Langmeier, M., Ginsburg, S. and Matile, Ph. 1993. Chlorophyll breakdown in senescent leaves: demonstration of Mg-dechelatase activity. -Physiol. Plant. 89: 347-353.The action of Mg-dechelatase was brought to light by incubating senescent rape cotyledons or chloroplasts under conditions which prevented the oxidative cleavage of chlorophyll-porphyrin. The accumulation of chlorophyllide and pheophorbide taking place under such conditions was considered as a measure of apparent activities of chlorophyllase and dechelatase, respectively. In excised cotyledons metal chelators such as 2,2'-dipyridyl and o-phenanthroline caused a marked accumulation of pheophorbide a, without affecting the apparent activity of chlorophyllase. Treatment of cotyledons with an inhibitor of cytoplasmic protein synthesis D-2-(4-methyl-2,6-dinitroanilino)-N-methyl-propionamide (D-MDMP) caused a reduced accumulation of pheophorbide a in the presence of dipyridyl, suggesting that the appearance and maintenance of Mg-dechelatase activity in senescent cotyledons requires continuous cytoplasmic protein synthesis. In isolated senescent chloroplasts (gerontoplasts) the cleavage of chlorophyll-porphyrin requires the supplementation with glucose-6-phosphate (Glc6P). Upon the incubation of gerontoplasts in the absence of Glc6P, a conspicuous accumulation of pheophorbide a occurred. Much smaller pools of pheophorbide a were produced when porphyrin cleavage was allowed in the presence of Glc6P. These phenomena were not observed in pre-senescent chloroplasts. In contrast to the apparent Mg-dechelatase activity, chlorophyllase activity did not change in a senescent-specific fashion. The lysis of gerontoplasts by freezing and thawing caused an enhancement of apparent chlorophyllase activity whereas the activity of Mgdechelata.se was lower than in the intact organelles. In the pre-sene.scent chloroplasts, lysis evoked a small apparent Mg-dechelatase activity, suggesting that in a latent form this enzyme may be present even before the onset of foliar senescence.

International audienceNitrogen nutrition of plants in organic farming depends largely on animal manure. In a pot experiment the hypothesis was tested that on a long-term organically managed soil (ORG) characterized by higher soil microbial activity, a greater portion of N applied as cattle manure is mineralized and taken up by plants than on a conventionally managed soil that had received exclusively mineral fertilizers (MIN). Dry matter yields and N uptake by Italian ryegrass were higher by around 20% on ORG than MIN soil. The N utilization of $^{15}$N labeled animal manure components and mineral N differed little between ORG and MIN. The major part of the increased N uptake on ORG compared with MIN was due to a significantly greater N supply from ORG soil. The increased capacity of the ORG soil to supply N to plants became more important at later cuts when N was severely limiting plant growth.Valeur fertilisante azotée d'un lisier de bovin appliqué sur des sols cultivés selon les règles de l'agriculture biologique ou conventionnelle. En agriculture biologique, la nutrition azotée des plantes dépend largement d'une utilisation efficace des engrais de ferme. L'objectif de ce travail était d'évaluer dans une expérience en pots l'aptitude de deux sols provenant d'un essai de longue durée, l'un cultivé selon les règles de l'agriculture biologique et n'ayant reçu que des engrais organiques (ORG) et l'autre cultivé selon les règles de l'agriculture conventionnelle n'ayant reçu que des engrais minéraux (MIN), à alimenter une culture de ray-grass italien après des apports de NO$_3$NH$_4$, de fèces avec/sans urine de bovin préalablement marqués à $^{15}$N. Le sol ORG est caractérisé par une activité microbiologique plus élevée. Le prélèvement d'azote par le ray-grass était plus élevé d'environs 20 % pour le sol ORG que pour le sol MIN. Peu de différences furent observées entre ORG et MIN pour l'utilisation par la plante de l'azote issu des fèces (17 à 22 % du N apporté), de l'urine (62 à 66 % du N apporté) et de l'engrais minéral (75 à 76 % du N apporté). L'augmentation du prélèvement de N par le ray-grass dans le sol ORG s'explique donc par une plus grande minéralisation de l'azote du sol

