Reactive oxygen species and cellular interactions between Mycosphaerella fijiensis and banana.

Globally, the banana plant (Musa spp) is the fourth most important crop after rice, wheat and corn (based on production in tons). It is cultivated in more than 100 tropical and subtropical countries, mainly by small producers and is a fundamental food source for millions of people. Black leaf streak disease (BLSD), caused by Mycosphaerella fijiensis Morelet (sexual phase) or Paracercospora fijiensis (Morelet) Deighton (asexual phase), is the main disease affecting the world's banana culture. This disease has a wide geographical distribution accounting for losses exceeding 50% of global banana production. We conducted a comparative histocytological study on the kinetics of the infection process using three banana genotypes with phenotypes that differ in resistance to BLSD: Grand Naine (Susceptible), Pisang Madu (Partially Resistant) and Calcutta 4 (Resistant). Experiments were conducted under controlled conditions with the objective of characterizing the cellular interaction processes between M. fijiensis and Musa acuminata. Conidia germination occurred 24 hours after inoculation. Germination rates were high (97%) and there were no significant differences between the three genotypes (P>0.147). The Peroxidase enzyme and H2O2 were associated with a hypersensitivity-like reaction in the resistant genotype Calcutta 4, indicating a possible role of the enzyme or its product as defense mechanisms against M. fijiensis in banana plants

A new technique for visualizing proanthocyanidins by light microscopy

International audienceWe describe a new technique for visualizing proanthocyanidin-containing elements in plant tissues. Our innovation is the fixation of condensed tannins with an exogenous protein prior to alcohol dehydration. In this way, tannins do not undergo partial solubilization during the dehydration sequence and appear as sharply contoured globules of various diameters

Early effects of the mutation laurina on the functioning and size of the shoot apex in coffee tree and analysis of the plastochron phases : relationships with the dwarfism of leaves

The current article presents the investigations into the effect of the laurina mutation on the functioning and size of the shoot apical meristem (SAM) in Coffea arabica. This monolocus and Mendelian mutation is known to have pleiotropic effects on tree shape and dwarfism. A comparison between the wild type C. arabica var. Bourbon and its natural dwarf mutant C. arabica var. laurina, also called Bourbon pointu, was carried out leading to three main results: (1) the effects appeared immediately after the emergence of the buttress but did not affect the dome-shaped SAM (size and shape); (2) the effects were located at the peripheral zone and maintained subsequently within the leaf primordia; (3) the effects consisted of reduction in both the size of primordia and the height of incipient internode, consequently resulting in dwarfism of mature leaves and internodes. By contrast, the laurina mutation had no effect on the relationship between the phyllochron and the plastochron, the decussate and opposite phyllotaxis, and the relative timing of SAM functioning within the plastochron

Laurina mutation affected Coffea arabica tree size and shape mainly through internode dwarfism

The two varieties-Bourbon (B) and its natural mutant Bourbon pointu (BP)-of Arabica coffee (Coffea arabica L.) differ by an epigenetic, monolocus, and recessive laurina mutation that results in pleiotropic effects, such as tree dwarfism and tree-shape modification. The objective of the study was to search for the origin of the differences in size and shape of the tree both at the macroscopic (length and number of internodes, branching angle) and at the microscopic levels (size and number of cells within the internode pith). At the macroscopic level, the laurina mutation acted only by decreasing the internode size. Neither the angle of branching nor the number of internodes was influenced by the mutation. At the microscopic level, the mutation lowered mainly the number of cells present along the longitudinal axis of the internode, and, at a lesser extent, the cell height. Especially, the internode size decreasing explained both the tree dwarfism and the tree-shape modification. In fact, the laurina mutation strengthened the dwarfism of plagiotropic internodes when compared to that of the orthotropic ones, and such an impact was mainly due to a strong cell number decrease. To summarize, two major pleiotropic effects of the laurina mutation can be explained only by a modification of the trade-off between meresis and auxesis during the internode growth. This opens new perspectives for the characterization of the other effects at the hormonal level, and then, for the identification of the gene at the molecular level

Starch gelatinization distribution and peripheral cell disruption in cooking rice grains monitored by microscopy

International audienc

Ultrastructural changes in coconut calli associated with the acquisition of embryogenic competence

Ultrastructural studies of 2,4-D (2,4 dichlorophenoxyacetic acid) induced coconut calli and of untreated controls enabled us to characterize early events in cellular reorganization leading to embryogenic cell individualization and subsequent development into proembryos. Embryogenic cells were characterized by special features that chiefly affected the nucleus, cytoplasm and cell wall: deep invaginations of the nuclear envelope, proliferation of dictyosomes, with emission of Golgi vesicles, directly related to an increase in cell wall thickness. Modification of the cell wall structure was studied and particular attention was paid to the cytolocalization of bêta-1,4-glucans, and of callose and pectin epitopes, using gold-conjugated probes. The first changes (detected 7-14 d after 2,4-D increase) involved the closure of plasmodesmata, breaking of symplastic continuity, and callose deposition. The acquisition of embryogenic competence was linked to the appearance of an outer layer of fibrillar material containing pectin epitope (mainly un-methyl-esterified), fully coating the embryogenic cells (21 d after the induction treatment). Some of the ultrastructural changes observed during the reprogramming of somatic cells towards embryogenesis can be likened to those accompanying the maturation of female gamete cells in many plant species. The possible significance of these observations is discussed. (Résumé d'auteur