Arrest of Stomatal Initials in Tradescantia Is Linked to the Proximity of Neighboring Stomata and Results in the Arrested Initials Acquiring Properties of Epidermal Cells

AbstractWe examined spatial relations of arrested stomatal initials and their differentiated state on leaves of the monocotyledon Tradescantia. The placement and proximity of stomata and arrested stomatal initials to the five nearest stomata were studied to test the hypothesis that if developing stomatal initials occur too close to one another, initials will arrest. The results showed that arrested stomatal initials were not randomly placed, but were closely associated with another stoma, most often in an adjacent cell file. The distance to their nearest stomatal neighbors was less than the equivalent distance between stomata that mature. After stomatal initials form, their position within or across cell files was not adjusted by cell division or expansion. Synergistic effects from several neighboring stomata could not be linked to stomatal arrest; rather, arrest was associated only with the nearest stomatal neighbor. Since the arrest of stomatal initials was distance dependent, a failure intrinsic to the arrested initials is not solely responsible for halting stomatal development. These data show that an inhibitory mechanism adjusts stomatal development to influence the final distribution of Tradescantia stomata. The pigmentation and expansion characteristics of arrested stomatal initials were like those of epidermal cells, indicating that the initials did not remain halted at a specific point in their development. The capacity of arrested initials to differentiate in the epidermal cell pathway indicates that they remain pluripotent after their initial specification and that the opportunity for patterning is long enough to permit their entry into the epidermal cell pathway

Space Experiment on Tuber Development and Starch Accumulation for CELSS

Potato explants (leaf, small stem section, and axillary bud), flown on STS-73, developed tubers of 1.5 cm diameter and 1.7 g mass during the 16 day period of spaceflight. The experiment was undertaken in the ASTROCULTURE(Trademark) experiment package under controlled temperature, humidity, lighting, and carbon dioxide concentrations. The tubers formed in the explant system under microgravity had the same gross morphology, the same anatomical configuration of cells and tissues, and the same sizes, shapes, and surface character of starch granules as tubers formed in a 1 g environment. The total accumulation of starch and other energy containing compounds was singular in space flight and ground control tubers. Enzyme activity of starch synthase, starch phosphorylase, and total hydrolase was similar in spaceflight and ground controls but activity of ADP-glucose pyrophosphorylase was reduced in the spaceflight tuber tissue. This experiment documented that potatoes will metabolize and accumulate starch as effectively in spaceflight as on the ground and thus this data provides the potential for effective utilization of potatoes in life support systems of space bases

A novel system for spatial and temporal imaging of intrinsic plant water use efficiency

Instrumentation and methods for rapid screening and selection of plants with improved water use efficiency are essential to address current issues of global food and fuel security. A new imaging system that combines chlorophyll fluorescence and thermal imaging has been developed to generate images of assimilation rate (A), stomatal conductance (gs), and intrinsic water use efficiency (WUEi) from whole plants or leaves under controlled environmental conditions. This is the first demonstration of the production of images of WUEi and the first to determine images of gs from themography at the whole-plant scale. Data are presented illustrating the use of this system for rapidly and non-destructively screening plants for alterations in WUEi by comparing Arabidopsis thaliana mutants (OST1-1) that have altered WUEi driven by open stomata, with wild-type plants. This novel instrument not only provides the potential to monitor multiple plants simultaneously, but enables intra- and interspecies variation to be taken into account both spatially and temporally. The ability to measure A, gs, and WUEi progressively was developed to facilitate and encourage the development of new dynamic protocols. Images illustrating the instrument's dynamic capabilities are demonstrated by analysing plant responses to changing photosynthetic photon flux density (PPFD). Applications of this system will augment the research community's need for novel screening methods to identify rapidly novel lines, cultivars, or species with improved A and WUEi in order to meet the current demands on modern agriculture and food production. © The Author 2013. Published by Oxford University Press on behalf of the Society for Experimental Biology