In mycorrhizal symbioses, susceptibility of a host plant to infection by fungi is influenced by environmental factors, especially the availability of soil phosphorus. This study describes morphological and biochemical details of interactions between a vesicular-arbuscular mycorrhizal (VAM) fungus and potato (Solanum tuberosum L. cv Russet Burbank) plants, with a particular focus on the physiological basis for P-induced resistance of roots to infection. Root infection by the VAM fungus Glomus fasciculatum ([Thaxt. sensu Gerdemann] Gerdemann and Trappe) was extensive for plants grown with low abiotic P supply, and plant biomass accumulation was enhanced by the symbiosis. The capacity of excised roots from P-deficient plants to produce ethylene in the presence or absence of exogenous 1-amino cyclopropane-1-carboxylic acid (ACC) was markedly reduced by VAM infection. This apparent inhibition of ACC oxidase (ACCOX) activity was localized to areas containing infected roots, as demonstrated in split-root studies. Furthermore, leachate from VAM roots contained a potent water-soluble inhibitor of ethylene generation from exogenous ACC by nonmycorrhizal (NM) roots. The leachate from VAM-infected roots had a higher concentration of phenolics, relative to that from NM roots. Moreover, the rates of ethylene formation and phenolic concentration in leachates from VAM roots were inversely correlated, suggesting that this inhibitor may be of a phenolic nature. The specific activity of extracellular peroxidase recovered in root leachates was not stimulated by VAM infection, although activity on a fresh weight basis was significantly enhanced, reflecting the fact that VAM roots had higher protein content than NM roots. Polyphenol oxidase activity of roots did not differ between NM and VAM roots. These results characterize the low resistance response of P-deficient plants to VAM infection. When plants were grown with higher abiotic P supply, the relative benefit of the VAM symbiosis to plant growth decreased and root infection was lower. The in vivo ACCOX activity was also greater in roots of plants grown on high levels of P compared with those grown on low levels, although the influence of VAM infection was partially to counteract the nutritional effect of P on ACCOX activity. Similar to ACCOX activity, extracellular peroxidase activity of roots increased linearly with increasing abiotic P supply, thus indicating a greater potential for resistance to VAM infection. These findings suggest that VAM fungi may alter phenolic metabolism of roots so as to hinder ethylene production and the root's ability to invoke a defense response. Raising the abiotic P supply to plants at least partially restores the capacity of roots to produce ethylene and may, in this way, increase the root's resistance to VAM infection. The VAM2 fungi are a small and distinct group of obligate, symbiotic fungi that are capable of association with roots of most terrestrial vascular plants (20). In exchange for photoassimilates, VAM fungi contribute to t...
Morphological and biochemical interactions between a vesicular-arbuscular mycorrhizal (VAM) fungus (Glomus fasciculatum [Thaxt. sensu Cerdemann] Cerdemann and Trappe) and potato (Solanum tuberosum L.) plants during the development of P deficiency were characterized. Nonmycorrhizal (NM) plants grown for 63 d with low abiotic P supply (0.5 mM) produced 34, 52, and 73% less root, shoot, and tuber dry matter, respectively, than plants grown with high P (2.5 mM). The total leaf area and the leaf area:plant dry weight ratio of low-P plants were substantially lower than those of high-P plants. Moreover, a lower shoot:root dry weight ratio and tuber:plant dry weight ratio in low-P plants than in high-P plants characterized a major effect of P deficiency stress on dry matter partitioning. In addition to a slower rate of growth, low-P plants accumulated nonreducing sugars and nitrate. Furthermore, root respiration and leaf nitrate reductase activity were lower in low-P plants than in high-P plants. Low abiotic P supply also induced physiological changes that contributed to the greater efficiency of P acquisition by low-P plants than by high-P plants. For example, allocation of dry matter and P to root growth was less restricted by P deficiency stress than to shoot and tuber growth. Also, the specific activities of root acid phosphatases and vanadatesensitive microsomal ATPases were enhanced in P-deficient plants. The establishment of a VAM symbiosis by low-P plants was essential for efficient P acquisition, and a greater root infection leve1 for Pstressed plants indicated increased compatibility to the VAM fungus. By 63 d after planting, low-P VAM plants had recovered 42% more of the available soil P than low-P N M plants. However, the VAM fungus only partially alleviated P deficiency stress and did not completely compensate for inadequate abiotic P supply. Although the