Plant Biology最新文献

Reduced competition and increased availability of abiotic resources shortly after a fire can favour growth and flowering of herbaceous species. These changes may also affect the pollinator community, reproductive success, and, potentially, the characteristics of progeny. However, anthropogenic increases in the frequency of fires could reverse the beneficial effects of fire. We evaluate the effect of fire frequency on sexual expression, pollination, female reproductive success, and early progeny vigour of Solanum palinacanthum, an andromonoecious resprouting herb in South American Chaco ecosystems. Measurements were performed at six sites along a gradient of fire frequency, ranging from 0 to 5 fires over 22 years. We found that plant size and the proportion of hermaphrodite (relative to male) flowers increased at intermediate fire frequency sites (twice burned) compared to unburned sites, but both declined at high-fire frequency sites. Pollinator visits were also more frequent in plants from the area with intermediate fire frequency. Although fire frequency did not enhance the probability of fruit set, it increased total fruit number in plants from the site burned twice. Seeds from sites with intermediate fire frequency had both higher mass and germination rates. Soil resources and maternal environmental effects shaped by fire frequency play a key role in the sexual reproduction and early progeny vigour of S. palinacanthum. Nonetheless, increased fire frequency due to human activities may override the beneficial effects of fire on plant reproduction.

Iron (Fe) is essential for plants and humans, with over 2 billion people suffering deficiency disorders because most plant foods, including cereals, are low in Fe. Durum wheat, a staple crop in Mediterranean regions, is facing increased droughts, which reduce plant yield and ability to acquire and use Fe. Therefore, understanding mechanisms underlying Fe acquisition and accumulation in durum wheat under drought is essential for both agronomic and nutritional purposes. Here, a durum wheat (Triticum turgidum subsp. durum) genotype with a purple grain pericarp was grown hydroponically under adequate (80 μM) or limited (10 μM) Fe, with or without water stress (induced with 10% PEG 6000) for 6 days. Fe accumulation decreased under Fe deficiency and drought, with the highest phytosiderophore (PS) release in Fe-deficient plants. Interestingly, despite adequate Fe availability, drought inhibited Fe accumulation in roots. This response was accompanied by increased release of PS from roots, although the increase was less than that observed with single or combined Fe deficiency. Both TdIRT1 and TdYS15 were upregulated by Fe deficiency but downregulated by drought and the combined stress. Drought stress and Fe deficiency led to increased ABA production, being 250-fold higher with respect to controls. TdIRT1 downregulation in plants exposed to the combined stress suggests a trade-off between water and Fe stress responses. Our findings demonstrate that the response to combined stress differs from, and is rarely additive to, the response to a single stressor, reinforcing the complexity of plant adaptation to combined environmental stresses.

Jasmonates regulate plant development and defence. In angiosperms, the canonical bioactive jasmonate is jasmonoyl-isoleucine (JA-Ile), which is formed in Arabidopsis thaliana by JAR1 and GH3.10. In contrast to other jasmonate biosynthesis or perception mutants, however, gh3.10 jar1 knockout lines are still fertile. Therefore we investigated whether further jasmonates and GH3 enzymes contribute to regulation of fertility. Jasmonate levels were analysed by liquid chromatography-mass spectrometry. The substrate range of recombinant GH3.10 and related GH3 enzymes was studied using non-targeted ex vivo metabolomics with flower and leaf extracts of A. thaliana and in vitro enzyme assays. Jasmonate application experiments were performed to study their potential bioactivity. In flowers and wounded leaves of gh3.10 jar1 knockout lines JA-Ile was below the detection limit. While 12-hydroxy-JA was identified as the preferred substrate of GH3.10, no other recombinant GH3 enzymes tested were capable of JA-Ile formation. Additional JA conjugates found in wounded leaves (JA-Gln) or formed in flowers upon MeJA treatment in the absence of JA-Ile (JA-Gln, JA-Asn, JA-Glu) were identified. The aos gh3.10 jar1 was introduced as a novel tool to test for the bioactivity of JA-Gln to regulate fertility. This study found JAR1 and GH3.10 are the only contributors to JA-Ile biosynthesis in Arabidopsis and identified a number of JA conjugates as potential bioactive jasmonates acting in the absence of JA-Ile. However, their contribution in regulating fertility is yet to be conclusively determined.

