Effect of ABA,arginine and sucrose on protein content of date palm somatic embryos

Abscisic acid (ABA), arginine and sucrose were evaluated for their effects on the morphology, germination rates and protein content of date palm somatic embryos (SE). Different concentrations of these supplements in the culture medium were used. The comparative study of SE length and thickness between treated and untreated SE revealed no differences, except for ABA (20 μM), which increased thickness. A decrease of water content (WC) in favor of an increase in dry weight (DW) was observed in all treated SE, especially with sucrose (90 g l⁻¹) and ABA (20 μM). Only ABA (20 and 4 μM) caused a proliferation rate of the cultures higher than those in the control. Although all the tested compounds increased protein content, ABA (20 μM) was more effective in protein enrichment than arginine and sucrose treatments. The SDS-PAGE protein profiles showed a significant difference between treated and untreated SE. A protein band of 22 kDa, identified as glutelin in a previous work, was accumulated after treatment with 20 μM ABA or 3 mM arginine. These findings may contribute to further understanding of the mechanisms involved in the accumulation of specific storage proteins in several plants.     

Comparative effect of drought duration on growth,photosynthesis, water relations,and solute accumulation in wild and cultivated barley species

Drought is a major factor limiting crop production worldwide. Barley is a well‐adapted cereal that is largely grown on dry marginal land where water and salinity are the most prevalent environmental stresses. This study was carried out to investigate the effects of drought stress and subsequent recovery on growth, photosynthetic activity, water relations, osmotic adjustment (OA), and solute accumulation of wild (Hordeum maritimum) and cultivated barley (H. vulgare L.). In a pot experiment, 60 d old seedlings were subjected to drought stress for 0, 7, 14, 21, or 28 d, and then re‐watered to recover for up to 21 d. Plants were harvested at the end of each of these drought/recovery treatments. Drought significantly reduced fresh and dry weights at the whole‐plant level, photosynthetic activities, and solute and water potentials, while increasing leaf Na⁺ and K⁺ concentrations. The adverse effects of drought on growth were more marked in cultivated barley than in wild barley and the reverse was true for photosynthetic activities. During recovery, all wild barley seedlings completely recovered. For cultivated barley seedlings, rehydration had a beneficial effect on growth and photosynthesis, independent of treatment duration, but complete recovery did not occur. The reduction in leaf solute potential at full turgor in drought‐stressed barley, relative to the control, suggests active OA which was more significant in wild barley than in cultivated barley. OA was mainly due to the accumulation of inorganic (K⁺ in cultivated barley and Na⁺ in wild barley) and organic (soluble sugars and proline) solutes. The results suggest that OA is an important component of the drought‐stress adaptation mechanism in wild barley, but is not sufficient to contribute to drought tolerance in cultivated barley. In the latter species, the results show that even short periods (as little as 7 d) of water deficit stress had considerable long‐term effects on plant growth.     

Development of zygotic and somatic embryos of Phoenix dactylifera L. cv. Deglet Nour: Comparative study

In order to improve somatic embryogenesis production in date palm Phoenix dactilyfera L. cv. Deglet Nour (DN), a comparative study between somatic (SE) and zygotic (ZE) embryos developments was carried out. The data showed that ZE maturation occurred from 10 to 19 weeks after pollination (WAP). During this period, the fresh weight (FW) and the dry weight (DW) of ZE increased progressively to reach a maximum level at 19 WAP. SE development occurred in three distinct stages. The DW remained constant during the two first stages, and declined slightly during the third and final stage. Embryo protein analysis revealed significant differences between ZE and SE. The ZE total protein level was initially low and increased to the maximum at mature stage. However, no significant change in total protein was detected during SE development. SDS-PAGE analysis showed a poor protein profile for SE, compared to that of ZE. In the latter, a 22 kDa protein was identified by N-terminal sequencing as a glutelin. This protein was accumulated rapidly during early development and remained at a relatively constant level during ZE development, and then declined progressively 12 days after embryo germination (DG). This protein seems to be absent in SE.     

