Plant peroxidases—an organismic perspective

Peroxidases are ubiquitous enzymes found in virtually all green plants, many fungi and aerobic bacteria. The isozymic heterogeneity of peroxidases appears to result from de novo synthesis, as well as an array of physiological/ecological determinants including hormones, light, gravity, and infection. Homologies among isoperoxidases from the same species are largely distinguished by the isoelectric point and as well as by protein sequence data. The basic and acidic peroxidases from a number of angiosperms show a greater functional and structural relationship within rather than between these groups. Peroxidases have phylogenetically-correlated similarities based on the chemical nature and redox potentials of the substrates which they can oxidize. Peroxidases often increase as a response to stress, and one of the principle roles of peroxidase appears to be cellular protection from oxidative reactions imposed on all photosynthetic plants. The relationships among the peroxidases, IAA and lignification emerge as a particular adaptation of vascular plants to the land environment. The great catalytic versatility of peroxidase as its predominant character and, therefore, no single major role need necessarily exist for this multifaceted enzyme.     

Plant lipid bodies and cell-cell signaling: A new role for an old organelle?

Plant lipid droplets are found in seeds and in post-embryonic tissues. Lipid droplets in seeds have been intensively studied, but those in post-embryonic tissues are less well characterised. Although known by a variety of names, here we will refer to all of them as lipid bodies (LBs). LBs are unique spherical organelles which bud off from the endoplasmic reticulum, and are composed of a single phospholipid (PL) layer enclosing a core of triacylglycerides. The PL monolayer is coated with oleosin, a structural protein that stabilizes the LB, restricts its size, and prevents fusion with adjacent LBs. Oleosin is uniquely present at LBs and is regarded as a LB marker. Although initially viewed as simple stores for energy and carbon, the emerging view is that LBs also function in cytoplasmic signalling, with the minor LB proteins caleosin and steroleosin in a prominent role. Apart from seeds, a variety of vegetative and floral structures contain LBs. Recently, it was found that numerous LBs emerge in the shoot apex of perennial plants during seasonal growth arrest and bud formation. They appear to function in dormancy release by reconstituting cell-cell signalling paths in the apex. As apices and orthodox seeds proceed through comparable cycles of dormancy and dehydration, the question arises to what degree LBs in apices share functions with those in seeds. We here review what is known about LBs, particularly in seeds, and speculate about possible unique functions of LBs in post-embryonic tissues in general and in apices in particular.     

Plant lectins specific for N-acetyl-β-D-galactosamine

N-Acetyl-D-galactosamine in β-linkage being ubiquitous in cell surface glycoproteins, their interaction with lectins specific for this sugar moiety may be a significant event in cell adhesion phenomena. This article discusses the common β-N-acetyl galactosamine-specific lectins, with particular stress on the lectin from winged beans (Psophocarpus tetragonolobus).     

Plant genome sequencing — applications for crop improvement

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Plant size: an ignored parameter in epiphyte ecophysiology?

A central objective of many ecophysiological investigations is the establishment of mechanistic explanations for plant distributions in time and space. The important, albeit mostly ignored, question arises as to the nature of the organisms that should be used as representative in pertinent experiments. We suggest that it is essential to use a demographic approach in physiological ecology, because physiological parameters such as photosynthetic capacity (PC, determined under non-limiting conditions with the oxygen electrode) may change considerably with plant size. A survey of ten vascular epiphyte species from Central Panama revealed an up to fivefold continuous increase in PC from small to large conspecifics. Moreover, the intraspecific variation in PC was almost always higher than the interspecific variation when comparing only large individuals. Theoretical considerations and additional evidence from other ecophysiological experiments corroborate the conclusion that size must be taken into account in the design of ecophysiological experiments with vascular epiphytes. In the past, most studies have ignored plant size, which may now lead to complications in the hitherto unambiguous interpretation of their results.     

Cross-validation of Non-linear Growth Functions for Modelling Tree Height–Diameter Relationships

Six non-linear growth functions were fitted to tree height–diameter data of ten conifer species collected in the inland Northwest of the United States. The data sets represented a wide range of tree sizes, especially large-sized trees. According to the model statistics, the six growth functions fitted the data equally well, but resulted in different asymptote estimates. The model prediction performance was evaluated using Monte Carlo cross-validation or data splitting for 25-cm diameter classes. All six growth functions yielded similar mean prediction errors for small- and middle-sized trees. For large-sized trees [e.g. DBH (diameter at breast height)>100 cm], however, five of the six growth functions (except the Gompertz function) overestimated tree heights for western white pine, western larch, Douglas-fir, subalpine fir, and ponderosa pine, but underestimated tree heights for western hemlock and Engelmann spruce. Among these five functions, the Korf/Lundqvist and Exponential functions produced larger overestimations. The Schnute, Weibull, and Richards functions were superior in prediction performance to others. The Gompertz function seemed always to underestimate tree heights for large-sized trees.     

