Effects of clonal integration on plant plasticity in Fragaria chiloensis

The ability of clonal plants to transport substances between ramets located in different microsites also allows them to modify the plastic responses of individual ramets to local environmental conditions. By equalising concentrations of substances between ramets, physiological integration might decrease responses to local conditions. However, integration has also been observed to increase plasticity and induce novel plastic responses in ramets. To ask how integration modifies plant plasticity in the clonal herb, Fragaria chiloensis, ramets were given either low light and high nitrogen or high light and low nitrogen, simulating a pattern of resource patchiness in their native habitat. Ramets in contrasting light/nitrogen treatments were either connected or single. Effects of light/nitrogen and connection were measured at three levels of morphological organisation, the organ, the ramet, and the clonal fragment. Connection between ramets reduced or had no effect on plastic responses in leaf size at the level of the plant organ. This suggested that integration dampened certain plastic responses. Connection induced a new plastic response at the level of the clonal fragment, an increase in allocation to vegetative reproduction in patches of low light and high nitrogen. It is concluded that clonal integration can have different effects on plant plasticity at different levels of plant organisation. It appears that, at least in this species, integration can increase plasticity at the level of the clonal fragment and concentrate vegetative reproduction in particular microsite types.     

Aboveground plant-to-plant electrical signaling mediates network acquired acclimation

Systemic acquired acclimation and wound signaling require the transmission of electrical, calcium, and reactive oxygen species (ROS) signals between local and systemic tissues of the same plant. However, whether such signals can be transmitted between two different plants is largely unknown. Here, we reveal a new type of plant-to-plant aboveground direct communication involving electrical signaling detected at the surface of leaves, ROS, and photosystem networks. A foliar electrical signal induced by wounding or high light stress applied to a single dandelion leaf can be transmitted to a neighboring plant that is in direct contact with the stimulated plant, resulting in systemic photosynthetic, oxidative, molecular, and physiological changes in both plants. Furthermore, similar aboveground changes can be induced in a network of plants serially connected via touch. Such signals can also induce responses even if the neighboring plant is from a different plant species. Our study demonstrates that electrical signals can function as a communication link between transmitter and receiver plants that are organized as a network (community) of plants. This process can be described as network-acquired acclimation.

A new type of plant-to-plant direct communication involving electrical signaling, reactive oxygen species, and photosystem networks is revealed.

In a Nutshell Background: An injured leaf (e.g. by insect herbivory or excess light) generates electric signals (ES) that spread to tissues, leaves, and organs of the entire plant. ES are mediated by changes in the activity of ion channels and are accompanied by waves of reactive oxygen species (ROS) and nonphotochemical quenching (NPQ). These waves are interdependent and propagate systemically throughout the plant. This process is essential for priming specific changes in gene expression and plant acclimation (e.g. cellular light memory). As a result, the entire plant enters a state of systemic acquired acclimation (SAA). Question: Could ES, ROS, and NPQ waves spread from an injured plant to neighboring plants, if their leaves touch? Until now, only indirect signaling routes like underground ES mediated by mycorrhizal networks between roots of different plants, or aboveground plant volatiles, were found to connect different plants. Findings: Under humid conditions, an injured plant can directly communicate a danger signal to other plants that touch it within a community of plants, like a meadow of dandelions. ES and ROS waves serve as plant-to-plant signals propagating on and in the leaf with a velocity of several millimeters per second or centimeters per minute, respectively. These signals can induce changes in NPQ, chloroplast retrograde signaling, gene expression, phytohormones, ROS signaling, and acclimation responses, in neighboring plants. Most of these complex communication responses can also be induced between two plants connected by a copper wire circuit, indicating that ES is the main player of plant-to-plant communication. We show that ES and ROS induce a new acclimation phenomenon termed “network acquired acclimation (NAA),” necessary for SAA induction within a plant community. Next steps: NAA may be considered as a new communication mechanism within plant ecosystems. However, whether NAA is a “side effect” of SAA, or confers an evolutionary advantage to plants living within the community, and to what extent can ES carry specific information and determine specific responses, are open questions.     

