STOMATA ON THE FRUITS AND SEEDS OF ESCHSCHOLZIA (PAPAVERACEAE)

Stomata are present on the outer and inner fruit walls and seed coats of Eschscholzia californica, E. covillei, E. glyptosperma, E. lemmonii and E. minutiflora. The stomata on the inner fruit wall and seed coat remain constantly open, even under plasmolyzing conditions, whereas those of the outer fruit wall are able to open and close. This allows for gas exchange in these chlorophyllous structures. Fibrous bundle caps in the costal regions of the fruit act as windows allowing light transmission to the photosynthetic seeds within. Preliminary results show that the total photosynthesis by the fruits and seeds of Eschscholzia californica together appears to at least balance respiratory losses, and under favorable conditions might significantly contribute to seed and fruit development. STOMATA are known to occur on the seeds of species in a number of apparently unrelated families: Amaryllidaceae, Bixaceae, Bombacaceae, Cannaceae, Capparidaceae, Dipterocarpaceae, Euphorbiaceae, Fagaceae, Flacourtiaceae, Geraniaceae, Iridaceae, Juglandaceae, Krameriaceae, Liliaceae, Magnoliaceae, Malvaceae, Meliaceae, Myrsinaceae, Polygalaceae, Rosaceae, Sterculiaceae, and Violaceae (Macloskie, 1884; Netolitzky, 1926; Corner, 1976). In the Papaveraceae, three genera, Argemone (Sachar, 1955), Eschscholzia (first reported by Meunier, 1891), and Bocconia (our observations of B. frutescens) are known to have seed coat stomata. Considerations of the function of seed coat stomata have appeared in the literature over the years. Netolitzky (1926) suggested that seed coat stomata function in some species in water uptake by the seed during germination, rather than in gas exchange. However Flint and Moreland (1943) found considerable photosynthetic activity in the seeds of Hymenocallis occidentalis after they are shed from the fruit and inferred that seed coat stomata allow for gas exchange within this green seed. Our work has led us to believe that the seed coat stomata in Eschscholzia function in photosynthetic gas exchange by the seed while it is I Received for publication 3 October 1978; revision accepted 10 January 1979. This work was supported in part by NSF Grant DEB7702234 to the second author. We thank Robert Pearcy and David Randall for assistance with measurements of photosynthesis; Donald Kyhos and Thomas Rost for critical reading of the manuscript; Barbara Rugeley for translating the French paper; and Rudolf Schmid for helpful suggestions both during early stages of this study and in reviewing the manuscript. still contained within the fruit. In this paper we will (1) describe the structure of Eschscholzia fruits and seeds with particular attention to features that are important for photosynthesis and gas exchange, and (2) provide preliminary data showing the occurrence of photosynthesis in the fruits and seeds. MATERIALS AND METHODS-For SEM studies fresh immature seeds and fruits of Eschscholzia californica, E. glyptosperma, E. minutiflora, E. lemmonii and E. covillei were fixed in FAA, dehydrated in an ethanol series, dried using the critical point method, attached to aluminum stubs with silver conductive paint and coated with gold in a vacuum evaporator or sputter coater. Unimbibed mature seeds of these and the remaining eight species in the genus were likewise attached to stubs and coated with gold. Specimens were observed with a Cambridge Stereoscan S4 scanning electron microscope. Fresh material was hand-sectioned for anatomical study and observed either unstained or stained with 0.25% toluidine blue 0. Unstained guard cells were plasmolyzed with glycerine. Additional material was fixed in FAA, dehydrated through a tertiary butyl alcohol series, embedded in "Paraplast," sectioned at 10 ,um, mounted and stained with safranin, fast green and crystal violet. Using an infra-red gas analyzer, we measured photosynthesis and respiration as changes in CO, concentration in a reference gas mixture as it passed through a chamber enclosing several capsules attached to a single plant of E. californica. The temperature was 24-25 C, and the experiments were repeated at various light intensities. After completion of measurements the seeds