Ontogenetic tissue modification of fruit peduncles
Plants are in various ways able to adapt the geometry and material properties of their organs, tissues and cells to changing conditions during development. Apple (Malus) fruit peduncles are highly modified stems with limited secondary growth because fruit ripening lasts only one season. They must reliably connect heavy fruits to the branch and cope with increasing fruit weight, which induces dynamic stresses under oscillating wind loads.
A recent study in Annals of Botany focuses on tissue modification of these small, exposed structures during fruit development. A combination of microscopic and mechanical test methods, as well as Raman spectroscopy was applied to study structure–function relationships in apple peduncles. Anatomical investigations were accompanied by biomechanical tests under static and dynamic loads to trace tissue differentiation and ontogenetic changes in properties of Malus peduncles throughout the growing season. Mechanical investigation of peduncles after successive removal of tissues revealed insights into the specific mechanical properties and function of different tissues.
The findings confirm previous assumptions that sclereids generally strengthen the plant structure. However, this work shows that brachysclereids contribute to the stiffness mostly under bending (flexural rigidity) rather than to the strength during tensile loads, and verifies their effect on viscous damping.
Horbens, M., Feldner, A., Höfer, M., & Neinhuis, C. (2014) Ontogenetic tissue modification in Malus fruit peduncles: the role of sclereids. Annals of Botany, 113(1), 105-118.
Image: Roberta F./Wikimedia Commons.
The weather’s been so bad in the UK recently that I’m not sure if spring – ‘one of the four conventional temperate seasons, following winter and preceding summer’ – with its attendant promise of life reinvigorated, etc, has actually arrived or not. Let’s assume it has, but as we await the long-overdue blossom on the trees, look to the future with a spring-blossom-related item.
Ashley Shade et al. have uncovered successional changes in the microbial community associated with blossom of apple (Malus domestica). Whilst we may be used to terrestrial successions of land plants taking hundreds of years, in keeping with the fast-cycling times of microbes these six-stage apple successions took place during the 7-day lifespan of the studied flowers. This previously unknown floroplane community included a preponderance of members of the Deinococcus–Thermus phylum (which include many species that are resistant to extreme radiation, as well as several thermophiles), and ‘TM7’ a so-called ‘candidate phylum’ (a major lineage of bacteria whose existence is known solely through environmental 16S r(ibosomal)RNA sequences, as to date no species has been grown in the lab). Together with the decoding of its genome, one hope for this unexpected insight into apple floral biology is that it will provide a basis for better disease management of this economically important fruit.
And hot on the heels of that research, Jonathan Leff and Noah Fierer have used similar techniques – culture-independent 16S rRNA gene pyrosequencing (which ‘by sequencing well-characterized hypervariable regions of genes such as 16S rRNA… sequence data provides… unambiguous and discriminatory information for microbial identification’) – to examine the microbiota of 11 store-bought ‘produce types’, which included fruit (yes, apple was one such) and vegetables (including mushrooms – are they strictly vegetables?). Demonstrating that the sampled fruit and veg harboured diverse bacterial communities – and the communities on each product were significantly distinct from one another – they conclude that ‘humans are exposed to substantially different bacteria depending on the types of fresh produce they consume with differences between conventionally and organically farmed varieties contributing to this variation’. Tantalisingly, differentiating between closely related taxa that may have pathogenic and non-pathogenic representatives was not an objective of that study (nor was adding to the discussion as to whether ‘organic’ or ‘conventional’ farmed produce might be ‘safer’ in this regard…).
So, an assessment of whether those produce-residing bacterial communities may impact human exposures to potential pathogens is awaited. But, until then, do remember to wash your fruit and veg before eating!
Choosing the correct candidate gene (two Viewpoint papers)
This is an exciting time to study how different non-model species use common developmental genes to create such diversity in the plant world. In many cases researchers tend to identify, within newly available sequences, genes that putatively encode proteins similar to those genetically characterized in model species. A great toolbox of methods to study gene expression now exists, most of which can be outsourced: so, what is left is for researchers to choose and obtain the right samples and look at the correct genes. Samach focuses on the latter task and reminds us that it is not a trivial one, and that negligence can lead to publication of incorrect interpretations. A considered response is given by Muñoz-Fambuenaet al., whose paper (Annals of Botany 108: 511–519) is highlighted in Samach’s critique.
Detail of the stigma of a flower of apple. Click to expand.
This month the inset cover image shows a detail of the stigma of a flower of apple, Malus × domestica. The acquisition of stigmatic receptivity is concomitant with secretion of arabinogalactan proteins (AGPs, strained green) into the intercellular spaces between cell walls (blue). The presence of AGPs in the pistil has been shown in divergent species, from monocots and eudicots to early-divergent angiosperms, and hence this finding opens a way for an understanding of glycoprotein evolution modulating pollen–pistil interactions in angiosperms. See Losada and Herrero.