Bright-field and electron microscopic investigations of sterility and salt tolerance in Arundo donax L. and of spontaneous lesion formation in map kinase- silenced Solanum lycopersicum

Over the past decade attempts have increased to identify alternative energy sources such as biomass, especially that of perennial grasses of which the most promising energy crop is Arundo donax L.. This species absorbs large amounts of N, P, Na and K as well as heavy metals, and consequently prevents pollution of the soil and spread of pollution into ground water systems. Unfortunately the potentially invasive nature of Arundo donax has discouraged research exploring other advantageous features of this species. The study reported here reveals that Arundo donax does not produce seeds and only reproduces by vegetative means. Both the male and female gametophyte development are arrested at a very early stage. The archesporial cells fail to produce megasporocytes, and the microspores do not initiate microgametogenesis. The degree and the mechanism of salt tolerance in Arundo donax prominently influences its biomass potential. Further investigation is needed to explore the operative physiological mechanism for this species. Sodium chloride tolerance and its uptake were compared in two ecotypes collected from a High Saline Environment and Low Salinity Environment. Plants were grown on 0% and 1% NaCl. Microscopic analyses indicate that plants from both ecotypes treated with 1% NaCl followed similar patterns of growth and development. The same treatment was repeated with plants regenerated from callus to determine the stability of the salt tolerance trait after transplantation. Both experiments showed that there is no significant difference in growth and development between the two ecotypes. Under pathogen attack plants initiate a defense response that prevents development of disease. One of the major defense mechanisms is the hypersensitive response (HR), which initiates cell death in the infected area including the infecting microbes. HR on the leaves is manifested as brown, desiccated, necrotic spots. In MAP kinases play an important role in the signal transduction leading to a HR. In a previous investigation, three MAP kinase genes were silenced simultaneously in tomato, and it was found that these plants displayed severe necrotic lesions on the leaves and the stem which led to death of the entire plant. Transmission electron microscopy was used to show that the expanding necrotic lesions in the MAPK loss-of-function plants exhibit features typical of HR-like programmed cell death. This indicates that the silenced MAPK kinases negatively regulate confinement of programmed cell death.