Developmental abnormalities in the ovule and embryo sac of ulluco (Ullucus tuberosus) and their effect on seed set

Summary Ulluco (Ullucus tuberosus) is a vegetatively propagated crop plant that flowers abundantly but sets only few seeds. We examined if the low seed/ovule ratio can be explained by morphological abnormalities in ovules, embryo sacs or embryos. In 35 clones growing in the actual area of cultivation in Ecuador and in 5 clones grown in Finland flowers were analysed by clearing technique. About half of all analysed clones contained ovules and embryo sacs whose development was arrested, in two clones there were embryo sacs whose cell patterns were abnormal and in four clones there were double embryo sacs. There were both normal and abnormal ovules and embryo sacs in the same plant. Genetic load is suggested to be one of the causes for the low sexual fertility found in ulluco. It may be incapable of maintaining homeostasis of development of the ovule and embryo sac in a varying environment. The occurrence of developmental abnormalities should be studied in each clone intended for inclusion in traditional breeding programmes.     

Linarin, a selective acetylcholinesterase inhibitor from Mentha arvensis

Linarin (acacetin-7-O-beta-d-rutinoside) from the flower extract of Mentha arvensis showed selective dose dependent inhibitory effect on acetylcholinesterase.     

Specific gravity responses of slash and loblolly pine following mid-rotation fertilization

Wood quality attributes were examined in six stands of slash pine (Pinus elliottii Engelm. var. elliottii) and loblolly pine (P. taeda L.) in the lower Coastal Plain of Georgia and Florida. Several plots comprised each stand, and each plot was divided so that it received three fertilizer treatments: a control treatment with herbaceous weed control at planting and brush control at mid-rotation only (control); 45 kg ha⁻¹ N + 56 kg ha⁻¹ P + herbaceous weed control at planting and 224 kg ha⁻¹ N + 45 kg ha⁻¹ P + brush control at mid-rotation (fertilizer with N at planting); and 56 kg ha⁻¹ P + herbaceous weed control at planting and 224 kg ha⁻¹ N + 45 kg ha⁻¹ P + brush control at mid-rotation (fertilizer without N at planting). Ring width, ring earlywood specific gravity (SG), ring latewood SG, whole ring SG, and ring percent latewood were measured on each of seven trees. Of these measurements, this study focused mainly on the properties related to SG. Examination of the rings showed that latewood SG was significantly lower in trees treated with fertilizers with and without N at planting in the two to three years following fertilization, but that latewood SG gradually returned to a level similar to the control. Fertilizer without N at planting may also have had a brief negative effect on earlywood SG following mid-rotation fertilization, but it was not as clear or lasting as the effect on latewood SG. Additionally, although slash and loblolly pine appear to differ in the developmental patterns of these SG properties, there were no significant differences in how these patterns interacted with treatment. This study demonstrated that fertilization treatments have similar short-term effects on the SG of slash and loblolly pines, particularly in latewood, but the trees will return to a SG pattern consistent with unfertilized trees within two or three years.     

Excess nitrogen fertilization and the structure of Scots-pine needles

The effects of excess nitrogen fertilization on the structure of Scots-pine needles (Pinus sylvestris) were examined in Finnish Lapland. The trees were fertilized with calcium ammonium-nitrate, and the levels of nitrogen applied were 0, 75, 150, 250, 500 and 1000 kg N/ha, respectively. The thickness and width of the needle and thicknesses of the tissues were measured, and the conditions of various celltypes were classified at the light-microscopy level. In addition, the areas of the cell organelles were measured and the conditions of the chlomplasts and other cell compartments observed at the ultrastructural level. Larger needles and a thicker adaxial mesophyll were observed following excess N application (250–1000 kg N/ha). The natural xeromorphic structure of the conifer needles became more mesomorphic, possibly influencing the protection afforded against environmental stresses. A high level of nitrogen fertilization caused changes in the central cylinder, especially in the vascular bundle and the sclerenchyma. The needle nitrogen concentration was high in the highly fertilized trees and the boron concentration was simultaneously extremely low. As a consequence of the changes in the central cylinder, photoassimilate transport from the mesophyll to the phloem may be disturbed at high fertilization levels. The changes at the ultrastructural level, i.e. injuries to the chloroplast thylakoids and the plasma membrane, and the formation of lipid accumulations, were indicators of the adverse effects of excess nitrogen. With an increasing atmospheric-nitrogen load, lower nitrogen fertilization levels in pine forests naturally adapted to low soil N should be considered in forest management.     

