Hormonal factors controlling the initiation and development of lateral roots

The decapitated primary root of 3-day-old Alaska pea seedlings has been used as a test system to determine the activities on lateral root formation of six auxins, six cytokinins and several other naturally-occurring compounds. Their effects were assessed on (1) the initiation of lateral root primordia, (2) the emergence of visible lateral roots, and (3) the elongation of these laterals. All the auxins, at the optimum concentration of 10^-4M, promoted the initiation of lateral root primordia, and all except 3-indolylpropionic acid inhibited the elongation of the resulting lateral roots. Their effects on the emergence of laterals were small and varied. All the cytokinins, at 10^-6M and above, inhibited both the initiation and the emergence of lateral roots, zeatin being the most powerful inhibitor. The emergence process was about twice as sensitive as the initiation of primordia to the presence of cytokinins. The cytokinin ribosides were generally less active than the free bases. Abscisic acid and xanthoxin inhibited both emergence and elongation, the concentration for 50% decrease of emergence being about 10^-4M. Gibberellic acid had little clear effect on any of the three criteria. Nicotinic acid and thiamine at 10^-3M promoted both the initiation of primordia and their emergence: pyridoxal phosphate stimulated both emergence and elongation but did not influence the initiation of primordia. Adenine and guanine had little effect but decreased root elongation some 25%. The strong inhibiting effect of the cytokinins may well be the basis for the marked inhibition exerted by the root-tip on lateral root formation, while the promoting effects of auxins may explain the previously observed promotion of lateral root formation by the young shoot and cotyledons.     

Structure of Labyrinthula sp. Zoospores*

SYNOPSIS. A species of Labyrinthula closely resembling L. algeriensis was isolated from marsh grass, Spartina alterniflora. Zoosporulation was obtained in ～50% of the cultures, which were grown on a modified Vishniac medium, when yeasts were used as food organisms; when the temperature was ～22 C; when thiamine (0.2 mg/l, biotin (1 μg/l, Ba (1 μg/l, and cholesterol (5 mg/l) were present; and when the cells were grown on a semisolid medium (0.6% agar) rather than higher concentrations of agar. The motile cells were similar to biflagellated fungal zoospores in that they were pyriform and laterally biflagellated. The anterior flagellum (13-15 μ long) possessed what appeared to be 2 rows of mastigonemes and was uniform in diameter while the posterior flagellum (6-10 μ) lacked mastigonemes and was tapered distally into a whiplash. The planonts are apparently not isogametes since planogametic copulation could not be induced and since synaptinemal complexes were not observed in sectioned presporangia.     

Two‐step vegetation response to enhanced precipitation in Northeast Brazil during Heinrich event 1

High resolution palynological and geochemical data of sediment core GeoB 3910‐2 (located offshore Northeast Brazil) spanning the period between 19 600 and 14 500 calibrated year bp (19.6–14.5 ka) show a land‐cover change in the catchment area of local rivers in two steps related to changes in precipitation associated with Heinrich Event 1 (H1 stadial). At the end of the last glacial maximum, the landscape in semi‐arid Northeast Brazil was dominated by a very dry type of caatinga vegetation, mainly composed of grasslands with some herbs and shrubs. After 18 ka, considerably more humid conditions are suggested by changes in the vegetation and by C_org and C/N data indicative of fluvial erosion. The caatinga became wetter and along lakes and rivers, sedges and gallery forest expanded. The most humid period was recorded between 16.5 and 15 ka, when humid gallery (and floodplain) forest and even small patches of mountainous Atlantic rain forest occurred together with dry forest, the latter being considered as a rather lush type of caatinga vegetation. During this humid phase erosion decreased as less lithogenic material and more organic terrestrial material were deposited on the continental slope of northern Brazil. After 15 ka arid conditions returned. During the humid second phase of the H1 stadial, a rich variety of landscapes existed in Northeast Brazil and during the drier periods small pockets of forest could probably survive in favorable spots, which would have increased the resilience of the forest to climate change.     

Why do host‐deprived seed beetles ‘dump’ their eggs?

Abstract.  If host seeds are absent, females of the seed beetle Callosobruchus maculatus sometimes 'dump' eggs on unsuitable substrates, which causes complete larval mortality and decreases female lifespan. To understand the possible function of this behaviour, the present study examines genetic variation in dumping behaviour between and within populations. When deprived of hosts, females from an African population are much more prone to dump eggs than Asian females, most of which dump no eggs over their lifetimes. Egg dumping therefore cannot be explained as a simple, species-wide constraint imposed by the accumulation of mature oocytes. A transfer experiment tested the hypothesis that dumping eggs improves a female's ability to exploit the subsequent availability of seeds, perhaps by preventing a disruption of oocyte maturation. Contrary to prediction, the number of eggs laid after females are transferred to seeds is inversely related to the number dumped during deprivation. Two bidirectional selection experiments revealed heritable variation in egg-dumping behaviour within the African population. Deprived females from the dumper line dump more than twice as many eggs as do females from the nondumper line. Pre-adult development time is significantly longer in the nondumper line, which suggests that trade-offs with other fitness components could maintain variation in egg-laying behaviour within populations. The divergent responses to host availability by African and Asian females may represent a pleiotropic effect of similarly divergent responses to host quality.     

Food consumption and utilization responses to dietary dilution with cellulose and water by velvetbean caterpillars, Anticarsia gemmatalis

Abstract Dilution of an artificial diet with water or cellulose to nutrient levels of 32% (undiluted), 19% and 10% fresh weight (fw) resulted in increased fw and dry weight (dw) food consumption (both absolute amounts and weight-relative rates) by velvetbean caterpillars, Anticarsia gemmatalis Hübner. Despite these increases, the absolute amount and relative rate of nutrient intake by the caterpillars declined with dilution, as did their dw gain and dw (% fw) and lipid (% dw) contents. The proportion of consumed food (dw, including cellulose) that was digested and absorbed declined with increased dietary cellulose; however, the proportion of consumed nutrients (dw, excluding cellulose) that was digested and absorbed was not affected by the presence of cellulose, although it increased slightly (but significantly) with dietary water. The efficiency with which the absorbed nutrients were converted to biomass energy showed a negative relationship with the various measures of food consumption and thus a positive relationship with dietary nutrient level.
The compensatory increases in feeding mitigated the deleterious impact of dietary dilution on growth, which would have declined further without the increased feeding. These data suggest that food consumption is regulated primarily through an evaluation of food nutrient level, and that the metabolic costs associated with the increased consumption and processing of food may be substantial, especially on the most diluted diets. Another hypothesized cost of increased feeding, reduced efficiency of digestion and absorption as food presumably passes more rapidly through the gut, was not detected.     

The genus Amphiporus Ehrenberg (Nemertea, Enopla, Monostiliferoidea)

The literature relating to the 145 nemertean species at one time or another included in the monostiliferoidean genus Amphiporus Ehrenberg, 1831 is reviewed. Because the designated type species, A. albicans , must be declared a nomen dubium , the status of the genus itself becomes uncertain. The 33 species which, at least in part, have previously been transferred to other genera are tabulated and the taxonomic status of the remaining forms is re-evaluated. Most are identified as nomina nuda, nomina dubia, species inquirendae or synonymous with other taxa, but one species, A. bimaculatus , is transferred to the genus Nipponnemertes .