Zur Frage der Stoffbewegungen in der Pflanze mit besonderer Berücksichtigung der Wanderung von Fluorochromen

Sumutwtary. The effect of metabolic inhibition of the sink tisslues oni translocation of 14C-labeled photosynthate was studied by cooling part or all of the sink region in a translocating sugar beet plant (Beta vuilgaris L. var Klein Wanzleben).W\hen the sinlk region was cooled, 4 phases were observed: a temporary declille, a perio(d of translocationi at the pre-treatment rate, a period of decline, and a new steadv' rate at 35 to 45 % of the original rate. The new rate persisted throlughout 26 hoturs of coolinig.Cooling half the blade of a developing leaf cautsed a decline in translocation to the uincooled half. When a portion of the beet was cooled, translocationi to a developing leaf located above the supply leaf node increased 30 %.Translocation into the treated region recovered rapidly and completely when cooling ceased indicating that cooling had not caused serious damage to tissues. Enhancement of the proportion of 14C as sucrose in the cooled portion of the sink leaf as compared with the corresponding warm side indicated that stucrose is the chief species of transprocess incluides active uptake inlto storage beet occulrs at aln unidimiinislhe(d rate alonig a traiiislocationi path niaintainie(d a 20 for periods of upl to 24 houirs while the source andl siniks were at 28 to 300. In contrast, translocationi in bean was greatly reduiced under these conditions.To determine the site of low temperature inhibition of translocation and to test the proposed active transport mechanism postulated for sink regions, I undertook a series of experiments using localize(d cooling of part or all of the sink. Materials and MethodsExperimental material consisted of 5-to 7-weekold sugar beet plants (Beta vulgaris L. var Klein Wanzleben) pruned to a simplified translocation system. Culture methods and preparation of plaint material were carried ouit as described previously (9, 10).The sink leaf, crown and top of the beet were cooled with a Haake model KT 62 controlled temperature bath. Coolant was circulated through a 9.5 mm inside diameter copper coil lining an acrylic plastic chamber 10 cm in diameter and 15 cm high (fig 1). Temperature was measured with a 1.1 mm diameter thermistor positioned against the stirface of the sink leaf. The temperature at this point showed short-term changes of less than 0.20 and could be held within ± 10 for at least 24 hours. The roots and lower part of the beet were mainlocate molecule arriving in the sink.The data suggest that the translocation anid growing areas.Ak number of mechasnisms have l)een propose(l for getneratinig the pressutre gra(lielnts postuilated in the pressuire-flow translocationi model (1,4,6,8,11,13,17). In this model system translocate is conceived as Imlovinig from a site of suipply (the source) to a place of utilization or storage (the sink). Attentionl has recently focused on the parenchyma cells associated with sieve elements in the source and sink regions (2,6,7,13). These cells (the pumps) were proposed to be the site of an active process by which stucrose is secrete...

Section: Resultsmentioning

confidence: 99%

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confidence: 99%

Effect of Sink Region Cooling on Translocation of Photosynthate

Geiger

1966

“…This flow is thought to be "powered" by turgor gradients which are osmotically produced (2, 17). The pressure flow mechanism is supported by abundant evidence obtained from studies of sieve tube exudation (2,20,21,26,28,29); movement of viruses (5, 6), dyes (1,3,7,8,21), '4C-assimilates, and plant regulators (4,16,27). Although the importance of pressure gradients is minimized by some workers (9, 25), the general view is that a pressure difference between source and sink is essential for phloem conduction.…”

Section: Introductionmentioning

confidence: 86%

Phloem Pressure Differences and ¹⁴C-Assimilate Translocation in Ecballium elaterium