Stomatal characteristics of ferns and angiosperms and their responses to changing light intensity at different habitats

气孔是植物与大气环境进行气体交换的重要通道, 在调控植物碳水平衡方面发挥着重要作用。为探讨生境和植物类型对气孔形态特征的影响以及气孔对光强变化的响应格局在不同植物间和不同生境条件下的变异, 选取开阔生境和林下生境的5种蕨类植物和4种被子植物, 测定了它们的气孔形态特征和气孔导度对光强变化的响应。此外, 还收集了8篇文献中开阔和林下生境的45种蕨类植物和70种被子植物的气孔密度和气孔长度数据, 以增大样本量从而更好地探讨不同生境条件下蕨类和被子植物气孔密度及长度的变异格局, 并通过分析生境和植物类型对气孔形态特征的影响来推测生境和植物类型对气孔响应行为的可能影响。实验结果表明, 与林下植物相比, 开阔环境下的植物气孔密度更大, 气孔长度更小, 气孔对光强降低的响应更敏感; 但植物类型对气孔形态特征的影响以及对气孔响应光强的敏感程度的影响均不显著。对文献数据的分析表明, 生境和植物类型对气孔形态特征均有显著影响。考虑到气孔响应快慢与气孔形态特征密切相关, 与蕨类植物相比, 被子植物小而密的气孔可能为其更快地响应环境变化提供了基础。研究表明生境和植物类型对气孔响应行为均有显著影响。     

不同生境条件下蕨类和被子植物的气孔形态特征及其对光强变化的响应

气孔是植物与大气环境进行气体交换的重要通道, 在调控植物碳水平衡方面发挥着重要作用。为探讨生境和植物类型对气孔形态特征的影响以及气孔对光强变化的响应格局在不同植物间和不同生境条件下的变异, 选取开阔生境和林下生境的5种蕨类植物和4种被子植物, 测定了它们的气孔形态特征和气孔导度对光强变化的响应。此外, 还收集了8篇文献中开阔和林下生境的45种蕨类植物和70种被子植物的气孔密度和气孔长度数据, 以增大样本量从而更好地探讨不同生境条件下蕨类和被子植物气孔密度及长度的变异格局, 并通过分析生境和植物类型对气孔形态特征的影响来推测生境和植物类型对气孔响应行为的可能影响。实验结果表明, 与林下植物相比, 开阔环境下的植物气孔密度更大, 气孔长度更小, 气孔对光强降低的响应更敏感; 但植物类型对气孔形态特征的影响以及对气孔响应光强的敏感程度的影响均不显著。对文献数据的分析表明, 生境和植物类型对气孔形态特征均有显著影响。考虑到气孔响应快慢与气孔形态特征密切相关, 与蕨类植物相比, 被子植物小而密的气孔可能为其更快地响应环境变化提供了基础。研究表明生境和植物类型对气孔响应行为均有显著影响。     

Light perception in plant disease defence signalling

Light is a predominant factor in the control of plant growth, development and stress responses. Many biotic stress responses in plants are therefore specifically adjusted by the prevailing light conditions. The plant cell is equipped with sophisticated light-sensing mechanisms that are localised inside and outside of the chloroplast and the nucleus. Recent progress has provided models of how the signalling pathways that are involved in light perception and in defence could operate and interact to form a plant defence network. Such a signalling network includes systems to sense light and regulate gene expression. Photo-produced H(2)O(2) and other reactive oxygen species in the cell also play an essential role in this regulatory network, controlling biotic and abiotic stress responses.     

Mycorrhizal colonization does not affect tolerance to defoliation of an annual herb in different light availability and soil fertility treatments but increases flower size in light-rich environments

Heterogeneous distribution of resources in most plant populations results in a mosaic of plant physiological responses tending to maximize plant fitness. This includes plant responses to trophic interactions such as herbivory and mycorrhizal symbiosis which are concurrent in most plants. We explored fitness costs of 50% manual defoliation and mycorrhizal inoculation in Datura stramonium at different light availability and soil fertility environments in a greenhouse experiment. Overall, we showed that non-inoculated and mycorrhiza-inoculated plants did not suffer from 50% manual defoliation in all the tested combinations of light availability and soil fertility treatments, while soil nutrients and light availability predominately affected plant responses to the mycorrhizal inoculation. Fifty percent defoliation had a direct negative effect on reproductive traits whereas mycorrhiza-inoculated plants produced larger flowers than non-inoculated plants when light was not a limiting factor. Although D. stramonium is a facultative selfing species, other investigations had shown clear advantages of cross-pollination in this species; therefore, the effects of mycorrhizal inoculation on flower size observed in this study open new lines of inquiry for our understanding of plant responses to trophic interactions. Also in this study, we detected shifts in the limiting resources affecting plant responses to trophic interactions.     