Effects of foliar potassium concentration on morphology, ultrastructure and polyamine concentrations of Scots pine needles

We examined the effects of three foliar potassium concentrations (high, intermediate and low) on the morphology, ultrastructure and polyamine concentrations of current-year and 1- and 2-year-old needles of 30-year-old Scots pine (Pinus sylvestris L.) trees. Foliar K concentration had only a slight effect on needle morphology. The sclerenchyma cell walls were thinner, the xylem area was larger, and the resin ducts were smaller in needles with a low K concentration than in needles with a high or intermediate K concentration. In addition, the bundle sheath cells were collapsed in needles having a low K concentration. The secondary growth of phloem tissue and the mesophyll area were greater in needles with a high or intermediate K concentration than in needles with a low K concentration, possibly indicating greater production of photoassimilates in these trees. At the ultrastructural level, mesophyll cells with enlarged central vacuoles and small vacuoles containing electron-dense material were common in needles having a low K concentration. Enlargement of the central vacuole coincided with an exponential increase in putrescine concentration in needles with a low K concentration, suggesting that the central vacuole may function as a storage site for putrescine.     

Phosphorus mineralization and microbial biomass in a Florida Spodosol: effects of water potential, temperature and fertilizer application

 Phosphorus mineralization and microbial biomass were measured in the surface 5 cm of a Spodosol (sandy, siliceous hyperthermic Ultic Alaquod) from north-central Florida. Soils from fertilized and unfertilized plantations of loblolly pine (Pinus taeda L.) were incubated at a range of water potentials (∼0, –3, –8, –10 and –1500 kPa) and temperatures (15  °C, 25  °C and 38  °C) for 14 days and 42 days. Increasing water potential and temperature increased specific P mineralization (mineralization expressed as a percentage of total P) regardless of fertilizer treatment. An increase in water potential from –10 kPa to –0.1 kPa resulted in an increase of between 38% and 239% in the concentration of KCl-extractable inorganic P, depending on incubation temperature and time. An increase in incubation temperature from 15  °C to 38  °C resulted in an increase of between 13% and 53% in KCl-extractable inorganic P. Changes in specific P mineralization with change in water potential or temperature were not affected by fertilizer application. This suggests that, although specific P mineralization was greater in the fertilized soils, environmental control of P mineralization was the same for both treatments. Specific P mineralization was most sensitive when soils were at higher water potentials, and decreased logarithmically to water potentials of between –3 kPa and –8 kPa. Specific P mineralization was relatively insensitive to changes in water potential when water potential was lower than –8 kPa. Microbial biomass C showed no consistent responses to changes of temperature or water potential and was not significantly correlated with specific P mineralization. Our results suggest that field estimates of P mineralization in these Spodosols may be improved by accounting for changes in soil water potential and temperature. Received: 30 October 1997     

Importance of dose metrics for lethal and sublethal sediment metal toxicity in the oligochaete worm Lumbriculus variegatus

