Polyhydroxyalkanoate synthesis in transgenic plants as a new tool to study carbon flow through beta-oxidation.

Transgenic plants producing peroxisomal polyhydroxy- alkanoate (PHA) from intermediates of fatty acid degradation were used to study carbon flow through the beta-oxidation cycle. Growth of transgenic plants in media containing fatty acids conjugated to Tween detergents resulted in an increased accumulation of PHA and incorporation into the polyester of monomers derived from the beta-oxidation of these fatty acids. Tween-laurate was a stronger inducer of beta-oxidation, as measured by acyl-CoA oxidase activity, and a more potent modulator of PHA quantity and monomer composition than Tween-oleate. Plants co-expressing a peroxisomal PHA synthase with a capryl-acyl carrier protein thioesterase from Cuphea lanceolata produced eightfold more PHA compared to plants expressing only the PHA synthase. PHA produced in double transgenic plants contained mainly saturated monomers ranging from 6 to 10 carbons, indicating an enhanced flow of capric acid towards beta-oxidation. Together, these results support the hypothesis that plant cells have mechanisms which sense levels of free or esterified unusual fatty acids, resulting in changes in the activity of the beta-oxidation cycle as well as removal and degradation of these unusual fatty acids through beta-oxidation. Such enhanced flow of fatty acids through beta-oxidation can be utilized to modulate the amount and composition of PHA produced in transgenic plants. Furthermore, synthesis of PHAs in plants can be used as a new tool to study the quality and relative quantity of the carbon flow through beta-oxidation as well as to analyse the degradation pathway of unusual fatty acids

Compactación del suelo durante la cosecha forestal: evolución de las propiedades físicas Soil compaction by forestry harvester operation: evolution of physical properties

Se realizaron ensayos en campo con el objeto de evaluar los efectos y la persistencia de la compactación inducida por diferentes intensidades de tránsito durante la cosecha forestal en una población de álamos (Populus sp.). Se trabajó con un tractor de tracción simple de 73,5 kW y un acoplado, con una masa de 4,2 Mg y 2,7 Mg, respectivamente. Se establecieron 3 tratamientos de tránsito: 1, 5 y 10 pasajes sobre una misma senda, contrastados con un testigo sin tránsito. Luego de cada tratamiento, y 3 años después de realizados los mismos, se efectuaron determinaciones de penetrometría, densidad aparente y humedad gravimétrica. Hubo incrementos significativos de resistencia a la penetración para los tratamientos con tránsito, alcanzando el de mayor intensidad valores entre el 76 y el 16 % en los primeros 40 cm de profundidad. La densidad aparente tuvo una tendencia similar limitada a una menor profundidad. Luego de 3 años, los efectos persistían a nivel subsuperficial, para el índice de cono en los sectores tránsitados con respecto a los no transitados, encontrándose diferencias significativas para el tratamiento de 10 pasajes respecto al de 1 pasaje hasta 50 cm. Aún con cargas por eje de 3 Mg, el incremento de la intensidad de tránsito induce compactación a nivel subsuperficial que persiste en el tiempo.<br>The long-term effects on soil compaction by different traffic intensities during forestry harvester operation were evaluated in field experiments on heavy clay, vertic Argiudol. A conventional 2WD 73.5 kW engine power tractor with a trailer, 4.2 Mg and 3.75 Mg total load respectively, were used on a multiclonal Populus deltoides (Marsh) 3x3 plantation. There were four treatments: one pass, five pass and ten repeated passes with the tandem over the same track, and a control plot without experimental traffic. Moisture content, bulk density and penetrometer resistances were evaluated before and immediately after the traffic treatments and three years later. Effects of induced soil compaction by traffic were especially marked on topsoil, with cone index increments between 76 and 16% in the first 40 cm of the surface layer after treatments. Bulk density had a similar tendency but limited to a 15 cm depth. Three years later, only subsoil cone index in the track line, below 20 cm depth, was significantly higher than the interline track soil cone index. The 10 passes treatment had significant differences compared to the 1 pass and no traffic control plot treatments from the surface layer to 50 cm depth, without differences with the 5 passes treatment in most of the studied soil layers. Subsoil compaction may be induced by repeated traffic with low axle load and their effects persist for a very long time