Epinasty in <i>Cynodon plectostachyum</i> R. Pilger induced by sucrose and its reversion by gibberellic acid and nitrogen compounds

Previously evidence has been presented to support the view that sucrose is responsible for the prostrate habit of some grasses. Thus it was demonstrated that detached apical pieces of stolons or rhizornes continued to grow horizontally if they were fed with high concentrations of sucrose. Otherwise, these organs would be expected to curve upwards. Further work was succesful in inducing, by mean of sucrose, a downward bending (epinasty) of detached stolons placed in an erect position. In this note, the methods are reported and the results briefly commented.Instituto de Fisiología Vegeta

Morfogénesis experimental en el Gramón (Cynodon dactylon)

En la presente comunicación se dan a conocer, de manera sucinta, los resultados de experimentos realizados con la maleza conocida como gramón con el fin de determinar los mecanismos biológicos que regulan su morfología.Academia Nacional de Agronomía y Veterinari

Morfogénesis experimental en el Gramón (Cynodon dactylon)

En la presente comunicación se dan a conocer, de manera sucinta, los resultados de experimentos realizados con la maleza conocida como gramón con el fin de determinar los mecanismos biológicos que regulan su morfología.Academia Nacional de Agronomía y Veterinari

Photonic Density and Spectral Composition as Determinants of Growth and Dry Matter Partition in <i>Artemisia verlotorum</i> L.

La arquitectura de las plantas puede ser modificada tanto por la cantidad como por la calidad de la radiación incidente Bajas relaciones R/RL (Z) aplicadas al final del día (EOD), reducen el tamaño de las hojas en algunas especies, mientras que las aumenta en otras. Además, se ha demostrado que el sistema fitocromo regula la partición de fotoasimilados en numerosas especies. El objetivo del presente trabajo fue estudiar los efectos de irradiaciones con luz roja (R) y roja lejana (RL) de baja energía aplicadas al final del día, como así también de diferentes niveles de densidad fotónica (DFFF) sobre el crecimiento y la morfología de la maleza "Yuyo de San Vicente". Dos grupos de 15 plantas fueron sometidas a irradiaciones EOD con bajos y altos valores de Z. Otros tres grupos se los sometió a distintos niveles de irradiancia en forma continua (100%; 50% y 10% de luz solar plena). Al cabo de 30 días se dió por finalizado el ensayo. Las plantas sometidas a diferentes valores de Z no modificaron su altura ni el número de hojas. El área foliar y la biomasa total se incrementaron con R. Alta relación R/RL provocó mayor desarrollo del sistema subterráneo Las plantas sometidas a sombreado intenso no modificaron significativamente su altura ni el número de hojas aunque si el peso seco de cada una de las fracciones. Es de destacar que aún con bajas irradiancias se formaron rizomas, lo que indica la capacidad de adaptación del “Yuyo de San Vicente” a condiciones de muy baja disponibilidad de DFFF, y medrar bajo canopeos densos.Artemisia verlotorum plants were irradiated with lights of different red/far red ratio during 60 min. At the end of the day High red/far ratio increased photoassimilate partitioning toward underground organs (roots and rhizomes) and enhanced total biomass and leaf area. Stem hight and leaf number were not modified. Photosynt­hetic photon density as low as 150 umol m-2 s-1 decreased both shoot and underground dry weight. However, the production of rhizomes was not hindered. It is concluded that phytochrome is involved in photoassim ilated distribution and that even under very weak photon flux, and consequently low photosynthetic activity, rhizomes were differentiated in this weed. According to these results it is logical to affirm that Artemisia verlotorumis a shade-tolerant plant capable to grow under dense canopies. Eradication of this weed by crop shading seem unlikely.Facultad de Ciencias Agrarias y Forestale

Oxidative stress, antioxidant capacity and ethylene production during ageing of cut carnation (Dianthus caryophyllus) petals

