Distinct effects of auxin and light on adventitious root development in Eucalyptus saligna and Eucalyptus globulus.

Adventitious rooting is essential for vegetative propagation of woody species. We studied the effects of auxin and light on the development of adventitious roots in cuttings obtained from seedlings of Eucalyptus saligna Smith and E. globulus Labill in an attempt to characterize the adventitious rooting process and identify factors controlling rhizogenesis. Root development was scored as rooting percentage, root density (roots per rooted cutting), mean rooting time and root length. In both species, rooting time was reduced in the presence of auxin. Cuttings from 2-month-old E. saligna seedlings were responsive to lower auxin concentrations than comparable cuttings from E. globulus seedlings. Cuttings from 3-month-old E. saligna seedlings rooted promptly and rooting was not significantly affected by light conditions. In contrast, rooting of cuttings from 3-month-old E. globulus seedlings exhibited recalcitrant behavior and no roots were formed if illuminated during the root formation phase. Effective root regeneration of E. globulus cuttings was obtained by a 4-day exposure to 10 mg l(-1) IBA and culture in darkness during the root formation step. Loss of rooting capacity with seedling age was more pronounced in E. globulus than in E. saligna. The possibility of switching adventitious rooting off and on by manipulating light regime and exogenous auxin supply in E. globulus, and the constitutive nature of rooting in E. saligna may provide useful models for examining the rooting process at the biochemical and molecular levels in Eucalyptus.

Brachycerine, a novel monoterpene indole alkaloid from Psychotria brachyceras.

Brachycerine (1), an unusual alkaloid from the leaves of Psychotria brachyceras, was characterized through spectroscopic data interpretation and its stereochemistry established by NOE difference techniques. Brachycerine (1) was found to be restricted to shoots in rooted cuttings of P. brachyceras (0.018 +/- 0.004% dry weight), and accumulation was unaffected by root induction treatment with auxin.

Regulation of Periplasmic Carbonic Anhydrase Expression in Chlamydomonas reinhardtii by Acetate and pH.

The effects of mixotrophic growth with acetate and growth medium pH on expression of extracellular carbonic anhydrase (CA) in Chlamydomonas reinhardtii were evaluated. Addition of 10 mM acetate to the culture medium resulted in reduction of CA activity that was parallel to the reduction generated by growth of the algae in high external CO2 concentrations. This reduction in activity is a consequence of lower level of the CA protein as determined by western analysis. Transcript abundance of cah-1, the gene encoding the low CO2-induced CA, is also reduced by the addition of acetate as verified by northern analysis. Measurements of photosynthesis and respiration suggest that the acetate-induced reduction of CA expression is not a function of lowered photosynthetic capacity, but may be the result of increased internal CO2 concentration generated by high, acetate-stimulated respiratory rates. Growth medium pH can also influence extracellular CA expression. The induction of CA activity, protein abundance, and transcript levels by exposure to limiting inorganic carbon (Ci) concentrations is much more pronounced at higher than at lower pH values. The relationship between pH regulation of CA expression and its role in the Ci-concentrating mechanism are discussed.

Characterization and expression of two cDNAs encoding carbonic anhydrase in Arabidopsis thaliana.

Two distinct cDNA clones encoding carbonic anhydrase (CA) were isolated from an Arabidopsis thaliana lambda YES library. One of these clones, CA1, encodes a 36.1-kD polypeptide and is essentially the same as a previously reported Arabidopsis CA cDNA (C.A. Raines, P.R. Horsnell, C. Holder, J.C. Lloyd [1992] Plant Mol Biol 20: 1143-1148). Comparison of the derived amino acid sequence from this clone with other plant CAs suggests the presence of a chloroplastic transit peptide, which, when cleaved, would render a mature protein of 24.3 kD. The other identified clone, CA2, encodes a 28.3-kD polypeptide, which in addition to other residue changes, is 78 amino acids shorter at the N terminus than the primary product of CA1. The two cDNAs exhibit 76.9% sequence similarity at the DNA level and 84.6% identity between the predicted amino acid sequences. A polyclonal antibody generated against pea CA (N. Majeau, J.R. Coleman [1991] Plant Physiol 100: 1077-1078) hybridized to two protein bands (25 and 28 kD) from a total leaf extract and to only one band (25 kD) from a chloroplastic protein extract. The data suggest that the CA2 protein is an extrachloroplastic form of CA, presumably localized in the cytoplasm. Southern analysis indicated that CA1 and CA2 are encoded by different genes. Northern analysis of total leaf RNA resulted in hybridization of CA1- and CA2-derived probes to two transcripts of 1.47 and 1.2 kb, respectively. These data provide additional evidence that the CA2 clone is a full-length cDNA and that two transcribed CA genes are present in the Arabidopsis genome. Transcript levels of CA1 and CA2 decreased 70 and 20%, respectively, when mature plants were transferred to dark for 24 h. Seedlings germinated in the dark showed CA1 and CA2 transcript abundance levels of 4 and 22%, respectively, when compared with light-germinated seedlings. These data suggest that expression of CA1 is light regulated and dependent of leaf and/or chloroplast development. A possible role for cytoplasmic CA in the plant cell is discussed.