Apomixis in plants generates clonal progeny with a maternal genotype through asexual seed formation. Hieracium subgenus Pilosella (Asteraceae) contains polyploid, highly heterozygous apomictic and sexual species, and Shirasawa et al. develop a collection of expressed SSR markers in order to construct linkage maps for Hieracium species. Previously identified apomixis loci that are responsible for two independent components of apomixis, LOSS OF APOMEIOSIS (LOA) and LOSS OF PARTHENOGENESIS (LOP), are successfully assigned to linkage groups. These maps will support the cloning of controlling genes at LOA and LOP loci in Hieracium and should assist with identification of quantitative loci that affect apomixis expressivity.
Leaf gas exchange is influenced by stomatal size, density, distribution between the leaf adaxial and abaxial sides, as well as by pore dimensions. Fanourakis et al. introgress segments of Solanum pennelli into a S. lycopersicum cultivar to generate 54 introgression lines (Ils), which they study in order to determine which traits underlie genetic differences in operating stomatal conductance (gs). They find a wide genetic variation in stomatal responsiveness to desiccation, a large part of which is explained by stomatal length. The pore area per stomatal area varies eight-fold among the ILs, and is the main determinant of differences in operating gs. Differences between operating gs based on pore dimensions and maximum gs based on stomatal dimensions are large, suggesting that stomata utilize only a small portion of their operating capacity.
Sustainable agroecosystems tend to have a positive impact on natural, social and human capital, while unsustainable ones deplete these assets, leaving fewer for the future. In this review, Pretty and Bharucha define sustainable intensification (SI) as a process or system where agricultural yields are increased without adverse environmental impact and without the conversion of additional non-agricultural land. They analyse recent evidence of the impacts of SI in both developing and industrialized countries, and demonstrate that both yield and natural capital dividends can occur. They conclude with observations on policies and incentives necessary for the wider adoption of SI, and indicate how SI could both promote transitions towards greener economies as well as benefit from progress in other sectors.
Our suitably erudite – albeit neophyte – botanical generation who knew about the functions of plant stems when quizzed previously (see Plant parts doing unexpected things: Part 1, posted previously) would probably do equally well when asked about the main roles of roots*. However, what they may be surprised to learn is that some roots photosynthesise (yes, like stems or leaves). We’re not talking about ‘typical’ soil-surrounded roots, but the so-called aerial roots of epiphytic plants perched high above the ground on trees – for example certain orchids. These photosynthetic roots dangle in the air that surrounds the epiphyte and its host plant. Whilst a photosynthetic capability is unusual for a root that is typically subterranean, you might expect that gain of this function might be at the expense of another, more typical root role, say absorption. But no, such roots still retain the capacity to absorb water from their surroundings. However, rather than rely on the assistance of root hairs as for their terrestrial, soil-rooted relatives, nature has equipped these aerial roots with an additional tissue, the velamen. The velamen is a remarkable multi-layered epidermis-like structure whose specially thickened cells not only absorb water from the humid air or rain water, but also help to reduce transpiration from the internal root tissues when the velamen cells are dried out. There is still much to uncover about the role of the velamen in the biology of epiphytes, but an interesting discovery has been made by Guillaume Chomicki et al., and one that relates not to the plant’s water relations but to the integrity of the root’s photosynthetic process. Recognising that levels of damaging ultraviolet B (UV-B) radiation are high in the epiphytes’ habitat, and knowing that UV-B screening compounds such as flavonoids help to protect leaves, the team wondered how similarly challenged, photosynthetic roots might be protected from UV-B harm. Using a nice combination of molecular and structural techniques – gene expression analyses, mass spectrometry, histochemistry and chlorophyll fluorescence – they demonstrated that UV-B exposure resulted in inducible production of two UV-B screening flavonoids within the living (i.e. young) velamen of Phalaenopsis × hybrida, but which compounds persist in the cell walls of the functional – dead – velamen tissue. Furthermore, and interestingly, this root mechanism of UV-B protection is apparently different from that employed by leaves. A case of same destination, different routes? Not bad for a dead tissue one could easily write-off as merely acting like a sponge!
* Which, for completeness, are generally assumed to be: anchorage of plant in soil, absorption of water/minerals from the soil, storage of reserve materials, and conduction of water/nutrients to/from the stem – Ed.
Recent molecular and histochemical analyses of nitrate transporters have cast doubt on the ability of the Enzyme–Substrate interpretation of analysis of nitrate influx isotherms to improve modelling of N uptake in agronomic models. Le Deunff and Malagoli advocate the use an alternative formalism, the Flow–Force theory, to describe ion isotherms based upon biophysical ‘flows and forces’ relationships of non-equilibrium thermodynamics. This formalism can be combined easily with changes in the nitrate influx rate induced by climatic and in planta factors formalized by polynomial curves. They argue that application of the Flow–Force formalism allows nitrate uptake to be modelled in a more realistic manner, and allows scaling-up in time and space of the regulation of nitrate uptake across the plant growth cycle.