Resistance to Plant Invasion? A Native Specialist Herbivore Shows Preference for and Higher Fitness on an Introduced Host

The response of native herbivores to the introduction of a new plant to the community has important implications for plant invasion. Under the Enemy Release Hypothesis introduced species become invasive because of reduced enemy control in the new range, while under the New Association Hypothesis introduced species lack effective defenses against native enemies because they do not share an evolutionary history. I tested the response of a native South-American specialist herbivore Utetheisa ornatrix (Lepidoptera: Arctiidae) to a native (Crotalaria incana) and an introduced host (Crotalaria pallida) (Fabaceae: Papilionoideae). I compared seed predation rates between the two hosts in the field, and I tested preference and performance traits with common garden experiments. Utetheisa ornatrix caused much higher seed predation rates on the introduced host than on the native host. Females also preferred to oviposit on the introduced over the native host. Additionally, larvae feeding on the introduced host had higher fitness (higher pupal weight) than larvae feeding on the native host. I discuss how the response of this specialist herbivore to this introduced host plant contradicts the predictions of the Enemy Release Hypothesis and support the New Association Hypothesis. This study shows that the New Association Hypothesis can also be true for specialist herbivores.     

Plant active components – a resource for antiparasitic agents?

Plant essential oils (and/or active components) can be used as alternatives or adjuncts to current antiparasitic therapies. Garlic oil has broad-spectrum activity against Trypanosoma, Plasmodium, Giardia and Leishmania, and Cochlospermum planchonii and Croton cajucara oils specifically inhibit Plasmodium falciparum and Leishmania amazonensis, respectively. Some plant oils have immunomodulatory effects that could modify host-parasite immunobiology, and the lipid solubility of plant oils might offer alternative, transcutaneous delivery routes. The emergence of parasites resistant to current chemotherapies highlights the importance of plant essential oils as novel antiparasitic agents.     

Plant associated protists—Untapped promising candidates for agrifood tools

The importance of host-associated microorganisms and their biotic interactions for plant health and performance has been increasingly acknowledged. Protists, main predators and regulators of bacteria and fungi, are abundant and ubiquitous eukaryotes in terrestrial ecosystems. Protists are considered to benefit plant health and performance, but the community structure and functions of plant-associated protists remain surprisingly underexplored. Harnessing plant-associated protists and other microbes can potentially enhance plant health and productivity and sustain healthy food and agriculture systems. In this review, we summarize the knowledge of multifunctionality of protists and their interactions with other microbes in plant hosts, and propose a future framework to study plant-associated protists and utilize protists as agrifood tools for benefiting agricultural production.     

The rhizosphere microbiome: Plant–microbial interactions for resource acquisition

While horticulture tools and methods have been extensively developed to improve the management of crops, systems to harness the rhizosphere microbiome to benefit plant crops are still in development. Plants and microbes have been coevolving for several millennia, conferring fitness advantages that expand the plant’s own genetic potential. These beneficial associations allow the plants to cope with abiotic stresses such as nutrient deficiency across a wide range of soils and growing conditions. Plants achieve these benefits by selectively recruiting microbes using root exudates, positively impacting their nutrition, health and overall productivity. Advanced knowledge of the interplay between root exudates and microbiome alteration in response to plant nutrient status, and the underlying mechanisms there of, will allow the development of technologies to increase crop yield. This review summarizes current knowledge and perspectives on plant–microbial interactions for resource acquisition and discusses promising advances for manipulating rhizosphere microbiomes and root exudation.     

Plant–plant facilitation increases with reduced phylogenetic relatedness along an elevation gradient

Environmental conditions can modify the intensity and sign of ecological interactions. The stress gradient hypothesis (SGH) predicts that facilitation becomes more important than competition under stressful conditions. To properly test this hypothesis, it is necessary to account for all (not a subset of) interactions occurring in the communities and consider that species do not interact at random but following a specific pattern. We aim to assess elevational changes in facilitation, in terms of species richness, frequency and intensity of the interaction as a function of the evolutionary relatedness between nurses and their associated species. We sampled nurse and their facilitated plant species in two 1000–2000 m. elevation gradients in Mediterranean Chile where low temperature imposes a mortality filter on seedlings. We first estimated the relative importance of facilitation as a mechanism adding new species to communities distributed along these gradients. We then tested whether the frequency and intensity of facilitation increases with elevation, taking into account the evolutionary relatedness of the nurse species and the facilitated species. We found that nurses increase the species richness of the community by up to 35%. Facilitative interactions are more frequent than competitive interactions (56% versus 44%) and facilitation intensity increased with elevation for interactions involving distantly related lineages. Our results highlight the importance of including an evolutionary dimension in the study of facilitation to have a clearer picture of the mechanisms enabling species to coexist and survive under stressful conditions. This knowledge is especially relevant to conserve vulnerable and threatened communities facing new climate scenarios, such as those located in Mediterranean-type ecosystems.