Do plant parts compete for resources? An evolutionary viewpoint

Simultaneously growing sinks are thought to compete for plant resources. Negative correlations, for example between grain number and stem mass in cereals, indeed resemble competition; but is the notion of intra-plant competition evolutionarily justified? Here we review intra-plant competition in light of two aspects of evolutionary biology: (a) major transitions that led to the reorganization of evolutionary individuals (e.g. isolated DNA molecules and independent cells) into new units of adaptation (e.g. chromosomes and multicellular organisms) with associated constraints to intra-individual conflict; and (b) genomic conflicts within individual plants with implications for resource allocation. Against this background, we look at apparent competition among genetically identical plant parts, and conclude that plants might use competition-like mechanisms to allocate resources, but only to the extent that these proximate mechanisms enhance overall plant fitness. In dealing with apparent competition among genetically different plant structures, we emphasize developing seeds attached to the same maternal plant, and the determination of yield components in annual crops. We propose that competition-like mechanisms among genetically different plant parts have been strongly shaped by the evolution of genomic conflict between parent and offspring, between female and male parents, and among siblings. By defining the number and potential size of grain simultaneously and before fertilization, a strong maternal control of resource allocation is exerted that favours uniform offspring size and partially counteracts genomic conflict.     

向光素调节植物向光性及其与光敏色素/隐花色素的相互关系

蓝光受体向光素(PHOT1/PHOT2)调节蓝光诱导的植物运动反应, 包括植物向光性、叶绿体运动、气孔运动和叶片伸展等。其中, 向光素介导的植物向光性能够促使植物弯向光源, 确保其以最佳取向捕获光源, 优化光合作用。光敏色素和隐花色素作为光受体也参与植物的向光性调节。该文综述了向光素介导的拟南芥(Arabidopsis thaliana)下胚轴向光弯曲信号转导及其与光敏色素、隐花色素协同作用的分子机制, 以期为改造植物光捕获能力及提高光利用效率提供理论基础。     

Flowering responses to light and temperature

Light and temperature signals are the most important environmental cues regulating plant growth and development. Plants have evolved various strategies to prepare for, and adapt to environmental changes. Plants integrate environmental cues with endogenous signals to regulate various physiological processes, including flowering time. There are at least five distinct pathways controlling flowering in the model plant Arabidopsis thaliana: the photoperiod pathway, the vernalization/thermosensory pathway, the autonomous floral initiation, the gibberellins pathway, and the age pathway. The photoperiod and temperature/vernalization pathways mainly perceive external signals from the environment, while the autonomous and age pathways transmit endogenous cues within plants. In many plant species, floral transition is precisely controlled by light signals(photoperiod) and temperature to optimize seed production in specific environments. The molecular mechanisms by which light and temperature control flowering responses have been revealed using forward and reverse genetic approaches. Here we focus on the recent advances in research on flowering responses to light and temperature.     

Phototropins promote plant growth in response to blue light in low light environments

Phototropins (phot1 and phot2) are plant-specific blue light receptors for phototropism, chloroplast movement, leaf expansion, and stomatal opening. All these responses are thought to optimize photosynthesis by helping to capture light energy efficiently, reduce photodamage, and acquire CO2. However, experimental evidence for the promotion of plant growth through phototropins is lacking. Here, we report dramatic phototropin-dependent effects on plant growth. When plants of Arabidopsis thaliana wild type, the phot1 and phot2 mutants, and the phot1 phot2 double mutant were grown under red light, no significant growth differences were observed. However, if a very low intensity of blue light (0.1 micromol m(-2) s(-1)) was superimposed on red light, large increases in fresh weight up to threefold were found in those plants that carried functional PHOT1 genes. When the intensity of blue light was increased to 1 micromol m(-2) s(-1), the growth enhancement was also found in the phot1 single mutant, but not in the double mutant, indicating that phot2 mediated similar responses as phot1 with a lower sensitivity. The effects occurred under low photosynthetically active radiation in particular. The well-known physiological phototropin-mediated responses, including chloroplast movement, stomatal opening, and leaf expansion, in the different lines tested indicated an involvement of these responses in the blue light-induced growth enhancement. We conclude that phototropins promote plant growth by controlling and integrating a variety of responses that optimize photosynthetic performance under low photosynthetically active radiation in the natural environment.     

The interplay between light and jasmonate signalling during defence and development

During their evolution, plants have acquired diverse capabilities to sense their environment and modify their growth and development as required. The versatile utilization of solar radiation for photosynthesis as well as a signal to coordinate developmental responses to the environment is an excellent example of such a capability. Specific light quality inputs are converted to developmental outputs mainly through hormonal signalling pathways. Accordingly, extensive interactions between light and the signalling pathways of every known plant hormone have been uncovered in recent years. One such interaction that has received recent attention and forms the focus of this review occurs between light and the signalling pathway of the jasmonate hormone with roles in regulating plant defence and development. Here the recent research that revealed new mechanistic insights into how plants might integrate light and jasmonate signals to modify their growth and development, especially when defending themselves from either pests, pathogens, or encroaching neighbours, is discussed.     

