Pk. Bhattacharya et al., CHANGES IN NUCLEAR MACROMOLECULES AND NUCLEOLAR VOLUME ASSOCIATED WITH SELECTIVE RIBOSOMAL CISTRON ACTIVATION BY ETHYLENE, Mechanism of ageing and development, 73(1), 1994, pp. 1-7
Pieces of leaf base tissue from the equatorial region of the third tur
gid onion (Allium cepa L.; yellow, sweet Spanish, quiescent tissue) le
af base with two visible major nucleoli (volume = 0.51 mu m(3)) and tw
o inactive minor nucleolar organizer regions (NORs) in the outer epide
rmal cells were placed in shallow water (time = T-0 control). After 3
h (T-3 control), the two visible nucleoli enlarged (178% of T-0) and c
hanged shape (from 88% round and 12% oval at T-0 to 5% round, 68% oval
, 20% elongated-oval, and 7% dumbbell). The minor NORs remained inacti
ve. Nuclear RNA and non-histone protein (nHP) increased (RNA = 128% an
d nHP = 134%, compared with T-0 data, set at 100%). The content of DNA
and histone protein (H) in nuclei remained unchanged. Major nucleoli
in pieces of onion placed in 10(-5) M ethylene enlarged and minor nucl
eoli became visible in 33% of the nuclei; i.e., ethylene acted as a se
lective ribosomal cistron regulator. The nucleolar volume (212% of T-0
) was statistically greater than those for T-0 and T-3. DNA and H rema
ined unchanged (not statistically different) but RNA (159% of T-0) and
nHP (169% of T-0) were greater (statistically significant) than those
for T-0 and T-3 controls. Cobalt chloride (10(-5) M Co) alone or in 1
0(-5) M ethylene (Co + E) inhibited the enlargement of some of the maj
or nucleoli and completely inhibited the appearance of minor nucleoli.
The nucleolar volumes for the cobalt and for cobalt-ethylene treatmen
ts were significantly less than those for T-3 controls and ethylene tr
eatment at T-3. DNA and histone did not change. RNA and nHP were signi
ficantly less than the amounts obtained in T-3 controls and ethylene t
reatments suggesting inhibition or reversal of the ethylene-induced ac
tivation. We infer that when ethylene activated minor NORs, it stimula
ted rRNA, mRNA, and nHP synthesis. The amounts of rRNA that moved from
the nucleus into the cytoplasm and of nHP that remained in the cytopl
asm are not known.