Pressure-induced cell wall instability and growth oscillations in pollen tubes

In the seed plants, the pollen tube is a cellular extension that serves as a conduit through which male gametes are transported to complete fertilization of the egg cell. It consists of a single elongated cell which exhibits characteristic oscillations in growth rate until it finally bursts, completing its function. The mechanism behind the periodic character of the growth has not been fully understood. In this paper we show that the mechanism of pressure - induced symmetry frustration occurring in the wall at the transition-perimeter between the cylindrical and approximately hemispherical parts of the growing pollen tube, together with the addition of cell wall material, is sufficient to release and sustain mechanical self-oscillations and cell extension. At the transition zone, where symmetry frustration occurs and one cannot distinguish either of the involved symmetries, a kind of 'superposition state' appears where either single or both symmetry(ies) can be realized by the system. We anticipate that testifiable predictions made by the model (f ∝ √P) may deliver, after calibration, a new tool to estimate turgor pressure P from oscillation frequency f of the periodically growing cell. Since the mechanical principles apply to all turgor regulated walled cells including those of plant, fungal and bacterial origin, the relevance of this work is not limited to the case of the pollen tube

Resiliency and Well-being as Moderators of Stress

College students experience a great deal of stress as they prepare for the transition from adolescence to adulthood. Furthermore, the ability to navigate stress and anxiety is challenged due to underdeveloped resiliency skills. Resiliency and well-being can act as a coping technique in building hope, commitment, accountability, and passion. The measurement of these factors can be an indication of how a person responds to stressful events or feelings. The study expected to see an interaction of resiliency as an overall moderator in the perception of stress based on actual stress level. The High Capacity Model of Resiliency Scale (H-CAP) was used for that specific testing of the components of resiliency. Stress was accounted for using the Undergraduate Stress Questionnaire (USQ), designed specifically for college students and typical stressful situations that they experience. Perceived stress was calculated using the Perceived Stress Scale (PSS). There was a positive correlation between actual stress and perceived stress as well as a significant difference in the stress level of the sample in comparison to the norms of the measures. Each component of resiliency reported a significant main effect with the stress scores, however; only commitment reported a significant interaction. This study has implications regarding the need for stress coping in college aged students

Observations on sexual dimorphism and social structure in the lizard Angolosaurus skoogi (Cordylidae) of the northern Namib Desert dunes

Angolosaurus skoogi is a large, herbivorous lizard of the northern Namib dune sea. Adults are sexually dimorphic in body size and colouration and these differences may be related to social organization. Whether the observed dimorphism is a result of the mating system, as is the case with several other herbivorous lizards, is unresolved. A scale character is described that provides an external indication of sex in non-reproductive individuals and thus provides a means of investigating questions pertaining to sexual dimorphism and other population level questions

A renaissance in voice analysers as tools for detection of deception?

"The current situation in the world, and especially the threat of terrorism, creates a demand for new technologies that allow observation of human psychophysiological reactions without entering into direct contact with the person and without that person’s knowledge, to evaluate the person’s honesty (deception), intentions, hidden information, and information provided. This has resulted in a revival of interest in devices and techniques for investigating emotional changes in the sound of the human voice (Widacki 2007)."(...

Simple method to estimate cell wall extensibility coefficient by using only two cardinal numbers

In this short communication we consider the extensibility properties of the cell wall. This is accomplished by a heuristically motivated equation for the expanding volume of the cell. The experimentally determined characteristic time t0 and temperature T0 are the only numbers required for evaluating the effective yielding coefficient F(t, T) in the respective time and temperature domains

Chemical Potential‑Induced Wall State Transitions in Plant Cell Growth

The pH/T duality of acidic pH and temperature (T) action for the growth of grass shoots was examined in order to derive the phenomenological equation of wall properties for living plants. By considering non-meristematic growth as a dynamic series of state transitions (STs) in the extending primary wall, the critical exponents were identified, which exhibit a singular behaviour at a critical temperature, critical pH and critical chemical potential (μ) in the form of four power laws: f ( ) ∝ −1 , f ( ) ∝ 1− , g ( ) ∝ −2− +2 and g ( ) ∝ 2− . The indices α and β are constants, while π and τ represent a reduced pH and reduced temperature, respectively. The convexity relation α + β ≥ 2 for practical pH-based analysis and β ≡ 2 “meanfield” value in microscopic (μ) representation were derived. In this scenario, the magnitude that is decisive is the chemical potential of the H+ ions, which force subsequent STs and growth. Furthermore, observation that the growth rate is generally proportional to the product of the Euler beta functions of T and pH, allowed to determine the hidden content of the Lockhart constant Ф. It turned out that the pH-dependent time evolution equation explains either the monotonic growth or periodic extension that is usually observed—like the one detected in pollen tubes—in a unified account