A nucleus-encoded factor, CRR2, is essential for the expression of chloroplast ndhB in Arabidopsis

The chloroplast NDH complex, NAD(P)H dehydrogenase, reduces the plastoquinone pool non-photochemically and is involved in cyclic electron flow around photosystem I (PSI). A transient increase in chlorophyll fluorescence after turning off actinic light is a result of NDH activity. We focused on this subtle change in chlorophyll fluorescence to isolate nuclear mutants affected in chloroplast NDH activity in Arabidopsis by using chlorophyll fluorescence imaging. crr2-1 and crr2-2 (chlororespiratory reduction) are recessive mutant alleles in which accumulation of the NDH complex is impaired. Except for the defect in NDH activity, photosynthetic electron transport was unaffected. CRR2 encodes a member of the plant combinatorial and modular protein (PCMP) family consisting of more than 200 genes in Arabidopsis. CRR2 functions in the intergenic processing of chloroplast RNA between rps7 and ndhB, which is possibly essential for ndhB translation. We have determined the function of a PCMP family member, indicating that the family is closely related to pentatrico-peptide PPR proteins involved in the maturation steps of organellar RNA.     

Miniaturizable homogenous time-resolved fluorescence assay for carboxypeptidase B activity

An epitope-unmasking, homogeneous time-resolved fluorescence (HTRF) assay has been developed for measuring carboxypeptidase B (CPB) activity in a miniaturized high-throughput screening format. The enzyme substrate (biotin-RYRGLMVGGVVR-OH) is cleaved by CPB at the C terminus, causing release of the C-terminal Arg residue. The product (biotin-RYRGLMVGGVV-OH) is recognized specifically by a monoclonal antibody (G2-10) which is labeled with Eu(3+)-cryptate ([Eu(3+)]G2-10 mAb), and the complex is detected by fluorescence resonance energy transfer using streptavidin labeled with allophycocyanin ([XL665]SA). The CPB HTRF assay is readily adapted from 96- to 1536-well format as a robust (Z(')>0.5) assay for high-throughput screening.     

Involvement of a plastid terminal oxidase in plastoquinone oxidation as evidenced by expression of the Arabidopsis thaliana enzyme in tobacco

Chlororespiration has been defined as a respiratory electron transport chain in interaction with photosynthetic electron transport involving both non-photochemical reduction and oxidation of plastoquinones. Different enzymatic activities, including a plastid-encoded NADH dehydrogenase complex, have been reported to be involved in the non-photochemical reduction of plastoquinones. However, the enzyme responsible for plasquinol oxidation has not yet been clearly identified. In order to determine whether the newly discovered plastid oxidase (PTOX) involved in carotenoid biosynthesis acts as a plastoquinol oxidase in higher plant chloroplasts, the Arabidopsis thaliana PTOX gene (At-PTOX) was expressed in tobacco under the control of a strong constitutive promoter. We showed that At-PTOX is functional in tobacco chloroplasts and strongly accelerates the non-photochemical reoxidation of plastoquinols; this effect was inhibited by propyl gallate, a known inhibitor of PTOX. During the dark to light induction phase of photosynthesis at low irradiances, At-PTOX drives significant electron flow to O(2), thus avoiding over-reduction of plastoquinones, when photo- synthetic CO(2) assimilation was not fully induced. We proposed that PTOX, by modulating the redox state of intersystem electron carriers, may participate in the regulation of cyclic electron flow around photosystem I.     

Effects of melatonin implants in pony mares. 1. Acute effects

The effects of melatonin implant treatment over a four week period on LH, estradiol (E2) and progesterone (P4) secretion during the breeding season were studied in ovary-intact and ovariectomized pony mares. Mares with melatonin implants had significantly higher daytime melatonin concentrations than mares with sharm implants (P = 0.0065). In ovariectomized mares, LH secretion did not differ between mares with melatonin and sham implants. In ovary-intact mares, melatonin implants altered the pattern of LH secretion (P = 0.0023) in such a way that an increase in LH secretion was observed during the periovulatory period. Estradiol and P4 secretion were unaffected by melatonin implants. These results suggest that constant administration of melatonin may enhance the secretion of LH during the periovulatory surge but does not adversely affect E2, P4 or basal LH secretion in mares during the breeding season.     

