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Quantitative Assessment of Some Factors Limiting Seed Set in Buckwheat

Seed Biology, Dep. of Crop and Soil Sciences, Cornell Univ. Agric. Exp. Stn., 617 Bradfield Hall, Cornell Univ., Ithaca, NY 14853-1901

View larger version (34K): [in a new window]   Fig. 1. Proportion of flowers (A), number of flowers open per raceme (B), and proportion of seeds aborted (C) as a function of weeks after seeding at pollination for all racemes or for racemes with one or more seeds previously set. Proportion of flowers resulting in seed set (D) as a function of weeks after seeding at pollination for all racemes or for all racemes after correction for abortion. Each point represents the mean ± SE of the mean of 10 replications. Error bars not shown if smaller than the symbol.

View larger version (162K): [in a new window]   Fig. 2. Differential interference contrast micrographs of cleared buckwheat ovules at anthesis. (A) There is a prominent hypostase (arrow) which is in continuity with the egg sac at the base of the ovule. The synergids, egg, and central cell nucleus are located in the distal part of the ovule near the micropyle (arrowhead indicates outermost cells of nucellus). Bar = 50 µm. (B) The relation between micropyle (arrowhead) and the egg cell complex. In fertile egg sacs, the egg and synergid cells are well defined and in close proximity to the micropyle. Bar = 20 µm. (C) Higher magnification of Fig. 2B showing relationship of the prominent central cell nucleus (arrow) to the synergids (arrowheads). The egg cell tends to lie over or under a synergid such that the central cell nucleus and egg cell are in close proximity to the synergid. In this illustration, the egg cell is not in the plane of focus. Bar = 10 µm. (D) Anthesis ovule with degenerated remains of megagametophyte. Bar = 20 µm.

View larger version (156K): [in a new window]   Fig. 3. Differential interference contrast micrographs of cleared ovules at 24 h after hand pollination. (A) Pendant proembryo (arrow) has increased in diameter to two fold that of the egg. The central cell/endosperm nuclei have migrated to the periphery of the vacuolated central cell in the the egg sac. Bar = 10 µm. (B) A more advanced, multicellular proembryo (arrow). The developing endosperm has multiple nuclei. Bar 20 µm. (C) Collapsing ovule at 24 hr after fertilization. The collapse of the ovule, as indicated by the withdrawal of the ovule from the inner ovary wall (arrowhead) is characteristic of both nonfertilized ovules at 24 h and aborting ovules after fertilization. Bar = 20 µm. (D) Pollen tube remnants converging from the three stylar canals at the micropyle (arrowhead). A nonfertilized egg was evident, but is not shown at the base of the micrograph. Bar = 10 µm.

View larger version (29K): [in a new window]   Fig. 4. Proportion of total ovules divided into four intervals (starting at base line) corresponding to proportion of total ovules fertilized with proembryo at 24 hr after fertilization (HAP), proportion of total ovules fertilized but aborted embryo by 24 HAP, proportion of total ovules with normal egg sac components but not fertilized, and proportion of total ovules with defective components in the egg sac and not fertilized as a function of weeks after seeding. Values represent the mean ± SE of the mean of three replications for normal proembryos and aborted embryos, and one to three replications for defective egg sac.