Lacking chloroplasts in guard cells of crumpled leaf attenuates stomatal opening: both guard cell chloroplasts and mesophyll contribute to guard cell ATP levels

Controversies regarding the function of guard cell chloroplasts and the contribution of mesophyll in stomatal movements have persisted for several decades. Here, by comparing the stomatal opening of guard cells with (crl‐ch) or without chloroplasts (crl‐no ch) in one epidermis of crl (crumpled leaf) mutant in Arabidopsis, we showed that stomatal apertures of crl‐no ch were approximately 65–70% those of crl‐ch and approximately 50–60% those of wild type. The weakened stomatal opening in crl‐no ch could be partially restored by imposing lower extracellular pH. Correspondingly, the external pH changes and K⁺ accumulations following fusicoccin (FC) treatment were greatly reduced in the guard cells of crl‐no ch compared with crl‐ch and wild type. Determination of the relative ATP levels in individual cells showed that crl‐no ch guard cells contained considerably lower levels of ATP than did crl‐ch and wild type after 2 h of white light illumination. In addition, guard cell ATP levels were lower in the epidermis than in leaves, which is consistent with the observed weaker stomatal opening response to white light in the epidermis than in leaves. These results provide evidence that both guard cell chloroplasts and mesophyll contribute to the ATP source for H⁺ extrusion by guard cells.     

Optimisation of energetic and reproductive gains explains behavioural responses to environmental variation across seasons and years

Animals switch between inactive and active states, simultaneously impacting their energy intake, energy expenditure and predation risk, and collectively defining how they engage with environmental variation and trophic interactions. We assess daily activity responses to long‐term variation in temperature, resources and mating opportunities to examine whether individuals choose to be active or inactive according to an optimisation of the relative energetic and reproductive gains each state offers. We show that this simplified behavioural decision approach predicts most activity variation (R² = 0.83) expressed by free‐ranging red squirrels over 4 years, as quantified through accelerometer recordings (489 deployments; 5066 squirrel‐days). Recognising activity as a determinant of energetic status, the predictability of activity variation aggregated at a daily scale, and the clear signal that behaviour is environmentally forced through optimisation of gain, provides an integrated approach to examine behavioural variation as an intermediary between environmental variation and energetic, life‐history and ecological outcomes.     

Cell wall architecture: normal development and environmental modification of guard cells of the Cyperaceae and related species*

Abstract. The development and cell wall architecture of guard cells in the Cyperaceae were studied with light and electron microscopy. Development occurs along parallel files and results in a stomatal complex that consists of two guard cells each flanked by a subsidiary cell. The developmental pattern and general morphology are thus similar to that in the Gramineae. Several key differences, however, were observed. Wall synthesis in the Cyperaceae, as observed in the polarization and fluorescence microscope, occurs suddenly, within three to four complexes along a file, but is more gradual in the Gramineae. Mature cell walls in the Cyperaceae predominantly contain microfibrils oriented radially relative to the pore, while those in the Gramineae contain axial microfibrils. This difference was demonstrated in numerous species using freshly-collected as well as preserved material. In Cyperus esculentus, however, the alignment of microfibrils appears to be subject to environmental modification. Plants grown in the greenhouse contain guard cells with axial microfibrils, compared to the radial arrangement found in those grown in the field. In the former, wall is deposited gradually, as in the Gramineae. On return to more stressful conditions, radially micellated guard cells again develop. In each case, the cortical cytoplasm adjacent to areas where the wall is to thicken contains microtubules oriented parallel to the microfibril alignment characteristic of that treatment. These results are discussed in terms of the role of varied wall architecture in stomatal mechanics, the regulation of cell wall biosynthesis, and the evolutionary relationship of the Cyperaceae, Gramineae, and other taxa.     

Organisms and responses to environmental change

There is great concern currently over environmental change and the biotic responses, actual or potential, to that change. There is also great concern over biodiversity and the observed losses to date. However, there has been little focus on the diversity of potential responses that organisms can make, and how this would influence both the focus of investigation and conservation efforts. Here emphasis is given to broad scale approaches, from gene to ecosystem and where a better understanding of diversity of potential response is needed. There is a need for the identification of rare, key or unique genomes and physiologies that should be made priorities for conservation because of their importance to global biodiversity. The new discipline of conservation physiology is one aspect of the many ways in which organismal responses to environmental variability and change can be investigated, but wider approaches are needed. Environmental change, whether natural or human induced occurs over a very wide range of scales, from nanometres to global and seconds to millennia. The processes involved in responses also function over a wide range of scales, from the molecular to the ecosystem. Organismal responses to change should be viewed in these wider frameworks. Within this overall framework the rate of change of an environmental variable dictates which biological process will be most important in the success or failure of the response. Taking this approach allows an equation to be formulated that allows the likely survival of future change to be estimated:Ps=(f(PF)xf(GM)xf(NP)xf(F)xf(D)xf(RA))/(ΔExf(C)xf(PR)xF(HS)),where Ps = Probability of survival; PF = Physiological flexibility; GM = Gene pool modification rate; NP = number in population; F = Fitness; D = Dispersal capability; RA = Resource availability; ΔE = rate of change of the environment; C = Competition; PR = Predation and parasitism; HS = Habitat separation. Functions (f) are used here to denote that factors may interact and respond in a non-linear fashion.     

