Physiological and proteomic analysis reveals the impact of boron deficiency and surplus on alfalfa (Medicago sativa L.) reproductive organs.

Boron (B), an essential element for increasing seed yield and germinability in alfalfa (Medicago sativa L.), plays a vital role in its reproductive processes. However, effects of B stress on physiological and proteomic changes in reproductive organs related to alfalfa seed yield and germinability are poorly understood. In order to gain a better insight into B response or tolerance mechanisms, field trials were designed for B deficiency (0 mg B L-1), B sufficiency (800 mg B L-1), and B surplus (1600 mg B L-1) application during alfalfa flowering to analyze the proteomics and physiological responses of alfalfa 'Aohan' reproductive organs. Results showed that B deficiency weakened the stress-responsive ability in these organs, while B surplus reduced the sugar utilization of 'Aohan' flowers and caused lipid membrane peroxidation in 'Aohan' seeds. In addition, four upregulated stress responsive proteins (ADF-like protein, IMFP, NAD(P)-binding Rossmann-fold protein and NAD-dependent ALDHs) might play pivotal roles in the response of 'Aohan' reproductive organs to conditions of B deficiency and B surplus. All of the above results would be helpful to understand the tolerance mechanisms of alfalfa reproductive organs to both B deficiency and B surplus conditions, and also to give insight into the regulatory role of B in improving seed yield and germinability in alfalfa seed production. In summary, B likely plays a structural and regulatory role in relation to lipid metabolism, carbohydrate metabolism, amino acid metabolism, and signal transduction, thus regulates alfalfa reproductive processes eventually affecting the seed yield and germinability of alfalfa seeds.

Boron: the essential element for vascular plants that never was.

Although a requirement for boron is a well-established feature of vascular plants, its designation, for almost a century, as essential is challenged and, instead, the proposal is made that it has never been so as conventionally defined. This is because an alternative interpretation of published evidence negates its compliance with one of the criteria for essentiality, that its effects are direct. The alternative, here postulated, is that boron is, and always has been, potentially toxic, a feature which, for normal growth, development and reproduction, needed to be nullified. This was enabled by exploitation of boron's ability to be chemically bound to compounds with cis-hydroxyl groups. Although particular cell wall carbohydrate polymers, glycoproteins and membrane glycolipids are among candidates for this role, it is here proposed that soluble phenolic metabolites of, or related to, the components of the pathway of lignin biosynthesis, themselves potentially toxic, are primarily used by vascular plants. When metabolic circumstances allow these phenolics to accumulate endogenously in the cytoplasm, their own inherent toxicity is also alleviated, partially at least, by formation of complexes with boron. This chemical reciprocity, enhanced by physical sequestration of the complexes in vacuoles and/or apoplast, thus achieves, in a flexible but indirect manner, a minimization of the inherent toxicities of both boron and relevant phenolics. In these ways, the multifarious outcomes of impairments, natural or experimental, to this interplay are responsible for the lack of consensus to explain the diverse effects observed in the many searches for boron's primary metabolic role, here considered to be nonexistent. In particular, since a toxic element cannot have 'deficiency symptoms', those previously so-called are postulated to be largely due to the expressed toxicity of phenylpropanoids. A principal requirement for the otherwise toxic boron is to nullify, by means of its indirect chemical and physical sequestration, such expression. In these ways, it is therefore neither an essential nor a beneficial element as currently strictly defined.

Mechanisms of organic acids and boron induced tolerance of aluminum toxicity: A review.

