Ingenious floral structure drives explosive pollination in Hydrilla verticillata (Hydrocharitaceae)

The floral biology and the role of staminal connective appendages during pollination of the endoparasite Bdallophytum americanum (Cytinaceae)

Bdallophytum americanum (Cytinaceae) is an endoparasitic plant species, meaning only the flowers emerge from the host during the reproductive season. Reports on the pollination biology of this species state that its primary pollinators are carrion flies attracted by the smell of the flowers and nectar as a reward. However, the functional role of one of the most outstanding attributes of B. americanum has been neglected. These are the staminal appendages formed by the apical overgrowth of connective tissue during anther development. To determine whether these staminal appendages play a role in pollination, we monitored a nectarless population of B. americanum. We described the inflorescence emergence, floral movements, and pollination and performed field experiments to test whether the absence of the staminal connective appendages affected the visitation frequency. Male inflorescences emerge early, and both male and female flowers open during the day and do not close. Hoverflies are the most frequent visitors to both floral sexes and carry the most pollen. Moreover, the movement of staminal appendages matching the pollen viability changes is reported for the first time. The staminal appendages are the structures where pollinators land before foraging. The field experiments showed that the visitation frequency decreased sharply without staminal appendages. As a landing platform, the staminal connective appendages in B. americanum are crucial for pollinator positioning and collecting viable pollen.

Bubbles help male flowers overcome obstacles during pollination in Hydrilla verticillata

PREMISE

Pollination in many aquatic plants takes place on the water surface, and the male flowers or stamens often produce gas bubbles underwater; however, the generation mechanism and function of these bubbles are unknown.

METHODS

A common submerged plant, Hydrilla verticillata, was used as experimental material to observe the structure of male flowers, analyze the process of bubble generation, and simulate the movement process of the male flower with attached gas bubble in water.

RESULTS

The aerenchyma inside the male plants of H. verticillata transported the gas produced by the plant's branches during photosynthesis to the male flower, and the formed gas bubbles became attached to the edge of the perianth. The gas accumulation rate in the attached bubbles increased with light intensity. Once the bubble diameter increased to approximately 3.3 mm, the male flowers with the bubble detached from the plant and floated to the water surface. The removal of the attached bubbles did not affect the male flower detached from the plant; however, the surfacing of male flowers without gas bubbles was easily prevented by the plant's branches in the water, and they could not reach the water surface to complete pollen dispersal.

CONCLUSIONS

The gas bubbles produced by male flowers of H. verticillata came from the gas produced by branches under light. These bubbles can help ascending male flowers bypass the obstacles in water and reach the surface to complete pollination.

High-speed video and plant ultrastructure define mechanisms of gametophyte dispersal

Dispersal of gametophytes is critical for land plant survivorship and reproduction. It defines potential colonization and geographical distribution as well as genetic mixing and evolution. C. T. Ingold's classic works on Spore Discharge in Land Plants and Spore Liberation review mechanisms for spore release and dispersal based on real-time observations, basic histology, and light microscopy. Many mechanisms underlying spore liberation are explosive and have evolved independently multiple times. These mechanisms involve physiological processes such as water gain and loss, coupled with structural features using different plant tissues. Here we review how high-speed video and analyses of ultrastructure have defined new biomechanical mechanisms for the dispersal of gametophytes through the dissemination of haploid diaspores, including spores, pollen, and asexual reproductive propagules. This comparative review highlights the diversity and importance of rapid movements in plants for dispersing gametophytes and considerations for using combinations of high-speed video methods and microscopic techniques to understand these dispersal movements. A deeper understanding of these mechanisms is crucial not only for understanding gametophyte ecology but also for applied engineering and biomimetic applications used in human technologies.

Flow, form, and force: methods and frameworks for field studies of macroalgal biomechanics

Macroalgae are ecologically important organisms that often inhabit locations with physically challenging water motion. The biomechanical traits that permit their survival in these conditions have been of interest to biologists and engineers alike, but logistical and technical challenges of conducting investigations in macroalgal habitats have often prevented optimal study of these traits. Here, we review field methods for quantifying three major components of macroalgal biomechanics in moving water: fluid flow, macroalgal form, and hydrodynamic force. The implementation of some methodologies is limited due to the current state and accessibility of technology, but many of these limitations can be remedied by custom-built devices, borrowing techniques from other systems, or shifting lab-based approaches to the field. We also describe several frameworks for integrating flow, form, and force data that can facilitate comparisons of macroalgal biomechanics in field settings with predictions from theory and lab-based experiments, or comparisons between flow conditions, habitats, and species. These methods and frameworks, when used on scales that are relevant to the examined processes, can reveal mechanistic information about the functional traits that permit macroalgae to withstand physically challenging water motion in their habitats, using the actual fluid flows, macroalgal forms, and physical forces that occur in nature.

Mutualisms and (A)symmetry in Plant-Pollinator Interactions

The majority of flowering plants relies on animal pollinators for sexual reproduction and many animal pollinators rely on floral resources. However, interests of plants and pollinators are often not the same, resulting in an asymmetric relationship that ranges from mutualistic to parasitic interactions. Our understanding of the processes that underlie this asymmetry remains fragmentary. In this Review, we bring together evidence from evolutionary biology, plant chemistry, biomechanics, sensory ecology and behaviour to illustrate that the degree of symmetry often depends on the perspective taken. We also highlight variation in (a)symmetry within and between plant and pollinator species as well as between geographic locations. Through taking different perspectives from the plant and pollinator sides we provide new ground for studies on the maintenance and evolution of animal pollination and on the (a)symmetry in plant-pollinator interactions.