<i>myo</i>-Inositol: Its Biosynthesis and Metabolism

Loewus, and F A; Loewus, Mary W.

doi:10.1146/annurev.pp.34.060183.001033

Cited by 249 publications

(51 citation statements)

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“…1 and 4). This was further exemplified by the sustained response to IP6, which suggested continued metabolism of IP6 to an active isomer since phytases and other phosphatases are prevalent in plants (16). The response was not due to nonspecific binding of calcium by these compounds since neither IP3 nor IP6 affected the levels of the 45Ca2' associated with the saponin-treated protoplasts (data not shown).…”

Section: Discussionmentioning

confidence: 93%

myo-Inositol Trisphosphate Mobilizes Calcium from Fusogenic Carrot (Daucus carota L.) Protoplasts

Rincón¹,

Boss²

1987

Plant Physiol.

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(2,14,25). IP3 may be phosphorylated to form other inositol phosphates (19) or hydrolyzed in a 3-step dephosphorylation into inositol and Pi by specific phosphatases (3).Although very little is known about signal transduction in higher plant cells, calcium has become recognized as a key regulator of plant metabolism (11,12,18,23,26). It activates protein kinases (13), and plays a critical role in cell division (12), secretion (7), protoplast fusion (10), and tropic responses (22,23). All of these physiological responses appear to be preceded by an increase of cytosolic free Ca2' concentration, but it is not clear whether the increase in cytosolic Ca24 concentration is due to an increase in Ca2`influx across the plasma membrane or to an increase in Ca2' release from internal stores (i.e. ER, vacuole, or mitochondria) or both.There is evidence that the biosynthesis and metabolism of polyphosphoinositides occur in higher plant cells (6,20,24 MATERIALS AND METHODS Protoplast Isolation. Wild carrot cells (Daucus carota L.) which yield fusogenic protoplasts, were grown in suspension culture as described previously (4). Protoplasts were isolated by placing 0.3 g of cells in 20 ml solution containing 2% Driselase (Plenum Scientific Co., Hackensack, NJ), 0.4 molal sorbitol, 2 mM EGTA, and 1 mm Mes (pH 4.8) at 25°C on a rotary shaker (125 rpm) for 1.5 h for the 45Ca24 efflux experiments and for 2 h for the 45Ca2+ influx experiments. The protoplasts were centrifuged (40g) and the supernatant discarded. The recovered protoplasts were washed twice with an osmoticum solution consisting of 0.45 molal sorbitol and 0.5 mM Mes (pH 6).4"Ca2 Influx. For calcium influx experiments, protoplasts (1-2 mg protein/ml) were incubated in 8 ml osmoticum containing 45Ca2" (0.4 MCi/ml) to a final Ca2" concentration of approximately 1 uM. The protoplast suspension was placed on the rotary shaker (90 rpm) at 25°C. At intervals, 3 aliquots of 200 ,l were taken and protoplasts spun in a Beckman Microfuge B through a supporting and separating gradient formed, in order from the bottom, by 50 Ml of 5% dextran (mol wt = 17,900) in osmoticum, 50 ,ul silicone oil (p = 1.03), 50 ,l 2 mM EGTA in osmoticum, and 50 gl silicone oil (p = 1.01). The protoplast pellet was collected at the bottom of the microfuge tubes. The microfuge tips were cut and the protoplast pellet resuspended in 300 Ml deionized H20. Aliquots of 100,l ofthe resuspended protoplasts were dissolved in 7 ml Scintiverse-Il (Fisher

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Section: Discussionmentioning

confidence: 93%

myo-Inositol Trisphosphate Mobilizes Calcium from Fusogenic Carrot (Daucus carota L.) Protoplasts

Rincón¹,

Boss²

1987

Plant Physiol.

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“…A 30 min pretreatment with 50 I~M U-73122 caused a dramatic reduction in the response to 0.666 M mannitol from an average peak height of 1.45 IIM to 0.65 IIM (Figure 7b). Lithium chloride interrupts phosphoinositide cycling by inhibiting myoinositol-l-phosphatase (IMP) (Berridge and Irvine, 1984;Loewus and Loewus, 1982), the enzyme which dephosphorylates inositol 1-phosphate to yield free inositol, the substrate required for de novo production of IP 3 (Loewus and Loewus, 1983;Gillaspy eta/., 1995). Lithium affects a number of processes in animals by its inhibition of IMP.…”

Section: +mentioning

confidence: 99%

Calcium signalling in Arabidopsis thaliana responding to drought and salinity

1997

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SummaryChanges in cytosolic free calcium concentration ([Ca2+]cyt) in response to mannitol (drought) and salt treatments were detected in vivo in intact whole Arabidopsis seedlings.Transient elevations of [Ca2+]cyl to around 1.5 p,M were observed, and these were substantially inhibited by pretreatment with the calcium-channel blocker lanthanum and to a lesser extent, the calcium-chelator EGTA. The expression of three genes, p5cs, which encodes Al-pyrroline-5-carboxylate synthetase (P5CS), the first enzyme of the proline biosynthesis pathway, rab18 and Iti78 which both encode proteins of unknown function, was induced by mannitol and salt treatments. The induction of all three genes by mannitol was inhibited by pretreatment with lanthanum. Salt-induced p5cs, but not rab18 and Iti78, expression was also inhibited by lanthanum. Induction of pScs by mannitol was also inhibited by the calcium channel-blockers gadolinium and verapamil and the calcium chelator EGTA, further suggesting the involvement of calcium signalling in this response. Mannitol induced greater levels of pScs gene expression than an isoosmolar concentration of salt, at both relatively high and low concentrations. However, calcium transients were of a similar magnitude and duration in response to both mannitol and isoosmolar concentrations of salt, suggesting that a factor other than calcium is involved in the discrimination between drought and salinity signals in Arabidopsis. In order to gauge the involvement of the vacuole as an intracellular calcium store in the response of Arabidopsis to mannitol, [CaZ+]cyt was measured at the microdomain adjacent to the vacuolar membrane. The results obtained were consistent with a significant calcium release from the vacuole contributing to the overall mannitol-induced [Ca2+]cyt response. Data obtained by using inhibitors of inositol signalling suggested that this release was occurring through IP3-dependent calcium channels.

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“…In sycamore and poplar the activities of the UDP-glucuronate decarboxylase and UDP-glucose dehydrogenase also increased during differentiation and the decarboxylase activity is always higher than that of the dehydrogenase which is probably rate limiting (Dalessandro and Northcote,198 lb). However, the dehydrogenase step can be bypassed using a direct route from glucose viamyo-inositol to UDP-D-glucuronic acid (Loewus and Loewus, 1983). There is evidence for the coexistence of both pathways with changing importance of either route during plant development (Tenhaken and Thulke 1996).…”

Section: The Biosynthesis Of Xylansmentioning

confidence: 99%