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Accueil du site → Doctorat → Israel → Physiological and molecular regulation of the annual flowering cycle in Ziziphus jujuba

Ben Gurion University of the Negev (2014)

Physiological and molecular regulation of the annual flowering cycle in Ziziphus jujuba

Meir, Michal

Titre : Physiological and molecular regulation of the annual flowering cycle in Ziziphus jujuba

Auteur : Meir, Michal

Université de soutenance : Ben Gurion University of the Negev

Grade : Doctor of Philosophy (PhD) 2014

Résumé partiel
Ziziphus jujuba Mill. (Rhamnaceae), known as the Chinese date or jujube, is a deciduous fruit tree, native to China and adapted to extreme temperatures and arid conditions, which makes it a good candidate as a fruit crop for the Negev Highlands. Z. jujuba is a multipurpose tree known for its edible fruit with a nutritional, as well as a medicinal, value ; it is also used for the production of wood, as an ornamental tree and as forage for honey production. According to the literature, Z. jujuba grows in various types of soils and is resistant to both alkalinity and salinity. Z. jujuba sheds all its leaves in the winter and enters dormancy until the spring, when new branches, bearing leaves and flowers, develop. Blooming occurs during the spring, and the fruit ripens during the summer. The flowers of the Ziziphus species exhibit “synchronous protandrous dichogamy”, i.e., the flowers of an individual plant mature in synchrony, and anther dehiscence precedes stigma receptivity, with little or no overlap between the male and female stages, also referred to as “temporal dioecism”. Flower opening in Ziziphus was also associated with herkogamy (segregation of sex organs in space), i.e., stamens diverging out, at the end of the male stage, in parallel to stigma elongation. Ziziphus species, including Z. jujuba, can be divided into three groups, according to the timing of anthesis onset, i.e., early morning (06:00- 08:00), late morning (08:00-10:00) and afternoon (12:00-14:00), thus enabling pollination between trees of different groups. The main goal of this research was to study environmental, physiological and molecular factors regulating the annual and diurnal flowering cycle of Z. jujuba trees. The specific objectives included : 1. Characterization of dormancy, dormancy release and factors inducing dormancy release. 2. Isolation of ZjLFY and ZjAP1 and analysis of their expression pattern in relation to the transition from dormancy to vegetative growth and flowering. 3. Assessment of the effect of photoperiod on the protandrous dichogamy synchrony daily cycling. 4. Analysis of the correlations between toxic mineral concentrations in the tissues and tree growth and flowering. Four Z. jujuba cultivars, Tamar, Lang, Ben-Li and Li, were used. The trees were either threeyear-olds, grown in an experimental plot in Sede Boqer, or 1-3 year-olds, grown in 10 L pots 5 under greenhouse conditions. In addition, detached lateral branches were also studied, in order to test whether this plant material can be used for future studies as a substitute for whole trees. My main hypothesis was that the transition from dormancy to vegetative growth and flowering is determined by environmental conditions and by changes in the expression of genes related to flower induction and/or flower development. Dormancy was evaluated by the determination of Z. jujuba’s chilling requirement under natural conditions, using detached branches, or by using trees grown under monitored cooling conditions, in comparison to trees that were deprived of exposure to low temperatures during the entire year. Trees were exposed to low temperatures (4°C or 10°C) and to optimal growth conditions [26/21°C (day/night) cycle and 14h/10h (light/dark)], in order to test the effect of chilling on dormancy release. The results indicate that chilling is not obligatory for dormancy release in Z. jujuba. Trees deprived of chilling conditions during two consecutive years broke dormancy similarly to trees grown under natural growth conditions. On the other hand, exposure to low temperatures did have an effect on the timing of dormancy release. Trees exposed to chilling broke dormancy significantly earlier in comparison to trees under control conditions [26/21°C (day/night) cycle and 14h/10h (light/dark)]. Experiments conducted on detached branches showed similar results, although the act of detaching a branch from the tree had an effect on dormancy release. Since detached branches never developed full flowers, for future studies related to flowering in Z. jujuba, it is recommended to use whole trees.

Mots clés : Jujube (Plant) — Flowering ; Plants, Flowering of — Flowering time — Experiments

Présentation (BGU)

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