A. Bones and T.-H. Iversen

The occurrence and distribution of myrosin cells and myrosinases has been followed in different organs during development of 7 species of the Brassicaceae. Using light and electron microscopy the myrosin cells were characterized morphologically and compared to other idioblasts in the tissue. Myrosin grains stain specifically with toluidine blue, methylene blue azur-II, lactophenol aniline blue and fuchsin. At the ultrastructural level myrosin grains were seen to contain proteins, and oleosomes occupy most of the myrosin cells at an early stage of development in young seedlings, together with precursors for mitochondria, plastids and microbodies. Changes in ultrastructure take place during development and light has a negative effect on the extent of cellular differentiation. Myrosin cells are generally found distributed in differentiated tissue, from the imbibition stage up to 192 h after germination. The relative area occupied by the myrosin cells has been calculated by morphometrical analyses and correlated to the cultivation period, plant organ and light conditions. Attempts have also been made to isolate myrosin cells as protoplasts and separate these from the normal root cell protoplasts. Myrosinase activity has been determined in comparable studies of the intact tissue and protoplasts isolated from the same. Activity decreased throughout the development of the plant but even at flowering myrosinase activity was still detected. The specific activity of the protoplasts was less than that of the intact root tissue but also here a decrease in activity was found with time after isolation. The specific activities of the enzymes have been correlated to the number and distribution of myrosin cells and the relevance of the term myrosin cell is discussed.

M.S. Costa, T.J. de Vasconcellos, C.F. Barros and C.H. Callado

P. Malea, T. Kevrekidis and S. Haritonidis

Zinc uptake in the upper (leaves) and lower ground parts (roots, stems, rhizoids) of Halophila stipulacea (Forsk.) Aschers, and leaf cell mortality were examined in laboratory experiments. The seagrass was incubated for 12 days in zinc concentrations between 10−4 and 10−7 M. At 10−6 and 10−7 M Zn concentrations, uptake was characterized by a rapid initial adsorption rate slowly decreasing up to the 4th day, after which an equilibrium was reached; the ‘equilibrium’ concentrations increased as the Zn in sea water increased. At the higher Zn concentrations (10−5 and 10−4M)the content in the plant continued to increase after the 4th day, perhaps due to the development of necrotic effects mainly evident in the teeth and epidermal cells as well as in the mesophyll cells of the leaves. A positive correlation between Zn content in the upper and lower parts of H. stipulacea was also found, whereas Zn uptake in leaves was significantly higher than in the root-rhizomes-rhizoids. It was also demonstrated that some zinc can leak from the tissues of this seagrass.

T.W. Hegarty and H.A. Ross

Seed germination under water stress, and seedling growth immediately after germination, have been investigated in a series of experiments. In the majority of species used in these experiments it was found that seedling growth immediately after germination could proceed at water potentials lower than those that permitted germination. This differential sensitivity to water stress could be reduced (i.e., the water potential of seed germination made more negative) by growth regulators and was completely removed by a combination of ethrel and kinetin in two of the species investigated, red clover and lucerne. Evidence suggests that the initiation of cell elongation is the process in germination most sensitive to water stress, and the work with growth regulators confirms that there are different effects on the initiation of germination and on subsequent growth. Differential sensitivity to moisture stress is suggested as a form of dormancy and we speculate on possible mechanisms that govern its control.

Mehreshan T. El Mokadem and Donald L. Keister

Electron transport mutants of Rhizobium japonicum 61A76 were isolated and have been partially characterized spectrally and biochemically. Mutants which are almost totally deficient in cytochromes c and aa 3 and with a reduced amount of cytochrome b grow normally under aerobic conditions. These mutants are symbiotically infective but form ineffective nodules.

G. Gottsberger, T. Arnold and H.F. Linskens

The nectar of Hibiscus rosa-sinensis L. shows an increase in amino acid concentration with the aging of the flowers, correlated with an increase in the number of detectable amino acids. The amino acid concentration of the nectar increased drastically after pollen addition both in Hibiscus and in the two other species investigated. The main amino acid responsible for this increase was proline. After puncturing or otherwise injuring a flower, the amino acid composition of the nectar is altered. In this case, the increase is due mainly to asparagine. Although contamination of nectar by pollen may be a common and natural event in many flowers, especially in those pollinated by butterflies, such an alteration in nectar constituents should be carefully discussed when considering amino acid concentration or composition in relation to pollinator—plant coevolutionary lines.

C. Grunwald, G. Schiller and M.T. Conkle

Judging from enzyme analysis of native stands in Israel, Aleppo pine (Pinus halepensis Mill.) in the eastern Mediterranean basin has unique genetic characteristics. Only four of thirty isozyme loci surveyed in trees of native stands are polymorphic. Each polymorphic locus has two alleles. Stand expected heterozygosity (He) values are low and range between.03 and.06. Native Aleppo pine has allele frequencies for two isozymes, alanine aminopeptidase (Aap) and catalase (Cat), that distinguish it from that growing in Europe and North Africa. Using allele frequency associations for three loci, three geographic groups of natural stands are identified. Alleles useful for detecting introgression from P. brutia Ten. are absent from the native stands sampled, but occur in planted populations. Six out of nine plantations studied have allele frequencies indicating the presence of some trees from foreign seed sources.

L. Drozdowska, O.P Thangstad, T. Beisvaag, K. Evjen, A. Bones and T.-H Iversen

The occurrence and distribution of myrosin cells and myrosinases have been followed using immunochemical techniques on samples taken from pistils before and after pollination, and seeds harvested at three different stages of maturity. Two Brassica napus cultivars (Jet Neuf and Bolko) with a high and a low glucosinolate seed content, respectively, were used. Two methods recently developed in our laboratory were applied for detection of the enzyme using light microscopy (LM) and transmission electron microscopy (TEM). In the first case, paraffin-embedded sections were sequentially incubated with a monoclonal anti-myrosinase antibody and with peroxidase- and fluorescein-isothiocyanate-conjugated secondary antibodies. For the TEM localization a polyclonal antibody raised in rabbit against a highly purified myrosinase from white mustard was used. Myrosinase activity was detected in the early stage during embryogenesis in both cultivars but was higher in the high glucosinolate cultivar. In the early stages of development, typical embryonic myrosinase cells could not be detected. Later they appear in cotyledons, hypocotyls, and radicles. A typical, specific, and positive LM localization of myrosinase in myrosin cells could be detected both in radicles and the cotyledons. In the radicle the positively identified cells are located in the second outermost cell layer in the peripheral cortex; in the cotyledon positively identified myrosin cells were found scattered around in the tissue. The positive TEM localization demonstrated gold particles uniformly distributed over the matrix in the myrosin grains.

T.A. Lie, P.C.J.M. Timmermans and G. Ladizinsky

European Rhizobium leguminosarum strains, effective on the cultivated pea, induced ineffective nodules on pea ecotypes elatius and abyssinicum, indigenous plants from Israel and Ethiopia, respectively. Effective nodules were formed on elatius plants by Rhizobium strains from soils of the Middle East, i.e. from regions where the elatius pea occurs naturally. No Ethiopian Rhizobium strains were available, but the Middle East Rhizobium ones were able to form an effective symbiosis with the abyssinicum peas. We conclude that there is a co-evolution between the local leguminous plants and the indigenous Rhizobium population within an isolated region.