Role of auxins and cytokinins in the development of lateral roots in wheat plants with several roots removed

The removal of four of five roots of 7–8-day-old wheat plants resulted in the activation of lateral root growth and the initiation of lateral root primordia on the remained root as compared to the main root of intact plants. The extent of this growth response depended on placing cut surface above or beneath the surface of the nutrient solution. The measurement of the IAA and cytokinin contents showed accumulation of these hormones in the root of experimental plants as compared to the main root of intact plants. IAA accumulation was correlated with the number of lateral roots and their primordia. The analysis of hormonal balance and their transport from the shoot to the root permits discussing the involvement of these hormones and their interaction in the control of root growth at the stages of both primordium initiation and development and lateral root elongation.     

Effect of the nitrogen-containing salt on the content of cytokinins in detached wheat leaves

The dynamics of the cytokinin content in detached leaves of wheat (Triticum durum, cv. Bezenchukskaya 139) seedlings moistened with ammonium nitrate or water (control) was studied by immunoenzyme analysis. Leaf treatment with water was accompanied by a transient accumulation of cytokinins, maybe due to their release from their O-glucosylated forms. An increase in the contents of zeatin and its riboside after their initial decrease in detached leaves treated with ammonium nitrate could not occur due to their release from stored forms (nucleotides or O-glucosides) because the contents of zeatin and its riboside increased simultaneously with the content of stored cytokinins. The accumulation of isopentenyladenosine and zeatin nucleotide, which occurred simultaneously with an increase in the content of zeatin and zeatin riboside, permits a supposition that cytokinins can be synthesized in detached wheat leaves treated with ammonium nitrate.     

Role of cytokinins in the regulation of stomatal conductance of wheat seedlings under conditions of rapidly changing local temperature

The influence of an air temperature increase by 4°C and nutrient solution cooling down to 5 ± 1°C on stomatal conductance and hormone level of seven-day-old wheat (Triticum durum L., cv. Bezenchukskaya 139) seedlings was studied. An elevated air temperature resulted in a rapid rise of stomatal conductance preceded by the increase in the level of cytokinins in leaves. Cooling of the nutrient solution induced gradual stomatal closure along with a decreasing cytokinin level in leaves. Hormone concentration in the xylem sap of wheat seedlings was determined, and the rate of hormone transport from the roots to shoots was calculated. The role of cytokinins in the regulation of stomatal conductance under conditions of local thermal treatments is discussed.     

Influence of temperature increase on evaportranspiration rate and cytokinin content in wheat seedlings

The content of cytokinins especially zeatin nucleotide decreased in shoots as a result of temperature increase. Simultaneously the cytokinins accumulated in roots. The changes in cytokinins distribution were followed by a decline of evapotranspiration after its initial temperature-induced uprising. This revised version was published online in July 2006 with corrections to the Cover Date.     

Contents of abscisic acid and cytokinins in shoots during dehydration of wheat seedlings

Accumulation of ABA in shoots during 30-min dehydration of wheat seedlings was accompanied by the decline in the content of zeatin nucleotide and the accumulation of zeatin 9-N-glucoside. The total content of zeatin derivatives as well as the content of free base of zeatin remained almost constant. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fast changes in growth rate and cytokinin content of the shoot following rapid cooling of roots of wheat seedling

Changes in the concentration of cytokinins were studied following root cooling. Simultaneously, the growth rate of the second leaf was monitored with a highly sensitive growth sensor attached to its tip. Cytokinins were separated by thin layer chromatography and immunoassayed using antibodies to zeatin riboside. The extension rate of the second leaf decreased within 15 minutes of cooling the nutrient medium from 24 °C to 4 °C. The concentration of cytokinins in shoots decreased with similar rapidity. In contrast cytokinins in roots increased slightly during the initial period of cooling before declining. The sharp decrease in cytokinin concentrations in shoots 15 minutes after cooling of roots may contribute to the abrupt inhibition of shoot growth.     

