ISSN:
1432-2048
Keywords:
Aleurone
;
Calcium transport
;
Endoplasmic reticulum (Ca2+ levels)
;
Gibberellin and Ca2+ transport
;
Golgi apparatus
;
Hordeum (Ca2+ transport)
;
Microsome
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract The steady-state levels of Ca2+ within the endoplasmic reticulum (ER) and the transport of 45Ca2+ into isolated ER of barley (Hordeum vulgare L. cv. Himalaya) aleurone layers were studied. The Ca2+-sensitive dye indo-1. Endoplasmic reticulum was isolated and purified from indo-1-loaded protoplasts, and the Ca2+ level in the ER was measured using the Ca2+-sensitive dye indo-1. Endoplasmic reticulum was isolated and purified from indo-1-loaded protoplasts, and the Ca2+ level in the lumen of the ER was determined by the fluorescence-ratio method to be at least 3 μM. Transport of 45Ca2+ into the ER was studied in microsomal fractions isolated from aleurone layers incubated in the presence and absence of gibberellic acid (GA3) and Ca2+. Isopycinic sucrose density gradient centrifugation of microsomal fractions isolated from aleurone layers or protoplasts separates ER from tonoplast and plasma membranes but not from the Golgi apparatus. Transport of 45Ca2+ occurs primarily in the microsomal fraction enriched in ER and Golgi. Using monensin and heat-shock treatments to discriminate between uptake into the ER and Golgi, we established that 45Ca2+ transport was into the ER. The sensitivity of 45Ca2+ transport to inhibitors and the Km of 45Ca2+ uptake for ATP and Ca2+ transport in the microsomal fraction of barley aleurone cells. The rate of 45Ca2+ transport is stimulated several-fold by treatment with GA3. This effect of GA3 is mediated principally by an effect on the activity of the Ca2+ transporter rather than on the amount of ER.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00391870
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