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Calmodulin levels in radish ( Raphanus sativus L.) seeds germinating at low calcium availability induced by EGTA treatments
Author(s) -
NEGRINI N.,
RIVETTA A.,
COCUCCI M.
Publication year - 1995
Publication title -
plant, cell and environment
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.646
H-Index - 200
eISSN - 1365-3040
pISSN - 0140-7791
DOI - 10.1111/j.1365-3040.1995.tb00349.x
Subject(s) - egta , incubation , raphanus , calcium , germination , calmodulin , botany , biology , chemistry , horticulture , biochemistry , zoology , organic chemistry
Incubation of radish ( Raphanus sativus L.) seeds in the presence of 1 or Smol m −3 Ca‐EGTA, which increased Ca 2+ activity in the incubation medium ( c . 0.24 or 0.37 mol m −3 at 24 h with respect to c . 0.13 mol m −3 in the control), did not affect germination, the restoration of K + net influx, the increase in DNA and RNA levels or protein synthesis. Incubation in 1 mol m −3 Na‐EGTA, which reduced Ca 2+ activity in the incubation medium (20 mmol m −3 at 24 h), decreased the total Ca 2+ level in embryo axes (‐21%), but only slightly inhibited the increase in fresh weight without affecting the restoration of K + net influx, the increase in DNA and RNA levels or protein synthesis. In the presence of 5 mol m −3 Na‐EGTA (Ca 2+ activity in the incubation medium was 0.6 mmol m −3 ), the decrease in the total Ca 2+ level was greater ( c . ‐27%) and the increases in fresh weight, DNA and RNA were inhibited by about 50, 39 and 40%, respectively. These results indicate that increased Ca 2+ availability does not affect germination and suggest that the effect of Na‐EGTA, at least up to 5 mol m −3 , is a result of an induction of Ca 2+ deficiency. The amount and specific activity of calmodulin (CaM) present in the soluble fraction (100 000 g ) of radish embryo axes greatly increased during the first 24 h of incubation ( c . 5‐fold and 7‐fold, respectively). This increase was very similar in the Ca‐EGTA‐treated seeds but was inhibited ( c . ‐38%) by 1 mol m −3 Na‐EGTA, even if the increases in DNA and RNA levels and protein synthesis were not significantly reduced. The lower amount of CaM after 24 h of incubation in 1 mol m −3 Na‐EGTA ( c . ‐30%) was due to a reduction in the fraction of CaM bound to a proteinaceous CaM inhibitor present in radish seeds [M. Cocucci & N. Negrini (1988) Plant Physiology 88, 910–914] and not involved in the metabolic reactivation of the seed. These results suggest that the level of CaM is controlled by Ca 2+ availability and that the CaM inhibitor has a role in controlling the amount of Ca‐CaM available for the Ca‐CaM‐dependent enzymes.