LIGHT AND HORMONAL CONTROL OF ROOT FORMATION IN ZEA MAYS CALLUS CULTURES

Callus cultures of Zea mays were used to study the interaction of light with exogenous cytokinin/auxin levels in the initiation, growth and development of roots. Three auxins, indoleacetic acid (IAA), naphthaleneacetic acid (NAA) and 2,4 dichlorophenoxyacetic acid (2,4 D) were remarkably different in their effects on callus growth and root initiation. NAA at concentrations of 5 and 25 μM produced the highest combined yields of callus and roots under low light conditions. No significant morphological effects on roots were observed with the three auxins tested nor did low and intermediate light intensities alter root development.
At intermediate light levels the addition of the cytokinin, zeatin, was also able to influence the differentiation of the callus tissue. Increasing the cytokinin/auxin ratio from low to high shifted the development from callus growth to abundant root formation. High light caused the formation of short, thick roots. This effect could be counteracted in part by zeatin which promoted elongation. These observations suggest that both, the cytokinin/auxin ratio and light play an important role in the development of monocotyledonous roots.     

Spectral sensitivity of the green photoreceptor of winged pea aphids

Intracellular recordings are obtained from photoreceptors in the retina of winged (alate) pea aphids Acyrthosiphon pisum (Harris). The responses to monochromatic light, applied in 10‐nm steps over the range 320–650 nm, reveal that all recordings are from green receptors and the spectral sensitivity function of these photoreceptors peaks at 518 nm. A comparison between the spectral sensitivity of the green receptors and extracellular electroretinogram recordings suggests that additional sensitivity to the short‐wavelength light (ultraviolet and/or blue) is also likely to be present in the compound eye of pea aphids. An analysis of the pea aphid genome, comparing its translated nucleotide sequences with the those of the opsin genes of other insect species, supports this electrophysiological finding, although it could not be established whether A. pisum, in addition to the green receptor, has both blue and ultraviolet receptors in the compound eye. The implications of these results for the visual ecology of herbivorous insects are discussed.     

Analysis of gene inheritance and expression in hybrids between transgenic sugar beet and wild beets

Reciprocal gene exchange between cultivated sugar beet and wild beets in seed production areas is probably the reason for the occurence of weed beets in sugar beet production fields. Therefore, when releasing transgenic sugar beet plants into the environment, gene transfer to wild beets ( Beta vulgaris ssp. maritima ) has to be considered. In this study the transfer of BNYVV- (beet necrotic yellow vein virus) resistance and herbicide-tolerance genes from two transgenic sugar beet lines that were released in field experiments in 1993 and 1994 in Germany to different wild beet accessions was investigated. In order to evaluate the consequences of outcrossing, manual pollinations of emasculated wild beet plants with homozygous transgenic sugar beet plants were performed. In the resulting hybrids the transgenes were stably inherited according to Mendelian law. Gene expression in leaves and roots of the hybrids was in the same range as in the original transgenic sugar beet plants. Moreover, it was found that in one of the wild beet accessions, transfer and expression of the BNYVV resistance gene did considerably increase the level of virus resistance.     

Life-Cycle of Trypanosoma conorhini. Influence of Temperature and Other Factors on Growth and Morphogenesis

SYNOPSIS. In continued observations on the in vitro growth and multiplication of the bloodstream trypanosome stage of Trypanosoma conorhini , a better medium was found for cultivating these forms at 37°C, but no subcultures could be obtained. The infectivity for mice of the blood type trypanosomes grown in vitro was comparable to that of the metacyclic trypanosomes. The only reproducing forms of T. conorhini found in the vertebrate were in the trypanosome stage.
It was also found that the in vitro reversion of the bloodstream trypanosome into crithidia, such as occurs in the invertebrate host and in the usual diphasic culture medium, is dependent on at least two factors: if incubated at 25–28° reversion did not occur in any of the liquid media tried (all containing blood serum and hematin or hemoglobin), unless total blood was part of the inoculum or washed red blood cells were added to the media; on the other hand, no reversion was seen, even in the presence of red blood cells if the cultures were incubated at 37°.     

Vibrational alarm communication in the damp-wood termite Zootermopsis nevadensis

Abstract. Vibrational alarm communication was studied in the New World, damp-wood termite Zootermopsis nevadensis (Isoptera: Termopsidae). Workers and soldiers react to disturbance such as sudden bright light or air currents by drumming their heads against the substratum. This drumming has been described as alarm signalling; its functional significance and perception by the nest mates, however, remained unclear. In the present study we analysed spectral and temporal properties and absolute amplitudes of the vibrational signals and used behavioural responses of the termites to determine the thresholds of the sense of vibration and to find out if and how the termites discriminate the conspecific alarm signals from the background noise.
The drumming signals are trains of pulses of vibrations of the substratum with a pulse repetition rate of about 20 Hz. The carrier frequency depends on the substratum; in the nests studied it was in the range 1–3 kHz. The highest vibrational amplitudes measured close to the signal emitters are usually about 10m/s² (acceleration, RMS). The threshold of the behavioural response is about 1m/s² over a wide range of frequencies (10 Hz to 5 kHz), indicating that the termites can detect these signals as vibrations of the substratum. The animals respond preferentially to temporal patterns similar those of the natural signals; temporal rather than spectral cues seem to be used for signal discrimination.     

FLYING SNAILS--HOW FAR CAN TRUNCATELLINA (PULMONATA: VERTIGINIDAE) BE BLOWN OVER THE SEA?

With populations of land snails of very small size like Vertiginidae,questions have arisen as to whether populations of relativelydistant islands in archipelagos are really isolated from eachother. Apart from other flight agencies, airborne transportof loose specimens is not improbable in stormy weather conditions.Currently, mechanisms of wind-borne transport of sand particlesover short and long distances have been intensively studied.The results are available in the literature on sediments, allowingthe calculation of probable flight distances for particles insuspension. For living snails of the Aegean species Truncatel-lina rothi,an average fall velocity of 2.6–2.7 m s^–1 has beendetermined in experiments under laboratory conditions. Applyingthese results, Truncatellina living on an island at 100 m altitudeand close to the coast could be transported up to several kilometersin heavy storms, which are not uncommon in the Aegean archipelago(Greece). This would imply that many of the Aegean islands arenot effectively isolated for minute snail species, and thatgenetic interchange between island populations is probably frequent. (Received 3 April 1996; accepted 27 January 1997)     

The effect of oxidized material on the vertical distribution of freshwater benthic fauna

The vertical distribution of representatives of the benthic groups: Ostracoda, Nematoda, Oligochaeta, Harpacticoida, Cyclopoida, and Chironomidae was determined. All groups had their highest numbers and biomass in the first 2 cm. The downward extent of oxidized material affected the distribution by dispersing the biomass more as seen by the deeper occurrence of groups when the oxidized material increased. Both the nematodes and oligochaetes were found to inhabit the first reduced layer when the oxidized material was less than normal.