Shoot and root morphogenesis from Eucalyptus grandis x urophylla callus

Eucalyptus grandis x urophylla plantlets were regenerated via indirect organogenesis. Histological assessment of their development focused on identifying the calli, the differentiation of shoots from the calli and the  shoot-root junction from the nascent shoots. Vascular tissue formation within the callus preceded that of  organised nodular structures, from which adventitious shoots were ultimately formed. Vascular systems  linked the nodular structures and their associated cambial meristems, observed at 15 to 22 days, were  hypothesized as being the centres of differentiation for shoot formation. Roots developed from isolated  adventitious shoots from either the callus created as a wounding response to isolation or from a region of the  stem immediately above the callus. Roots developed from the latter had integrated root and shoot vascular  systems, whereas those originating from the callus were not connected vascularly; however, this connection could be created during ex vitro acclimatization. The implications of the findings for increased plant yields  through indirect morphogenesis were discussed.Key words: Eucalyptus, indirect organogenesis, microscopy

In vitro cryopreservation of date palm caulogenic meristems

Cryopreservation is the technology of choice not only for plant genetic resource preservation but also for virus eradication and for the efficient management of large-scale micropropagation. In this chapter, we describe three cryopreservation protocols (standard vitrification, droplet vitrification, and encapsulation vitrification) for date palm highly proliferating meristems that are initiated from vitro-cultures using plant growth regulator-free MS medium. The positive impact of sucrose preculture and cold hardening treatments on survival rates is significant. Regeneration rates obtained with standard vitrification, encapsulation-vitrification, and droplet-vitrification protocols can reach 30, 40, and 70%, respectively. All regenerated plants from non-cryopreserved or cryopreserved explants don't show morphological variation by maintaining genetic integrity without adverse effect of cryogenic treatment. Cryopreservation of date palm vitro-cultures enables commercial tissue culture laboratories to move to large-scale propagation from cryopreserved cell lines producing true-to-type plants after clonal field-testing trials. When comparing the cost of cryostorage and in-field conservation of date palm cultivars, tissue cryopreservation is the most cost-effective. Moreover, many of the risks linked to field conservation like erosion due to climatic, edaphic, and phytopathologic constraints are circumvented. (Résumé d'auteur

Cryopreservation as a tool for the conservation of Eucalyptus genetic variability: concepts and challenges

An essential criterion of Eucalyptus tree breeding programmes employed by the commercial forestry sector is the maintenance of potentially  important species and genotypes for periods commensurate with field testing. Current methods for this purpose include conservation stands, clonal hedges and maintenance of cuttings in greenhouses and hydroponic systems. However, these methods, especially the maintenance of conservation stands and clonal hedges, require large tracts of land, which are now unavailable. The latter methods also have other disadvantages in that they are labour intensive and may be expensive to maintain. The conservation method of cryopreservation (the maintenance of plant cells, tissues and organs at subzero temperatures) may offer a cost-effective alternative with significant benefits, including the maintenance of plant material for theoretically  unlimited periods. This field of science has experienced significant breakthroughs in the last two decades, especially in terms of the understanding of the physical, chemical and biological processes that occur during the freeze–thaw cycles. Consequently, several effective mechanisms of reducing the risk of ice crystal damage have been developed, resulting in the successful cryopreservation of numerous wild and domesticated plant species. Apart from germplasm conservation, cryopreservation may also be employed as a means of maintaining genetically engineered transformants while field testing is conducted. This is particularly advantageous considering the large numbers of transformants that can be generated during genetic engineering trials. Cryopreservation should, therefore, be considered a potentially important tool in commercial breeding strategies. This paper details the benefits and advantages of the technology, and also identifies and explains some of the key challenges that still exist, especially those associated with the cryopreservation of highly hydrated and/or desiccation-sensitive material such as Eucalyptus axillary buds. Southern Forests 2009, 71(2): 165–17

Desiccation-induced loss of seed viability is associated with a 10-fold increase in CO2 evolution in seeds of the rare tropical rainforest tree Idiospermum australiense

• Here the relationship was investigated between metabolic activity, state of hydration and seed viability in the desiccation-intolerant (recalcitrant) seeds of Idiospermum australiense, a rare and primitive angiosperm tree restricted to wet tropical forest. • Seed CO2 evolution rate, R, was monitored in fully hydrated (control) seeds and seeds that were allowed to desiccate under ambient conditions over a period of c. 90 d. • During desiccation R increased dramatically toward a peak at a seed relative water content of 39 ± 3% (relative to maximum water content, which corresponded to 0.45 ± 0.03 g water g-1 d. wt) followed by a decline toward zero with total desiccation. This peak constituted a 10-fold increase in mean R, relative to the control. Exposing seeds to O2-free air at this peak induced a further large, but transient, increase in CO2 evolution, indicating that the peak developed in the presence of oxidative phosphorylation, rather than due to the absence of it. • The magnitude and mode of the observed increase in CO2 evolution in response to desiccation is unlike any reported so far and thus adds new information about metabolic changes that may occur as the water content of desiccation-intolerant seeds declines