Ability of bacterium Bacillus subtilis to produce cytokinins and to influence the growth and endogenous hormone content of lettuce plants

Hormone production by micro-organisms selected as antagonists of pathogenic fungi and the effect of their introduction into soil on hormone content and growth of lettuce plants were studied. Hormones in bacterial cultural media and in plant extracts were immunopurified and assayed using specific antibodies to indolyl-3-acetic acid (IAA), abscisic acid (ABA), and different cytokinins (zeatin riboside (ZR), dihydrozeatinriboside (DHZR) and isopentenyladenosine (iPA)). ZR was shown to be the main cytokinin present in bacterial cultural media as a complex with a high molecular weight component. Inoculation of lettuce plants with bacteria increased the cytokinin content of both shoots and roots. Accumulation of zeatin and its riboside was greatest in roots shortly 2days after inoculation, when their content was 10 times higher than in control. Changes in the content of other hormones (ABA and IAA) were observed at the end of experiments only. Accumulation of cytokinins in inoculated lettuce plants was associated with an increase in plant shoot and root weight of approximately 30% over 8days.     

Effect of increased irradiance on the hormone content,water relations,and leaf elongation in wheat seedlings

In wheat (Triticum durum Desf., cv. Bezenchukskaya 139) seedlings, an increase in irradiance from 20 to 400 μmol/(m² s) PAR enhanced transpiration and increased stomatal conductance by three times on the background of reduced relative water content (RWC). After this treatment, leaves quickly ceased to grow and became even shrunk later. In 40 or 50 min, leaf growth was resumed. At this period, we observed an increase in hydraulic conductivity and RWC and also in leaf extensibility. As soon as 10 min after treatment, some changes in hormone content were noted. In the zones of leaf growth and its mature part, zeatin and zeatin riboside were accumulated, whereas ABA accumulation was observed in the zone of leaf growth and in the roots. The results obtained indicate that leaf expansion at increased irradiance was related to changes in cell-wall extensibility and hydraulic conductivity. The first effect could be due to cytokinin accumulation, whereas the second one, to ABA accumulation.     

Endogenous cytokinins mediate growth-stimulating and protective action of the HUMI preparation on wheat plants inoculated with Tilletia caries

Humic substances (HS) and preparations created on their basis are known to be effective in growth stimulation and improvement of resistance and productivity of different plant species. We have revealed that the presowing semidry treatment of wheat seeds with preparation HUMI (NVP ‘BashIncom’, Ufa, Bashkortostan, Russia) promoted seedling growth and increased wheat yield. This effect is likely to be due to the shifts induced by HUMI in the hormonal system of plants associated with a 1.5-fold persistent accumulation of cytokinins (CKs) without any changes in the contents of indoleacetic acid (IAA) and abscisic acid (ABA). Meanwhile, presowing treatment with HUMI had a stabilizing effect on the state of the hormonal system in the course of ontogenesis of wheat inoculated with teliospores Tilletia caries. Obtained data about prevention of the decline in the cytokinin content in HUMI-treated infected wheat is fundamental in the implementation of immuno-stimulatory effect of HUMI resulting in the suppression of the growth and development of pathogens.     

Synergistic effects of cadmium and NaCl on the growth,photosynthesis and ion content in wheat plants

The addition of NaCl to cadmium had significant synergistic effect on the wheat root and shoot fresh mass, relative growth rate and net assimilation rate, while showed no significant effects on the dry mass production, leaf area, leaf area ratio, leaf mass ratio and specific leaf area. Additive depression of the rate of photosynthesis and the stomatal conductance was recorded, while no significant effect on the transpiration rate was observed. The Cd stress disturbed the mineral nutrition of the wheat plants either directly or indirectly, NaCl markedly reduce the uptake and internal concentration of K and Ca in the shoot. The combination of cadmium and NaCl showed no additive effects on the content of ions in the root as well as in the shoot of wheat plants.     

