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-fornaed 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 rain. 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 ofpolysome 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 laM) 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 potysome populations bound with the cytoskeleton CBP and CMBP, both in control sample as well as in samples treated with 1 and 10/aM ABA solution, was only a few per cent. It should be noted that when the ABA concentration was higher (100 laM) (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 + VIE (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 ~aM) 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 taM) 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.

A Role for F-Actin in Hexokinase-Mediated Glucose Signaling

“…Researchers have been able to isolate four defined populations of polysomes: free, membrane bound, actin bound, and actin membrane bound polysomes. In one study, ABA treatment of germinating embryos from triticale caryopses is reported to greatly increase the abundance of the cytoskeleton-associated polysomes (Weidner et al, 2000). In this study, disruption of F-actin by LatB or CytoD did not affect expression of RBCS-LUC or ASN1-LUC in the absence of HXK1 and Glc, but only blocked the HXK1 plus Glcdependent repression of LUC expression (Fig.…”

Effect of osmotic stress on in vitro translational capacity of polysomes and on the composition of polysome-associated proteins in germinating seeds of pea (Pisum sativum L.)

“…Their results confirmed some subsequent findings reported by Weidner et al [20], who observed that most of exogenous 14C-amino acids were incorporated, in the embryonic tissue of pea, in the newly formed polypeptide chain, synthesized with the CMBP population. They claimed that the CBP population may play an important role in the synthesis of the so-called stress proteins [20,21]. According to Kosowska et al [36], there must be some mechanism of regulating translation which is activated in seeds germinating under osmotic stress that enables synthesis of specific proteins despite the total protein synthesis being reduced.…”

“…Higher translational activity of the CBP population than that of the FP or MBP fractions in bean tissues had been shown previously by Klyachko et al [41]. Their results confirmed some subsequent findings reported by Weidner et al [20], who observed that most of exogenous 14C-amino acids were incorporated, in the embryonic tissue of pea, in the newly formed polypeptide chain, synthesized with the CMBP population. They claimed that the CBP population may play an important role in the synthesis of the so-called stress proteins [20,21].…”

“…The changes in the composition of polysomal proteins presented in this paper may play an important role in the regulation of translation under stress conditions and can result in the differentiated translational activity of particular fractions of polysomes, which had been demonstrated earlier [19,20,39,41,42]. The end products from in vitro translation of polysomes also reflect the activity of mRNAs that respond to stress [43].…”

“…Changes in the distribution of polysomes between the particular fractions reflect changes in the complement of proteins, as each population of polysomes is engaged in the synthesis of specific proteins [16]. Thus, the FP population is mainly involved in the synthesis of soluble proteins of the cytoplasm, cellular nucleus, mitochondria and peroxisomes [17]; the MBP population is engaged in the production of secretory proteins, lysosome proteins and the proteins which are an integral component of the plasmatic membrane and intracellular membranes, including the endoplasmic reticulum [16,17]; finally, the CBP and CMBP populations are responsible for the synthesis of cytoskeleton and stress proteins [16,[18][19][20][21]. The largest share in the total polysome pool consists of the CBP population, which sometimes reaches 70% of the total polysome content [22].…”