Functional Imaging of Plants: A Nuclear Magnetic Resonance Study of a Cucumber Plant

Functional magnetic resonance imaging was used to study transients of biophysical parameters in a cucumber plant in response to environmental changes. Detailed flow imaging experiments showed the location of xylem and phloem in the stem and the response of the following flow characteristics to the imposed environmental changes: the total amount of water, the amount of stationary and flowing water, the linear velocity of the flowing water, and the volume flow. The total measured volume flow through the plant stem was in good agreement with the independently measured water uptake by the roots. A separate analysis of the flow characteristics for two vascular bundles revealed that changes in volume flow of the xylem sap were accounted for by a change in linear-flow velocities in the xylem vessels. Multiple-spin echo experiments revealed two water fractions for different tissues in the plant stem; the spin-spin relaxation time of the larger fraction of parenchyma tissue in the center of the stem and the vascular tissue was down by 17% in the period after cooling the roots of the plant. This could point to an increased water permeability of the tonoplast membrane of the observed cells in this period of quick recovery from severe water loss.     

Variation in Translocation during the Photoperiod: Experiments Feeding 11CO2 to Sunflower

An array of 14 miniature Geiger counters arranged along petioleand stem has been used to follow the translocation kineticsfor ¹¹C assimilate in sunflower. Experiments over a 2 d periodindicate that (a) speed is insensitive to time of day and (b)the loading delay in the morning is comparable to that in thelate afternoon but smaller than that at mid-day. There is evidencefor substantial accumulation and retention of label along thepath on all occasions.     

Phosphorus nutrition of jarrah (Eucalyptus marginata) seedlings

Summary Effects of calcium phosphate supply on plant dry matter and phosphorus concentrations of parts of jarrah (Eucalyptus marginata) seedlings grown in a lateritic topsoil from the jarrah forest were examined in two glasshouse trials. Phosphorus deficiency depressed root and shoot dry weights and severely deficient leaves were smal and purple with prominent red major veins. Phosphorus deficiency severely reduced stem phosphorus levels (0.5% to 0.02%, experiment 1). Phosphorus concentrations were higher in bark than wood and the amount of phosphorus in the bark was sensitive to stem age and phosphate supply. Phosphorus adequate plants had bark phosphorus concentrations in the range 0.2–0.9% compared to <0.1% in deficient plants (experiment 2). Jarrah leaves accumulated dry matter up to 80 days after expansion and some leaves exported phosphorus during this period. Bark analysis may therefore be preferable to leaf analysis for detecting phosphorus deficiency in this species.     

Effects of Root Pruning on Translocation of Photosynthates in Phaseolus vulgaris L

Root pruning increased the level of ethanol soluble sugars inred kidney bean plants (Phaseolus vulgaris L. ) grown in aeratednutrient solution. However, the concentration gradient of thesesugars down the stem and its translocation velocity remainedunchanged. Removal of 50% of the roots had no effect on thetotal photosynthates exported from source leaves but the finaldistribution pattern of photosynthates was altered; less movingtoward the upper plant parts, and accumulation occurring inthe lower stems. Translocation velocity of photosynthates towardthe upper plant parts was drastically reduced by root pruning. Key words: Phaseolus vulgaris, Photosynthate translocation, Root pruning     

Boron Deficiency and Translocation Profiles in Sunflower

The distribution of carbon-14 down the stems of comparable boron-deficient and boron-sufficient sunflower plants after photosynthesis of ¹⁴CO₂ by a single exposed leaf was investigated. In boron-deficient plants the advancing front of radioactivity was always found less far down the stem than in boron-sufficient plants. The general shape of the profile is the same in the two sets of plants. We conclude that the velocity of translocation is reduced in the boron-deficient plants.     