The objective of this work was to study the role of free radicals in relation to ethylene production during ageing of cut carnation petals. Ethylene production by freshly cut flowers was negligible, but 8 d after cutting ethylene production began to increase and reached a peak by day 9, before beginning to decline again. The efflux of electrolytes (membrane damage index) increased 101% and 2, 7-dichlorofluorescein oxidation rate (oxidative stress index) increased 53% from day 8 to day 11 after detachment. Ethylene peak was either (a) not affected significantly by the supplementation of exogenous ethylene on the day of cutting, or (b) expanded between days 7-9 after ethylene supplementation on day 6 of cutting, or (c) was inhibited by amino-oxyacetic acid and paraquat treatments. After ethylene supplementation, conductivity and 2,7-dichlorofluorescein oxidation increased significantly as compared to control petals, and the activity of antioxidant enzymes was not affected. However, both w-tocopherol and glutathione content decreased significantly after ethylene supplementation on day 6 after detachment. Amino-oxyacetic acid treatment prevented the increases in conductivity and 2,7dichlorofluorescein oxidation, did not alter the activities of antioxidant enzymes and significantly increased the content of a-tocopherol and glutathione as compared to control carnation petals. Paraquat treatment paralleled qualitatively ethylene supplementation after 6 d of cutting. Taken as a whole, the data presented here may be understood as experimental evidence of a close association between ethylene production and oxidative stress in ageing of cut carnations.Instituto de Fisiología Vegeta

Net photosynthetic and transpiration rates in a chlorophyll-deficient isoline of soybean under well-watered and drought conditions

The gas exchange traits of wild type soybeans (cv. Clark) and a near-isogenic, chlorophyll-deficient line homozygous for the recessive allele y9 (y9y9) were compared under either well-watered or water-stress conditions. Mature leaves of y9 had a 65% lower chlorophyll content than wild type. However, the net photosynthetic rate (PN) of y9 leaves was only 20% lower than in the wild type, irrespective of water availability. Transpiration rates (E) were significantly higher in leaves of y9, compared to the wild type, either under well-watered or stress conditions. The higher E of y9 correlated with increased stomatal conductance, particularly in the abaxial epidermis, where more than 70% of the stomata were located. The combination of lower PN and increased E resulted in a significant decrease of water use efficiency in y9, at both water availability levels. The relative water content decreased in stressed leaves, much more in y9 than in wild type leaves, probably because of the higher E of the mutant line.Instituto de Fisiología Vegeta

Emission of water stress ethylene in wheat (Triticum aestivum L.) ears : Effects of rewatering

In this work it has been found that ethylene production increased only slightly under conditions of a moderate or severe water stress. However, the rehydration of the plants at full turgor after desiccation caused a high emission of ethylene. The desiccation would not irreversibly inactivate the enzymes of the ethylene pathway, since rehydration made the synthesis recommence almost immediately. Water deficit also increased the free radical levels and the antioxidant scavengers, such as superoxide dismutase. Free radicals promote the conversion of 1-amino-cyclopropane-1-carboxylic acid to ethylene, then it is logical to think that both chemical species are involved in the phenomenon of the acceleration of the grain maturity before the plant collapses.Instituto de Fisiología Vegeta

Senescence of Flag Leaves and Ears of Wheat Hastened by Methyl Jasmonate

Treatment of flag leaves and ears of wheat plants with MJ (jasmonic acid methylester) (10−5 and 10−4m) did not increase ethylene production, but it did accelerate senescence as indicated by the loss of chlorophyll. MJ also caused the closure of stomata, and consequently the rates of transpiration and photosynthesis decreased. Early maturity shortened the grain filling period, so the thousand grain weight was lower. Although ethylene elicited the same physiologic effects, the syndrome of senescence by MJ is independent of the former. We conclude that senescence and death in wheat are far from being elucidated; however, MJ and ethylene seem to participate in the phenomenon.Facultad de Ciencias Agrarias y Forestale

The effect of two planting dates on the physiological age and yielding potential of seed potatoes grown in a warm temperate climate in Argentina