Uptake of zinc by rye,bread wheat and durum wheat cultivars differing in zinc efficiency

Effect of zinc (Zn) nutritional status on uptake of inorganic ⁶⁵Zn was studied in rye (Secale cereale, cv. Aslim), three bread wheat (Triticum aestivum, cvs. Dagdas, Bezostaja, BDME-10) and durum wheat (Triticum durum, cv. Kunduru-1149) cultivars grown for 13 days in nutrient solution under controlled environmental conditions. The cultivars were selected based on their response to Zn deficiency and to Zn fertilization in calcareous soils under field conditions. When grown in Zn-deficient calcareous soil in the field, the rye cultivar had the highest, and the durum wheat the lowest Zn efficiency. Among the bread wheats, BDME-10 showed higher susceptibility to Zn deficiency and Bezostaja and Dagdas were less affected by Zn deficiency. Similarly to field conditions, in nutrient solution visual Zn deficiency symptoms (i.e. necrotic lesions on leaf blade) appeared to be more severe in Kunduru-1149 and BDME-10 and less severe in rye cultivar Aslim. Under Zn deficiency, shoot concentrations of Zn were similar between all cultivars. Cultivars with adequate Zn supply did not differ in uptake and root-to-shoot translocation rate of ⁶⁵Zn, but under Zn deficiency there were distinct differences; rye showed the highest rate of Zn uptake and the durum wheat the lowest. In the case of bread wheat cultivars, ⁶⁵Zn uptake rate was about the same and not related to their differential Zn efficiency. Under Zn deficiency, rye had the highest rate of root-to-shoot translocation of ⁶⁵Zn, while all bread and durum wheat cultivars were similar in their capacity to translocate ⁶⁵Zn from roots to shoots. When Zn²⁺ activity in uptake solution ranged between 117 p M and 34550 pM, Zn-efficient and Zn-inefficient bread wheat genotypes were again similar in uptake and root-to-shoot translocation rate of ⁶⁵Zn. The results indicate that high Zn efficiency of rye can be attributed to its greater Zn uptake capacity from soils. The inability of the durum wheat cultivar Kunduru-1149 to have a high Zn uptake capacity seems to be an important reason for its Zn inefficiency. Differential Zn efficiency between the bread wheat cultivars used in this study is not related to their capacity to take up inorganic Zn. This revised version was published online in June 2006 with corrections to the Cover Date.     

Soil salinity effects on transpiration and net photosynthetic rates,stomatal conductance and Na+ and Cl− contents in durum wheat

Leaf gas exchange, plant growth and leaf ion content were measured in wheat (Triticum durum L. cv. HD 4502) exposed to steady- state salinities (1.6, 12.0 and 16.0 dS nr⁻¹) for 8 weeks. Salinity reduced leaf area and number of tillers, and increased Na⁺ and Cl⁻ concentrations in leaves. Leaf- to- leaf gradients of these ions were observed. The oldest leaf contained 6 to 8 times more Na⁺ and Cl⁻ than the flag leaf. Net photosynthetic rate (P_N), transpiration rate (E) and stomatal conductance (g_S) were the highest in flag leaf, declined in the middle and fully expanded leaves, and were minimum in the oldest leaves. These processes were reduced by salinity with similar leaf- to- leaf gradients. Intercellular CO₂ concentrations in the older leaves were higher than in the flag leaf in non-saline plants, and increased similarly with salinity. Leaf age was the major factor in reducing P_N, and senescence processes were promoted by salinity.     

Effects of arbuscular mycorrhizal fungi and drought stress on growth and nutrient uptake of two wheat genotypes differing in drought resistance

 The effects of an arbuscular mycorrhizal (AM) fungus and drought stress on the growth, phosphorus, and micronutrient uptake of two wheat genotypes exhibiting differences in drought resistance were investigated. Plants were grown on a low P (4 mg kg^–1 soil) silty clay (Typic Xerochrept) soil-sand mix. Mycorrhizal infection was higher under well-watered than under dry soil conditions and the drought-resistant genotype CR057 had a higher mycorrhizal colonization than the drought-sensitive genotype CR006. Total and root dry matter yields and total root length were higher in mycorrhizal than in nonmycorrhizal plants of both genotypes. CR057 had higher total dry matter but not root dry matter than CR006 plants. The enhancement in total dry matter due to AM inoculation was 42 and 39% under well-watered and 35 and 45% under water-stressed for CR057 and and CR006, respectively. For both genotypes, the contents of P, Zn, Cu, Mn, and Fe were higher in mycorrhizal than in nonmycorrhizal plants and higher under well-watered than under dry soil conditions. The enhancement of P, Zn, Cu, Mn, and Fe uptake due to AM inoculation was more pronounced in CR006 than in CR057, particularly under water-stressed conditions. Thus CR006 benefitted from AM infection more than the CR057 under dry soil conditions, despite the fact that CR057 roots were highly infected. It appears that CR006 is more dependent on AM symbiosis than CR057. Accepted: 12 February 1997     