根区缓冲降温处理对葡萄叶片冻害的影响

为探索根区降温条件对葡萄(Vitis vinifera)叶片冻害的影响,以1年生美乐葡萄(V.vinifera cv.‘Merlot’)幼苗为试材,设置根区正常降温和缓冲降温2种降温条件,人工模拟霜冻,分析了叶片冻害指数和叶片的荧光参数。结果表明,根区正常降温会导致根系受冻,同时叶片发生严重的冻害,冻害指数达74.36%;根区缓冲降温使根区温度保持在0°C以上,叶片冻害指数降低53.29%,仅有21.07%的叶片遭受了冻害。根区缓冲降温处理能有效提高叶片霜冻恢复过程中光化学淬灭系数(qP)和天线色素转化效率(F_v~'/F_m~'),加快PSII光合电子传递量子效率(Φ_(PSII))的恢复,提高热耗散能力(NPQ),减轻霜冻后的光抑制(F_v/F_m),有利于叶片霜冻后的恢复。     

The use of a temperature-profiled position transducer for the study of low-temperature growth in Gramineae

A device is described for measuring linear extension of grass leaves during controlled cooling and heating of the growing region. The instrument was employed to investigate the sensitivity to temperature of the expanding third and fourth leaves of Lolium temulentum L. seedlings. Using a stepped temperature profile it was established that there was no lag in the response of growth rate to rapid changes in temperature below 16°C. If cooling was continued to the point where growth ceased (1°C) but no further, then rates of growth on rewarming were enhanced over the chilling range and reverted to the original rate at 20°C. Cooling to successively lower subzero temperatures before rewarming abolished the hysteretic enhancement, progressively raised the temperature at which growth resumed and decreased the rate of extension until, at-5.3°C, no recovery occurred. The temperature sensitivity of growth, measured as Q₁₀, was essentially constant when cooling from 20°C to 5°C, with 5°C-grown leaf tissue exhibiting a higher mean Q₁₀ than tissue developed at 20°C. The possible physiological significance of these data is discussed.Abbreviations LVDT linear variable displacement transformer - Pe, Fx temperatures at which growth ceases during cooling and resumes during rewarming     

Cryopreservation of human peripheral blood stem cells: optimal cooling and warming conditions

Peripheral blood stem cells are being used to reconstitute human bone marrow function after ablative therapy of blast transformation of chronic myelogenous leukemia. Studies were undertaken to establish the optimum cooling and warming conditions of the preservation of colonyforming activity in the peripheral blood of patients with CML.The results show that maximum recovery of CFU-c activity occurs after cooling at 3 °C/min, an average of 50% better than the recovery following cooling at 1 °C/min. CFU-c recovery decreased with decreasing warming rate, but high recovery was obtained with warming rates as low as 10 °C/ min. Viable cell count did not correlate with CFU-c recovery, therefore it represents a poor index for quality control.These results suggest that for clinical purposes bulk samples in flat bags with high surface area to volume ratios, frozen at a rate of 3 °C/min and thawed as rapidly as possible, should give maximum recovery of stem cell activity.     

Translocation of photoassimilate from leaves of two popyploid genotypes of tall fescue differing in photosynthetic rates

The photosynthetic rate of a decaploid genotype (1-16-2) of tall fescue ( Festuca arundinacea Schreb.) is about twice that of a common hexaploid genotype (V6-802) (Plant Physiol. 72: 16–21, 1983). Translocation of photosynthate out of the leaves is a possible means of regulating carbon assimilation. To evaluate this possibility, we have examined a) translocation velocity, b) time course of translocation from leaves, c) photoassimilate partitioning pattern into whole plants in pulse and chase experiments, and d) interveinal distances between two ploidy genotypes. Most of the ¹⁴C accumulated in sucrose, and the labelled carbon moved down the leaf blades at similar velocities (6 to 10 cm h⁻¹) in both genotypes. Recent ¹⁴C assimilate was rapidly translocated from the fed area of the leaf blade. For example, the decaploid and the common hexaploid had translocated 40 and 26% of the ¹⁴C, respectively, at 6 h, and 79 and 49% of the ¹⁴C, respectively, at 24 h. Partitioning of ¹⁴C among plant organs was considerably different between the genotypes after a 24 h chase. For example, out of the total ¹⁴C recovered from the whole plant, the decaploid had retained 40% in the labelled leaf with 10, 33 and 29% in other leaves, stem bases and roots, respectively; whereas the hexaploid had retained 91% in the labelled leaf with 4, 3 and 2% in other leaves, stem bases and roots, respectively. However, the higher rate of translocation was correlated with greater interveinal distances in the decaploid genotype. These results suggested that the higher translocation percentage in the decaploid than the hexaploid genotype was due to greater sink activity.     