The effect of two planting dates upon the physiological age of seed tubers, measured by their incubation period, and their yielding potential was studied during a three-year period with two medium-early and one medium-late cultivar. Although seed tubers of the December planting were physiologically significantly younger than those obtained from the November planting in two of the three seasons studied, no reliable effect upon tuber yield was found. Reasons for this lack of relation are discussed. The accumulated day-degrees above 17°C (daily mean temperature) during the bulking period of the seed crop modified the incubation period of the tubers clearly.Der Einfluss zweier Pflanztermine auf das physiologische Alter von Pflanzkartoffeln und ihr Ertragspotential wurde während einer Dreijahresperiode an zwei mittelfrühen Sorten, Spunta und Kennebec, und einer mittelspäten Sorte, Bonaerense la Ballenera MAA, in warmer gemässigter Klimazone in Argentinien geprüft. Saatbestände aus November- und Dezemberpflanzungen von 1979, 1980 und 1981 wurden im November 1980, 1981 und 1982 in vergleichenden Ertragsversuchen gepflanzt. Das physiologische Alter der Knollen wurde bei der Pflanzung durch die Inkubationsperiode (Claver, 1973, 1975) gemessen. Abb. 1 zeigt die meteorologischen Daten der vier Vegetationsperioden. Es ergaben sich signifikante Unterschiede im physiologischen Alter zwischen den Sorten und den Pflanzterminen (Tab. 1). Bei Lagerung der Saatkartoffeln in Mieten im Feld beschleunigte sich das physiologische Alter (Tab. lc). Die Gesamtknollenerträge schwankten zwischen den Sorten in 1980/81 und 1982/83 (Tab. 2a und 2c), es ergaben sich jedoch keine signifikanten Unterschiede zwischen Pflanzgut der beiden Pflanztermine, obwohl sich zwischen beiden Pflanzterminen Unterschiede im physiologischen Alter ergaben. Der Gesamtknollenertrag war 1982/83 am höchsten (Tab. 2c), obwohl die Pflanzknollen physiologisch die Ältesten waren. Es ist unwahrscheinlich, dass eine hohe prozentuale Infektionsrate mit PLRV und PVY der Pflanzknollen von Spunta und Kennebec aus der Dezemberflanzung den Einfluss des physiologischen Alters auf den Ertrag derart überdeckte, dass keine signifikanten Unterschiede mehr gefunden werden konnten (Abb. 2). Weil die Unterschiede im physiologischen Alter innerhalb einer Sorte jedoch klein waren, waren andere ertragsbestimmende Faktoren offensichtlich wichtiger als die Unterschiede im Alter. Die akkumulierten Tagesgrade über einer täglichen Temperatur von 17°C während der Periode des Knollenansatzes hatten eine klare Änderung der Inkubationsperiode zur Folge.L'effet de deux dates de plantation sur l'âge physiologique de tubercules de semence et sur leur rendement potentiel a été étudié durant une période de trois années avec deux variétés demi-hâtives, Spunta et Kennebec, et une demi-tardive, Bonaerense la Ballenera MAA, cultivées dans un climat chaud d'Argentine. Les plants récoltés en novembre et décembre des années 1979, 1980 et 1981 ont été plantés en novembre 1980, 1981 et 1982 selon des essais comparables de rendement. L'âge physiologique des tubercules était évalué à la plantation par la période d'incubation (Claver, 1973, 1975). Les relevés météorologiques pour les quatres saisons sont donnés dans la fig. 1. On observait des différences significatives dans l'âge physiologique entre les variétés et les dates de plantation (tabl. 1). Quand les tubercules de semence étaient conservés en silo au champ, l'âge physiologique était avancé (tabl. lc). Le rendement total en tubercules était différent entre variétés pour 1980/81 et 1982/83 (tabl. 2a et 2c) mais il n'y avait pas de différences significatives entre les plants des deux dates de plantation bien qu'il y ait des différences significatives dans leur âge physiologique. Le rendement total en tubercules était plus élevé en 1982/83 (tabl. 2c) malgré des tubercules de semence physiologiquement plus vieux. Il est peu probable que le taux important d'infection par les virus de l'enroulement et Y des semences de Spunta et Kennebec observé de l'âge physiologique des plants sur les rendements, ceux-ci ne présentant aucune différence significative (fig. 2). De plus, parce que les différences d'âge physiologique des semences au sein d'une variété sont-faibles, d'autres facteurs déterminants que le rendement doivent avoir été plus importants que la différence d'âge. Le cumul jour-degrés au-dessus de la température journalière de 17°C durant la période de tubérisation des tubercules de semence modifie sensiblement la durée d'incubation des plants (fig. 3).Instituto de Fisiología Vegeta