Hormonal Control of the Shoot-to-Root Ratio Is Not Related to Water Deficiency in Wheat Plants under Mineral Deficiency

We measured the content of hormones, the rate of growth, and some parameters of water regime (water content, transpiration, and stomatal and hydraulic conductivities) one and two days after wheat plant transfer from 10 to 1% Hoagland-Arnon nutrient medium. It was shown that, a day after dilution of nutrient solution, the content of various cytokinin forms decreased in the xylem sap, shoots, and roots. This decrease was most pronounced in the case of zeatin in the xylem sap and zeatin riboside in the mature zone of the first leaf. ABA was found to accumulate in shoots. A day after dilution of nutrient solution, we observed root elongation evidently induced by mineral nutrient deficiency, and this accelerated root growth was maintained later. Two days after dilution of nutrient solution, we observed the slowing of shoot weight accumulation, whereas root weight remained unchanged. Plant growth response could be related to ABA accumulation in shoots and cytokinin depletion in the whole plant. A reduced hydraulic conductivity and water content in the growing leaf zone was detected only two days after dilution of nutrient solution. Thus, changes in the growth rates and hormone contents could not result from disturbances in water regime induced by mineral nutrient deficiency.     

Sulfhydryl groups in root-cell plasma membranes of wheat genotypes differing in Zn efficiency

Sulfhydryl groups were quantified in root-cell plasma membranes of two genotypes of wheat ( Triticum aestivum cv. Warigal and T. turgidum conv. durum cv. Durati) differing in Zn efficiency. Smaller amounts of 5,5'-dithio-bis(2-nitrobenzoic acid)-reactive sulfhydryl groups were found in Zn-deficient than in Zn-sufficient roots; and also in Zn-inefficient genotype Durati compared to Zn-efficient Warigal, regardless of Zn supply. Upon transfer of 15-day-old Zn-deficient plants into solutions containing various Zn²⁺ activities, a Zn-dependent increase in the amount of reactive sulfhydryl groups was evident in roots of both genotypes, but occurred only in Warigal when 20-day-old plants were used, indicating irreversible physiological damage in Durati plants due to prolonged Zn deficiency. Upon transfer into solutions of increasing Zn²⁺ activities, the increase in total Zn concentration in roots was about an order of magnitude smaller than the increase in amounts of reactive sulfhydryl groups in the roots of both genotypes, suggesting that, in wheat roots, a relatively small amount of Zn is required for preventing oxidation of sulfhydryl groups into disulfides. The amount of reactive sulfhydryl groups in the roots is positively related to Zn efficiency of wheat genotypes and may be one of the mechanisms that, under conditions of Zn deficiency, allow better growth and productivity of Zn-efficient genotypes in comparison to Zninefficient ones.     

Role and function of cytokinin oxidase in plants

Cytokinin oxidase (CK oxidase) is widely distributed in plants and is the only enzyme that has been shown unequivocally to catalyze the catabolism of specific cytokinins (CKs) to inactive products that lack the N⁶-unsaturated side chain. Thus, the enzyme is thought to play a major role in controlling the level or species of CKs in plant tissues. However, despite its discovery more than 25 years ago, little attention has been given to the elucidation of its role and function in plant growth and development. This review seeks to bring in to context the current state of knowledge regarding the biochemical and molecular properties, regulation in undifferentiated and differentiated tissues, and recent results from studies using transgenic plants in an attempt to provide a more comprehensive understanding of the physiological significance of the enzyme in plants. Notwithstanding species, tissue and other specific differences, in general, CK oxidase appears to contribute to CK homeostasis in plants. However, complete clarity as to its function awaits purification of the protein to homogeneity and the ultimate development of requisite molecular probes.     