The Contributory Length of Sieve Tubes in Isolated Segments of Willow, and the Effect on it of Low Temperatures

Using isolated stem segments in which a gradient of ³²P-phosphateactivity had been established, it has been demonstrated thatthe magnitude of the contributory length is much greater thanthe 16 cm previously measured by Weatherley et al. (1959). On cooling a portion of a stem segment between an aphid colonyand the high-activity end of a segment, a pattern of specificactivity changes were observed in collected honeydew which showthat the effect of cooling was to increase the magnitude ofthe contributory length. It is considered that this increaseprovides cogent evidence in favour of the concept that movementof solutes across the lateral wall of the sieve tube is directlyor indirectly dependent upon metabolic energy, whilst the longitudinalmovement down the sieve tube is not so dependent.     

Short-term phosphate uptake kinetics in Zostera noltii Hornem: a comparison between excised leaves and sediment-rooted plants

Short-term phosphate uptake by excised leaves of Zostera noltii Hornem. as well as by leaves of sediment-rooted plants were characterized and compared in a kinetic framework. Time courses of phosphate disappearance were measured over a wide range of initial substrate concentrations. Phosphate uptake determined by this perturbation method did not follow Michaelis-Menten kinetics. Both excised leaves and sediment-rooted plants exhibited a biphasic uptake pattern as a function of phosphate concentration. However, rooted plants showed higher uptake rates and accumulated higher amounts of phosphate than excised leaves. The results point out the importance of the structural and functional coupling between shoots and underground parts during the nutrient foliar uptake processes. Our study also indicates that Zostera noltii leaves function as a phosphate sink in the water column.A second objective of this work is to compare the perturbation and the multiple flask methods in determining the uptake kinetic parameters. The obtained results support that both methods provide valuable and complementary information in determining the uptake rates.     

Sensitivity of human embryonic stem cells to different conditions during cryopreservation

Low cell recovery rate of human embryonic stem cells (hESCs) resulting from cryopreservation damages leads to the difficulty in their successful commercialization of clinical applications. Hence in this study, sensitivity of human embryonic stem cells (hESCs) to different cooling rates, ice seeding and cryoprotective agent (CPA) types was compared and cell viability and recovery after cryopreservation under different cooling conditions were assessed. Both extracellular and intracellular ice formation were observed. Reactive oxidative species (ROS) accumulation of hESCs was determined. Cryopreservation of hESCs at 1 °C/min with the ice seeding and at the theoretically predicted optimal cooling rate (TPOCR) led to lower level of intracellular ROS, and prevented irregular and big ice clump formation compared with cryopreservation at 1 °C/min. This strategy further resulted in a significant increase in the hESC recovery when glycerol and 1,2-propanediol were used as the CPAs, but no increase for Me₂SO. hESCs after cryopreservation under all the tested conditions still maintained their pluripotency. Our results provide guidance for improving the hESC cryopreservation recovery through the combination of CPA type, cooling rate and ice seeding.     

MOVEMENT OF EELWORMS: V. OBSERVATIONS ON APHELENCHOIDES RITZEMA-BOSI (SCHWARTZ, 1912) STEINER, 1932 ON FLORISTS' CHRYSANTHEMUMS

Adults of Aphelenchoides ritzema-bosi tend to migrate up the stems of chrysanthemum plants in stationary water films possibly by a negatively geotropic response. A current of water down the stem opposes such an upward movement. Greatest mobility occurred in thick films of water in places with a high concentration of epidermal hairs as at the top of the stem and on the undersurface of leaves. Ciné films of movement in thick and thin films showed that there were fundamental differences in the type of locomotion in these two environments. Invasion of leaves via stomata was observed and the method of movement is described. The presence of A. ritzema-bosi in leaves appears to render the epidermis permeable to water. During dry weather there is little movement inside the leaf, but after rainfall activity increases as water enters the leaf. Spread of eelworm infestation in the leaf occurs in the mesophyll and across veins although initially these act as barriers. Emergence occurs via the stomata, chiefly on the undersurface. When the leaf is wet, about 50% of the eelworms emerge in the first hour. During wet weather many eelworms were recovered from the surfaces of leaves and it is suggested that eelworms spread mostly under these conditions.     

