Global annual losses in agricultural production from salt-affected land are in excess of US$12 billion and rising. Shabala identifies physiological mechanisms conferring salinity tolerance in halophytes that can be introduced into non-halophyte crop species to improve their performance under saline conditions. The specific traits that are discussed and advocated include: manipulation of trichome shape, size and density to enable their use for external Na+ sequestration; increasing the efficiency of internal Na+ sequestration in vacuoles by the orchestrated regulation of tonoplast NHX exchangers and slow and fast vacuolar channels, combined with greater cytosolic K+ retention; controlling stomata aperture and optimizing water use efficiency by reducing stomata density; and efficient control of xylem ion loading.
It’s a tribute to the fantasticness of plants – and photosynthesis in particular – that even animals want to be like them. Arguably, none more so than some sea slugs, which for many millennia have eaten seaweeds and integrated their chloroplasts into their bodies (a phenomenon known as kleptoplasty). The assumption that underlies such acquisitive behaviour is that the new owners use those sequestered verdant powerhouses as a fuel source for their own purposes. A lovely idea – and one that will have found its way into the textbooks, and featured in lectures based thereon. But! Gregor Christa et al. have concluded that, while such ‘stolen plastids’ display light-dependent CO2 fixation (i.e. photosynthesis), light is not essential for the studied sea slugs – Elysia timida and Plakobranchus ocellatus – to stave off starvation. Indeed, they conclude that the internalized plastids seem to be a slowly digested food source rather than a source of solar power. In other words, this is an example of plants feeding the planet (again!). However, another bonus of this work is that animals are still just animals and not proxy plants. Which is good, because, to paraphrase one Harold Woolhouse, if one wants to understand the biology of plants one will ultimately have to work on… plants.
[However, if you wish to study animals that penetrate each other in the head during sex, then that’s where sea slugs really come into their own. But if you want more on photosynthetic animals, check out this article by Sarah Rybak – Ed.]
Exotic plant species impact belowground processes by influencing resource availability through enhanced microbial activity as a consequence of litter inputs. We have little understanding of the impact of microbe-driven nutrient fluctuations on biomass accumulation of invasive species. In a recent article in AoB PLANTS, Bajpai and Inderjit attempt to determine whether soil community-driven nitrogen availability influences invader biomass. They discovered that soil communities cultured by Ageratina adenophora, a neotropical invader in Asia, retain available nitrogen that influences the biomass of the invader. Through soil manipulation experiments they found that A. adenophora grows better in soil with higher available nitrogen content. Ageratina adenophora-invaded soil had higher microbial activity and available nitrogen due to higher inputs of terpene-rich litter compared to soil not yet invaded by it. Their results provide evidence that microbe-linked nitrogen availability exerts a positive impact on A. adenophora biomass accumulation, emphasizing the importance of soil community-driven nitrogen availability in invasion success.
Extreme water stress episodes induce tree mortality, but the mechanistic relationships linking stem embolism and species drought performance remain poorly understood. Barigah et al. study potted juvenile trees of beech (Fagus sylvatica) and poplar (Populus deltoides × P. nigra) and find that the xylem pressure inducing 50 % mortality differs sharply between the species, being 1.75 and 4.5 MPa in poplar and beech, respectively. However, the relationships between tree mortality and the degree of cavitation in the stems are similar, with mortality occurring suddenly when >90 % cavitation has occurred. This is in contrast to the 50 % embolism threshold reported for conifers. The results demonstrate that massive cavitation is probably a causal factor for tree mortality under extreme water stress conditions.
Trichomes are epidermal outgrowths generally associated with protection against desiccation and herbivores. These structures are widely distributed on plant parts but evolutionary studies of trichomes are still scarce. Nogueira et al. integrate phylogenetic and morpho-anatomical data in a study on the evolutionary history of the tribe Bignonieae in order to understand current patterns of diversity of trichome types. They find considerable topological variation in the evolution of glandular and non-glandular trichomes, suggesting that the most recent common ancestor of Bignonieae probably presented different trichome types on different plant parts. The descriptions and ontology presented will greatly facilitate comparisons between morphological variants and functional studies of trichomes.
The coexistence of forest tree species has often been linked to differences in their response to light availability during the regeneration stage. Van Couwenberghe et al. study natural regenerated shade-tolerant Fagus sylvatica and shade-intermediate Quercus petraea seedlings and find that no rank reversal occurs between the two species along a light gradient, or along density, mixture or seedling-size gradients. The results thus do not support the classical assumption that spatial heterogeneity in a canopy opening would explain the coexistence of the two species studied. Instead, it is suggested that the main driver of the dynamics of these mixed stands is spatial variation in local size hierarchies among seedlings, which may be caused by differences in seedling emergence time or initial seedling performance.
