ABA Uptake in Source and Sink Tissues of Sugar Beet

The mode of abscisic acid (ABA) uptake was studied in excised leaf and root tissue discs of sugar beet (Beta vulgaris L.). Discs were incubated in buffered medium that contained 1 mm CaCl₂ and [¹⁴C]ABA. The sensitivity of ABA uptake to metabolic inhibitors and temperature indicated that the ABA transport system had an energy-dependent component. Energy-dependent uptake was greater in leaf than in root tissue (70% and 50%, respectively). Energy-dependent uptake by both tissues and passive uptake by root tissues were highly pH dependent. Maximal uptake was observed at pH 5.5. Leaf tissue incubated in the dark showed a 50% reduction of uptake as compared with tissue under light. The decrease was due to reduced passive uptake.     

Diurnal Changes in the Sugar and Organic Anion Concentrations in Red Beet Leaves

Marked diurnal fluctuations in the concentrations of ethanolsoluble sugars and organic anions occurred in red beet leaves.These fluctuations were related to solar radiation and air temperature.Leaves from four plots which had received different manurialtreatments contained significantly different mean sugar andanion concentrations, but the patterns of the diurnal fluctuationswere not affected by the manurial treatments. The results indicated a daily production of photosynthate equalto about 19 per cent per day (leaf-weight basis), compared tothe net assimilation rate of 17 per cent per day as estimatedfor similar plants from dry-weight increase. From the results no evidence can be adduced to support the hypothesisthat sugar accumulated in the leaves to an extent which inhibitedphotosynthesis.     

Sink to Source Transition of Populus Leaves

Development of the Populus leaf is presented as a model system to illustrate the sequence of events that occur during the sink to source transition. A Populus leaf is served by three leaf traces, each of which consists of an original procambial trace bundle that differentiates acropetally and continuously from more mature procambium in the stem and a complement of subsidiary bundles that differentiates bidirectionally from a leaf basal meristem. During development these subsidiary bundles maintain continuity through the meristematic region of the node. The basipetally developing subsidiary bunles form phloem bridges that serve to integrate adjacent leaf traces of the stem vasculature. Distal to the node the acropetally developing bundles from all three leaf traces are reoriented in a precise and orderly sequence to form tiers of petiolar bundles. These tiers of bundles extend into the midrib where bundles diverge at intervals as the major lateral veins. The dorsal-most tier of bundles extends to the lamina tip and each successive tier of bundles contributes to lateral veins situated more proximally in the lamina. Although the midrib and the major vein system differentiate acropetally in the lamina, they mature basipetally. Maturation of the mesophyll and other lamina tissues also mature basipetally. As a consequence of the basi-petal maturation process, the lamina tip matures very early and begins exporting photosynthates while the lamina base is still importing from other leaves. The transition of a leaf from sink to source status must therefore be considered as a progression of structural and functional events that occur in synchrony.     

Osmotic Response of Sugar Beet Source Leaves at CO(2) Compensation Point

As sugar beet source leaves lowered the CO₂ concentration to compensation point in a closed atmosphere, leaf thickness and relative water content decreased. Leaf water potential declined rapidly from −0.5 to −1.4 megapascals. At 340 microliters CO₂ per liter, water potential and sucrose, glucose, and fructose contents were steady in photosynthesizing source leaves. Within 90 minutes after leaves were exposed to a CO₂ concentration at the compensation point, leaf sucrose content declined to 60% of the preteatment level, rapidly in the first 30 minutes and then more slowly. During the subsequent 200 minutes, sucrose content increased to 180% of pretreatment level. Glucose and fructose remained unchanged during the treatment. Degradation of starch was sufficient to account for the additional sucrose that accumulated. Labeled carbon lost from starch appeared in sucrose and several other compounds that likely contributed to the recovery in leaf water content.     

