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The ribonucleic acid synthesized by excised shoots of dwarf pea (Pisum sativum L. cv. Progress No. 9) during short labeling periods has been characterized. Thirty per cent of the total 32Pi incorporated in 1 hour is found in the ribosomal fraction. This labeled RNA was polydisperse (6-18 Svedberg units) and after chromatography on a methylated albumin-kieselguhr column about 80% of the radioactivity appeared in two peaks. One of these appeared on the shoulder of heavy ribosomal RNA ("mRNA") while the other was tenaciously bound to the column (TB-RNA).In the presence of high NaCl concentration, about half of the polydisperse RNA interacted with ribosomal RNA and eluted as "mRNA" while the remainder eluted as TB-RNA.This interaction in the presence of salt seems to result in the alteration of secondary structure because the "mRNA" fraction had a high sedimentation coefficient (45-50 Svedberg units). The polydisperse RNA approaches DNA in low cytidylate and guanylate content. After short periods of labeling TB-RNA showed higher adenylate content than "mRNA." The radioactivity from the "mRNA" peak can be chased, and these counts may represent a class of shortlived messenger RNA molecules with an average half-life of 10 to 15 minutes. The other component, TB-RNA, could not be chased and accumulated radioactivity during the chase period.In bacteria and viruses the information for the sequence of amino acids in a polypeptide chain is encoded into messenger RNA. Presence of a similar fraction has been suggested in some higher plants (5,6,21,26,39). All of our knowledge about messenger RNA from higher plants is presumptive and based on analogy to microorganisms; in no case has this fraction been purified or characterized, nor has its rate of synthesis or its stability been studied.We chose a dwarf pea as the experimental material because we have been investigating the RNA synthesized by nuclei isolated from shoots of this plant (19), and the knowledge obtained from the system in vivo may be applicable to the results obtained with isolated nuclei. MATERIALS AND METHODS Uptake and Incorporation of Labeled Precursors. Dwarf pea seeds (Pisum sativum L., cv. Progress No. 9) were surfacesterilized for 7 to 10 min in 1% sodium hypochlorite, implanted in 500-ml Erlenmeyer flasks containing moist, sterile vermiculite, and allowed to germinate at 23 C in continuous light. At the end of 5 or 6 days, shoots 0.8 to 1 cm long were excised and 10 or 15 shoots were incubated in 25-ml Erlenmeyer flasks under aseptic conditions with labeled uridine or 32Pj (carrier-free H3u2PO4, neutralized) in 2 ml of water containing 100 ,ug of chloramphenicol. Flasks were transferred to a shaker, and, after incubation for various times, the shoots were washed thoroughly in ice-cold 0.05 M KH2PO4 and deionized water and were then extracted for nucleic acids.In experiments designed to study the relationship between uptake and incorporation, the labeled shoots were homogenized in ethanol, 80% (v/v,) and the nucleic acids were determined (33). The ...

The patterns of phytohormones distribution, their native function and possible origin of hormonal regulation across the green plant lineages (chlorophytes, charophytes, bryophytes and tracheophytes) are discussed. The five classical phytohormonesauxins, cytokinins, gibberellins (GA), abscisic acid (ABA) and ethylene occur ubiquitously in green plants. They are produced as secondary metabolites by microorganisms. Some of the bacterial species use phytohormones to interact with the plant as a part of their colonization strategy. Phytohormone biosynthetic pathways in plants seem to be of microbial origin and furthermore, the origin of high affinity perception mechanism could have preceded the recruitment of a metabolite as a hormone. The bryophytes represent the earliest land plants which respond to the phytohormones with the exception of gibberellins. The regulation by auxin and ABA may have evolved before the separation of green algal lineage. Auxin enhances rhizoid and caulonemal differentiation while cytokinins enhance shoot bud formation in mosses. Ethylene retards cell division but seems to promote cell elongation. The presence of responses specific to cytokinins and ethylene strongly suggest the origin of their regulation in bryophytes. The hormonal role of GAs could have evolved in some of the ferns where antheridiogens (compounds related to GAs) and GAs themselves regulate the formation of antheridia.During migration of life forms to land, the tolerance to desiccation may have evolved and is now observed in some of the microorganisms, animals and plants. Besides plants, sequences coding for late embryogenesis abundant-like proteins occur in the genomes of other anhydrobiotic species of microorganisms and nematodes. ABA acts as a stress signal and increases rapidly upon desiccation or in response to some of the abiotic stresses in green plants. As the salt stress also increases ABA release in the culture medium of cyanobacterium Trichormus variabilis, the recruitment of ABA in the regulation of stress responses could have been derived from prokaryotes and present at the level of common ancestor of green plants. The overall hormonal action mechanisms in mosses are remarkably similar to that of the higher plants. As plants are thought to be monophyletic in origin, the existence of remarkably similar hormonal mechanisms in the mosses and higher plants, suggests that some of the basic elements of regulation cascade could have also evolved at the level of common ancestor of plants. The networking of various steps in a cascade or the crosstalk between different cascades is variable and reflects the dynamic interaction between a species and its specific environment.

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The role of purine and pyrimidine ribosides, nucleotides and substituted xanthines in the differentiation of chloronema filaments in suspension cultures of protonema of the moss Funaria hygrometrica Hedw. has been examined. Cyclic adenosine-3',5'-monophosphate (cAMP) and mono-and dibutyryl cAMP evoked the maximum response in wild-type protonema. ADP and ATP also enhanced chloronema differentiation but were less active than cAMP; pyrimidine derivatives were completely inactive. Inhibitors of cyclic-nucleotide phosphodiesterase aminophylline, theophylline and ICI 58, 301 (3-acetamido-6-methyl-8-n-propyl-s-triazolo-(4,3a)-pyrazine)-mimicked the effect of cAMP. A leaky, chloronema-repressed mutant was isolated and in this mutant cAMP was much more active than cyclic guanosine monophosphate and ADP in enhancing chloronema differentiation. These results strongly indicate that cAMP is involved in chloronema differentiation in Funaria, and a hypothesis on growth regulation in protonema cell cultures is proposed.