Biology subjects

McAdam, S.

Publications and source records attributed to McAdam, S..

5 recordsLinked to original sources

bioRxiv2023

Wind speed affects the rate and kinetics of stomatal conductance

Understanding the relationship between wind speed and gas exchange in plants is a longstanding challenge. Our aim was to investigate the impact of wind speed on maximum rates of gas exchange and the kinetics of stomatal responses. We conducted experiments using an infrared gas analyzer equipped with a controlled leaf fan, enabling precise control of the boundary layer conductance. We first showed that the chamber was adequately mixed even at extremely low fan speeds (down to 200 rpm, equivalent to a wind speed of 0.0005 m s-1) and evaluated the link between fan speed, wind speed, and boundary layer conductance. We observed that higher wind speeds led to increased gas exchange of both water vapor and CO2 in Arabidopsis, presumably due to its effect on transpiration and the consequential reduction in epidermal pressure that led to stomatal opening. We documented that stomatal opening in response to light was three times faster at a fan speed of 10000 rpm (wind speed of 2 m s-1) compared with 500 rpm (0.25 m s-1) in Vicia faba, while the latter exhibited an opening rate that was similar to those of epidermal peels. The increase of stomatal conductance under high wind was observed in four species under field conditions. Our findings demonstrate the importance of the size of the boundary layer on determining maximum rates of gas exchange and the kinetics of gas exchange responses to environmental changes.

plant biology↗

bioRxiv2023

Passive stomatal closure under extreme drought in an angiosperm species

The phytohormone abscisic acid (ABA), synthesized as leaf turgor declines, plays a major role in closing stomata in species from this lineage, but recent reports of some angiosperms having a peaking-type ABA dynamic in which under extreme drought ABA levels decline to pre-stressed levels raises the possibility that passive stomatal closure by leaf water status alone can occur in species from this lineage. To test this hypothesis, we conducted instantaneous rehydration experiments in the peaking-type species Umbellularia californica through a long-term drought in which ABA levels declined to pre-stress levels yet stomata remain closed. We found that when ABA levels were lowest during extreme drought stomata of U. californica were passively closed by leaf water status alone, with stomata reopening rapidly to maximum rates of gas exchange on instantaneous rehydration. This contrasts with leaves early in drought in which ABA levels are highest, where we found stomata do not reopen on instantaneous rehydration. The transition from ABA driven stomatal closure to passively driven stomatal closure as drought progresses in this species occurs at very low water potentials facilitated by highly embolism resistant xylem. These results have important implications for understanding stomatal control during drought in angiosperms.

plant biology↗

bioRxiv2023

Stomatal dynamics are regulated by leaf hydraulic traits and guard cell anatomy in nine true mangrove species

Stomatal regulation is critical for mangroves to survive water deficits and highly fluctuating ambient water availability in the hyper-saline intertidal zone. Despite the importance of stomatal regulation in mangroves very little is known about stomatal sensitivity to vapour pressure deficit (VPD), and the co-ordination of this trait with stomatal morphology and leaf hydraulic traits in these species. We measured the stomatal response to a step increase in vapour pressure deficit (VPD) in situ, stomatal anatomy, leaf hydraulic vulnerability and pressure-volume traits in nine true mangrove species of five families. We aimed to answer two questions: (1) Does stomatal morphology determine stomatal dynamics in response to a high VPD in mangroves and (2) do leaf hydraulic traits influence stomatal sensitivity to VPD in mangroves? We found that the stomata of mangrove plants highly sensitive to VPD, and that species with higher maximum stomatal conductance had slower stomatal responses to an increase in VPD, and that stomatal density and size were correlated with the speed of stomatal closure at high VPD across the closely-related species. We also found that a higher leaf capacitance (Cleaf) and more resistance to leaf hydraulic vulnerability were associated with slower stomatal responses to an increase in VPD. Our results demonstrate that the dynamics of the stomatal response to an increase in VPD are regulated by leaf hydraulic traits and stomatal morphology. Our work provides a quantitative framework to better understand stomatal regulation in mangroves in an environment with highly dynamic water availability.

ecology↗

bioRxiv2021

THESEUS1 modulates cell wall stiffness and abscisic acid production in Arabidopsis thaliana

Plant cells can be distinguished from animal cells by their cell walls and high turgor pressure. Although changes in turgor and stiffness of cell walls seem coordinated, we know little about the mechanism responsible for coordination. Evidence has accumulated that plants, like yeast, have a dedicated cell wall integrity maintenance mechanism. This mechanism monitors the functional integrity of the wall and maintains it through adaptive responses when cell wall damage occurs during growth, development, and interactions with the environment. The adaptive responses include osmo-sensitive-induction of phytohormone production, defence responses as well as changes in cell wall composition and structure. Here, we investigate how the cell wall integrity maintenance mechanism coordinates changes in cell wall stiffness and turgor in Arabidopsis thaliana. We show that the production of abscisic acid (ABA), the phytohormone modulating turgor pressure and responses to drought, depends on the presence of a functional cell wall. We find that the cell wall integrity sensor THESEUS1 modulates mechanical properties of walls, turgor loss point and ABA biosynthesis. We identify RECEPTOR-LIKE PROTEIN 12 as a new component of cell wall integrity maintenance controlling cell wall damage-induced jasmonic acid production. Based on the results we propose that THE1 is responsible for coordinating changes in turgor pressure and cell wall stiffness. Significance statementPlants need to constantly adapt to a changing environment. This includes responses to biotic and abiotic stress. Key elements influencing the response to abiotic stress are the plant cell walls surrounding all cells and the phytohormone abscisic acid, which influences turgor pressure in plants. Turgor pressure in plant cells is much higher than in animal cells and a key driver of plant growth and development. Here we investigate the mechanism regulating cell wall stiffness and coordinating changes in stiffness and turgor. We characterize key elements of the mechanism and dissect its mode of action. This knowledge will enable us to pursue novel approaches to improve plant resistance to drought stress, which is crucial in a rapidly changing environment.

plant biology↗

bioRxiv2021

Timing of meristem initiation and maintenance determines the morphology of fern gametophytes

The alternation of generations in land plants occurs between the sporophyte phase and the gametophyte phase. The sporophytes of seed plants develop self-maintained, multicellular meristems, and these meristems determine plant architecture. The gametophytes of seed plants lack meristems and are heterotrophic. In contrast, the gametophytes of seed-free vascular plants, including ferns, are autotrophic and free-living, developing meristems to sustain their independent growth and proliferation. Compared to meristems in the sporophytes of seed plants, the cellular mechanisms underlying meristem development in fern gametophytes remain largely unknown. Here, using confocal time-lapse live imaging and computational segmentation and quantification, we determined different patterns of cell divisions associated with the initiation and proliferation of two distinct types of meristems in fern gametophytes. Our results reveal how the simple timing of a switch between two meristems has considerable consequences for the divergent gametophyte morphologies of two closely related ferns from Pteridaceae (Pteris and Ceratopteris). Our result provides evolutionary insight into the function and regulation of gametophyte meristems in seed-free vascular plants. HighlightLive-imaging of cell growth and division in apical initials and lateral meristems reveals that the timing of a switch between the two meristem identities drives morphology variation in fern gametophytes.

plant biology↗