THE INFLUENCE OF HUMIDITY, PHOTOPERIOD, AND TEMPERATURE ON THE DORMANCY AND ACTIVITY OF HELIX LUCORUM L. (GASTROPODA, PULMONATA)

The dormancy of Helix lucorum from N. Greece is controlled primarilyby low humidity. Photoperiod and temperature have no directeffect, except in the anomalous combination of long cool daysor short hot days. Adults hibernate more readily than juveniles.The duration of hibernation (before rejection of the calcareousepiphragm) is only slightly shorter at high temperatures. (Received 15 December 1985;     

Differentiation and Multiplication of Dyskinetoplastic Trypanosoma cruzi in Tissue Culture and in the Mammalian Host*

SYNOPSIS. In cultures of the Y strain of Trypanosoma cruzi treated with acriflavine, a very high proportion of the crithidiae may be dyskinetoplastic. These crithidiae cannot be maintained in subcultures but are able to differentiate into (dyskinetoplastic) metatrypanosomes. In tissue cultures infected with these metatrypanosomes, or with blood trypanosomes and treated with acriflavine, dyskinetoplastic T. cruzi is able to go thru the whole sequence of stages that characterizes its cycle in the vertebrate host: penetration by trypanosomes into cells, differentiation into leishmaniae, multiplication in this phase and differentiation again into trypanosomes. The same may occur in the mammalian host itself. The physiological implications of these findings are discussed and special attention is called to polymorphism of blood forms of T. cruzi, which probably has the same significance it has in the brucei-evansi group of trypanosomes.     

Reserve Lipids in Stem Root Primordia of Poplar

Lipids are reserve substances in stem root primordia of poplarand occur as droplets approximately uniformly in all cells ofroot primordia. In ultrathin sections they appear as sphericalelectron-dense particles (0.5–1.4 µm diameter),filling up virtually all the available space in the cytoplasm.The presence of lipids in stem root primordia was demonstratedin several species of the genus Populus from the section Aigeirosand Tacamahaca, as well as in another representative of thefamily Salicaceae, viz. in the genus Salix.     

Production of Melanins by Ceruloplasmin

It was shown that ceruloplasmin, apart from the known oxidative conversion of dopamine into melanin, can also produce (DHI)-melanin from 5,6-dihydroxyindole and THP-melanin from tetrahydropapaveroline. Ceruloplasmin acts as an oxidase and the kinetic parameters for these oxidative reactions are reported. Since these ceruloplasmin-catalyzed reactions occur also at pH 7.4, they could have a significant physiological impact. This ceruloplasmin-oxidasic activity is enhanced by copper ions and inhibited by chelators, such as ethylenediaminetetraacetic acid (EDTA) and desferoxamine (DEF). Some possible implication of melanin production in blood are discussed.     

Activity and Compartmentation of Photosynthetic Carboxylases in Normal and Chloroplast-mutant Maize Leaves

The activity of ribulose-l,5-diphosphate carboxylase (RudiP-carboxylase) and phosphoenolpyruvate carboxylase (PEP-carboxylase) measured in vitro was independent from the chlorophyll content of the leaves. The relatively high activity of PEP-carboxylase as compared to the RudiP-carboxylase activity was particularly pronounced in the mutants. Realization of the potential (in vitro measured) carboxylating activities in fixation of CO₂in vivo was practically complete in normal leaves. In the mutants, however, CO₂ fixation was lower than the level permitted by the carboxylase activity. This could be explained only in part by the impaired rate of photophosphorylation. Compartmentation of PEP-carboxylase was different in normal and mutant leaves: in contrast to the normal ones, parenchyma-sheath cells of the mutants exhibited high PEP-carboxylase activity. Competition of PEP-carboxylase with RudiP-carboxylase for CO₂ in the mutants led to accumulation of organic acids, and can account for their low photosynthetic activity.     

Callus Initiation and Organized Development from Zamia pumila Embryo Explants

Explants derived from Zamia pumila embryos were cultured ona Murashige and Skoog basal medium supplemented with naphthaleneaceticacid (NAA), N⁴-benzylaminopurine (BAP), or combinations of thetwo at 27 °C in darkness. NAA was invariably required forcallus initiation, and its minimal effective concentration was0.1 mg l^–1. BAP was not always required, and dependingon the explant type and NAA concentration, BAP either enhanced,suppressed, or had little effect on the frequency of callusinitiation. High frequency of callus initiation occurred with1.0 mg l^–1 NAA combined with 0.01 or 1.0 mg l^–1BAP. When the concentration of NAA was high relative to thatof BAP, friable callus was produced. As the relative BAP concentrationwas increased, a more compact callus formed. Compact-nodularcallus developed at equal concentrations of NAA and BAP overa wide range of absolute concentrations. Friable callus formedroots only. Compact-nodular callus formed roots, shoots andembryo-like structures. Root and shoot formation predominatedand were of nearly equal frequency. Formation of embryo-likestructures was infrequent. Zamia pumila, callus differentiation, callus formation, embryo culture, naphthaleneacetic acid, N⁴-benzylaminopurine