Aluminum is a major limiting abiotic factor for plant growth and productivity on acidic soils. The primary disorder of aluminum toxicity is the rapid cessation of root elongation. The root apex is the most sensitive part of this organ. Although significant literature evidence and hypothesis exist on aluminum toxicity, the explicit mechanism through which aluminum ceases root growth is still indefinable. The mechanisms of tolerance in plants have been the focus of intense research. Some plant species growing on acidic soils have developed tolerance mechanisms to overcome and mitigate aluminum toxicity, either by avoiding entry of Al3+ into roots (exclusion mechanism) or by being able to counterbalance toxic Al3+ engrossed by the root system (internal tolerance mechanism). Genes belonging to ALMT (Aluminum-activated malate transporter) and MATE (Multidrug and toxin compounds extrusion) have been identified that are involved in the aluminum-activated secretion of organic acids from roots. However, different plant species show different gene expression pattern. On the other hand, boron (B) (indispensable micronutrient) is a promising nutrient in the tolerance to aluminum toxicity. It not only hinders the adsorption of aluminum to the cell wall but also improves plant growth. This review mainly explains the critical roles of organic acid and B-induced tolerance to aluminum by summarizing the mechanisms of ALMT, MATE, internal detoxification, molecular traits and genetic engineering of crops.

[FTIR Spectroscopic Characterization of Material Composition in Functional Leaf of Cotton under Stress of Potassium and Boron].

Potassium (K) and boron (B) are essential nutrient elements for plants, and the elements play an important role for plant growth, development and physiological metabolism. Cotton has a higher demand for K and B; K deficiency or B deficiency often occurs in cotton though. To reveal the component changes in functional leaf of cotton under K and B stress and investigate effects on material composition from K and B. A pot experiment was conducted at Huazhong Agricultural University. (1) the characteristic peaks at 1 546.86, 1 438.85, 1 153.39 and 1 024.17 cm(-1) disappeared due to B deficiency, and relative absorbance of other characteristic peaks was decreased compared with normal, which suggested that the structures of protein, fiber, soluble sugar and ribosome in cotton functional leaf changed and decreased in cotent when lack of K. (2) the relative absorbance of all characteristic peaks was increased in the B-deficient cotton leaves compared with normal, suggesting B deficiency leads to the accumulation in leaves of protein, and fiber, soluble sugar and other carbohydrates because of the hindered transportation. (3) lack of both potassium and boron, induced significant changes to both the locations and relative absorbance of characteristic peaks, and the content of protein, and soluble sugar and other carbohydrates increased, while the content of nucleic acids and polysaccharides dropped. K deficiency led to the structures of protein, fiber, soluble sugar and ribosome in cotton functional leaf changed and decreased in content; B deficiency gave rise to the accumulation in leaves of protein, and fiber, soluble sugar and other carbohydrates; the content of protein and soluble sugar and other carbohydrates increased, while the content of nucleic acids and polysaccharides dropped when K and B were all in short supply.

Effects of boron nutrition and water stress on nitrogen fixation, seed δ15N and δ13C dynamics, and seed composition in soybean cultivars differing in maturities.

Therefore, the objective of the current research was to investigate the effects of foliar B nutrition on seed protein, oil, fatty acids, and sugars under water stress conditions. A repeated greenhouse experiment was conducted using different maturity group (MG) cultivars. Plants were well-watered with no foliar B (W - B), well-watered with foliar B (W + B), water-stressed with no foliar B (WS - B), and water-stressed with foliar B (WS + B). Foliar B was applied at rate of 0.45 kg · ha(-1) and was applied twice at flowering and at seed-fill stages. The results showed that seed protein, sucrose, fructose, and glucose were higher in W + B treatment than in W - B, WS + B, and WS - B. The increase in protein in W + B resulted in lower seed oil, and the increase of oleic in WS - B or WS + B resulted in lower linolenic acid. Foliar B resulted in higher nitrogen fixation and water stress resulted in seed δ (15)N and δ (13)C alteration. Increased stachyose indicated possible physiological and metabolic changes in carbon and nitrogen pathways and their sources under water stress. This research is beneficial to growers for fertilizer management and seed quality and to breeders to use (15)N/(14)N and (13)C/(12)C ratios and stachyose to select for drought tolerance soybean.

