@article{perera_love_heilmann_thompson_boss_2002, title={Up-regulation of phosphoinositide metabolism in tobacco cells constitutively expressing the human type I inositol polyphosphate 5-phosphatase}, volume={129}, ISSN={["1532-2548"]}, DOI={10.1104/pp.003426}, abstractNote={Abstract
               To evaluate the impact of suppressing inositol 1,4,5-trisphosphate (InsP3) in plants, tobacco (Nicotiana tabacum) cells were transformed with the human type I inositol polyphosphate 5-phosphatase (InsP 5-ptase), an enzyme which specifically hydrolyzes InsP3. The transgenic cell lines showed a 12- to 25-fold increase in InsP 5-ptase activity in vitro and a 60% to 80% reduction in basal InsP3 compared with wild-type cells. Stimulation with Mas-7, a synthetic analog of the wasp venom peptide mastoparan, resulted in an approximately 2-fold increase in InsP3 in both wild-type and transgenic cells. However, even with stimulation, InsP3 levels in the transgenic cells did not reach wild-type basal values, suggesting that InsP3 signaling is compromised. Analysis of whole-cell lipids indicated that phosphatidylinositol 4,5-bisphosphate (PtdInsP2), the lipid precursor of InsP3, was greatly reduced in the transgenic cells. In vitro assays of enzymes involved in PtdInsP2 metabolism showed that the activity of the PtdInsP2-hydrolyzing enzyme phospholipase C was not significantly altered in the transgenic cells. In contrast, the activity of the plasma membrane PtdInsP 5 kinase was increased by approximately 3-fold in the transgenic cells. In vivo labeling studies revealed a greater incorporation of 32P into PtdInsP2 in the transgenic cells compared with the wild type, indicating that the rate of PtdInsP2 synthesis was increased. These studies show that the constitutive expression of the human type I InsP 5-ptase in tobacco cells leads to an up-regulation of the phosphoinositide pathway and highlight the importance of PtdInsP2 synthesis as a regulatory step in this system.}, number={4}, journal={PLANT PHYSIOLOGY}, author={Perera, IY and Love, J and Heilmann, I and Thompson, WF and Boss, WF}, year={2002}, month={Aug}, pages={1795–1806} }
 @inproceedings{boss_perera_love_heilmann_2001, title={Altering phosphoinositide metabolism by expressing human type I inositol polyphosphate 5 ' phosphatase in tobacco cells}, volume={12}, number={2001 Nov}, booktitle={Molecular Biology of the Cell}, author={Boss, W. F. and Perera, I. Y. and Love, J. and Heilmann, I.}, year={2001}, pages={820} }
 @article{heilmann_perera_gross_boss_2001, title={Plasma membrane phosphatidylinositol 4,5-bisphosphate levels decrease with time in culture}, volume={126}, ISSN={["1532-2548"]}, DOI={10.1104/pp.126.4.1507}, abstractNote={Abstract
               During the stationary phase of growth, after 7 to 12 d in culture, the levels of phosphatidylinositol 4,5-bisphosphate (PtdInsP2) decreased by 75% in plasma membranes of the red alga Galdieria sulphuraria. Concomitant with the decrease in PtdInsP2 levels in plasma membranes, there was an increase in PtdInsP2 in microsomes, suggesting that the levels of plasma membrane PtdInsP2 are regulated differentially. The decline of PtdInsP2 in plasma membranes was accompanied by a 70% decrease in the specific activity of PtdInsP kinase and by reduced levels of protein cross-reacting with antisera against a conserved PtdInsP kinase domain. Upon osmotic stimulation, the loss of PtdInsP2from the plasma membrane increased from 10% in 7-d-old cells to 60% in 12-d-old cells, although the levels of inositol 1,4,5-trisphosphate (InsP3) produced in whole cells were roughly equal at both times. When cells with low plasma membrane PtdInsP2 levels were osmotically stimulated, a mild osmotic stress (12.5 mm KCl) activated PtdInsP kinase prior to InsP3 production, whereas in cells with high plasma membrane PtdInsP2, more severe stress (250 mm KCl) was required to induce an increase in PtdInsP kinase activity. The differential regulation of a plasma membrane signaling pool of PtdInsP2 is discussed with regard to the implications for understanding the responsive state of cells.}, number={4}, journal={PLANT PHYSIOLOGY}, author={Heilmann, I and Perera, IY and Gross, W and Boss, WF}, year={2001}, month={Aug}, pages={1507–1518} }
 @article{heilmann_shin_huang_perera_davies_2001, title={Transient dissociation of polyribosomes and concurrent recruitment of calreticulin and calmodulin transcripts in gravistimulated maize pulvini}, volume={127}, ISSN={["1532-2548"]}, DOI={10.1104/pp.127.3.1193}, abstractNote={In plants, sugars are the main respiratory substrates and important signaling molecules in the regulation of carbon metabolism. Sugar signaling studies suggested that sugar sensing involves several key components, among them hexokinase (HXK). Although the sensing mechanism of HXK is unknown, several experiments support the hypothesis that hexose phosphorylation is a determining factor. Glucose (Glc) analogs transported into cells but not phosphorylated are frequently used to test this hypothesis, among them 3-O-methyl-Glc (3-OMG). The aim of the present work was to investigate the effects and fate of 3-OMG in heterotrophic plant cells. Measurements of respiration rates, protein and metabolite contents, and protease activities and amounts showed that 3-OMG is not a respiratory substrate and does not contribute to biosynthesis. Proteolysis and lipolysis are induced in 3-OMG-fed maize (Zea mays L. cv DEA) roots in the same way as in sugar-starved organs. However, contrary to the generally accepted idea, phosphorous and carbon nuclear magnetic resonance experiments and enzymatic assays prove that 3-OMG is phosphorylated to 3-OMG-6-phosphate, which accumulates in the cells. Insofar as plant HXK is involved in sugar sensing, these findings are discussed on the basis of the kinetic properties because the catalytic efficiency of HXK isolated from maize root tips is five orders of magnitude lower for 3-OMG than for Glc and Man.}, number={3}, journal={PLANT PHYSIOLOGY}, author={Heilmann, I and Shin, J and Huang, J and Perera, IY and Davies, E}, year={2001}, month={Nov}, pages={1193–1203} }