Calcification in the Green Alga Halimeda: IV. THE ACTION OF METABOLIC INHIBITORS ON PHOTOSYNTHESIS AND CALCIFICATION

The effects of a number of metabolic inhibitors on calcificationand photosynthesis in Halimeda tuna, H. discoidea, and H. macrolobaare described. The inhibitors used are CCCP, DNP, DCMU, azide,cyanide, chloramphenicol, cycloheximide, and Diamox. The effectsof these inhibitors, although complex, are consistent with ourmodel of calcification in Halimeda. Inhibition of photosyntheticCO₂ uptake inhibits calcification as does stimulation of respiratoryCO₂ evolution (i.e. uncoupling). There is also indirect evidencefor the presence of a possible light stimulated H⁺ efflux whichinhibits calcification. The observed calcification rate is thereforethe result of a number of factors which affect the concentrationof CO^–and the pH in the intercellular space of the Halimedathallus. The results obtained with the carbonic anhydrase inhibitor Diamoxprovide further evidence for the effective separation of theintercellular space from the external medium by the appressedperipheral utricles.     

Vegetative anatomy and systematics of subtribe Dendrobiinae (Orchidaceae)

Anatomy of leaf, stem, and root of more than 100 species in subtribe Dendrobiinae (Orchidaceae) was studied with the light microscope to provide a comparative anatomical treatment of these organs, to serve as an independent source of evidence that might be taxonomically important, and to recommend such reinterpretations of existing classifications as are suggested by a phylogenetic assessment of data. We based our classification on that of Rudolf Schlechter as the most complete and widely accepted today. We found that the anatomy of plants in subtribe Dendrobiinae reflects a high degree of morphological diversity, and many of the anatomical characters appear to be homoplasous. When these anatomical data are used to interpret the systematic relationships among the genera, they indicate that Dendrobium is not monophyletic and that Cadetia and Pseuderia are apparently nested within the structure of Dendrobium when section Grastidium is chosen as a functional outgroup. Lack of resolution in the strict consensus tree illustrates the difficulty of determining the phylogenetic relationships of many of Schlechter's sections using anatomical characters. Nevertheless, we recommend that his sectional classification, with appropriate modifications based on available data, be retained for the present, pending a more detailed understanding of the phylogeny of Dendrobiinae based on morphology, micromorphology, anatomy, and DNA studies.     

RNAi-mediated resistance to Potato spindle tuber viroid in transgenic tomato expressing a viroid hairpin RNA construct

Because of their highly ordered structure, mature viroid RNA molecules are assumed to be resistant to degradation by RNA interference (RNAi). In this article, we report that transgenic tomato plants expressing a hairpin RNA (hpRNA) construct derived from Potato spindle tuber viroid (PSTVd) sequences exhibit resistance to PSTVd infection. Resistance seems to be correlated with high-level accumulation of hpRNA-derived short interfering RNAs (siRNAs) in the plant. Thus, although small RNAs produced by infecting viroids [small RNAs of PSTVd (srPSTVds)] do not silence viroid RNAs efficiently to prevent their replication, hpRNA-derived siRNAs (hp-siRNAs) appear to effectively target the mature viroid RNA. Genomic mapping of the hp-siRNAs revealed an unequal distribution of 21- and 24-nucleotide siRNAs of both (+)- and (–)-strand polarities along the PSTVd genome. These data suggest that RNAi can be employed to engineer plants for viroid resistance, as has been well established for viruses.     

Brachiopod orientation to water movement: functional morphology

Previous work by the author has shown that Laqueus californianus. Terebratulina unguicula , and. to a lesser extent, Hemithyris psittacea will actively reorient to water currents in the laboratory; Terebratalia transversa will not. This active reorientation is effected primarily by the dorsal adjustor muscles; the ventral adjustors function to depress and tilt the shell. The torque around the pedicle generated by drag on the shell is low at moderate current speeds. The dorsal adjustor muscles are competent to resist these torques up to current speeds of 35 cm/s for L. californianus and H. psittacea and 56 cm/s for T. unguicula . Shell shape, gross pedicle form, and form of the pedicle foramen are unreliable indicators of a brachiopod's ability to actively reorient. Shape of the pedicle bulb and position and size of the pedicle connectives are better indicators but. on functional grounds, the dorsal adjustor muscle morphology is the best indicator of active reorientation. An angle α (the maximum possible rotation of the shell that can be produced by contraction of one of the dorsal adjustor muscles) correlates well with both the maximum observed rotations and the exhibition of active reorientation to currents. For fossil material, the existence of dorsal adjustor muscle scars that touch medially should also be a good indicator of active reorientation ability.     

