Physiological and biochemical changes with special reference to mangiferin and oxidative enzymes level in malformation resistant and susceptible cultivars of mango (Mangifera indica L.)

Changes in biophysical attributes, mangiferin and polyphenol oxidase (PPO), catalase and peroxidase activities in malformation resistant mango cultivar Elaichi were studied at various stages of flower development and compared with susceptible cvs. Amrapali, Beauty Mc-lin and Dashehari. Accumulation of mangiferin was maximum (96.0 and 108.0 mg g⁻¹ FW) in Elaichi prior to flower bud differentiation (September) and at full bloom (February), while these were minimum (59.0 and 74.0 mg g⁻¹ FW) in susceptible cv. Beauty Mc-lin. Mangiferin promoted vegetative growth and exhibited inhibitory role on the occurrence of malformation. It was also found that the resistant cultivar had highest activity of PPO as compared to susceptible ones. There was no significant difference in the enzymes catalase and peroxidase activity at early stage of flower differentiation but at flower bud burst stage the catalase activity was enhanced significantly in cv. Elaichi (25.28 unit min⁻¹ g⁻¹ FW) in comparison to Amrapali (16.20 unit min⁻¹ g⁻¹ FW), Beauty Mc-lin (18.39 unit min⁻¹ g⁻¹ FW) and Dashehari (17.50 unit min⁻¹ g⁻¹ FW). The resistant cultivar had high leaf temperature (30.30 °C) and diffusion resistance (476.14 m mol m⁻² s⁻¹) during the flowering but the rate of transpiration and relative humidity (RH) were high in susceptible cultivars. Results of the present study clearly indicate that level of mangiferin could be considered as a potential biochemical indicator for screening mango genotypes to malformation.     

Rootstock influences the response of pistachio (Pistacia vera L. cv. Kerman) to water stress and rehydration

Pistachio cultivation requires the use of rootstock because grafting is the only form of vegetative propagation. The main commercial rootstocks are Pistacia integerrima L., Pistacia atlantica Desf., Pistacia terebinthus L. and Pistacia vera L. Pistachio is considered to be a drought and saline-resistant crop; however, there is little information describing varietal responses of rootstocks to water stress. Some studies have suggested that P. terebinthus L. is the most drought and cold resistant rootstock. The effect of the rootstock on the water relations of the grafted plant is crucial for improving crop performance under water stress conditions and for developing the best irrigation strategy. This work studied the physiological response to water stress of pistachio plants (P. vera L. cv. Kerman) grafted onto three different rootstocks P. terebinthus L., P. atlantica Desf. and a hybrid from crossbreeding P. atlantica Desf. × P. vera L. Plant physiological responses were evaluated during a cycle of drought and subsequent recovery in potted plants. Parameters measured were soil moisture, trunk diameter, leaf area, leaf number, leaf and stem dry weight, stem water potential, leaf stomatal conductance. The results showed different responses of cv. Kerman depending on the rootstock onto which it had been grafted. The hybrid rootstock was associated with a higher degree of stomatal control and reduced leaf senescence compared to P. atlantica and P. terebinthus, despite being associated with the most vigorous shoot growth. P. terebinthus enabled very effective stomatal control but was also associated with the most rapid leaf senescence. P. atlantica was associated with less vigorous shoot growth and similar levels of water stress as occurred with the others rootstocks under conditions of high evaporative demand, which was associated with lower stomatal control. The selection of the most effective rootstock choice for different environmental conditions is discussed.     

ISSR polymorphism in Indian wild orange (Citrus indica Tanaka,Rutaceae) and related wild species in North-east India

Inter simple sequence repeats (ISSR) polymorphism in Citrus indica Tanaka (Rutaceae), an endemic and threatened wild species, was examined along with three other closely related wild taxa (C. medica L., C. latipes (Swingle) Tanaka, and C. sp. ‘Memang athur’) by analyzing 53 representative accessions sampled from North-east India. Jaccard's similarity values among 53 accessions of Citrus ranged from 0.46 to 0.97 (average = 0.75). Genetic similarity values among all the 34 accessions of C. indica were found in the range of 0.82 to 0.97 with an average of 0.90. Heterozygosity (Ht = 0.123) and Shannon's information index (I = 0.188) values estimated for C. indica revealed significantly low level of genetic variation within the species. UPGMA dendrogram grouped all 53 accessions of Citrus into four major clusters: Cluster I – C. latipes; Cluster II – C. medica; Cluster III – ‘Memang athur’ and Cluster IV – C. indica. The dendrogram placed all the 34 accessions of C. indica in five sub-clusters under Cluster IV. The placement of C. indica accessions in various sub-clusters and groups in the dendrogram was based on molecular differentiation of individual accessions rather than their geographical origin. Very low genetic diversity and destruction of its natural habitat pose serious threat to C. indica even in the Citrus Gene Sanctuary in Nokrek Biosphere Reserve (NBR) in Meghalaya. Low genetic variability, heterozygosity and Shannon's information index in C. medica, C. latipes and ‘Memang athur’ are also concerns that need to be addressed for developing appropriate strategies to conserve the genetic diversity extant in these valuable genetic resources.     