Summary: Purpose: To study the possible relation between spontaneous recurrent seizures (SRS) and the derangement of cognitive memory.Methods: Status epilepticus (SE) was induced in adult LongEvans rats by pilocarpine (320 mgkg, i.p.) and interrupted after 2 h by clonazepam (CZPs mgkg, i.p.). In addition to the animals that were given pilocarpine and CZP (group P), two groups received ketamine (100 mgkg, i.p.): the first group 15 minutes after SE onset (group K15), and the second immediately after the CZP (group K120). Control groups were formed from animals not treated with pilocarpine as well as animals that received pilocarpine but did not develop motor seizures. Spatial cognitive memory was tested in the Morris water maze.Results: Testing was impossible for more than 6 days after SE in group P. Ketaniine shortened this period for the two groups that received it. During the silent period, deteriorated cognitive memory progressively improved, but the performance of group P started to worsen before the appearance of SRS. Group K120 only expressed a tendency toward declining performance, whereas group K15 never developed SRS, and the behavior of these animals did not differ from that of the controls after the postseizure period was over. Histologically, massive hippocampal cell loss was seen in group P. Ketamine protected hippocampal cells in a time-dependent manner; group K15 did not exhibit any obvious necrosis in the hippocampus.Conclusions: There is no close relation between cognitive functions and the appearance of SRS, because ketamine, administered 120 min after the beginning of SE, prevented the derangment of cognitive functions but not the appearance of The effects of antiepileptic treatment and epilepsy itself on cognitive function are of great interest because of their impact on patients' quality of life (1). Declarative memory is a principal component of cognitive functions. The brain appears to process different kinds of information in separate ways and to store them differently. Declarative knowledge provides an explicit, consciously accessible record of previous, individual experience and a sense of familiarity about this experience. Nondeclarative learning usually occurs in an incremental and automatic manner with no conscious awareness of exactly what has been learned. In animals, cognitive mechanisms can be most convincingly demonstrated in situations that cannot be solved by a direct response to stimuli but require a memory-stored model of the outside world (cognitive maps) and lists of the expected consequences of various actions. Place-navigation tasks, such as the Morris water maze, are suitable models of rat cognitive behavior, which is analogous to declarative memory in human beings (2). Pilocarpine-induced status epilepticus (SE) in rats represents not only a model of severe seizures (3), but also a model of chronic epileptogenesis. After SE and a latent (silent) period lasting 2 to 3 weeks, spontaneous recurrent seizures (SRSs) appear (4). Morphologic changes observed a few days after ...

Summary: Purpose: We wished to characterize the convulsant effect of homocysteic acid (HCA) in developing rats.Methods: Seizures were induced in 7-, 12-, 18-, and 25-dayold rats by intraperitoneal (i.p.) administration of D,L-HCA and in 12-day-old rats by i.p. injection of L-and D-stereoisomers of HCA. The animals were observed for 30 min after injection. The incidence, latencies, pattern of motor seizures, and all behavioral phenomena were noted. Fifty percent convulsant dose (CD,,) values were calculated by probit analysis. Electrocorticograms (ECoG) were recorded after injection.Results: HCA did not elicit minimal clonic seizures whereas generalized tonic-clonic seizures (GTCS) occurred in all the age groups studied. Flexion (emprosthotonic) convulsions occurred to postnatal day 18. ECoG recordings exhibited delta activity in younger pups and sharp graphoelements in older pups, but electroclinical correlation was poor. Young animals were more sensitive to the convulsant effect of D,L-HCA. In addition, D-H€A was significantly more effective than L-HCA in inducing both flexion and generalized seizures.Conclusions: Our data clearly indicate that seizures induced by HCA differ from those evoked by homocysteine. There are no qualitative differences in the motor pattern of seizures induced by the two stereoisomers of HCA, but marked differences were apparent in the very first signs of their action. These differences might be due to interaction with different glutamate receptor subtypes.

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