M. Schmid et al., Programmed cell death in castor bean endosperm is associated with the accumulation and release of a cysteine endopeptidase from ricinosomes, P NAS US, 96(24), 1999, pp. 14159-14164
Citations number
34
Categorie Soggetti
Multidisciplinary
Journal title
PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF THE UNITED STATES OF AMERICA
The cells of the endosperm of castor bean seeds (Ricinus communis) undergo
programmed cell death during germination, after their oil and protein reser
ves have been mobilized. Nuclear DNA fragmentation first was observed at da
y 3 in the endosperm cells immediately adjacent to the cotyledons and progr
essed across to the outermost cell layers by day 5. We also detected the ac
cumulation of small organelles known as ricinosomes, by using an antibody a
gainst a cysteine endoprotease. By the time the nuclear DNA was susceptible
to heavy label by terminal deoxynucleotidyltransferase-mediated dUTP nick
end labeling, the ricinosomes had released into the cytoplasm their content
of cysteine endoprotease, which became activated because of the cleavage o
f its propeptide, The cysteine endoprotease is distinguished by a C-termina
l KDEL sequence, although it is not retained in the lumen of the endoplasmi
c reticulum and is a marker for ricinosomes. Homologous proteases are found
in the senescing tissues of other plants, including the petals of the dayl
ily, Ricinosomes were identified in this tissue by electron microscopy and
immunocytochemistry. It seems that ricinosomes are not unique to Ricinus an
d play an important role in the degradation of plant cell contents during p
rogrammed cell death.