Oxygen-dependent electron transport and protection from photoinhibition in leaves of tropical tree species

The roles of photorespiration and the Mehlerperoxidase pathway in sustaining electron transport and protection from photoinhibition were studied in outer canopy leaves of two species of tropical trees: the drought-deciduous Pseudobombax septenatum (Jacq.) Dug. and the evergreen Ficus insipida Willd. Ficus had a higher photosynthetic capacity than Pseudobombax and also a greater capacity for light-dependent electron transport under photorespiratory conditions (in the absence of CO₂). As a consequence, in the absence of CO₂, Ficus was able to maintain a largely oxidized electron-transport chain at higher photon flux densities than Pseudobombax. Under the same light conditions, photoinhibition (reduction in F_v/F_m) was always greater in Pseudobombax than Ficus, was increased when leaves were exposed to 2% O₂ in nitrogen compared to 21% O₂ in CO₂-free air, but was not increased by the absence of CO₂. Rates of electron transport due to the Mehler-peroxidase pathway (assessed in 2% O₂ in nitrogen) ranged between 16–40 mol · m^–2·s^–1 in both species. As the dry season approached and Pseudobombax neared leaf senescence there was a decline in the capacity for photorespiratory flux to maintain electron transport in Pseudobombax, but not in Ficus. Ratios of light-dependent electron transport to net CO₂ fixation for Pseudobombax, Ficus and two other species in the field, Luehea seemannii Tr. & Planch, and Didymopanax morototoni (Aubl.) Dec. & Planch., ranged from 6.2 (Ficus) to 16.7 (Pseudobombax). High in-situ rates of photorespiration combined with the decreased capacity of Pseudobombax for photorespiratory flux as the dry season approached indicates a decreased capacity to protect against photooxidative damage. This may contribute to the promotion of leaf senescence in Pseudobombax during the transition from wet to dry season.Abbreviations F_v/F_m ratio of variable to maximum chlorophyll a fluorescence - NPQ nonphotochemical fluorescence quenching - PFD photon flux density - Q_A primary electron acceptor of PSII This research was supported by a grant from the Mellon Foundation. We thank Monica Mejia and Juan Posada for assisting with the fluorescence measurements and Aurelio Virgo for assisting with the field CO₂-exchange measurements.     

Transfer of Brassica tournefartii (TT) genes to allotetraploid oilseed Brassica species (B. juncea AABB, B. napus AACC, B. carinata BBCC): homoeologous pairing is more pronounced in the three-genome hybrids (TACC, TBAA, TCAA, TCBB) as compared to allodiploids (TA, TB, TC)

For the transfer of genes from B. tournefortii (TT) to the allotetraploid oilseed brassicas, B. juncea AABB, B. carinata BBCC and B. napus AACC, B. tournefortii was first crossed with the three basic diploid species, B. campestris (AA), B. nigra (BE) and B. oleracea (CC), to produce the allodiploids TA, TB and TC. These were tetraploidized by colchicine treatment to produce the allotetraploids TTAA, TTBB and TTCC, which were further crossed with B. juncea and B. napus to produce three-genome hybrids with substitution-type genomic configurations: TACC, TBAA and TCAA. These hybrids along with another hybrid TCBB produced earlier, the three allodiploids, their allotetraploids and the four diploid parent species were studied for their male meiotic behaviour. The diploid parent and the allotetraploids (TTAA, TTBB and TTCC) showed regular meiosis although the pollen viability was generally low in the allotetraploids. In the allodiploids (TA, TB and TC) only some end-to-end associations were observed without any clearly discernible chiasmata or exchange points. Chromosomes involved in end-to-end associations were randomly distributed at the metaphase/anaphase-I stages. In contrast, the three-genome hybrids (TACC, TBAA, TCAA and TCBB) showed normal bivalents whose number exceeded the expected bivalent values. Bivalents arising out of homoeologous pairing were indistinguishable from normal pairs by their disjunction pattern but could be distinguished on the basis of the heteromorphy of the homoeologous chromosomes. The three-genome hybrids could be backcrossed to allotetraploid oilseed brassicas as they had some fertility. In contrast, the allodiploids could neither be selfed nor back-crossed. On the basis of their meiotic stability, in terms of more pronounced homoeologous pairing and fertility for backcrossing, the three-genome configurations provide the best possible situation for the introgression of alien genes from the secondary gene pool to the allotetraploid oilseed crops B. juncea, B. napus and B. carinata.     

A new family of dispersed repeats from Brassica nigra: characterization and localization

The 459-bp HindIII (pBN-4) and the 1732-bp Eco RI (pBNE8) fragments from the Brassica nigra genome were cloned and shown to be members of a dispersed repeat family. Of the three major diploid Brassica species, the repeat pBN-4 was found to be highly specific for the B. nigra genome. The family also hybridized to Sinapis arvensis showing that B. nigra had a closer relationship with the S. arvensis genome than with B. oleracea or B. campestris. The clone pBNE8 showed homology to a number of tRNA species indicating that this family of repeats may have originated from a tRNA sequence. The species-specific 459-bp repeat pBN-4 was localized on the B. nigra chromosomes using monosomic addition lines. In addition to the localization of pBN-4, the chromosomal distribution of two other species-specific repeats, pBN34 and pBNBH35 (reported earlier), was studied. The dispersed repeats pBN-4 and pBNBH35 were found to be present on all of the chromosomes, whereas the tandem repeat pBN34 was localized on two chromosomes.     

