A better understanding of wheat gluten

Effects of nitrogen on ω-gliadins in wheat grain

Effects of nitrogen on ω-gliadins in wheat grain

Wheat is the most important food crop in the temperate world, being used to produce bread, pasta, noodles and a range of other baked goods and foods. The ability to produce this wide range of products is largely determined by the grain storage proteins (prolamins), which form a viscoelastic network, called gluten, in dough formed from wheat flour. The classification into gliadins and glutenins has proved to be remarkably durable, but does not reflect the true molecular and evolutionary relationships of the proteins.

The ω-gliadin storage proteins of wheat are of interest in relation to their impact on grain processing properties and their role in food allergy, particularly the ω-5 sub-group and wheat-dependent exercise-induced anaphylaxis. The ω-gliadins are also known to be responsive to nitrogen application. A recent study published in Annals of Botany compares the effects of cultivar and nitrogen availability on the synthesis and deposition of ω-gliadins in wheat grown under field conditions in the UK, including temporal and spatial analyses at the protein and transcript levels.

The results show that wheat ω-gliadins vary in amount and composition between cultivars, and in their response to nitrogen supply. Their spatial distribution is also affected by nitrogen supply, being most highly concentrated in the sub-aleurone cells of the starchy endosperm under higher nitrogen availability.

 

Wan, Y., Gritsch, C.S., Hawkesford, M.J., & Shewry, P.R. (2014) Effects of nitrogen nutrition on the synthesis and deposition of the ω-gliadins of wheat. Annals of Botany, 113(4), 607-615. doi: 10.1093/aob/mct291

A new website introducing genetic engineering

The Journey of a Gene is a new website at UNL-Nebraska that teaches the basics of genetic engineering. There’s a combination of videos, some from YouTube and some specifically made as well as some interactive sections.

The video above, explaining what a gene is, is an example of what they’re bringing in. Later they explain the role of promoters and coding and you get elements like the video below explaining how to use the interactive elements.

I tend to be wary of websites a teaching tools by themselves. There are very few good ones. However, I don’t know if they have some sort of special unit at UNL, but this is the second time I’ve found useful interactive animations produced there. They also do some handy astronomy tools. As one of AoB Blog’s non-botanists, I found the videos genuinely helpful in explaining some of the genetic engineering process.

It’s hard to say why some sites work and some don’t. If it was easy to spot why something was rubbish, then it’d be easy to fix. In this case, I think building it around one specific problem, Soybean Sudden Death Syndrome, means that you have an idea of what the context is. It’s not just random information; there’s actually a point to it. That kind of narrative structure means that the sections follow on from each other in a sensible way.

If you’re a new student and want a little extra help getting your head around what a gene is, and how DNA inheritance works when you start crossing and backcrossing plants, then you should definitely give the site a go. I can’t guarantee you’ll be genetic engineering your own plants by the end of the course, but you might at least have a better understanding of how it happens.

A tip o’ the hat to Agriview for pointing me at this.

Pollen limitation and reduced reproductive success

Mating dynamics in Prunus virginiana

Mating dynamics in Prunus virginiana

A vast quantity of empirical evidence suggests that insufficient quantity or quality of pollen may lead to a reduction in fruit set, in particular for self-incompatible species. A recent study in Annals of Botany uses an integrative approach that combines field research with marker gene analysis to understand the factors affecting reproductive success in a widely distributed self-incompatible species, Prunus virginiana (Rosaceae).

The results show that even though P. virginiana is a widespread species, fragmented populations can experience significant reductions in fruit set and pollen limitation in the field. Detailed examination of one fragmented population suggests that these linitations may be explained by an increase in biparental inbreeding, correlated paternity and fine-scale genetic structure. The consistency of the field and fine-scale genetic analyses, and the consistency of the results within patches and across years, suggest that these are important processes driving pollen limitation in the fragment.

 

Suarez-Gonzalez, A., & Good, S.V. (2014) Pollen limitation and reduced reproductive success are associated with local genetic effects in Prunus virginiana, a widely distributed self-incompatible shrub. Annals of Botany, 113 (4): 595-605. doi: 10.1093/aob/mct289.

