Light-induced changes in the amounts of the 36000-Mr polypeptide of NADPH-protochlorophyllide oxidoreductase and its mRNA in barley plants grown under a diurnal light/dark cycle

Seedlings of barley were grown either in continuous darkness or under a diurnal 12 h light/12 h dark cycle and the effects on NADPH-protochlorophyllide oxidoreductase were followed at two different levels. Firstly, the relative content of the mRNA encoding the NADPH-protochlorophyllide oxidoreductase was measured by dot-blot hybridization. Secondly, changes in the enzyme polypeptide were monitored either by the method of immunoblotting or by immunogold labelling of ultrathin sections of Lowicryl-embedded leaf tissue. Our results demonstrate that drastic diurnal changes in the level of mRNA sequences and the enzyme protein are unlikely to occur in plants which have been grown under natural light/dark conditions. In the dark, protein and mRNA accumulation occurs at an early developmental stage. These results are difficult to reconcile with the suggestion that the massive accumulation of mRNA and enzyme protein in dark-grown seedlings is primarily the consequence of an artificially extended darkperiod. In addition to the plastid-specific NADPH-protochlorophyllide oxidoreductase a closely related polypeptide has been detected outside the plastid in the surrounding cytoplasm (Dehseh et al. 1986b, Planta 169, 172–183). During the diurnal light/dark treatment of seedlings the concentrations of the two protein populations did not show any variation indicative of an exchange between the two protein populations across the plastid envelope.Abbreviation poly(A)⁺RNA polyadenylated RNA     

Influx of na, k, and ca into roots of salt-stressed cotton seedlings : effects of supplemental ca

High Na⁺ concentrations may disrupt K⁺ and Ca²⁺ transport and interfere with growth of many plant species, cotton (Gossypium hirsutum L.) included. Elevated Ca²⁺ levels often counteract these consequences of salinity. The effect of supplemental Ca²⁺ on influx of Ca²⁺, K⁺, and Na⁺ in roots of intact, salt-stressed cotton seedlings was therefore investigated. Eight-day-old seedlings were exposed to treatments ranging from 0 to 250 millimolar NaCl in the presence of nutrient solutions containing 0.4 or 10 millimolar Ca²⁺. Sodium influx increased proportionally to increasing salinity. At high external Ca²⁺, Na⁺ influx was less than at low Ca²⁺. Calcium influx was complex and exhibited two different responses to salinity. At low salt concentrations, influx decreased curvilinearly with increasing salt concentration. At 150 to 250 millimolar NaCl, ⁴⁵Ca²⁺ influx increased in proportion to salt concentrations, especially with high Ca²⁺. Potassium influx declined significantly with increasing salinity, but was unaffected by external Ca²⁺. The rate of K⁺ uptake was dependent upon root weight, although influx was normalized for root weight. We conclude that the protection of root growth from salt stress by supplemental Ca²⁺ is related to improved Ca-status and maintenance of K⁺/Na⁺ selectivity.     

Basic peroxidases in isolated vacuoles of nicotiana tabacum L.

Vacuoles of tobacco mesophyll and of suspension-cultured cells were isolated in order to study the localization of peroxidase isoenzymes. Only basic peroxidases were detectable by electrophoretic separation of the vacuolar sap. Some of the basic peroxidases have formerly been described as an ionically bound cell-wall fraction. This fraction, however, was found to be an artifact produced by incomplete cell breakage. Reinvestigation of isolated cell walls confirmed that mainly acidic peroxidases are localized in the cell walls where they move freely or are bound. As a consequence of former and present results we think it probable that all of the peroxidase isoenzymes are secretory proteins because they have to be transported from the sites of synthesis in the cytoplasm to the sites of function, the extracytoplasmic spaces, cell wall (acidic peroxidases), and vacuole (basic peroxidases).Abbreviation ER endoplasmic reticulum - PAGE polyacrylamide gel electrophoresis     

Fast charge translocations associated with partial reactions of the Na,K-pump: II. Microscopic analysis of transient currents

Summary Nonstationary pump currents which have been observed in K⁺-free Na⁺ media after activation of the Na,K-ATPase by an ATP-concentration jump (see the preceding paper) are analyzed on the basis of microscopic reaction models. It is shown that the behavior of the current signal at short times is governed by electrically silent reactions preceding phosphorylation of the protein; accordingly, the main information on charge-translocating processes is contained in the declining phase of the pump current. The experimental results support the Albers-Post reaction scheme of the Na,K-pump, in which the translocation of Na⁺ precedes translocation of K⁺. The transient pump current is represented as the sum of contributions of the individual transitions in the reaction cycle. Each term in the sum is the product of a net transition rate times a dielectric coefficient describing the amount of charge translocated in a given reaction step. Charge translocation may result from the motion of ion-binding sites in the course of conformational changes, as well as from movement of ions in access channels connecting the binding sites to the aqueous media. A likely interpretation of the observed nonstationary currents consists in the assumption that the principal electrogenic step is the E₁-P/P-E₂ conformational transition of the protein, followed by a release of Na⁺ to the extracellular side. This conclusion is supported by kinetic data from the literature, as well as on the finding that chymotrypsin treatment which is known to block the E₁-P/P-E₂ transition abolishes the current transient. By numerical simulation of the Albers-Post reaction cycle, the proposed mechanism of charge translocation has been shown to reproduce the experimentally observed time behavior of pump currents.     

