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Temperature effects on plant gametophyte performance and their consequences for seed reproduction in wild plants

Year: 2026
Type: dissertation
Abstract: Research is increasingly focusing on understanding the impacts of climate change on seed plant reproduction. Despite the ongoing efforts, gaps and biases still remain as most studies focus on cultivated crops and model species like Arabidopsis thaliana, with limited research on wild plants. Furthermore, methodological gaps such as the lack of standardized protocols for developing in vitro germination media for unstudied species or groups still exist. The main aim of this thesis was to address these gaps by developing new methods for pollen research based on protocols in literature and investigate the impacts of temperature stress on plant sexual reproduction, with a particular emphasis on gametophytic performance in both wild and cultivated plants. Chapter 1 introduces the research context of the thesis, highlighting existing gaps and biases in gametophytic studies. It provides a brief overview of the developmental stages of male (pollen) and female (ovule) gametophytes, the impacts of climate change-induced heat waves on gametophytic performance and the compensatory mechanisms they employ. Chapter 2 is the methodological paper with a compendium of optimized in vitro pollen germination media (PGM) recipes from over 1800 articles published from 1926 to 2019. The compendium consists of 1572 PGM successfully used in 816 species from 412 genera and 114 families (monocots and dicots). Key components used include sucrose (89%), H3BO3 (77%), Ca2+ (59%), Mg2+ (44%), and K+ (39%). Notably, concentrations of sucrose, calcium, and magnesium varied significantly across categories, highlighting the need for group-specific considerations in PGM composition. I therefore identified general rules for creating PGM tailored to different species groups, considering factors such as research focus (wild vs. cultivated species), phylogenetic relatedness, pollen physiology, biochemistry, and stigma properties. The compendium serves as a valuable data resource for PGM and facilitates future pollen research endeavors. Chapter 3 examines the patterns and drivers of pollen temperature tolerance (cold and heat) across diverse plant populations and species globally. To achieve this, I compiled a dataset spanning 1933 to 2020, comprising cardinal temperatures (minimum, optimal, and maximum) for pollen germination and tube growth in 198 plant species. I investigated pollen temperature limits (PTLs) by examining their correlation with the thermotolerance of vegetative tissues and assessing variability at the intra- and interspecific levels across the species with contrasting phylogeny, cultivation history, biology, and ecology. The findings revealed positive correlations between PTLs and thermotolerance in vegetative tissues. At the species level, PTLs ranged from 6.1 to 39.5 ⁰C, displaying significant differences among growth forms and cultivation histories. While there were variations in pollen cold tolerance among species populations, optimum and maximum temperatures remained stable. Phylogenetic analysis indicated family-level conservation in pollen cold tolerance, contrasting with the evolutionary independence of heat tolerance. Climate emerged as a significant driver of PTLs, with species at higher elevations and latitudes exhibiting enhanced tolerance. Cultivated species displayed narrower temperature tolerances, highlighting potential vulnerabilities to global warming. Overall, this study sheds light on the complex relationships among pollen temperature limits, plant traits, and environmental factors, providing essential insights into the impact of climate change on plant reproduction. In chapter 4, the impacts of chronic heat stress (CHS) at moderate (35/30 °C) and severe (40/35 °C) levels, on gametophyte performance and subsequent seed quantity, quality, and germination in four wild Silene species (Silene coeli-rosa, Silene gallica, Silene laeta, and Silene noctiflora) were investigated. I measured six traits related to the male (anther length, pollen production, and size) and female (ovary length, ovule production, and size) gametophyte performance, along with leaf chlorophyll fluorescence. Seeds from treated plants were used to measure seed mass and production, while seed germination was evaluated in terms of germination percentage, speed, and synchrony. The results revealed that both CHS treatments had a negative impact on overall plant performance. All male gametophyte traits, ovary size, and ovule production were significantly reduced in CHS treatments, resulting in fewer seeds, but seed mass remained unaffected. Although the final germination percentage showed weak significant differences in the severe treatment, heat stress did not negatively impact seed germination. Treated plants exhibited significantly faster germination, with no effect on germination synchrony. Climate change-induced heat waves can adversely affect seed reproduction in wild plant populations, potentially impacting their long-term survival. In chapter 5, the adaptive and acclimation potential of six male (anther length, pollen production, and size) and female (ovary length, ovule production, and size) gametophytic traits in eleven distinct populations of wild Silene vulgaris across a temperature gradient in Europe were examined. First, plants were cultivated in a common garden to reveal pre-adaptation of gametophytic traits to the local conditions. Next, flowering plants were subjected to chronic heat stress (CHS) treatments (moderate [35/30 °C] and severe [40/35 °C]) to assess the acclimation potential of gametophytic traits. Results from the common garden showed no intraspecific variation in gametophytic traits across the temperature gradient, suggesting limited influence of these traits on sexual adaptation to local habitats. Plants from colder climates produced more seeds with higher mass than those from warm climates. Under both CHS treatments, female gametophytes showed a higher ability to acclimate than males, with moderate CHS leading to increased ovary size and ovule numbers and severe CHS reducing ovule numbers but increasing their size. All pollen traits decreased under both CHS, with severe stress causing more significant reductions, thus translating to low seed quality and quantity. Acclimation potential did not vary among populations across the temperature gradient under both CHS treatments, except for pollen size under severe CHS, which was larger in warmer climates than in colder regions. Overall, the lack of adaptation and acclimation mechanisms in gametophytic traits suggests potential reliance on alternative strategies like shifting flowering time and phenotypic plasticity to cope with climate change-induced heat waves. Chapter 6 provides a synthesis of the key findings from the four main chapters. The main conclusion drawn is that climate change-induced heat waves can have significant and complex impacts on the reproductive processes, particularly pollen performance, of both wild and cultivated plants. To obtain more precise estimates of the impact of heat stress on seed production, it is crucial to conduct further research that includes a broader array of genotypes or species. Additionally, the chapter discusses potential areas for exploration in future studies within this field.
DOI: 10.5283/epub.59361
Language: English
Open Access status: green
OpenAlex ID: W7119123073
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