Oxygen Electrode Measurements of Potato Slice Respiration at 0{degrees} C.

The use of the oxygen electrode in measuring the respirationrate of potato slices between o° C. and 27° C. is described.When slices are transferred from 27° C. to o° C. therespiration rate adjusts to the level characteristic of thelow temperature within 2 or 3 minutes. The slices have a highoxygen affinity and the respiration rate at o° C. is approximately10 per cent. of the rate at 24° C. in both freshly cut slicesand slices aged 24 hours, during which time respiration increasesfourfold.     

Development of Ethylene Biosynthesis in Pear Fruits at --1 {degrees}C

Knee, M. 1987. Development of ethylene biosynthesis in pearfruits at — 1 °C.—J. exp. Bot. 38: 1724–1733. The regulation of ethylene synthesis in pear fruits was investigated.During storage for 60 d at — 1 °C the rate of ethylenesynthesis increased 100-fold but the concentration of 1-aminocyclopropane-l-carboxylicacid (ACC) increased only 2-fold and ACC synthase activity waslow. On transfer to 15 °C after storage at — 1 °Cethylene synthesis increased 10-fold within 10 h but ACC synthaseactivity only increased rapidly after 24 h; the decline in ACClevels during the first 16 h at 15 °C was insufficient tosustain ethylene synthesis. Ethylene synthesis was further investigatedusing discs cut from the mid cortex of pear fruits. Synthesiswas inhibited by aminoethoxyvinylglycine (AVG) and amino-oxyaceticacid at all stages of ripening. The rate of synthesis and ACCsynthase activity increased rapidly after slicing of pears heldat — 1 °C but more slowly in discs cut from pearsimmediately after harvest. Cycloheximide (CHI) inhibited theseincreases and reversed increases resulting from pre-incubationof discs. A combination of CHI and AVG abolished the capacityof discs to synthesize ACC and ethylene production was curtailed.Cordycepin and actinomycin-D were less effective as inhibitorsof the development of ethylene synthesis and ACC synthase activitythan as inhibitors of incorporation of 5-[³H] uridine into totalRNA or poly A rich RNA. The ability of discs to develop ethylenesynthesis and ACC synthase activity in the presence and absenceof cordycepin increased concurrently during storage of wholefruits at — 1 °C. This suggested that mRNA for ACCsynthase was formed at — 1 °C. Key words: 1-Aminocyclopropane-l-carboxylic acid, ethylene, fruit ripening, Pyrus communis L. (fruit ripening)     

Photophosphorylation in Attached Leaves of Helianthus annuus at Low Water Potentials

The in situ response of photophosphorylation and coupling factor activity to low leaf water potential (ψ_L) was investigated using kinetic spectroscopy to measure the flash-induced electrochromic absorption change in attached sunflower (Helianthus annuus L. cv IS894) leaves. The electrochromic change is caused by the formation of an electric potential across the thylakoid membrane associated with proton uptake. Since depolarization of the thylakoid membrane following flash excitation is normally dominated by proton efflux through the coupling factor during ATP formation, this measurement can provide direct information about the catalytic activity of the coupling factor. Under low ψ_L conditions in which a clear nonstomatal limitation of net photosynthesis could be demonstrated, we found a strong inhibition of coupling factor activity in dark-adapted leaves which was probably caused by an increase in the energetic threshold for the activation of the enzyme at low ψ_L. While this result supported earlier in vitro findings, we further discovered that the light-dependent reduction of coupling factor reversed any observable effect of low ψ_L on the energetics of activation or on photophosphorylation competence. Furthermore, coupling factor was reduced, even in severely droughted sunflower, almost immediately upon illumination. Based on these measurements, we conclude that the nonstomatal limitation of photosynthesis observed by us and others in droughted plants cannot be explained by impaired coupling factor activity.     

