Partitioning of shoot and root dry matter and carbohydrates in bean plants suffering from phosphorus, potassium and magnesium deficiency

The influence of varied supply of phosphorus (10 and 250 mmolP m^–3) potassium (50 and 2010 mmol K m^–3) and magnesium(20 and 1000 mmol Mg m^–3) on the partitioning of dry matterand carbohydrates (reducing sugars, sucrose and starch) betweenshoots and roots was studied in bean (Phaseolus vulgaris) plantsgrown in nutrient solution over a 12 d period. Shoot and rootgrowth were quite differently affected by low supply of P, K,and Mg. The shoot/root dry weight ratios were 4.9 in the control(sufficient plants), 1.8 in P-deficient, 6.9 in K-deficientand 10.2 in Mg-deficient plants. In primary (source) leaves,but not in trifoliate leaves, concentrations of reducing sugars,sucrose and starch were also differently affected by low nutrientsupply. In primary leaves under K deficiency and, particularlyMg deficiency, the concentrations of sucrose and reducing sugarswere much higher than in control and P-deficient plants. Magnesiumdeficiency also distinctly increased the starch concentrationin the primary leaves. In contrast, in roots, the lowest concenfrationsof sucrose, reducing sugars and starch were found in Mg-deficientplants, whereas the concentrations of sucrose and starch wereparticularly high in P-deficient plants. There was a close relationshipbetween shoot/root dry weight ratios and relative distributionof total carbohydrates (sugars and starch) in shoot and roots.Of the total amounts of carbohyd rates per plant, the followingproportions were parti tioned to the roots: 22.7% in P-deficient,15.7% in control, 3.4% in K-deficient and 0.8% in Mg-deficientplants. The results indicate a distinct role of Mg and K in the exportof photosynthates from leaves to roots and suggest that alterationin photosynthate partitioning plays a major role in the differencesin dry matter distribution between shoots and roots of plantssuffering from mineral nutrient deficiency. Key words: Bean, carbohydrates, magnesium nutrition, phosphorus nutrition, potassium nutrition, shoot/root growth     

Measurements of pH, sucrose and potassium ions in the phloem sap of castor bean (Ricinus communis) plants

The composition of phloem sap, sampled at different heights along, the stem of castor bean ( Ricinus communis L. cv. Gibsonii) plants, was determined. A gradient in pH was observed; the highest pH values occurred near the shoot apex, decreasing towards the base of the stem. The sucrose content of the exudate exhibited a similar gradient. The concentration of potassium ions was highest near the uppermost, full-grown leaves, decreasing towards the apex and the base of the stem. The importance of these findings for the understanding of phloem translocation and unloading is discussed.     

The response to oxidative stress induced by magnesium deficiency in kidney bean plants

To understand the plant response to oxidative stresses, we studied the influence of magnesium (Mg⁺⁺) deficiency on the formation of hydrogen peroxide (H₂O₂), malondialdehyde (MDA), and protease activity in kidney bean plants. The expression pattern of proteins under Mg⁺⁺ deficiency also was examined via two-dimensional electrophoresis. The formation of H₂O₂ and MDA increased in the primary leaves of plants grown in a nutrient solution deficient in Mg⁺⁺. Protease activity in Mg⁺⁺-deficient plants was also higher than in those grown with sufficient Mg⁺⁺. The expression pattern of the proteins showed that 25 new proteins were generated and 64 proteins disappeared under Mg⁺⁺-deficient conditions. Therefore, a deficiency in Mg⁺⁺ may cause oxidative stress and a change in protein expression. Some of these proteins may be related to the oxidative stress induced by Mg⁺⁺ deficiency.     

Rhizosphere acidification as a response to iron deficiency in bean plants

Iron deficiency in higher plants causes accumulation of salts of organic acids in the roots, the most characteristic being citrate. We show that citrate and malate accumulate in beans (Phaseolus vulgaris L. var Prélude), not because of a lack of the iron-containing enzyme aconitase (EC 4.2.1.3), but in close coupling to the extrusion of protons during rhizosphere acidification, one of the `Fe-efficiency' reactions of dicotyledonous plants. When proton excretion is induced in roots of control bean plants by addition of fusicoccin, only malate, not citrate, is accumulated. We propose that iron deficiency induces production of organic acids in the roots, which in beans leads to both proton excretion and an increased capacity to reduce ferric chelates via the induced electron transfer system in the root epidermis cells.     

