A study led by Dr. Yin-Zheng Wang examined the preconception motion in Chirita pumila, exposing its association with water-sensitive contractile cells that broaden when taking in water. These cells, filled with an unique reticular structure, are accountable for the stigmas bidirectional movements. These movements form a pollen channel, which facilitates self-pollination, a likely evolutionary adaptation to unpredictable insect cross-pollination environments.
Digging deeper through physiological investigations, the team observed that upon water absorption, a particular cell type, which constitutes about half of the stigmas volume, goes through substantial growth. These newly recognized cells have been called “contractile cells.”
Qualities of Contractile Cells
The research study group found that contractile cells are filled with reticular structures and the nuclei were squeezed to the edges, whereas parenchyma cells are consisted of generally large central vacuoles by Cryo-SEM. After taking in water, the contractile cells significantly elongate to more than 8 times, still filled with a network structure.
This reveals that the reticular structure is the main mechanism of water level of sensitivity, that is, the reticular structure water absorption and growth drive contraction cell elongation, resulting in preconception movement. CLSM revealed that FM4-64 fluorescence signals moved from the plasma membrane to the vacuole membrane in the parenchyma cells, however there was no vacuole membrane signal in contractile cells, and the weak signals at various wavelengths of red and green showed a big elongation of the contractile cells.
A research study led by Dr. Yin-Zheng Wang investigated the preconception motion in Chirita pumila, exposing its association with water-sensitive contractile cells that broaden when absorbing water. These cells, filled with a special reticular structure, are responsible for the stigmas bidirectional movements. Dr. Yin-Zheng Wang from the Institute of Botany at the Chinese Academy of Sciences has actually led a study that discovered the preconception of Chirita pumila displays motion. Digging much deeper through anatomical examinations, the group observed that upon water absorption, a particular cell type, which makes up about half of the preconceptions volume, goes through considerable growth. These freshly recognized cells have been named “contractile cells.”
A-H, Contractile cells in Cryo-SEM/TEM (A-D) and parenchymal cell (E-H) ； I-L, Contractile cells (K, L) and parenchymal cell (I, J) in CLSM with FM4-64 fluorescence signal ； M, ER-tracker golgi-tracker and red green fluorescence signal in stigma through CLSM ； N-Q, Stigma motion and self-pollination connect with circadian rhythm of humidity. Credit: Science China Press
The lack of vacuoles in the contractile cells validates that the water-sensitive substance that absorbs water and expands is a network structure, not a vacuole.
TEM and fluorescence signal analysis revealed that the network structure was caused by endoplasmic reticulum with granular ribosomes, which was entirely various from parenchyma cells. RNA-seq analysis revealed that the expression profiles of restricted cells were significantly various from those of parenchyma cells.
Water-sensitive experiment on the stigma laminae in lateral view. With water stimulation, the stigma laminae bends quickly and powerfully, which supplies a powerful pressure on the two adherent anthers. Credit: Science China Press.
Stigma Movement and Reproductive Implications.
Through field observation, the authors further discovered that the preconception of the plant showed a bidirectional opening and closing-bending movement, and the contractile cells drove the preconception circadian rhythm with changes in humidity. In addition, the preconception movement leaves a pollen channel connecting the anther space between the 2 stigma lobes, which continually squeezes the anther, causing pollen to be forced directly to the receptive surface area of the preconception through this channel.
Therefore, the motion of the stigma transforms a flower system based on cross-pollination by pests into among strict self-pollination. This reproductive strategy including the transition from outcrossing to predominant self-pollination has likely developed due to the fact that of the unsure environment for cross-pollination by insects in which Chirita pumila happens and represents an unique proximate mechanism of reproductive guarantee.
Referral: “A brand-new kind of cell associated to organ movement for selfing in plants” by Yin-Zheng Wang, Yan-Xiang Lin, Qi Liu, Jing Liu and Spencer C H Barrett, 10 August 2023, National Science Review.DOI: 10.1093/ nsr/nwad208.