Size-fractionated mesozooplankton biomass, metabolism and grazing along a 50{degrees}N-30{degrees}S transect of the Atlantic Ocean

Size-fractionated mesozooplankton grazing and metabolism wereinvestigated along the wide latitudinal range (50°N–30°S)covered during the Atlantic Meridional Transect (AMT) 11 cruise.Five different oceanic provinces were traversed in this cruise:North Atlantic Drift (NADR), North Atlantic Subtropical Gyral(NAST), Canary Coastal (CNRY), Eastern Tropical Atlantic (ETRA),and South Atlantic Gyral (SATL). CNRY and ETRA were affectedby the upwelling Mauritanian and equatorial respectively andprimary production in these provinces was higher than in theoligotrophic subtropical gyres (NAST and SATL). Both mesozooplanktonand phytoplankton biomass were highest around the equator. Theamount of chlorophyll a ingested daily by copepods was noticeablyhigher in mesotrophic than in oligotrophic provinces as shownby the spatial distribution of gut content values and the highabundances of copepods recorded at the equator. Grazing impactalong the transect ranged from 0.2 to 5.6% of the phytoplanktonstanding stock and from 1.6 to 14.5% of primary production.If only phytoplankton >2 µm are considered, the rangesare 1.0–19.4% (stock) and 3.4–44.7% (primary production).Grazing impact upon both phytoplankton biomass and primary productionfollowed a spatial distribution similar to that of chlorophylla ingestion, with higher values in upwelling zones than in thegyres. Weight-specific rates of respiration and NH₄⁺ and PO₄^3–excretion showed large variability both along the transect andwithin provinces, but did not differ between provinces. Therefore,zooplankton assemblages inhabiting the different provinces visitedin the AMT 11 seem to be adapted to the prevailing thermal conditions.Given the substantial proportion of nitrogen and phosphorusthat are supplied to primary producers through the excretoryactivity of mesozooplankton (the percentage of nitrogen andphosphorus requirements of phytoplankton accounted for by mesozooplanktonexcretion was >30% in all the provinces) it follows thatthey may play a crucial role as nutrient regenerators, especiallyin the oligotrophic gyres where regenerated production dominates.     

Rapid Propagation of Changes in Velocity of Translocation along the Phloem Pathway of Helianthus annuus L.

Localized interruptions of the phloem pathway of sunflower plants,by heat ringing, caused prompt falls in rate of translocationat sites up to 50 cm distant from the ring. The velocity withwhich this change in rate was propagated down the phloem wasan order of magnitude greater than the velocity of translocationitself. It is argued that the findings give support to the pressure-flowhypothesis but do not fit so well with certain other ideas concerningpossible systems by which translocation could be brought about.     

A Theory for Circumnutations in Helianthus annuus

A theory is given for circumnutations in plants, especially hypocotyls of Helianthus annuus, which were used as experimental material The theory is based on the lateral auxin transport, which arises when a gravitational force component acts on the plant. With a suitable time delay between stimulus and response, oscillations or circumnutations should arise. It is possible to describe these oscillation phenomena by the solutions of a differential equation, derived in this paper. The time delay has a central role in this equation. The time delay is assumed to be identical with the geotropic reaction time for the hypocotyls. The ratio between the periodic time for the circumnutations and the reaction time for geotropic curvatures was found to be approximately constant in the temperature region investigated (namely 15–40°C), which supports the theory. Different methods of recording the circumnutations were used, 8 mm film camera technique being the most frequently employed. The introduction of a weighting function for describing the plants “memory” of the stimulation makes it possible to relate the periodic time of the circumnutations to the reaction time for geotropic curvatures. The necessity of this weighting function as well as of the time delay in the equations is emphasized. An explanation of the “Fünfphasen-bewegungen”, reported in the literature, is presented.     

Characteristics of action potentials in Helianthus annuus

The action potentials induced by nondamaging electrical stimuli in 16- to 22-day-old plants of Helianthus annuus were examined. Typical recordings are presented. Mean values of their amplitudes and conduction velocities in the stem, the strength-duration relation, the 'all-or-none' law and the refractory periods have been determined. The amplitude and velocity of propagation were essentially identical in the upward and downward direction, but greater in the upper than in the lower half. In 'electrically active' plants, the rheobase value is 2 V, the minimum period for stimulation is 1.8 s. and the chronaxie 2.3 s. It is noted that the excitability level between similar plants on the same day and in the same plant on different days is highly variable and undergoes periodic changes.     

