Significant role for polysomes associated with the cytoskeleton in the control of protein synthesis during germination of triticale caryopses in the presence of abscisic acid

Abstract

The influence of abscisic acid (ABA) on the process of polysome formation and synthesis of newly-formed proteins by different polysome populations was studied. Triticale caryopses were germinated in water or various ABA concentrations for 48 hrs, and afterwards they were transferred to a solution of 14C-amino acids and germinated for an additional 30 min. Embryos were separated from caryopses, and four polysome populations were isolated: the FP (free polysomes), MBP (membrane-bound polysomes), CBP (cytoskeleton-bound polysomes) and CMBP (cytoskeleton-membrane-bound polysomes). ABA retarded both the process of polysome formation and their activity in forming new proteins in vivo in all studied fractions. Participation of polysomes in total ribosomal materials (sub-units, monosomes and polysomes) of each polysome population in the control sample was as follows: FP — 77; MBP — 72; CBP — 70 and CMBP — 66 %, whereas in sample treated by ABA (100 µM) it was accordingly: 17; 23; 27 and 28%. The largest population made up FP (in control sample 69%), participation of MBP was always lower and ranged from about 19 to 30 %. Participation of polysome populations bound with the cytoskeleton CBP and CMBP, both in control sample as well as in samples treated with 1 and 10 µM ABA solution, was only a few per cent. It should be noted that when the ABA concentration was higher (100 µM) (process of germination was strongly inhibited), participation of those two populations (CBP and CMBP) was much increased in embryos, respectively to about 18 and 20 %. In both the control group and in embryonal tissue treated with ABA increasing incorporation of radioactive precursors to newly-formed proteins in vivo in fractions of polysomes isolated by following buffers: C (FP), C + PTE (MBP), C + Tris (CBP) and buf. U (CMBP) was observed. It should be noted, that the biggest incorporation of 14C-amino acids into nascent polypeptide chains was found in the last polysome population (CMBP). In the sample treated with ABA (100 µM) the activity of this fraction (CMBP) in forming new proteins is several times, and in the case of FP dozens of times, more intense. Increased participation of CBP and CMBP in embryos of triticale caryopses treated with ABA (100 µM) and the largest incorporation of 14C-amino acids into nascent polypeptide chains synthesised by CMBP, may indicate the important role of proteins formed by polysomes associated with cytoskeleton in inhibition of germination and seedling growth by ABA.