Microbial responses to environmental arsenic

Microorganisms have evolved dynamic mechanisms for facing the toxicity of arsenic in the environment. In this sense, arsenic speciation and mobility is also affected by the microbial metabolism that participates in the biogeochemical cycle of the element. The ars operon constitutes the most ubiquitous and important scheme of arsenic tolerance in bacteria. This system mediates the extrusion of arsenite out of the cells. There are also other microbial activities that alter the chemical characteristics of arsenic: some strains are able to oxidize arsenite or reduce arsenate as part of their respiratory processes. These type of microorganisms require membrane associated proteins that transfer electrons from or to arsenic (AoxAB and ArrAB, respectively). Other enzymatic transformations, such as methylation-demethylation reactions, exchange inorganic arsenic into organic forms contributing to its complex environmental turnover. This short review highlights recent studies in ecology, biochemistry and molecular biology of these processes in bacteria, and also provides some examples of genetic engineering for enhanced arsenic accumulation based on phytochelatins or metallothionein-like proteins.     

Forty years of Mitchell's proton circuit: From little grey books to little grey cells

It is more than forty years since Peter Mitchell published his first 'little grey book' laying out his chemiosmotic hypothesis. Although ideas about the molecular mechanisms of the proton pumps have evolved considerably since then, his concept of 'coupling through proton circuits' remains remarkably prescient, and has provided the inspiration for the research careers of this author and many others. This review is a personal account of how the proton circuit has been followed from the little grey book, via brown fat and calcium transport to investigations into the life and death of neurons, Hercule Poirot's 'little grey cells'.     

Microcosm responses to environmental perturbants

A flow-through microcosm facility using unfiltered ocean source water is described. “Stagnation” cleaning has proven to be a simple and effective way of maintaining seawater distribution systems free of fouling organisms and is recommended. A valveless system for regulating water flow is also recommended. The microcosm facility has been used experimentally as an extension of field surveys being conducted in Hawaiian harbors. Examples of two essentially different types of microcosm experiments are presented to illustrate this interactive approach to environmental research. One approach disturbs an established microcosm community with specific environmental perturbants and follows both the community response and recovery over prolonged time periods. Examples of perturbation by elevated nutrients and by elevated copper concentrations are given. The ability of reef flat communities to trap and retain phosphorus even in a flow-through system is demonstrated. Added copper is shown to result in a number of responses not seen in the legislatively-preferred copper toxicity tests. The second approach involves transferring substrates from the field into the microcosm and following response with time. Again, two examples are given—one involving the transfer of fouling panels, the other, of sediments. Profound changes are seen when fouling panels are transferred from a high-nutrient into a low-nutrient environment. Nutrient-rich sediments, however, are shown not to influence water-column nutrient concentrations in the microcosms, but do acquire increased infaunal populations over a 3-month period. Finally, an example of how the findings of the microcosm experiments are applied in the field is provided. The case is made that although this approach necessarily involves multivariate experimental preparations which sometimes lack precision, it is nevertheless a required and fruitful procedure in the search for better understanding of the environmental dynamics of harbor communities.     

A simple method forIn Situ hybridization to RNA in guard cells ofVicia Faba L.: The expression of aquaporins in guard cells

Because the epidermis ofV. faba L. leaves easily can be peeled into strips of one cell layer, we developed a simple method ofin situ hybridization using epidermal peels as a substitute for paraffin, resin and cryosections. Our method sufficiently detected the expression of broad bean aquaporin 1 in guard cells. RT-PCR revealed higher expression of aquaporins (AQPs) in guard cells compared to other leaf cell types; this indicates the importance of AQP for bulk water flow across guard cell membranes and, therefore, for stomatal movements.     

The conceptual approach to quantitative modeling of guard cells

Much of the 70% of global water usage associated with agriculture passes through stomatal pores of plant leaves. The guard cells, which regulate these pores, thus have a profound influence on photosynthetic carbon assimilation and water use efficiency of plants. We recently demonstrated how quantitative mathematical modeling of guard cells with the OnGuard modeling software yields detail sufficient to guide phenotypic and mutational analysis. This advance represents an all-important step toward applications in directing “reverse-engineering” of guard cell function for improved water use efficiency and carbon assimilation. OnGuard is nonetheless challenging for those unfamiliar with a modeler’s way of thinking. In practice, each model construct represents a hypothesis under test, to be discarded, validated or refined by comparisons between model predictions and experimental results. The few guidelines set out here summarize the standard and logical starting points for users of the OnGuard software.     

Asynchrony in the growth and motility responses to environmental changes by individual bacterial cells

Knowing how individual cells respond to environmental changes helps one understand phenotypic diversity in a bacterial cell population, so we simultaneously monitored the growth and motility of isolated motile Escherichia coli cells over several generations by using a method called on-chip single-cell cultivation. Starved cells quickly stopped growing but remained motile for several hours before gradually becoming immotile. When nutrients were restored the cells soon resumed their growth and proliferation but remained immotile for up to six generations. A flagella visualization assay suggested that deflagellation underlies the observed loss of motility. This set of results demonstrates that single-cell transgenerational study under well-characterized environmental conditions can provide information that will help us understand distinct functions within individual cells.