St. Kester et al., PRIMING AND ACCELERATED AGING AFFECT L-ISOASPARTYL METHYLTRANSFERASE ACTIVITY IN TOMATO (LYCOPERSICON-ESCULENTUM MILL) SEED, Journal of Experimental Botany, 48(309), 1997, pp. 943-949
Damage and degradation of cellular proteins is observed during age-ind
uced seed deterioration. L-isoaspartyl protein methyltransferase (EC 2
.1.1.77) is an enzyme hypothesized to play a role in limiting and repa
iring age-induced damage to proteins. Tomato (Lycopersicon esculentum
Mill, 'New Yorker') seeds were assayed for changes in L-isoaspartyl me
thyltransferase activity during accelerated ageing and after osmotic p
riming, Accelerated ageing of seeds for 1-4 d at 45 degrees C and 100%
relative humidity reduced germination from 94% to 71%, increased the
mean time of germination (MTG) from 2.4 to 5.8 d, and was accompanied
by a correlative decrease in L-isoaspartyl methyltransferase activity
(r(2) = 0.90). Aged and untreated seeds were primed for 7 d at 20 degr
ees C in darkness using aerated solutions of 3% KNO3 or polyethylene g
lycol 8000 (PEG) with equivalent osmotic potential (-1.25 MPa), Primin
g with KNO3 decreased the MTG, but did not improve germination percent
age for untreated seeds, Priming did not affect L-isoaspartyl methyltr
ansferase activity in untreated seeds, but restored activity in aged s
eeds primed in KNO3 to levels near that of untreated seeds, Priming wi
th PEG did not effectively improve the MTG or increase L-isoaspartyl m
ethyltransferase activity. During germination, L-isoaspartyl methyltra
nsferase activity remained constant for 48 h post-imbibition and then
declined, suggesting that the enzyme was developmentally regulated and
inactivated or degraded as radicle emergence occurred.