Growth, gas exchange and function of antioxidant defense system in two contrasting rice genotypes under Zn and Fe deficiency and hypoxia

For study of underlying physiological mechanisms for genotypic differences in tolerance to Zn and Fe deficiency and hypoxia, two contrasting rice genotypes (Oryza sativa L. cv. Amol and Dashti) were studied in nutrient solution with or without aeration. Growth of the lowland genotype (Amol) was significantly improved in nutrient solution without aeration, the opposite was observed for upland genotype (Dashti). Tolerance of Amol to low Zn was higher than Dashti, in contrast the former genotype was more susceptible to Fe deficiency. Photo-chemistry of leaves was affected strongly by Fe but not Zn deficiency. Low supply of Zn and Fe impaired photosynthetic capacity of plants mainly via stomatal limitation and the amount of reduction in net assimilation rate correlated well with differential growth reduction under Zn and Fe deficiency stress. Under hypoxia, plants had lower stomatal conductance and transpiration rate leading to improved photosynthetic water use efficiency. Activity of ascorbate peroxidase (APX) and guaiacol peroxidase (POD) induced by low Zn supply, but low Fe caused reduction of APX, CAT and POD. Activity of SOD decreased in low Zn plants, but increased in plants suffered from Fe deficiency. Increased APX activity in response to hypoxic conditions in Amol was associated with higher tolerance in this genotype, in contrast POD activity only monitored stress conditions without any protecting role. A close correlation was observed between accumulation of O2.– and differential sensitivity of genotypes to hypoxia

Propriedades da rizosfera de genótipos de arroz submetidos à anoxia e a diferentes disponibilidades de zinco e ferro

The objective of this work was to study possible mechanisms involved in root-induced changes of rhizosphere physicochemical properties of rice genotypes, under anoxia and low supply of Zn and Fe. Two rice genotypes, including an upland and a lowland ones, were grown in hydroponic medium under adequate and low supply of Zn and Fe, with or without aeration. Anoxia increased shoot dry weight, root length and uptake of Zn and Fe in lowland Amol genotype, but reduced these parameters in upland Gasrol-Dashti genotype. The amount of oxygen released by roots was statistically higher in 'Amol'. The highest acidification potential of roots was observed in the lowland genotype under low supply of Zn, and in the upland genotype under Fe starvation. The highest oxalate (only organic acid detected) exudation from roots was observed in Zn and Fe deficient Gasrol-Dashti genotype. Zinc deficiency caused reduction of alcohol dehydrogenase and stimulation of lactate dehydrogenase activity, particularly in shoot. The ability to induce changes in the rhizosphere properties has a great contribution for the adaptation of both lowland and upland rice genotypes to specific soil conditions.O objetivo deste trabalho foi estudar possíveis mecanismos envolvidos em mudanças nas propriedades físico-químicas da rizosfera, em genótipos de arroz sob anoxia e baixo suprimento de Zn e Fe. Dois genótipos de arroz, um de terras altas e outro de várzeas, foram cultivados em meio hidropônico, com suprimento adequado ou baixo de Zn e Fe, em condições anóxicas ou aeradas. A anoxia aumentou a massa de matéria seca da parte aérea, o comprimento de raízes e a absorção de Zn e Fe, no genótipo de várzeas Amol, mas reduziu esses parâmetros no genótipo de terras altas Gasrol-Dashti. A quantidade de oxigênio liberada pelas raízes foi superior no 'Amol'. Maior potencial de acidificação das raízes foi observado no genótipo de várzeas, sob baixo suprimento de Zn, e no genótipo de terras altas, sob baixo suprimento de Fe. A maior exsudação de oxalato ocorreu com o 'Gasrol-Dashti', com deficiência de Zn e Fe. A deficiência de Zn reduziu a atividade da álcool desidrogenase e estimulou a da lactato desidrogenase, especialmente na parte aérea. A habilidade em induzir mudanças em propriedades da rizosfera possui grande importância na adaptação a condições específicas do solo, em ambos os genótipos

