How do plants make mitochondria?

Plant mitochondria can differ in size, shape, number and protein content across different tissue types and over development. These differences are a result of signaling and regulatory processes that ensure mitochondrial function is tuned in a cell-specific manner to support proper plant growth and development. In the last decade, the processes involved in mitochondrial biogenesis are becoming clearer, including; how dormant seeds transition from empty promitochondria to fully functional mitochondria with extensive cristae structures and various biochemical activities, the regulation of nuclear genes encoding mitochondrial proteins via regulators of the diurnal cycle in plants, the mitochondrial stress response, the targeting of proteins to mitochondria and other organelles and connections between the respiratory chain and protein import complexes. All these findings indicate that mitochondrial function is a part of an integrated cellular network, and communication between mitochondria and other cellular processes extends beyond the known exchange or transport of metabolites. Our current knowledge now needs to be used to gain more insight into the molecular components at various levels of this hierarchical and complex regulatory and communication network, so that mitochondrial function can be predicted and modified in a rational manner.     

How do plants feel the heat?

In plants, the heat stress response (HSR) is highly conserved and involves multiple pathways, regulatory networks and cellular compartments. At least four putative sensors have recently been proposed to trigger the HSR. They include a plasma membrane channel that initiates an inward calcium flux, a histone sensor in the nucleus, and two unfolded protein sensors in the endoplasmic reticulum and the cytosol. Each of these putative sensors is thought to activate a similar set of HSR genes leading to enhanced thermotolerance, but the relationship between the different pathways and their hierarchical order is unclear. In this review, we explore the possible involvement of different thermosensors in the plant response to warming and heat stress.     

How do macrophyte distribution patterns affect hydraulic resistances?

In eutrophic river systems, macrophytes attain high biomass with reduced drainage and increased flooding risk. To avoid these problems, water managers remove vegetation. Total removal, however, increases wash out of macro-invertebrate communities reducing the ecological value of rivers. Partial vegetation removal reduces this washout and prevents an increase in hydraulic resistance. In this, study the hydraulic performance of three partial vegetation removal patterns was tested. From the results it was seen that hydraulic resistance, expressed as Manning's n, was varying between 0.025 m^−1/3 s and 0.050 m^−1/3 s. Compared with the empty situation, the different distribution patterns increased resistance between 14 and 23%. Hydraulic resistance of these patterns was also significantly influenced by the species present in the vegetation patches. Three groups of macrophyte plants (emerged, floating leaved and submerged) with significantly different hydraulic resistances were determined. The emerged species Sparganium erectum generated the least resistance with an average friction of 0.03 m^−1/3 s. Stuckenia pectinata and Potamogeton natans had slightly higher friction values around 0.4 m^−1/3 s. Ranunculus penicillatus and Callitriche platycarpa had average friction values around 0.05 m^−1/3 s.The proposed vegetation removal patterns are good alternatives to create a management system, which minimally increases hydraulic resistance but still guarantees the ecological functions.     

How do the macrocyclic lactones kill filarial nematode larvae?

The macrocyclic lactones (MLs) are one of the few classes of drug used in the control of the human filarial infections, onchocerciasis and lymphatic filariasis, and the only one used to prevent heartworm disease in dogs and cats. Despite their importance in preventing filarial diseases, the way in which the MLs work against these parasites is unclear. In vitro measurements of nematode motility have revealed a large discrepancy between the maximum plasma concentrations achieved after drug administration and the amounts required to paralyze worms. Recent evidence has shed new light on the likely functions of the ML target, glutamate-gated chloride channels, in filarial nematodes and supports the hypothesis that the rapid clearance of microfilariae that follows treatment involves the host immune system.     

Q&A: How do plants respond to cytokinins and what is their importance?

Cytokinins comprise a family of signaling molecules essential for regulating the growth and development of plants, acting both locally and at a distance. Although much is known about their biosynthesis and transport, important open questions remain.     

