Sustained biological control of the cassava mealybugPhenacoccus manihoti [Hom.: Pseudococcidae] byEpidinocarsis lopezi [Hym.: Encyrtidae] in Nigeria

Following the successful introduction ofEpidinocarsis lopezi (De Santis) for biological control of the cassava mealybug (CM)Phenacoccus manihoti Mat.-Ferr. in southwestern Nigeria in 1981 and 1982, 11 groups of cassava fields were sampled every 2 weeks up to 1988 for impact assessment. After 1984, CM populations remained mostly below 10 per tip despite the presence of native hyperparasitoids, demonstrating the long-term success of biological control byE. lopezi in the region. Indigenous polyphagous coccinellids were found only during peak host densities, whereas the specificE. lopezi was common throughout the year. During some periods, percentage parasitism indicated delayed density dependence. Since 89% of all sampled cassava tips had no CM at all and the parasitisme is very mobile, parasitization rates were also calculated for individual infested tips (N=4,878). Parasitism increased slightly with host density on tips having between 1 and 10 CM of the 3^rd and 4^th instars, indicating positive density dependence. Such tips comprised 64% of all infested tips. At higher host densities, parasitism rates fell rapidly. The results are discussed in view of different theories on population regulation by biological control agents.      

Evolutionary analysis of the multigene pregnancy-specific β1-Glycoprotein family: Separation of historical and nonhistorical signals

The pregnancy-specific ₁-glycoproteins (PSG) form a large family of closely related proteins. Using newly developed methods of sequence analysis, in combination with protein modeling, we provide a framework for investigating the evolution and biological function of genes like the PSG. Evolutionary trees, based on C-terminal sequence, group PSG genes in a manner consistent with their genomic organization. Trees constructed using the N-terminal domain sequences are unreliable as an indicator of phylogeny because of non-neutral processes of sequence change. During duplication of the PSG genes, evolutionary pressures have resulted in a gradient of constrained change across each gene. The N-terminal domains show a nonrandom pattern of amino acid substitutions clustered in the immunoglobulin complementarity-determining region (CDR)-like regions, which appear to be important in the function of the protein.     

Overexpression of MerT, the mercuric ion transport protein of transposon Tn501, and genetic selection of mercury hypersensitivity mutations

The small (116 amino acids) inner membrane protein MerT encoded by the transposon Tn501 has been overexpressed under the control of the bacteriophage T7 expression system. Random mutants of MerT were made and screened for loss of mercuric ion hypersensitivity. Several mutantmerT genes were selected and sequenced: Cys24Arg and Cys25Tyr mutations abolish mercury resistance, as do charge-substitution mutations in the first predicted transmembrane helix (Glyl4Arg, Glyl5Arg, Gly27Arg, Ala18Asp), and the termination mutations Trp66Ter and Cys82Ter.     

Stratification of density in dry deciduous forest using satellite remote sensing digital data—An approach based on spectral indices

Forest density expressing the stocking status constitutes the major stand physiognomic parameter of Indian forest. Density and age are often taken as surrogate to structural and compositional changes that occur with the forest succession. Satellite remote sensing spectral response is reported to provide information on structure and composition of forest stands. The various vegetation indices are also correlated with forest canopy closure. The paper presents a three way crown density model utilizing the vegetation indices viz., advanced vegetation index, bare soil index and canopy shadow index for classification of forest crown density. The crop and water classes which could not be delineated by the model were finally masked from normalized difference vegetation index and TM band 7 respectively. The rule based approach has been implemented for land use and forest density classification. The broad land cover classification accuracy has been found to be 91.5%. In the higher forest density classes the classification accuracy ranged between 93 and 95%, whereas in the lower density classes it was found to be between 82 and 85%.     

Cardiac phosphocreatine deficiency induced by GPA during postnatal development in rat

The effect of chronic administration of -guanidinopropionic acid (GPA) on the protein profiling, energy metabolism and right ventricular (RV) function was studied in the rat heart during the weaning and adolescence period. GPA was given in tap water (1–1.5%) using pair drink controls. The feeding of animals with GPA solution for a six week period resulted in elevation of heart to body weight ratio due to body growth retardation. GPA accumulated in the myocardium up to 67.37 ± 5.3 moles.g dry weight and the tissue content of total creatine, phosphocreatine and ATP was significantly decreased to 15%, 9% and 65% of control values respectively. Total activity of creatine kinase (CK) was not changed, but the proportion of mitochondrial (Mi) CK isoenzyme was decreased; the percentage of MB isoenzyme of CK was significantly higher. GPA treatment resulted in an elevation of the content of cardiac collagenous proteins and decrease of non-collagenous proteins in the heart; in parallel, a decrease of the collagen I to collagen III ratio was detected. The function of the RV was assessed using an isolated perfused heart with RV performing pressure-volume work. As compared to pair-drink controls, RV function was significantly impaired the GPA group: at any given right atrial filling pressure, the RV systolic pressure and the rate of pressure development were decreased by almost a factor of two. Elevation of the RV diastolic pressure with increasing pulmonary artery diastolic pressure was also significantly steeper in the GPA group which also showed decrease of cardiac output, especially at high outflow resistance. It may be assumed that chronic administration of GPA deeply influenced metabolic parameters, protein profiles and contractile function of the developing heart. On the other hand, concentrations of glucose, total lipids and triglycerides in blood plasma were not affected. All these data confirm the concept that the CK system is of central importance both for heart function and for the regulation of normal growth of cardiac myocytes.     