Contrastive response of Phlomis tuberosa to salinity and UV radiation stresses

Growth, photosynthetic characteristics and antioxidant defense system were investigated under salinity stress and UV radiation in Phlomis tuberosa (Lamiaceae) grown under environmentally controlled conditions for two weeks. Salinity at 40 mM results in significant reduction of shoot growth up to 20%, while UV radiation at 10 kJ m-2 d-1 did not affect plants dry matter production. Salinity did not influnce PSII photochemistry, while UVA+B radiation caused a significant reduction of maximum quantum yield of PSII. The net photosynthesis rate was inhibited by both salinity and UV stress following reduced stomatal conductance. Leaf osmotic and water potential were decreased by salinity but not UV radiation. Activity of antioxidant enzymes increased under both salinity and UV radiation stress, however, membrane damage was occurred only under UV stress. Our data implied that, high salinity sensitivity in this species was mainly attributable to the salt-induced disturbance in water relations and reduced assimilation rate rather than to other factors such as damage to PSII, oxidative stress or membrane damage. However, PSII photoinhibition, membrane damage and significant reduction of net assimilation rate were not able to affect negatively plants performance under UV stress implying involvement of other factors in high UV stress tolerance in Phlomis tuberosa

Effect of light intensity on photosynthesis and antioxidant defense in boron deficient tea plants

Tea (Camellia sinensis (L.) O. Kuntze) plants were grown at adequate (46 μM) or low (<2.5μM) boron (B) supply in the nutrient solution under low (LL, 50 μmol m-2s-1), intermediate (IL, 250 μmol m-2s-1) and high (HL, 500 μmol m-2s-1) light intensities. Boron deficiency hardly affected photochemical events under LL conditions, but alleviated reduction of efficiency of photosynthetic energy conversion in IL and HL plants. The optimum light intensity for CO2 as-similation was IL for the young and HL for the old leaves. Activity of ascorbate peroxidase and superoxide dismutase and concentration of proline was lower under IL compared to LL and HL conditions. Compared to the old leaves, in the young leaves photochemical events were more protected under excess light and low B supply. Antioxidant defense system involved in the protection of leaves against excess light under IL conditions while thermal dissipation performed this role under HL conditions. Alleviation of high light stress effect on the photochemical events could be attributed to the B deficiency-induced activation of antioxidant defense system

Flora of heavy metal-rich soils in NW Iran and some potential hyper-accumulator and accumulator species

In the northwestern part of Iran (Azerbaijan province), there are numerous, active mining areas with heavymetal-rich soils. The plant vegetation growing on these soils could represent a specific flora having potential hyperaccumulators, accumulators and excluder species. In this work, soils rich in Ni, Zn, Cu andMn and plants were identified during April to September in 2002–2003. Plant species belonging to 39 families were collected and the heavy metals in the above-ground parts of specimens were analyzed. For the majority of species, though metal concentrations were orders of magnitude higher than plants growing on soils without mineralization, the concentrations were below the threshold defining hyper-accumulation. The Ni, Zn, Cu and Mn excluder species that grow on metal rich soils but restrict metal absorption and/or transport into shoots were also identified. These species are suitable for the rehabilitation and stabilization of contaminated lands around mining areas as well as the remediation of agricultural soils affected by wastewaters of metal smelters in mining sites of NW Iran

Responses of antioxidant defense capacity and photosynthesis of bean (Phaseolus vulgaris L.) plants to copper and manganese toxicity under different light intensities