Modulation of catecholamine storage and release by the pituitary-interrenal axis in the rainbow trout,Oncorhynchus mykiss

This study examined the effects of pituitary-interrenal hormones on catecholamine storage and release in the rainbow trout Oncorhynchus mykiss. An extract of trout pituitary elicited the release of adrenaline, but not noradrenaline, using an in situ perfusion preparation. A variety of doses of adrenocorticotropic hormone (2–2000 mU) caused the release of both catecholamines in situ which was unaffected by pre-treatment with the ganglion blocker, hexamethonium, or the serotonergic receptor antagonist, methysergide, but was abolished in calcium-free media. Intra-arterial injections of adrenocorticotrophic hormone in vivo caused an elevation of plasma adrenaline but not noradrenaline levels. Injections of cortisol in situ did not elicit catecholamine release. Trout given an intraperitoneal implant of cortisol (50 mg·kg^-1 body weight) had significantly higher plasma cortisol concentrations when compared to controls after 7 days of implantation. Increases in the levels of stored catecholamines were observed in various regions of the kidney and posterior cardinal vein following 3 and 7 days of cortisol treatment. The ability of the chromaffin cells to release catecholamines in response to cholinergic stimulation was assessed in situ after 7 days of treatment. Basal (non-stimulated) adrenaline outflowing perfusate levels were greater in the cortisol-treated fish. Cortisol treatment increased the responsiveness of the catecholamine release process to low doses of the cholinoceptor agonist carbachol. Three or 7 days of cortisol treatment did not alter the in vitro activity of the enzyme phenylethanolamine-N-methyl-transferase. The results of this study demonstrate that interactions within the pituitary-adrenal axis can influence both catecholamine storage and release in the rainbow trout.Abbreviations ACTH adrenocorticotropic hormone - AK anterior third of the kidney - APCV anterior third of the PCV - HPLC high performance liquid chromatography - MK middle third of the kidney - M1 maximum value - MPCV middle third of the PCV - MS222 ethyl-aminobenzoate - P1 pre value - PCA perchloric acid - PCV posterior cardinal vein - PK posterior third of the kidney - PNMT phenylethanolamine-N-methyltransferase - PPCV posterior third of the PCV - rbc red blood cells - SEM standard error of the mean - TK total kidney (i.e. the sum of the AK, MK, and PK) - TPCV total PCV (i.e. the sum of the APCV, MPCV and PPCV)     

Differences in haemolymph proteins in relation to diapause and wing dimorphism inPyrrhocoris apterus (L.) (Heteroptera: Pyrrhocoridae)

Three different cultures of dimorphic bug,Pyrrhocoris apterus, were analyzed concerning diapause and its relation to wing morph pattern. The proportion of macropterous bugs was considerably higher (36%) in the Mediterranean culture from Israel than that (1.3%) in the temperate culture from the Czech Republic. The macropterous morph- and brachypterous morphrelated types of reproduction arrest, differing by the length of pre-oviposition period, were distinguished in cultures analyzed. The reproduction arrest with an average pre-oviposition period of 38.2 days in Mediterranean macropters and 18.5 days in macropters from selected macropterous strain, was found to be typical for macropterous morph. Two different photoperiodic conditions induced macropterous morph-related reproduction arrest, the long-day (18 h light-6 h dark) photoperiod in macropterous strain macropters and the short-day (12 h light-12 h dark) photoperiod in Mediterranean macropters. The brachypterous morph-related reproduction arrest, characterized by pre-oviposition period longer than 90 days, occurred predominantly in diapausing brachypterous bugs. While the hibernal diapause of brachypterous bugs was characterized by a very high level of the 78- and 82-kDa proteins in haemolymph, their content in haemolymph of macropters during macropterous morph-related reproduction arrest was almost as low as in the reproductive adults. The variation of reproduction arrest in relation to wing dimorphism represents an important feature in the life strategy ofP. apterus.     

