EFFECT OF IRON DEFICIENCY ON ROOT FERRIC CHELATE REDUCTASE,PROTON EXTRUSION,BIOMASS PRODUCTION AND MINERAL ABSORPTION OF CITRUS ROOT STOCK ORANGE JASMINE (MURRAYA EXOTICA L.)

Three-week iron (Fe) deficiency stress experiments were conducted using two citrus root stocks, Fe-deficiency tolerant Orange Jasmine (OJ, Murraya exotica L.) and the sensitive Flying Dragon [FD, Poncirus trifoliata var. monstrosa (T. Ito) Swingle]. Root ferric chelate reductase activity and proton extrusion increased in OJ between 12 and 18 d of stress, whereas there was no change in FD. Dry weight of OJ roots increased in contrast to FD which decreased. The Mn content in OJ remained the same even under Fe stress. Zn content in OJ roots doubled while that of FD increased 4-folds. The shoot/root Fe accumulation ratio increased in OJ while it decreased in FD. OJ apparently has mechanisms for increasing root biomass, controlling Fe reutilization and regulating manganese (Mn) and zinc (Zn) absorption in response to Fe deficiency. These mechanisms could help maintain homeostasis under heavy metal stress, which would be useful for improved growth of economically important citrus species.     

INHERITANCE OF RESISTANCE TO IRON DEFICIENCY CHLOROSIS IN CHICKPEA (CICER ARIETINUM L.)

Iron (Fe)-deficiency chlorosis causes considerable yield losses in chickpea (Cicer arietinum L.) when susceptible genotypes are grown in calcareous soils with high pH. The most feasible method for alleviating Fe deficiency is the selection of suitable cultivars resistant to Fe deficiency chlorosis. ICC 6119 (desi type), which is Fe-deficient chlorosis, was crossed with CA 2969 and Sierra (kabuli types), resistant to Fe deficiency chlorosis. Inheritance of resistance to Fe deficiency in chickpea revealed that the resistance was controlled by a single dominant gene in these genotypes crossed. A negative selection for resistance to Fe deficiency chlorosis will be effective after segregating generations.     

ADVANCES IN DIAGNOSIS OF IRON DEFICIENCY IN AVOCADO

Several methods for determination of extractable iron (Fe; or so-called “active Fe”) have been proposed. In this study, three methods of Fe extraction were tested: 1.5% phenanthroline (pH 3) and 1 M hydrochloric acid (HCl) from fresh leaves, and 1 M HCl from oven-dry leaves. A six-year-old avocado orchard (cultivar ‘Hass’), grown on a calcareous soil in the proximity of Cabildo (Valparaíso region, Chile), was selected for the study. Samples of mature (5–7 moths-old) leaves of different degree of chlorosis were collected. Total Fe concentrations in chlorotic leaves were similar or even greater than in green leaves. Regressions between the extractable Fe concentrations and the leaf SPAD-color were statistically significant for phenanthroline method, while non-significant for HCl methods. Thus, phenanthroline method was superior over others for diagnosis of Fe deficiency in avocado. Phenanthroline-extractable Fe concentration of 6 mg kg^?1 was considered as a critical value for mature avocado leaves.     

ROOT FERRIC CHELATE REDUCTASE IS REGULATED BY IRON AND COPPER IN STRAWBERRY PLANTS

In the present experiment, we studied the interaction between copper (Cu) and iron (Fe) in strawberry plants grown in nutrient solutions containing different concentrations of Fe. Plants grown in the absence of iron (Fe0) had the characteristic symptoms of Fe deficiency, with smaller chlorotic leaves, less biomass, acidification of the nutrient solution, and roots that were smaller and less ramified, while no symptoms of Fe deficiency were observed in plants grown with Fe. A greater amount of Cu was found in roots of chlorotic plants than in those grown with Fe, while plants grown with 20 μM of Fe (Fe20) in the nutrient solution had a greater amount of Fe compared with plants from the other treatments. Chlorotic plants (Fe0) and plants grown with the greatest level of Fe (Fe20) had a greater root ferric chelate reductase (FC-R; EC 1.16.1.17) activity compared with the other treatments with 5 or 10 μM Fe in the nutrient solution. The same pattern was obtained for relative FC-R mRNA concentration and for the sum of Fe and Cu contents in shoots (leaves plus crowns). The DNA obtained from amplification of the FC-R mRNA was cloned and several of the inserts analysed by single strand confirmation polymorphism (SSCP). Although there were different SSCP patterns in the Fe20 treatment, all the inserts that were sequenced were very similar, excluding the hypothesis of more than one FC-R mRNA species being present. The results suggest that Cu as well as Fe is involved in FC-R expression and activity, although the mechanism involved in this regulation is unknown so far. Both small contents of Fe and Cu in plants led to an over-expression of the FC-R gene and enhanced FC-R activity in strawberry roots.     

