We describe a protocol using chamber slides and media to immobilize plant cotyledons for confocal imaging of the epidermis over several days of development, documenting stomatal differentiation. Fluorophore-tagged proteins can be tracked dynamically by expression and subcellular localization, increasing understanding of their possible roles during cell division and cell-type differentiation.
Imaging in vivo dynamics of cellular behavior throughout a developmental sequence can be a powerful technique for understanding the mechanics of tissue patterning. During animal development, key cell proliferation and patterning events occur very quickly. For instance, in Caenorhabditis elegans all cell divisions required for the larval body plan are completed within six hours after fertilization, with seven mitotic cycles1; the sixteen or more mitoses of Drosophila embryogenesis occur in less than 24 hr2. In contrast, cell divisions during plant development are slow, typically on the order of a day 3,4,5 . This imposes a unique challenge and a need for long-term live imaging for documenting dynamic behaviors of cell division and differentiation events during plant organogenesis. Arabidopsis epidermis is an excellent model system for investigating signaling, cell fate, and development in plants. In the cotyledon, this tissue consists of air- and water-resistant pavement cells interspersed with evenly distributed stomata, valves that open and close to control gas exchange and water loss. Proper spacing of these stomata is critical to their function, and their development follows a sequence of asymmetric division and cell differentiation steps to produce the organized epidermis (Fig. 1).
This protocol allows observation of cells and proteins in the epidermis over several days of development. This time frame enables precise documentation of stem-cell divisions and differentiation of epidermal cells, including stomata and epidermal pavement cells. Fluorescent proteins can be fused to proteins of interest to assess their dynamics during cell division and differentiation processes. This technique allows us to understand the localization of a novel protein, POLAR6, during the proliferation stage of stomatal-lineage cells in the Arabidopsis cotyledon epidermis, where it is expressed in cells preceding asymmetric division events and moves to a characteristic area of the cell cortex shortly before division occurs. Images can be registered and streamlined video easily produced using public domain software to visualize dynamic protein localization and cell types as they change over time.
This time-lapse confocal technique allows longitudinal studies of fluorescently tagged protein expression and localization in individual cells of the Arabidopsis cotyledon epidermis, which in the case of POLAR and other dynamically changing proteins is critical to a proper understanding of their function. Previously, sustained time lapse imaging has been used to examine Arabidopsis root fungal infection11 and meristem growth5,12, but adding the cotyledon epidermis expands the vers…
The authors have nothing to disclose.
We thank Amanda Rychel for assistance in developing the time lapse protocol and Lynn Pillitteri for constructing POLAR::POLAR-eGFP. We are also grateful to ABRC for providing the pm-rb construct. This protocol was developed through a support from the PRESTO award from Japan Science Technology and Agency. Research on POLAR was also supported by the University of Washington Royalty Research Fund (RRF-4098) and the National Science Foundation (MCB-0855659). KMP is an NSF Graduate Research Fellow (DGE-0718124), and KUT is an HHMI-GBMF investigator.
Name of reagent | Company | Catalog Number | Comments |
Bacto Agar | BD | 214010 | |
One-chamber slide | Nunc (Thermo Scientific) | 155360 | Or two-chamber (155379) |
Laser scanning confocal microscope | Zeiss | LSM700 | Zen 2009 software |
20x objective lens | Zeiss | 420650-9901 | NA 0.8, Plan-APOCHROMAT |
Dissecting microscope | Benz (National) | 431TBL | Illuminates from below |
#5 forceps, biology tip | Roboz Surgical Instrument | RS-4978 | Very fine tips are critical |