Phosphate starvation-inducible pyrophosphate-dependent phosphofructokinase occurs in plants whose roots do not form symbiotic associations with mycorrhizal fungi

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Abstract

Previously, we reported that phosphate (Pi) starvation of suspension cells or seedlings of Brassica nigra results in a large elevation in the activity of pyrophosphate-dependent phosphofructokinase (EC 2.7.1.90) (PFP). However, other researchers have found that Pi deprivation either causes a significant reduction or no change in extractable PFP activity of Catharanthus roseus suspension cells, or roots of Nicotiana tabacum and Phaseolis vulgaris seedlings. The present study was undertaken to examine the prevalence of Pi starvation-inducible PFP in seedlings, root cultures, or suspension cells of a variety of plant species differing in phylogenetic relatedness to B. nigra. In all species examined, fresh weights were decreased and acid phosphatase (EC 3.1.3.2) activities were increased by Pi limitation. Brassica napus suspension cells, Arabidopsis thaliana seedlings, and roots of B. napus, B. carinata, B. oleracea, Beta vulgaris, Fagopyrum esculentum, Sinapis alba, and S. arvensis seedlings grown with Pi-limited media contained 170–510% greater PFP activity than did nutrient-sufficient controls. In five of these species the induction of PFP activity by Pi limitation was based in part upon an increased susceptibility of the enzyme to its allosteric activator, fructose-2,6-bisphosphate. By contrast, the PFP activity in Pi-deprived Lycopersicon esculentum root cultures and Nicotiana silvestris suspension cells decreased by 45–65% relative to Pi-sufficient controls. Immunoblotting of extracts from A. thaliana seedlings, S. arvensis, F. esculentum and B. oleracea roots, and B. napus suspension cells probed with potato tuber PFP antibodies indicated that the upregulation of PFP activity by Pi stress in these species was not correlated with an alteration in the amount or subunit composition of PFP. Our findings suggest that induction of PFP during long-term Pi starvation may be characteristic of members of the Cruciferae, Chenopodiaceae and Polygonaceae families whose roots do not form symbiotic associations with mycorrhizal fungi.

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