THE ROLE OF ROOTS IN THE NUTRITION OF AQUATIC VASCULAR PLANTS

Rooted stems of three aquatic species were cultured in a two-compartment apparatus which allowed the upper and lower portions of the stem to be kept in different nutrient solutions. P³² was supplied to either the upper or lower compartment. At the end of a 10-day growth period, the specific activity of phosphate was determined in axillary shoots which developed during the course of the experiment from buds in the upper compartment. The results indicated that most of the phosphate in these shoots was not absorbed from the ambient medium but was derived from the rooted stem base in the lower compartment (over 90 % in Myriophyllum brasiliense, 59 % in M. spicatum, and 74 % in Elodea densa). These results give a very different but probably more accurate picture of phosphate absorption in rooted aquatic vascular plants than short-term experiments, in which phosphate is readily taken up from the ambient medium by leaves of M. spicatum and E. densa. In M. brasiliense the amount of phosphate translocated is related to the mass of roots present. Evidence is presented that normal growth of axillary shoots occurs even when all mineral ions have to be obtained by translocation from the lower compartment.     

Anatomical investigations of resprouting in Cardopatum corymbosum L. (Asteraceae): A hemicryptophyta living on erosion-prone slopes in a Mediterranean climate

Abstract

Cardopatum corymbosum is a perennial hemicryptophyta species living on erosion-prone steep slopes where it forms very small, scattered communities that resist soil erosion. The aim of this study was to understand better the life cycle of this species before suggesting its use for eco-engineering purposes to stop soil erosion. We examined anatomical preparations with a light microscope, and plant anatomy was reconstructed by examining sequential cross sections of the stem cut from the shoot apex to the root collar. A single sprout above the root collar produces a rosette of leaves at the beginning of spring and a floral axis at the end of summer. The leaves and the floral axis die at the end of summer, whereas the basal portion of the new stem remains alive and forms, together with the root system, the perennial portion of this plant. This stem zone is named “transition zone” and presents leaf traces converging in the centre where they give rise to a vascular cylinder with a cambium ring dividing a secondary xylem from a secondary phloem. New buds form in the cortex of the transition zone that are quiescent and are not visible externally until the following spring when they resume growth and generate a new sprout. These buds should be considered adventitious because: (1) they form independently of leaves; and (2) their annual production could represent the plant's response to ensure its survival after the loss of the above-ground portion of the stem. Given the efficient resprouting strategy coupled with a perennial root system, C. corymbosum is a good candidate for bio-engineering applications against the soil erosion typical of steep slopes in Mediterranean climates. This species could be considered for intensive re-vegetation in order to produce a protective soil covering.     

Effects of Low Root Temperature on Ion Uptake and Ion Translocation in Wheat

Roots of wheat seedlings (Triticum aestivum L. cv. Weibulls Starke) were cooled (+1°C) for 24 h while the shoots were kept at 25°C. The treatment induced an increased water deficit in the leaves. Fresh weight, dry weight, and the uptake and distribution of potassium and calcium were measured before and after cooling. Growth, measured both as fresh weight and dry weight increase, was reduced during the cold treatment. Afterwards (at 20°C), growth recovered to nearly pre-stress rates. Analysis of the potassium fluxes in and out of the roots by ⁸⁶Rb techniques showed that influx, and to a lesser extent efflux, were inhibited at low temperature. The result was a net potassium uptake rate of one-third that of unstressed plants. After the cooling period the potassium influx increased to the rate of control plants. The potassium efflux increased to one and one-half times the rate of unstressed wheat so that net uptake was negative. The increase in potassium efflux was explained by a higher permeability of the root cell membranes after cooling. The net uptake of calcium was reduced to one-third by root cooling. Contrary to potassium uptake, calcium uptake increased under post-stress conditions, partly due to a low efflux rate. During root cooling there was a redistribution of dry matter from the leaves down towards the lower part of the shoot. Afterwards the original distribution of dry matter was reestablished. The net flow of potassium and calcium followed a similar pattern as dry matter, suggesting a growth-regulated flow.     