Why do females find ornaments attractive? The coercion‐avoidance hypothesis

Vertebrates show two major classes of sexually dimorphic traits: weaponry and ornaments. However, Darwin could not explain why their expression varies so much across lineages. We argue that coercion-avoidance can explain both the existence and taxonomic distribution of ornaments. Females maximize their fitness when they can freely choose their mates, but males are expected to use sexually dimorphic weaponry not only to displace other males, but also to overcome female preferences and thus acquire matings by force whenever they can. Females should therefore avoid coercive males and avoid using weaponry as a criterion for male quality wherever possible, and rely on male viability indicators that cannot be used to coerce females (i.e. ornaments). Ornaments predominate in birds and weaponry in mammals because female choice is less costly in birds, due to higher intrinsic female behavioural freedom and lower male monopolization potential. We also predict that specialized coercive organs occur where females have low behavioural freedom but males benefit little from weaponry in male–male contests. A review of the empirical evidence supports the basic predictions of this coercion-avoidance hypothesis. We also present a simple mathematical model that confirms the logic of this hypothesis.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 372–382.     

How do frequent fires in the Cerrado alter the lepidopteran community?

Despite the great biodiversity of lepidopterans, there are few studies focusing on caterpillars and the effects of fire on their community structure in the Cerrado. The aim of this study was to evaluate the effects of frequent fires every 2 years for 16 years, on the Lepidoptera larval community hosted on Byrsonima coccolobifolia (Malpighiaceae). The study was carried out in the Cerrado sensu stricto in the Reserva Ecológica of the Instituto Brasileiro de Geografia e Estatística (IBGE-RECOR) (15°55′–15°58′S, 47°52′–47°55′W), in Distrito Federal, Brazil, from December 2005 to August 2006. We selected two burned parcels, one of which was burned during the mid-dry season (FM) and the other of which burned in the late dry season (FL), in addition to a preserved, unburned parcel (FA). In each parcel, 900 plants of B. coccolobifolia were inspected for caterpillars, which were then collected and reared in a laboratory of the University of Brasilia. We found 480 caterpillars from 49 species distributed in 16 Lepidoptera families. The frequency of plants with larvae, the number of caterpillars and species composition varied among parcels. In the unburned parcel the frequency of plants with caterpillars was 2.4 and 5.2 times higher than in burned parcels (FM and FL), respectively. The species richness did not differ among parcels, and an asymptotic curve was nearly reached in only the unburned parcel. The dominant species in the preserved parcel was Cerconota achatina (Elachistidae). In the FM, the dominant species was Concana mundissima (Noctuidae) and in the FL, the dominant species was Stenoma salome (Elachistidae). The dissimilarity between unburned and burned parcels was 64%. Results indicated that fire events have a strong negative impact on caterpillar abundance and species composition.     

How do plants “notice” attack by herbivorous arthropods?

Precise and deep comprehension of plant responses to herbivorous arthropods requires detailed knowledge of how a plant “notices” the attack. Herbivore attack is not restricted to plant wounding by feeding, but instead different phases of attack that elicit a plant response need to be distinguished: touch, oviposition and feeding. Touch, secretions released with eggs and regurgitate delivered during feeding may act in concert as elicitors of plant defence. Here, we discuss the current knowledge of what a plant “notices” during the different phases of herbivore attack and how it responds at the molecular, physiological and ecological level. Understanding the mechanisms of plant responses to the different phases of herbivore attack will be a key challenge in unravelling the complex communication pathways between plants and herbivores.     

The Out-of-India hypothesis: What do molecules suggest?

The remarkable geological and evolutionary history of peninsular India has generated much interest in the patterns and processes that might have shaped the current distributions of its endemic biota. In this regard the “Out-of-India” hypothesis, which proposes that rafting peninsular India carried Gondwanan forms to Asia after the break-up of Gondwana super continent, has gained prominence. Here we have reviewed molecular studies undertaken on a range of taxa of supposedly Gondwanan origin to better understand the Out-of-India scenario. This re-evaluation of published molecular studies indicates that there is mounting evidence supporting Out-of-India scenario for various Asian taxa. Nevertheless, in many studies the evidence is inconclusive due to lack of information on the age of relevant nodes. Studies also indicate that not all Gondwanan forms of peninsular India dispersed out of India. Many of these ancient lineages are confined to peninsular India and therefore are relict Gondwanan lineages. Additionally, for some taxa an “Into India” rather than “Out-of-India” scenario better explains their current distribution. To identify the “Out-of-India” component of Asian biota it is imperative that we understand the complex biogeographical history of India. To this end, we propose three oversimplified yet explicit phylogenetic predictions. These predictions can be tested through the use of molecular phylogenetic tools in conjunction with palaeontological and geological data.     