ADVERSE EFFECTS OF HUMIC SUBSTANCES FROM DIFFERENT ORIGIN ON LUPIN AS RELATED TO IRON SOURCES

Humic substances improve the efficiency of different iron (Fe) sources overcoming Fe deficiency chlorosis of plants. However, applied at high rates, they can promote negative effects on plants. The main objective of this work was to study the potential adverse effect of three humic acids from different origin when they were applied with two effective Fe sources for plants: Fe- ethylenediaminedihydroxyphenylacetic acid (EDDHA) and Vivianite. To this end, an experiment with lupin (Lupinus albus L.) was performed involving two factors: (i) Fe source, and (ii) humic substances from three different origin (composted cork, leonardite, and compost obtained from a mixture of olive husk with cotton gin trash) applied at 0, 0.1, and 0.5 g organic carbon (C) kg^?1 of growing media. At the rates used, humic substances promoted adverse effects on plant development, chlorophyll meter readings, and Fe content in lupin grown in calcareous media. Overall, the effect on dry matter and Fe content in plants was more relevant when Fe was supplied with Vivianite, the effect on chlorophyll meter readings being more significant when Fe was applied as Fe-EDDHA. Differences were also observed depending on the source of humic substances, those from leonardite promoting the greatest decrease in dry matter in roots and shoots. These humic substances possessed the highest values of spectroscopy index for aromaticity (A₂₅₄ ). On the other hand, the application of humic substances from olive husk compost, which exhibited the lower aromaticity index, resulted in the smallest decrease in dry matter production and chlorophyll meter readings. Dry matter in roots decreased logarithmically with increased values of the estimates of the amounts of aromatic compounds accumulated in the growing media (R² = 0.92; P < 0.01) with Vivianite as Fe source. Thus, the effects decreasing dry matter production, particularly in roots, and chlorophyll meter readings can be ascribed at least partially to the presence of phytotoxic aromatic compounds in humic substances.     

Response of ungrafted rootstocks and rootstocks grafted with wine grape varieties (Vitis sp.) to ‘lime-induced chlorosis’

The ungrafted rootstocks 41B, 1103P, 110R and 140Ru, the grafted combinations of 41B, 1103P and 110R with Xinomavro (one of the most important red wine grape varieties in Greece), as well as those of 1103P, 110R and 140Ru with Chardonnay, were evaluated for 'lime-induced chlorosis' tolerance by growing them with a) basic nutrient solution (BNS), b) BNS + 10 mM bicarbonate, c) BNS without iron (Fe) and d) BNS without zinc (Zn), in hydroponics. The ungrafted 140Ru followed by 41B under high bicarbonate presented the lowest degree of chlorosis; however only 41B presented non-differentiated biomass production and root/shoot ratio. Chlorotic symptoms in combination with plant growth parameters should be used as a tool for grapevine rootstock lime-tolerance screening whereas leaf Fe concentration and root ferric chelate reductase (FCR) activity should not. Lime-stress conditions affected plant mineral nutrition by depressing leaf nitrogen (N), phosphorus (P), calcium (Ca), magnesium (Mg) and increasing potassium (K), and zinc (Zn).     

IRON EFFICIENCY IN KENTUCKY BLUEGRASS NOT RELATED TO PHYTOSIDEROPHORE RELEASE

Some Kentucky bluegrass (KBG; Poa pratensis L.) is susceptible to iron (Fe)-deficiency chlorosis. Under Fe-deficiency stress, phytosiderophore is produced and released by the roots of many grasses to solubilize soil Fe and enhance uptake. In other species, quantifying phytosiderophore screens for Fe-deficiency resistant cultivars. A hydroponic study was conducted at 1 and 10 μM solution Fe to variously stress ‘Baron’, ‘Award’, ‘Limousine’, and ‘Rugby II’ KBG cultivars. One μM Fe solution produced more Fe-deficiency stress in all cultivars compared to 10 μM, resulting in greater chlorosis and phytosiderophore release but reduced shoot and root Fe concentrations and shoot weight. Of the four cultivars, Baron was the most susceptible to Fe deficiency and exhibited severe Fe chlorosis and low shoot Fe but, surprisingly, produced the most phytosiderophore. These results imply that Fe-deficiency susceptibility in KBG may be less related to phytosiderophore release and more related to inefficient uptake or utilization mechanisms.     

