Phosphate Starvation Inducible Metabolism in Lycopersicon esculentum

Abstract

Three-day-old suspension cultured cells of Lycopersicon esculentum transferred to a Pi-depleted medium had 2.7 times the excreted acid phosphatase (Apase) activity of cells transferred to a Pi-sufficient medium. Cell growth during this time period was identical for the two treatments. Excreted Apase activity was resolved into two fractions on a Sephadex G-150 column. Most of the phosphate starvation inducible (psi) enhancement in activity was in the lower molecular weight fraction. These two fractions exhibited different substrate versus pH activity profiles. With a native polyacrylamide gel electrophoresis assay, the lower molecular weight fraction resolved into two bands of activity. Both column fractions resolved into the same single band of activity with sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The apparent molecular weight of this enzyme was 57 kilodalton. These data indicate that L. esculentum has at least two isozymes of the psi-excreted Apase and that these isozymes may associate to form high molecular weight aggregates. Labeling studies using [3SJmethionine show that the psi response in tomato cells is complex and involves changes in the steady state levels of several excreted proteins.Data from a number ofdifferent experimental systems indicate that plants have evolved starvation rescue systems composed of psi2 gene systems which effectively act to increase the concentration of exogenous Pi (9,21,24 Enzyme activity was mainly extracellular with the heaviest concentration in corner spaces between the epidermal and hypodermal layers. Based on the apparent intraspatial organization of regions of high activity, this worker proposed a specific secretory apparatus and further suggested the possibility of a subcutaneous pore through which the enzyme could be released to the root surface. Bieleski and Johnson (1) studied the psi induction and location ofApase in duckweed (S. oligorrhiza). They showed that Apase in control plants was located primarily in and around the vascular strands. In Pi-deficient plants, psi Apase activity was 10 to 20 times control with enzyme activity primarily located in the epidermis of the root and undersurface of the frond, the tissue locations most likely to be in contact with the external environment. They placed plants in solutions containing phosphatase substrates. Control plants hydrolyzed the substrates at 4 to 8% of the rates of tissue homogenates whereas Pi-deficient plants hydrolyzed substrate at 30 to 40% ofthe homogenate rate. When 32P-labeled glucose-l-phosphate was supplied to intact plants, more 32Pi appeared in the medium than in the tissue. The pattern of appearance was consistent with hydrolysis of substrate in the external apoplast followed by uptake into the cell.A number of other workers have found plant Apase activity either in the cell wall space or secreted by roots into the external medium. Oparka and Johnson (17) found Apase in the intercellular spaces of Nymphoides pelata. Hirata et al. (12) observed psi stimulation of excretion ...

Purification and properties of acid phosphatase secreted from lupin roots under phosphorus-deficiency conditions

“…2), and also few symptoms of phosphorus deficiency were noted in the plants in the --P treatment. These results indicate that lupin plants quickly responded to phosphorus deficiency and secreted acid phosphatase before their growth or metabolism was markedly disturbed, which supported the concept of a biochemical early warning system proposed by Goldstein et al (1988).…”

Induction of an Extracellular Cyclic Nucleotide Phosphodiesterase as an Accessory Ribonucleolytic Activity during Phosphate Starvation of Cultured Tomato Cells

“…A function of tomato extracellular cyclic nucleotide phosphodiesterase in RNA hydrolysis is also implied by its induction kinetics during cell culture growth, which are mirrored by induction kinetics of extracellular RNase LE (Nü rnberger et al, 1990;Kö ck et al, 1995Kö ck et al, , 1998 and extracellular acid phosphatase (Goldstein et al, 1988a(Goldstein et al, , 1988b. The data suggest co-regulated de novo synthesis and secretion of a set of Pi-starvation-inducible nucleolytic enzymes to rapidly mobilize Pi from RNA substrates under Pi-limiting conditions, which is observed for tomato cell cultures grown in ϩRNA/ϪPi medium.…”

“…Phosphorus starvation leads to an increased expression of Pi mobilizing enzymes and regulatory proteins such as nucleases, phosphatases, high-affinity Pi transporters, Pi-binding proteins, and Pi sensor protein kinases that monitor extracellular Pi availability (Oshima and Halvorson, 1994;Torriani-Gorini, 1994). In higher plants, the existence of an analogous multigene Pistarvation-inducible rescue system has been proposed (Goldstein et al, 1988a(Goldstein et al, , 1988b. However, evidence for a hypothetical plant pho regulon is fragmentary.…”

“…Induction of phosphoenolpyruvate phosphatase and pyrophosphate-dependent phosphofruc-tokinase in B. nigra cells has been proposed as a Pirecycling system that bypasses Pi-and adenylate-requiring steps in glycolysis, thus permitting carbon metabolism to proceed in Pi-starved cells (Duff et al, 1989;Theodorou et al, 1992). Pi starvation of tomato cell cultures leads to the co-regulated induction and secretion of extracellular acid phosphatase (Goldstein et al, 1988a(Goldstein et al, , 1988b and of extracellular and intracellular ribonucleases (Nü rnberger et al, 1990;Lö ffler et al, 1992).…”

Attenuation of Phosphate Starvation Responses by Phosphite in Arabidopsis

“…In vascular plants, the existence of an analogous multigene Pi starvation-inducible rescue system has been proposed (Goldstein et al, 1988), and several putative components of a plant pho regulon have been described. These include Pi starvation-inducible acid phosphatases with broad substrate specificity (Duff et al, 1994;del Pozo et al, 1999; Baldwin et al, 2001), phosphoenolpyruvate phosphatase and pyrophosphate-dependent phosphofructokinase (Theodorou and Plaxton, 1993), ribonucleases (Green, 1994), phosphodiesterases (Abel et al, 2000), Pi transporters (Raghothama, 2000), and several genes of unknown function (Liu et al, 1997; Burleigh and Harrison, 1999 Article, publication date, and citation information can be found at www.plantphysiol.org/cgi…”