Plant Biology最新文献

Nature offers a bewildering diversity of flower colours. Understanding the ecology and evolution of this fantastic floral diversity requires knowledge about the visual systems of their natural observers, such as insect pollinators. The key question is how flower colour and pattern can be measured and represented to characterise the signals that are relevant to pollinators. A common way to interpret flower colours is using animal vision models that incorporate the spectral sensitivity of a focal observer (e.g. bees). These vision models provide a measure of colour contrast, which represents the perceived chromatic difference between two objects, such as a yellow flower against green leaves. Colour contrast is a behaviourally and physiologically validated proxy for relative conspicuousness of a stimulus. A growing number of studies attempt to interpret flower colouration through parameters that are grafted on to principles of human colour perception. A perpetuating measure to describe floral colours is via saturation, which is a metric in human perception describing a certain aspect of colourfulness and is, in pollination literature, often referred to as ‘spectral purity’. We caution against the concept, calculation and biological interpretation of ‘spectral purity’ and similar measures that rest on an anthropocentric view, because it does not represent the diversity and complexity of animal visual systems that are the natural observers of flowers. We here discuss the strengths and weaknesses of common ways to interpret flower colouration and provide concrete suggestions for future colourful research.

Plants with the C₄ photosynthetic pathway can withstand water stress better than plants with C₃ metabolism. However, it is unclear whether C₄ photosynthesis can be preliminarily activated in droughted cotton leaves, and if this contributes to increase in water use efficiency (WUE). An upland cotton (Gossypium hirsutum L., Xinluzao45) was used to determine gas exchange, stomatal and vein anatomy, phosphoenolpyruvate carboxykinase (PEPC) and Rubisco enzyme activity, and carbon isotope composition (δ¹³C) under well-watered, mild or moderate water stress. Water stress triggered reduced photosynthesis, stomatal conductance, and Rubisco activity, but higher vein density (VD), PEPC activity, and WUE. The correlations between δ¹³C and each of VD and PEPC activity implied that these coordinately contributed to higher leaf WUE via a preliminary induction of C₄ photosynthetic pathway. Preliminary C₄ photosynthesis indicated by more PEPC enzyme and veins offers an effective way to improve leaf WUE and potentially aids in acclimation to adverse growing conditions.

Isoleucic acid (ILA) was identified in human patients with maple syrup urine disease (MSUD) half a century ago. MSUD patients, who are defective in the catabolism of branched-chain amino acids (BCAAs), that is, isoleucine, leucine, and valine, have urine with a unique maple syrup odour related to the accumulation of BCAA breakdown products, largely 2-keto acid derivatives and their reduced 2-hydroxy acids including ILA. A decade ago, ILA was identified in Arabidopsis thaliana. Subsequent studies in other plant species indicated that ILA is a ubiquitously present compound. Since its identification in plants, several efforts have been made to understand the biological significance and metabolic pathway of ILA. ILA plays a positive role in plant signalling for defence responses against bacterial pathogens by increasing the abundance of salicylic acid aglycone through competitive inhibition of SA deactivation by glucosylation. Here, we review recent progress in the characterization of ILA biosynthesis and function in plants and discuss current knowledge gaps and future directions in ILA research.

Plant individuals within a species can differ markedly in their leaf chemical composition, forming so-called chemotypes. Little is known about whether such differences impact the microbial communities associated with leaves and how different environmental conditions may shape these relationships. We used Tanacetum vulgare as a model plant to study the impacts of maternal effects, leaf terpenoid chemotype, and the environment on the leaf bacterial community by growing plant clones in the field and a greenhouse. We hypothesized that all three factors affect the bacterial community of the leaves and that terpenoid and bacterial profiles as well as chemodiversity and microbial diversity are correlated. The results revealed that the leaf microbial community was significantly influenced by plant maternal effects and environmental conditions (field vs. greenhouse), but not by the leaf terpenoid profile. There was also no evidence for a correlation between terpenoid profiles and bacterial community composition and diversity. Overall, a higher number of unique amplicon sequence variants were found in the leaves of clones grown under field conditions than in those grown in the greenhouse. We also identified interactions between individual terpenoids and specific members of the leaf bacterial community. Our study suggests that terpenoid chemodiversity has, overall, little effect on the leaf bacterial community, but some terpenoids might affect specific beneficial species. While more studies are needed to investigate the relationship between plant chemodiversity and plant microbiomes, our results highlight the importance of integrating plant maternal effects, chemodiversity, and environment in understanding plant-microbiome interactions.