Diffusible gibberellins and phototropism in Helianthus annuus

Summary Endogenous gibberellins were obtained in agar from the lower cut surface of upright sunflower shoot-tips. Exposure to unilateral light of the tips standing on agar, with the lower cut ends bisected by a vertical glass barrier at right angles to incident light, resulted in approximately 8 times the quantity of gibberellins moving into the agar below the shaded side than into the agar below the illuminated side. These results are similar to those reported earlier for gibberellins and geotropism in sunflower shoots, and suggest than the development of both light-and gravity-induced growth curvatures involve an asymmetry in gibberellin distribution across elongating internodes.     

Changes in cell wall ultrastructure induced by sudden flooding at 25{degrees}C in Pisum sativum (Fabaceae) primary roots

Cellular degeneration is essential for many developmental and stress acclimation processes. Undifferentiated parenchymatous cells in the central vascular cylinder of pea primary roots degenerate under hypoxic conditions created by flooding at temperatures >15°C, forming a long vascular cavity that seems to provide a conduit for longitudinal oxygen transport in the roots. We show that specific changes in the cell wall ultrastructure accompanied previously detected cytoplasmic and organellar degradation in the cavity-forming roots. The degenerating cells had thinner primary cell walls, less electron-dense middle lamellae, and less abundant cell wall homogalacturonans in altered patterns, compared to healthy cells of roots grown under cold, nonflooded conditions. Cellular breakdown and changes in wall ultrastructure, however, remained confined to cells within a 50-μm radius around the root center, even after full development of the cavity. Cells farther away maintained cellular integrity and had signs of wall synthesis, perhaps from tight regulation of wall metabolism over short distances. These observations suggest that the cell degeneration might involve programmed cell death. We also show that warm, nonflooded or cold, flooded conditions that typically do not induce vascular cavity formation can also induce variations in cell wall ultrastructure.     

Sequence Analysis of a 25-kb Segment in the 17{degrees}-19{degrees} Region of the Bacillus subtilis Chromosome Containing ada Locus

As a part of the Bacillus subtilis genome sequencing project,we have determined a 25-kb sequence covering the 17°–19°region. This region contains 26 complete open reading frames(ORFs) including the alkA and adaA/B operon, which encode genesfor adaptive response to DNA alkylation. A homology search forthe newly identified 21 ORFs revealed that 4 of them exhibita significant similarity to known proteins, e.g., methicillin-resistantStaphylococcus aureus (MRSA) protein homolog, proteins involvedin chloramphenicol resistance, glucosamine synthase and an ABCtransporter protein. The remaining 17 ORFs did not show anysignificant sequence similarities to known gene products inthe database.     

A microsatellite marker in Helianthus annuus L.

The importance of genetic polymorphism detected by microsatellites is now well established in mammalian genomes. Sequences with a CA repeat, specific to sunflower, Helianthus annuus L., were found by screening a genomic library in M13. After amplification, some polymorphism was detected on these sequences within a sample of cultivars and populations.     

Characteristics of light-induced H+ transport in spinach chloroplast at lower temperatures II. A possible role of structured water in H+ transport of chloroplast near 0{degrees}C

