Effects of Gibberellic Acid on the Rhizome and Rhizoids of the Algal Coenocyte, Caulerpa prolifera, in Culture

Treatment of the large coenocyte Caulerpa prolifera with a hormonallevel of GA₂ resulted in increased elongation of the rhizomeand more frequent initiation of rhizoids when the hormone wasadded to the Erdschreiber culture medium. No effect of GA₂ wasfound on the rate of initiation or elongation of blades. Theseresults suggest that the recently discovered gravimorphogeneticeffect on rhizoid development is mediated by endogenous gibberellin. Caulerpa prolifera, coenocyte, green alga, gibberellic acid     

Variation among 41 Genotypes of Tomato (Lycopersicon esculentumMill.) for Crossability toL. peruvianum(L.) Mill.

Even with the aid of tissue culture, crosses betweenLycopersiconesculentum(E) andL. peruvianum(P) typically yield few progeny.To determine whether some E genotypes produce more progeny perfruit that others when crossed with P, 41 E genotypes were crossedwith pollen bulked from five P accessions. This first experiment(expt 1) was replicated over 2 years. In a second experiment(expt 2), differences among three genotypes each of E and P,and among individual plants within E genotypes were investigated.The E genotypes for expt 2 were chosen for relatively high andlow crossability based on results of expt 1. The P genotypesfor expt 2 were from different accessions than those used inexpt 1. For both experiments, the 15 largest ovules from eachripe fruit were cultured aseptically for 1 month. Out of 1228fruit, 753 hybrids were obtained. For expt 1, significant genotypeby year interactions were observed. Within each year, therewere significant differences among E genotypes for crossability.In expt 2, significant effects were found for E genotypes, butnot for interactions between E and P genotypes, P genotypes,nor plants within E genotypes. Moreover, general crossabilityfor E genotypes using bulked pollen (expt 1) was indicativeof general crossability with three P accessions not presentin the bulk (expt 2). Thus, selecting E genotypes of high crossabilityto P is the key to obtaining progeny for gene introgression.Rare production of ExP seed which was large and had brown seedcoats typical of E seed indicated strong selection pressureto maintain separate species, but gene exchange in nature maybe possible albeit at a low rate over long periods of time. Interspecific hybridization; Lycopersicon esculentum; Lycopersicon peruvianum; ovule culture; speciation     

Regulation of Release and Mode of Action of Crustacean Chromatophorotropins

Pigment movements in crustacean chromatophores are regulatedby pigment-concentrating and pigment-dispersing neurosecretoryhormones. The release of these hormones from the neurosecretorysystem is thought to be controlled by neural signals. Althoughthe exact cellular sources of chromatophorotropins and the natureof synaptic input to the neurosecretory system remain unresolved,recent pharmacological studies on fiddler crabs indicate thatcertain biogenic amines contribute to the release of some ofthe chromatophorotropins. The current evidence suggests that:5-hydroxytryptamine stimulates the release of RPDH (red pigmentdispersing hormone), dopamine triggers the release of RPCH (redpigment concentrating hormone), and norepinephrine stimulatesthe release of BPDH/MDH (black pigment/melanin dispersing hormone).Nothing is known of the regulation of release of leucophorotropinsand xanthophorotropins. Like most other peptide hormones, crustacean chromatophorotropinsare thought to exert their effect by first binding to receptorson the cell surface and then triggering a series of events leadingto cellular responses, but the details are far from clear. Recentwork suggests that hormone-induced pigment movements may bemodulated/mediated by alterations in cyclic nucleotide levelsand/or by changes in Ca²⁺ distribution or flux. Both cyclicnucleotides and Ca²⁺ may modulate motility by regulating theintegrity and/or function of cytoskeletal elements, but thedetails of this mechanism and the precise roles of cytoskeletalelements in the pigment-translocating process remain unresolved.