Surface Remodelling of Reticulocytes produced in Response to Erythroid Stress

ACCELERATED erythropoiesis is associated with the production of reticulocytes of excessive size, perhaps as the result of skipped divisions during erythroid cell proliferation in the bone marrow¹. Isotopic studies have been interpreted as showing that these “stress reticulocytes” are short-lived and are replaced by progressively smaller cells with more normal life spans^1–6. It has recently been suggested, however, that stress reticulocytes are not destroyed in toto but are made smaller by a process of remodelling or surface fragmentation⁷; loss of only portions of these cells could explain most of the isotopic findings, although the residual cells might remain intact.     

Autotropism in Fungal Spores

Autotropism was examined in germinating spore pairs of Rhizopusstolonifer, Mucor plumbeus, Trichoderma viride, and Botrytiscinerea. When germinated on agar surfaces the first three speciesexhibited negative autotropism, B. cinerea being neutral inits autotropic behaviour. More pronounced negative autotropismwas shown by the first three species when germinated on a filmof Cellophane applied to an agar surface. Under these conditionsB. cinerea displayed positive autotropism. Spore pairs of R. stolonifer germinated on agar containing cellulosepowder or charcoal showed less negative autotropism than onagar alone. Touching spore pairs of each species showed a markedtendency towards cis-ness, i.e. germ-tubes beginning on thesame side of a line joining the two spore centres, under theculture conditions described, the one exception being the reductionin cis-ness recorded when R. stolonifer was germinated on agarcontaining charcoal. Time courses of germination were determined for single sporesand touching spore pairs of R. stolonifer and M. plumbeus anda significant promotion was obtained in the spore pairs as comparedwith the single spores. Although both these species exhibitmarked negative autotropism there was a strong tendency forthe positive germ-tube, i.e. one beginning more nearly towardsits neighbour, to emerge before the negative germ-tube in thosespore pairs having one germtube positive and the other negativein orientation. Also, in R. stolonifer, the replacement of germination-promotersby germination-inhibitors in filtrates from spore suspensionsas they age is correlated with a change from positive to negativeautotropism in germinating members of (+ –) spore pairs. Possible mechanisms are discussed to account for the observedeffects.