Impacts of water stress on gas exchange,water relations,chlorophyll content and leaf structure in the two main Tunisian olive (Olea europaea L.) cultivars

Leaf structural adaptations for the reduction of water loss were examined in two olive (Olea europaea L.) cultivars (Chemlali and Chétoui) growing under water stress conditions. Leaf measurements included leaf tissue thickness, stomatal density, trichome density, specific leaf area, leaf density, water relations, and gas exchange. We found considerable genotypic differences between the two cultivars. Chemlali exhibited more tolerance to water stress, with a thicker palisade parenchyma, and a higher stomatal and trichome density. Chemlali leaves also revealed lower specific leaf area and had higher density of foliar tissue and lower reduction in net CO₂ assimilation rate. The mechanisms employed by these two cultivars to cope with water deficit are discussed at the morpho-structural level. The morphological and structural characteristics of the leaves are in accordance with physiological observations and contribute to the interpretation of why the olive cv. Chemlali is more drought-tolerant than cv. Chetoui. Furthermore, from the behaviour of Chemlali plants we consider this cultivar very promising for cultivation in semi-arid areas.     

Variation in DPPH scavenging activity and major volatile oil components of cassumunar ginger, Zingiber montanum (Koenig), in response to water deficit and light intensity

Cassumunar ginger, Zingiber montanum (Koenig) Link ex Dietr. (Zingiberaceae), is called Phlai in Thailand. The current study investigates the levels of antioxidant activity and major volatile oil components in cassumunar ginger exposed to varying water deficits (0, 30, 60, 90 and 120 days before harvest) and light intensities (100%, 50% and 25% sunlight). A 120-day water deficit resulted in high volatile oil content and increased sabinene content, but DPPH scavenging activity was not affected. The quantity of volatile oil in the cassumunar ginger exposed to a 120-day water deficit was almost twice that of both the control and the sample exposed to a 30-day deficit. The highest terpinen-4-ol content was obtained after a 60-day water deficit, and (E)-1-(3′,4′-dimethoxyphenyl) butadiene content tended to decrease with prolonged water deficiency. The antioxidant activities of cassumunar ginger were 52.98%, 41.75% and 42.93% in plants grown at 100%, 50%, and 25% sunlight, respectively. Light intensity of 50% or 25% increased the biomass of cassumunar ginger but decreased the volatile oil content; antioxidant activity was not significantly affected.     

Effects of water deficit on the vegetative response,yield and oil quality of olive trees (Olea europaea L., cv Coratina) grown under intensive cultivation

An experiment was carried out in a young high-density olive grove (556 plants ha⁻¹—Olea europaea L., cv Coratina) located in Southern Italy to evaluate the effect of different soil water availability on the vegetative and productive performances of olive trees also looking into the quality of the resulting oils. Trials were carried out over a 3-year period on trees subjected to irrigation and grown under rainfed conditions. Vegetative tree response, as shoot elongation and trunk diameter, was evaluated. Yield per plant, fruit characteristics, oil quality indices (free fatty acid content, peroxide value, UV adsorption at 232 and 270 nm, total phenols, α-tocopherol content) were determined for both irrigated and non-irrigated treatments in the ‘on’ years 1997 and 1999 (6th and 8th year after planting, respectively).     

