Effect of Sink-Source Manipulations on the Photosynthetic Rate and Carbohydrate Content of Cucumber Cotyledons

Mayoral, M. L., Plaut, Z. and Reinhold, L. 1985. Effect of sink-sourcemanipulations on the photosynthetic rate and carbohydrate contentof cucumber cotyledons.-J. exp. Bot. 36 1551–1558. The photosynthetic rate of cucumber cotyledons (Cucumis sativuscv. Dahla) reached a maximum value of 12 mg dm^–2 h^–1,10 d after emergence. In 12-d-old seedlings removal of one cotyledondoubled the CO₂ fixation rate of the other, as observed 3 dafter treatment. When the primary leaf was removed, the photosyntheticrate of the cotyledons was decreased by 33%. At this stage ofgrowth elimination of the roots as a sink for assimilates bygirdling the hypocotyl affected neither the photosynthetic ratenor the carbohydrate content of the cotyledons. By contrast,in 18-d-old seedlings removal of the first leaf brought abouta 42% increase in the photosynthetic rate of the cotyledons.The simultaneous removal of the first leaf and one cotyledondoubled the rate of CO₂ fixation of the remaining cotyledon.Girdling the hypocotyl lowered the photosynthetic rate of thecotyledons by 73%. In both 12- and 18-d-old seedlings a decreaseor increase in the sink-source ratio was correlated with anincrease or a decrease respectively in the carbohydrate contentof the cotyledons. The stomatal resistance of the cotyledonswas not affected by any of the treatments. The effect of sink-sourcemanipulations on photosynthesis and on the level of carbohydratespresent in the cotyledons was more evident in those seedlingsgrowing under high light intensity (580 µE m^–2 s^–1),than in those exposed to 300 µE m^–2 s^–1 Key words: Sink-source relationship, cotyledons, photosynthesis     

Relationship Between Spatial Pattern of Basal Bodies and Membrane Skeleton (Epiplasm) During the Cell Cycle of Tetrahymena: cdaA Mutant and Anti-Membrane Skeleton Immunostaining

Microtubular basal bodies and epiplasm (membrane skeleton) are the main components of the cortical skeleton of Tetrahymena. The aim of this report was to study functional interactions of basal bodies and epiplasm during the cell cycle. The cortex of Tetrahymena cells was stained with anti-epiplasm antibody. This staining produced a bright epiplasmic layer with a dark pattern of unstained microtubular structures. The fluorescence of the anti-epiplasm antibody disappeared at sites of newly formed microtubular structures, so the new basal body domains and epiplasmic layer could be followed throughout the cell cycle. Different patterns of deployment of new basal bodies were observed in early and advanced dividers. In advanced dividers the fluorescence of the epiplasmic layer diminished locally within the forming fission line where the polymerization of new basal bodies largely extincted. In wild type Tetrahymena, the completion of the micronuclear metaphase/anaphase transition was associated with a transition from the pattern of new basal body deployment and epiplasm staining of the early divider to the pattern of the advanced dividers. The signal for the fission line formation in Tetrahymena (absent in cdaA1 Tetrahymena mutationally arrested in cytokinesis) brings about 1) transition of patterns of deployment of basal bodies and epiplasmic layer on both sides of the fission line; and 2) coordination of cortical divisional morphogenesis with the micronuclear mitotic cycle.     

The Stimulatory Effect of Indole-3-Acetic Acid on the Uptake of Amino-Acids by Tissue 1Helianthus annuus

Indole-3-acetic acid was observed to bring about a prompt andmarked increase in the amount of ¹⁴C accumulated by segmentsof sunflower hypocotyl from solutions of labelled glutamic acid,glycine, and lysine. The curve relating magnitude of effectto indole-3-acetic acid concentration followed the comparablecurves for water uptake and extension growth. The accumulation of ¹⁴C was related to the external concentrationof glutamic acid by a curve which departed only slightly fromlinearity. The percentage increase in ¹⁴C accumulation broughtabout by auxin did not decline to any appreciable extent withincreasing external concentration of glutamic acid. Under nitrogen the amount of ¹⁴C taken up from solutions oflabelled glutamic acid in 1·75 hour was cut down by approximatelyone-third, and the auxin effect was abolished. The Q₁₀ for ¹⁴Caccumulation between 16° C. and 26° C. was 1·2in the absence of indole-3-acetic acid, and was 1·3 inits presence. When net water uptake was eliminated by the addition of mannitolto the external solution, ¹⁴C accumulation in auxin-free mediawas not depressed. The percentage increase in ¹⁴C accumulationbrought about by auxin, however, was markedly reduced. The fate of the ¹⁴C accumulated was investigated by means ofchromatography on resin columns and on filter paper. About 30–40percent, of the ¹⁴C was in the form of glutamic acid after approximatelya hours' treatment. No marked difference in the level of glutamicacid was observed between auxin-treated and control segments.The effect of auxin was more evident on the amounts of otherradioactive derivatives, as yet unidentified. It was observed that, not only was the amount of CO₂ evolvedin respiration higher in the presence of indole-3-acetic acid,but that this CO₂ was richer in ¹⁴C, i.e. in auxin-treated tissueglutamic acid formed a larger proportion of the substrate respired. The possible implications of these observations are discussed.It is pointed out that indole-3-acetic acid may have achievedits effect by stimulating a transfer process, by lessening adiffusion resistance, or by promoting a process or processeswhich, by removing free amino-acids within the cell, maintainan inward diffusion gradient.     