[Comparative study of the urinary excretion of boron, calcium, magnesium and phosphorus in postmenopausal women with and without osteoporosis]. / Estudio comparativo de la excreción urinaria de boro, calcio, magnesio y fósforo en mujeres posmenopáusicas con y sin osteoporosis.

In order to compare the possible relationship between urinary concentrations of boron, calcium, magnesium and phosphorus in serum and urine of postmenopausal women with and without osteoporosis, we selected 45 postmenopausal women over 47 years of age, divided into two groups: group I clinically healthy postmenopausal women and group II postmenopausal women with osteoporosis, without chronic kidney and hepatic diseases or diabetes mellitus. We determined the boron (B), phosphorus (P), total calcium (Ca) and total magnesium (Mg) in the urine of two hours, by atomic emission spectroscopy with induction-coupled plasma (ICPA-ES). Total calcium and total magnesium in serum were determined by atomic flame absorption spectroscopy (FAAS) and inorganic phosphorus in serum, and creatinine in serum and urine, by molecular absorption spectrometry. The preliminary results suggest the existence of a significant difference (p < 0.05) in boron and phosphorus concentrations in the urine of two hours between the groups. The model of linear regression analysis used showed a relationship between urinary concentrations of boron/creatinine index and calcium/ creatinine, magnesium/creatinine and phosphorus/creatinine indexes in the urine of postmenopausal women with osteoporosis.

Is boron nutritionally relevant?

Evidence from numerous laboratories using a variety of experimental models, including humans, shows that boron is a bioactive beneficial element. Much evidence has come from studies that did not require nutritional or environmental stressors or fastidious methods in diet preparation or environmental control. The evidence includes deprivation studies showing that boron is necessary for some higher animals to complete the life cycle, and that realistic low boron intakes result in impaired bone health, brain function, and immune response. Thus, low boron intake is a relevant nutritional concern, which diets rich in fruits, vegetables, nuts, and pulses can prevent.

Boron in plants: deficiency and toxicity.

Boron (B) is an essential nutrient for normal growth of higher plants, and B availability in soil and irrigation water is an important determinant of agricultural production. To date, a primordial function of B is undoubtedly its structural role in the cell wall; however, there is increasing evidence for a possible role of B in other processes such as the maintenance of plasma membrane function and several metabolic pathways. In recent years, the knowledge of the molecular basis of B deficiency and toxicity responses in plants has advanced greatly. The aim of this review is to provide an update on recent findings related to these topics, which can contribute to a better understanding of the role of B in plants.

Boron and the evolutionary development of roots.

Experimental work has shown that Boron (i.e., Boric acid, B) is an essential and multifunctional microelement for vascular plant development. In addition to its other functions, which include xylem development and lignin biosynthesis, we now know that B is involved in phytohormone-signaling and influences the mechanical properties of intercellular pectins. From these data, we conclude that B played an important role during the evolutionary development of lignified tissues, and that it may have been involved in the evolution of vascular plant roots, as hypothesized by D. H. Lewis in 1980. Herein, we review the data pertaining to Lewis' hypothesis, present experimental results on the role of B in root (vs. rhizoid) formation in sunflower vs. a liverwort, and describe the appearance of roots in the fossil record. Open questions are addressed, notably the lack of our knowledge concerning soil microbes and their interactive roles with the micronutrient B during root formation.

Involvement of auxin and CKs in boron deficiency induced changes in apical dominance of pea plants (Pisum sativum L.).