With approximately 31,000 species, orchids begin life as mycoheterotrophs, relying on fungi to meet their carbon demands. Notably, some green orchids retain the ability to acquire carbon through fungal associations (partial mycoheterotrophy) and occasionally produce albino or, more rarely, variegated phenotypes. A linear relationship has been observed between leaf chlorophyll content and dependence on fungal-derived carbon, particularly in orchids associated with ectomycorrhizal (ECM) fungi, but whether such plasticity is similarly robust among orchids associated with non-ECM fungi remains underexplored. Here, we focused on the green, variegated, and albino forms of Cremastra variabilis, which likely lack ECM associations, to investigate (i) whether the degree of mycoheterotrophy, indicated by ¹³C enrichment, correlates with chlorophyll content, and (ii) whether nutritional shifts align with changes in plant structure and mycorrhizal communities. Our results show that rhizoctonia fungi were dominant in green individuals with high chlorophyll levels and lacking coralloid rhizomes, whereas albino and most variegated individuals possessing coralloid rhizomes primarily associate with Psathyrellaceae fungi. Chlorophyll content and carbon stable isotope abundances were negatively correlated, indicating a gradient of increasing mycoheterotrophy from green to albino forms in individuals with coralloid rhizomes. In conclusion, C. variabilis maintains a flexible balance between photosynthesis and mycoheterotrophy, likely shaped by its subterranean morphology and fungal associations, with wood-decaying Psathyrellaceae fungi providing greater support for mycoheterotrophic nutrition than rhizoctonia fungi.

All orchids exhibit mycoheterotrophy during their early development stages, which predisposes certain species to retain this nutritional mode into adulthood. Consequently, many orchids adopt partial mycoheterotrophy, a mixotrophic strategy combining carbon acquisition through both autotrophy and mycoheterotrophy. However, whether this strategy represents an ancestral trait remains contested. This study examines the fungal symbionts and nutritional strategies of the early-diverging orchid Apostasia wallichii and a sympatric, photosynthetic orchid, Cystorchis variegata, in tropical Asia (Sabah, Malaysian Borneo). Specifically, we explored their potential nutritional modes and mycobionts by analysing δ¹³C and δ¹⁵N isotopic profiles and employing high-throughput DNA sequencing. Community profiling via metabarcoding revealed that the A. wallichii individuals investigated were predominantly associated with putatively saprotrophic Botryobasidium fungi, while C. variegata was simultaneously associated with non-ectomycorrhizal rhizoctonias, saprotrophic non-rhizoctonia fungi, and ectomycorrhizal fungi. Additionally, stable isotope analysis showed that both A. wallichii and C. variegata were significantly enriched in ¹³C and ¹⁵N compared to co-occurring autotrophic plants, indicating partial mycoheterotrophy. Our findings, particularly the discovery of partial mycoheterotrophy associated with non-ectomycorrhizal fungi in A. wallichii, suggest that partial mycoheterotrophy in green orchids may be more widespread than previously believed and could represent an ancestral trait intrinsic to orchids.

Moderately saline water has been proposed as a potential irrigation resource for crops such as forage sorghum (Sorghum bicolor × Sorghum bicolor nothosubsp. drummondii) in drought-prone regions. However, it is not yet fully understood how salinity affects growth and potential toxicity of sorghum. Sorghum produces the cyanogenic glucoside dhurrin, which can cause hydrogen cyanide (prussic acid) poisoning in grazing animals. To address this, two glasshouse experiments were conducted. Experiment 1 assessed tolerance of sorghum to a range of salt treatments (0, 12.5, 25, 50, 100 and 150 mM NaCl). Experiment 2 assessed whether moderately saline irrigation would relieve drought stress by growing sorghum under three treatments: no watering (drought), watering with freshwater, or watering with 50 mM NaCl. All treatments lasted 7 weeks. In Experiment 1, salinities as low as 25 mM NaCl significantly reduced biomass, despite sorghum being able to exclude sodium from entering transpiring leaves at NaCl concentrations up to 50 mM. Foliar concentrations of dhurrin positively correlated with salinity and exceeded the safe threshold for cattle of ≥12.5 mM NaCl. In Experiment 2, moderately saline water effectively alleviated drought stress of sorghum, with significant reductions in growth and photosynthesis in the drought treatment compared to the 50 mM NaCl treatment. While sorghum's survival and growth may be boosted by moderately saline irrigation during droughts, its cyanogenic glucoside concentrations should be monitored to ensure safety for grazing animals.