Schadenfreude (taking pleasure in the misfortunes of others) is not the most attractive of human traits, but it can be so satisfying. And I bet there’s more than a little of that throughout the world occasioned by the discovery that the model plant Arabidopsis thaliana seems not to be such a good model after all. And the reason for this global wave of ‘arabidisenchantia’ relates to a rather fundamental property of cells known as nonsense-mediated mRNA decay (NMD). NMD is a so-called surveillance pathway that reduces errors in gene expression by eliminating aberrant m(essenger)RNAs that would otherwise encode incomplete polypeptides. Important though this process is for cell survival, it had been assumed that plants used it in a different way to animals because a gene for a key protein – SMG1 (phosphatidylinositol 3-kinase-related kinase) – in the pathway had not been identified in Arabidopsis thaliana (afka* ‘the universal plant’), nor in fungi. However, and thanks to iconoclastic (albeit probably unintentionally) work by James Lloyd and Brendan Davies, we [arabothalocentric plant biologists and those who needs must rely on their abundantly-funded researches - which is pretty much all of the rest of us...] can all sleep more soundly in our beds. They show that SMG1 – the gene that codes for SMG1 – is not animal-specific, but is found ‘in a range of eukaryotes, including all examined green plants [my emphasis] with the exception of A. thaliana’. The misconception about the importance of SMG1 in plants appears to have arisen because the gene was lost from A. thaliana ’s genome 5–10 millions of years ago. Interestingly, SMG1 is found in the genome of the closely related A. lyrata… So, A. thaliana is unique after all(!), though not in quite the way its promoters (pun intended…?) might have liked. But if thale cress has carelessly lost this gene, what else has it lost (but which may have been retained by more typical plants)…? I predict more Arabidopsis applecart-upsetting in the future…
* afka = as formerly known as…
Angiosperm trees generally form tension wood, a special type of secondary xylem, in response to a gravitational stimulus. Nugroho et al. find that pre-treatment with paclobutrazole and uniconazole-P, inhibitors of the synthesis of gibberellin, to inclined Acacia mangium seedlings inhibits negative gravitropism of the stems. The inhibitors suppress increases in the thickness of gelatinous layers and the elongation of gelatinous fibres in the tension wood. In contrast, pre-treatment with gibberellin stimulates the elongation of these fibres. The results suggest that gibberellin is important for the development of gelatinous fibres, and therefore in gravitropism.
Many abiotic variables affect plants, e.g. levels of light, carbon dioxide and water. One of the most important of those non-biotic factors is temperature. Now, given its importance you could be forgiven for assuming that it is recorded accurately and correctly. Unfortunately, that isn’t always the case. Take for instance the temperature of the meristem (symbolised as Tmeristem), which is important in driving plant development. For such a crucial aspect of plant biology studies have largely relied on measuring the temperature of the air surrounding the plant (Tair). Tair is measured because it is assumed to represent the meristem temperature because plants are poikilotherms (organisms whose ‘internal temperature varies considerably … Usually the variation is a consequence of variation in the ambient environmental temperature’). Whilst that assumption may seem reasonable – and it does save the would-be investigator the trouble of penetrating the umpteen layers of developing leaves, etc, that may sheathe the apical meristem, it is nonetheless an assumption. And the veracity of assumptions must be tested, which is what Andreas Savvides et al. did. Guess what they found! That’s right: Tmeristem differed from Tair – ranging between –2.6 and 3.8 °C in tomato, and –4.1 and 3.0 °C in cucumber(!). As the team conclude, ‘for properly linking growth and development of plants to temperature… Tmeristem should be used instead of Tair’.
If you’re now intrigued by detecting temperatures within cells, you might like to explore the nanoscale thermometer developed by G. Kucsko et al. Using ‘quantum manipulation of nitrogen vacancy (NV) colour centres in diamond nanocrystals’ it can detect temperature variations as small as 44 mK(!) and can measure the local thermal environment at length scales as low as 200 nm(!!). Or, if you want a more biological approach, check out the genetically encoded sensor that fuses green fluorescent protein to a thermosensing protein derived from Salmonella, as showcased by Shigeki Kiyonaka et al. Although proof of this particular principle was demonstrated with thermogenesis in the iconic mitochondria of brown adipocytes (and the somewhat less iconic endoplasmic reticulum of myotubes), the team envisage it could be used to investigate this phenomenon in other living cells. Maybe even within the cone cells of tropical cycads that undergo impressive increases in temperature, where Tcone can be markedly greater that Tair. In view of concerns about global temperature changes and effects of temperature on regulation of such economically important processes as flowering, accurate temperature information in planta – and an appreciation of the temperature that plants are actually responding to – is likely to become increasingly important.
[For a useful set of slides summarising Savvides et al.’s work, visit slideshare.net. For a less physics-oriented interpretation of the Nature nanoscale thermometry article try the accompanying ‘News and Views’ item by Konstantin Sokolov – Ed.].
The Orchidaceae have a history of recurring convergent evolution in floral function as nectar production has evolved repeatedly from an ancestral nectarless state. Hobbhahn et al. study the South African orchid genus Disa and find that independent nectary evolution has involved both repeated recapitulation of secretory epidermis, which is present in the sister genus Brownleea, and innovation of stomatal nectaries. These contrasting nectary types and positional diversity within types imply weak genetic, developmental or physiological constraints in ancestral, nectarless Disa. With its morphologically diverse solutions to the problem of nectar production, Disa is a good example illustrating the contribution of functional convergence to phenotypic diversification, which probably also underlies the extensive diversity of nectary types and positions in the orchid family.