Physiological responses of lupinus mutabilis to phosphorus nutrition and season of growth

The response to phosphorus (P) concentration in the nutrient solution (0–0.5 mol P m^‐3) was studied in Lupinus mutabilis Sweet cv. Potosi in two different seasons (winter and spring). Phosphorus deficiency was more severe on growth than on photosynthesis and the season of growth dramatically influenced the optimal concentration of P for plant growth; root biomass was proportionally less affected than shoot biomass. During winter, growth and photosynthesis of plants supplied with 0.02–0.5 mol P m^‐3 were not significantly different, whereas in spring, rates of growth and photosynthesis were faster at the 0.5 mol P m^‐3 level. Stomatal conductance decreased with deficient P independently of leaf water relations. Severe P deficiency limited carbon (C) assimilation rates due to reduction in stomatal conductance and mesophyll photosynthetic capacity. Decreased sucrose/starch in P‐deficient leaves was a consequence of the observed source/sink imbalance which was more marked in winter. Hydraulic conductance was not a limiting factor for leaf expansion under low P. In conclusion, growth and metabolic changes observed in lupins grown at low P supply can be ascribed to an adjustment at the whole plant level, preventing a large drop in leaf P, reducing shoot growth and facilitating P uptake through higher root biomass.     

Comparison of image analysis and direct measurement of UPOV taxonomic characteristics for variety discrimination as determined over five growing seasons, using industrial chicory as a model crop

Tests for distinctness, uniformity and stability (DUS) are an essential component of variety registration and granting plant breeders’ rights. This study, performed on industrial chicory (Cichorium intybus L.), included (1) an evaluation of the discriminating power of the UPOV characteristics and (2) a comparison of the root shape between the UPOV-based characteristics and characteristics determined via image analysis. Five consecutive growing periods were studied to assess the long-term stability of the parameters. Lack of discriminating power of characteristics for examining distinctness may impede breeding progress by failing to discriminate novel candidate varieties. However, a balance needs to be set so that newly introduced characteristics or new evaluation methodologies are not too powerful as to damage the protection of registered varieties. The results showed great differences in the discriminating power of the UPOV characteristics. The elimination of some of these low-discriminating characteristics would probably result in savings, but would have no consequences on the decisions taken by DUS testing authorities. Image analysis-derived characteristics could either replace currently-used parameters or provide additional characteristics with good discriminating power, determined in an objective and standardized way. Here we discuss possible implications for variety registration.     

Physiological changes in boysenberry fruit during growth and ripening

Summary

Boysenberries (Rubus hybrid) were harvested at five developmental stages (green, “turning”, pink, red and purple) to study changes associated with flavour, colour and firmness, with a particular focus on the different enzymes involved in chlorophyll degradation or cell wall degradation. The level of reducing and non-reducing sugars increased 109- and 52-fold, respectively, between the “turning” and the purple stage. Titratable acidity increased by 84% between the green and the pink stage, but dropped by 41% between the red stage and full ripening. Total phenols displayed their highest values in green and “turning” fruit. Chlorophyll a and b degradation occurred mainly during the early stages of development, and was paralleled by a 2.3-fold increase in chlorophyllase activity and a 5-fold increase in Mg-dechelatase activity between the green and the red stages. Chlorophyll peroxidase activity was high at the green stage, but did not change significantly after the “turning” stage. This is the first report on the activity of chlorophyll-degrading enzymes in Rubus spp. fruits. Anthocyanins increased 11-fold between the “turning” and the pink stages, and an additional eight-fold between the pink and the purple stages. Fruit firmness decreased noticeably during ripening, with a concomitant 10.75-fold increase in polygalacturonase activity, beginning at the “turning” stage. Endo- -1,4-glucanase and -galactosidase activities rose 9.2- and 6.7-fold, respectively, after the pink stage and paralleled the major softening process taking place between the pink and purple stages, when fruit firmness decreased from 3.83 N to 0.29 N. Pectin methylesterase activity was high in pink and red fruit, but decreased by 21% as the fruit turned from red to purple. This is the first report on cell wall enzyme activities whose combined action might be required for the breakdown of natural cell wall substrates during ripening in boysenberry, as happens in other soft fruits.     