Glucose-6-phosphate dehydrogenase in tobacco callus strains differing in their growth and their requirement for auxin and cytokinin

The cytokinin-autonomous strain (A_s) of tobacco callus differs from the original cytokinin-dependent strain (D) and from the cytokinin- and auxin-autonomous strain (A₄) by a significantly lower activity of glucose-6-phosphate dehydrogenase (G-6-PDH). Changes in the total G-6-PDH activity were associated with differences in the number of G-6-PDH isozymes. The A_s strain contained only one isozyme, four isozymes were found in D and A₄ strains.     

Optimized cultivation of highly-efficient degradation bacterial strains and their degradation ability towards pyrene

Two bacterial strains,Pyl and Py4,have been tamed and isolated through long cultivation with polycyclic aromatic hydrocarbon-pyrene as the single carbon source.It has been proven that they are both highly-efficient pyrene degrading bacteria and both Bacillus sp..The pyrene degradation ability of separated Pyl,Py4 and the consortium of equal Pyl and Py4 was studied in this project.It is shown that pyrene degradation rates were 88% in 10hr by Py1,84% in 14hr by Py4,and 88% in 8hr by the consortium.It was also determined that the best degradation temperatures were 37℃ and pH 7.0 respectively.The influence of different nutrient substrates added in the degradation experiments was also studied.It was shown that sodium salicylate,sodium acetate and yeast exuact had obvious simulative effect,but glucose had no obvious effect.     

Drought effects on photosynthesis and fluorescence in hard wheat cultivars grown in the field

Net photosynthesis of the flag leaf of hard wheat ( Triticum durum L. evs Valforte, Produra, Adamello, Karel, Appulo and El Amel from the collection of the Instituto di Cerealicultura. Foggia, Italy) of different water potential has been studied on three consecutive years. Net photosynthesis was measured in natural conditions with a LI-COR portable instrument and in saturating CO₂ with an oxygen electrode. Net photosynthesis and stomatal conductance were significantly lower in the unirrigated leaves. However, the ratio of intercellular CO₂, concentration (C₁) to ambient CO₃ concentration (C_a) around the stressed plants was similar to the irrigated control. The maximal rate of photosynthesis in saturating CO₂, (P_nmax). measured in the second year of the experiment, was quite close to photosynthesis under natural conditions, indicating that CO₂ supply was not limiting. These results suggest that altered mesophyll photosynthetic capacity, rather than stomatal closure, causes the observed reduction in photosynthesis in the unirrigated plants. The variable fluorescence yield (_v/F_m) in predarkened leaves measured for two consecutive years, did not show differences between treatments or between cultivars. However, the analysis of the slow transients, measured the last year of the experiment, showed a linear relation between the fluorescence decline from the maximum initial level (P) and maximum photosynthesis (P_nmax).     

The effects of endogenous cytokinin content on benzyladenineenhanced nitrate reductase induction

Foliar application of benzyladenine (BA) has been shown to enhance nitrate-dependent induction of nitrate reductase (NR; EC 1.6.6.1) in etiolated wheat ( Triticum aestivum L.) seedlings. Whether similar enhancement occurs in light-grown plants, or whether endogenous cytokinin content affects this enhancement is unknown. Since the cytokinin content of etiolated plants probably differs from that of light-grown seedlings, the NR response of each to exogenous root- or shoot-applied BA in wheat (cv. Red Bob) was examined. Endogenous cytokinins present in untreated control tissues prior to BA application and changes that occurred after a 22 h (12 h dark followed by 10 h of light) period were determined using a combined HPLC-immunoassay method. Shoot application of BA enhanced the induction of NR in etiolated seedlings in a concentration-dependent manner but failed to enhance NR induction in light-grown plants. Root-applied BA enhanced NR induction in both etiolated and light-grown seedlings. Endogenous root cytokinin levels were similar in both etiolated and light-grown plants. In contrast, shoots of 6 day-old light-grown seedlings contained at least 20 times the amount of total cytokinins measured in shoots from etiolated plants of the same age. Total cytokinin content of the light-grown plants diminished after the 22-h period while that measured in etiolated seedlings increased. The responsiveness of seedlings to BA was correlated with endogenous cytokinin levels in that enhancement of NR induction by exogenous BA was low in tissues which contained high concentrations of cytokinin at the time of BA application. These results may prove useful in interpretation of gene responses to exogenous plant growth regulators.