Optical sensors for monitoring water uptake in plants

The monitoring of water uptake in plants is becoming increasingly important. Optical sensors offer considerable advantages over conventional methods and several sensors have been developed including an optical potometer that monitors water uptake from individual roots, the detection of xylem cavitation using audio acoustic emissions with an interferometric force feedback microphone, and an optical fiber displacement transducer that detects changes in leaf thickness in relation to leaf-water potential.

Rice seed quality development and temperature during late development and maturation

The potential longevity of japonica rice (Oryza sativa L. subsp. japonica) seed is particularly sensitive to high temperature – and thus climate change – during development and maturation. Cultivar Taipei 309 was grown at 28/208C (12 h/12 h) and then from 19 DAA (days after 50% anthesis), when seeds were just over half filled, at 28/208C, 30/228C, 32/248C or 34/268C (12 h/12 h). Whereas ability to germinate ex planta had been achieved in almost all seeds by 24 DAA, only half the population were desiccation tolerant. Desiccation tolerance continued to increase over the subsequent 28 d, similarly at all four temperatures. Subsequent longevity, assessed by p50 (period in days to reduce viability to 50% in hermetic storage at 408C with c. 15% moisture content), increased progressively at 28/208C until 38 DAA, and remained constant until the final harvest (52 DAA). The three warmer temperature regimes provided similar longevity to 28/208C at any one harvest, except at 38 DAA where the warmest (34/268C) was poorer. That temperature regime also provided greater seed-to-seed variability within each survival curve. The results confirm that appreciable improvement in seed quality occurs during seed development and also subsequent maturation in japonica rice, but that increase in temperature from 28/208C to 34/268C during late seed filling onwards has comparatively little effect thereon. Comparison with previous investigations suggests that seed quality development may be less sensitive to high temperatures during late development and maturation than during the early seed development that precedes it.

Reconstruction of historical pollination rates reveals linked declines of pollinators and plants

Widespread reports of low pollination rates suggest a recent anthropogenic decline in pollination that could threaten natural and agricultural ecosystems. Nevertheless, unequivocal evidence for a decline in pollination over time has remained elusive because it was not possible to determine historical pollination rates. Here we demonstrate a widely applicable method for reconstructing historical pollination rates, thus allowing comparison with contemporary rates from the same sites. We focused on the relationship between the oil-collecting bee Rediviva peringueyi (Melittidae) and the guild of oil-secreting orchid species (Coryciinae) that depends on it for pollination. The guild is distributed across the highly transformed and fragmented lowlands of the Cape Region of South Africa. We show that rehydrated herbarium specimens of Pterygodium catholicum, the most abundant member of the guild, contain a record of past pollinator activity in the form of pollinarium removal rates. Analysis of a pollination time series showed a recent decline in pollination on Signal Hill, a small urban conservation area. The same herbaria contain historical species occurrence data. We analyzed this data and found that there has been a contemporaneous shift in orchid guild composition in urban areas due to the local extirpation of the non-clonal species, consistent with their greater dependence on seeds and pollination for population persistence.

Ornamental Mediterranean plants in the UK: root adaptations to hypoxia and anoxia

Mediterranean species are popular landscape plants in the UK and well suited to the predicted climate change scenarios of hotter, drier summers. What is less clear is how these species will respond to the more unpredictable rainfall patterns also anticipated, where soil water-logging may become more prevalent, especially in urban environments where soil sealing can restrict drainage. Pot experiments on flooding of four Mediterranean species (Cistus × hybridus, Lavandula angustifolia ‘Munstead’, Salvia officinalis and Stachys byzantina) showed that the effects of waterlogging were only severe when the temperature was high and flooding prolonged. All plants survived the flooding in winter, but during the summer a 17-day flood resulted in the death of 30-40% of the Salvia officinalis and Cistus × hybridus. To examine the response of roots to oxygen deprivation over a range of conditions from total absence of oxygen (anoxia), low oxygen (hypoxia) and full aeration, rooted cuttings of Salvia officinalis were grown in a hydroponic-based system and mixtures of oxygen and nitrogen gases bubbled through the media. Anoxia was found to reduce root development dramatically. When the plants were subjected to a period of hypoxia they responded by increasing the production of lateral roots close to the surface thus enabling them to acclimate to subsequent anoxia. This greatly increased their chances of survival.

