PLANT PHYSIOLOGY , Vol 115, Issue 1 51-60, Copyright © 1997 by American Society of Plant Biologists
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CELL BIOLOGY AND SIGNAL TRANSDUCTION |
Increases in Cytosolic Ca2+ in Parsley Mesophyll Cells Correlate with Leaf Senescence
F. Y. Huang, S. Philosoph-Hadas, S. Meir, D. A. Callaham, R. Sabato, A. Zelcer and P. K. Hepler
Department of Biology, University of Massachusetts, Amherst, Massachusetts, 01003 (F.-Y.H., D.A.C., P.K.H.)
The ability to maintain the cytoplasmic Ca2+ concentration ([Ca2+]cyt) at
homeostatic levels has been examined during leaf senescence in detached
parsley (Petroselinum crispum) leaves. Fluorescence ratiometric imaging of
mesophyll cells isolated from parsley leaves at various senescence stages
and loaded with the Ca2+ indicator fura-2 has revealed a distinct elevation
of [Ca2+]cyt, which was positively correlated with the progress of leaf
senescence. This initial increase of [Ca2+]cyt, which was first observed in
cells isolated from 3-d-senescent leaves, occurred 1 d before or in
parallel with changes in two established senescence parameters, chlorophyll
loss and lipid peroxidation. However, the [Ca2+]cyt elevation followed by 2
d the initial increase in the senescence-associated proteolysis. Whereas
the [Ca2+]cyt of nonsenescent cells remained at the basal level, the
elevated [Ca2+]cyt of the senescent cells was a long-lasting effect.
Experimental retardation of senescence processes, achieved by pretreatment
of detached leaves with the cytokinin benzyladenine, resulted in
maintenance of homeostatic levels of [Ca2+]cyt in cells isolated from
3-d-senescent leaves. These observations demonstrate for the first time to
our knowledge a correlation between elevated [Ca2+]cyt and the process of
senescence in parsley leaves. Such senescence-associated elevation of
[Ca2+]cyt, which presumably results from a loss of the cell's capability to
extrude Ca2+, may serve as a signal inducing subsequent deteriorative
processes.
