auxin may be involved in the low-phosphorus response in root hairs. [ABSTRACT FROM AUTHOR]

Maintenance of realistically low solution P concentrations under controlled conditions is a major difficulty in studies of P nutrition. In this report, we describe a relatively simple and economical sand culture system capable of sustaining plant growth to maturity tinder controlled yet realistic P regimes. The system uses Al2O3 as a solid-phase P buffer, and modern process control technology to control irrigation and addition of other mineral nutrients. Aspects of the design, use and potential applications of automated solid-phase systems are discussed. The system was used to grow Phaseolus vulgaris to maturity at 0.4 mmol m-3, 1.0 mmol m-3 and 27 mmol m-3 P with and without mycorrhizal inoculation. At flowering, low solution P concentrations were associated with reduced leaf concentrations of P in nonmycorrhizal plants, and reduced leaf concentrations of Ca in both mycorrhizal and non-mycorrhizal plants. Mycorrhizal inculation increased leaf P, K, Mg and Mn concentrations, but reduced leaf N concentration. Low P regimes reduced final seed yield by diminishing both the number of pods per plant and the number of seeds per pod. Mycorrhizal inoculation significantly enhanced seed yield under low P regimes by increasing seed weight, the number of pods per plant, and the number of seeds per pod. [ABSTRACT FROM AUTHOR]

Soybean (Glycine max (L.) Merr) plants were grown under controlled conditions in an experiment designed as a 4 x 4 factorial. The factors were N or P nutrition, with different strains of Rhizobium japonicum or N-fertilization as levels of the first factor and different species of vesiculararbuscular mycorrhizal (VAM) fungi or P fertilization as levels of the other. Organisms used were R. japonicum strains USDA 110, USDA 136, and 61A118, and the VAM fungi Glomus versiforme (Karst.) Berch, Glomus fasciculatum (Thaxt. sensu Gerd.) Gerd. and Trappe, and Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe. There were 16 treatments: nine Rhizohium+Glomus combinations, three Rhizohium+P and three Glomus+N combinations, and one non-symbiotic set of plants supplied with N +P. The tripartite symbioses were evaluated by analysis of variance against the Rhizobium+P and Glomus+N comparison treatments for effects on root and leaf dry mass, root N and P content, nodule mass and activity, and VAM colinization. Significant to highly significant main effects and interactions were found in virtually ali evaluations due to both Rhizobium strain and VAM-fungal species. We conclude that different endophyte isolates affect not only the host plant, but also the development and function of their coendophytes. These findings establish the existence of inter-endophyte compatibility, an important consideration when selecting or engineering for desirable endophyte traits. [ABSTRACT FROM AUTHOR]