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The role of urea in the translocation of 59Fe from 59FeEDTA-treated leaves was studied in durum wheat ( Triticum durum) grown for 2 weeks in nutrient solution and until grain maturation in soil culture. Five-cm long tips of the first leaf of young wheat seedlings or flag leaves at the early milk stage were immersed twice daily for 10 s in 59FeEDTA solutions containing increasing amounts of urea (0, 0.2, 0.4 and 0.8% w/v) over 5 days. In the experiment with young wheat seedlings, urea inclusion in the 59FeEDTA solution increased significantly translocation of 59Fe from the treated leaf into roots and the untreated part of shoots. When 59Fe-treated leaves were induced into senescence by keeping them in the dark, there was a strong 59Fe translocation from these leaves. Adding urea to the 59Fe solution did not result in an additional increase in Fe translocation from the dark-induced senescent leaves. In the experiment conducted in the greenhouse in soil culture until grain maturation, translocation of 59Fe from the flag leaves into grains was also strongly promoted by urea, whereas 59Fe translocation from flag leaves into the untreated shoot was low and not affected by urea. In conclusion, urea contributes to transportation of the leaf-absorbed Fe into sink organs. Probably, nitrogen compounds formed after assimilation of foliar-applied urea (such as amino acids) contributed to Fe chelation and translocation to grains in wheat. [ABSTRACT FROM AUTHOR]

The effect of Zn2+ on the plasma membrane permeability and superoxide radical (O-2) formation in roots was studied with cotton (Gossypium hirsutum L. cv. Delta- pine 15/21) plants grown in nutrient solution with different Zn2+ supply. Compared to Zn-sufficient plants, the plasma membrane permeability of Zn-deficient plants was increased as indicated by a 3-, 5- and 2.5-fold increase in root cell leakage of K+ NO-3 and organic carbon compounds, respectively. Resupply of Zn2+ to Zn-deficient plants for 12 h substantially decreased this leakage. The effects of Zn2+ on membrane permeability were closely correlated with the levels of O-2 measured by electron spin resonance (ESR) spectroscopy in the microsomal membrane fraction and in the cytosol fraction of root cells. The amplitudes of the O-2-derived Tiron ESR signal also coincided with a O-2-generating oxidase activity which was strongly dependent on the presence of NADPH and FAD. The results suggest that Zn2+ directly affects the integrity of the plasma membrane, at least in part. by interfering with O-2, generation by a membrane-bound NADPH oxidase. [ABSTRACT FROM AUTHOR]

The effect of varied supply of p (2.5 × 10-5 to 6 × 10-5 M) and Zn (0 to 10-5 M) on up-take and concentrations of P and Zn was studied in cotton (Gossypium hirsutum L. cv. Deltapine 15/21) grown in nutrient solution under controlled environmental conditions. At a given Zn supply, increasing levels of P had no significant effect on the concentrations of total Zn in plants. However, increasing levels of P induced or enhanced visual Zn deficiency symptoms when the Zn concentration in the nutrient solution was low. The concentrations of water-soluble Zn in roots and shoots constituted 60% of the total Zn concentrations for plants grown with low P and 30% for plants grown with high P. The concentration of water-soluble Zn in leaves, but not total Zn, was closely correlated with visual Zn deficiency symptoms, levels of chlorophyll, superoxide dismutase and membrane permeability. The critical deficiency concentration of water-soluble Zn in cotton leaves was in the range of 6 to 7 μg (g dry weight)-1 or about 1.0 μg (g fresh weight)-1. The results show that high P concentrations in plant tissue decrease the physiological availability of Zn. Water-soluble Zn in the tissue appears to be a suitable indicator for Zn nutritional status in general and phosphorus-induced Zn deficiency in particular. Also in field-grown orange trees (Citrus sinensis) visual Zn deficiency symptoms in leaves were closely related to the concentration of water-soluble Zn. [ABSTRACT FROM AUTHOR]

