Drying half of the root-zone from mid fruit growth to maturity in ‘Hass’ avocado (Persea americana Mill.) trees for one season reduced fruit production in two years

We tested the effect of extended drying of half the root system on fruit yield and fruit Ca concentration, an indirect measure of fruit quality, in avocado (Persea americana Mill. cv Hass). In a field experiment on a sandy soil, withholding irrigation and plastic sheeting was used to dry the root-zone beneath the whole canopy (DD) or half the canopy (WD), compared with well-watered trees (WW). The irrigation water contained added nutrients and was slightly saline. Yield, shoot growth, leaf conductance, leaf and fruit water status and mineral concentrations of leaves and fruit were studied. The responses of treated trees were assessed in the following season during which normal irrigation practices were restored. With respect to yield, the WD treatment behaved the same as the DD treatment. It reduced yield by more than half and proportionately more than the reduction in water supply thus reducing irrigation efficiency. Re-watering did not restore yield of WD or DD-trees in the next season. The WD and DD treatments had no effect on the concentration of Ca in the fruit mesocarp and so are unlikely to affect fruit quality. The main impact of reduced water supply on the trees was fruit abscission and this was linked to dry soil around the roots rather than the water status of the leaves or fruits. We conclude that extended drying of half of the root-zone in one season reduced irrigation efficiency for two seasons by promoting the abscission of developing fruit to the same extent as occurred when the whole root system was exposed to extended drying.     

The physiological tolerance of the grey carpet shark (<Emphasis Type="Italic">Chiloscyllium punctatum</Emphasis>) and the epaulette shark (<Emphasis Type="Italic">Hemiscyllium ocellatum</Emphasis>) to anoxic exposure at three seasonal temperatures

The epaulette shark (Hemiscyllium ocellatum) and the grey carpet shark (Chiloscyllium punctatum) are commonly found in periodically hypoxic environments. The ecophysiological time available for these animals to safely exploit these niches during different seasonal temperatures was examined. The time to loss of righting reflex (T _LRR) was examined in response to an open ended anoxic challenge at three seasonal temperatures (23, 25 and 27°C). Ventilation rates were measured in an open ended anoxic challenge at 23°C and during 1.5 h of anoxia followed by 2 h of re-oxygenation at 23 and 25°C. The mean T _LRR of epaulette and grey carpet sharks was inversely proportional to temperature. The T _LRR was similar between species at 23°C; however, grey carpet sharks had significantly reduced T _LRR at higher temperatures. During the standardised anoxic challenge, epaulette sharks entered into ventilatory depression significantly earlier at 25°C. During re-oxygenation, epaulette sharks exposed to anoxia at 23°C had no significant increase in ventilation rates. However, after anoxic challenge and re-oxygenation at 25°C, epaulette sharks showed a significant increase in ventilation rates during re-oxygenation. Grey carpet sharks displayed no evidence of ventilatory depression during anoxia. However, during re-oxygenation, grey carpet sharks had significantly elevated ventilation rates above pre-experimental levels and control animals. These data demonstrate that the anoxia tolerance times of both species were temperature dependent, with a significant reduction in the T _LRR occurring at higher temperatures. Epaulette sharks had a significantly greater T _LRR at higher temperatures than grey carpet sharks, which did not enter into a ventilatory depression.     

The role of impulse on the initiation of particle movement under turbulent flow conditions

Fundamental to our understanding of erosional and transport phenomena in earth-surface dynamics and engineering is knowledge of the conditions under which sediment motion will begin when subjected to turbulent flow. The onset criterion currently in use emphasizes the time-averaged boundary shear stress and therefore is incapable of accounting for the fluctuating forces encountered in turbulent flows. We have validated through laboratory experiments and analytical formulation of the problem a criterion based upon the impulse imparted to a sediment grain. We demonstrate that in addition to the magnitude of the instantaneous turbulent forces applied on a sediment grain, the duration of these turbulent forces is also important in determining the sediment grain's threshold of motion, and that their product, or impulse, is better suited for specifying such conditions.     