Ever since 1959/60 with ‘World Refugee Year’ we’ve seen all manner of ‘International Years of’ (IYO). These global ‘observances’ are endorsed by the United Nations, an international organisation established after the Second World War and whose noble and worthy objectives include maintaining international peace and security, promoting human rights, fostering social and economic development, protecting the environment, and providing humanitarian aid in cases of famine, natural disaster, and armed conflict. Developing the notion that global problems require global solutions and action – and few issues are more pressing and global than food security – 2015 is the IYO (or on…) Soils (or IYS at it is officially abbreviated). If you wonder what the connection between soils and food is, then the former is the rooting medium that supports (both literally and nutritionally) the great majority of human’s staple crops – whether cereal (e.g. rice, wheat, maize, sorghum), legumes (e.g. chickpeas, lentils, soybean) or tubers (e.g. sweet potato, cassava, potato). Quite simply, without soil we wouldn’t be able to grow the plants to feed Man or the animals he eats. But it has to be the right kind of soil, with sufficiency of the 17 nutrients essential for plant growth and development, minimal levels of harmful compounds such as heavy metals or salts, and with enough freshwater to help sustain plant life. In many areas of the world such suitable soils are diminishing resources as a result of phenomena such as desertification and salinisation (the latter ironically often a consequence of irrigation by human intervention). Recognising the central importance of soil to food security – and doing its bit to engender a Brown Revolution*, the Food and Agriculture Organization (FAO) of the United Nations has been nominated to implement IYS 2015, with the aims of increasing awareness and understanding of the importance of soil for food security and essential ecosystem functions. We wish them well in that worthy endeavour. But there’s more! For 2015 is also the IYO Light and Light-Based Technologies (IYL 2015). Although this IYO is much more about raising awareness of how optical technologies promote sustainable development and provide solutions to worldwide challenges in energy, education, agriculture, communications and health, amongst the thousands of words devoted to this ‘event’, but almost as an after-thought, it does dedicate 78 words to the most important light-related phenomenon of photosynthesis when it considers light in nature (alongside rainbows, sunsets and northern lights…). So, two IYOs with strong plant themes (even if the photosynthetic pre-eminence of light is somewhat ‘hidden under a bushel’).. But until we have an International Year of Plants, we’ll have to make the most of The Fascination of Plants Day 2015 on 18th May (2015)…
* This is but one of a many-hued spectrum of agriculture-related revolutions (which includes the mid-20th century’s better known Green Revolution), but which is distinct from the other brown revolutions pertaining to leather or cocoa production in India.
[So that you can be ready before the next IYO happens, here’s advance notice that 2016 is the IY of camelids (camels, llamas, alpacas, vicuñas, and guanacos), and pulses (the edible, dried seeds of members of the legume family, e.g. beans, lentils). And to whet your appetite for IYS 2015, five fascinating facts about soil can be found at the CropLife website – Ed.]
An interesting paper has moved into free access in Annals of Botany: Caught in the act: pollination of sexually deceptive trap-flowers by fungus gnats in Pterostylis (Orchidaceae). It sounds like a very specific paper, and in some ways it is, but it’s also a helpful starting point for looking at sexual deception and pollination.
Typically we think of plants rewarding pollinators with nectar, but there’s no compelling reason that plants have to do this. All they need is to be pollinated. In fact attracting insects that are foraging through many plants for sugars could lead to valuable pollen being dumped on an incompatible plant, so if a plant could evolve a trick to attract insects to their own specific species, that could be a big advantage. Some orchids do this with sexual deception, but Phillips et al. point out that recent discoveries of deception in Asteraceae and Iridaceae mean that it could be a much more common method of pollination than realised.
The usual victims of sexual deception are Hymenoptera and Diptera. Phillips et al. found fungus gnats Mycetophilidae were pollinating Pterostylis sanguinea. They suspected that these orchids used sexual deception for pollination, so they looked closer. What gives their very specific question wider importance is that first they tackled the question: What exactly does pollination by sexual deception mean?
Dynamic processes occurring at the soil–root interface crucially influence soil physical, chemical and biological properties at a local scale around the roots, and are technically challenging to capture in situ. Rudolph-Mohr et al. introduce a novel combination of neutron and fluorescence imaging to study the spatiotemporal patterns of oxygen, pH and water content distribution in the rhizosphere of living roots of lupin (Lupinus albus) grown in rhizotrons. The combined imaging set-up enables them to relate observed changes in soil pH and oxygen levels to root structure and soil water content non-destructively.
A common hypothesis explaining plants’ invasive success is the evolution of increased competitive ability (EICA). Joshi et al. study the invasive plant Lythrum salicaria (purple loosestrife) and carefully distinguish between competitive effects and responses of invasive and native plants, under both intra- and interspecific competition. They find that while intraspecific competition results in no differences in competitive effects or responses between native and invasive plants, interspecific competition produces greater competitive effects and responses of invasive plants in terms of both biomass and seed production. They conclude that under interspecific competition there is strong support for the EICA hypothesis, with an evolutionarily increased competitive ability in invasive populations of L. salicaria.
Arctic-Alpine species in the northern hemisphere are occasionally derived from Tertiary relict groups, but the genus Pyrola (Ericaceae) appears to be exceptional and lineages may have arisen multiple times. Liu et al. reconstruct the biogeographic history of Pyrola based on a phylogenetic analysis, and find that three circumboreal lineages have arisen independently, and at least two of these appear to have originated in Asia. The cool, high-altitude habitats of many Pyrola species together with the fact that diversification in the genus coincided with global cooling from the late Miocene onwards fits a hypothesis of pre-adaptation to become circumboreal within this group.