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1. Growth and transcriptional response of wheat and rice to the tertiary amine BMVE

   https://doi.org/10.3389/fpls.2023.1273620  

   Dharni, Jaspinder Singh ; Shi, Yu ; Zhang, Chi ; Petersen, Chris ; Walia, Harkamal ; Staswick, Paul ( January 2024 , Frontiers in Plant Science)

   Seed vigor is largely a product of sound seed development, maturation processes, genetics, and storage conditions. It is a crucial factor impacting plant growth and crop yield and is negatively affected by unfavorable environmental conditions, which can include drought and heat as well as cold wet conditions. The latter leads to slow germination and increased seedling susceptibility to pathogens. Prior research has shown that a class of plant growth regulators called substituted tertiary amines (STAs) can enhance seed germination, seedling growth, and crop productivity. However, inconsistent benefits have limited STA adoption on a commercial scale

   We developed a novel seed treatment protocol to evaluate the efficacy of 2-(N-methyl benzyl aminoethyl)-3-methyl butanoate (BMVE), which has shown promise as a crop seed treatment in field trials. Transcriptomic analysis of rice seedlings 24 h after BMVE treatment was done to identify the molecular basis for the improved seedling growth. The impact of BMVE on seed development was also evaluated by spraying rice panicles shortly after flower fertilization and subsequently monitoring the impact on seed traits.

   BMVE treatment of seeds 24 h after imbibition consistently improved wheat and rice seedling shoot and root growth in lab conditions. Treated wheat seedlings grown to maturity in a greenhouse also resulted in higher biomass than controls, though only under drought conditions. Treated seedlings had increased levels of transcripts involved in reactive oxygen species scavenging and auxin and gibberellic acid signaling. Conversely, several genes associated with increased reactive oxygen species/ROS load, abiotic stress responses, and germination hindering processes were reduced. BMVE spray increased both fresh and mature seed weights relative to the control for plants exposed to 96 h of heat stress. BMVE treatment during seed development also benefited germination and seedling growth in the next generation, under both ambient and heat stress conditions.

   The optimized experimental conditions we developed provide convincing evidence that BMVE does indeed have efficacy in plant growth enhancement. The results advance our understanding of how STAs work at the molecular level and provide insights for their practical application to improve crop growth.

    

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2. Responses of seedling growth and survival to post‐germination cotyledon removal: An investigation among seven oak species

   https://doi.org/10.1111/1365-2745.13153  

   Yi, Xianfeng ; Bartlow, Andrew W. ; Curtis, Rachel ; Agosta, Salvatore J. ; Steele, Michael A. ; Heard, ed., Matthew ( March 2019 , Journal of Ecology)

   Rodents regularly rely on emerged epicotyls to locate and remove cotyledons still containing valuable nutrients. However, the extent to which acorn characteristics influence tolerance to post‐germination predation has received little attention.

   Here, we investigated the impact of cotyledon removal following epicotyl emergence on seedling performance and survival of seven oak (Quercus) species. We imitated cotyledon predation at different stages of seedling establishment and development in order to detect effects on seedling height, leaf number and tissue/component mass.

   Seedling growth and survival were negatively affected by cotyledon loss regardless of oak species. However, these negative effects decreased as the epicotyl length at which cotyledons were removed increased. We also found that there was a threshold epicotyl length above which seedling survival and performance were relatively unaffected in white oak species compared to red oak species.

   Following cotyledon removal, early germinating white oak (sectionQuercus) seedlings survived and/or grew better than the late germinating red oak (sectionLobatae) seedlings. This was likely caused by a difference in dependence on cotyledon reserves, which ultimately affected the ability of seedlings to tolerate cotyledon removal.

   Synthesis.From an evolutionary perspective, this is likely to follow from the early germination in white oaks and the ability of seed consumers to locate young seedlings from the emerging epicotyls. Our study has implications for forest regeneration by suggesting additional opportunities for white oak species to establish following epicotyl emergence. Future studies should consider quantifying the rates of post‐germination cotyledon loss.

    

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3. Lipophilic signals lead to organ‐specific gene expression changes in Arabidopsis seedlings

   https://doi.org/10.1002/pld3.242  

   Cannon, Ashley E. ; Yan, Chengshi ; Burks, David J. ; Rao, Xiaolan ; Azad, Rajeev K. ; Chapman, Kent D. ( July 2020 , Plant Direct)