It has previously been shown that boron (B) deficiency inhibits growth of the plant apex, which consequently results in a relatively weak apical dominance, and a subsequent sprouting of lateral buds. Auxin and cytokinins (CKs) are the two most important phytohormones involved in the regulation of apical dominance. In this study, the possible involvement of these two hormones in B-deficiency-induced changes in apical dominance was investigated by applying B or the synthetic CK CPPU to the shoot apex of pea plants grown in nutrient solution without B supply. Export of IAA out of the shoot apex, as well as the level of IAA, Z/ZR and isopentenyl-adenine/isopentenyl-adenosine (i-Ade/i-Ado) in the shoot apex were assayed. In addition, polar IAA transport capacity was measured in two internodes of different ages using 3H-IAA. In B-deficient plants, both the level of auxin and CKs were reduced, and the export of auxin from the shoot apex was considerably decreased relative to plants well supplied with B. Application of B to the shoot apex restored the endogenous Z/ZR and IAA level to control levels and increased the export of IAA from the shoot apex, as well as the 3H-IAA transport capacity in the newly developed internodes. Further, B application to the shoot apex inhibited lateral bud growth and stimulated lateral root formation, presumably by stimulated polar IAA transport. Applying CPPU to the shoot apex, a treatment that stimulates IAA export under adequate B supply, considerably reduced the endogenous Z/ZR concentration in the shoot apex, but had no stimulatory effect on IAA concentration and transport in B-deficient plants. A similar situation appeared to exist in lateral buds of B-deficient plants as, in contrast to plants well supplied with B, application of CKs to these plants did not stimulate lateral bud growth. In contrast to the changes of Z/ZR levels in the shoot apex, which occurred after application of B or CPPU, the levels of i-Ade/i-Ado stayed more or less constant. These results suggest that there is a complex interaction between B supply and plant hormones, with a B-deficiency-induced inhibition of IAA export from the shoot apex as one of the earliest measurable events.

Boron deficiency and concentrations and composition of phenolic compounds in Olea europaea leaves: a combined growth chamber and field study.

Boron deficiency is the most frequent micronutrient disorder in olive (Olea spp.) orchards. We tested the hypothesis that plant boron status affects phenolic metabolism, which, in turn, influences several ecophysiological traits of olive (Olea europaea L.) trees, by studying the effects of boron deficiency on leaf phenolic compounds of olive in a growth chamber experiment (CE) and a field experiment (FE). In the CE, a semi-hydroponic system was used to control nutrient supply. Plants received complete nutrient solution containing either 23 (control) or 0 microM H3BO3 (boron-deficient treatment). In the FE, boron-deficient trees were chosen based on visible boron-deficiency symptoms and analysis of their leaf boron concentration. Boron deficiency caused significant accumulation of phenolic compounds in leaves of CE plants (1.7 to 5.8 times more, depending on leaf age), but not in leaves of FE plants. However, in both experiments, the concentration of an unidentified phenolic compound, with a UV-spectrum resembling that of caffeic acid, increased in response to boron deficiency (by a factor of 40 to 184 in the CE and by a factor of three in the FE). Regression analysis showed that the concentration of this compound was negatively correlated to leaf boron concentration, irrespective of growth conditions and treatment. We conclude that, under field conditions, boron deficiency may not be the only factor determining the concentration of total phenolics, but it may be responsible for the accumulation of a distinct phenolic metabolite in olive leaves.

Boron deficiency increases putrescine levels in tobacco plants.

Polyamine concentrations were determined in leaves and roots of tobacco plants (Nicotiana tabacum L.) subjected to a short-term boron deficiency. A decrease in the growth of shoots and, especially, roots was found under this mineral deficiency. Boron deficiency did not lead to a significant decrease in leaf or root ion concentrations when compared to control treatment; however, as expected, leaf boron concentration was lower in boron-deficient plants in comparison to the control. In leaves, the levels of free putrescine and spermidine were similar in both treatments. In roots, a short-term boron deficiency caused an increase in free putrescine. Moreover, boron-deficient plants had higher conjugated polyamine concentration than boron-sufficient plants, which was especially evident for conjugated putrescine in leaves. A possible link between boron and polyamine levels is proposed and discussed.

Environmental implications of adopting a dominant factor approach to salinity management.

