Effects of seed burial on germination, protein mobilisation and seedling survival in Dodonaea viscosa.

Ecological restoration of disturbed areas requires substantial knowledge of the germination of native plants and the creation of novel methods to increase seedling establishment in the field. We studied the effects of soil matrix priming on the germination of Dodonaea viscosa seeds, which exhibit physical dormancy. To this end, we buried both pre-scarified (in H2SO4, 3 min) and non-pre-scarified seeds in the Parque Ecológico de la Ciudad de México. After seeds were unearthed, they were post-scarified for 0, 2, 6 and 10 min and their germination percentages compared to the germination of a control batch of laboratory-stored seeds. For both control and unearthed seeds, the protein pattern was determined in the enriched storage protein fraction in SDS-PAGE gels stained with Coomassie blue. Percentage germination increased as the scarification time increased. Pre-scarification significantly increased percentage germination of post-scarified seeds in relation to the control and non-pre-scarified seeds. In seeds unearthed from the forest site, the buried pre-scarified seeds had relatively high percentage germination, even in the absence of post-scarification treatment. A 48-kDa protein was not found in unearthed, pre-scarified seeds nor in the control germinated seeds, indicating that mobilisation of this protein occurred during soil priming. Burying seeds for a short period, including the beginning of the rainy season, promoted natural priming, which increased protein mobilisation. Functionally, priming effects were reflected in high percentage seedling survival in both the shade house and the field. Seed burial also reduced the requirement for acidic post-scarification.

Ovule and seed development of Lacandonia schismatica (Lacandoniaceae).

Ovule and seed development is described for Lacandonia schismatica, a species whose androecium is surrounded by the gynoecium. The ovule in each carpel is basal, anatropous, tenuinucellate, and bitegmic. The female gametophyte is formed by the micropylar megaspore cell, after a coenocytic stage of the four megaspore nuclei. The mature female gametophyte has the normal complement of seven cells and eight nuclei. We propose a new type of female gametophyte development on the basis of the coenocytic stage of the tetrad, the cellularization of the tetrad, and the survival of the micropylar spore. At seed dispersal time, the embryo has ~10-20 cells. Endosperm development is of the nuclear type. At maturity, endosperm cells show starch and protein inclusions as well as polysaccharides in their thick walls. The seed coat is formed from the outer integument; the inner one disappears. The exotesta contains tannin. The fruit (achene) wall is two-layered. The maturation of the fruits in a flower is synchronous, and they separate from the receptacle for dispersal.

Morph-biased male sterility in the tropical distylous shrub Erythroxylum havanense (Erythroxylaceae).

This study explores whether ecological factors, such as pollinators and pollen flow, or variation in pollen and ovule development account for the observed differences (approximately twofold) in the reproductive output of pin and thrum individuals of Erythroxylum havanense. The importance of ecological factors was assessed by means of comparison of the identity of pollinators and the rates of flower visitation, and by performing controlled hand pollinations and measurements of fruit set. In addition, we described the pollen and ovule development of thrum and pin individuals. Our results indicate that pollinators of E. havanense do not distinguish between floral morphs. The differences in fruit set between pin and thrum plants held even after hand pollination and, therefore, the observed differences in reproductive output between floral morphs of E. havanense cannot be explained in terms of asymmetrical pollen flow. There were no differences in the pattern of gynoecium development between the pin and thrum morphs, however androecium development showed marked differences between the morphs, and there was a resemblance between the developmental pathways leading to male sterility of the thrum morph of E. havanense with that of species with cytoplasmic male sterility (CMS).