Hydraulic redistribution is considered a crucial dryland mechanism that may be important in temperate environments facing increased soil drying-wetting cycles. We investigated redistribution of soil water from deeper, moist to surface, dry soils in a mature mixed European beech forest and whether redistributed water was used by neighbouring native seedlings. In two experiments, we tracked hydraulic redistribution via (1) ²H labeling and (2) ¹⁸O natural abundance. In a throughfall exclusion experiment, ²H water was applied to 30-50 cm soil depth around mature beech trees and traced in soils, in coarse and fine roots, and in the rhizosphere. On five additional natural plots, the ¹⁸O signal was measured in seedlings of European beech, Douglas fir, silver fir, sycamore maple, and Norway spruce at dawn and noon after a rain-free period. We found a significant enrichment in ²H in surface soil fine roots of mature beech, and an indication for transfer of this water into their rhizosphere, suggesting hydraulic redistribution from deeper, moist to drier surface soils. On four of the five additional plots, δ¹⁸O of seedlings' root water was lower at dawn than at noon. This indicated that dawn root water originated from soil layers deeper than the seedlings' rooting depth, suggesting hydraulic redistribution by neighbouring mature trees. Hydraulic redistribution equated to about 10% of daily transpiration in mature beech trees, and contributed to root water in understory seedlings, emphasizing hydraulic redistribution as a notable mechanism in temperate forests. Transport mechanisms and potential of different tree species to redistribute water should be further addressed.

Tree responses to drought are well studied, but the interacting effects of drought timing on growth, water use, and stress legacy are less understood. We investigated how a widespread conifer, Scots pine, responded to hot droughts early or late in the growing season, or to both. We measured sap flux, stem growth, needle elongation, and leaf water potential (Ψ_leaf) to assess the impacts of stress timing on drought resilience in Scots pine saplings. The early summer hot drought had peak temperatures of 36.5 °C, while the late summer hot drought peaked at 38.2 °C. Soil water content during both periods declined to ca. 50% of control values. The early-season hot drought caused growth cessation already at Ψ_leaf - 1.1 MPa, visible as an almost 30 days earlier end to needle elongation, resulting in needles 2.7 cm shorter, on average. This reduction in leaf area decreased productivity, resulting in a reduction of 50% in seasonal transpiration. However, the reduced water use of early-stressed saplings appeared to enhance resistance to a late-season drought, as reflected in a smaller decline in Ψ_leaf and lower tree water deficit compared to saplings that did not experience early-season stress. In summary, we observed persistant drought legacy effects from early-season hot-drought stress, as evident in a 35% reduction of leaf area, which impacted tree water use, stress resistance, and productivity. These structural adjustments of leaf development and reduced bud mass from early-season stress could be critical in evergreen conifers, whose long-lived foliage influences future water use and growth potential.

Some plant species produce an extraordinary diversity of specialized metabolites. The diverse class of terpenes is characteristic for many aromatic plants, and terpenes can occur as both emitted volatiles and stored compounds. Little is known about how intraspecific chemodiversity and phenotypic integration of both emitted volatile and stored terpenes differ intra-individually across plant development and between different plant parts, and studies considering both spatial and temporal scales are scarce. To comprehensively investigate this diversity, we used the aromatic plant Tanacetum vulgare that differs in foliar terpene composition, forming chemotypes. We collected emitted volatile terpenes of both young and old leaves during the rosette, elongated stem, and flowering stage as well as emitted volatiles of flower heads at the flowering stage. Moreover, at the flowering stage, stored terpenes were extracted from different plant parts, including roots. Terpene profiles were measured with (TD)-GC-MS. The composition of emitted volatile terpenes depended on the specific combination of chemotype, plant part, and time point; the chemodiversity of emitted volatiles was mainly affected by the development stage, indicating that at specific development stages individuals require a higher chemodiversity, potentially to mediate different interactions. For stored terpenes, intra-individual differences, mostly between aboveground and belowground plant parts, were found only for specific components of chemodiversity, such as richness and evenness, but not for functional Hill diversity. Phenotypic integration differed mainly across development stage and plant part for emitted volatile terpenes, and across chemotype and plant part for stored terpenes. Our results suggest that intraspecific chemodiversity of terpenes and their integration is a highly plastic trait that may be shaped in dependence of interactions with the environment, and the value that each plant part contributes to the fitness of an individual. Such variation on different scales, both spatially and temporally, should be considered in chemical ecological studies.