The development and persistence of alternative ecosystem states in a large,shallow lake

1. Palaeolimnological data were used to investigate drivers of the community of primary producers in Lake Mattamuskeet, North Carolina, U.S.A. This is a large, shallow lake with two basins currently dominated by phytoplankton and macrophytes. The two basins were divided in 1940 by the building of a roadway across the lake, which also corresponded with the divergence in their ecosystem state. 2. Photosynthetic pigments, organic matter and nutrients (P, N, C, S) were analysed in sediment cores from each basin to reconstruct the primary producer community over the past c. 100 years. We sought to answer two questions. First, what changes to the ecosystem resulting from the building of the roadway caused the development of different primary producer communities in the two basins? Second, why have the alternative ecosystem states persisted despite a variety of human perturbations since 1940? 3. K‐means cluster analysis and principal component analysis were applied to identify three sediment types based on photosynthetic pigment data: sediments indicating low productivity (low pigment concentrations), sediments associated with macrophytes (chlorophyll a and b) and with phytoplankton (alloxanthin and aphanizophyll). In addition, other palaeolimnological proxies measured, such as loss on ignition, total phosphorus, total organic carbon/total nitrogen and other nutrients, were different in post‐1940 sediments within the two basins. 4. These differences suggest characteristics, such as nutrient cycling, water depth and other physical changes resulting from roadway construction, combined to establish and maintain the differing communities of primary producers in the two basins. Furthermore, Fe/S dynamics and waterfowl herbivory probably contributed to the development of the two ecosystem states.     

Nitrate Uptake by Manganese-Deficient Lemon Plants

The uptake of nitrate and water was followed in Eureka lemon (Citrus limon (L.) Burm. f.) plants grown in solution culture in a greenhouse under short (3–6 months) and long-term (22–24 months) Mn-nutrition stress. Uptake was determined from depletion in the nutrient solution. Under short-term stress, manganese-deficient plants absorbed 14.5% more nitrate and 3.4% more water than the control plants, on a weight basis. Under long-term stress there was a three-fold increase in nitrate and a two-fold increase in water uptake in the Mn-deficient plants. The intensive nitrate uptake under Mn-deficiency stress was more spectacularly demonstrated in plants which were exposed also to low nitrogen supply. The low-nitrogen Mn-deficient plants absorbed more nitrate, had less stunted growth and developed fewer visible symptoms of both N and Mn deficiencies than high-nitrogen Mn-deficient plants.     

The biology of some Argiope species from New Guinea: predatory behaviour and stabilimentum construction (Araneae: Araneidae)

Three species of Argiope: A. picta, A. aemula and A. reinwardti were studied at Wau, New Guinea. The stabilimenta in 548 webs of these species were classified into 18 categories, and the frequency of occurrence of each category was recorded. The data from this study are compared with previous records on the variation in the form of the devices built by spiders of the genera Argiope and Gasteracantha and related to theories about stabilimentum function.
Studies of the predatory behaviour of the three species show that this is, in general, similar to that of Argiope argentata . Data are cited to show that the spiders discriminate lepidopterans from insects of similar size. Particular attention was paid to the question of whether the species interrupt predatory sequences, after the attack phase, with a stage during which they rest at the hub of the web before transporting the prey. Unlike Argiope argentata these species interrupt a high proportion of predatory sequences that are initiated by bite/wrap attacks. This aspect of their behaviour is evaluated and discussed.     

Cold-Inhibited Phloem Translocation in Sugar Beet: II. CHARACTERIZATION AND LOCALIZATION OF THE SLOW-COOLING RESPONSE

Experiments were undertaken on a simplified sugar beet systemto characterize the phloem translocation response to slow coolingtreatments that were applied to the source leaf petiole. Inthese experiments the temperature was decreased by 4°C every16 min, such that the tissue temperature was lowered from 25°Cto 1°C over a period of 80 min. Our results indicated thatan initial slow cooling treatment, on a given test plant, causedno change in the rate of translocation. However, all subsequentslow cooling regimes that were applied to the same petiole positionelicited a characteristic step-type inhibition. This inhibitionaveraged about 10% of the original translocation rate in allcases with no recovery being observed. The data suggest thatthe initial cooling treatment induced an alteration in the petioletissue which facilitated the inhibition phenomenon during subsequentslow coolings. This alteration was shown to be localized withinthe upstream region of the chilled petiole segment, followingan initial slow cooling, or throughout the chilled petiole segmentafter an initial quick cooling from 25°C to 1°C. Resultsalso show that the alteration is a long-lived phenomenon thathas no detectable influence on the quick-cooling induced transientinhibition of translocation. Key words: Phloem, Translocation, Cooling response, Petiole