A new genus and species of rodent from the Brazilian Atlantic Forest (Rodentia: Cricetidae: Sigmodontinae: Oryzomyini), with comments on oryzomyine biogeography

We describe in this paper a new genus and species of cricetid rodent from the Atlantic Forest of Brazil, one of the most endangered eco‐regions of the world. The new form displays some but not all synapomorphies of the tribe Oryzomyini, but a suite of unique characteristics is also observed. This new forest rat possesses anatomical characteristics of arboreal taxa, such as very developed plantar pads, but was collected almost exclusively in pitfall traps. Phylogenetic analyses of morphological (integument, soft tissue, cranial, and dental characters) and molecular [nuclear – Interphotoreceptor retinoid binding protein (Irbp) – and mitochondrial – cytochrome b– genes] datasets using maximum likelihood and cladistic parsimony approaches corroborate the inclusion of the new taxon within oryzomyines. The analyses also place the new form as sister species to Eremoryzomys polius, an Andean rat endemic to the Maranon valley. This biogeographical pattern is unusual amongst small terrestrial vertebrates, as a review of the literature points to few other similar examples of Andean–Atlantic Forest pairings, in hylid frogs, Pionus parrots, and other sigmodontine rodents. © 2011 The Linnean Society of London, Zoological Journal of the Linnean Society, 2011, 161 , 357–390.     

Transport of Amino Acids in Barley Leaf Tissue: II. THE KINETICS OF UPTAKE OF AN UNNATURAL ANALOGUE

A detailed analysis is presented of the relationship betweenexternal concentration and the rate of uptake of an amino-acidanalogue, -aminoisobutyric acid, by barley leaf strips. Theresults are compatible with the operation of specific uptakemechanisms in the case of both freshly cut and ‘aged’tissue. Determination of the fraction of uptake susceptibleof inhibition by a competing amino acid suggested that a paralleldiffusion pathway, if any, plays only a minor role. Indicationsfor a dual amino-acid uptake mechanism were obtained. The principaleffect of ageing appears to be exerted on uptake in the lowerconcentration range.     

The Uptake of 2-Deoxy-dGlucose by Isolated Ricinus Cotyledons

The uptake of the non-metabolizable glucose analogue, 2-deoxy-d -glucose (DOG) has been followed in isolated cotyledons of Ricinus communis L. Within 2 min of immersion in a labelled DOG medium, DOG phosphate (DOG-P) was detectable in the tissue. DOG uptake was relatively rapid for 30 min after which it slowed down but nevertheless continued for many hours; DOG was eventually accumulated against a concentration gradient. Internal DOG-P concentration also rose for the first 30 min, but then reached a plateau. The relationship between uptake and external concentration was close to linear during the first hour, and subsequently curvilinear. Analysis of “wash-out” curves indicated that after very rapid exit from the surface and free space of the tissue, the half-time for exit of the remaining 85% of the absorbed DOG was approximately 250 min. By comparison, the half-time for exit of sorbitol was 30 min. No DOG-P could be detected in the wash-out solutions. When cotyledons were transferred to labelled medium after preloading in non-labelled DOG, the specific activity of the internal DOG pool rose faster than that of the DOG-P. Both curves flattened out when their specific activity was less than half that of the external medium. Addition of d -glucose to the medium depressed DOG-P formation, but only when the incubation period was less than 45 min. Arguments are presented for concluding (a) that DOG uptake is mediated by a specific uptake mechanism; (b) that more than one internal DOG pool is involved; and (c) that the observed phosphorylation is not a necessary step in the entry process into either of the pools, whether the latter are in series or in parallel.