Background, Aims, and Scope  There is an increasing demand for controlled toxicity tests to predict biological effects related to sediment metal contamination. In this context, questions of metal-specific factors, sensitivity of toxicity endpoints, and variability in exposure duration arise. In addition, the choice of the dose metrics for responses is equally important and is related to the applicability of the concept of critical body residue (CBR) in exposure assessments, as well as being the main focus of this study. Methods  Experiments were conducted to assess toxicity of Cd, Cr, Cu and Pb to the oligochaete worm Lumbriculus variegatus with the aim of determining CBRs for two response metrics. Mortality and feeding activity of worms exposed to sediment-spiked metals were used as end-points in connection with residue analyses from both the organisms and the surrounding media. Results  LC50 values were 0.3, 1.4, 5.2, and 6.7 mg/L (from 4.7 μmol/L to 128.0 μmol/L), and the order of toxicity, from most toxic to least toxic, was Cu > Cd > Pb>Cr. By relating toxicity to body residue, variability in toxicity among the metals decreased and the order of toxicity was altered. The highest lethal residue value was obtained for Cu (10.8 mmol/kg) and the lowest was obtained for Cd (2.3 mmol/kg). In the 10-d sublethal test, both time and metal exposure were an important source of variation in the feeding activity of worms. The significant treatment effects were observed from worms exposed to Cd or Pb, with the controls yielding the highest feeding rate. However, quantitative changes in the measured endpoint did not correlate with the exposure concentrations or body residues, which remained an order of magnitude lower than in the acute exposures. Discussion  Both response metrics were able to detect a toxic effect of the metals. However, the ranking of metal toxicity was dependant on the choice of the dose metric used. An attempt to form a causal mortality-mediated link between tissue residues and metal toxicity was successful in water-only exposures. The results also indicated that egestion rate was a sensitive toxicity end point for predicting the effects of sediment contamination. Conclusions  By relating the biological response with the tissue metal residues, toxicity data was comparable to both environmental media as well as different response metrics and time scales. The results also revealed the importance of metal toxicity ranking on a molar basis and, furthermore, a direct link to the CBR concept was established. Recommendations and Perspectives  There is a growing demand for methods to assess the effects of contaminated sediments to benthic fauna and whole aquatic ecosystems. Such information is needed for sediment quality guidelines that are currently being developed in many countries and remediation processes. The use of body residues as a dose metric in metal toxicity studies may help to overcome difficulties related to bioavailability issues commonly faced in sediment toxicity studies. ESS-Submission Editor: Prof. Dr. Henner Hollert (henner.hollert@bio5.rwth-aachen.de)     

Conversion of Carbohydrates in Herbaceous Crops during Anaerobic Digestion

The methane yields and conversion of pentoses (xylose) and hexoses (cellulose) in hemp, maize, and white lupin were studied over 30 days of anaerobic digestion. Preservation of hemp increased the methane yield by 23% compared with the fresh hemp. The increased methane yield of hemp was verified by the enhanced conversion of C6 sugars, increasing from 48% to about 70%, whereas the conversion of C5 sugars increased from only 9% to nearly 50%. The consumption of all carbohydrates in fresh maize was almost complete in the 30 days of anaerobic digestion. Hence, there was no major difference in carbohydrate consumption between fresh and preserved maize during biogas production. Fresh white lupin produced the highest methane yield (343 ± 33 dm(3) kg(-1) TS) in this work, mainly due to its highest amount of proteins. Conversion of C6 sugars was 80%, but that of C5 sugars was notably less at 46%.     

Breeding for value in a changing world: past achievements and future prospects

Large-scale tree improvement programs began in the 1950s. Tree improvement is now part of operational silviculture programs in many companies and countries around the world and tree breeding programs have produced very impressive results: (1) realized gains in plantations being established today of some 40–50 % in volume yield above unimproved material for many programs; (2) increased efficiencies in all aspects of breeding, selection, testing and deployment; and (3) a shortening of the generation interval by a factor of two from approximately 30 years in the first generation to less than 15 years today for pine programs. What about the future? What should tree breeders be thinking, planning and doing to ensure that results 60 years from now are even more impressive than those from the previous 60 years? Tree breeders today live in a rapidly changing world faced with: increasing demands for food, energy and water; globalization leading to an interconnectedness of markets and rapid spread of exotic organisms; climate change and its implications for genetic deployment; burgeoning technology in robotics, communications and molecular tools; shifting ownership patterns of forest land; and the real possibility of completely new forest products and markets in the future. Three ideas for “Breeding for Value in a Changing World” are: (1) adopt a robust philosophy that aims to ensure maximum value produced per ha even in a future world that will be quite different; (2) embrace technology at every phase in the tree improvement process; and (3) encourage interdisciplinary teams of scientists to solve complex problems that require expertise ranging from molecular to landscape scales.