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Stomata are integral to water transport in plants because evaporation of water throught the stomatal pore draws water through the water conducting tissue. This pore also enables gas exchange, especially carbon dioxide entrance. Among bryophytes, stomata are restricted to sporophytes of mosses and three hornwort genera. This study of the anatomy and ultrastructure of the stomata in Phaeoceros and Folioceros was undertaken to evaluate homology of stomata among basal embryophytes. Light microscope studies indicate that the reniform guard cells of hornworts contain a large vacuole, one to two starch-filled plastids and a peripheral nucleus. Compared to other epidermal cells, the guard cells walls are thickened, especially adjacent to the pore. Transmission electron microscopy revealed that the pronounced cell wall is of three layers, each containing parallel microfibrils oriented in different directions. Intercellular spaces are found internal to the stomata in the assimilative cells. Such evidence, combined with the fact that other epidermal cells lack chloroplasts, implies that hornwort stomata function in gas exchange. To evaluate whether or not these stomata open and close as a result of osmotic changes, we have performed histochemical studies on potassium and organic ion sequestration in guard cells. The role of stomata in transpiration will be evaluated in regards to water transport through the sporophyte. Comparisions will be made with stomata of lycophytes and mosses.

Microtubules are essential components of eukaryotic cells. Myriad proteins associate with microtubules to facilitate the organization and operation of microtubule arrays. Various M icrotubule A ssociated P roteins (MAPs) assist the assembly and function of mitotic spindles and interphase arrays. Nine MAP65 genes exist in the genome of the acentrosomal model plant, Arabidopsis thaliana, and the function of majority of these proteins is unclear. To address this knowledge gap, we demonstrate the localization of A. thaliana MAP65-6 and MAP65-7 fusion proteins expressed from native promoters in interphase cells of developing A. thaliana seedlings. Analyses of these fusion proteins co-expressed with alpha-tubulin 6 reporters indicate that MAP65-6 and MAP65-7 bind a subset of interphase microtubules. Co-expression of GFP: MAP65-6 with mCherry: MAP65-2 from native promoters in A. thaliana showed overlapping localization patterns on interphase microtubule bundles. Collectively, these data suggested that MAP65-2 , -6, and -7 bind cortical microtubule bundles in plant interphase microtubule arrays., Competing Interests: The authors declare that there are no conflicts of interest present., (Copyright: © 2023 by the authors.)

Stomatal pores are adjustable microscopic holes on the surface of photosynthetic tissues that help regulate multiple aspects of plant physiology. Stomatal pores facilitate gas exchange necessary for photosynthesis, water transport, and temperature regulation. Pore size is influenced by many intertwined environmental, molecular, cellular, and physiological cues. Accurate and precise measurements of pore size is important for understanding the mechanisms that adjust pores and plant physiology. Here we investigate whether conventional pore measurements of width are appropriate for the economically important crop plant Zea mays . Our studies demonstrate that pore area is a more sensitive measurement than width in this plant., Competing Interests: The authors declare that there are no conflicts of interest present., (Copyright: © 2023 by the authors.)