Ethylene receptor expression is regulated during fruit ripening, flower senescence and abscission

Using theArabidopsis ethylene receptorETR1 as a probe, we have isolated a tomato homologue (tETR) from a ripening cDNA library. The predicted amino acid sequence is 70% identical toETR1 and homologous to a variety of bacterial two component response regulators over the histidine kinase domain. Sequencing of four separate cDNAs indicates that tETR lacks the carboxyl terminal response domain and is identical to that encoded by the tomatoNever ripe gene. Ribonuclease protection showed tETR mRNA was undetectable in unripe fruit or pre-senescent flowers, increased in abundance during the early stages of ripening, flower senescence, and in abscission zones, and was greatly reduced in fruit of ripening mutants deficient in ethylene synthesis or response. These results suggest that changes in ethylene sensitivity are mediated by modulation of receptor levels during development.     

A comparison of calcium binding inCallinectes sapidus premolt and postmolt cuticle homogenates: Implications for regulation of biomineralization

Cuticle tissue homogenates (CTHs) fromCallinectes sapidus premolt cuticle bound approximately 367% more Ca²⁺ ions than did those from the postmolt cuticle. ThepH-stat assay which was used to comparein vitro CaCO₃ nucleation times confirmed that the premolt CTHs had greater inhibitory activity than did the postmolt CTHs. This inhibitory activity was indicated by CaCO₃ nucleation times in excess of control values. Premolt nucleation times exceeded those of postmolt samples by approximately 340%. A positive correlation was observed between Ca²⁺ binding and calcification inhibitory activity for both premolt and postmolt CTHs. Heat pretreatment of CTHs at 70°C for a 24-hr period had no significant effect on their Ca²⁺ binding. However, this heat pretreatment decreased their calcification inhibitory activity. Pretreatment of CTHs with Ca²⁺ diminished their calcification inhibitory activity. These results are consistent with a mechanism for inhibition of biocalcification by these proteins which involves their initial reversible binding to nascent calcite nuclei growth steps and kinks, rather than theirin vivo interaction with free Ca²⁺ ions in solution.     

A cell-based reporter assay for the identification of protein kinase C activators and inhibitors

Transmission of extra cellular signals across biological membranes results in the generation of lipid metabolites which in turn influence specific cellular events such as cell growth or differentiation. Many of these lipid messengers can activate protein kinase C (PKC) isozymes of which one function is to perpetuate the extracellular signals to the nucleus by phosphorylating other targets proteins. We have engineered mammalian cell lines to identify and evaluate activators and inhibitors of PKC-dependent and independent signal transduction pathways. The A31 mouse fibroblast cell line, has been stably transfected with a construct containing a triplet repeat of the TPA response element (TRE) upstream of a thymidine kinase promoter fused to the human growth hormone (hGH) gene. A31 cells containing this reporter construct exhibit significant increases in hGH secretion following stimulation by phorbol esters or other mitogens. The levels of hGH secretion are modulated in this system using different pharmacological agents. We demonstrate that this assay can be used to identify specific and general inhibitors as well as activators of the signal transduction pathway mediated by PKC isozymes. (Mol Cell Biochem141: 129–134, 1994)     

Oscillatory reaction-diffusion equations on rings

We study the behavior of traveling waves in - systems on both homogeneous and inhomogeneous rings. The stability regions in parameter space of - waves were previously known [15, 19]; the results are extended here. We show the existence of Hopf bifurcations of traveling waves and the stability of the limit cycles born at the Hopf bifurcation for some parameter ranges. Using a Lindstedt-type perturbation scheme, we formally construct periodic solutions of the - system near a Hopf bifurcation and show that the periodic solutions superimposed on the original traveling wave have the effect of altering its overall frequency and amplitude. We also study the - system on an annulus ofvariable width, which does not possess reflection symmetry about any axis. We formally construct traveling waves on this variable-width annulus by a perturbation scheme, and find that perturbing the width of the annulus alters the amplitude and frequency of traveling waves on the domain by a small (order ²) amount. For typical parameter values, we find that the speed, frequency, and stability are unaffected by the direction of travel of the wave on the annulus, despite the rotationally asymmetric inhomogeneity. This indicates that the - system on a variable-width domain cannot account for directional preferences of traveling waves in biological systems.     