   In plants,N‐acylethanolamines (NAEs) are most abundant in desiccated seeds and their levels decline during germination and early seedling establishment. However, endogenous NAE levels rise in seedlings when ABA or environmental stress is applied, and this results in an inhibition of further seedling development. When the most abundant, polyunsaturated NAEs of linoleic acid (18:2) and linolenic acid (18:3) were exogenously applied, seedling development was affected in an organ‐specific manner. NAE 18:2 primarily affected primary root elongation and NAE 18:3 primarily affected cotyledon greening and expansion and overall seedling growth. The molecular components and signaling mechanisms involved in this pathway are not well understood. In addition, the bifurcating nature of this pathway provides a unique system in which to study the spatial aspects and interaction of these lipid‐specific and organ‐targeted signaling pathways. Using whole transcriptome sequencing (RNA‐seq) and differential expression analysis, we identified early (1–3 hr) transcriptional changes induced by the exogenous treatment of NAE 18:2 and NAE 18:3 in cotyledons, roots, and seedlings. These two treatments led to a significant enrichment in ABA‐response and chitin‐response genes in organs where the treatments led to changes in development. InArabidopsisseedlings, NAE 18:2 treatment led to the repression of genes involved in cell wall biogenesis and organization in roots and seedlings. In addition, cotyledons, roots, and seedlings treated with NAE 18:3 also showed a decrease in transcripts that encode proteins involved in growth processes. NAE 18:3 also led to changes in the abundance of transcripts involved in the modulation of chlorophyll biosynthesis and catabolism in cotyledons. Overall, NAE 18:2 and NAE 18:3 treatment led to lipid‐type and organ‐specific gene expression changes that include overlapping and non‐overlapping gene sets. These data will provide future, rich opportunities to examine the genetic pathways involved in transducing early signals into downstream physiological changes in seedling growth.

    

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4. A seed–seedling conflict for Atriplex polycarpa shrubs competing with exotic grasses and their residual dry matter

   https://doi.org/10.1002/ecs2.3455  

   Coleman, Mitchell L. ; Mayence, C. Ellery ; White, Michael D. ; Jacobsen, Anna L. ; Pratt, R. Brandon ( April 2021 , Ecosphere)

   Native saltbush,Atriplex polycarpa, shrub populations are widely diminished and fragmented in the southern San Joaquin Desert of California due to habitat conversion and invasion by exotic annual grasses of mostly Mediterranean origin. The role these grasses play in saltbush population demography is not well understood. We hypothesized that saltbush seedling recruitment and growth is limited by the competitive interactions with exotic grasses, preventing saltbush stands from maintaining their populations and expanding. We predicted that saltbush seedling recruitment would be reduced by (1) light and moisture competition with the grasses; and (2) the physical barrier of grass residual dry matter (RDM) formed during senescence. To test our predictions, we investigated saltbush seedling recruitment under field conditions across six saltbush populations. We examined how variations in edaphic structure and water availability by site may have affected saltbush seedling recruitment and longer‐term population dynamics. In experimental plots where saltbush seeds were sowed, exotic grass RDM reduced saltbush seedling emergence compared to seeds sown in the absence of RDM; competition post‐emergence was not significant. Saltbush seedlings transplanted into the field had lower mortality and less herbivory in invaded grassy habitats compared to seedlings planted in bare zones in between established, mature saltbush shrubs. Edaphic variation and water availability by site were likely key factors affecting the success of both grass invasion and saltbush recruitment. Our results suggest that there is a seed–seedling conflict: Sites favorable for saltbush seedling emergence (minimal grass cover among mature shrubs) are unfavorable for seedling survival due to high herbivory. Conversely, sites favorable for saltbush seedling survival (high grass coverage away from mature shrubs) are unfavorable for seedling emergence. The RDM produced by grasses represents an important stabilizing feedback favoring continued grass dominance.

    

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5. Multi‐population seedling and soil transplants show possible responses of a common tropical montane tree species ( Weinmannia bangii ) to climate change

   https://doi.org/10.1111/1365-2745.13443  

   Tito, Richard ; Vasconcelos, Heraldo L. ; Feeley, Kenneth J. ; Barua, ed., Deepak ( June 2020 , Journal of Ecology)

   A possible response of many plant species to global warming is migration to higher elevations. However, these migrations may not be required if species can tolerate higher temperatures, or may be prevented if there are other factors such as changes in soil conditions that make upslope areas unsuitable.

   We used a set of 3‐year field transplant experiments in the remote Peruvian Andes to simulate two possible responses of an abundant tropical montane cloudforest tree species (Weinmania bangii) to global warming: (a) ‘upward migration’, in which case seedlings ofW. bangii'swere grown at their current elevation/temperature but in soils transplanted from higher elevations and (b) ‘migration failure’, in which case seedlings were transplanted downslope along with their home soils into areas that are 1°C or 2°C warmer. We conducted separate experiments with populations from the upper/leading edge, middle and lower/trailing edges ofW. bangii'selevational/thermal range to assess the influence of local adaptation on responses to changes in temperature or soil.

   We found that seedling survival and growth were not affected by changes in soil conditions, regardless of the origin population. However, seedling survival decreased with temperature. A simulated warming of 1°C caused a significant reduction in the survival of seedlings transplanted from the mid‐range population, and 2°C warming caused a severe decrease in the survival of seedlings transplanted from both the mid‐range and bottom‐edge populations.

   Synthesis. Our findings reveal that rising temperatures are a serious threat to plants, especially in populations growing in the hotter portion of their species’ range. At least in the case ofW. bangii,novel soil conditions will not limit the establishment or growth of seedlings at higher elevations. As such, decreases in the survivorship at lower elevations may be offset through upward migrations as temperatures continue to increase.

    

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