Light-induced H⁺ transport in spinach chloroplasts at lowertemperatures was investigated with a glass electrode. Half-decaytime of the H⁺ transport on turning off the illumination increasedwith lowering of the temperature. However, near the freezingpoint of bulk water, the H⁺ transport showed no dependency ontemperature. An Arrhenius plot of the apparent first-order rate constantof H⁺ transport showed a break at about 8°C. Below thatcritical temperature, activation energy was about 0 kcal/mole. The break temperature in the Arrhenius plot shifted by 2–3°Cto a higher temperature in the presence of 10% glycerol, aneffective water structure-enhancing agent. On the other hand,addition of 5 mM NaSCN, known as a potent water structure breaker,abolished the break and a constant activation energy was obtainedover the entire low temperature range. A similar effect wasobserved in the presence of 50 mM urea. On the basis of these results, we propose a mechanism for theH⁺ transport of chloroplasts at lower temperatures involvingstructured water, where rapid proton transfer between hydrogen-bondedstructured water molecules takes place. (Received September 11, 1975; )     

Environmentally induced nuclear 2C DNA content instability in Helianthus annuus (Asteraceae)

Experiments were conducted to detect developmental and environmental factors that influence nuclear DNA content in H. annuus inbred lines RHA 271 and RHA 299. DNA content (2C) was determined by laser flow cytometry of nuclei isolated from the first leaf pair of seedlings grown in a greenhouse and in growth chambers. DNA content of greenhouse grown seedlings was highly variable, ranging from 3.2 to 8.0 pg for RHA 299 and 5.2 to 8.2 pg for RHA 271. DNA content only weakly correlated to the position of the achene in the head from which the seedlings derived, and not at all to the position of the head on the plant. Experimentally varied environmental parameters of heat stress and water deficit, phosphate fertilizer levels in the substrate, and pH had little or no effect on the DNA content of seedlings. Seedlings grown with increased levels of substrate nitrogen in the form of NH₄NO₃ showed a significant increase in the mean DNA content. Plants grown in one of two types of growth chambers possessed less variability in DNA content, 6.2–8.4 pg for RHA 299 and 6.8–7.4 pg for RHA 271. Plants grown in a second growth chamber were highly variable with DNA content ranging from 3.0 to 8.6 pg for RHA 299 and 3.0 to 7.8 pg for RHA 271. Measurable physical differences between the growth chambers were irradiance level and the ratio of red to far red light. The hypothesis is presented that DNA stability of sunflowers is influenced by light quantity and/or quality.     

Ten-hour preservation of guinea pig isolated hearts perfused at low flow with air-saturated Lifor solution at 26{degrees}C: comparison to ViaSpan solution

There is no suitable solution to preserve hearts for longer than 5 h between donor explant and recipient implant. Lifor is a fully artificial preservation medium containing both a nonprotein oxygen and nutrient carrier (nanoparticles) and cellular nutrients, including amino acids and sugars. We proposed that recirculated Lifor solution would satisfactorily preserve guinea pig isolated hearts perfused at low flow with no added O(2) at room temperature for 10 h. Hearts were isolated from 21 guinea pigs and perfused with Krebs-Ringer (KR) solution (97% O(2) and 3% CO(2)) at 37 degrees C. Heart rate, inflow and outflow O(2) tension, coronary flow, left ventricular pressure (LVP), and maximal and minimal rate of change in LVP (dLVP/dt) were measured. After baseline measurements, hearts were perfused with recirculated Lifor or ViaSpan equilibrated with room air at 15% of control flow at 26 degrees C for 10 h. Hearts were then perfused at 100% flow with KR for 2 h at 37 degrees C. A time control (untreated) group was perfused only with KR solution for 15 h. Lifor arrested and protected hearts against diastolic contracture and maintained a low O(2) extraction. Compared with time controls, Lifor led to a higher developed LVP and coronary flow; %O(2) extraction and cardiac efficiency were similar between these two groups. Hearts similarly treated with ViaSpan exhibited diastolic contracture and lower %O(2) extraction during treatment and, upon reperfusion with KR, exhibited continued diastolic contracture, no return of heart rate or contractility, low coronary flow, low %O(2) extraction, and marked infarction. For long-term cardiac protection, a suitable preservation solution recirculated at low flow and room temperature without supplemental O(2) would reduce the support apparatus required for transport. Lifor was far superior to ViaSpan in meeting these requirements.     

