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.)

Abstract

IntroductionChanges in the environment, such as drought, salinity, high or low temperature, are an important factor which affects the growth of crops and the volume of crop yields [1][2][3]. Very important legume grown and consumed extensively worldwide is pea [4]. As a rich source of proteins, carbohydrates, fibre, vitamins and minerals, peas are important in human nutrition [5]. Pea is the fourth leading legume in terms of consumption in the world after soybean, peanuts and bean [6]. One of the major abiotic stress often occurs in Europe is osmotic stresses induced with polyethylene glycol (within −0.5 MPa). The earliest metabolic change caused by water stress is a decreased amount of polysomes [7]. Once the polysomes have been disaggregated, the plant growth is inhibited due to a slower protein synthesis rate [7][8][9]. Considerable reduction in the amount of polysomes in plant tissues is observable after osmotic stress lasting for just 20-30 minutes [10]. Decrease of the content of polysomes in response to abiotic stresses is connected with the process of "switching" the expression of genes from those participating in the growth and development of plants under unstressed conditions to the ones active in response to stress [11].In plant tissues, polysomes can occur as free polysomes (FP), endoplasmic reticulum membrane-bound polysomes (MBP) [12], cytoskeleton-bound polysomes (CBP) [13,14] and cytoskeleton-membrane-bound polysomes (CMBP) [15]. 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]. Polysomes contain mRNAs, which may undergo selective translation, result in modification of protein synthesis in response to stress conditions in plants [23,24].The objective of this study was to indicate differences in the composition of polysome-bound proteins and in the products of in vitro translation in pea (Pisum sativum L.) seeds germinating under unstressed conditions and under long-and short-term osmotic stress (−0.5 MPa) followed by post-stress recovery. AbstractPlant growth throughout the world is often limited by unfavourable environmental conditions. This paper reports results of a study on long-and short-term osmotic stress (−0.5 MPa) followed by a recovery on in vitro translational capacity of polysomes a...