Differences in the success of sugar maple and red maple seedlings on acid soils are influenced by nutrient dynamics and light environment

Variation in tolerance to nutrient limitations may contribute to the differential success of sugar maple ( Acer saccharum Marsh.) and red maple ( Acer rubrum L.) on acid soils. The objectives of this study were to examine these relationships as influenced by light environment and test whether sensitivity to nutrient stress is mediated by oxidative stress. First-year sugar maple and red seedlings were grown on forest soil cores contrasting in nutrient availability under high or low light intensity. Foliar nutrition, photosynthesis, growth and antioxidant enzyme activity were assessed. Photosynthesis and growth of sugar maple were significantly lower on nutrient-poor soils and were correlated with leaf nutrient status with Ca and P having the strongest influence. For red maple, only chlorophyll content showed sensitivity to the nutrient-poor soils. High light exacerbated the negative effects of nutrient imbalances on photosynthesis and growth in sugar maple. Antioxidant enzyme activity in sugar maple was highest in seedlings growing on nutrient-poor soils and was inversely correlated with photosynthesis, Ca, P, and Mg concentrations. These results suggest that: (1) sugar maple is more sensitive to nutrient stresses associated with low pH soils than red maple; (2) high light increases sugar maple sensitivity to nutrient stress; (3) the negative effects of nutrient imbalances on sugar maple may be mediated by oxidative stress.     

Origin,distribution and mapping of RAPD markers from wildPetunia species inPetunia hybrida Hort lines

We have established the first linkage map forPetunia hybrida based upon both RAPD and phenotypical markers. The progeny studied consisted of 100 BC1 individuals derived from the [(St40xTlvl)xTlvl] back-cross. Each morphological marker has previously been mapped onto one of the seven chromosomes. The map consists of 35 RAPD loci of which 24 were affected onto chromosomes while 10 loci were not affected. The loci covered 262.9 cM with a mean distance of 8.2 cM. They are dispersed over seven linkage groups, of which six are carried on identified chromosomes. The RAPD markers were also applied on a set of tenP. hybrida, lines chosen for their diversity and on a set of seven wild species corresponding to the possible ancestors of theP. hybrida species. The markers were found both in the wild species as well as inP. hybrida lines indicating that they are inherited and are stable enough to establish similarities and to suggest relationships between species. Eight out of the ten lines carry different linkage groups of RAPD markers, which suggest that recombinant events occurred between chromosomes which originated in the wild species.     

Evidence for 18O labeling of photorespiratory CO2 in photoautotrophic cell cultures of higher plants illuminated in the presence of 18O2

The ¹⁸O-enrichment of CO₂ produced in the light or during the post-illumination burst was measured by mass spectrometry when a photoautotrophic cell suspension of Euphorbia characias L. was placed in photorespiratory conditions in the presence of molecular ¹⁸O₂. The only ¹⁸O-labeled species produced was C¹⁸O¹⁶O; no C¹⁸O¹⁸O could be detected. Production of C¹⁸O¹⁶O ceased after addition of two inhibitors of the photosynthetic carbon-oxidation cycle, aminooxyacetate or aminoacetonitrile, and was inhibited by high levels of CO₂. The average enrichment during the post-illumination burst was estimated to be 46 ± 15% of the enrichment of the O₂ present during the preceding light period. Addition of exogenous carbonic anhydrase, by catalyzing the exchange between CO₂ and H₂O, drastically diminished the ¹⁸O-enrichment of the produced CO₂. The very low carbonio-anhydrase level of the photoautotrophic cell suspension probably explains why the ¹⁸O labeling of photorespiratory CO₂ could be observed for the first time. These data allow the establishment of a direct link between O₂ consumption and CO₂ production in the light, and the conclusion that CO₂ produced in the light results, at least partially, from the mitochondrial decarboxylation of the glycine pool synthesized through the photosynthetic carbon-oxidation cycle. Analysis of the C¹⁸O¹⁶O and CO₂ kinetics provides a direct and reliable way to assess in vivo the real contribution of photorespiratory metabolism to CO₂ production in the light.     

Bioecological consequences of an accidental hydrocarbon discharge on the rocky shore of the high Normandy coast. Results one year after the oil pollution on the november 26th 1974]

We have followed, during one year, the ecological consequences of an accidental oil pollution on four rocky shores of the norman coast. In the shores where the detergents have not been used, the mussels have progressively excreted the hydrocarbons accumulated in their organism ; the other fixed animals have not been changed. In the shores where the detergents have been used their spreading had not only noxious demoecological consequences, but also synecological consequences with modifications of the fixed species which have colonized the rocks. These observations prove that the use of detergents to clean the polluted shores is not without care.