Boron stress is an environmental factor affecting plant development and production. Recently, microRNAs (miRNAs) have been found to be involved in several plant processes such as growth regulation and stress responses. In this study, miRNAs associated with boron stress were identified and characterized in barley. miRNA profiles were also comparatively analyzed between root and leave samples. A total of 31 known and 3 new miRNAs were identified in barley; 25 of them were found to respond to boron treatment. Several miRNAs were expressed in a tissue specific manner; for example, miR156d, miR171a, miR397, and miR444a were only detected in leaves. Additionally, a total of 934 barley transcripts were found to be specifically targeted and degraded by miRNAs. In silico analysis of miRNA target genes demonstrated that many miRNA targets are conserved transcription factors such as Squamosa promoter-binding protein, Auxin response factor (ARF), and the MYB transcription factor family. A majority of these targets were responsible for plant growth and response to environmental changes. We also propose that some of the miRNAs in barley such as miRNA408 might play critical roles against boron exposure. In conclusion, barley may use several pathways and cellular processes targeted by miRNAs to cope with boron stress.

-This study reports measurements of stomatal conductance, relative water content and water potential (Ψ L ) from three dominant evergreens (Ceratonia siliqua L., Quercus coccifera L. and Olea oleaster Hoffmgg. et Link) growing in four coastal sites of Turkey. In particular, a fully vegetated site (H) was selected and compared for the above parameters to three degraded sites (D1, D2 and D3) with decreasing vegetation covers. From the integral of the diurnal time course of Ψ L , the water stress impact on each species (WSIS) was calculated. C. siliqua and Q. coccifera showed similar WSIS's, increasing significantly from H to D3. O. oleaster was sensitive both to summer drought and to increasing site degradation. The impact of water stress was scaled up from the species to the vegetation level (WSIV) as WSIV = Σ WSIS S (1-f s ) where f s was the relative frequency of the species studied. WSIV was rather sensitive to the impoverishment of vegetation and was correlated to vegetation density as estimated both by field observations and remotely sensed Normalized Difference Vegetation Index. desertification / leaf water potential / Mediterranean evergreens / Normalized Difference Vegetation Index / water stress impact Résumé -Diagnostiquer l'état de l'eau dans la plante : un outil pour quantifier le stress hydrique au niveau régional dans les régions sèches méditerranéennes. Cette étude rapporte les mesures de conductance stomatique, de la teneur relative en eau et du potentiel hydrique (Ψ L ) d'arbres à feuilles persistantes (Ceratonia siliqua L., Quercus coccifera L. et Olea oleaster Hoffmgg. Et Link) croissant sur 4 sites côtiers de Turquie. En particulier, un site totalement recouvert de végétation (H) a été sélectionné et comparé, pour les paramètres ci-dessus, à 3 sites dégradés (D1, D2 et D3) ayant une couverture végétale de plus en plus faible. A partir de l'intégrale de Ψ L , pour le cycle diurne, l'impact du stress hydrique de chaque espèce (WSIS) a été calculé. C. siliqua et Q. coccifera montrent des WSIS similaires, augmentant significativement de H à D3. O. oleoaster a été sensible à la fois à la sécheresse estivale et à l'accroissement de la dégradation du site. Un changement d'échelle, du niveau de l'espèce à celui de la végétation, a été réalisé pour l'impact du stress hydrique (WSIV) par la transformation WSIV = Σ WSISs (1-f s ) ou f s est la fréquence relative de l'espèce étudiée. WSIV est particulièrement sensible à l'appauvrissement de la végétation et est corrélé à la densité de la végétation estimée à la fois par des observations aux champs et par l'indice normalisé de différentiation de la végétation par observation satellitaire. désertification / potentiel hydrique des feuilles / arbre à feuilles persistantes méditerranéen / index normalisé de différentia-tion des espèces / impact du stress hydrique Ann. For. Sci. 58 (2001) 113-125 113

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Boron is found naturally in the earth's crust in the oxidized form as borax and colemanite, particularly in the oceans, sedimentary rocks, coal, shale, and some soils. It is never found in the elemental form in nature possessing a complex chemistry similar to that of silicon, with properties switching between metals and non-metals. Boron has become an important and strategic element in terms of developing technologies. It is released into the environment mainly through the weathering of rocks, volatilization from oceans, geothermal steam, burning of agricultural refuse and fuel wood, power generators (coal/oil combustion), glass industry, household use of boron-containing products (including soaps and detergents), borax mining and processing, leaching from treated wood and paper, chemical plants, and sewage/sludge disposal, but a major proportion originates from the weathering of rocks. Boron is regarded as an essential element for human beings, animals and plants. Boron occurs in soils at concentrations ranging from 10 to 300 mg kg −1 depending on the type of soil, amount of organic matter, and amount of rainfall. The treatments lead to significant increases in the productivity of some plants but in certain cases a decrease is seen as the boron level increases with the boron content of irrigation water, in particular on the soils with a heavy texture, high CaCO 3 and clay content. Lack of boron in plants results in necrosis but excess amounts are said to produce poisonous effects. Turkey produces more than 60% of the world's borax, with important boron reserves located in Susurluk, Bigadic and Sindirgi regions of Balikesir, Kestelek-Bursa, Emet-Kutahya, the largest reserves occur in Kirka-Eskisehir. Therefore, there is a naturally occurring high level of boron in the ground waters in some of these areas due to the excess amounts of boron given out to the environment during washing and purification processes which result in the pollution of cultivated areas. An attempt will be made here to present an overview of the plant diversity on the boron contaminated soils in Turkey, effects of different concentrations of boron on the germination ability of some plants and possible candidates for phytomining of the soils showing boron toxicity symptoms.

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