Growth and Sink to Source Transition in Developing Leaves of Sugarbeet

The growth and sink to source transition (cessation of assimilateimport) in light-grown leaves were compared to those of dark-grownleaves. Darkening chambers were placed over sugarbeet (Betavulgaris L.) plants so that new leaves emerged and grew in thedark. New leaves emerged at 1.8 day intervals, regardless ofthe light conditions. The dark-grown leaves were reversiblyretarded in overall growth; they were unable to photosynthesize,but attained photosyn-thetic, vein loading and export capacityafter exposure to sufficient amount and duration of light. Despitethe inability to fix carbon, dark-grown leaves showed dry weightgain. The increase in the dry weight, however, was localizedin the petiole and major veins and not in the laminar tissue.Despite metabolic differences in the two leaf types, sink tosource transition occurred in about a week in both light- anddark-grown leaves; and assimilate importing stopped at about8 days after emergence. While sink to source transition (asdetermined by assimilate import) per se did not appear to belight-regulated, the ability to accumulate sucrose in the veinsfor export out.of leaves was light dependent. This was basedon the observation that post-transitional dark-grown leaveswhich had ceased importing could not export exogenously appliedsucrose unless they were exposed to light for several days.The data indicated that transition is developmentally regulatedand not coupled to photosynthetic capacity. ¹Contribution No. D-15192-1-89 from the New Jersey AgriculturalExperiment Station. This work was funded in part by the BeetSugar Development Foundation and Rutgers Universi ty ResearchCouncil and was submitted as partial fulfillment for M.S. degreeby Lynne H. Pitcher. (Received August 22, 1990; Accepted January 9, 1991)     

Alkali Cation/Sucrose Co-transport in the Root Sink of Sugar Beet

The mechanism of sucrose transport into the vacuole of root parenchyma cells of sugar beet was investigated using discs of intact tissue. Active sucrose uptake was evident only at the tonoplast. Sucrose caused a transient 8.3 millivolts depolarization of the membrane potential, suggesting an ion co-transport mechanism. Sucrose also stimulated net proton efflux. Active (net) uptake of sucrose was strongly affected by factors that influence the alkali cation and proton gradients across biological membranes. Alkali cations (Na⁺ and K⁺) at 95 millimolar activity stimulated active uptake of sucrose 2.1- to 4-fold, whereas membrane-permeating anions inhibited active sucrose uptake. The pH optima for uptake was between 6.5 and 7.0, pH values slightly higher than those of the vacuole. The ionophores valinomycin, gramicidin D, and carbonyl cyanide m-chlorophenylhydrazone at 10 micromolar concentrations strongly inhibited active sucrose uptake. These data are consistent with the hypothesis that an alkali cation influx/proton efflux reaction is coupled to the active uptake of sucrose into the vacuole of parenchyma cells in the root sink of sugar beets.     

Changes of Sugar Levels in Cucumber Leaves during Ammonium Toxicity

Toxic effects of high concentrations of ammonia were studied in the cucumber plant (Cucumis sativus cv. Suisei No. 2). When the cucumber plant was cultured with 200 mg/l NH₃-N (as NH₄Cl), some characteristic symptoms, probably due to ammonium toxicity, appeared in the leaves after about 1 week, while no such symptoms were observed in the plants cultured with 20 mg/1 NH₃-N. The level of free sugars in 20 mg/l NH₃-N treated plants decreased with time and was lower than that in plants treated with 200 mg/l NH₃-N. Specially distinct differences were found as regards the levels of fructose and glucose. After 9 days' culture the content of glucose in 200 mg/l NH₃-N plants was 17 times higher than that of 20 mg/l NH₃-N plants. From the results of an incorporation of photosynthesized ¹⁴CO₂ for 3 hours into newly synthesized glucose it is evident that this accumulation of glucose can not be the degradative product of a glucose polymer such as starch. The levels of starch were also studied, and it was found that the starch level decreased due to ammonium toxicity. These results suggest that the translocation of glucose after its synthesis is inhibited by ammonium toxicity, at least up to starch synthesis.     