 

Biomechanical responses of hemlock to herbivory

Biomechanical responses of hemlock to herbivory

Biomechanical responses of hemlock to herbivory

Exotic invasive herbivores can overwhelm poorly defended native hosts, and result in reduced growth and survival. Severe damage may also alter the biomechanics of the attacked plant. Soltis et al. study the impact of feeding by hemlock woolly adelgid, Adelges tsugae, on the biomechanics of eastern hemlock trees, Tsuga canadensis, and find evidence of weakness and brittleness in attacked twigs and needles. Changes in resource allocation may contribute to these mechanical effects, and can increase plant susceptibility to subsequent mechanical stresses, such as wind or snow load. The interaction between herbivory and physical environmental stresses is probably accelerating the decline of eastern hemlock in North America.

Density × species evenness effects on coexistence and growth

Density × species evenness effects on coexistence and growth

Density × species evenness effects on coexistence and growth

There is considerable evidence for the presence of positive species diversity–productivity relationships in plant populations, but the parameters determining the type and strength of the relationship are poorly defined. Collet et al. study a tree plantation that mixes beech (Fagus sylvatica) and sycamore (Acer pseudoplatanus) according to a double gradient of density and species’ proportion, and find that density and tree size are the primary factors determining individual growth and stand productivity. Mixtures of these two functionally similar species have highest production at maximum evenness, indicating a complementary effect between them. The presence of a mixture combines both stabilizing mechanisms (individuals from both species show higher growth when surrounded by individuals from the other species) and equalizing mechanisms (the two species have very similar growth curves) that, in turn, determine the species’ relative dominance.

Bizarre flowers, chloride ions and auxin, and the role of pectin in stomatal development – this week in Annals of Botany

Emmotum harleyi Floral structure of Emmotum (Icacinaceae sensu stricto or Emmotaceae), a phylogenetically isolated genus of lamiids with a unique pseudotrimerous gynoecium, bitegmic ovules and monosporangiate thecae
The Icacinaceae consist of a group of early branching lineages of lamiids whose relationships are not yet resolved and whose detailed floral morphology is poorly known. The most bizarre flowers occur in Emmotum: the gynoecium has three locules on one side and none on the other. It has been interpreted as consisting of three fertile and two sterile carpels or of one fertile carpel with two longitudinal septa and two sterile carpels. This study focuses on the outer and inner morphology of the gynoecium to resolve its disputed structure.

 

Molecular cloning of two novel peroxidases and their response to salt stress and salicylic acid in the living fossil Ginkgo biloba
Peroxidase isoenzymes play diverse roles in plant physiology, such as lignification and defence against pathogens. The actions and regulation of many peroxidases are not known with much accuracy. A number of studies have reported direct involvement of peroxidase isoenzymes in the oxidation of monolignols, which constitutes the last step in the lignin biosynthesis pathway. However, most of the available data concern only peroxidases and lignins from angiosperms. This study describes the molecular cloning of two novel peroxidases from the ‘living fossil’ Ginkgo biloba and their regulation by salt stress and salicylic acid.

 

Role of chloride ions in the promotion of auxin-induced growth of maize coleoptile segments
The mechanism of auxin action on ion transport in growing cells has not been determined in detail. In particular, little is known about the role of chloride in the auxin-induced growth of coleoptile cells. Moreover, the data that do exist in the literature are controversial. This study describes experiments carried out with maize, a classical model system for studies of plant cell elongation growth. These results suggest that chloride ions play a role in the IAA-induced growth of maize coleoptile segments.

 

Developmental changes in guard cell wall structure and pectin composition in the moss Funaria: implications for function and evolution of stomata
In seed plants, the ability of guard cell walls to move is imparted by pectins. Arabinan rhamnogalacturonan I (RG1) pectins confer flexibility while unesterified homogalacturonan (HG) pectins impart rigidity. Recognized as the first extant plants with stomata, mosses are key to understanding guard cell function and evolution. Moss stomata open and close for only a short period during capsule expansion. This study examines the ultrastructure and pectin composition of guard cell walls during development in Funaria hygrometrica and relates these features to the limited movement of stomata. This is the first study to demonstrate changes in pectin composition during stomatal development in any plant.

 

Stevia hits the mainstream with ‘Life’

Last year Aurélien Azam blogged about Stevia in his post, Can we find all the tastes we like in the Wild? He mentions Stevia in it and if you don’t remember it, then Coca Cola will try to change that. Stevia is the plant behind the new Coke variety, Life.