The tympanal hearing organ of the parasitoid fly Ormia ochracea (Diptera, Tachinidae, Ormiini)

Tympanate hearing has evolved in at least 6 different orders of insects, but had not been reported until recently in the Diptera. This study presents a newly discovered tympanal hearing organ, in the parasitoid tachinid fly, Ormia ochracea. The hearing organ is described in terms of external and internal morphology, cellular organization of the sensory organ and preliminary neuroanatomy of the primary auditory afferents. The ear is located on the frontal face of the prothorax, directly behind the head capsule. Conspicuously visible are a pair of thin cuticular membranes specialized for audition, the prosternal tympanal membranes. Directly attached to these membranes, within the enlarged prosternal chamber, are a pair of auditory sensory organs, the bulbae acusticae. These sensory organs are unique among all auditory organs known so far because both are contained within an unpartitioned acoustic chamber. The prosternal chamber is connected to the outside by a pair of tracheae. The cellular anatomy of the fly's scolopophorous organ was investigated by light and electron microscopy. The bulba acustica is a typical chordotonal organ and it contains approximately 70 receptor cells. It is similar to other insect sensory organs associated with tympanal ears. The similarity of the cellular organization and tympanal morphology of the ormiine ear to the ears of other tympanate insects suggests that there are potent constraints in the design features of tympanal hearing organs, which must function to detect high frequency auditory signals over long distances. Each sensory organ is innervated by a branch of the frontal nerve of the fused thoracic ganglia. The primary auditory afferents project to each of the pro-, meso-, and metathoracic neuropils. The fly's hearing organ is sexually dimorphic, whereby the tympanal membranes are larger in females and the spiracles larger in males. The dimorphism presumably reflects differences in the acoustic behavior in the two sexes.     

Species turnover between Afromontane and eastern African lowland faunas: patterns shown by amphibians

Abstract. Following the recognition of a discrete East African lowland amphibian fauna (Poynton, 1990), this paper investigates the possible recognition of an Afromontane amphibian fauna in southern Africa. Species turnover in a transect from the Mozambique/KwaZulu-Natal border area through Swaziland to the Eastern Transvaal highveld is described, and compared with previously described transects through Mozambique to Zimbabwe, and KwaZulu-Natal to the central Free State. Turnover in the Swaziland transect shows two peaks. Marked turnover at the edge of the interior plateau is taken to indicate an eastern border of an Afromontane fauna; the other peak, at the western edge of the coastal lowland, is taken to mark the border of an East African lowland fauna. A transition zone with a transitional assemblage occurs on the plateau slopes between the two borders. The Zimbabwean transect shows a similar pattern. The KwaZulu-Natal to Free State transect shows a broad transition from upland to lowland assemblages, which parallels the extensive intermingling of upland and lowland floristic elements in that area. A north-south turnover across the three transects shows northern species becoming progressively excluded from highland areas as they extend southwards, while southern species become limited to the highlands as they extend northwards. The cohesive north-south turnover pattern is consistent with the idea of a single Afromontane biogeographical unit, which can be related to a tropical East African lowland unit through a complex pattern of species turnover.     

中国太湖1950年以来主要环境的变化和迅速富营养化的开始

太湖是我国第三大淡水湖,面积２３５０ｋｍ＾２,位于长江三角洲（面积３５０００ｋｍ＾２）的中部,自６０００年前太湖形成以来,湖泊经历了几个主要变化,１９５０年以前太湖最明显的变化发生在海侵和湖盆大小,海侵是太湖形成的主要原因。太湖形成后,在不同的干燥和湿润时期,湖盆经历了由一系列的小湖或统一湖盆之间的波动,但一般来说,近２０００年以来,湖盆的大小在增大,然而１９５０年以后,为适应人口的增长,许多浅水     

Use of low temperature sem to locate free water in frozen,hydrated seed tissues of Glycine max (Leguminosae)

Low temperature field emission electron microscopy was used to determine the location of free water in soybean seeds. Frozen, hydrated soybean seeds were fractured, the water etched from the fractured surface, and then part of the etched surface was refractured. The resulting surface, which contained a freeze-fractured face as well as a freeze-etched face was coated with platinum and viewed on the cryostage of a low temperature field emission electron microscope. Two surfaces could be viewed simultaneously to determine the location of water in the seed tissue. Viewing the fractured surface gave an indication of the extent of hydration of the tissue. Viewing the etched surface detailed the macro- and microanatomy of the tissue. Viewing the intersection between the fractured and etched surfaces allowed observation of the environment of partially etched cells and organelles. The technique avoids artifacts associated with chemical fixation, dehydration, and critical-point drying, procedures that affect the water content of the seed. The technique does not affect the degree of hydration of the seed and can be used to localize water in the inter- and intracellular environment of the seed. This technique could find wide application in studies of water relationships of seeds during development, maturation, and imbibition.     

INVITED SPECIAL PAPER: History of the botanical teaching laboratory in the United States

The establishment of teaching laboratories for botany in the United States was strongly influenced in the early part of the 19th century by the founding of a laboratory of natural history at the Rensselaer School by Amos Eaton who inspired numerous educators, particularly women. By midcentury and later, botany programs were established at land-grant colleges and the so-called “new Botany” movement spread from them. In the latter part of the century additional changes were brought about by the influence of German laboratory activity and botanists’ reactions to the introduction of the Huxley-Martin biology programs to America. During these times, Americans were improving their own manufactured microscopes, laboratory supplies, and equipment capabilities. By the beginning of the 20th century, laboratory teaching of botanical subjects was widely accepted as normal in universities and colleges, as well as in some high schools.