Sheikholeslam

Currier²

1977

The role of phloem turgor pressure in 14C-assimilate translocation in Ecballium elaterium A. Rich was studied. The direction of translocation was manipulated by two methods: darkening, or defoliation, of the upper or lower halves of the shoots. After 24 hours of labeled assimilate movement, sieve tube turgor levels were measured with the phloem needle technique. Distribution of label, determined by autoradiography and counting, revealed a direct correlation between the direction of assimilate transport and the pressure difference. Phloem turgor levels always decreased in the stem of darkened shoots; this resulted in greater pressure differences in the stem between the source leaf receiving '4CO2 and treated regions.Opinions have been divided for a long time as to the mechanism of phloem translocation. Most plant physiologists agree that there is a mass flow of sieve tube sap, solutes, and water moving as a stream through mature sieve tubes. This flow is thought to be "powered" by turgor gradients which are osmotically produced (2, 17). The pressure flow mechanism is supported by abundant evidence obtained from studies of sieve tube exudation (2,20,21,26,28,29); movement of viruses (5, 6), dyes (1,3,7,8,21), '4C-assimilates, and plant regulators (4,16,27). Although the importance of pressure gradients is minimized by some workers (9, 25), the general view is that a pressure difference between source and sink is essential for phloem conduction.Little has been done in the way of direct measurement of turgor gradients in sieve tubes. Hammel (13) provided direct evidence of relatively high phloem pressure in the source region of Quercus rubrum by using the "phloem needle," but there is an obvious need for more quantitative data, using plants grown under controlled conditions. The objective of the present study was to measure the phloem turgor pressure in different parts of the plant and to determine the relation of pressure differences to "4C-assimilate movement in this tissue. Phloem pressure measurements were made by slowly pushing the needle into the stem to a depth of about 2 to 3 mm. On penetration of a phloem bundle by the needle tip, the air column in the capillary was instantaneously compressed by a surge of the dye solution. The pressure value was obtained by reading the length of the compressed air column and referring to the calibration curve. Further technical details can be found in Hammel's paper (13). Not all measurements were successful, but in the majority of attempts, positive readings were obtained. Occasionally a test failed because the inner or outer phloem of the bundle was missed, or because the needle tip was blocked. Usually the needle entered the external phloem. A rapid compression of the air column was considered to indicate a good reading, and only these readings were included in the data. MATERIALSTracer Experiments and Turgor Measurements. Radioactive CO2 was prepared from "4C-sodium bicarbonate solution and applied to a mature leaf attached to a median node. Approximately half ...

“…The transfer of assimilates from the leaf mesophyll into the sieve tubes is a selective process (23). Most investigators think that the assimilate transfer requires metabolic energy (2,4,6,9,13,18,23).…”

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confidence: 99%

“…degree. 2 Present address: Institut fur Pflanzenschutz, der Universitat Hohenheim, 7000 Stuttgart-Hohenheim, Germany.…”

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confidence: 99%

Translocation and Metabolic Conversion of ¹⁴C-Labeled Assimilates in Detached and Attached Leaves of Phaseolus vulgaris L. in Different Phases of Leaf Expansion

Köcher

Leonard

1971

Leaf excision greatly affected the actual levels of "C-assimilates in laminas and petioles of primary bean leaves (Phaseolus vulgaris L.) following a transport period. However, it did not affect the percentage of starch in the insoluble residue; starch decreased from 20% of the insoluble residue after exposure to "CO2 to 3 % after 5 hr in both attached and detached leaves. The transition from import to export of attached and detached leaves was at the same stage, i.e., when the cotyledons were 63 to 85% depleted. The composition of the "C-assimilates in importing leaves was different from that in exporting leaves. In the former, only 5% of the soluble label was free sugar, while 74% was free sugar in the latter. The failure of importing leaves to export was not due to the labeled substances being nontransferable. Extracts from importing leaves applied to exporting leaves were exported; these extracts were high in amino acids and organic acids but low in free sugar. However, exporting leaves exposed to "CO2 appeared to export sugars more readily than amino acids. Cotyledon excision did not delay transition of leaves from import to export. Actually, excision seemed to enhance slightly the transition of the primary leaves from import to export.The source-to-sink concept of movement of food materials in the phloem of higher plants is supported by numerous experiments (1,3,8). It has been shown that a leaf during its ontogeny functions first as a metabolic sink and later, before it has expanded to its final size, as a metabolic source (3,12,17 by factors in other parts of the plant? How is this shift related to intensity of photosynthesis and composition of the metabolites? We attempted to obtain some answers to these questions by conducting studies on the primary leaves of bean (Phaseolus vulgaris L.) in different phases of expansion. Comparisons were made on the transport and metabolism of "C-assimilates in attached and detached leaves. Hartt and Kortschak (10), working with sugarcane, came to the conclusion that results from detached leaves were applicable to translocation in the entire plant. Leonard and Glenn (14,15) concluded from their work with excised bean leaves that these could be used in certain studies on the translocation of both assimilates and leafapplied substances. Also, results from our current work indicate that detached leaves can aid with studies on transport in leaves, especially on the transition from import to export.