Genome relationship betweenPsathyrostachys huashanica andP. fragilis (Poaceae)

Hybrids between the Chinese endemic speciesPsathyrostachys huashanica Keng and the SW. Asian speciesP. fragilis (Boiss.)Nevski (all 2n = 14) developed normally but were completely sterile. Meiotic analyses revealed a high chiasma frequency indicating that the two species as well asP. juncea (Fisch.)Nevski share the same basic genome (called N). The hybrid nature of the plants was established through karyotype analysis and Giemsa C-banding.     

On the carrying behaviour of basic South American primates

InCallithrix, Saguinus, Aotus, andCallicebus other group members than the mother participate in infant care. Differences among these species are obvious in respect to the time of being off any caregiver, and in respect to the carrying position (Aotus andCallicebus). Alloparental care, a basic behaviour pattern in these species, has evolved from the parking behaviour of the prosimians. The infants are «parked» at other group members.     

Arterial supply of the choriocapillaris of anuran amphibians (Rana temporaria,Rana esculenta)

Summary The pattern of the vascular supply to the choroid of the frog eye was studied in toto with the use of the injection-replication-SEM technique. The choroid of anuran amphibians is composed mainly of the choriocapillaris. In both species studied (Rana temporaria, Rana esculenta), an independent arterial supply to the choriocapillaris supplemented that from the ciliary arteries. This additional vascular route arises from the optic artery, a separate branch of the arteria infundibularis superficialis. The optic artery, accompanied by its vein within the vascular sheath of the optic nerve, joins the rich arterial capillary network of the choriocapillaris and supplies the posterior pole of the ocular bulb. The superficial capillary network displays a dense collar around the entrance of the optic nerve into the eye and is composed of a circular meshwork of small capillaries, several layers deep. More peripherally, however, it becomes single layered. This capillary network, as a whole, establishes numerous connections with the adjacent choriocapillaris at the posterior pole of the ocular bulb. In anuran amphibians the complex arrangement of both arterial systems supporting the choriocapillaris may be regarded as a more complete equivalent of the short posterior ciliary arteries of mammals.     

The superficial vascular hyaloid system in the eye of the frogs,Rana temporaria and Rana esculenta

Summary The angioarchitecture of the superficial vascular hyaloid system (membrana vasculosa retinae) of the frog eye was studied by means of scanning electron microscopy of vascular corrosion casts. The terminal vessels form a single-layered sheath intimately adjacent to the vitreal side of the avascular retina. The hyaloid system is subdivided by the ventral venous trunk into three central areas: the dorsal, the temporo-ventral, and the naso-ventral area. Toward the ora serrata, the hyaloid system is bordered by an arterial ring, and by nasal and temporal venous branches forming more or less complete hemicircles. A vascular zone composed of several tongue-like sectors establishes an inter-connection between the peripheral vascular rings and the central areas of the fundus. The arterial blood is supplied from the arterial ring. The drainage of the hyaloid system is provided via two routes: (1) the Y-shaped ventral trunk collects blood from the central areas, (2) the two peripheral venous branches drain the tongue-like sectors. The vessels within the dorsal area follow preferentially a dorso-ventral meridional direction. This densely capillarized territory corresponds in localization to the area centralis retinae. The ultrastructure of microvessels of the hyaloid system is characterized by features typical for capillaries of the central nervous system.     

Testing the “methanochondrion concept”: are nucleotides transported across internal membranes in Methanobacterium thermoautotrophicum?

In order to test the Methanochondrion concept, uptake of adenine nucleotides in various membrane preparations of Methanobacterium thermoautotrophicum was studied. The uptake showed properties which are in general interpreted as indicative of a transport mechanism: (i) kinetics in the time range of minutes, (ii) temperature dependence, (iii) substrate specificity and (iv) failure to remove the substrate by extensive washing.However, nucleotide transport as an interpretation of this uptake can definitely be excluded. Not only an exchange mechanism of the mitochondrial type, but also a general exchange or an uniport mechanism was ruled out. In contrast, the nucleotide uptake was shown to be actually a tight and specific binding of ADP and ATP to binding sites at the interior side of the cell membrane. This was conclusively demonstrated in protoplasts obtained from M. thermoautotrophicum cells. In these protoplasts which do not contain internal membranes also nucleotide binding was observed, but only after disruption of the plasma membrane by osmotic lysis, which leads to the exposure of binding sites.