Environmental stresses (salinity, drought, heat/ cold, light and other hostile conditions) may trigger in plants oxidative stress, generating the formation of reactive oxygen species (ROS). These species are partially reduced or activated derivatives of oxygen, comprising both free radical ðO ÁÀ 2 ; OHÁ; OH 2 ÁÞ and non-radical (H 2 O 2 ) forms, leading to cellular damage, metabolic disorders and senescence processes. In order to overcome oxidative stress, plants have developed two main antioxidants defense mechanisms that can be classified as non-enzymatic and enzymatic systems. The first class (non-enzymatic) consists of small molecules such as vitamin (A, C and E), glutathione, carotenoids and phenolics that can react directly with the ROS by scavenging them. Second class is represented by enzymes among them superoxide dismutase, peroxidase and catalase which have the capacity to eliminate superoxide and hydrogen peroxide. In this review, we have tried to explore the related works, which have revealed the changes in the basic antioxidant metabolism of plants under various abiotic constraints.

Effect of some growth regulators on some fruit characteristics and productivity of the Barhee date palm tree cultivar (Phoenix dactylifera L.).Abstract -Introduction. The date palm tree is one of the fruit trees most cultivated in the Arabian Gulf States. Bioregulators were used for the quality and productivity improvement of date palm tree fruits. A study was conducted to assess the relative effectiveness of GA 3 , NAA, ethephon and a mixture of growth regulators on some fruit characteristics and productivity of the Barhee date palm tree cultivar. Materials and methods. Five selected female uniform date palm trees of the cultivar Barhee were pollinated on March 5-15, 1994March 5-15, , 1995March 5-15, and 1996 placing eight fresh male strands on the female spadix center (flower cluster).Ten flower clusters were used on each tree and divided into five groups of two flower clusters. Each of these groups was subjected to one of the following treatments: control (water), 150 mg GA 3 × L -1 , 100 mg NAA × L -1 , 1 000 mg ethephon × L -1 and a mixture of these three growth regulators. Then the fruit setting, fruit flesh and dry matter percentages, the total soluble solids, the fruit ripening, and the fruit weight per bunch and per tree were measured. Results and discussion. The data showed that the application of GA 3 or ethephon on flower clusters of Barhee date palm trees had no constant effect on fruit characteristics and productivity of trees. NAA or growth regulator mixture applications on Barhee flower clusters reduced the fruit dry matter and fruit ripening percentages and increased the fruit weight per bunch and per tree. Conclusion. Treatments of Barhee date palm flower clusters, 20 d after pollination, with NAA or the specific growth regulator mixture decreased the dry matter percentage and the fruit ripening and increased the fruit flesh percentage and the date palm tree yield, therefore, these treatments could be recommended to improve the productivity of date palm trees in the region. Gulf States / Phoenix dactylifera / plant growth substances / spraying / nutrient improvement / crop yield Effet de quelques régulateurs de croissance sur certaines caractéristiques de production du cultivar Barhee de palmier dattier (Phoenix dactylifera L.).Effect of regulators on the Barhee date palm tree 325

This study was carried out during three successive seasons 2011, 2012 and 2013 at a private orchard located in Al-Hello in Ajman Emirate (UAE). The experiment was designed to study the effect of organic manure and NPKS as soil application on yield, fruit quality, and fruit mineral nutrient content of Khenazi date palm cultivar grown in sandy soil. Fertilization treatments consisted of N1, 600g or N2, 1000g (urea 46%N), P 800g (triple superphosphate, 48% P2O5), K 1200g (potassium sulphate, 50% K2SO4) and S 700g sulphur (90% granular S), in addition to organic manure. Al experimental trees received 100g mixture of micronutrients, with the exception of the control. The results showed that combination treatments and organic manure significantly affected fruit weight, flesh weight, fruit volume, moisture content and fruit TSS. Application of different fertilization treatments significantly affected yield components of fruit, number of fruits/strand, fruit number/bunch, fruit set percent and total fruit yield / palm. The study revealed that combination of fertilizers improved fruit nutrient content of N, P, K, Ca, Mg, Fe, Zn, Mn and Cu. Moisture and TSS% content, number of fruits/strand, number of fruits/bunch, fruit nutrients content of Fe, Mn and Zn were significantly different due to the application of N1+K+S.

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Date palm trees are among the most plentiful fruit trees in the Arabian Gulf States. Bioregulators have been used for the improvement of quality and productivity of date plam tree fruits. Application of gibberellic acid (GA3), naphthalene acetic acid (NAA), and ethephon, separately or in a mixture, has significant effects on fruit set, fruit dry matter percentage, fruit soluble percentage, fruit ripening, and yield of date palm trees. A study was conducted to assess relative effectiveness of GA3, NAA, ethephon, and a mixture of growth regulators on some fruit characteristics, and productivity of `Barhee' date plam trees. Five uniform female `Barhee' date palm trees were pollinated on 5–15 Mar. 1994, 1995, and 1996 by placing eight fresh male strands on female spadix centers (flower cluster). Ten flower clusters were used on each tree, and every two flower clusters were subjected to one of the following treatments: control (water), 150 mg·L–1 GA3, 100 mg·L–1 NAA, 1000 mg·L–1 ethephon, and a mixture of growth regulators. The fruit set (%), dry matter (%), total soluble solids (°Brix), fruit ripening (%), and fruit weight (kg per bunch and per tree) were measured. The data showed that the application of GA3 or ethephon on flower clusters of `Barhee' date palm trees had no constant effect on fruit characteristics and productivity of trees. NAA or a mixture of growth regulators reduced fruit dry matter percentage, fruit ripening percentage, and increased fruit weight per bunch and per tree. Spraying `Barhee' date palm flower clusters with NAA or a mixture of growth regulators 20 days after pollination decreased dry matter percentage, fruit ripening, and increased fruit flesh percentage and tree yield.