Injury-induced Cyanogenesis in Vegetative and Reproductive Parts of Two Grevillea Species and their F1 Hybrid

When leaves of three Grevillea species were macerated, hydrogencyanide was only released from the soft, immature ones. Thebark but not wood of young stems was weakly cyanogenic. Thegreatest concentration of cyanoglucosides occurred in peduncles,flower buds, open flowers, immature seeds and germinants. Nocyanide was released from nectar, pedicels, dry fruit, elaiosomesand dry walls mature seeds. Addition of ß-glucosidase,and sometimes water only, increased cyanogenesis in young leaves,bark, some seed and fruit walls, and embryos of mature seeds.The endogenous levels of ß-glucosidase were sufficientto release all the cyanide present in at least 80% of cases. Young leaves and germinants of G. bipinnatifida (resprouter)released more cyanide than those of G. banksii, while flowerbuds, stigmatic region, styles, perianths and ovaries of G.banksii (non-sprouter) released far more cyanide than thoseof G. bipinnatifida. The interspecific and intraplant distributionof cyanoglucosides is consistent with the expected impact ofbeneficial and herbivorous animals on long term fitness of thesespecies. The F1 hybrid (G. 'Robyn Gordon') tended to have intermediatecyanoglucoside levels between the two putative parents.Copyright1993, 1999 Academic Press Grevillea bipinnatifida, G. banksii, G. 'Robyn Gordon', cyanide, herbivory, ß-glucosidase, cyanogenesis     

NOR-Chromosome morphology and evidence for rDNA selection in phylactolaemates

Silver-stained chromosome spreads from the phylactolaemate ectoprocts Fredericella indica, Fredericella browni, Plumatella repens, Pectinatella magnifica and Asajirella gelatinosa show that each of these species has a single pair of NORs. In the first four species each NOR is immediately adjacent to the centromere of a large metacentric chromosome. Giemsa-stained preparations from Cristatella mucedo show centromeric gapping in a similar large metacentric, indicating the same type of NOR-chromosome. In Asajirella gelatinosa the two NORs are on a pair of smaller chromosomes, and are not immediately adjacent to a centromere. A close NOR-centromere association would inhibit meiotic crossing over in the NOR region. Since in phylactolaemates reproduction is primarily asexual, often by formation of statoblasts, there is potential intraclonal selection for favorable ribosomal DNA (rDNA) mutations, including from simultaneous germination of otherwise genetically identical statoblasts within a limited area and competition between cell lines within statoblasts. Inhibition of meiotic crossing over within the NOR would maintain its integrity during periods when intraclonal selection would not be occurring. This suggests that a more rapid rate of rDNA evolution is possible in phylactolaemates than in most other organisms, and is consistent with a derivation of this group from the morphologically similar phoronids, despite phylogenetic interpretations of rDNA sequence data that suggest the two groups are not closely related.     

Does the rare Banksia goodii have inferior vegetative,reproductive or ecological attributes compared with its widespread co-occurring relative B. gardneri?

Banksia goodii (rare) and B. gardneri var. gardneri (widespread) are closely related rhizomatous evergreen subshrubs of south western Australian scrub-heath and woodland. B. goodii is restricted to sixteen populations, most of which are remnants on roadsides due to landscape fragmentation from agricultural activities. Bioclimatic profiles indicate that B. gardneri spans a wider range of climates than B. goodii. However, their post-fire survival and resprouting vigour, rates of seedling growth and soil penetration and susceptibility to seedling predators are similar. Both have the potential for geographic range extension, especially B. goodi. Seedlings of both species survived for at least 3 years at sites with 2 (but not 3) months shorter and 1 month longer growing seasons than experienced by natural B. goodii populations. Seedling establishment did not occur in the absence of fire and was low (1.3% of released intact seeds for B. goodii) even following en masse release of seeds after fire. Sowing of intact seeds, especially in cleared areas and with protection from herbivores, increased this to 35%. Fire survival among adults of both species was 100% following two fires. B. goodii, which roots along its rhizomes, produces ramets, while B. gardneri, with a lignotuber instead, does not. Seed production, pre-dispersal granivory and canopy seed storage are low but similar for both species, although B. gardneri has a superior level of germination. The biology of B. gardneri thus provides few insights as to why B. goodii is rare. There were no differences in topo-edaphic attributes, community structure, shading or litter cover between localized sites where either species occurred alone or together. Differences in present or prehistoric fire regimes, clearing (habitat fragmentation), susceptibility to generalist fungal pathogens, or impacts of alien invasives, cannot explain the distribution of B. goodii relative to B. gardneri. The rarity of B. goodii may be a result of its recent origin, habitat specialization (dense woodland), and the impacts of habitat fragmentation within its current range, rather than inferior vegetative, reproductive and/or ecological attributes.     

Diapause termination in two species of damselflies

Larvae of two species of damselflies, Enallagma hageni and E. aspersum, were collected in southwestern North Carolina and subjected to different combinations of daylength (SD, 11 hr day; LD, 14 hr day) and temperature to determine the factor critical in the termination of diapause. Diapausing larvae were collected in September, and 15 comparable groups of each species were given pretreatments (SD, 10°C; LD, 10°C; or SD, 21°C) for 2, 4, or 8 weeks and then transferred to SD, 21°C or LD, 21°C until emergence. Control groups were maintained under both photoperiods at 21°C.Response times (days from collection to emergence) for both species showed that rapid development required transfer to LD, 21°C regardless of the type of pretreatment or length of exposure. Larvae transferred to LD, 21°C after exposure to any of the three types of pretreatment for equal lengths of time developed at similar rates. Pretreatments at 10°C, which were equally effective with SD or LD, stimulated subsequent rapid development at LD, 21°C to a greater extent than continuous exposure to LD, 21°C conditions, and the longer the exposure to 10°C, the faster the subsequent response. Pretreatments at SD, 21°C also resulted in rapid development, similar to that of larvae exposed to 10°C, upon transfer to LD, 21°C conditions. Long daylengths administered only during pretreatments did not effect rapid development, since all larvae responded slowly when transferred to SD, 21°C. Diapause termination, therefore, was effected by LD, 21°C conditions preceded by exposure to either low temperatures, during which the photoperiod was not important, or short daylengths at 21°C.     

The mating system of a homothallic fission yeast

Summary Exposed to iodine vapors, colonies of a homothallic strain of Schizosaccharomyces pombe were of two classes: P, with many black streaks, and d, with scarcely any. Contiguous P and d colonies, but not contiguous P colonies nor contiguous d colonies, gave the iodine junction reaction, a black line along the common boundary of two colonies. Neither class could be purified. On replating, a P colony gave rise to a P plate, which contained mostly P but also d colonies; a d colony gave rise to a d plate, which contained mostly d but also P colonies. The P/d colony ratio of a fresh isolate (if isolated as a P colony) was very high or (if isolated as a d conoly) very low. It fell, if initially high, or rose, if initially low, on subsequent replatings of the same isolate. Maintained for many generations, an isolate attained a fairly constant P/d colony ratio that was less than unity. Tetrad analysis showed 2:2 segregation of the classes. We conclude that a homothallic clone is a mixture of two types of cells: P, which gives rise to a P colony, and d, to a d colony. The two types are sexually complementary and interconvertible. The rate of intercoversion of P to d exceeds that of d to P by a factor of about 2.NRCC no.: 17334