A shift in sensitivity to auxin within development of maize seedlings.
The auxin-induced changes in cytosolic concentrations of Ca(2+) and H(+) ions were investigated in protoplasts from maize coleoptile cells at 3rd, 4th and 5th day of development of etiolated seedlings. The shifts in [Ca(2+)](cyt) and [H(+)](cyt) were detected by use of fluorescence microscopy in single protoplasts loaded with the tetra[acetoxymethyl]esters of the fluorescent calcium binding Fura 2, or pH-sensitive carboxyfluorescein, BCECF, respectively. Both the auxin-induced shifts in the ion concentrations were specific to the physiologically active synthetic auxin, naphthalene-1-acetic acid (1-NAA), and not to the non-active naphthalene-2-acetic acid (2-NAA). Regardless of the age of the seedlings, the rise in [Ca(2+)](cyt) was prior to the acidification in all investigated cases. The maximal acidification coincided with the highest amplitude of [Ca(2+)](cyt) change, but not directly depended on the concentration of 1-NAA. Within aging of the seedlings the amplitude of auxin-induced [Ca(2+)](cyt) elevation decreased. The shift in auxin-induced acidification was almost equal at 3rd and 4th day, but largely dropped at 5th day of development. The acidification was related to changes in the plasma membrane H(+)-ATPase activity, detected as phosphate release. The decrement in amplitude of both the tested auxin-triggered reactions well coincided with the end of the physiological function of the coleoptile. Hence the primary auxin-induced increase in [Ca(2+)](cyt), which is supposed to be an important element of hormone signal perception and transduction, can be used as a test for elucidation of plant cell sensitivity to auxin.
Shishova
Maria
M
Department of Plant Physiology and Biochemistry, St. Petersburg State University, 199034 St. Petersburg, Russia.
Yemelyanov
Vladislav
V
Rudashevskaya
Elena
E
Lindberg
Sylvia
S
D002118:Calcium; D018548:Cotyledon / Q000166:cytology; D003600:Cytosol; D004305:Dose-Response Relationship, Drug; D006859:Hydrogen; D006863:Hydrogen-Ion Concentration; D007210:Indoleacetic Acids / Q000494:pharmacology; D009280:Naphthaleneacetic Acids / Q000494:pharmacology*; D011523:Protoplasts; D036226:Seedlings / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development*; D003313:Zea mays / Q000166:cytology / Q000187:drug effects* / Q000254:growth & development*
D007210:Indoleacetic Acids; D009280:Naphthaleneacetic Acids; C034182:1-naphthaleneacetic acid; D006859:Hydrogen; D002118:Calcium