Gene expression in cytokinin-and light-mediated plastogenesis of Cucurbita cotyledons: ribulose-1,5-bisphosphate carboxylase/oxygenase

Abstract

The effects of a cytokinin (N(6)-benzyladenine, BA) and light on plastogenesis have been studied in detached Cucurbita cotyledons using the key enzyme of photosynthetic CO2 fixation, ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBPCase), as an example of a coordinated program of plastid and nucleo-cytoplasmic gene expression. Treatment of etiolated cotyledons with either BA in darkness or in light or light alone results in a marked and correlated stimulation of enzyme activity, quantity and biosynthesis (in-vivo [(14)C]leucine incorporation into immunoprecipitated enzyme protein), indicating an increase of de-novo synthesis under the influence of the two effectors. Cell-free translation of non-polyadenylated (poly(A)(-))RNA in an Escherichia coli system and total RNA in a wheat-germ system likewise demonstrate a light and hormone-dependent increase in the amounts of translatable mRNAs for the large (LS) and small subunits (SS) of RuBPCase (among other polypeptides). Hybridisation of poly(A)(-)RNA with a nick-translated LS gene of spinach RuBPCase reveals also two-to three-fold BA-or light-induced enhancement of LS mRNA content. Indications for stimulation of SS mRNA transcription are derived from inhibitor experiments with cordycepin. We conclude that the observed stimulation of de-novo RuBPCase synthesis by cytokinin and by light can be referred to the level of mRNA transcription, but it remains open whether this is a primary action. Furthermore, our results indicate that the coaction of the two exogenous factors is additive at different steps of RuBPCase formation, indicating independent actions in the causal chain between effector-signal transduction and RuBPCase gene expression.

Regulation of Phosphoenolpyruvate Carboxylase and Crassulacean Acid Metabolism Induction in Mesembryanthemum crystallinum L. by Cytokinin

“…Plant Mol Biol inexsd prehydrt evdleaveiscnistacelerithatnedg (Fig.7) rgRep 6: [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28] The present evidence is consistent with a negative regula- …”

Changes in Protein Synthesis upon Cytokinin-Mediated Adventitious Bud Induction and during Seedling Development in Norway Spruce, Picea abies

“…Furthermore, we have identified one of these proteins (protein 63, Table I) as a component of the photosystem II oxygen-evolving complex (our unpublished data). This result confirms and extends the findings of Ellis and Judd (6) from embryonic cotyledons of Pinus ponderosa, but is in apparent disagreement with a number of studies which show a stimulatory effect of cytokinin on chloroplast development (1, 9) and the expression of chloroplast related genes (7,8,12,14). We believe that this discrepancy can be explained by the chloroplast development in our system being primarily dependent on the developmental stage of the tissue, and thus the suppression of chloroplast development would be a consequence of the general inhibition of seedling maturation that results from the bud-induction treatment.…”

Calcium Variously Mediates the Effect of Cytokinin on Chlorophyll and LHCPII Accumulation During Greening in Barley Leaves and Cucumber Cotyledons

“…The CK effect on enhancement of LHCPII in the presence of EGTA was reduced somewhat in barley leaves but more strongly in cucumber cotyledons, suggesting that calcium is only partially involved in the effect of CK on the increase of LHCPII accumulation. Earlier studies demonstrated that CK may increase the steady-state mRNA level of certain chloroplast genes that depend on mRNA synthesis, processing and stability (Lerbs et al, 1984;Kasten et al, 1997). Flores and Tobin (1988) sought to verify whether CK treatment influences LHCP mRNA by increasing the rate of transcription or by decreasing the rate of mRNA turnover.…”