Cytokinin effects on tetrapyrrole biosynthesis and photosynthetic activity in barley seedlings.
Cytokinin promotes morphological and physiological processes including the tetrapyrrole biosynthetic pathway during plant development. Only a few steps of chlorophyll (Chl) biosynthesis, exerting the phytohormonal influence, have been individually examined. We performed a comprehensive survey of cytokinin action on the regulation of tetrapyrrole biosynthesis with etiolated and greening barley seedlings. Protein contents, enzyme activities and tetrapyrrole metabolites were analyzed for highly regulated metabolic steps including those of 5-aminolevulinic acid (ALA) biosynthesis and enzymes at the branch point for protoporphyrin IX distribution to Chl and heme. Although levels of the two enzymes of ALA synthesis, glutamyl-tRNA reductase and glutamate 1-semialdehyde aminotransferase, were elevated in dark grown kinetin-treated barley seedlings, the ALA synthesis rate was only significantly enhanced when plant were exposed to light. While cytokinin do not stimulatorily affect Fe-chelatase activity and heme content, it promotes activities of the first enzymes in the Mg branch, Mg protoporphyrin IX chelatase and Mg protoporphyrin IX methyltransferase, in etiolated seedlings up to the first 5 h of light exposure in comparison to control. This elevated activities result in stimulated Chl biosynthesis, which again parallels with enhanced photosynthetic activities indicated by the photosynthetic parameters F(V)/F(M), J (CO2max) and J (CO2) in the kinetin-treated greening seedlings during the first hours of illumination. Thus, cytokinin-driven acceleration of the tetrapyrrole metabolism supports functioning and assembly of the photosynthetic complexes in developing chloroplasts.
Yaronskaya
Elena
E
Institute of biophysics and cell engineering, National academy of sciences of Belarus, Akademicheskaya 27, 220072 Minsk, Belarus.
Vershilovskaya
Irina
I
Poers
Yvonne
Y
Alawady
Ali E
AE
Averina
Natalia
N
Grimm
Bernhard
B
D000622:Aminolevulinic Acid / Q000378:metabolism; D002245:Carbon Dioxide / Q000378:metabolism; D002734:Chlorophyll / Q000378:metabolism; D003583:Cytokinins / Q000494:pharmacology*; D003624:Darkness; D001467:Hordeum / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism*; D008027:Light; D008190:Lyases / Q000378:metabolism; D010788:Photosynthesis / Q000187:drug effects; D010937:Plant Growth Regulators / Q000494:pharmacology*; D011521:Protochlorophyllide / Q000378:metabolism; D036226:Seedlings / Q000187:drug effects / Q000254:growth & development / Q000378:metabolism; D045725:Tetrapyrroles / Q000096:biosynthesis*
D003583:Cytokinins; D010937:Plant Growth Regulators; D045725:Tetrapyrroles; D002734:Chlorophyll; D002245:Carbon Dioxide; D011521:Protochlorophyllide; D000622:Aminolevulinic Acid; D008190:Lyases; C086788:magnesium chelatase