Hierarchical plant responses and diversity loss after nitrogen addition: testing three functionally-based hypotheses in the Inner Mongolia grassland

Background

Numerous studies have shown that nitrogen (N) deposition decreases biodiversity in terrestrial ecosystems. To explain the N-induced species loss, three functionally based hypotheses have been proposed: the aboveground competition hypothesis, the belowground competition hypothesis, and the total competition hypothesis. However, none of them is supported sufficiently by field experiments. A main challenge to testing these hypotheses is to ascertain the role of shoot and root competition in controlling plant responses to N enrichment. Simultaneously examining both aboveground and belowground responses in natural ecosystems is logistically complex, and has rarely been done.

Methodology/Principal Findings

In a two-year N addition experiment conducted in a natural grassland ecosystem, we investigated both above- and belowground responses of plants at the individual, species, and community levels. Plants differed significantly in their responses to N addition across the different organizational levels. The community-level species loss was mainly due to the loss of perennial grasses and forbs, while the relative abundance of plant species was dependent mainly on individual-level responses. Plasticity in biomass allocation was much smaller within a species than between species, providing a biological basis for explaining the functionally based species loss. All species increased biomass allocation to aboveground parts, but species with high belowground allocations were replaced by those with high aboveground allocations, indicating that the increased aboveground competition was the key process responsible for the observed diversity loss after N addition in this grassland ecosystem.

Conclusions/Significance

Our findings shed new light on the validity of the three competing hypotheses concerning species loss in response to N enrichment. They also have important implications for predicting the future impacts of N deposition on the structure and functioning of terrestrial ecosystems. In addition, we have developed a new technique for ascertaining the roles of aboveground and belowground competition in determining plant responses to N fertilization.     

Why no feeding frenzy? Mechanisms of nutrient acquisition and utilization during infection by the rice blast fungus Magnaporthe oryzae

Magnaporthe oryzae is a devastating pathogen of rice and wheat. It is a hemibiotroph that exhibits symptomless biotrophic growth for the first 4 to 5 days of infection of susceptible cultivars before becoming necrotrophic. Here, we review recent advances in our understanding of how M. oryzae is able to grow, acquire nutrients, and interact with the plant cell during infection. In particular, we describe direct mechanisms (such as the integration of carbon and nitrogen metabolism by trehalose-6-phosphate synthase 1) and indirect mechanisms (such as the suppression of host responses) that allow M. oryzae to utilize available host nutrient. We contrast the ability of M. oryzae to voraciously metabolize a wide range of carbon and nitrogen sources in vitro with the carefully orchestrated development it displays during the biotrophic phase of in planta growth and ask how the two observations can be reconciled. We also look at how nutrient acquisition and effector biology might be linked in order to facilitate rapid colonization of the plant host.     

Phenotypic characterization of a photomorphogenic mutant

Light is arguably the most important abiotic factor controlling plant growth and development throughout their life cycle. Plants have evolved sophisticated light-sensing mechanisms to monitor fluctuations in light quality, intensity, direction and periodicity (day length). In Arabidopsis, three families of photoreceptors have been identified by molecular genetic studies. The UV-A/blue light receptors cryptochromes and the red/far-red receptors phytochromes control an overlapping set of responses including photoperiodic flowering induction and de-etiolation. Phototropins are the primary photoreceptors for a set of specific responses to UV-A/blue light such as phototropism, chloroplast movement and stomatal opening. Mutants affecting a photoreceptor have a characteristic phenotype. It is therefore possible to determine the specific developmental responses and the photoreceptor pathway(s) affected in a mutant by performing an appropriate set of photobiological and genetic experiments. In this paper, we outline the principal and easiest experiments that can be performed to obtain a first indication about the nature of the photobiological defect in a given mutant.     

From seed to seed: the role of photoreceptors in Arabidopsis development

As sessile organisms, plants have evolved a multitude of developmental responses to cope with the ever-changing environmental conditions that challenge the plant throughout its life cycle. Of the many environmental cues that regulate plant development, light is probably the most important. From determining the developmental pattern of the emerging seedling, to influencing the organization of organelles to best maximize energy available for photosynthesis, light has dramatic effects on development during all stages of plant life. In plants, three classes of photoreceptors that mediate light perception have been characterized at the molecular level. The phytochromes recognize light in the red portion of the spectrum, while cryptochromes and phototropins perceive blue and UVA light. In this review, we discuss the different aspects of development that are regulated by these photoreceptors in the model plant species Arabidopsis thaliana and how the phytochromes, cryptochromes, and phototropins bring about changes in development seen in the growing plant.