Effects of explant type, culture media and growth regulators on callus induction and plant regeneration of Chinese jiaotou (Allium chinense)

To establish an efficient protocol of shoot regeneration from callus, effects of explant type, culture media and plant growth regulators on callus induction and shoot regeneration of Chinese jiaotou (Allium chinense) were evaluated. The results showed that basal plate was the best explant for callus induction (47.5%) when cultured on B5 medium supplemented with 0.1 mg l⁻¹ 6-benzylaminopurine (BA) and 1.0 mg l⁻¹ 2,4-dichlorophenoxyacetic acid (2,4-D), and B5 was the best medium to induce callus formation with 49.3% of the explants forming callus. The highest callus induction (65.2%) was achieved culturing basal plate on B5 medium supplemented with 0.1 mg l⁻¹ BA and 1.0 mg l⁻¹ 2,4-D after 8 weeks of culture. The best callus proliferation was observed on B5 medium with 1.5 mg l⁻¹ 2,4-D. Shoots regenerated at the highest frequency of 58.8% with 4.5 shoots when calli were cultured on B5 medium with 0.1 mg l⁻¹ BA and 1.0 mg l⁻¹ a-naphthaleneacetic acid (NAA). This protocol provides a basis for future studies on genetic improvement and could be applied to large-scale multiplication systems for commercial nurseries of Allium chinense.     

Indole acetic acid differently changes growth and nitrogen metabolism in Pisum sativum L. seedlings under chromium (VI) phytotoxicity: Implication of oxidative stress

The present study investigated impact of exogenous application of indole acetic acid (IAA; 10 and 100 μM) in pea seedlings under hexavalent chromium (Cr VI; 50, 100 and 250 μM). Cr and 100 μM IAA alone as well as in combination decreased seed germination rate compared to control. However, under Cr phytotoxicity, addition of 10 μM IAA recovered seed germination rate to the level of control. Exposure of pea seedlings to Cr and 100 μM IAA during their early stage caused decrease in fresh mass, length, protein and nitrogen contents of roots and shoots compared to control. Treatment of pea seedlings with Cr resulted in a rapid accumulation of this metal in roots and shoots. Moreover, addition of 100 μM IAA together with Cr, further increased accumulation of this metal in roots and shoots compared to Cr treatments alone. Treatment of pea seedlings with Cr and 100 μM IAA, resulted in a marked decrease in nitrate reductase, nitrite reductase, glutamine synthetase and glutamate synthase (GOGAT) activities (except 50 μM Cr alone for GOGAT), and an increase in ammonium content and glutamate dehydrogenase activity. Parameters related with oxidative stress, i.e. superoxide radicals and reactive carbonyl groups (protein oxidation) were increased by Cr and 100 μM IAA compared to control. By contrast, addition of 10 μM IAA together with Cr, alleviated negative effect of Cr on growth, protein, nitrogen and nitrogen metabolism, and led to decrease in oxidative injuries caused by Cr. The data indicate that 10 μM IAA protects pea seedlings during the early growth period against Cr phytotoxicity by regulating Cr accumulation and oxidative damage. However, addition of 100 μM IAA together with Cr showed opposite responses.     

Floral induction (FI) in longan (Dimocarpus longan, Lour.) trees. III: Effect of shading the trees on potassium chlorate induced FI and resulting hormonal changes in leaves and shoots

Previous experiments demonstrated that treatment of longan trees with potassium chlorate (KClO₃) induces “off season floral induction” (FI) even in the absence of the naturally required cool temperature [Manochai, P., Sruamsiri, P., Wiriya-alongkorn, W., Naphrom, D., Hegele, M., Bangerth, F., 2005. Year around off season flower induction in longan (Dimocarpus longan, Lour.) trees by KClO₃ applications: potentials and problems. Sci. Hortic. 104, 379–390]. Potassium chlorate, however, cannot replace the presence of functional mature leaves and sufficient light intensity. Here we examined in more detail the effect of shade (about 10% of natural sunlight) on KClO₃ affected hormone concentrations/transport of leaves and shoot apical buds (SAB) and their interactions with FI.     

Floral induction (FI) in longan (Dimocarpus longan, Lour.) trees: Part I. Low temperature and potassium chlorate effects on FI and hormonal changes exerted in terminal buds and sub-apical tissue

Floral induction (FI) in longan (Dimocarpus longan, Lour.) trees was achieved in controlled greenhouse experiments by low temperature (LT) and by the application of potassium chlorate at high temperature (HT + KClO₃) during two consecutive seasons. The latter treatment was successful also at temperatures above 20 °C. The present experiment was conducted to investigate possible alterations in the concentrations of plant hormones exerted by these two methods and to relate them to the floral induction process. The following hormones were examined by radioimmunoassay in the shoot apical buds (SAB), and in sub-apical bark and wood: the auxin indole-3-acetic acid (IAA); gibberellins (GAs); and the cytokinins zeatin/zeatin riboside (Z/ZR) and isopentenyl-adenine/isopentenyl-adenosine (iP/iPA).