Effect of ammonium on uptake of phosphorus,potassium, calcium and magnesium by intact soybean plants

Summary The effect of a wide range of ammonium concentrations (1.78×10^–5 to 3.57×10^–3 M) on the uptake and tissue content of P, K, Ca and Mg in intact soybean (Glycine max (L.) Merr. Cv. Amsoy) plants at different growth stages was studied. A stimulatory effect of ammonium on the uptake and content of P was observed over the entire concentration range, whereas this effect was observed only up to 500 M of ammonium with respect to K. At higher levels (>500 M), ammonium suppressed the uptake and content of K. Inhibition by high levels (>357 M) of ammonium was also found for the uptake and content of Ca and Mg. Inhibition of uptake of K, Ca and Mg by high levels of ammonium may be an important factor in the mineral nutrition of soybean plants. re]19760420     

Reactive oxygen species and root hairs in Arabidopsis root response to nitrogen, phosphorus and potassium deficiency

Plant root sensing and adaptation to changes in the nutrient status of soils is vital for long-term productivity and growth. Reactive oxygen species (ROS) have been shown to play a role in root response to potassium deprivation. To determine the role of ROS in plant response to nitrogen and phosphorus deficiency, studies were conducted using wild-type Arabidopsis and several root hair mutants. The expression of several nutrient-responsive genes was determined by Northern blot, and ROS were quantified and localized in roots. The monitored genes varied in intensity and timing of expression depending on which nutrient was deficient. In response to nutrient deprivation, ROS concentrations increased in specific regions of the Arabidopsis root. Changes in ROS localization in Arabidopsis and in a set of root hair mutants suggest that the root hair cells are important for response to nitrogen and potassium. In contrast, the response to phosphorus deprivation occurs in the cortex where an increase in ROS was measured. Based on these results, we put forward the hypothesis that root hair cells in Arabidopsis contain a sensing system for nitrogen and potassium deprivation.     

Reactivation of phloem export in mature maize leaves after a dark period

Mature leaves of corn plants (Zea mays L. cv. Prior) which were darkened for 48 h contain neither bundle-sheath starch nor glucose, and their sucrose content is below 5 M. In such leaves phloem export has ceased. When re-illuminated, photosynthetic sucrose production starts without delay, but the sucrose: glucose ratio is 1.25:1. Obviously, most of the new-formed sugar is utilized locally. Labeling with ¹⁴CO₂ has shown that phloen export starts 30 to 40 min after the onset of photosynthesis, when the sucrose: glucose ratio has increased to 13:1. The first newly formed starch can be detected when phloem export is reactivated. Glucose content remains constantly low af about 2 M for at least 2 h, and it never exceeds 10 M. Radioactivity in the exporting veins is about five times higher after 2 to 7 h of re-illumination than in the 14-h-day plant. Therefore, phloem export is either intensified during the period of reactivation or exported assimilates are partly unloaded along their way. Comparison of photosynthetic activity of equal-sized leaf strips has shown that both accumulation of photosynthates and radioactivity of exporting veins are about three times higher in the detached strip than in the strip which remained attached to the mother plant.     

Magnesium deficiency enhances resistance to paraquat toxicity in bean leaves

Effects of deficient (20mmol m^?3) and sufficient (1000 mmol m^?3) magnesium (Mg) supply and of varied light intensity (100 μmol m^?2 s^?1 to 580 μmol m^?2 s^?1) on paraquat-dependent chlorophyll destruction in bean (Phaseolus vulgaris) plants grown in nutrient solution were studied over a 12-d period using leaf discs or intact primary leaves. Treatment of leaf discs with 10mmol m ³ paraquat for 15h caused severe chlorophyll loss, especially with increasing light intensity. This chlorophyll destruction by paraquat was very much higher in Mg-sufficient than Mg-deficient leaves. The occurrence of paraquat resistance in Mg deficient leaves was already apparent after 6d growth in nutrient solution, i.e. before any decrease in chlorophyll or growth by Mg deficiency was evident. Also, following foliar application of paraquat (10–140 mmol m^?3) to intact plants, Mg-deficient plants were much more resistant to paraquat, even following longer exposure duration (72 h) and four to 14 times higher paraquat concentrations than those received by Mg sufficient plants. From experiments where exogenous scavengers of superoxide radical (O₂^.-), hydroxyl radical (OH^·) and singlet oxygen (¹O₂) were applied to leaf discs, it appears that O₂^.-, and partly, OH^· are the main O₂ species which contribute to chlorophyll destruction by paraquat. The results demonstrate that Mg-deficient bean plants become highly resistant to O₂^.--mediated and light-induced paraquat injury. The mode of this paraquat resistance is attributed to well-known stimulative effects of Mg deficiency on O₂^.- and H₂O₂ scavenging enzymes and antioxidants.     

