| Growth, development, and physiology of potato (Solanum tuberosum L.) plants in response to P nutrition and during interactions with four species of vesicular-arbuscular mycorrhizal (VAM) fungi (Glomus spp.) were investigated. Leaf area development and plant growth were significantly decreased by P deficiency. The extent to which tuber growth was limited by P deficiency depended upon the timing of tuber initiation. P-deficient plants had enhanced levels of non reducing sugars and nitrate, possibly as a result of low rates of root respiration and leaf nitrate reductase activity. The accumulation of mineral nutrients was much less for low-P plants than for high-P plants, indicating a restricted capacity for nutrient uptake. The specific activities of root acid phosphatases and vanadate-sensitive microsomal ATPases were enhanced in P-deficient plants. The establishment of a VAM symbiosis by low-P plants significantly contributed to plant P acquisition, and a greater level of root infection for P-stressed plants indicated enhanced plant compatibility to VAM fungi.;The protein content and microsomal ATPase activity of roots on a fresh weight basis were significantly increased by VAM infection. In contrast, the capacity of excised roots to produce ethylene was markedly decreased by VAM infection. Furthermore, leachate from VAM roots contained a potent water-soluble inhibitor of ethylene generation. As the specific activities of extracellular peroxidase and polyphenol oxidase were unaffected by VAM infection, these results characterize the low resistance response of P-deficient plants to VAM infection. High-P plants showed less of a growth response to VAM infection and had a low level of root infection, indicating high-P plants as less compatible with VAM fungi. In support of this, both ethylene production and extracellular peroxidase activity of roots increased linearly with abiotic P supply, thus indicating a greater potential for resistance to VAM infection. |