Unidirectional waves on rings: Models for chiral preference of circumnutating plants

Twining plants exhibit a striking oscillation of their stems in their quest for a support. The oscillations, called circumnutation, have periods generally of 1–5 hr, and virtually all species have a preferred direction of twining. I seek to explain these chiral asymmetries in plant behavior by hypothesizing a chiral asymmetry in plant anatomy. Such asymmetries already exist, for example, in phyllotaxis. I explore wave phenomena on asymmetric but isotropic rings, and seek systems which will only support (stable) waves in one direction around the ring, and not in the other. Simulations indicate that (1) oscillatory reaction-diffusion systems do not support unidirectional waves on rings; (2) excitable reaction-diffusion systems do support unidirectional waves on rings; and (3) unidirectional phase-locking (discrete unidirectional waves) occurs in rings of coupled oscillators. Thus, chiral asymmetries of circumnutating plants cannot be explained by continuum oscillator phenomena, but can be explained by general discrete oscillators, or excitable phenomena on the continuum.     

Daytime rest behavior of the Welsh pony (Equus caballus) mare and foal

Upright and recumbent rest of 15 Welsh pony foals and their mothers was studied over a 2 year period. During their first week of life, the foals spent 32% of the time in recumbent rest. Subsequently, the percentage of time spent in recumbent rest decreased, but was still greater than for the foal's mother by Week 21, when the foals spent 6.5% of their time in recumbent rest. Adults spent little time in recumbent rest. Foals rested upright only 3.5% of the time during their first week of life. Mares rested upright more than foals did to Week 13, at which time peak values for time spent in upright rest occurred for both mares (32.5%) and foals (23%). Subsequently, mares and foals spent equal, but decreasing, amounts of time resting upright. The total time spent resting by the foals decreased gradually, and was characterized by a transition from recumbent rest to upright rest. Foals were more likely to be resting, either recumbent or upright, if their mother was resting upright. During the late spring, summer, and early autumn, mares and foals were most likely to be resting upright between 09:00 and 17:00 h.     

α-phenyl-tert-butyl-nitrone inhibits free radical release in brain concussion

Traumatic brain injury (TBI) is one of the important causes of mortality and morbidity. The pathogenesis of the underlying brain dysfunction is poorly understood. Recent data have suggested that oxygen free radicals play a key role in the primary and secondary processes of acute TBI. We report direct electron spin resonance (ESR) evidence of hydroxyl (·OH) radical generation in closed-head injury of rats. Moderate brain concussion was produced by controlled and reproducible mechanical, fixed, closed-head injury. A cortical cup was placed over one cerebral hemisphere within 20 min of the concussion, perfused with artificial cerebrospinal fluid (aCSF) containing the spin trap agent pyridyl-N-oxide-tert-butyl nitrone (POBN, 100 mM), and superfusate samples collected at 10 min intervals for a duration up to 130 min post brain trauma. In addition, POBN was administered systematically (50 mg/kg body wt.) 10 min pretrauma and 20 min posttrauma to improve our ability to detect free radicals. ESR analysis of the superfusate samples revealed six line spectra (α_N = 15.4 and α^β_H = 2.5 G) characteristic of POBN-OH radical adducts, the intensity of which peaked 40 min posttrauma. The signal was undetectable after 120 min. Administration of α-phenyl-tert-butyl-nitrone (PBN), a spin adduct forming agent systemically (100 mg/kg body wt. IP 10 min prior to concussion) alone or along with topical PBN (100 mM PBN in aCSF),6significantly (P< 0.001) attenuated the ESR signal, suggesting its possible role in the treatment of TBI.     

Wax as a Mechanism for Protection against Photoinhibition — A Study of Cotyledon orbiculata

The leaves of the Crassulacean acid metabolism plant Cotyledon orbiculata have a waxy coating which is highly reflective but can be easily removed by brushing. This provided an ideal system in which to investigate the role of epidermal wax as a possible photoprotectant. Removal of the wax, prior to exposure to natural sunlight, resulted in substantial decreases in F_v/F_m and in severe cases evidence of photoinhibitory damage, as indicated by a rise in F_o. Leaves from which wax had been removed also showed higher conversion of violaxanthin to zeaxanthin than waxed leaves. Recovery of brushed leaves over a 12 day period was correlated with an increase in the total pool of xanthophyll cycle components. This study suggests that the presence of highly reflective wax on the epidermis may confer significant photoprotection to plants exposed to high solar radiation environments.