Mastoparan-Induced Intracellular Ca2+ Fluxes May Regulate Cell-to-Cell Communication in Plants

Abstract

The relationship of CaZ+ and plasmodesmatal closure was examined in staminal hairs of Setcreasea purpurea by microinjecting cells with active mastoparan (Mas-7), inactive mastoparan (Mas-1 7), active inositol-1,4,5-trisphosphate (IP,), or inactive I P, . Calcium green dextran 10,000 was used to study cellular free Caz+, and carboxyfluorescein was used to monitor plasmodesmatal closure.When Mas-7 was microinjected into the cytoplasm of cell 1 (the tip cell of a chain of cells), a rapid increase i n calcium green dextran-10,000 fluorescence was observed in the cytoplasmic areas on both sides of the plasmodesmata connecting cells 1 and 2 during the same time that the diffusion of carboxyfluorescein through them was blocked. The inhibition of cell-to-cell diffusion was transient, and the closed plasmodesmata reopened within 30 s. The elevated Ca2+ level near plasmodesmata was also transient and returned t o base level in about 1.5 min. The transient increase in CaZ+, once initiated in cell 1, repeated with an oscillatory period of 3 min. Elevated Caz+ and oscillations of Caz+ were also observed near interconnecting cell walls throughout the chain of cells, indicating that the signal had been transmitted. Previously, we reported that IP, closed plasmodesmata; now we report that it stimulated Ca2+ and oscillations similar to Mas-7. The effect was specific for similar concentrations of Mas-7 over Mas-1 7 and active IP, over inactive IP,. It is important that the Ca2+ channel blocker La3+ eliminated the responses from Mas-7 and I P, , indicating that an influx of Ca2+ was required. These results support the contention that plasmodesmata functioning is regulated via Ca2+ and that IP, may be an intermediary between the stimulus and CaZ+ elevations.

Blue light-induced kinetics of H + and Ca 2+ fluxes in etiolated wild-type and phototropin-mutant Arabidopsis seedlings

“…Such changes may play some regulatory role. There is growing evidence that Ca 2ϩ waves often spread across large groups of similar contiguous cells (38)(39)(40)(41). The reported speed range of 1-25 m⅐s Ϫ1 (38) is also consistent with our observations (Fig.…”

“…4). Such Ca 2ϩ waves are believed to be crucial for the growth of pollen tubes (42) or root hairs (43) and for coordination of physiological processes between spatially separated plant tissues (39). A Ca 2ϩ wave in staminal hairs of Setcreasea may spread from one cell to another through plasmodesmata, with a speed of about 10 m͞sec (42).…”

Increasing Plasma Membrane Phosphatidylinositol(4,5)Bisphosphate Biosynthesis Increases Phosphoinositide Metabolism inNicotiana tabacum

“…Taken together, the data indicate that when stimuli induce an increase in the PI pathway in plants, there will be an increased demand for ATP as the system responds and then recovers the PI pools to a prestimulated state. If Ins(1,4,5)P 3 increases cytosolic calcium in plants as predicted based on early microinjection experiments (Gilroy et al, 1990;Tucker and Boss, 1996), then there must be a continuous and rapid transport of Ca 2þ out of the cells or into intracellular stores to retain homeostasis in the Hs PIPKIa lines. We observed an increase in ER calcium binding proteins, CRT and BiP, in the Hs PIPKIa lines, indicating that the ER is sensing a change in calcium homeostasis.…”

Measurement of Ca2+ Fluxes during Elicitation of the Oxidative Burst in Aequorin-transformed Tobacco Cells

“…Ca 2ϩ is already believed to serve as a second messenger in such important plant processes as stomatal closure (27,28), geotropism (29), control of circadian rhythms (30), pollen tube elongation (31,32), regulation of plasmadesmata aperture (33), response to physical stress (34), and phytochrome phototransduction (35). Nevertheless, its accurate quantitation during cellular signaling events has until recently proven very difficult.…”