Bulbing of onions (Allium cepa L.): The role of endogenous ethylene*

Abstract Bulbing of onions under naturally increasing daylengths was typically associated with elevated rates of ethylene evolution (10?20 mm³× 10³ g^?1h^?1) during the initial stages of bulbing, followed by a decline to very low rates (1 mm³× 10³ g^?1h^?1) towards bulb maturation. However, detailed comparisons conducted under controlled photoperiodic conditions showed only slight differences in the course of ethylene evolution between inductive and non-inductive lighting regimens. Bulbing was not prevented by hypobaric ventilation or by treatments with the ethoxy analogue of rhizobitoxine, but Ag⁺ interfered with bulbing. Although exogenous ethylene induces bulbing under non-inductive photoperiodic conditions, the role of endogenous ethylene in the natural process requires further clarification.     

Genetics of resistance to bacterial speck of tomato caused by Pseudomonas syringae pv. tomato

Two tomato cultivars, Ontario 7710 and Rehovot 13, and their F₁, F₂, F₃ and backcross progenies were screened for resistance to bacterial speck (Pseudomonas syringae pv. tomato) of tomato. The results support the hypothesis that the resistance factors contained in the two parents are non-allelic and controlled by two different genes.     

Flower development in the passion fruit Passiflora edulis requires a photoperiod‐induced systemic graft‐transmissible signal

Different organisms use gradual seasonal changes in photoperiod to correctly time diverse developmental processes, such as transition to flowering in plants. Florigen is a systemic signal formed in leaves exposed to specific environmental cues, mainly photoperiodic, and capable of triggering flower induction in several species. Here we show that in Passiflora edulis, a perennial climbing vine, flower initiation occurs throughout the year; however, without long photoperiods, flower primordia show arrested growth and differentiation at an early stage. Our results support the existence of a positive, systemic, graft‐transmissible signal, produced in mature leaves under LDs, that is required for normal flower development beyond sepal formation. Our results also suggest that Gibberellin acts to inhibit flower development. We provide evidence for genetic variation in the response to short photoperiods. A genotype capable of forming developed flowers under short photoperiods produces a positive graft transmissible signal allowing normal flower development under short days in a cultivar which normally aborts flower development under these conditions. We believe these findings contribute towards discovering the chemical nature of this interesting mobile signal involved in flower development.     

Inheritance and sources of resistance to bacterial speck of tomato caused by Pseudomonas syringae pv. tomato

Inheritance of resistance to bacterial speck of tomato was determined by analysing F₁ F₂ and backcross progenies of crosses involving a susceptible (VF-198) and a resistant cultivar (Rehovot-13). The results fit the hypothesis that resistance is controlled by a single dominant gene in interaction with minor genes. Cultivar susceptibility to Pseudomonas syringae pv. tomato was tested under greenhouse conditions under high inoculum pressure using infested tomato seeds together with infested soils and spray-inoculated wounded plants. Of 21 species, cultivars and lines, Rehovot-13, Ontario 7710 and Lycopersiconpimpinellifolium P.I. 126927 were found to be resistant to the pathogen. VF-198 and Tropic-VF were the most susceptible. Extra Marmande, Saladette, Acc.339944–3 and the wild type Lycopersicon esculentum var. cerasiforme were moderately resistant.     

Morphological Differentiation induced by Prostaglandin in Mouse Neuroblastoma Cells in Culture

PROSTAGLANDIN is known to affect concentrations of cyclic AMP in some cells¹. Dibutyryl cyclic AMP induces irreversible differentiation of mouse neuroblastoma cells in vitro², which raises the question of whether prostaglandin would mimic this effect. I report here that prostaglandins (PG)E₁ and PGE₂ induce irreversible morphological differentiation of mouse neuroblastoma cells in culture as shown by axon formation, whereas PGF₂α does not.     

Morphologic Differentiation of Mouse Neuroblastoma Cells induced <Emphasis Type="Italic">in vitro</Emphasis> by Dibutyryl Adenosine 3′:5′-Cyclic Monophosphate

The mechanism of mammalian neural differentiation is still obscure; but the availability of mouse neuroblastoma cells in vitro provides an opportunity to study some possible inducers of differentiation and this may help to elucidate the events involved at the molecular level. We have reported¹ that X-irradiation of mouse neuroblastoma cells in vitro induces the formation of axons. The differentiated cells seem to undergo maturation: the soma and nucleus increase in size and the cytoplasm becomes granular. Here we report that N⁶O² dibutyryl adenosine 3′:5′-cyclic monophosphate (dibutyryl cyclic AMP) induces axon formation in mouse neuroblastoma cells in vitro.