GEMMIFEROUS FERN GAMETOPHYTES—VITTARIACEAE

Approximately 10 % of all fern species reproduce vegetatively in the gametophytic stage by means of gemmae. Gametophyte morphologies in these species depart radically from the commonly figured heart-shaped type and expand considerably the opportunities for physiological and morphological studies utilizing fern gametophytes. Original observations on four species of vittarioid ferns are presented and compared with earlier observations on gametophytes of this family. Vittarioid gametophytes grow from a discontinuous marginal meristem which results in a much branched thallus of indeterminant growth. Aerial branches of the gametophytes terminate in gemma production, which proceeds by a regular and predictable sequence of events. The sequence may differ considerably among species but is remarkably constant within species. Archegonia are produced on short ventral branches, and antheridia are produced primarily on germinating gemmae. Ananthacorus angustifolius is the only known member of the Vittariaceae which does not produce gemmae and is considered to represent the primitive condition. In this species antheridia are scattered over the thallus, suggesting that a change in the mode of control of antheridium production may have evolved in the family along with gemma production.     

Evidence for the identification of lymphocyte activating factor as the adherent cell-derived mediator responsible for enhanced antibody synthesis by nude mouse spleen cells

Human adherent peripheral blood leukocytes spontaneously elaborate both a thymocyte proliferative factor and a factor which augments the in vitro anti-sheep erythrocyte (SRC) plaque-forming cell (PFC) response of nu/nu mouse spleen cells. Nonadherent leukocytes do not spontaneously elaborate either factor. The adherent cell-derived factors appear to have an identical molecular weight (approximately 14,500 Daltons) as determined by Sephadex gel filtration. The data support the hypothesis that the molecule(s) mediating both enhancing activities is identical to the previously described adherent leukocyte product, LAF.     

A phosphatase resistant substrate for the assay of protein kinase C in crude tissue extracts.

Protein kinase C (PKC) is routinely assayed, after it is partially purified over DEAE-cellulose chromatography to eliminate any interfering protein kinases and phosphatases, by measuring the transfer of gamma-phosphate of [gamma-32P]ATP to H1 histone. Recently, it has been shown that a synthetic peptide, comprising residues 4-14 of myelin basic protein (MBP4-14), is a very selective PKC substrate which is not phosphorylated effectively by cyclic AMP-dependent protein kinase, casein kinase I and II, Ca2+/calmodulin dependent protein kinase II or phosphorylase kinase [Yasuda, I., Kishimoto, A., Tanaka, S-I., Tominaga, M., Sakurai, A. and Nishizuka, Y. (1990) BBRC 166, 1220-1227]. We report here that once MBP4-14 is phosphorylated, it is not dephosphorylated by okadaic acid-sensitive phosphatases (protein phosphatases 1, 2A and 3) or other protein phosphatases such as calcineurin and/or PP 2C present in hippocampal homogenates. Therefore, MBP4-14 can be used for PKC assay in crude extracts of neural tissue.     

Prevalence of Trypanosoma theileri in Louisiana cattle

Cattle (from 5 sites in Louisiana) were examined by blood culture for the presence of Trypanosoma theileri. A prevalence of 81% was found in the 291 cattle examined. A greater number of beef cattle (93%) than dairy cattle (73%) was infected. Differences in prevalence in cattle from different regions of the state were not noted.     

Regulation of root weight ratio is mediated by sucrose: Opinion

The role of sucrose in controlling RWR is exercised in both short term (substrate, osmolyte in phloem) and long term (regulation of expression of key genes in both mature source leaves and in sinks). Sucrose is a necessary, but not a sufficient, component of the mechanisms controlling RWR, with the key role of integrating the carbon balance between source and sink under the influence of a variable environment.     

Short-term control of root: shoot partitioning

We present data showing that the fraction of the available photosynthatepartitioned between the root and the shoot of a barley seedlingis affected by the supply of photosynthate from the source leaf:an increased fraction of the exported photosynthate goes tothe shoot when supply is reduced. Also, if the roots are cooleda short time before reducing the supply of photosynthate, thenthe effect of a reduced supply upon partitioning is reversedwith an increased fraction then going to the root. We concludethat the distribution of available photosynthate between competingsinks is influenced by source supply as well as sink function.The reported source-sink interactions are consistant with thepredictions of a recently pro posed model of source-sink interaction(Minchin et al., 1993). The concept of marginal partitioningis introduced to describe the distribution, between all of thesinks, of a small change in photosynthate supply. Key words: Carbohydrate partitioning, shoot : root ratio, source-sink interactions     

Interleukin 2 (IL-2) activity during tumor growth: IL-2 production kinetics,absorption of and responses to exogenous IL-2

A temporal study assessed the relationship between fibrosarcoma growth and immunologic encumberance due to the inability of BALB/c mouse splenocytes to elaborate the lymphokine Interleukin 2 (IL-2). Nylon-wool fractionation and antiserum treatments suggested the existence of a mildly nylon-wool-adherent, anti-Lyt 2-sensitive tumor-induced suppressor T (T_s,) cell which significantly decreased IL-2 activity. Absorption investigations indicated that ligand-activated tumor-bearing host (TBH) spleen cells were less receptive to IL-2 than their normal counterparts. When splenocytes were antiserum treated before absorption, removal of Lyt 2⁺ (suppressor T) cells resulted in greater IL-2 absorption by the remaining cells. Purified IL-2 only partially restored suppressed TBH spleen cell mitogen- or alloantigen-induced blastogenesis; whereas, normal host reactivity was significantly augmented. The collective data suggest that TBH spleen cells were capable of producing IL-2 and of responding to the IL-2 amplification signal when tumor-induced T_s cells were depleted.