Resource competition among flowers is expected to influence variation in seed output within inflorescences, but the extent to which flower position affects competitive interactions is still incompletely understood. To investigate position effects on seed output in the perennial, monoecious macrophyte Sagittaria trifolia, we compared components of seed production (fruit set, seed number per fruit, and seed size) in control inflorescences to that in inflorescences from which half of the female flowers were experimentally removed, either from basal positions, from upper positions, or from across the inflorescence. Basal and upper flower removal reduced total seed output per inflorescence, while the throughout removal treatment maintained a seed yield comparable to the control. There was some increase in different reproductive components in each removal treatment and the magnitude of this increase depended on the positions of the flowers removed. Basal flower removal led to a higher number of seeds per fruit, whereas upper flower removal resulted in an increased fruit set, which successfully provided partial compensation for seed production. In the throughout removal treatment, both fruit set and seed set improved significantly, achieving full compensation compared to the control. The results indicate that resource competition is strongest among flowers belonging to the same whorl, and that the potential for reallocation of resources among whorls varies with flower position in S. trifolia. The results demonstrate the need to consider position effects for an understanding of factors driving variation in resource allocation and fruit production in plant populations.

This study explores the impact of geographic barriers on the distribution and survival of Mediterranean endemic species, focusing on Centranthus sect. Nervosae, a tetraploid species complex found in Corsica and Sardinia. The aim is to analyse how these barriers influence genetic diversity, population structure, and phylogeographic pattern, thereby impacting conservation strategies and future resilience of the selected study species. Genotyping involved biparental markers (16 nuclear microsatellites for the population genetic survey) and Sanger sequencing of uniparental markers (six plastid sequences for the phylogeographic survey). Screening of microsatellites revealed a diploidisation process, and haplotype fixation in plastid sequence was observed across all populations. Results from both survey methods clearly indicate that isolation and barriers have significantly impacted the genetic structure of populations, subjecting them to genetic drift, bottlenecks and related evolutionary phenomena. Over time, these factors have resulted in the observed low haplotypic variability and nuclear microsatellite diversity. Reduced genetic variability, combined with factors such as inbreeding and genetic drift, highlight the vulnerability of these populations to extinction. Consequently, this multi-approach survey has contributed to defining conservation strategies, stressing the need to preserve genetic diversity and mitigate the impacts of human activities and environmental changes on endemic plant communities in island-like environments. The study emphasises the importance of integrating multiple marker types to deepen our understanding of conservation genetics and evolutionary history, thereby contributing to the assessment, and planning of potential safeguarding strategies for such endemic species.

The freezing-induced formation of embolisms in xylem conduits presents one of the challenges faced by evergreen leaves in frost-experiencing regions. Given that the probability of permanent embolism formation is related to the conduit diameter, we hypothesized that diameters of the vessels in evergreen leaves should be smaller than in deciduous leaves. We used live botanical garden collections to sample leaves of 21 evergreen and 47 deciduous species originating from various temperate biotopes and representing a broad taxonomic diversity. We determined the diameters of the largest vessels in their petioles. After controlling for conductive path length, the vessels in evergreen leaves were significantly smaller than those in deciduous leaves. Our results suggest a selective advantage of vessel diameter reduction for the evergreen leaf habit in cold climates. This result recapitulates the contrast between deciduous and evergreen species previously reported for stems. Moreover, the strong scaling relationships of vessel diameter with distance to leaf tip found in both leaf forms suggest that evolutionary reduction in vessel diameter associated with the evergreen habit may necessitate leaf size reduction, consistent with the trend documented in other studies.