Development of the Stem Tuber in Kohlrabi

Stem swelling in kohlrabi (KR) normally occurred between thethird and fifth node and followed initiation of meristematicactivity in pith parenchyma cells; this usually began about7 weeks after germination and was associated with the deathof parenchyma cells in the centre of the pith lower down thestem. Cell division began just above this region, at about thethird node and zones of dividing cells extended upwards andlaterally, giving rise to more centres of active division. Carbohydrateanalyses showed that fructose, glucose, starch, and an unidentifiedsugar accumulated in the stem. Melezitose appeared in the stemand raffinose in the leaves only after visible bulbing had occurred.Sucrose content fluctuated in both leaves and stems and in thelatter was positively correlated with hours of sunshine on theday before sampling. The contents of gibberellin-like substancesin the leaves of KR were compared at two stages of developmentwith those of marrowstem kale (MSK). Gibberellins were presentin both acidic and neutral fractions in KR tissues and the amountswere similar to those in MSK. Stem swelling in KR could notbe attributed to a gross deficiency of gibberellins. Inter- and intra-varietal approach-grafts were made with KRand MSK plants. With KR as ‘scion’ partner, stemelongation of the scion was not greatly affected by the natureof the stock, but stem swelling was much reduced on MSK stocks.Stem swelling in MSK scions was greater on KR stocks than onMSK. Retention of stock leaves and buds above the union tendedto inhibit elongation of the scion partner and also inhibitedstem swelling in KR scions on MSK stocks. Application of gibberellicacid to leaves of MSK stocks from which the terminal bud hadbeen removed, increased both stem elongation and swelling inKR scions. KR scions top-grafted on defoliated MSK stocks showedvigorous stem elongation without swelling. MSK scions top-graftedon KR stocks showed reduced stem elongation with abnormal stemthickening. It is suggested that high auxin levels may preventbulbing in KR and that gibberellin-like substances may facilitateboth stem elongation and bulbing when auxin levels are low. Applying gibberellic acid (GA₃) or indole-3-acetic acid (IAA)alone or in combination, to young intact plants of KR increasedstem height and checked stem swelling. Application of benzyladenine(BA) at 10^–4 M accelerated swelling and checked stem elongation.GA₃ applied with BA (10^–4 M) increased both stem heightand girth, both with or without added IAA. It was concludedthat the requisite conditions for stem swelling included thepresence of a kinin² and a low level of auxin. High levels ofauxin prevented stem swelling, whether applied as IAA to youngintact plants or as natural auxins from leaves and buds of MSKplants grafted to KR scions. Although applied gibberellins usuallytended to prevent swelling, native gibbereltins appeard to playa minor role in controlling its initiation which probably occurswhen the auxin/kinin ratio in the plant reaches a critical lowlevel.     

Estimation of Conductivity and Conducting Area of Poplar Stems using a Radioactive Tracer

Radioactive solution was forced through stems of poplar underknown pressures. The velocity of the solution was monitoredby Geiger tubes spaced along the stem, and by dividing velocityinto the rate at which the solution was seen to exude from thedistal end, the total cross-sectional area of the functionalconduits was estimated. This amounted to 13 per cent of thecross-sectional area of the vessels. A value of 9.5±0.6 x 10^–9 m⁴s^–1N^–1was obtained for the conductivity with a range of 4.0–22.3X 10^–9 m⁴s^–1N^–1.     

Factors accelerating pyrimidine production in <Emphasis Type="Italic">Deinococcus radiophilus</Emphasis>

In studying the pyrimidine synthesising pathway in Deinococcus radiophilus two instances of anomalous behaviour were observed. One was the strikingly different results obtained for two types of assay for carbamoyl phosphate synthetase. Both depend on the fixation of ¹⁴C from the substrate bicarbonate to give radioactive products. In the coupled assay the carbamoyl phosphate product of the enzyme is converted to carbamoyl aspartate in the presence of aspartate and aspartate transcarbamoylase. In the direct assay aspartate is omitted from the reaction mixture and the carbamoyl phosphate is converted to urea. It was found that the radioactive counts in the direct assay were about 5% of those measured in the coupled assay. The second anomaly was that omission of glutamine from both assay mixtures had no significant effect on the fixation of radioactive carbon. These results suggested that aspartate amino-N could be the source of nitrogen for glutamine synthesis by a substrate-channelled pathway which delivered glutamine to carbamoyl phosphate synthetase, and that externally added glutamine could not access its binding site on the enzyme.