Release of protoplasts in the yeast phase of Histoplasma capsulatum without added enzyme

Cells of the yeast phase of the dimorphic systemic fungus pathogen Histoplasma capsulatum readily released large numbers of intact protoplasts without degradation of their cell walls by snail or microbial enzymes, previously regarded as a requirement for all yeast and mycelial fungal forms. Over 90 percent of "B" type yeast cells in the early logarithmic phase of growth released living protoplasts when incubated at 37 degrees C with 2 molar magnesium sulfate, whereas "A" type yeast cells required prior exposure for 24 hours to 2-deoxy-D-glucose before incubation in the 2 molar magnesium sulfate.     

Long term and seasonal courses of leaf area index in a semi-arid forest plantation

Effective leaf area index (LAI_e) in the semi-arid Pinus halepensis plantation, located between arid and semi-arid climatic zones at the edge of the Negev and Judean deserts, was measured bi-annually during four years (2001-2004) and more intensively (monthly) during the following two years (2004-2006) by a number of non-contact optical devices. The measurements showed a gradual increase in LAI_e from ∼1 (±0.25) to ∼1.8 (±0.11) during these years. All instruments, when used properly, gave similar results that were also comparable with actual leaf area index measured by litter collection and destructive sampling and allometric estimates. Because of the constraint of clear sky conditions, which limited the use of the fisheye type sensors to times of twilight, the fisheye techniques were less useful. The tracing radiation and architecture of canopies system, which includes specific treatment of two levels of clumpiness of the sparse forest stand, was used successfully for the intensive monitoring. The mean clumpiness index, 0.61, is considered representative for the specific environment. Finally, the LAI_e measurements at the start of each season were used to constrain phenology-based estimates of annual LAI_e development, resulting in a continuous course of LAI_e in the forest over the five-year period. Intra-seasonal LAI_e variation in the order of 10% of total LAI_e predicted by the model was also observed in the intensive TRAC measurements, giving confidence in the TRAC system and indicating its sensitivity and applicability in woodlands even with low LAI_e values. The results can be important for forest management decision support as well as for use in evaluation of remote sensing techniques for forests at the lowest range of LAI_e values.     

Contents of Volume 50

Volume Contents

Contents of Volume 50     

Water use efficiency and uptake patterns in a runoff agroforestry system in an arid environment

Water is the most limiting factor for plant production in arid to semiarid regions. In order to overcome this limitation surface runoff water can be used to supplement seasonal rainfall. During 1996 we conducted a runoff irrigated agroforestry field trial in the Turkana district of Northern Kenya. The effects of two different Acacia saligna (Labill.) H. Wendl. tree planting densities (2500 and 833 trees per ha), tree pruning (no pruning vs. pruning) and annual intercrops (no intercrop vs. intercrop: Sorghum bicolor (L.) Moench during the first season and Vigna unguiculata (L.) Walp. during the second season) on water use were investigated. The annual crops were also grown as monocrops. Water consumption ranged from 585 to 840 mm during the first season (only treatments including trees). During the second season, which was shorter and the plants relied solely on stored water in the soil profile, water consumption was less than half of that during the first season. Highest water consumptions were found for non-pruned trees at high density and the lowest were found for the annual crops grown as monocrops. Tree pruning decreased water uptake compared to non-pruned trees but soil moisture depletion pattern showed complementarity in water uptake between pruned trees and annual intercrops. The highest values of water use efficiency for an individual treatment were achieved when the pruned trees at high density were intercropped with sorghum (1.59 kg m^–3) and cowpea (1.21 kg m^–3). Intercropping and high tree density increased water use efficiency in our runoff agroforestry trial. We ascribe the observed improvement in water use efficiency to the reduction of unproductive water loss from the bare soil.This revised version was published online in November 2005 with corrections to the Cover Date.     

The use of soybean leaflet angle data for irrigation scheduling

Summary The feasibility of scheduling soybean [Glycine max (L.) Merr.] irrigation by using terminal leaflet angle data was evaluated by simultaneously measuring the angles to the horizontal of the uppermost terminal leaflet and soil moisture contents on plots with different soil moisture regimes during and following a drying cycle. Severe water stress was avoided. The percentage of leaflets with an angle greater than or equal to 45 degrees correlated significantly with both water content in the top 0.45 m of soil and the ET/Epan ratio.     

Disseminated fungal infection in two species of captive sharks

In this report, two cases of systemic mycosis in captive sharks are characterized. These cases were progressive and ultimately culminated in terminal disease. Paecilomyces lilacinus, an uncommon pathogen in human and veterinary medicine, was associated with areas of necrosis in the liver, heart, and gill in a great hammerhead shark (Sphyrna mokarran). Fungal growth was observed from samples of kidney, spleen, spinal fluid, and coelomic cavity swabs. Dual fungal infection by Exophiala pisciphila and Mucor circinelloides was diagnosed in a juvenile zebra shark (Stegostoma fasciatum). Both fungi were present in the liver, with more severe tissue destruction associated with E. pisciphila. E. pisciphila also produced significant necrosis in the spleen and gill, while M. circinelloides was associated with only minimal tissue changes in the heart. Fungal cultures from liver, kidney, and spleen were positive for both E. pisciphila and M. circinelloides. Identification of P. lilacinus and M. circinelloides was based on colonial and hyphal morphology. E. pisciphila was identified by sequence analysis of the 28S rRNA D1/D2 region and the internal transcribed spacer (ITS) region between the 18S and 28S rRNA subunit. These cases, and a lack of information in the literature, highlight the need for further research and diagnostic sampling to further characterize the host-pathogen interaction between elasmobranchs and fungi.     

Effect of root and water distribution in lysimeters and in the field on the onset of crop water stress

Summary Lysimeters have been frequently used to study crop response to the onset of water stress. To test the representativeness of lysimeter derived criteria for the onset of crop water stress, spring wheat (Triticum aestivum L.) was grown in two field plots with 1.0 m deep lysimeters in the center of each plot. One plot was well-watered while the second was subjected to a drying period with no irrigation. Crop water stress was assessed by monitoring leaf water potential ( _l ), stomatal diffusive resistance (r _s ), canopy temperature (CT), evapotranspiration (ET), and soil water content in both plots and lysimeters. The rate of change of all these measured parameters, when compared to the well-watered field control-plot revealed that the field-grown plants showed signs of water stress long before the lysimeter-grown plants. Water stress developed gradually for the field crop, but the transition from the well-watered to the stressed condition happened abruptly for the lysimeter-grown plants. Once this transition occurred, the lysimeter-grown plants were more drought stressed than the field-grown plant. Water profiles measured inside the lysimeter were different from those measured in the adjacent plots. An increase in root length density with depths below 0.6 m was observed in the lysimeters as opposed to a quasimonotonic decrease with depth in the field. The response of the lysimeter-grown plants was a result of the anomalous water content and root distribution. We conclude that threshold values of ET, _l , r _s , and CT for the onset of water stress obtained when deep-rooted crops grown in a shallow lysimeter are subjected to drought periods may not be directly applicable to field situations.