Significant increases in pulping efficiency in C4H-F5H-transformed poplars: improved chemical savings and reduced environmental toxins

The gene encoding ferulate 5-hydroxylase (F5H) was overexpressed in poplar (Populus tremula x Populus alba) using the cinnamate-4-hydroxylase (C4H) promoter to drive expression specifically in cells involved in the lignin biosynthetic pathway and was shown to significantly alter the mole percentage of syringyl subunits in the lignin, as determined by thioacidolysis. Analysis of poplar transformed with a C4H-F5H construct demonstrated significant increases in chemical (kraft) pulping efficiency from greenhouse-grown trees. Compared to wild-type wood, decreases of 23 kappa units and increases of >20 ISO brightness units were observed in trees exhibiting high syringyl monomer concentrations. These changes were associated with no significant modification in total lignin content and no observed phenotypic differences. C4H-F5H-transformed trees could increase pulp throughputs at mills by >60% while concurrently decreasing chemicals employed during processing (chemical pulping and bleaching) and, consequently, the amount of deleterious byproducts released into the environment.     

Cloning and expression of desoxyhemigossypol-6-O-methyltransferase from cotton (Gossypium barbadense)

Terpenoids play an important role in defense against insects and pathogens in cotton. These terpenoids contain phenolic groups. Metabolites in which the phenolic group has been converted to a methoxy group are less toxic to most insects and pathogens and thus may alter resistance. Here is reported the cloning of a gene from Gossypium barbadense that encodes the enzyme that methylates the phenolic group of desoxyhemigossypol (dHG) exclusively at the 6-position, dHG-6-O-methyltransferase (dHG-6-OMT). Partial peptide sequences from digests of purified dHG-6-OMT were used to design primers for RT-PCR amplification of cDNA fragments from poly(A) mRNA. Fragments were extended to full length using 5' and 3' RACE. The resulting cDNA codes for a 365-residue polypeptide with a calculated molecular weight of 40.6 kDa, in agreement with the molecular mass of purified dHG-6-OMT. When expressed in Escherichia coli, the bacterial lysates showed a high specificity for the methylation of desoxyhemigossypol, differentiating the cloned gene from other pathogen-induced methyltransferases.     

The expression of histamine H4 receptor mRNA in the skin and other tissues of normal dogs

The histamine 4 (H₄) receptor was first cloned and characterized in 2000 using the human H₃ receptor DNA sequence. The H₄ receptor has been shown to participate in various aspects of inflammation, such as chemotaxis, upregulation of adhesion molecule expression and modulation of cytokine secretion. The primary goal of this study was to determine whether H₄ receptor mRNA is expressed in normal canine skin by performing an RT‐PCR. An additional goal was to determine the expression of this receptor in the colon, liver, spleen and kidney. Tissues were collected from five healthy, young‐adult pit bull dogs. Samples were immediately placed in RNAlater^® solution and stored at ?20°C until processed. The amplified products in all skin samples in addition to the colon, liver, spleen and kidney (variable expression) had the expected size of 400–500 bp. The sequenced amplicons matched the National Center for Biotechnology Information published sequence for the canine H₄ receptor. The study results showed that canine normal skin expresses the H₄ receptor mRNA. Further studies using immunohistochemistry should be conducted to demonstrate the expression of the H₄ receptor at the protein level and to localize the expression of this receptor in the skin.     

Varietal susceptibility to damage in potatoes

Summary Samples of 62 varieties of potato grown under identical conditions were harvested with much and little damage. From the much damaged samples the damage index was calculated for each variety. The less damaged samples were examined with a Lampe penetrometer for skin hardness and hardness after removing 2 mm of tissue. The varieties were ranked in order of damage susceptibility, and though generally damage index and surface penetrometer reading were inversely related, some varieties gave anomalous results, showing prediction by penetrometer of susceptibility to mechanical damage to be unreliable. Penetrometer readings for the skin and the tissue 2 mm deep were compared to see if susceptibility to bruising is influenced by the relative strengths of inner and outer tissue. The susceptibility of varieties bruised by a standard technique was compared with that predicted. The relative strength of skin and internal tissue gave only a very approximate guide to bruising susceptibility.