Cotton (Gossypium hirsutum L. cv. Deltapine 15/21) plants were precultured for 19 to 25 days under controlled climatic conditions in nutrient solutions with different levels of Zn. With the onset of visual Zn‐deficiency symptoms the pH of the nutrient solution decreased from 6.0 to about 5.0. In contrast, Zn‐sufficient plants raised the pH of the nutrient solution to about 7.0. In short‐term studies it could be demonstrated that the Zn nutritional status of the plants remarkably influenced the uptake and translocation rates of mineral nutrients. Compared to Zn‐sufficient plants, P uptake rate in severely Zn‐deficient plants was increased by a factor of 2 to 3, whereas the uptake rates of K, Ca and particularly NO3 decreased. The accumulation of P in the roots of Zn‐deficient plants was either not affected or even lower than in Zn‐sufficient plants. Thus, Zn deficiency had a specific enhancement effect on root to shoot transport of P. This enhancement effect of Zn deficiency on uptake and transport of P was similar at nutrient solution pH values of 7.0 and 5.8; i.e. it was not the result of acidification of the nutrient solution. After application of 36CI, 86Rb and 32P to plant stems, basipetal transport of 36CI and 86Rb was not affected by the Zn nutritional status of the plants. However, in Zn‐deficient plants, only 7.8% of the 32P was translocated basipetally compared to 34% in the Zn‐sufficient plants. A resupply of Zn for 19 h to Zn‐deficient plants enhanced basipetal 32P transport. The results indicate that a feedback mechanism in the shoots is impaired in Zn‐deficient plants which controls the P uptake by roots and especially the P transport from roots to shoots. As a result of this impairment toxic concentrations of P accumulate in the leaves. The mechanism responsible is likely the retranslocation of P in the phloem from shoots to roots. [ABSTRACT FROM AUTHOR]

The effect of withholding Zn on the uptake, translocation and accumulation of P was studied in cotton plants (Gossypium hirsutum L. cv. Deltapine 15/21) grown in nutrient solutions under controlled environmental conditions. The influence of P on the uptake rate, translocation and distribution of 65Zn in the plants was also examined. Increasing the P supply resulted in severe Zn deficiency symptoms (interveinal chlorosis) as well as P toxicity symptoms, which were characterized by leaf puckering and grayish‐brown marginal necrosis. Zinc deficiency markedly increased the uptake and translocation rates of P over the whole concentration range tested (5x10‐5 to 1.25x10‐3M). Uptake and translocation rates of P increased with both level of P and severity of Zn deficiency. This often caused P toxicity symptoms on Zn‐deficient leaves. In contrast to P, the concentrations of K and Mg in the leaves were not affected by Zn deficiency. Similar results were obtained for sunflower (Helianthus annuus L.) and buckwheat (Fagopyrum esculentum Moench) plants. Higher P concentrations in Zn‐deficient leaves or shoots could not be attributed wholly to reduced shoot growth. This was also evident when Zn deficiency was compared with other micronutrient (Fe, Mn, and Cu) deficiencies. Only Zn‐deficient plants showed enhanced uptake and translocation of P. In experiments with 65Zn, a high P supply did not depress uptake and translocation of Zn. From the results obtained it is concluded that the P‐induced Zn deficiency in cotton, as well as in other species, is primarily caused by enhanced P uptake and translocation and not by inhibition of Zn uptake. [ABSTRACT FROM AUTHOR]

The role of urea in the translocation of (59) Fe from (59) FeEDTA-treated leaves was studied in durum wheat (Triticum durum) grown for 2 weeks in nutrient solution and until grain maturation in soil culture. Five-cm long tips of the first leaf of young wheat seedlings or flag leaves at the early milk stage were immersed twice daily for 10 s in (59) FeEDTA solutions containing increasing amounts of urea (0, 0.2, 0.4 and 0.8% w/v) over 5 days. In the experiment with young wheat seedlings, urea inclusion in the (59) FeEDTA solution increased significantly translocation of (59) Fe from the treated leaf into roots and the untreated part of shoots. When (59) Fe-treated leaves were induced into senescence by keeping them in the dark, there was a strong (59) Fe translocation from these leaves. Adding urea to the (59) Fe solution did not result in an additional increase in Fe translocation from the dark-induced senescent leaves. In the experiment conducted in the greenhouse in soil culture until grain maturation, translocation of (59) Fe from the flag leaves into grains was also strongly promoted by urea, whereas (59) Fe translocation from flag leaves into the untreated shoot was low and not affected by urea. In conclusion, urea contributes to transportation of the leaf-absorbed Fe into sink organs. Probably, nitrogen compounds formed after assimilation of foliar-applied urea (such as amino acids) contributed to Fe chelation and translocation to grains in wheat., (© 2014 Scandinavian Plant Physiology Society.)