Contribution to the improvement of olive tree somatic embryogenesis by mineral and organic analysis of zygotic embryos

Summary In the last decade, little research has been done to introduce biotechnology methods for the propagation of this species, and especially through somatic embryogenesis. In fact, this technique has proved to be a very efficient tool for both multiplication and breeding.For some refractory species, somatic embryogenesis was possible only after the determination of the composition of the zygotic embryos at different development stages. This may also be possible for the olive tree because of the recalcitrance of different types of olive tree tissues for embryogenesis. In this study, we aimed to determine the content of macro, microelements (Mg, K, P, Ca, N, Na, Mn and Fe) and some organic compounds (sucrose and proteins) during three stages of seeds development: just in the beginning of their growth (April), at their differentiation stage (July) and at their maturation stage (October) and this for two local cultivars Chemlali of Sfax and Meski.Our results revealed that in the beginning of the embryo development of the two cultivars, all mineral elements are at their highest levels exceptionally for P and Na. Besides, the differentiation stage is characterised by a marked decrease notably in K, N, Mg, Ca, Mn, Fe levels and an increase in Na element. The maturation stage shows also low levels of macro and micronutrients except P and Na whose levels were relatively higher.On the other hand, the analysis of the protein levels of Chemlali and Meski showed that the maximum concentrations were obtained in July.As for the sucrose contents, the highest levels were observed in the beginning for both Chemlali and Meski and showed a marked decrease at the maturation phase.     

First reported case of spontaneous hermaphrodism in female date palm (Phoenix dactylifera L.), cv ‘Alligue’

The date palm (Phoenix dactylifera L.) is dioecious with male flowers deficient in functional gynoecium and female flowers deficient in functional androecium borne on separate palms. The presence of male and female flowers on the same plant, a phenomenon known as monoecy, is unusual in male date palms.

This study reports for the first time on hermaphrodite (bisexual) flowers borne by two female date palms, ‘Alligue’, that were found growing in an open field in Degache, southern Tunisia. The observations on these two female palms were compared with hermaphrodite male date palms growing in the same location. Hermaphrodite female date palm inflorescence branches bear female flowers predominantly near their base, in contrast to the hermaphrodite flowers that are found primarily toward their upper part. The position of the hermaphrodite flowers in hermaphrodite male date palms is reversed: inflorescence branches bear male flowers toward the upper part while the hermaphrodite flowers are found at the base. Histological examination of female hermaphrodite flowers revealed that they had three carpels and 1–6 stamens. Hermaphrodite flowers on male plants were usually also composed of three carpels of variable size, and six stamens. Hermaphrodite flowers on both female and male palm trees turn generally into parthenocarpic fruits. The present data support the theory that dioecious plants are derived from a common hermaphrodite ancestor. Floral hermaphroditism in date palm should be investigated in relation to the in planta self-fertilization process to identify sex markers and genes that control sex organ development.     

Molecular and Structural Characterizations of Lipases from Chlorella by Functional Genomics

Microalgae have been poorly investigated for new-lipolytic enzymes of biotechnological interest. In silico study combining analysis of sequences homologies and bioinformatic tools allowed the identification and preliminary characterization of 14 putative lipases expressed by Chlorella vulagaris. These proteins have different molecular weights, subcellular localizations, low instability index range and at least 40% of sequence identity with other microalgal lipases. Sequence comparison indicated that the catalytic triad corresponded to residues Ser, Asp and His, with the nucleophilic residue Ser positioned within the consensus GXSXG pentapeptide. 3D models were generated using different approaches and templates and demonstrated that these putative enzymes share a similar core with common α/β hydrolases fold belonging to family 3 lipases and class GX. Six lipases were predicted to have a transmembrane domain and a lysosomal acid lipase was identified. A similar mammalian enzyme plays an important role in breaking down cholesteryl esters and triglycerides and its deficiency causes serious digestive problems in human. More structural insight would provide important information on the enzyme characteristics.