A procedure for purifying the chloroplast envelope subfractionates it into two membrane fractions ofcomparable quantities. This procedure differs from previous ones in that the chloroplasts are ruptured by freezing and thawing in hypertonic medium rather than by osmotic shock. The two membrane fractions have qualitatively similar polar lipid compositions but differ in their content of individual lipids, specifically monogalactosyldiacylglycerol and phosphatidylcholine. The two fractions also differ in their constituent polypeptides and in their appearance when examined by electron microscopy. The light (density = 1.08 g/ ml) and heavy (density = 1.13 g/ml) membrane fractions have been tentatively identified as the outer and inner envelope membranes, respectively.The chloroplasts ofhigher plants are enclosed by a pair ofclosely spaced membranes, the envelope, consisting of an outer membrane in contact with the cytoplasm of the cell and an inner membrane bounding the matrix or stroma of the organelle. The chloroplast envelope mediates the complex interactions between the chloroplast and the cell cytoplasm. For example, both reactants and products of photosynthesis must be transported across the envelope (1). In addition, those chloroplast proteins that are synthesized on cytoplasmic ribosomes must cross the envelope to reach their correct location (2). The envelope is also the site of various biosynthetic reactions, including those responsible for the formation of the galactolipids, major components of both envelope and thylakoid membranes (1).The two membranes of the envelope have major differences in both structure and function, as shown by studies of isolated intact chloroplasts. It has been shown by freeze-fracture electron microscopy that the density of intramembranous particles is much lower in the outer membrane than in the inner, suggesting that the protein content ofthe outer membrane is lower (3). Also, experimental evidence indicates that the outer membrane is nonspecifically permeable to low molecular weight compounds although the inner is impermeable to such compounds and contains several translocator systems for the transport of metabolites (4).In previously published procedures for the purification of envelopes from intact chloroplasts, the plastids are first broken by hypotonic lysis and the envelopes are then isolated by centrifugation (1). Unfortunately, during isolation, the inner and outer membranes presumably become an inseparable mixture. This makes it impossible to use these preparations to investigate the reported differences between the two membranes or to determine which one contains which biosynthetic enzymes.We report here a new procedure for preparing the chloroplast envelope that subfractionates the envelope into two distinct fractions tentatively identified as the inner and outer membranes.MATERIALS AND METHODS Percoll, uridine-5'-diphosphogalactose, and trypsin inhibitor (Type I-P from beef pancreas) were from Sigma. Trypsin and chymotrypsin were from Boehringer Mannheim an...

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SUMMARY The fixation of cells of petiolar hairs of tomato was monitored by phase contrast and Nomarski interference contrast microscopy. Because the cuticle covering these hairs is relatively impermeable some fixatives enter only the base of the hair so that a ‘fixation front’ can be followed through a single cell. The basal end of such a cell may be immobilized by the fixative while the apical end is still streaming. A variety of fixatives were tested at room temperature and at 273–278 K. All procedures tested failed to stabilize a pleomorphic canalicular system that is a dominant feature of these cells so that no clue to the presence of this system can be seen in sectioned material. It is therefore very desirable that images of fixed cells be compared to the structure of similar cells which are still alive.

Summary: Résumé: Zusammenfassung The influence of temperature and relative humidity (r.h.) on the efficacy of glufosinate ammonium was investigated in controlled environment growth chambers using a tolerant species, barley (Hordeum vulgare L. cv. ‘Samson’), and a susceptible species, green foxtail (Setaria viridis (L.) Beauv.). The shoot ammonia concentration and visual injury of plants treated with glufosinate‐ammonium doses of 100 and 800 g ha−1 were compared at day/night temperature regimes of 8/5,15/10 and 22/17°C at 60% r.h. The effect of relative humidity levels of 40% and 95% on the shoot ammonia concentration, visual injury and dry weight accumulation of glufosinate‐ammonium treated plants was tested at temperature regimes of 15/10 and 22/17°C, with both species treated with 800 g ha−1. In addition, green foxtail treated with 100 g ha−1. was tested at both r.h. levels at 22/17°C. As the temperature de creased, less ammonia was produced in treated green foxtail plants. However, ammonia levels were comparable at all temperature regimes for barley. Lowest temperatures resulted in delayed injury to both species, but only small differences in injury existed among temperature regimes 288 h after spraying. The activity of glufosinate ammonium on both species was significantly de creased by low r.h. For example, when grown at 22/17°C, green foxtail survived the potentially lethal dose of 100 g ha−1 at 40% r.h. and accumulated 70% of the dry weight of control plants, but was killed at 95% r.h. Of the two environmental factors examined, r.h. had the most significant effect on the phytotoxic action of glufosinate‐ammonium. L'influence de la température et de I'humidité relative sur I'efficacité du glufosinate‐ammonium L'influence de la température et de 1'humidité relative (hr) sur I'efficacité du glufosinate ammonium a étéétudiée en chambre climatique en utilisant une espéce d'orge tolérante (Hor deum vulgare L. cv ‘Samson’) et une espéce sensible la svtaire verte (Setaria viridis L. Beauv). La concentration en ammoniaque des pieds et les dégats visuels des plantes traitérs avec des doses de glufosinate ammonium de 100 et 800 g/ ha−1 ont été comparés pour des régimes de températures jour/nuit de 8/5, 15/10 et 22/17°C à 60% hr. L'effet de taux d'humidité relative de 40 et 95% sur la teneur en ammoniaque des pieds, les dégats visuels et (l'accumulation de matiére séche chez des plantes traitéres au glufosinate ammonium a été testéà des régimes de températures de 15/10 et 22/17°C, pour les 2 espéces traitées à 800 g ha−1. En outre, la sétaire verte traitée à 100 g hr−1 a été testée aux 2 hr à 22/17°C. Quand la température diminue, il y a moins d'ammoniaque produit chez les sétaires vertes trailérs. Cependant les taux d'ammon iaque ont été comparables à toutes les tempéra tures chez 1'orge. Les températures les plus basses ont abouti à un retard de phytotoxicité ches les 2 espéces, mais à peu de différences entre les régimes de températures 288 h après 1'application. L'activité du glufosinate ammon ium chez les deux ...

Soybean (Glycine max (L.) Merr.) protoplasts have been surface-labelled with cationized ferritin, and the fate of the label has been followed ultrastructurally. Endocytosis of the label occurs via the coated-membrane system. The pathway followed by the label, once it has been taken into the interior of the protoplast, appears to be similar to that found during receptor-mediated endocytosis in animal cells. Cationized ferritin is first seen in coated vesicles but rapidly appears in smooth vesicles. Labelled, partially coated vesicles are occasionally observed, indicating that the smooth vesicles may have arisen by the uncoating of coated vesicles. Structures which eventually become labelled with cationized ferritin include multivesicular bodies, dictyosomes, large smooth vesicles, and a system of partially coated reticula.