Carbon Assimilation and Leaf Water Status in Sugar Beet Leaves during a Simulated Natural Light Regimen

Carbon assimilation and leaf water status were studied in sugar beet (Beta vulgaris L., Klein E-type multigerm) leaves during a light period in which illumination either increased rapidly to full irradiance or changed gradually in a sinusoidal manner as generally occurs during a natural day. A light regimen that simulated the light of a natural day was produced by adjusting irradiance with a neutral-density filter under the control of a computer. Under this light regimen, photosynthesis, transpiration, and stomatal conductance followed the irradiance pattern very closely and ribulose bisphosphate carboxylase was nearly fully activated. When illumination was increased rapidly at the beginning of a light period, transpiration also increased quickly, causing leaves to wilt to some extent. The activation state of ribulose bisphosphate carboxylase increased to only 52%, but ribulose bisphosphate level was nearly twice as high as during the simulated natural day. In spite of the differences in activation state and ribulose bisphosphate levels, photosynthesis rates were very similar under both regimens. Nevertheless, differences in parameters between leaves under the two irradiance regimens can affect how a plant responds to internal or external factors, and therefore, the rate at which irradiance increases at the beginning of a light period is an important consideration when interpreting data.     

Saturation and Utilization of Nitrate Pools in Pea and Sugar Beet Leaves

The critical periods in the saturation of pea and sugar beet leaves with nitrate absorbed by roots were discriminated. In peas, during the first 14 h, all nitrate penetrating leaf cells was concentrated in the cytosol (metabolic pool). During the second period (14–62 h), nitrate began to flow into the vacuole (storage pool), and the filling of the metabolic pool continued. Metabolic pool was saturated by the end of this period (62 h). During the third period (62–110 h), further nitrate accumulation in the cell occurred because of expanding of the storage pool. Its saturation (similarly as total cell saturation) commenced 86 h after the start of nitrate uptake. In sugar beet leaves, both metabolic and storage nitrate pools were saturated by the end of the first period (14 h), and the sizes of these pools did not change during the second period (14–86 h). When pea plants were transferred to the nitrate-free medium, nitrate efflux began from the storage pool until its complete exhausting after 3 days. In sugar beet leaves, nitrate was still present in the storage pool 4 days after plant transfer to the nitrate-free medium. In both crops, nitrate export from the storage pool was aimed at the maintenance of the optimum nitrate concentration in the metabolic pool and, thus, at the maintenance of nitrate reductase activity. A functional diversity of nitrate compartmentation in the cells of various plant species is discussed.     

Sucrose-Phosphate Synthase,Sucrose Synthase,and Invertase in Sugar Beet Leaves

The activity of sucrose-phosphate synthase (SPS) in sugar beet (Beta vulgaris L.) leaves was shown to exceed considerably the synthesizing activity of sucrose synthase (SS). The rise in SPS activity was related to the daylight period; i.e., it was associated with the rate of photosynthesis. The highest SPS activity was characteristic of fully expanded source leaves. In young developing leaves (leaves expanded to less than half of their final size), which represent the sink organs, the SPS activity was 2.5 times lower. At all stages of leaf development, the synthesizing SS activity was rather low. The diurnal change of SS activity was independent of photosynthesis and showed a slight rise from 6:00–8:00 p.m. Under field conditions, the highest SPS activity was found in leaves in the terminal stage of their development (105-day-old plants); the synthesizing activity of SS showed little changes during this period. The activity of soluble acid invertase was characteristic of young leaves. In mature leaves, the activity of this enzyme correlated with the daylight period. These changes occurred on the background of low sucrose content in leaves. The regulation of SPS, SS, and invertase activity is discussed. It is supposed that compartmentation of these enzymes in the photosynthesizing cell is important for transport, metabolism, and the osmotic function of sucrose in leaves.     

Photosynthetic Electron Transport and Carbon Metabolism during Altered Source/Sink Balance in Single-Rooted Soybean Leaves

