Postpollination drop production in hybrid larch is not related to the diurnal pattern of xylem water potential

Abstract

The hourly production of postpollination drops in the ovules of three hybrid larch trees (Larix x marschlinsii Coaz) was examined and compared with the measured diurnal pattern of xylem water potential of the same trees under non-stressed conditions during two reproductive seasons. There was no consistent relationship between xylem water potential and ovular drop production in hybrid larch. Individual trees that showed a diurnal drop production in one year did not follow a similar pattern the other year. One tree produced drops in over half of its ovules hourly, regardless of the measured xylem water potential. Variation in number of drops produced per ovule and drop mass was observed between the three trees both years, and between years for two of the trees. This variation was not in response to xylem water potential or environmental conditions. Here we report the first simultaneous measurements of branch water status and the production of ovular secretions for any conifer. We conclude that the postpollination drop production of hybrid larch is not regulated by a tree's overall water status, but is under the control of localized structures such as the cone or the ovule.

Pollination drops as dynamic apoplastic secretions

“…In some species, such as Taxus, drops are secreted from an intact nucellus (O'Leary and von Aderkas, 2006), whereas in others such as Picea (Owens and Blake, 1984), the drop is partially secreted from the living nucellus, but also includes breakdown products associated with nucellar degeneration associated with formation of the pollination chamber. To this end, further investigation of drop composition should also look at the degradome, namely, polypeptides and peptides under 10 kDa.…”

The Evolution of Sexual Fluids in Gymnosperms From Pollination Drops to Nectar

“…This pattern is repeated for the first few days of the pollination period, but then a drop is secreted that lasts for many days and nights without retracting, before its final retraction ends the pollination period (Owens et al, 1980). Cones of L. x marschlinsii produced post-pollination prefertilization drops in rhythms that were independent of the diurnal water potential patterns of the trees to which they were attached, which led to the conclusion that at least in some species the regulation of secretion is controlled at the cone and even the ovule level (O’Leary and von Aderkas, 2006).…”

The behavior of pollination drop secretion in Ginkgo biloba L.

“…It has been suggested that the duration of the PD is largely determined by its cone or ovule, 29,30 and ecological conditions. 3 For example, the PD can persist for several weeks in other species, e.g., Taxusbrevifolia and Juniperus communis.…”

“…Ovules were collected and fixed in an improved FAA solution (50% alcohol:glacialacetic-acid:formaldehyde = 89:6:5) for 4 h at room temperature and then kept for 12 h at 4°C. Then, they were dehydrated in a graded ethanol series (30,50,70,80,90, and 100%, 15 min each step). After drying at critical point, the specimens were coated with a layer of gold, and observed under a Hitachi H-300 SEM 32 Semi-thin sections.…”

“…Ovules were collected during pollination and prefixed in 2.5% (v/v) glutaraldehyde plus 1.5% (w/v) paraformaldehyde in 0.1 M phosphate buffer (pH 7.4), for 20 h at room temperature. After being postfixed in 1% (w/v) osmium tetroxide for 6 h at 4°C, the samples were rinsed twice, and then dehydrated in an alcohol series (30,50,70,80,90, and 100%, 15 min each step). The samples were infiltrated and finally embedded in Spurr's resin.…”