Ectopic expression of soybean leghemoglobin in chloroplasts impairs gibberellin biosynthesis and induces dwarfism in transgenic potato plants

We have characterized potato (Solanum tuberosum L.) plants expressing a soybean leghemoglobin that is targeted to plastids. Transgenic plants displayed a dwarf phenotype caused by short internode length, and exhibited increased tuberization in vitro. Under in vivo conditions that do not promote tuberization, plants showed smaller parenchymal cells than control plants. Analysis of gibberellin (GA) concentrations indicated that the transgenic plants have a substantial reduction (approximately 10-fold) of bioactive GA(1) concentration in shoots. Application of GA(3) to the shoot apex of the transformed plants completely restored the wild type phenotype suggesting that GA-biosynthesis rather than signal transduction was limiting. Since the first stage of the GA-biosynthetic pathway is located in the plastid, these results suggest that an early step in the pathway may be affected by the presence of the leghemoglobin.

Photochemical damage and comparative performance of superoxide dismutase and ascorbate peroxidase in sugarcane leaves exposed to paraquat-induced oxidative stress

The physiological responses of sugarcane (Succharion officinarum L.) to oxidative stress induced by methyl viologen (paraquat) were examined with respect to photochemical activity, chlorophyll content, lipid peroxidation and superoxide dismutase (SOD) and ascorbate peroxidase (APX) activities. Thirty-day-old sugarcane plants were sprayed with 0, 2, 4, 6 and 8 mM methyl viologen (MV). Chlorophyll fluorescence was measured after 18 It and biochemical analyses were performed after 24 and 48 h. Concentrations of MV above 2 mM caused significant damage to photosystem II (PSII) activity. Potential and effective quantum efficiency of PSII and apparent electron transport rate were greatly reduced or practically abolished. Both chlorophyll and soluble protein contents steadily decreased with MV concentrations above 2 mM after 24 It of exposure, which became more pronounced after 48 It, achieving a 3-fold decrease. Insoluble protein contents were little affected by MV. Oxidative stress induced by MV was evidenced by increases in lipid peroxidation. Specific activity of SOD increased, even after 48 h of exposure to the highest concentrations of MV, but total activity on a fresh weight basis did not change significantly. Nondenaturing YAGE assayed with H2O2 and KCN showed that treatment with MV did not change Cu/Zn-SOD and MnSOD isoform activities. In contrast, APX specific activity increased at 2 mM MV but then dropped at higher doses. Oxidative damage induced by MV was inversely related to APX activity. It is suggested that the major MV-induced oxidative damages in sugarcane leaves were related to excess H2O2, probably in chloroplasts, caused by an imbalance between SOD and APX activities, in which APX was a limiting step. Reduced photochemical activity allowed the early detection of the ensuing oxidative stress. (c) 2007 Elsevier Inc. All rights reserved.

Impacts of land-use pattern on soil water-content variability on the Loess Plateau of China

Long-term vegetation restoration carried out on the slopes of the Loess Plateau of China employed different spatial and temporal land-use patterns but very little is known about the effects of these patterns on soil water-content variability. For this study the small Donggou catchment was selected to investigate soil water-content distributions for three spatial scales, including the entire catchment area, sampling transects, and land-use systems. Gravimetric soil water contents were determined incrementally to a soil depth of 1.20 m, on 10 occasions from April to October, 2007, at approximately 20-day intervals. Results indicated that soil water contents were affected by the six land-use types, resulting in four distinct patterns of vertical distribution of soil moisture (uniform, increasing, decreasing, and fluctuating with soil depth). The soil water content and its variation were also influenced in a complex manner by five land-use patterns distributed along transects following the gradients of five similar slopes. These patterns with contrasting hydrological responses in different components, such as forage land (alfalfa)-cropland-shrubland or shrubland-grassland (bunge needlegrass)-cropland-grassland, showed the highest soil water-content variability. Soil water at the catchment scale exhibited a moderate variability for each measurement date, and the variability of soil water content decreased exponentially with increasing soil water content. The minimum sample size for accurate data for use in a hydrological model for the catchment, for example, required many more samples for drier (69) than for wet (10) conditions. To enhance erosion and runoff control, this study suggested two strategies for land management: (i) to create a mosaic pattern by land-use arrangement that located units with higher infiltration capacities downslope from those with lower soil infiltrabilities; and (ii) raising the soil-infiltration capacity of units within the spatial mosaic pattern where possible.

Effects of sewage sludge amendment on the properties of two Brazilian oxisols and their humic acids

The effect of sewage sludge (SS) amendment on the general properties of the top layers of a sandy and a clayey oxisols and on the nature of their humic acid (HA) fractions was evaluated by chemical and physico-chemical techniques. The amended soils, especially the sandy soil, benefited of SS amendment by increasing their pH to above neutrality and enhancing the contents of C, N, P, and Ca and cation exchange capacity. The SS-HA-like sample showed larger H and N contents and a greater aliphatic character and humification degree than the HAs isolated from non-amerided soils. The composition and structure of amended soil HAs were affected by SS application as a function of soil type and layer. In particular, N-containing groups and aliphatic structures of SS-HA-like sample appears to be partially incorporated in the amended soil HAs, and these effects were more evident in the HAs from the sandy oxisol. (C) 2007 Elsevier Ltd. All rights reserved.

Are there costs in the repeated mating activities of female Southern stink bugs Nezara viridula?

Mating is an energy demanding process, imposing risks to physical injuries, pathogen infection and predation. Nevertheless, repeated and multiple mating are widespread even in insect species where nuptial gifts are not involved. The effects of repeated mating, by the same male, are examined on the reproductive performance of female Southern green stink bug Nezara viridula (L.). Fecundity is reduced in females mated three or four times, although there is increased longevity. Females mated once or twice produce more egg clusters and concentrate egg-laying activity in the early part of adult life, whereas those mating more often lay eggs throughout the life span, with fewer egg clusters. Although fecundity is negatively affected by the number of matings, egg fertility remains unaffected.

Pupal Development of Ceratitis capitata (Diptera: Tephritidae) and Diachasmimorpha longicaudata (Hymenoptera: Braconidae) at Different Moisture Values in Four Soil Types

This study aimed to evaluate adult emergence and duration of the pupal stage of the Mediterranean fruit fly, Ceratitis capitata (Wiedemann), and emergence of the fruit fly parasitoid, Diachasmimorpha longicaudata (Ashmead), under different moisture conditions in four soil types, using soil water matric potential Pupal stage duration in C capitata was influenced differently for males and females In females, only soil type affected pupal stage duration, which was longer in a clay soil In males, pupal stage duration was individually influenced by moisture and soil type, with a reduction in pupal stage duration in a heavy clay soil and in a sandy clay, with longer duration in the clay soil As allude potential decreased, duration of the pupal stage of C capitata males increased, regardless of soil type C capitata emergence was affected by moisture, regardless of soil type, and was higher in drier soils The emergence of D longicaudata adults was individually influenced by soil type and moisture factors, and the number of emerged D longicaudata adults was three times higher in sandy loam and lower in a heavy clay soil Always, the number of emerged adults was higher at higher moisture conditions C capitata and D longicaudata pupal development was affected by moisture and soil type, which may facilitate pest sampling and allow release areas for the parasitoid to be defined under field conditions.