The single-rooted leaf of soybean (Glycine max L. Merr.) wasused to study electron transport and various reactions involvedin carbon metabolism under conditions of altered source/sinkbalance. When the leaves grown for 5 d under a regime of 10h of light per day (the standard growth condition, 500–580µmol photons m²s^–1) were treated for 6 or 7 d withcontinuous light to alter the source/sink balance of photosynthates(the sink limit condition), the photo-synthetic rate decreasedto 54% of that in leaves grown under the standard condition.The decrease in photosynthesis due to the treatment with continuouslight was associated with a large increase in the resistanceto the movement of CO₂ from surfaces of mesophyll cell wallsto intercellular sites of photosynthesis. The treatment alsocaused large increases in levels of NADPH and ATP and in theratio of ATP to ADP in the leaves. The levels of ribulose 1,5-bisphosphateand dihydroxyacetone phosphate in the treated leaves rose to460% and 160% of those in the control leaves, respectively,while the level of 3-phosphoglycerate in the former fell to80% of the level in the latter. The treatment also caused thelevels of almost all of the other phosphorylated intermediatesin photosynthetic carbohydrate metabolism, with the exceptionof fructose 6-phos-phate and adenosine diphosphate glucose,to increase by 110% to 200%. These results indicate that, underthe sink limit condition, the significant decrease in photosyntheticactivity was due to inactivation of photosynthetic carbohydratemetabolism rather than to a decline in photoelectron transport.Our observations also suggest that the accumulation of variousphosphorylated intermediate results in a limitation of levelsof Pj in chloroplast stroma and that, under such conditions,the activity of ribulose 1,5-bisphosphate carboxylase is reducedand there is a subsequent decrease in photosynthetic activity. (Received August 8, 1988; Accepted April 19, 1989)     

Drought Stress Memory in Sugar Beet: Mismatch Between Biochemical and Physiological Parameters

In a greenhouse study, we aimed to determine whether a temporary water deficit induces ‘drought memory’ in sugar beet (Beta vulgaris L.), and whether this effect can be quantified by alterations in the fluorescence signature of the leaves. Plants were subjected to three consecutive water deficit phases, each followed by a recovery period, and in each cycle new, fully developed leaves were analyzed. Changes in the photosynthetic performance and pigment fluorescence were recorded with a hand-held fluorescence sensor, a laser-induced fluorescence spectrometer, and a leaf gas exchange analyzer. Parameters such as osmotic potential, proline, and chlorophyll content were used as indicators for biochemical modifications and quantification of stress intensity. In general, the evaluated cultivars showed a similar response pattern to water deficit, although the intensity of the stress-induced modification was not always on the same level in the distinct parameters. The long-term and repeated drought caused a decrease of net photosynthesis, increase of far-red fluorescence, and a decrease of both the ‘Simple Fluorescence Ratio’ and the fluorescence lifetime (LT mean) in the blue spectral region. In the second drought cycle, changes in osmotic potential and proline content were lower, but alterations in photosynthesis and fluorescence were as strong as in the first and third drought cycles. This indicates that even if a drought stress memory might occur, it was not possible to precisely identify it using gas exchange and pigment fluorescence determinations. Irrespective of that, the photosynthesis and chlorophyll fluorescence-based parameters (RF, SFR) clearly indicated with high temporal resolution the response of sugar beet plants to the stress, and their partial recovery.     

Translocation of C Sucrose in Sugar Beet during Darkness

The time-course of arrival of ¹⁴C translocate in a sink leaf was studied in sugar beet (Beta vulgaris L. cultivar Klein Wanzleben) for up to 480 minutes of darkness. Following darkening of the source leaf, translocation rapidly declined, reaching a rate approximately 25% of the light period rate by 150 minutes. Comparison of data from plants that were girdled 1 cm below the crown with data from ungirdled plants indicates that after about 150 minutes darkness the beet root becomes a source of translocate to the sink leaf. After about 90 minutes darkness, starch-like reserve polysaccharide from the source leaf begins to contribute ¹⁴C to ethanol soluble pools in that leaf. Because of a 15% isotope mass effect, sucrose, at isotopic saturation, reaches a specific activity which is about 85% of the level of the supplied CO₂. The source leaf sucrose specific activity remains at the isotopic saturation level for about 150 minutes of darkness, after which time input from polysaccharide reserves causes the specific activity to drop to about 55% of that of the supplied CO₂. Sucrose specific activity determinations, polysaccharide dissolution measurements, and pulse labeling experiments indicate that following partial depletion of the sucrose pool, source leaf polysaccharide contributes to dark translocation. Respired CO₂ from the source leaf appears to be derived from a pool which, unlike sucrose, remains at a uniform specific activity.     