specific activities of acid phosphatases and microsomal ATPases were only marginally influenced by VAM infection, VAM roots characteristically had a higher protein concentration and, consequently, enhanced microsomal ATPase and acid phosphatase activities on a fresh weight basis compared with N M roots. Morphological and ultrastructural details of VAM plants are discussed i n relation to the influence of the VAM symbiosis on P nutrition of potato.Second only to N, P is the mineral nutrient for which availability is most likely limiting to plant growth. The concentration of P in the soil solution is in the micromolar range, and moreover, this element diffuses slowly in soils. Hence, depletion of P in the root zone commonly limits further
Crowth, development, and mineral physiology of potato (Solanum tuberosum l.) plants in response to infection by three species of vesicular-arbuscular mycorrhizal (VAM) fungi and different levels of P nutrition were characterized. P deficiency in no-P and low-P (0.5 mM) nonmycorrhizal plants developed between 28 and 84 d after planting. By 84 d after planting, P deficiency decreased plant relative growth rate such that no-P and low-P plants had, respectively, 65 and 45% less dry mass and 76 and 55% less total P than plants grown with high P (2.5 mM). A severe reduction in leaf area was also evident, because P deficiency induced a restriction of lateral bud growth and leaf expansion and, also, decreased the relative plant allocation of dry matter to leaf growth. Root growth was less influenced by P deficiency than either leaf or stem growth. Moreover, P-deficient plants accumulated a higher proportion of total available P than high-P plants, indicating that P stress had enhanced root efficiency of P acquisition. Plant P deficiency did not alter the shoot concentration of N, K, Mg, or Fe; however, the total accumulation of these mineral nutrients in shoots of P-stressed plants was substantially less than that of high-P plants. P uptake by roots was enhanced by each of the VAM symbionts by 56 d after planting and at all levels of abiotic P supply. Species differed in their ability to colonize roots and similarly to produce a plant growth response. In this regard, Glomus intraradices (Schenck and Smith) enhanced plant growth the most, whereas Glomus dimorphicum (Boyetchko and Tewari) was least effective, and Glomus mosseae ([Nicol. and Cerd.] Cerd. and lrappe) produced an intermediate growth response. l h e partia1 alleviation of P deficiency in no-P and low-P plants by VAM fungi stimulated uptake of N, K, Mg, Fe, and Zn. VAM fungi enhanced shoot concentrations of P, N, and Mg by 28 d after planting and, through a general improvement of overall plant mineral nutrition, promoted plant growth and development.
Consumer wine preferences are not well understood. Anecdotally it is believed that preferences evolve over time, from sweet whites to full-bodied reds, as consumers become more experienced and familiar with wine. However, little is known about the change in wine preference or confidence with education and training. This research explored changes in consumers' hedonic and confidence ratings for five commercial British Columbian (BC) wines (Ehrenfelser, Chardonnay, rosé, Pinot noir, Cabernet-Merlot) over a 12-week education/training period. Consumers (n = 133) completed a wine survey and evaluated the wines during the first and twelfth week of a university wine course, consisting of wine education and sensory training. Consumers provided hedonic (degree-of-liking) and confidence (degree-of-sureness) ratings for the visual, aroma and flavor characteristics of the wines, on 9-point and 5-point scales, respectively, before and after the 12-week wine course. Consumers were classified by gender (female, male), age and ethnicity. Kruskal Wallis, Mann-Whitney, Friedman, Wilcoxon Signed Rank and Chi-square tests and Spearman correlation coefficients were used to explore the effects of education/training on hedonic and confidence ratings. In general, consumers' hedonic (visual, aroma, flavor) ratings increased significantly with education/training for the white and rosé wines (Ehrenfelser, Chardonnay, rosé) over the 12-week period. In contrast, consumer confidence increased substantially for all wine types. Surveys revealed, for the three largest subgroups of consumers (North American (NA), n = 38; European (EU), n = 31; Asian, n = 54), that NA and EU consumers had significantly higher frequency-of-purchase, frequency-of-purchase of Canadian wine, frequency-of-consumption and self-rated wine knowledge than Asian consumers. However, Asian consumers were willing to pay more for a bottle of wine compared to NA and EU consumers. This research provided insight into the millennial consumers and explored the nature and magnitude of changes in hedonic and confidence ratings with wine education/training.
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