Additive or multiplicative models of crop response on which salinity management theory have been developed may lead to an erroneous perception regarding compensative interaction among salinity and other growth factors. We present results from studies of biomass production and transpiration of corn (Zea mays L. cv. Jubilee), melon (Cucumis melo L. subsp. melo cv. Galia), tomato (Lycopersicon esculentum Mill. cv. 5656), onion (Allium cepa L. cv. HA 944), and date palms (Phoenix dactylifera L. cv. Medjool) under salinity combined with water or nitrate (growth promoters) or with boron (growth inhibitor). The measured crop responses were to the more severe stress rather than to combinations of the individual effects of the various stresses. Consequences of shifting management of saline water to a dominant factor approach include reduction of environmental contamination and conservation of water resources.

Effect of dietary boron on the aging process.

Total boron concentrations in Drosophila changed during development and aging. The highest concentration of boron was found during the egg stage, followed by a decline during the larval stages. Newly emerged flies contained 35.5 ppm boron. During the adult stage the boron concentration increased by 52% by 9 weeks of age. Adding excess dietary boron during the adult stage decreased the median life span by 69% at 0.01 M sodium borate and by 21% at 0.001 M sodium borate. Lower concentrations gave small but significant increases in life span. Supplementing a very low boron diet with 0.00025 M sodium borate improved life span by 9.5%. The boron contents of young and old mouse tissues were similar to those of Drosophila and human samples. Boron supplements of 4.3 and 21.6 ppm in the drinking water, however, did not significantly change the life span of old mice fed a diet containing 31.1 ppm boron.

Relation of boron to the composition and mechanical properties of bone.

A review of the experimental studies relating boron to biological effects on appendicular and axial bones in animal models suggests that numerous influences, known and unknown, affect the responsiveness of bone to dietary boron. Degrees of skeletal response to boron are modified by other nutritional variables that include calcium, magnesium, vitamin D, and fluoride. Evidence suggests that appendicular and axial bones may differ in their responses. Tests of the mechanical properties of bones may provide useful criteria for assessing the impacts of boron status on bone. These tests might resolve questions about optimal intakes of boron because mechanical properties sometimes respond to boron when composition of bones does not. Difficulty in interpreting some of the existing research arises because of the incipient state of knowledge regarding boron nutriture, to analytical problems associated with determining accurately the small quantities of boron in feed and tissues, and to technological difficulties in controlling extraneous exposure of experimental animals to boron. Yet there is considerable evidence that both compositional and functional properties of bone are affected by boron status.

The biochemical effects of physiologic amounts of dietary boron in animal nutrition models.

This review summarizes evidence that supports working hypotheses for the roles of boron in animal model systems. It is well established that vascular plants, diatoms, and some species of marine algal flagellates have acquired an absolute requirement for boron, although the primary role of boron in plants remains unknown. Recent research findings suggest that physiologic amounts of supplemental dietary boron (PSB) affect a wide range of metabolic parameters in the chick and rat model systems. Much of the current interest in boron animal nutrition began with the initial finding that PSB stimulates growth in cholecalciferol (vitamin D3)-deficient chicks, but does not markedly affect growth in chicks receiving adequate vitamin D3 nutriture. The finding suggests that boron affects some aspect of vitamin D3 metabolism or is synergistic with vitamin D3 in influencing growth. Vitamin D3 regulates energy substrate utilization, and current research findings indicate that dietary boron modifies that regulatory function. The concentration of circulating glucose, the most thoroughly investigated metabolite to date, responds to PSB, especially during concomitant vitamin D3 deficiency. In chicks, PSB substantially alleviated or corrected vitamin D3 deficiency-induced elevations in plasma glucose concentrations. The influence of vitamin D3 on cartilage and bone mineralization is mediated in part through its role as a regulator of energy substrate utilization; calcification is an energy-intensive process. There is considerable evidence that dietary boron alleviates perturbations in mineral metabolism that are characteristic of vitamin D3 deficiency. In rachitic chicks, PSB alleviated distortion of the marrow sprouts of the proximal tibial epiphysial plate, a distortion characteristic of vitamin D3 deficiency.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of dietary boron in rats fed a vitamin D-deficient diet.