Nutritional disorders between potassium,magnesium, calcium,and phosphorus in soil

A new soil testing procedure has been used to demonstrate the effect of an overfertilization by potassium during the preceding years. The total concentration of cations was governed by the amount of soluble anions and the proportion between the different cations was dependent on exchange reactions and is described by activity ratio. High activity ratio between potassium and calcium induced Ca-deficiency, which resulted in a restricted root functioning shown by periodic decreases of nutrient uptake rates and plant growth rate. P-deficiency restricted root growth, but although ammonium phosphate was most effective to increase P-concentration in soil extracts and P-absorption by plants, ordinary superphosphate gave the highest yield and the best utilization of the absorbed phosphorus, magnesium, and calcium.     

Absorption of magnesium and its influence on the uptake of phosphorus,potassium, and calcium by intact groundnut plants

Plant and Soil - In this investigation absorption characteristics of magnesium were investigated by intact groundnut (Arachis hypogaea L.) plants from dilute nutrient solutions over an extended...     

Transport of sucrose, not hexose, in the phloem

Several lines of evidence indicate that glucose and fructose are essentially absent in mobile phloem sap. However, this paradigm has been called into question, especially but not entirely, with respect to species in the Ranunculaceae and Papaveraceae. In the experiments in question, phloem sap was obtained by detaching leaves and placing the cut ends of the petioles in an EDTA solution. More hexose than sucrose was detected. In the present study, these results were confirmed for four species. However, almost identical results were obtained when the leaf blades were removed and only petiole stubs were immersed. This suggests that the sugars in the EDTA solution represent compounds extracted from the petioles, rather than sugars in transit in the phloem. In further experiments, the leaf blades were exposed to (14)CO(2) and, following a chase period, radiolabelled sugars in the petioles and EDTA exudate were identified. Almost all the radiolabel was in the form of [(14)C]sucrose, with little radiolabelled hexose. The data support the long-held contention that sucrose is a ubiquitous transport sugar, but hexoses are essentially absent in the phloem stream.     

Recognition of phlorizin by the carriers of sucrose and hexose in broad bean leaves

Phlorizin (1-[2-(β- d -glucopyranosyloxy)-4, 6-dihydroxyphenyl]-3-(4-hydroxyphenyl)-1-propanone) is a well-known non-transported inhibitor of glucose uptake in animal cells. The effects of this compound were studied on the transmembrane potential difference (PD) of broad bean ( Vicia faba L. cv. Aguadulce) mesophyll cells, and on the uptake of amino acids and sugars by the leaf tissues. Phlorizin (5 m M ) induced a marginal depolarization (7 to 10 mV) of the normal PD (-140 mV), and a slight decrease in the uptake of glycine and serine. By contrast, phlorizin induced a stronger inhibition of the uptake of glucose and 3–O-methylglucose, and more particularly of sucrose uptake and phloem loading. In tissues aged for 12 h, 5 m M phlorizin inhibited the absorption of sucrose from a 1 m M solution by 70%. Kinetic experiments demonstrated that phlorizin acted as a competitive inhibitor for the sucrose carrier and for the hexose carrier. Efflux experiments showed that the counter-exchange of sucrose and of 3–O-methylglucose was also phlorizin-sensitive. Overall, the data show that phlorizin is recognized by the hexose carrier and, more efficiently, by the sucrose carrier of the material investigated, but that it is not transported across the membrane.     

Volatiles released from bean plants in response to agromyzid flies

Liriomyza sativae Blanchard and Liriomyza huidobrensis (Blanchard) (Diptera: Agromyzidae) are two invasive flies in China that have caused economical damage on vegetables and ornamental plants. In this article, we report the profiles of emitted volatiles from healthy, mechanically damaged, and leafminer-damaged bean, Phaseolus vulgaris L., plants. Among 25 emitted volatiles identified, (E)-2-hexen-1-al, (3E)-4,8-dimethyl-1,3,7-nonatriene (DMNT), (Z)-3-hexenyl acetate, (Z)-3-hexen-1-ol, (syn)- and (anti)-2-methylpropanal oxime, (syn)-2-methylbutanal oxime, linalool, and (E,E)-α-farnesene were consistently released from damaged bean plants. Combined amounts of these nine compounds made up more than 70% of the total volatiles emitted from each treatment. No qualitative differences in volatile emission were found between bean plants damaged by the two fly species; however, amounts of several major compounds induced by L. huidobrensis damage were significantly higher than those from plants damaged by L. sativae. The mechanically damaged plants released a higher proportion of green leaf volatiles than plants in the other treatments, whereas leafminer-damaged plants produced more terpenoids and oximes. Furthermore, the volatile profiles emitted from plants, damaged by adult leafminers, by second instar larvae, and even the plants with empty mines left by leafminer larvae (the pupal stage) were significantly different. The identification of volatile oximes released from damaged plants was confirmed and is discussed in a behavioral and biological control context.Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Ultrastructural effects in potato leaves due to antisense-inhibition of the sucrose transporter indicate an apoplasmic mode of phloem loading

