What We Do Not Know About Differentiation

The outstanding recent advances in the analysis of differentiationare in concept and method. In this paper examples are providedto demonstrate that formulation of the problem of differentiationin terms of biosynthesis and its control poses questions innew and more manageable ways. As examples, reference will bemade to: (1) the question of control of the sets of specializedproperties by which we define a cell type; (2) propagabilityof differentiated states; (3) developmental bias in relationto intracellular events; and (4) the mechanisms of extrinsiccontrol of differentiation. Particular attention, also, willbe focused on the relationship of morphogenetic to biosyntheticevents.     

Quantal Division and a Postmitotic State in Myoblast Differentiation

The reversible arrest of myoblast differentiation by ethidium bromide (EB) has been used to examine the nature of the transition from the proliferative state to terminal differentiation resulting in fusion into muscle fibers. If EB is introduced at the time that myoblasts are shifted to medium that induces fusion, all apparent cytodifferentiation is suspended. When such EB arrested myoblasts are released from EB inhibition they fuse without reentering the cell cycle. If EB arrested myoblasts are released into proliferation promoting medium rather than medium that induces fusion they neither fuse nor proliferate. In this case they remain quiescent in the proliferating medium for an extended period, however, if these myoblasts are subsequently shifted to medium that induces fusion, they fuse without reentering the cell cycle. Apparently the myoblasts have become postmitotic and competent to fuse into muscle fibers during their initial exposure to fusion inducing medium, even though cytodifferentiation has been blocked. Exposure of these postmitotic fusion competent myoblasts to proliferation promoting medium does not stimulate them to reenter the cell cycle but does prevent fusion into muscle fibers. These results are most consistent with a quantal division model of myoblast differentiation rather than a gradual transition from the proliferative state to a state in which fusion occurs.     

Movement, persistence and performance of fungitoxicants applied as pruning wound treatments on apple trees

The systemic fungicides triadimenol, fenpropimorph, furmecyclox and carben-dazim, applied to pruning wounds as solutions in a non-aqueous solvent containing N-methyl–2-pyrrolidone moved predominantly towards the trunk. Coriolus versicolor, introduced deliberately, moved both proximally and distally irrespective of whether it was introduced in the dormant or growing season. Natural resistance to damage by chemical or C. versicolor appeared to be greater in the growing than in the dormant season and was inhibited when a cationic surfactant was used to aid penetration of fungitoxicant into the wood. Against C. versicolor the non-systemic fungicide captafol was ineffective, furmecyclox or fenpropimorph gave some protection and triadimenol was very effective. Carbendazim, although inactive against wood-rotting basidiomycetes, moved extensively within the wood and persisted well, and so could be an effective treatment for ascomycete pathogens. It also stimulated callus formation. The mercuric oxide preparation Santar was effective in these experiments and also stimulated callus formation.     

Polyphagy,flightlessness, and reproductive output of females: a case study with bagworms (Lepidoptera: Psychidae)

Abstract 1. We evaluated the relation between plant‐mediated larval traits and the fitness of female bagworms, Thyridopteryx ephemeraeformis Haworth (Lepidoptera: Psychidae) by sampling 29 populations of bagworms on five plant genera (Thuja, Pinus, Picea, Juniperus, and Gleditsia). 2. Compared with those on other genera of plants, female larvae on Thuja attained a larger size at pupation and developed faster. The superior quality of Thuja as a larval food plant resulted in a higher potential fitness of females, as indicated by a low level of pupal mortality and high fecundity. 3. The fecundity of females increased with pupal size on different plant genera, and the effect of host plant genus was negligible compared with pupal size. 4. The mating success of females varied among different populations (0–37% unmated females), but neither host plant, emergence time, nor the size of females had a significant influence on the proportion of mated females. 5. The conversion of adult biomass into reproductive tissue, measured as the ratio between the biomass of eggs divided by the biomass of calling females, increased with the pupal size of females and approached 90% for large females. The high rate of egg conversion in bagworms may be related to the neoteny of short‐lived females that invest little in somatic tissue.     

Quantitation of malaria sporozoites in the salivary glands of wild Afrotropical Anopheles

The number of malaria sporozoites in the salivary glands was determined microscopically for 1137 wild, naturally infected Anopheles from western Kenya. Infective Anopheles gambiae Giles sensu lato (n = 874) contained a geometric mean (GM) of 962 sporozoites and An.funestus Giles (n = 263) contained 812. No significant differences were detected in geometric mean numbers of sporozoites between species, collection techniques or sites. Of the infective An.gambiae, 1.7% (15/874) contained more than 41,830 sporozoites, the maximum observed for An.funestus. Microscopic techniques were found to be more sensitive than enzyme-linked immunosorbent assays (ELISA) for detecting low-grade sporozoite infections in salivary glands. Salivary gland sporozoites from 83.6% of the 1137 gland infections were identified by ELISA as either Plasmodium falciparum Welch (n = 910), P.ovale Stephens (n = 7), P.malariae Grassi & Feletti (n = 3) or mixed (n = 30). The 187 gland infections which could not be identified by ELISA contained significantly fewer sporozoites (GM = 242) than those which could be identified (GM = 1200).