Although boron has long been known to be a required nutrient for plants, it was not until recently that there was any suggestion of a nutritional requirement for animals and humans. Addition of boron to the diet of vitamin D-deficient chicks indicated that boron may play a role in animal nutrition. Studies with rats have demonstrated that supplemental dietary boron has most marked effects when the diet is deficient in known nutrients. We observed higher apparent-balance values of calcium, magnesium, and phosphorus for rats fed a vitamin D-deprived diet with dietary supplemental boron (2.72 ppm), than for rats fed the same diet without added boron (0.16 ppm). The treatment group with dietary supplemental boron demonstrated a high degree of variability in response to boron. We hypothesize that relatively large and variable vitamin D stores in weanling rats from a colony supplemented with 3000 IU vitamin D/kg diet accounted for the observed variable response. A recent, unpublished study using weanling rats from a low-vitamin D colony appears to support this hypothesis.

Biochemical and physiologic consequences of boron deprivation in humans.

Boron deprivation experiments with humans have yielded some persuasive findings for the hypothesis that boron is an essential nutrient. In the first nutritional study with humans involving boron, 12 postmenopausal women first were fed a diet that provided 0.25 mg boron/2000 kcal for 119 days, and then were fed the same diet with a boron supplement of 3 mg boron/day for 48 days. The boron supplementation reduced the total plasma concentration of calcium and the urinary excretions of calcium and magnesium, and elevated the serum concentrations of 17 beta-estradiol and testosterone. This study was followed by one in which five men over the age of 45, four postmenopausal women, and five postmenopausal women on estrogen therapy were fed a boron-low diet (0.23 mg/2000 kcal) for 63 days, then fed the same diet supplemented with 3 mg boron/day for 49 days. The diet was low in magnesium (115 mg/2000 kcal) and marginally adequate in copper (1.6 mg/2000 kcal) throughout the study. This experiment found higher erythrocyte superoxide dismutase, serum enzymatic ceruloplasmin, and plasma copper during boron repletion than boron depletion. The design of the most recent experiment was the same as the second study, except this time the diet was adequate in magnesium and copper. Estrogen therapy increased plasma copper and serum 17 beta-estradiol concentrations; the increases were depressed by boron deprivation. Estrogen ingestion also increased serum immunoreactive ceruloplasmin and erythrocyte superoxide dismutase; these variables also were higher during boron repletion than depletion for all subjects, not just those ingesting estrogen.(ABSTRACT TRUNCATED AT 250 WORDS)

Proposed physiologic functions of boron in plants pertinent to animal and human metabolism.

Boron has been recognized since 1923 as an essential micronutrient element for higher plants. Over the years, many roles for boron in plants have been proposed, including functions in sugar transport, cell wall synthesis and lignification, cell wall structure, carbohydrate metabolism, RNA metabolism, respiration, indole acetic acid metabolism, phenol metabolism and membrane transport. However, the mechanism of boron involvement in each case remains unclear. Recent work has focused on two major plant-cell components: cell walls and membranes. In both, boron could play a structural role by bridging hydroxyl groups. In membranes, it could also be involved in ion transport and redox reactions by stimulating enzymes like nicotinamide adenine dinucleotide and reduced (NADH) oxidase. There is a very narrow window between the levels of boron required by and toxic to plants. The mechanisms of boron toxicity are also unknown. In nitrogen-fixing leguminous plants, foliarly applied boron causes up to a 1000% increase in the concentration of allantoic acid in leaves. In vitro studies show that boron inhibits the manganese-dependent allantoate amidohydrolase, and foliar application of manganese prior to application of boron eliminates allantoic acid accumulation in leaves. Interaction between borate and divalent cations like manganese may alter metabolic pathways, which could explain why higher concentrations of boron can be toxic to plants.