DNA barcodes for Mexican Cactaceae, plants under pressure from wild collecting

DNA barcodes could be a useful tool for plant conservation. Of particular importance is the ability to identify unknown plant material, such as from customs seizures of illegally collected specimens. Mexican cacti are an example of a threatened group, under pressure because of wild collection for the xeriscaping trade and private collectors. Mexican cacti also provide a taxonomically and geographically coherent group with which to test DNA barcodes. Here, we sample the matK barcode for 528 species of Cactaceae including approximately 75% of Mexican species and test the utility of the matK region for species-level identification. We find that the matK DNA barcode can be used to identify uniquely 77% of species sampled, and 79-87% of species of particular conservation importance. However, this is far below the desired rate of 95% and there are significant issues for PCR amplification because of the variability of primer sites. Additionally, we test the nuclear ITS regions for the cactus subfamily Opuntioideae and for the genus Ariocarpus (subfamily Cactoideae). We observed higher rates of variation for ITS (86% unique for Opuntioideae sampled) but a much lower PCR success, encountering significant intra-individual polymorphism in Ariocarpus precluding the use of this marker in this taxon. We conclude that the matK region should provide useful information as a DNA barcode for Cactaceae if the problems with primers can be addressed, but matK alone is not sufficiently variable to achieve species-level identification. Additional complementary regions should be investigated as ITS is shown to be unsuitable

Sugars in crop plants

We review current knowledge of the most abundant sugars, sucrose, maltose, glucose and fructose, in the world's major crop plants. The sucrose-accumulating crops, sugar beet and sugar cane, are included, but the main focus of the review is potato and the major cereal crops. The production of sucrose in photosynthesis and the inter-relationships of sucrose, glucose, fructose and other metabolites in primary carbon metabolism are described, as well as the synthesis of starch, fructan and cell wall polysaccharides and the breakdown of starch to produce maltose. The importance of sugars as hormone-like signalling molecules is discussed, including the role of another sugar, trehalose, and the trehalose biosynthetic pathway. The Maillard reaction, which occurs between reducing sugars and amino acids during thermal processing, is described because of its importance for colour and flavour in cooked foods. This reaction also leads to the formation of potentially harmful compounds, such as acrylamide, and is attracting increasing attention as food producers and regulators seek to reduce the levels of acrylamide in cooked food. Genetic and environmental factors affecting sugar concentrations are described.

Patents for plants: context and current status

One of the important themes in any discussion concerning the application of genetic transformation technology in horticulture or elsewhere is the role of Intellectual Property Rights (IPR). This term covers both the content of patents and the confidential expertise, usually related to methodology and referred to as “Trade Secrets”. This review will explain the concepts behind patent protection, and will discuss the wide-ranging scope of existing patents that cover novel genotypes of plants as well as all aspects of transgenic technology, from selectable markers and novel promoters to methods of gene introduction. Although few of these patents have any significant commercial value there are a small number of key patents that may restrict the “freedom to operate” of any company seeking to exploit the methods in the production of transgenic varieties. Over the last twenty years, these restrictions have forced extensive cross-licensing between ag-biotech companies and have been one of the driving forces behind the consolidation of these companies. Although such issues may have limited relevance in the horticultural sector, and are often considered to be of little interest to the academic scientist working in the public sector, they are of great importance in any debate about the role of “public-good breeding” and of the relationship between the public and private sectors.

Manipulating resource allocation in plants

The distribution of nutrients and assimilates in different organs and tissues is in a constant state of flux throughout the growth and development of a plant. At key stages during the life cycle profound changes occur, and perhaps one of the most critical of these is during seed filling. By restricting the competition for reserves in Arabidopsis plants, the ability to manipulate seed size, seed weight, or seed content has been explored. Removal of secondary inflorescences and lateral branches resulted in a stimulation of elongation of the primary inflorescence and an increase in the distance between siliques. The pruning treatment also led to the development of longer and larger siliques that contained fewer, bigger seeds. This seems to be a consequence of a reduction in the number of ovules that develop and an increase in the fatty acid content of the seeds that mature. The data show that shoot architecture could have a substantial impact on the partitioning of reserves between vegetative and reproductive tissues and could be an important trait for selection in rapid phenotyping screens to optimize crop performance.

Extracellular release of a heterologous phytase from roots of transgenic plants: does manipulation of rhizosphere biochemistry impact microbial community structure?

To maintain the sustainability of agriculture, it is imperative that the reliance of crops on inorganic phosphorus (P) fertilizers is reduced. One approach is to improve the ability of crop plants to acquire P from organic sources. Transgenic plants that produce microbial phytases have been suggested as a possible means to achieve this goal. However, neither the impact of heterologous expression of phytase on the ecology of microorganisms in the rhizosphere nor the impact of rhizosphere microorganisms on the efficacy of phytases in the rhizosphere of transgenic plants has been tested. In this paper, we demonstrate that the presence of rhizosphere microorganisms reduced the dependence of plants oil extracellular secretion of phytase from roots when grown in a P-deficient soil. Despite this, the expression of phytase in transgenic plants had little or no impact on the microbial community structure as compared with control plant lines, whereas soil treatments, such as the addition of inorganic P, had large effects. The results demonstrate that soil microorganisms are explicitly involved in the availability of P to plants and that the microbial community in the rhizosphere appears to be resistant to the impacts of single-gene changes in plants designed to alter rhizosphere biochemistry and nutrient cycling.

