No abstract

Alpine plants have evolved to fit their life cycle into the short vegetative season of mountain habitats.Fritillaria tubiformis Gren. & Godr. subsp. moggridgei (Boiss. & Reuter ex Planch.) Rix (Liliaceae) is an endemic alpine geophyte, bearing seeds with underdeveloped embryos. Seeds are dispersed in August and embryos complete their development by spring when seeds germinate. In order to optimize seed banking procedures and to develop a proper germination protocol for plant regeneration, we studied embryo morphogenesis and analyzed how this process is influenced by temperature. Radicle protrusion occurred after an incubation of 5 months at 4°C. Under these conditions, underdeveloped embryos reached maturity and acquired a well-defined shoot apex. At the time of dispersal, abundant storage compounds were present in seeds. Lipids and lipid/proteins were uniformly distributed within the embryo and the endosperm, respectively. At late stages of embryo development, starch granules were localized at the cotyledonary tip and were also detected around the shoot meristem. Results suggested that F. tubiformisembryos resumed growth over a large range of temperatures, but were only able to complete development at low temperatures after which they were able to germinate by spring.

Field grown Mentha piperita can be colonized by a fungal endophyte, PGP-HSF, which heavily infects roots and enhances growth of in vitro grown plants. In this work, the time course of fungal development and its morphogenetic effects on plant growth, as well as phosphorus shoot concentration, were analyzed. Fungal infection induced longer shoots and roots and increased adventitious root branching. Microscopic analyses showed that hyphae grew between the walls of rhizodermal cells, produced a progressively thicker sheath and colonized the senescent rhizodermal cells. Plant mechanical defences developed early after the contact between hyphae and rhizodermal cells, and specialized host-fungus interfaces were not observed. Phosphorus concentration was lower in colonized plants than in controls. Our data support a passage of carbon from the plant to the fungus, but no transfer of mineral nutrients from the fungus to the root. The role of PGP-HSF on the enhancement of host growth is discussed.

Root plasticity of Nicotiana tabacum in response to phosphorus starvation Abstract Tobacco plants under low phosphate exhibited increased total and tap root length, as a result of higher apex activity, but decreased root branching in comparison to the plants grown with high-Pi. The possible mechanisms and significance of these alterations, which differed from those typical of stress-induced morphogenetic responses, are discussed.