Ultrastructure and movements of cell structures in normal pea and an ageotropic mutant

The pea mutant (Pisum sativum ageotropum) and the normal pea (P. sativum cv. Sabel) were compared in order to see if there were any differences in root anatomy or submorphology which could explain the presumed ageotropic behaviour of the mutant. In both types the root cap consists of a central core (columella) distinct from the peripheral part. The core contains five to six rows of columella cells, each consisting of 10 to 16 storeys of statocytes. The ultrastructure of the columella cells in the two types is very similar; the main difference is confined to the distribution of rough endoplasmic reticulum (ER), which in the mutant statocytes is evenly distributed throughout the cell, while in the normal pea statocytes it is mainly concentrated in the distal part at the “floor” of the cell. Using light micrographs, the movement of amyloplasts and nuclei have been followed in detail during a 40 min inversion period. The pattern of movement of the amyloplasts is apparently identical in the two types and the distances moved during the inversion period are 39 μm and 44 μm in the normal and mutant statocytes, respectively. The nucleus has not been observed to move in normal pea; a slight rearrangement of the nucleus position can be observed during the period 30 to 40 min after the start of inversion of the mutant. Based on magnified electron micrographs of the statocytes a morphometrical analysis was made of five cell structures – amyloplasts, nuclei, mitochondria, vacuoles and ER – which appeared to be freely movable or redistributable under the influence of the gravitational force.     

Long-term exposure of Boeckellagibbosa (Copepoda, Calanoida) to in situ levels of solar UVB radiation

1. The freshwater calanoid copepod Boeckella gibbosa is typical of high elevation lakes and ponds in Patagonia (Argentina). Previous studies have shown that this species is highly tolerant to short-term exposure to natural and artificial UVB radiation, and that its tolerance is due to photoreactivation by longer wavelength radiation. In this study, we investigate the potential sublethal effects of solar radiation after prolonged exposure.
2. We incubated B. gibbosa at 1 m depth in oligotrophic Lake Toncek for 24 days. The incubation chambers were 1.2 l acrylic cylinders covered with appropriate filters in order to obtain three radiation treatments: visible radiation only, visible radiation + UVA and visible radiation + UVA + UVB.
3. The three treatments did not differ significantly in variables considered as indicators of survival (number of individuals), reproduction (proportion of ovigerous females, clutch size) and development (instar composition). Although resistance to solar UVB radiation is certainly a requisite to live in transparent high elevation habitats, the fact of being effectively exposed to natural levels of UVB radiation does not seem to have measurable consequences on an already adapted species, such as B. gibbosa     

Triterpeneglycosides as Inhibitors of Fungal Growth and Metabolism

Avenacin, the resistance factor ioat roots against Ophiobolus graminisi ν graminis, and a related triterpeneglycoside, aescin, inhibited growth of various fungi, while the growth of a few fungi was unaffected. The triterpenoidal saponins tested seemed to be fungicidal, as the mycelia did not grow after exposure to the inhibitors. The fungicidal effect, however, depended on the medium used. The inhibitors did not seem to act primarily on the endogenous respiration, since the oxygen uptake, although much reduced, continued after the time required to destroy the growth capacity. The leakage of UV-absorbing substances from fungi, sensitive to the inhibitors, and the decrease of UV-absorbing substances in the transient pool of the cells indicate a change in the cell membrane.     

A fast and inexpensive DNA extraction/purification protocol for brown macroalgae

Here we describe a rapid method for extracting DNA from dried brown algae material using a microtitre plate system in conjunction with a milling instrument. The method allows the preparation of nuclear and organelle DNA of quality suitable for polymerase chain reaction amplification. It combines high throughput with low cost per sample: DNA from 192 samples can be extracted in c. 3 h for < €0.40 per sample, nearly tenfold cheaper than commercially available kits. Furthermore, by using microtitre plates, efficient storage and downstream processing is facilitated.