Alternatives to Sedum on green roofs: Can broad leaf perennial plants offer better ‘cooling service’?

Green roof plants alter the microclimate of building roofs and may improve roof insulation. They act by providing cooling by shading, but also through transpiration of water through their stomata. However, leaf surfaces can become warmer when plants close the stomata and decrease water loss in response to drying substrate (typically associated with green roofs during summers), also reducing transpirational cooling. By using a range of contrasting plant types (Sedum mix – an industry green roof ‘standard’, Stachys byzantina, Bergenia cordifolia and Hedera hibernica) we tested the hypothesis that plants differ in their ‘cooling potential’. We firstly examined how leaf morphology influenced leaf temperature and how drying substrate altered that response. Secondly, we investigated the relationship between leaf surface temperatures and the air temperatures immediately above the canopies (i.e. potential to provide aerial cooling). Finally we measured how the plant type influenced the substrate temperature below the canopy (i.e. potential for building cooling). In our experiments Stachys outperformed the other species in terms of leaf surface cooling (even in drying substrate, e.g. 5 oC cooler compared with Sedum), substrate cooling beneath its canopy (up to 12 oC) and even - during short intervals over hottest still periods - the air above the canopy (up to 1 oC, when soil moisture was not limited). We suggest that the choice of plant species on green roofs should not be entirely dictated by what survives on the shallow substrates of extensive systems, but consideration should be given to supporting those species providing the greatest eco-system service potential.

Flooding tolerance in four 'Garrigue' landscape plants: implications for their future use in the urban landscapes of north-west Europe?

Within a changing climate, Mediterranean ‘Garrigue’ xerophytes are increasingly recommended as suitable urban landscape plants in north-west Europe, based on their capacity to tolerate high temperature and reduced water availability during summer. Such species, however, have a poor reputation for tolerating waterlogged soils; paradoxically a phenomenon that may also increase in north-west Europe due to predictions for both higher volumes of winter precipitation, and short, but intensive periods of summer rainfall. This study investigated flooding tolerance in four landscape ‘Garrigue’ species, Stachys byzantina, Cistus × hybridus, Lavandula angustifolia and Salvia officinalis. Despite evolving in a dry habitat, the four species tested proved remarkably resilient to flooding. All species survived 17 days flooding in winter, with Stachys and Lavandula also surviving equivalent flooding duration during summer. Photosynthesis and biomass production, however, were strongly inhibited by flooding although the most tolerant species, Stachys quickly restored its photosynthetic capacity on termination of flooding. Overall, survival rates were comparable to previous studies on other terrestrial (including wetland) species. Subsequent experiments using Salvia (a species we identified as ‘intermediate’ in tolerance) clearly demonstrated adaptations to waterlogging, e.g. acclimation against anoxia when pre-treated with hypoxia. Despite anecdotal information to the contrary, we found no evidence to suggest that these xerophytic species are particularly intolerant of waterlogging. Other climatic and biotic factors may restrict the viability and distribution of these species within the urban conurbations of north-west Europe, but we believe increased incidence of flooding per se should not preclude their consideration.

What limits insect fecundity? Body size- and temperature-dependent egg maturation and oviposition in a butterfly

1. Large female insects usually have high potential fecundity. Therefore selection should favour an increase in body size given that these females get opportunities to realize their potential advantage by maturing and laying more eggs. However, ectotherm physiology is strongly temperature-dependent, and activities are carried out sufficiently only within certain temperature ranges. Thus it remains unclear if the fecundity advantage of a large size is fully realized in natural environments, where thermal conditions are limiting. 2. Insect fecundity might be limited by temperature at two levels; first eggs need to mature, and then the female needs time for strategic ovipositing of the egg. Since a female cannot foresee the number of oviposition opportunities that she will encounter on a given day, the optimal rate of egg maturation will be governed by trade-offs associated with egg- and time-limited oviposition. As females of different sizes will have different amounts of body reserves, size-dependent allocation trade-offs between the mother’s condition and her egg production might be expected. 3. In the temperate butterfly Pararge aegeria , the time and temperature dependence of oviposition and egg maturation, and the interrelatedness of these two processes were investigated in a series of laboratory experiments, allowing a decoupling of the time budgets for the respective processes. 4. The results show that realized fecundity of this species can be limited by both the temperature dependence of egg maturation and oviposition under certain thermal regimes. Furthermore, rates of oviposition and egg maturation seemed to have regulatory effects upon each other. Early reproductive output was correlated with short life span, indicating a cost of reproduction. Finally, large females matured more eggs than small females when deprived of oviposition opportunities. Thus, the optimal allocation of resources to egg production seems dependent on female size. 5. This study highlights the complexity of processes underlying rates of egg maturation and oviposition in ectotherms under natural conditions. We further discuss the importance of temperature variation for egg- vs. time-limited fecundity and the consequences for the evolution of female body size in insects.