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Zusammenfassung 62 Kartoffelsorten wurden unter gleichen Bedingungen angebaut. W?hrend der Ernte mit einem Siebkettenroder wurden von jeder Sorte Muster entnommen, sowohl nach zu starkem Schütteln des Siebes, um viele mechanische Sch?den zu verursachen, als auch nach Reduzierung der Schüttelbewegung, um den Schaden auf dem Minimum zu halten. Die ersten Muster wurden mit P-Kresol (Robertson, 1961) behandelt, um die Identifizierung der oberfl?chlichen mechanischen Sch?den (aber nicht Blaufleckigkeit) und den für jede der acht Gr?ssenklassen errechneten Schadenindex zu erleichtern. Die zweiten Muster wurden für die Prüfungen der Schalenfestigkeit mit dem Lampe-Penetrometer gebraucht (Lampe, 1959). Für jede Knolle wurde eine Oberfl?chen-Ablesung mit dem Penetrometer gemacht; dann wurde eine 2 mm dicke Scheibe von der Knolle entfernt und eine zweite Ablesung vorgenommen. Der Vergleich mit der Oberfl?chen-Ablesung mit jener 2 mm tiefer zeigt relative St?rke der Schale und des inneren Gewebes. Es wird angenommen, dass wenn das Schalengewebe viel st?rker ist als das innere Gewebe, die Entwicklung von Blaufleckigkeit m?glich ist, w?hrend bei relativ festerem innerem Gewebe keine Blaufleckigkeit entstehen dürfte. Die Sorten wurden klassifizicrt als sehr früh, früh, mittelfrüh und mittelsp?t, und in den Tabellen 1–4 sind sie in absteigender Reihenfolge ihres Schadenindexes nach Gewicht aufgeführt, so das die am leichtesten zu besch?digenden Sorten in jeder Tabelle oben und die gegen Besch?digungen am widerstandsf?higsten Sorten am Schluss stehen. W?hrend im allgemeinen eine Sorte mit einem hohen Schadenindex eine kleinere Belastung im Penetrometer anzeigt und umgekehrt, gibt es dafür einige Ausnahmen, z.B. Craig's Alliance, Dunbar Rover, Ulster Classic und Désirée. Die Ergebnisse zeigen, dass ein Penetrometer nicht immer ein verl?ssliches Instrument für die Vorhersage der Empfindlichkeit einer Sorte auf mechanische Sch?den darstellt. Es hat sich auch gezeigt, dass der Gebrauch des Penetrometers als Hilfsmittel zur Vorhersage sortenbedingter Empfindlichkeit auf Blaufleckigkeit unzuverl?ssig ist. Wenn bei einigen Sorten durch Fallenlassen einer Stahlkugel auf die Knollen Blaufleckigkeit induziert wird (Tabelle 5), zeigt sich, dass die Hypothese des Einflusses der relativen Festigkeit des ?usseren und inneren Gewebes auf die Empf?nglichkeit der Sorten für Blaufleckigkeit nicht aufrechterhalten werden kann.

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Résumé Soixante-deux variétés ont été mises en végétation dans des conditions identiques. Au cours de la récolte avec une arracheuse-élévatrice, on a prélevé des échantillons doubles, l'un après agitation excessive des cha?nes pour causer le maximum de dommages mécaniques, l'autre après réduction de l'agitation des cha?nes pour réduire les dommages au minimum. On a traité le premier échantillon avec du p-crésol (Robertson, 1961) pour faciliter l'identification des dommages mécaniques de surface (mais non les taches cendrées) et on a calculé l'indice d'endommagement (Robertson, 1966) pour chacune des 8 classes de grosseur. Le second échantillon a été utilisé pour les tests de dureté de la peau au moyen du pénétromètre Lampe (Lampe, 1959). On fait une première lecture de surface sur chaque tubercule, puis une seconde après enlèvement d'une tranche de 2 mm. La comparaison de la lecture de surface avec celle à 2 mm de profondeur révèle les résistances du tissu de surface et du tissu interne. Il est supposé que si le tissue de surface est beaucoup plus fort que le tissu interne, le développement des taches cendrées peut être possible, tandis qu'avec un tissu interne relativement fort les taches cendrées ne peuvent se produire. Les variétés sont classées dans les catégories: première précocité, seconde précocité, récolte principale, tardive; les tableaux 1 à 4 montrent les variétés dans leur catégorie, classées par ordre décroissant d'indice d'endommagement par poids, les variétés sensibles se trouvant donc au sommet des colonnes, les plus résistantes en dessous. Alors qu'en général une variété avec un haut indice d'endommagement montre une faible charge de pénétration avec le pénétromètre et vice-versa, il appara?t quelques exceptions, par example Craig's Alliance, Dunbar Rover, Ulster Classic et Désirée. Ces résultats montrent que le pénétromètre n'est pas toujours un instrument valable pour prévoir la susceptibilité d'une variété aux dommages mécaniques. L'usage du pénétromètre en tant qu'aide pour prévoir la susceptibilité d'une variété aux taches cendrées s'est également montré non valable. L'induction de meurtrissures sur quelques-unes des variétés en laissant tomber des boules d'acier sur les tubercules (tableau 5) a montré que l'hypothèse de l'influence des résistances relatives des tissus externes et internes sur la prédisposition des variétés aux meutrissures n'est pas confirmée.