To study the export of sugars from leaves and their long-distance transport, sucrose-proton/co-transporter activity of potato was inhibited by antisense repression of StSUT1 under control of either a ubiquitously active (CaMV 35S ) or a companion-cell-specific (rolC) promotor in transgenic plants. Transformants exhibiting reduced levels of the sucrose-transporter mRNA and showing a dramatic reduction in root and tuber growth, were chosen to investigate the ultrastructure of their source leaves. The transformants had a regular leaf anatomy with a single-layered palisade parenchyma, and bicollateral minor veins within the spongy parenchyma. Regardless of the promoter used, source leaves from transformants showed an altered leaf phenotype and a permanent accumulation of assimilates as indicated by the number and size of starch grains, and by the occurrence of lipid-storing oleosomes. Starch accumulated throughout the leaf: in epidermis, mesophyll and, to a smaller degree, in phloem parenchyma cells of minor veins. Oleosomes were observed equally in mesophyll and phloem parenchyma cells. Companion cells were not involved in lipid accmulation and their chloroplasts developed only small starch grains. The similarity of ultrastructural symptoms under both promotors corresponds to, rather than contradicts, the hypothesis that assimilates can move symplasmically from mesophyll, via the bundle sheath, up to the phloem. The microscopical symptoms of a constitutively high sugar level in the transformant leaves were compared with those in wild-type plants after cold-girdling of the petiole. Inhibition of sugar export, both by a reduction of sucrose carriers in the sieve element/companion cell complex (se/cc complex), or further downstream by cold-girdling, equally evokes the accumulation of assimilates in all leaf tissues up to the se/cc complex border. However, microscopy revealed that antisense inhibition of loading produces a persistently high sugar level throughout the leaf, while cold-girdling leads only to local patches containing high levels of sugar. Received: 4 March 1998 / Accepted: 7 April 1998     

Antioxidative response to cadmium in roots and leaves of tomato plants

Treatment of tomato seedlings (Lycopersicon esculentum Mill. cv. 63/5 F1) with increasing CdCl₂ concentrations in the culture medium resulted in Cd accumulation more important in roots than in leaves. Biomass production was severely inhibited, even at low Cd concentration. Cd reduced chlorophyll content in leaves and enhanced lipid peroxidation. An increase in antioxidative enzyme (superoxide dismutase, ascorbate peroxidase, guaiacol peroxidase, glutathione reductase) activities was more pronounced in leaves than in roots, while catalase activity increased only in roots. In addition, changes in isoenzyme composition were observed using the non-denaturing polyacrylamid gel electrophoresis.     

Identification of Glycine Max MicroRNAs in response to phosphorus deficiency

MicroRNAs (miRNAs) are endogenous small RNAs regulating plant development and stress responses. In addition, phosphorus (P) is an important macronutrient for plant growth and development. More than two hundred miRNAs have been identified in Glycine Max and a few of miRNAs have been shown to respond to P deficiency, however, whether there are other miRNAs involved in P deficiency response is largely unknown. In this study, we used high-throughput small RNA sequencing and whole-genome-wide mining to identify the potential miRNAs in response to P deficiency. After sequencing, we deduced 183 known, 99 conserved and 126 novel miRNAs in Glycine Max. Among them, in response to P deficiency, the expressions of 27 known, 16 conserved and 12 novel miRNAs showed significant changes in roots, whereas the expressions of 34 known, 14 conserved and 7 novel miRNAs were significantly different in shoots. Furthermore, we validated the predicated novel miRNAs and found that three miRNAs in roots and five miRNAs in shoots responded to P deficiency. Some miRNAs were P-induced whereas some were P-suppressed. Together these results indicated that the miRNAs identified might play important roles in regulating P signaling pathway.