HSP25 in isolated perfused rat hearts: Localization and response to hyperthermia

Recent investigations concentrate on the correlation between the myocardial expression of the inducible 70-kDa heat shock protein (HSP70i) by different stress conditions and its possible protective effects. Only few studies have focused on the involvement of small heat shock proteins in this process. We analyzed the location of the small heat shock protein HSP25 in isolated cardiomyocytes as well as its location and induction in isolated perfused hearts of rats. By immunofluorescence microscopy HSP25 was found to colocalize with actin in the I-band of myofibrils in cardiomyocytes of isolated perfused hearts as well as in isolated neonatal and adult cardiomyocytes. Hyperthermic perfusion of isolated hearts for 45 min resulted in modulation of different parameters of heart function and in induction of HSP25 and HSP70i. Temperatures higher than 43°C (44–46°C) were lethal with respect to the contractile function of the hearts. Compared to control hearts perfused at 37°C, significant increases during hyperthermic perfusion at 42°C and 43°C were obtained for heart rate, contraction velocity and relaxation velocity. In response to hyperthermia at 43°C and after subsequent normothermic perfusion for 135 min at 37°C, left ventricular pressure, contraction velocity and relaxation velocity remained significantly elevated. However, heart rate returned to control values immediately after the period of heat treatment. HSP25 is constitutively expressed even in normothermic perfused hearts as shown by Western blotting. Hyperthermia increased the content of HSP25 only in the left ventricular tissue. In contrast, HSP70i was strongly induced in all analyzed parts of the myocardium (left ventricle, right ventricle, septum). Our findings suggest a differential regulation of HSP25 and HSP70i expression in response to hyperthermia in isolated perfused hearts. The constitutively expressed HSP25 seems to be located adjacent to the myofibrils which implies a specific role of this protein even under unstressed conditions for the contractile function of the myocardium.     

Far-red enrichment and photosynthetically active radiation level influence leaf senescence in field-grown sunflower

Basal leaves frequently senesce before anthesis in high population density crops. This paper evaluates the hypothesis that quantitative and qualitative changes in the light environment associated with a high leaf area index (LAI) trigger leaf senescence in sunflower ( Helianthus annuus L.) canopies. Mean leaf duration (LD, time from achievement of maximum leaf area) of leaf 8 was significantly ( P < 0.05) reduced from 51 to 19 days as crop population density was increased from 0.47 to 4.76 plants m⁻². High compared to low plant population density was associated with earlier reduction in the photosynthetically active radiation (PAR) and red/far-red ratio (R/FR) reaching the target leaf. However the changes in R/FR preceded those in PAR. When the light environment of individual leaves of isolated plants growing under field conditions was manipulated using filters and FR-reflecting mirrors, LD was positively and linearly related with the mean daily PAR (MDR) received in the FR- (no FR enrichment) treatments. FR enrichment of light reaching the abaxial surface of the leaf significantly ( P < 0.05) reduced LD by 9 days at intermediate PAR levels with respect to FR-controls, but did not affect LD at the maximum PAR used in these experiments. However, when light reaching both leaf surfaces was enriched with FR, LD (for leaves receiving maximum PAR) was 13 days shorter than that of the FR- control. These results show that basal leaf senescence in sunflower is enhanced both by a decrease in PAR and by a decrease in R/FR.     

The development of phloem anastomoses between vascular bundles and their role in xylem regeneration after wounding in Cucurbita and Dahlia

The differentiation of phloem anastomoses linking the longitudinal vascular bundles has been studied in stem internodes of Cucurbita maxima Duchesne, C. pepo L. and Dahlia pinnata Cav. These anastomoses comprise naturally occurring regenerative sieve tubes which redifferentiate from interfascicular parenchyma cells in the young internodes. In all three species, severing a vascular bundle in a young internode resulted in regeneration of xylem to form a curved by-pass immediately around the wound. The numerous phloem anastomoses in these young internodes were not involved in this process, the regenerated vessels originating from interfascicular parenchyma alone. Conversely, in mature internodes of Dahlia, the regenerated vessels originated from initials of the interfascicular cambia, and their phloem anastomoses did not influence the pattern of xylogenesis. On the other hand, in old internodes of Cucurbita, in which an interfascicular cambium was not yet developed, the parenchyma cells between the bundles had lost the ability to redifferentiate into vessel elements, and instead, regenerated vessels were produced in the phloem anastomoses. Thus, the wounded region of the vascular bundle was not bypassed via the shortest, curved pathway, but by more circuitous routes further away from the wound. Some of the regenerated vessels produced in the phloem anastomoses were extremely wide, and presumably efficient conductors of water. It is proposed that the dense network of phloem anastomoses developed during evolution as a mechanism of adaptation to possible damage in mature internodes by providing flexible alternative pathways for efficient xylem regeneration in plants with limited or no interfascicular cambium.This paper is dedicated to the memory of the late Isaac Blachmann (deceased 19 November 1995), father-in-law of the senior author, for encouragement and advice throughout the yearsThis research was supported by an International Scientific Exchange Award to R.A. from the Israel Academy of Sciences and The Royal Society.     

Root,shoot and soil parameters required for process-oriented models of crop growth limited by water or nutrients

A review is given of the prospects for using process-oriented models of water and nutrient uptake in improving integrated agriculture. Government-imposed restrictions on the use of external inputs will increase the likelihood of (temporary) nutrient or water stress in crop production in NW Europe and thus a better understanding is required of shoot-root-soil interactions than presently available. In modelling nutrient and water uptake, three approaches are possible: 1) models-without-roots, based on empirically derived efficiency ratios for uptake of available resources, 2) models evaluating the uptake potential of root systems as actually found in the field and 3) models which also aim at a prediction of root development as influenced by interactions with environmental factors. For the second type of models the major underlying processes are known and research can concentrate on model refinement on the one hand and practical application on the other. The main parameters required for such models are discussed and examples are given of practical applications. For the third type of models quantification of processes known only qualitatively is urgently needed.