Coca Cola Life and Death

The marketing department at Coca Cola are about to discover that if the green bottle is called ‘Life’ there’s an obvious name for the red bottle.

Stevia rebaudiana leaves are complicated sugar factories. Initially they import carbohydrates, but as leaf area increases photosynthesis means they start producing more sugars to supply the rest of the plant. The key chemicals are Steviol glycosides. These are, for the same concentration, around 300 times more sweet than sugar. The exciting feature is that human body cannot produce any calories from these sugars. For marketing, it’s the fact that it’s a plant that’s the chemical factory that’s news. If it’s made in a plant then you can label it: From Natural Sources.

But this is one of those situations where natural is probably not a synonym for good.

Stevia growing naturally in Paraguay. #156515950 / gettyimages.com

Abdel-Rahman et al. (2011) report on Stevia, among other natural products in Toxological Sciences, and note that in aqueous, crude or partially purified form Stevia can be bad news for rats. One side-effect can be reduced fertility in female rats. It’s always best to be wary from directly applying animal tests to humans, but they also note that the Guarani Indians of Paraguay would make something a bit like a tea from the Stevia leaves. They used it as an oral contraceptive.

For this reason it’s a relief that the sweetener isn’t natural, but a highly processed form of Stevia. But how does it taste?

I set up a comparison taste test with Coca Cola Life (green bottle) and the Cola Cola from the red bottle – which for ease of labelling we’ll call Death. I also added Coke Zero as a third option. All bottles were chilled and the opened with ice added. I then ignored protests from the tasters that they weren’t that thirsty.

The taste test followed a predictable pattern.

After glass 1 Zero: “Hmm.”
After glass 2 Death: “That’s definitely the full-fat Coke and the first is Stevia.”
After glass 3 Life: “Euww! No, that’s Stevia isn’t it?”

Stevia has a distinctive taste, and one that’s unexpected in Coke. Success will depend on how much the public develop a taste for it.

If it does succeed, the payoff could be big. As well as the battle against obesity, Stevia-derived sweeteners promise other benefits including fighting diabetes, high-blood pressure and tooth decay. However for now if it’s a choice between liberty from health issues or Death, a good chunk of the public will opt for Death.

The hidden cost of frankincense

A while back we covered a paper in Annals of Botany on tapping frankincense for resin. The mapping of the canals in the tree promised to improve the efficieny of tapping. Now in Tree Physiology Mengistu et al. have a paper Frankincense tapping reduces the carbohydrate storage of Boswellia trees, that’s recently become free access.

Boswellia Trees

Boswellia Trees in Ethiopia. Photo by Motuma Tolera.

Mengistu et al. show that tapping for resin reduces the trees’ stores of starches and sugars. They also show that stores deplete anyway, as the tree uses them itself. The resin is part of a store that tides the tree over the dry period, and get replenished during the wet period.

The paper ties in well with the Annals paper. In that Tolera et al. argued resin tapping could be done just as effectively with fewer cuts. Fewer cuts means less chance for disease to enter the tree. In the TreePhys paper Mengistu et al. argue that fewer cuts also means that trees have more of a chance to hold on to necessary stores of carbon, if they need them.

The evidence is that intensive tapping of Boswellia papyrifera is a problem and that the trees need some respite. However, there is also a religious imperative to tap them. Balancing supply and demand looks likely to remain a contentious problem.

Intracellular ice and cell survival in seeds of Acer

Intracellular ice and cell survival in seeds of Acer

Intracellular ice and cell survival in seeds of Acer

Efforts to cryopreserve germplasm of recalcitrant-seeded species are hampered by potentially lethal intracellular freezing events. Wesley-Smith et al. study embryonic axes of silver maple, Acer saccharinum, subjected to various drying, cooling and warming treatments and find that intracellular ice formation is not necessarily lethal. In fully hydrated axes cooled at an intermediate rate, the interiors of many organelles are apparently ice-free and this may prevent the disruption of vital intracellular machinery. The findings challenge the accepted paradigm that intracellular ice formation is always lethal, as the results show that cells can survive intracellular ice if crystals are small and localized in the cytoplasm.