ADAPTABILITY MECHANISM OF NITROGEN-EFFICIENT GERMPLASM OF NATURAL VARIATION TO LOW NITROGEN STRESS IN BRASSICA NAPUS

Previous studies showed that wide genotype differences in nitrogen (N) efficiency exists among cultivars of rapeseed (Brassica napus L.), but the mechanisms behind those differences are still unknown. In the present study, our aim was to analyze the adaptability mechanism of N-efficient rapeseed to low-N stress by employing two genotypes of natural variation in N efficiency. Nitrogen-efficient genotype, ‘BG51’, and N-inefficient genotype, ‘BG88’, were grown in a solution culture experiment under conditions of high-N (6.0 mM N) and low-N (0.6 mM N) supply. After growing 30 d, roots and shoots were sampled for the analysis of dry weight, N concentration and accumulation, N use efficiency (NUE), N transport efficiency (NTE), root system vigor parameters, nitrate redutase (NR) activity, and glutamine synthetase (GS) activity. Nitrogen deficiency decreased shoot and root dry weight significantly, but ‘BG51’ exhibited a significantly lower decrease in shoot dry weight and had significantly higher biomass production than ‘BG88’. Under low N supply ‘BG51’ accumulated more N in shoot, root and whole plant than ‘BG88’, and presented higher NUE in both shoot and root. Low-N stress induced an increase in maximum root length by 28.3% for ‘BG88’ and 55.1% for ‘BG51’ compared with the high-N treatment. And ‘BG51’ presented larger root volume, higher root vigor, larger root total absorbing area and root active absorbing area than ‘BG88’ in low-N treatment. Furthermore, ‘BG51’ had significantly higher NR and GS activity in both leaf and root in low N treatment than ‘BG88’, while there was no evident difference between them in high N treatment. These results suggested that N-efficient rapeseed germplasm of natural variation involves an integrated adaptability mechanism responding to low-N stress. Namely, N-efficient genotype could form more developed root system to accumulate more N, and presented efficient N assimilation by higher NR activity and GS activity than N-inefficient genotype. These ultimately resulted in high tolerance of N-efficient genotype to low-N stress and high biomass production.     

水稻品种对石灰性土壤缺Zn耐性机理的研究

选用缺Zn敏感水稻品种IR26和耐缺Zn水稻品种IR8192－31－2,采用营养液培养的方法,研究了水稻品种耐石灰性土壤Zn与HCO^-3关系的生理生化机制。在低锌浓度下,HCO^-3严重抑制敏感品种根系生长,而对耐性品种影响很小;HCO^-3增加增加了两种水稻品种根中的苹果酸和柠檬酸浓度,但敏感品种增加的幅度大,以上结果表明HCO^-3对敏感品种根生长的抑制,并诱发缺Zn是由于根中有机酸过度积累导致的,HCO^-3显著提高敏感品种根中PEP羧化酶活性可能是HCO^-3增加其有机酸只累,从而影响根生长及Zn有效性机理的重要过程。     

高pH值和铁素对毛白杜鹃和迎红杜鹃根系Fe~(3+)还原酶活性的影响

以耐碱性不同的两种杜鹃花(毛白杜鹃和迎红杜鹃)的组培苗为材料,对其根系Fe3+还原酶活性与铁素和pH值间的关系进行研究,结果表明:培养最初阶段高pH值(NaHCO3提供)与铁素共同诱导根系Fe3+还原酶活性增加;Fe3+对根系Fe3+还原酶活性的诱导作用具有类似于代谢途径中的底物诱导效应;在10d的缺铁处理中,迎红杜鹃根系Fe3+还原酶活性增加,而毛白杜鹃没有增加,说明缺铁对酶活性的诱导存在种间差异;杜鹃花根系Fe3+还原酶活性与植物耐碱性存在正相关。     

GROWTH AND BIOMASS PARTITIONING IN TOMATO IN RELATION TO RATIO OF NITROGEN:PHOSPHORUS SUPPLY

Tomato (Lycopersicon esculentum) plants were grown in hydroponic culture with nitrogen (N): phosphorus (P) supply ratios from 18:1 to 2:1. Nitrate and phosphate were supplied daily in pre-set ratios to maintain a constant P concentration, giving varying degrees of N limitation. Plant dry weight, weights of plant fractions and N and P concentrations in plant parts were measured at 9 and 18 days. Relative growth rate was related to ratio of N:P supplied, with higher ratios giving a higher growth rate, but a noticeably reduced rate was only apparent at 4:1 and 2:1 ratios. Relative growth rate was largely independent of internal N and P concentrations, although there was an optimum internal N:P ratio of approximately 14:1. The plants took up N and P at rates adjusting towards this 14:1 ratio. Depressed relative growth rate of plants inadequately supplied N was linearly correlated with decreased shoot fraction.