Comparative impacts of water stress on the leaf anatomy of a drought-resistant and a drought-sensitive olive cultivar

The effects of drought on several major morphological and anatomical features of leaves were investigated in an attempt to explain the origin of the difference in drought resistance between two olive (Olea europaea L.) cultivars, ('Chemlali' and 'Meski') previously demonstrated to be drought-resistant and drought-sensitive, respectively. Under water deficit conditions, 'Chemlali' maintained higher rates of photosynthetic assimilation and lower rates of transpiration compared to 'Meski'. In the present study, we found cultivar-dependent differences in leaf morpho-anatomical adaptations to drought stress. When subjected to water stress, the leaves of 'Chemlali' increased the thickness of their upper palisade and spongy parenchyma by 17% and 22%, respectively, compared with only 9% and 13% in the case of 'Meski'. A thicker palisade parenchyma could contain larger numbers of CO(2)-fixation sites, while a thicker spongy parenchyma could result in easier diffusion of CO(2) to these sites. Furthermore, stomatal density (SD) in 'Chemlali' leaves increased by 25% (vs. 7% for 'Meski' leaves) during drought treatment, which could also enhance the external supply of CO(2). Other morpho-structural traits implicated in the control of water loss were enhanced more in 'Chemlali' than in 'Meski' leaves. Under conditions of lower water availability, leaf size decreased by 24% in 'Chemlali' (vs. 15% in 'Meski'), trichome density (TD) increased by 25% (while remaining unchanged in 'Meski'), and the thickness of the upper and lower epidermis increased by 32% and 25%, respectively (while remaining unchanged in 'Meski'). The above morpho-anatomical adaptations should improve the water-use efficiency of the tree. These differential changes in leaf morphology and anatomy can explain, at least in part, the difference in drought resistance between the two cultivars. In particular, the upper palisade parenchyma, the spongy parenchyma, SD, and TD could be considered key structural features of leaves that govern the ability of a tree to withstand water stress. They could therefore be used as criteria to select olive cultivars that are more resistant to drought

Water relations and drought-induced embolism in olive (Olea europaea) varieties 'Meski' and 'Chemlali' during severe drought

We examined the effects of drought on the water relations, osmotic adjustment and xylem vulnerability to embolism of olive (Olea europaea L.) varieties, 'Meski' and 'Chemlali'. Two-year-old self-rooted cuttings growing in sand-filled pots in a greenhouse were subjected to water stress by withholding water for 60 days. Water relations and gas exchange measurements showed that 'Chemlali' was more drought resistant than 'Meski' and had a greater capacity for osmotic adjustment through solute accumulation. However, when water stress was acute, the effect of osmoregulation on leaf cell turgor was largely counteracted by xylem cavitation. Cavitation vulnerability curves showed that both varieties were highly resistant to embolism formation. The xylem water potential inducing 50% loss of stem conductivity approached -7 MPa in 'Meski' and only slightly less in 'Chemlali'. Although the difference between varieties in susceptibility to xylem embolism was small, it appears to account in large part for the difference between them in the ability to tolerate severe drought

Salt-induced oxidative stress in rosemary plants:Damage or protection?

Mechanisms of photoprotection and antioxidant protection, including changes in chlorophylls, xanthophyll cycle components and levels of low-molecular-weight chloroplastic antioxidants (lutein, beta-carotene and alpha-tocopherol) were studied together with levels of malondialdehyde, a product of lipid peroxidation, in the response of rosemary (Rosmarinus officinalis L) plants to salt stress. Plants were exposed to increasing NaCl concentrations (50, 100 and 150 mM) for 6 weeks, and two concentrations of the following chloride salts: KCl, CaCl(2), MgCl(2) and FeCl(3), were used together with 100 mM NaCl to explore the extent to which these salts can alter the mechanisms of photoprotection, antioxidant protection and malondialdehyde accumulation in leaves. Increasing concentrations of NaCl decreased leaf water contents and photosynthetic pigment levels, while the contents of alpha-tocopherol and malondialdehyde increased. but with completely different kinetics. alpha-Tocopherol levels increased in a dose-dependent manner as stress progressed, while malondialdehyde levels increased at the highest dose (150 mM NaCl) but only during early phases of stress. Furthermore, although the addition of chloride salts to NaCl-treated plants apparently improved leaf physiological status, in terms of water and chlorophyll contents, plants showed an increased photoprotective demand and increased oxidative stress, particularly in FeCl(3)-treated plants. It is concluded that (i) rosemary plants can withstand moderate doses of NaCl in the medium (at least 150 mM NaCl for 6 weeks), (ii) oxidative stress may be a mechanism for protecting plants from moderate doses of salt stress rather than causing damage to plants, and (iii) the addition of chloride salts to NaCl-treated plants may dramatically increase the photoprotective demand and oxidative stress of leaves, while plant growth is not negatively affected. (C) 2010 Elsevier B.V. All rights reserved

First Report of in vitro Biological Agent to Biocontrol of Date Palm Stipe Rot Affected by Fusarium brachygibbosum by Using Pergularia tomentosa L., Aqueous Extract

Palm (Phoenix dactylifera L.) is a specie cultivated in Mauritania. The present study is focus on the potential of the aqueous extract of the Pergularia tomentosa L., as biological control agent against Fusarium brachygibbosum, the main agent of the date palm stipe rot disease in Mauritania. Fungal pathogen was isolated from symptomatic date palm stipe rot disease in Mauritania. The morphological characterization and the molecular identification by sequencing ITS1, ITS2 5.8 RNAr region showed homology of 98% with Fusarium brachygibbosum strain UOA/HCPF 16982 s during in vitro tests on leaves performed to verify its phytopathogenicity. the inhibitory effect of aqueous extract of Pergularia tomentosa L. on the phytopathogenic isolate (Fusarium brachygibbosum) of date palm, on mycelial growth and spore germination was observed. In fact, in vitro on PDA, mycelial growth ranged from 39.23 to 67.7 %, depending on the concentration of the aqueous extract of P. tomentosa. The aqueous extract showed a reduction of spore germination varying from 5.3 to 23.8 %. The minimum inhibitory concentrations varied from 1 to 100 mg/ml. the various extracts give high antioxidant activities exhibited by DPPH assay. Multivariant analysis by PCA plot and the heatmap were done, to evaluate the correlation between the tested parameters. These results suggest the use of Pergularia tomentosa L., extract as a biological agent to control and reduce damage caused by Fusarium brachygibbosum