Effects of toxic concentrations of Cu and Mn were studied in bean (Phaseolus vulgaris) plants under different light intensities. Exposure of plants to 100 pM Cu, inhibited their growth up to 79%, while similar concentrations of Mn caused only a slight (21%) reduction of plants dry weight. Net assimilation rate (A) was inhibited with similar extent by both heavy metals and FJF0 ratio decreased particularly by Mn treatment. With the exception of ascorbate peroxidase in Cu treated plants, activity of catalase, superoxide dismutase and glutathione reductase were stimulated by both heavy metals with similar extent. Change in guaiacol peroxidase activity was correlated with growth response, increased by Cu but was not affected by Mn toxicity. Similar to peroxidase activity, accumulation of proline monitored the stress conditions but did not cause more protection against Cu toxicity. On the other hand, concentration of H202 and malondialdehyde indicated a higher oxidative stress simultaneous with higher growth in the Mn than Cu treated plants. Results imply that, growth response to Cu and Mn could be reflected neither by the chlorophyll fluorescence nor the net assimilation rate. Additionally, antioxidant defense capacity did not involve in different response to Cu and Mn in bean plants

Sugar beet profits from intercropping with wheat both under optimum and deficient phosphorus supply

An experiment was conducted with wheat and sugar beet as monocrop and intercrop under low or adequate phosphorus supply. Dry matter production of shoot and roots were decreased in wheat while increased in sugar beet under intercrop conditions. Photosynthesis rate was diminished under intercrop conditions in wheat while elevated in sugar beet concomitant with reduction of transpiration rate and higher water use efficiency in the latter species. Phosphorus, potassium and iron contents were also lower in intercrop wheat while increased in sugar beet. The same effect of intercropping on biomass and nutrients uptake was observed in the short term hydroponic experiment. Interestingly, three root parameters including length, soluble carbohydrates and activity of secretory acid phosphatase that are characteristics for phosphorus-deficient plants were enhanced in both species by intercropping irrespective the phosphorus supply level. These data suggested an interspecific interaction beyond the different nutrient acquisition capacity in the intercrop pots.V raziskavi je bil opravljen poskus s pšenico in sladkorno peso v čisti kulturi in medsetvi v razmerah primerne in pomankljive preskrbe s fosforjem. V razmerah medsetve sta se biomasi korenin in poganjkov zmanšali pri pšenici a povečali pri sladkorni pesi. Podobno se je pri pšenici v medsetvi zmanjšala fotosinteza in povečala pri sladkorni pesi s hkratnim zmanjšanjem transpiracije in večjoučinkovitostjo izrabe vode. Pravtako so bile vsebnost fosforja, kalija in železa manjše pri pšenici v medsetvi in večje pri sladkorni pesi. Podoben učinek medsetve na biomaso in vsebnost hranil je bil opazen v kratkotrajnem hidroponskem poskusu. Zanimivo je, da so se neglede na preskrbo s fosforjem v medsetvi pri obeh vrstah povečali parametri korenin kot so njihova dolžina, vsebnost topnih ogljikovih hidratov in aktivnost izločenih kislih fosfataz, kar je značilnost rastlin, ki rastejo v pomanjkanju fosforja. Podatki nakazujejo na medvrstne interakcije, ki presegajo razlike v sposobnosti privzema hranil v lončnem poskusu z medsetvijo

Morphological and anatomical modifications in leaf, stem and roots of four plant species under boron deficiency conditions

El boro es un componente estructural de las paredes celulares ysu deficiencia causa interrupción del desarrollo. En este trabajo, seestudia la influencia del bajo suplemento de B sobre la morfologíay anatomía del nabo (Brassica rapa L.), lombarda (Brassica oler-acea L. var. capitata f. rubra), tabaco de pota (Nicotiana rustica L.)y apio (Apium graveolens L.). Se observaron síntomas visuales entodas las especies. El examen microscópico de secciones trans-versales de hojas, tallos y raíces mostró disminución del diámetrode elementos traqueales y desorganización del tejido del floema.Así mismo, se produjo hipertrofia del parénquima foliar en tabaco yadelgazamiento de paredes celulares en células del colénquimadel tallo, en apio. Las alteraciones anatómicas fueron más pronun-ciadas en limbo, seguidas de peciolo, tallo y raíces. Estos resulta-dos señalan importantes interrupciones en el desarrollo de losprimordios foliares y los haces vasculares con carestía de B