Histology of Callogenesis and Somatic Embryogenesis Induced in Stem Fragments of Cork Oak (Quercus suber) Cultured In Vitro

Calluses able to produce somatic embryos were formed duringin vitro culture of shoot fragments of cork oak (Quercus suberL.).Histological monitoring of these fragments during cultureshowed that it was the cortical parenchyma cells which underwentdedifferentiation before calluses were formed by repeated divisions.The calluses consisted of parenchyma cells surrounded by a fewlayers of meristematic cells. Proembryos formed in groups aroundthe edge of some calluses. Histological examination showed thatthey were produced by the evolution of two different categoriesof cell: one category had the appearance of ‘embryogenic’cells with very thick walls, a small vacuole rich in starchand a well-developed nucleus with a prominent nucleolus. Theother cells were very bulky with large vacuoles; their morphologywas similar to that of suspensor cells encountered in embryogenesisin gymnosperms. The ontogenic stages were similar to those describedin zygotic embryos of the genus Quercus. Nevertheless, mostof the embryonic structures deviated from normal developmentand at all stages produced secondary proembryos. Cork-oak, Quercus suber L, histology, callogenesis, somatic embryogenesis, embryogenic cells, starch, secondary embryogenesis     

Localization of sulfolipid labeling within cells and chloroplasts

Spinach chloroplasts were purified on gradients of Percoll which preserved envelope impermeability and CO₂-dependent oxygen evolution in the light. Application of ³⁵SO₄ to purified chloroplasts resulted in a light-dependent labeling of a lipid component which was indentified as sulfoquinovosyl diacylglycerol. Fractionation of chloroplasts showed that after 5 min of labeling most of the newly synthesized sulfolipid was present in thylakoids. Only a small percentage was recovered from the envelopes. Molecular species from envelopes and thylakoids were identical. The molecular species did not change during incubation times ranging from 5 min up to 4.5 h. Mesophyll protoplasts from ³⁵SO₄-labeled oat primary leaves were gently disrupted and separated into organelles by sucrose gradient centrifugation. Labeled sulfolipid was located almost exclusively in the chloroplasts. This, in combination with the experiments carried out with isolated chloroplasts, indicates that the final assembly steps in the biosynthesis of sulfolipid are confined to the chloroplasts.     

ZUR AUSLÖSUNG DER EIABLAGE BEI DER APHIDOPHAGEN GALLMÜCKE APHIDOLETES APHIDIMYZA (DIPTERA: CECIDOMYIIDAE)

Die Eiablage von Aphidoletes aphidimyza (Rond.) konnte im Experiment durch Honigtau oder durch tote Blattläuse (Myzus persicae, Aphis fabae und Acyrthosiphon pisum), jedoch wesentlich stärker durch beide zusammen ausgelöst werden. Siphonensekret von Acyrthosiphon pisum wurde ebenfalls belegt. Dagegen gelang es nicht, die Gallmücken durch klebrige Substanzen, deren Konsistenz der des Honigtaus ähnlich ist, zur Eiablage zu bringen. Während Exuvien der Erbsenblattlaus für sich allein fast keine Wirkung zeigten, lösten sie in Kombination mit Honigtau die Eiablage ebenso stark aus wie die toten Blattläuse mit Honigtau. Dagegen waren kleine Steinchen in Blattlaus-Größe anstelle der Exuvien unwirksam. Auch Duftstoffe von Blattläusen und Honigtau führten nicht zur Eiablage. Von den Bestandteilen des Honigtaus waren bestimmte Kohlehydrate und Aminosäuren schwach, andere, vor allem Fruktose und Arginin, besser wirksam; reproduzierbar war die Wirkung nur in Kombination mit getöteten Blattläusen.     

Salinity reduction of the end-Triassic sea from the Alpine region into northwestern Europe

A palaeoecological analysis of the Penarth Group (='Rhaetic') of southern England and Wales is undertaken in terms of a species-richness comparison with the Zlambach and Kössen Beds of the Austrian Alps. The three groups studied, bivalves, foraminifers and ostracodes, comprise the most important invertebrate faunas occurring in the deposits cited. All show significant diversity from the Alps into northwest Europe. Coupled with the disappearance of stenohaline elements including ammonites, and taking into account other facies information, the evidence suggests a transgression of a shallow epicontinental sea in northwest Europe at the end of the Triassic. The salinity of this sea (˜25–30%□) was appreciably below that of the Tethyan ocean.     

Crown Gall on Castor Bean Leaves: II. FORMATION OF SECONDARY TUMOURS

Secondary tumours were formed on the cotyledonary leaf petiole,the hypocotyl, and first true leaf of castor bean seedlingsafter inoculating the blades of the cotyledonary leaves withAgrobacterium tumefaciens. Depending on the strain of bacteriaemployed, 0 to 80 per cent of the plants developed secondarytumours. The ability of different strains to initiate secondarytumours was not obviously correlated with their relative effectivenessin initiating primary tumours. Though all produced primary tumours,five out of ten auxotrophic strains failed to yield secondarytumours, whereas only one out of 14 prototrophic strains failedto do so. Both the number of plants developing secondary tumoursand the frequency with which these tumours occurred on differentparts of the plant were positively correlated with the concentrationof the primary inoculum. Tumours also developed on the cotyledonaryleaf petiole and on the hypocotyl after vacuum infiltrationof A. tumefaciens into the blade of cotyledonary leaves. Inmost instances (9 out of 11 plants) no tumours were formed onthe blade of the infiltrated leaf. Thus, tumour formation equivalentto secondary tumours can occur in the absence of a primary tumouror an overt primary wound. Excision of inoculated leaves showedthat the stimulus for secondary tumour formation moves fromthe blade to the hypocotyl within 24 h. Attempts to demonstratethe presence of a sub-cellular tumour-initiating agent in homogenatesof inoculated leaves were unsuccessful. A. tumefaciens, however,was found in the petiole of the cotyledonary leaf and in thehypocotyl within 24 h of inoculation. The migrating agent responsiblefor secondary tumour formation in castor beans is concludedto be intact bacteria.     

Intracellular phosphorylation of benzyladenosine is related to apoptosis induction in tobacco BY-2 cells

Treatment of tobacco BY‐2 cells with micromolar concentration of benzyladenosine ([9R]BA) resulted in the loss of cell viability in a time‐ and concentration‐dependent manner. Cell death induced by [9R]BA exhibited typical apoptotic hallmarks including cell shrinkage, chromatin condensation and degradation of nuclear DNA to characteristic high molecular weight (HMW) as well as nucleosomal size fragments. Externally added [9R]BA was very rapidly and almost quantitatively phosphorylated within BY‐2 cells. Accumulation of [9R]BA‐monophosphate was accompanied by massive production of endogenous reactive oxygen species (ROS), intracellular ATP depletion, and these events were followed by the loss of cell viability. Inhibition of intracellular phosphorylation of [9R]BA by adenosin kinase inhibitor, 5′‐amino‐5′‐deoxyadenosine (AdAs), diminished ROS production, ATP depletion, and consequently prevented cells from death. Selective inhibition of ROS production without restoring ATP production, however, did not provide any protection to cells. In contrast, even enhanced phosphorylation of [9R]BA caused by adenosine that simultaneously revived ATP synthesis reduced the number of dying cells. This is the first evidence of a direct relationship between intracellular phosphorylation of [9R]BA and apoptosis induction in BY‐2 cells. ATP depletion but not ROS production is the key secondary event that determines the cellular decision between life and death.