Changes in Physiological Parameters of Sugar Beet (Beta vulgaris L.) Genotypes in Response to High Temperature under Two Different Climates

Russian Journal of Plant Physiology - Having increased the temperature of different regions, global climate change can affect plants’ growth and development. This study aimed to explore the...     

The Role of Leaves in the Perception of Vernalizing Temperatures in Sugar Beet

Annual and biennial sugar beet varieties require long days toinduce flowering but the biennial genotypes additionally requirevernalization. Previous research has suggested that the inabilityof non-vernalized biennial plants to flower can be explainedby a lack of competence of the leaves to respond to long days.In this study defoliation experiments were used to investigatewhich leaves could perceive long daylengths and, in particular,whether leaves initiated from a non-vernalized shoot apicalmeristem could perceive vernalizing temperatures and producea floral stimulus in long days. Annual and vernalized biennialplants flowered if young leaves (i.e. those formed during orafter vernalization) were kept on the plants, but they did notflower if only older expanded leaves (including those expandedprior to vernalization) were present. No evidence was obtainedto indicate that the older leaves contained inhibitors of floweringand it seems most likely that there is a decline in responsivenessto daylength with increasing leaf age. Exposure to vernalizingtemperatures accelerated flowering of the annual and was essentialfor flowering of the biennial. The presence of a single leafinitiated, but not expanded, prior to the transfer of biennialplants to vernalizing temperatures was sufficient to induceflowering. This indicates that expanding leaves do not needto be initiated from a vernalized apical meristem to becomecompetent to produce a floral stimulus in long days. Key words: Beta vulgaris L., sugar beet, vernalization, flowering     

Uptake and Physiological Effects of Cadmium in Sugar Beet (Beta vulgaris) Related to Mineral Provision

Sugar beet seedlings (Beta vulgaris L. cv. Monohill) were grownfor 14 d on a nutrient solution based on the nutrient proportionsin healthy plants. Nutrients were supplied either once at relativelyhigh concentrations, or in small amounts with a daily incrementalincrease of 0?15 or 0?20 in accordance with an exponential growthrate. Cadmium (0, 0?6, 2?3, 50 or 20?0 µmol) was introducedeither by a single addition or in daily increments of 0?15 or0?20. Cadmium uptake, expressed as a percentage of total Cd²⁺supplied, decreased with increasing total C^d2+ content and withdecreasing availability of nutrients. With a daily supply ofcadmium, net uptake, transport and content per unit of dry weightin roots and shoots were related to the total Cd²⁺ supplied.Cadmium caused growth retardation, increased root/whole-plantratio, and decreased root-tip respiration and photosynthesis.At high initial nutrient concentrations, Cd²⁺ decreased thecontents of sucrose, glucose, fructose, and starch per unitof dry weight. The opposite was found if nutrients were addeddaily. In the latter case, the dry weight/fresh weight ratioalso increased. The effects of cadmium were related to [Cd²⁺]in proportion both to the root absorption area and to the nutrientconcentration. Key words: Sugar beet, mineral provision, cadmium uptake, sugar formation, growth     

Effect of Benzyladenine and Hydroxybenzyladenosine on Gas Exchange of Bean and Sugar Beet Leaves

Using bean seedlings, the effects of benzyladenine (BA) on stomatal conductance (g_s), transpiration rate (E), and net photosynthetic rate (P_N) were examined in order to find out dose and time responses. In bean seedlings, BA appli roots in concentrations of 1, 5, 10, and 20 µM increased g_s and P_N of leaves already 1 h after application. E was not markedly affected and water use efficiency (WUE) was increased. However, the effects were mostly transient and after 24 h P_N only at 1 and 5 µM BA was increased, and other parameters were not affected or even decreased. In sugar beet seedlings, the effects of hydroxybenzyladenosine (HBA) in addition to those of BA on the same parameters were determined. The both cytokinins were applied in 1, 5, 10, and 20 µM concentrations either to roots or sprayed on leaves However, the effects were inconsistent and the positive effect was observed only after 24 h on P_N in plants with roots immersed in 5 and 10 µM BA, or 10 µM HBA, and on E in plants sprayed with 5 µM BA or 10 µM HBA. Thus the stimulation of gas exchange by exogenously applied cytokinins is rather exceptional than general.