Endocytosis in erythrocytes and ghosts: occurrence at 0 degrees C after ATP preincubation

Two steps were required for ATP-dependent endocytosis in resealed erythrocyte ghosts. The first step required incubation with Mg-ATP at 37 °C, while the second step required primaquine and occurred at 0 or at 37 °C. These two steps were apparently also required for ATP-dependent endocytosis in erythrocytes. Endocytosis in white ghosts was similar to that in resealed ghosts and erythrocytes; the main difference was that the requirement of primaquine for the second step was less strict in white ghosts; in them, appreciable endocytosis took place with no added primaquine. Nonetheless, endocytosis in all three types of cells was stimulated by primaquine. The fluidity of the membranes as sensed by spin-labeled phosphatidylcholine was measured with and without primaquine. The fluidity of erythrocytes was increased by addition of primaquine or by conversion of the erythrocytes to white ghosts; the effect primaquine had on the fluidity of white ghosts was not detectable by the spin label. This suggested that a fluidizing or loosening of the membrane structure was required for the second step of ATP-dependent endocytosis, and that this loosening could be accomplished either by primaquine or by the process of preparing white ghosts.     

Systemic acquired resistance in sunflower (Helianthus annuus L.)

Systemic acquired resistance (SAR) to infection by Botrytis cinerea in the leaves of sunflower (Helianthus annuus L.) plants was induced following cotyledon inoculation with B. cinerea or treatment with abiotic inducers. Salicylic acid (SA), benzo-(1,2,3)-thiadiazole-7-carbothioic S-methyl ester (BTH), 2,6-dichloroisonicotinic acid (INA) or EDTA protected sunflower plants against Botrytis infection, that was revealed by a reduction in the number and area of the necrotic lesions in upper leaves after challenge inoculation with the pathogen. SA and BTH were more potent inducers than INA, EDTA or pre-inoculation with the fungus. In addition to resistance to B. cinerea, the upper leaves have also developed resistance to maceration by a mixture of cell wall-degrading enzymes. Calcium nitrate inhibited both the protective effect and the resistance of leaf discs to cell-wall degrading enzymes. All the tested chemicals increased the synthesis and excretion of sunflower phytoalexins--coumarins scopoletin and ayapin and induced the PR-proteins chitinase and 1,3-beta-glucanase, being the inducer effect of each activator correlated with the level of protection against B. cinerea (BTH > SA > INA > EDTA). Thus, SAR induction is mediated by general increase of plant defence responses. This is the first report on SAR in sunflower.     

Ent-Kaurene Biosynthesis in Extracts of Helianthus annuus L. Seedlings

Kaurene synthetase B activity (conversion of copalyl pyrophosphate to ent-kaurene) is readily detectable in crude cell-free extracts of 3- to 4-day old dark-grown sunflower (Helianthus annuus cv. Mammoth) seedlings, whereas little or no kaurene synthetase AB activity (conversion of geranylgeranyl pyrophosphate to ent-kaurene) can be found in these extracts under comparable assay conditions. A low amount of AB activity is evident only if an extensively dialyzed extract is used in low concentrations as the enzyme source. One factor which may contribute to the low apparent levels of AB activity is the presence of inhibitory factors in the crude sunflower extract since these extracts can be shown to act as a potent inhibitor of Marah macrocarpus endosperm kaurene synthetase AB activity. Heat treatment (100°C) or dialysis of the sunflower extract reduces the amount of its inhibitory activity. Also, it was observed that low concentrations of extensively dialyzed sunflower extracts act to stimulate M. macrocarpus AB activity. There is no evidence for the presence of an inhibitory factor for M. macrocarpus kaurene synthetase B activity in sunflower extracts. However, there does appear to be present in the crude preparation of sunflower extract a dialyzable factor(s) that impedes its own B activity. There is little information to date on the nature of these inhibitory and stimulatory factors for kaurene synthetase activity or their possible roles in physiological regulation. The possible presence of such factors should be considered, however, when attempting to evaluate kaurene synthetase activities in extracts of vegetative plants.