Genetic diversity and population structure of Acidovorax avenae subsp. avenae isolated from sugarcane in Argentina

A significant increase in the occurrence of red stripe (caused by Acidovorax avenae subsp. avenae) has been observed in the last decade in Argentina. Considering that no extensive sampling of the main sugarcane-producing area in the country has been conducted to characterize the diversity and population structure of A. avenae subsp. avenae, molecular markers were employed to analyse 112 isolates from Tucumán. By using repetitive element polymorphism-based polymerase chain reaction (rep-PCR) almost all isolates were differentiated and grouped into 10 clusters, revealing a high genetic diversity. Using the amplified fragment length polymorphism (AFLP) technique, five pairs of isolates were discriminated that could not be distinguished with rep-PCR. Cluster analysis showed no clear association between isolate clustering, sugarcane host genotype, crop age, type of tissue sampled, fertilization, or year of sampling. Linkage equilibrium analysis by using rep-PCR data indicated that the population has some degree of clonality. Three housekeeping genes were also sequenced: ugpB and pilT sequences were highly similar to A. avenae subsp. avenae sequences from other Argentinian isolates, whereas the lepA sequence did not reveal significant similarity. An additional four housekeeping genes could not be amplified, suggesting the existence of differences in those regions. Subsequently, virulence of 14 A. avenae subsp. avenae isolates was evaluated under controlled conditions. Results showed a differential level of aggressiveness among the isolates on a resistant sugarcane variety. This study confirmed that rep-PCR is an adequate tool for genetic analysis and population structure characterization in bacteria, and revealed both high genetic diversity and clonal population structure of A. avenae subsp. avenae in Tucumán, Argentina.     

Heme oxygenase-1 activity is involved in the control of Toxoplasma gondii infection in the lung of BALB/c and C57BL/6 and in the small intestine of C57BL/6 mice

Heme oxygenase-1 (HO-1) is an enzyme that catabolizes free heme, which induces an intense inflammatory response. The expression of HO-1 is induced by different stimuli, triggering an anti-inflammatory response during biological stress. It was previously verified that HO-1 is able to induce indoleamine 2,3-dioxygenase (IDO), an enzyme that is induced by IFN-γ in Toxoplasma gondii infection. To verify the role of HO-1 during in vivo T. gondii infection, BALB/c and C57BL/6 mice were infected with the ME49 strain and treated with zinc protoporphyrin IX (ZnPPIX) or hemin, which inhibit or induce HO-1 activity, respectively. The results show that T. gondii infection induced high levels of HO-1 expression in the lung of BALB/c and C57BL6 mice. The animals treated with ZnPPIX presented higher parasitism in the lungs of both lineages of mice, whereas hemin treatment decreased the parasite replication in this organ and in the small intestine of infected C57BL/6 mice. Furthermore, C57BL/6 mice infected with T. gondii and treated with hemin showed higher levels of IDO expression in the lungs and small intestine than uninfected mice. In conclusion, our data suggest that HO-1 activity is involved in the control of T. gondii in the lungs of both mouse lineages, whereas the hemin, a HO-1 inducer, seems to be involved in the control of parasitism in the small intestine of C57BL/6 mice.     

Histopathology of durable adult plant resistance to leaf rust in the Brazilian wheat variety Toropi

Leaf rust, caused by the fungus Puccinia triticina is a major disease of wheat (Triticum aestivum) worldwide. This disease is prevalent in southern South America where the environmental conditions and high genetic variability of P. triticina favour epidemics. The primary means of controlling pathogenic P. triticina races has been through using wheat varieties containing race-specific resistance genes. The defence mechanisms involved in durable race non-specific resistance to P. triticina are probably distinct from those involved in non-durable race-specific resistance. We investigated the histological components of resistance to P. triticina present in three wheat genotypes: the race non-specific resistant Brazilian variety Toropi; the race-specific resistant line RL6010 Lr9; and the susceptible Brazilian variety BRS 194. Plants of these three genotypes were inoculated with P. triticina race MFP and tissue samples excised from flag leaves at various times after inoculation to assess the number of infective structures, frequency of cell death and the accumulation of autofluorescent cells and hydrogen peroxide. The genotypes showed different resistance mechanisms active at different times during the infection process. Our results for Toropi indicate that there was a reduction in the extent of formation of stomatal appressoria and all subsequent structures. During attempted penetration we also observed the production of autofluorescent compounds and late cell death, but not peroxide formation. This non-specific resistance to P. triticina involves both pre-haustorial and post-haustorial mechanisms which may be responsible for maintaining the low disease severity observed in this variety even under high inoculum pressure.     

Tissue composition and allometric growth of carcass of lambs Santa Inês and crossbreed with breed Dorper

Tropical Animal Health and Production - This study aimed to assess the tissue composition and allometric growth of carcasses of Santa Inês and crossbred Dorper x Santa Inês lambs confined...