PLANT PHYSIOLOGY , Vol 101, Issue 1 147-160, Copyright © 1993 by American Society of Plant Biologists
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PLANT-MICROBE INTERACTIONS |
Influence of Vesicular-Arbuscular Mycorrhizal Fungi on the Response of Potato to Phosphorus Deficiency
DAJ. McArthur and N. R. Knowles
Department of Plant Science, 4-10 Agriculture/Forestry Center, University of Alberta, Edmonton, Alberta, Canada T6G 2P5
Morphological and biochemical interactions between a vesicular-arbuscular
mycorrhizal (VAM) fungus (Glomus fasciculatum [Thaxt. sensu Gerdemann]
Gerdemann 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 vanadate-sensitive 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 level for P-stressed 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 NM 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 NM
roots. Morphological and ultrastructural details of VAM plants are
discussed in relation to the influence of the VAM symbiosis on P nutrition
of potato.