How do bryophytes govern generative recruitment of vascular plants?

Interactions between vascular plants and bryophytes determine plant community composition in many ecosystems. Yet, little is known about the importance of interspecific differences between bryophytes with respect to their effects on vascular plants. We compared the extent to which species-specific bryophyte effects on vascular plant generative recruitment depend on the following underlying mechanisms: allelopathy, mechanical obstruction, soil moisture and temperature control. We sowed 10 vascular plant species into monospecific mats of six chemically and structurally diverse bryophytes, and examined 1-yr seedling recruitment. Allelopathic effects were also assessed in a laboratory phyto-assay. Although all bryophytes suppressed vascular plant regeneration, there were significant differences between the bryophyte species. The lack of interactions indicated the absence of species-specific adaptations of vascular plants for recruitment in bryophyte mats. Differences between bryophyte species were best explained by alterations in temperature regime under bryophyte mats, mostly by reduced temperature amplitudes during germination. The temperature regime under bryophyte mats was well predicted by species-specific bryophyte cushion thickness. The fitness of established seedlings was not affected by the presence of bryophytes. Our results suggest that climatically or anthropogenically driven changes in the species' composition of bryophyte communities have knock-on effects on vascular plant populations via generative reproduction.     

How do trees die? A test of the hydraulic failure and carbon starvation hypotheses

Despite decades of research on plant drought tolerance, the physiological mechanisms by which trees succumb to drought are still under debate. We report results from an experiment designed to separate and test the current leading hypotheses of tree mortality. We show that piñon pine (Pinus edulis) trees can die of both hydraulic failure and carbon starvation, and that during drought, the loss of conductivity and carbohydrate reserves can also co‐occur. Hydraulic constraints on plant carbohydrate use determined survival time: turgor loss in the phloem limited access to carbohydrate reserves, but hydraulic control of respiration prolonged survival. Our data also demonstrate that hydraulic failure may be associated with loss of adequate tissue carbohydrate content required for osmoregulation, which then promotes failure to maintain hydraulic integrity.     

How do toxins from Bacillus thuringiensis kill insects? An evolutionary perspective

Three-domain Cry toxins from the bacterium Bacillus thuringiensis (Bt) are increasingly used in agriculture to replace chemical insecticides in pest control. Most chemical insecticides kill pest insects swiftly, but are also toxic to beneficial insects and other species in the agroecosystem. Cry toxins enjoy the advantages of high selectivity and the possibility of the application by sprays or transgenic plants. However, these benefits are offset by the limited host range and the evolution of resistance to Bt toxins by insect pests. Understanding how Bt toxins kill insects will help to understand the nature of both problems. The recent realization that ABC transporters play a central role in the killing mechanism will play an important role in devising solutions.     

How do plants respond to nutrient shortage by biomass allocation?

Plants constantly sense the changes in their environment; when mineral elements are scarce, they often allocate a greater proportion of their biomass to the root system. This acclimatory response is a consequence of metabolic changes in the shoot and an adjustment of carbohydrate transport to the root. It has long been known that deficiencies of essential macronutrients (nitrogen, phosphorus, potassium and magnesium) result in an accumulation of carbohydrates in leaves and roots, and modify the shoot-to-root biomass ratio. Here, we present an update on the effects of mineral deficiencies on the expression of genes involved in primary metabolism in the shoot, the evidence for increased carbohydrate concentrations and altered biomass allocation between shoot and root, and the consequences of these changes on the growth and morphology of the plant root system.