     

Photosynthetic responses of forest understory tree species to long-term exposure to elevated carbon dioxide concentration at the Duke Forest FACE experiment

We examined the photosynthetic responses of four species of saplings growing in the understory of the Duke Forest FACE experiment during the seventh year of exposure to elevated CO2 concentration ([CO2]). Saplings of these same species were measured in the first year of the Duke Forest FACE experiment and at that time showed only seasonal fluctuations in acclimation of photosynthesis to elevated [CO2]. Based on observations from the Duke Forest FACE experiment, we hypothesized that after seven years of exposure to elevated [CO2] significant photosynthetic down-regulation would be observed in these tree species. To test our hypothesis, photosynthetic CO2-response and light-response curves, along with chlorophyll fluorescence, chlorophyll concentration and foliar N were measured twice during the summer of 2003. Exposure to elevated [CO2] continued to increase photosynthesis in all species measured after seven years of treatment with the greatest photosynthetic increase observed near saturating irradiances. In all species, elevated [CO2] increased electron transport efficiency but did not significantly alter carboxylation efficiency. Quantum yield estimated by light curves, chlorophyll concentration, and foliar nitrogen concentrations were unaffected by elevated [CO2]. Contrary to our hypothesis, there is little evidence of progressive N limitation of leaf-level processes in these understory tree species after seven years of exposure to elevated [CO2] in the Duke Forest FACE experiment.     

Relationships between net photosynthesis and foliar nitrogen concentrations in a loblolly pine forest ecosystem grown in elevated atmospheric carbon dioxide

We examined the effects of elevated carbon dioxide concentration ([CO2]) on the relationship between light-saturated net photosynthesis (A(sat)) and area-based foliar nitrogen (N) concentration (N(a)) in the canopy of the Duke Forest FACE experiment. Measurements of A(sat) and N(a) were made on two tree species growing in the forest overstory and four tree species growing in the forest understory, in ambient and elevated [CO2] FACE rings, during early and late summer of 1999, 2001 and 2002, corresponding to years three, five and six of CO2 treatment. When measured at the growth [CO2], net photosynthetic rates of each species examined in the forest overstory and understory were stimulated by elevated [CO2] at each measurement date. We found no effect of elevated [CO2] on N(a) in any of the species. The slope of the A(sat)-N relationship was 81% greater in elevated [CO2] than in ambient [CO2] when averaged across all sample dates, reflecting a differential CO2 effect on photosynthesis at the top and bottom of the canopy. We compared A(sat)-N relationships in trees grown in ambient and elevated [CO2] at two common CO2 concentrations, during late summer 2001 and both early and late 2002, to determine if the stimulatory effect of elevated [CO2] on photosynthesis diminishes over time. At all three sample times, neither the slopes nor the y-intercepts of the A(sat)-N relationships of trees grown in ambient or elevated [CO2] differed when measured at common CO2 concentrations, indicating that the responses of photosynthesis to long-term elevated [CO2] did not differ from the responses to a short-term increase in [CO2]. This finding, together with the observation that N(a) was unaffected by growth in elevated [CO2], indicates that these overstory and understory trees growing at the Duke Forest FACE experiment continue to show a strong stimulation of photosynthesis by elevated [CO2].