The content and activity of magnesium chelatase in green barley (Hordeum vulgare) leaves treated with 5-aminolevulinic acid | Содержание и активность магнии-хелатазы в зеленых листьях ячменя (Hordeum vulgare), обработанных 5-аминолевулиновой кислотой

The Mg-porphyrins has been proposed to play an important role as signaling molecules implicated in the plastid-to-nucleus communication. To get more information on the regulation of chlorophyll (Chl) biosynthesis and on Mg-porphyrin functions the content and activity of the key enzyme involved in Chl biosynyhesis, magnesium chelatase (MCH) were investigated in the green barley leaves that accumulated extensive amounts of porphyrins from exogenous 5-aminolevulinic acid (ALA) in darkness. Parallel, the content of S_adenosyl-L-methionin:Mg-protoporphyrin IX methyltransferase (MTF), the next enzyme of Chl biosyntesis pathway, as well as the amount of the main protein of the light-harvesting Chl-binding complexes of photosystem 2, Lchb1, were analyzed. The presented data illustrated that the reduction of MCH activity to zero values during the maximum accumulation of MgProto from ALA was due to the considerable decrease of the contents of CHLH and CHLI subunits of MCH. Besides, the decrease of the content of MTF was observed when the accumulation of MgProto reached the maximum level. Our results prove that MgProto is a negative effector of the expression of the nuclear genes encoding CHLI and CHLH subunits of MCH and MTF. The difference between the control and ALA-fed barley leaves in respect to the content of Lhcb1 protein was not found, probably because of the various contributions of MgProto and its monomemthlyl ester in the regulation of the expressions of Lhcb1 genes. It supports the possible role of MgProto E as a positive plastid-derived signal. Moreover, the stabilizing effect of ALA on Lhcb1 protein could not br excluded. The results obtained testify to the important regulatory role of MgProto in chloroplast-to-nucleus signalling and demonstrate one of the presumed mechanisms controlling the level of accumulation of photodynamic Mg-prophyrin molecules participating in the generation of reactive oxygen species and photo destruction of plant cells.