Cowpea ribonuclease: properties and effect of NaCl-salinity on its activation during seed germination and seedling establishment.
Pitiúba cowpea [Vigna unguiculata (L.) Walp] seeds were germinated in distilled water (control treatment) or in 100 mM NaCl solution (salt treatment), and RNase was purified from different parts of the seedlings. Seedling growth was reduced by the NaCl treatment. RNase activity was low in cotyledons of quiescent seeds, but the enzyme was activated during germination and seedling establishment. Salinity reduced cotyledon RNase activity, and this effect appeared to be due to a delay in its activation. The RNases from roots, stems, and leaves were immunologically identical to that found in cotyledons. Partially purified RNase fractions from the different parts of the seedling showed some activity with DNA as substrate. However, this DNA hydrolyzing activity was much lower than that of RNA hydrolyzing activity. The DNA hydrolyzing activity was strongly inhibited by Cu(2+), Hg(2+), and Zn(2+) ions, stimulated by MgCl(2), and slowly inhibited by EDTA. This activity from the most purified fraction was inhibited by increasing concentrations of RNA in the reaction medium. It is suggested that the major biological role of this cotyledon RNase would be to hydrolyze seed storage RNA during germination and seedling establishment, and it was discussed that it might have a protective role against abiotic stress during later part of seedling establishment.
Gomes-Filho
Enéas
E
Departamento de Bioquímica e Biologia Molecular, Universidade Federal do Ceará, P.O. Box 6039, 60455-900, Fortaleza, Ceará, Brazil. egomesf@ufc.br
Lima
Carmen Rogélia Farias Machado
CR
Costa
José Hélio
JH
da Silva
Ana Cláudia Marinho
AC
da Guia Silva Lima
Maria
M
de Lacerda
Claudivan Feitosa
CF
Prisco
José Tarquinio
JT
D018548:Cotyledon / Q000187:drug effects / Q000378:metabolism; D004591:Electrophoresis, Polyacrylamide Gel; D004797:Enzyme-Linked Immunosorbent Assay; D007887:Fabaceae / Q000187:drug effects / Q000201:enzymology*; D018525:Germination / Q000187:drug effects; D010940:Plant Proteins / Q000302:isolation & purification / Q000378:metabolism*; D012260:Ribonucleases / Q000302:isolation & purification / Q000378:metabolism*; D054712:Salinity; D036226:Seedlings / Q000187:drug effects / Q000201:enzymology*; D012639:Seeds / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D012965:Sodium Chloride / Q000494:pharmacology*
D010940:Plant Proteins; D012965:Sodium Chloride; D012260:Ribonucleases