Phytochrome regulation of peroxidase activity in maize V. Role of RNA and protein synthesis

The phytochrome mediated enhancement of peroxidase activityin maize leaves was repressed by inhibitors of cytoplasmic proteinsynthesis, whereas inhibitors of RNA and organelle protein synthesiswere ineffective. Continuous far-red light had no effect onthe DNA level in the leaves, but it increased the RNA levelafter a lag of 2 hr. Under continuous far-red light the totalcontent of polyribosomes also increased after a lag of 2 hr.Isolated polyribosomes from far-red grown plants showed an enhancedrate of the in vitro incorporation of amino acids into proteinsas compared to dark grown plants. These results indicate thatthe phytochrome regulation of peroxidase activity occurs atthe translational level. ¹Present address: School of Life Sciences, University of Hyderabad,Hyderabad-500001, India (Received July 25, 1979; )     

Early protein synthesis during germination of barley embryos and its relationship to RNA synthesis

In barley embryo, protein synthesis as judged from the incorporationof labelled precursors, starts at about 15 min after the commencementof germination. Evidence suggests that these early proteinsare essential for germination and are programmed by a conservedpolyadenylate-containing mRNA, preserved in dry embryos. Althoughlow DNA-dependent RNA polymerase activity is present in drybarley embryos, RNA synthesis does not commence immediatelyafter water imbibition. It is initiated only after 2 hr of germinationand its synthesis requires the presence of early proteins. Furthermore,the activity of RNA polymerase increases with an increase ingermination time and after 40 hr of germination, the activityof RNA polymerase is about fivefold higher than that in dryembryo. However, cydoheximide completely blocks the enhancedactivity of RNA polymerase, suggesting a role of early proteinsin the initiation of new RNA synthesis in this developmentalsystem. (Received October 26, 1979; )     

Role of light in the regulation of the nitrate reductase level in wheat (Triticum aestivum)

The relationship between light and NR synthesis was studiedin excised wheat leaves. In light, there was a 14 fold increasein the NR level as compared to the dark controls. Sucrose didnot have any effect on NR synthesis. In the dark, a significantamount of intracellular nitrate was detected, but there wasvery little NR activity. Measurement of the decay rates of NRin the dark and light showed that NR activity disappeared fasterin light than in the dark. Exposure to short durations of blue,red and white light caused an increase in the NR synthesis.Further, this response was found to be phytochrome controlled.We propose that the process of nitrate reduction influencesNR synthesis. (Received January 11, 1979; )     

Phytochrome regulation of nitrate reductase in wheat

In excised wheat leaves, the activity of nitrate reductase was enhanced by a brief pulse of red light and this increase was reversed by far-red light irradiation. Even under continuous far-red light, nitrate reductase activity increased by 258% after 18 h. When leaves were kept in distilled water during exposure to red light and then transferred to potassium nitrate, there was no difference in endogenous nitrate concentration. The nitrate reductase activity was the same whether leaves were floated in potassium nitrate or in distilled water during irradiation. Partial to complete inhibition of enzyme activity was observed when leaves were incubated in actinomycin-D and cycloheximide respectively, following 4 h of red light irradiation.In vitro irradiation of extract had no significant effect on nitrate reductase activity