S-methylmethionine reduces cell membrane damage in higher plants exposed to low-temperature stress.

S-methylmethionine (SMM), an important intermediate compound in the sulphur metabolism, can be found in various quantities in majority of plants. The experiments were designed to determine the extent to which SMM is able to preserve cell membrane integrity or reduce the degree of membrane damage in the course of low-temperature stress. By measuring electrolyte leakage (EL), it was proved that SMM treatment reduced cell membrane damage, and thus EL, during low-temperature stress in both the leaves and roots of peas, maize, soy beans and eight winter wheat varieties with different levels of frost resistance. Investigations on the interaction between SMM and polyamine biosynthesis revealed that SMM increased the quantities of agmatine (Agm) and putrescine (Put) as well as that of spermidine (Spd), while it had no effect on the quantity of spermine (Spn). Using a specific inhibitor, methylglyoxal-bis-guanyl hydrazone (MGBG), it was proved that the polyamine metabolic pathway starting from methionine played no role in the synthesis of Spd or Spn, so there must be an alternative pathway for the synthesis of SMM-induced polyamines.

Synthesis of gluten-forming polypeptides. 1. Biosynthesis of gliadins and glutenin subunits.

Five winter wheat cultivars--GK Othalom (HMW-GS composition 2*, 7+8, 5+10), Ukrainka (1, 7+8, 5+10), Palotás (2*, 7+9, 5+10), Ködmön (2*, 7+8, 5+10), and Csongrád (2*, 7+9, 2+12)--grown in Hungary and harvested in the year 2005 were studied. The biosynthesis of gluten-forming polypeptides was followed starting at the 12th day after anthesis to the 53rd. Fresh kernel weight, moisture, and dry matter content of fresh kernels and gliadin and glutenin contents were determined. Gliadin components, total amounts of HMW and LMW polypeptides, and individual HMW polypeptides were determined using a RP-HPLC technique. Although considerable quantitative differences were observed concerning the content of total protein, gliadin, glutenin, and individual gluten-forming polypeptides, the character of accumulation of protein components--determined on the basis protein mass/kernel--was the same for the all of the cultivars studied and could be presented by a sigmoid curve. Small quantities of the gliadin and glutenin monomers may be detected in early stages of kernel development, but the bulk of these proteins is synthesized in later stages of development. It is generally suggested by specialists that the formation and accumulation of glutenin polymers starts later than the synthesis of monomers. Experimental data presented in this paper confirm this suggestion and show that in the first phase of protein synthesis the monomers are in "free" form; polymeric glutenin is detected only later. HMW glutenin subunits are synthesized synchronously, and quantitatively the polypeptides coded by chromosomes D and B dominate.

Ferritin2 gene in paraquat-susceptible and resistant biotypes of horseweed Conyza canadensis (L.) Cronq.

Ferritins, the multimeric iron storage proteins, are the main regulators of the cellular level of uncomplexed iron. Ferritins are encoded by small gene families and expressed differentially under various developmental conditions depending on iron availability, effect of hormones or oxygen radical generating agents. In the present work the primary structure of the ferritin2 gene from resistant and susceptible biotypes of horseweed Conyza canadensis was determined. This gene was found to exhibit great similarity and possess all the structural characteristics of known plant ferritin2 genes. The C. canadensis ferritin2 genes had identical primary structure in the two biotypes and were upregulated by paraquat (Pq) in both susceptible and resistant plants. The enhanced expression level was probably connected with defence reactions in the plants after Pq treatment.