Badra Bouamama

Abscisic acid signals reorientation of polyamine metabolism to orchestrate stress responses via the polyamine exodus pathway in grapevine.

Polyamines (PAs) have been suggested to be implicated in plant responses to abiotic and biotic stress. Grapevine is a model perennial plant species whose cultivars respond differently to osmotic stress. In this study, we used two cultivars, one sensitive (S) and one tolerant (T) to drought. In adult vines subjected to drought under greenhouse conditions, total PAs were significantly lower in the control T- and higher in the control S-genotype and significantly increased or decreased, respectively, post-treatment. Soluble Put and Spd exhibited the greatest increase on d 8 post-treatment in the T- but not in the S-genotype, which accumulated soluble Spm. Abscisic acid (ABA) was differentially accumulated in T- and S-genotypes under drought conditions, and activated the PA biosynthetic pathway, which in turn was correlated with the differential increases in PA titers. In parallel, polyamine oxidases (PAOs) increased primarily in the S-genotype. ABA at least partially induced PA accumulation and exodus into the apoplast, where they were oxidized by the apoplastic amine oxidases (AOs), producing H2O2, which signaled secondary stress responses. The results here show that the ABA signaling pathway integrates PAs and AOs to regulate the generation of H2O2, which signals further stress responses or the PCD syndrome.

Investigations on the leaf anatomy and ultrastructure of grapevine (Vitis vinifera) under heat stress

Leaf anatomical and ultrastructural responses of “Razegui” and “Muscat Italia” grapevine cultivars to high temperatures were studied under controlled conditions (T > 36°C), based on photonic and electron microscopy. Histological studies performed on leaves from heat‐stressed and control grapevines revealed thicker leaf blades under high temperature conditions. Environmental scanning electron microscopy of leaf surfaces from both cultivars allowed observing sinuate epidermal cells on the leaves of grapevines cultivated under heat stress and irregular giant oblong pores on their adaxial surface. When observed by transmission electron microscopy, leaf cross sections in grapevines cultivated under high temperature conditions exhibited folded cuticle and cell wall on the adaxial epidermis layer. Therefore, significantly greater cell wall thicknesses were measured under heat stress than control conditions in both cultivars. Regarding chloroplasts, they were more globular in shape under heat stress compared with control conditions and had disorganized thylakoids with a reduced thickness of grana stacking. The size of starch granule decreased, while the number of plastoglobules increased with heat stress, indicating a reduced carbon metabolism and a beginning of senescence within the 3‐month heat stress period. This study confirms widespread adaptive properties in two grapevine cultivars in response to high temperature stress. Microsc. Res. Tech., 2011.

Development and evaluation of a GFLV inverted repeat construct for genetic transformation of grapevine

Grapevine Fanleaf virus (GFLV) is one of the most damaging and widespread nepovirus in grapevine, causing the fanleaf disease. Here, we report the development of inverted repeat (IR) constructs, consisting of GFLV-derived sequences, for genetic transformation of grapevine to induce GFLV-specific silencing. The IR construct was designed with fragments of a conserved region of the GFLV movement protein (MPc) gene from a Tunisian isolate (GFLV tun) and with cassettes containing the neomycin phosphotransferase or bar gene as selectable marker. For proof of concept, the IR construct was transferred into Nicotiana benthamiana by Agrobacterium mediated transformation. Challenge inoculation of T1 transgenic plant lines with the relevant virus resulted in plants showing resistance, recovery, retarded infection and susceptibility. Northern blot analysis, using a virus-derived sequence (MPc) as probe, could detect transgene specific small interfering RNA in resistant transgenic N. benthamiana plants after GFLV inoculation. Embryogenic cells of grapevine (Vitis vinifera cv Arich dressé) were transformed with the IR construct in combination with the bar gene using A. tumefaciens strain LBA4404. After molecular characterization of regenerated putative transgenic grapevine plants, Northern blot analysis detected different levels of IR transcripts in independent transgenic grapevine lines indicating a post-transcriptional gene silencing.

Somatic embryogenesis and plantlet regeneration from immature anthers of Opuntia ficus-indica

Summary An in vitro protocol has been developed for callus induction, somatic embryogenesis, and plant regeneration in the Barbary fig (Opuntia ficus-indica) cultivars ‘Gialla’ and ‘Moore’. Immature anthers cultivated in the dark on induction medium which consisted of Chée and Pool medium containing 2.0 mg l–1 2,4-dichlorophenoxyacetic acid (2,4-D) and 2.5 mg l–1 thidiazuron (TDZ), produced primary nodular and greenish calli within 6 – 8 weeks. Periodic transfer of nodular calli on induction medium in the dark induced the formation of compact embryogenic masses after 4 – 5 months of cultivation, with induction rates of 58.97 ± 1.10% and 61.15 ± 1.16% for ‘Moore’ and ‘Gialla’, respectively. Various distinct stages were observed during the development of somatic embryos on induction medium, including pro-embryogenic, globular, heart-, torpedo-, and cotyledonary-shaped somatic embryos, as well as secondary somatic embryos. Further development of somatic embryos was accomplished using half-strength Murashige and Skoog medium containing 1% (w/v) activated charcoal under a 16-h photoperiod. Bipolarity of the somatic embryos was confirmed by environmental scanning electron microscopy. Regenerated plantlets with well-developed cladodes and roots were transferred to a greenhouse and acclimatised successfully.

Conservation priorities for endangered coastal North African Pennisetum glaucum L. landrace populations as inferred from phylogenetic considerations and population structure analysis

The increasing anthropologic pressure and the modernization of agriculture have led to a forsaking of pearl millet traditional cultivars, inducing a progressive loss of the genetic variability encompassed in this locally adapted germplasm. Imperatively, national efforts based on robust data gleaned from genetic surveys have to be undertaken in order to set up suitable conservation priorities. In this study, in addition to the assessment of the genetic diversity and population structure among and within a set of seven pearl millet landrace populations from coastal North Africa, demographic and phylogenetic data, conservation priority scores were calculated according to Vane-Wright et al. (1991). To date, genetic diversity of pearl millet in North Africa is still poorly documented. The present survey reports for the first time the use of highly informative nSSR markers (PIC = 0.74) on Pennisetum glaucum landraces representative of the Mediterranean coastline of North Africa. A high level of genetic diversity was obtained within the investigated landraces (He = 0.80) at the population level. FST, AFC-3D, and Bayesian clustering underlined significant differentiation and an apparent genetic structure, according to geographical origin. Phylogenetic considerations integrated with demographic and genetic information enabled conclusive inferences of highly prioritized populations for conservation. Populations Haouaria, Hammem Laghzez, Mahdia, and Medenine, representatives of the main pearl millet growing areas in Tunisia and cultivated in the North African littoral, should be strongly recommended for an ex situ conservation program. Dynamic on-farm conservation method is also required as it allows the local landraces to evolve in different environments, while maintaining their adaptation potentials.