Evaluation of Selected Parameters in a Sugar Beet Translocation System

The kinetics of "4C-assimilates in the soybean leaf were studied in pulse labeling and steady state labeling experiments. "4C-Sucrose apparently served as the ultimate source, at least, of translocated "4C-sucrose. However, since the specific activity of leaf sucrose reached a maximum within 5 minutes after pulse labeling, whereas that of exported sucrose did not reach a maximum until at least 20 minutes, it appeared that there were two sucrose compartments in the leaf. A possible physical basis for the two compartments may be the mesophyll (a photosynthetic compartment) and a specialized "paraveinal mesophyll" (a nonphotosynthetic compartment), through which photosynthate must pass on its way to the veins.The 14C kinetics of sterol glucoside, and probably esterified sterol glucoside, were similar to those for "4C-sucrose export. Sterol glucoside was labeled only in its glucose moiety and was the only stem lipid which became strongly labeled during "4C-sucrose translocation. These sterol derivatives may act as membrane carriers of sucrose between the translocation stream and surrounding cells.

“…Relative on the relative volumes (7/1) of photosyn mesophyll. The model differs from that of for sugar beet (11), which assumes the 1 sucrose pool.…”

Section: Discussionmentioning

confidence: 97%

Kinetics of C-14 Translocation in Soybean

Fisher

1970

“…Translocation rate was calctulated by muiltiplying the first derivative of cturve-fitted GM-ratemeter data by efficiency and specific activity factors as described previouisly (10). In those experiments in which the entire sink region was cooled, the distribution pattern between sink organs (sink leaf, crown, beet, roots, base of supply leaf petiole) was presumed to remain tunchanged dturing cooling, and translocation rates could be calctulated from the ratemeter data.…”

Section: Methodsmentioning

confidence: 99%

“…Culture methods and preparation of plaint material were carried ouit as described previously (9,10).…”

Section: Methodsmentioning

confidence: 99%

“…Where oily a portion of the sink region was cooled, tates were calcuilated for delivery into the treated portion of the sink becatuse of possible change in relative distribuition between sink organs caused by localized cooling. In cases where the sink leaf was covered with the sink leaf cooling jacket an average translocation rate was calculated from the form of the typical cuirve for approach to isotopic equilibrium (10) and the 14C content of the sink. Details of methods for ion chamber assay of total 14C and chromatographic analysis of 14C_suicrose were given previouisly (10).…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Effect of Sink Region Cooling on Translocation of Photosynthate

Geiger

1966

Self Cite

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...

“…However, most evidence indicates that the kinetics in the stem are determined primarily by the rate of tracer efflux from the leaf (8). In their work with sugar beet, Geiger and Swanson met with conspicuous success in their mathematical treatment of translocation (11) by paying close attention to the kinetics of 'IC-sucrose in the source leaf (10). Nevertheless, the over-all kinetics of translocated compounds in the source leaf are not necessarily an indication of their rate of efflux from the leaf.…”

mentioning

confidence: 99%

Kinetics of C-14 Translocation in Soybean

Fisher

1970

Based largely on data from soybean, some mathematical models are derived to describe the transport kinetics of 14C-photosynthate. The effects of leaf size, leaf shape, and translocation velocity on the rate of tracer efflux from the leaf are considered, and it is shown that the duration of these effects will approximate the time required for tracer to reach the petiole from the farthest point of the leaf. This duration is designated as the "kinetic size" of the leaf. Although its effect will be slight in the case of soybean (about 2 to 3 minutes), a considerable effect of the kinetic size will be found in the case of large leaves, or when the translocation velocity is low.Source pool kinetics in soybean are described by a twocompartment model, one compartment representing a photosynthetic compartment and the second (the source pool) a nonphotosynthetic compartment next to the veins.The kinetics in the petiole are approximated by a twocompartment model representing the translocation stream and tissues outside the translocation stream. A combination of the models predicts fairly accurately the translocation kinetics observed in soybean.The models are compared with others in the literature. Although the assumptions are in substantial agreement with those made by Evans, Ebert, and Moorby, they are inconsistent with the model based on the movement of transcellular strands presented by Canny and Phillips.The use of radioactive tracers in translocation studies has encouraged the development of several mathematical models of translocation (5,6,12,17). Since, at least in some cases, the proposed theories for phloem transport would be expected to result in different kinetic observations, these models have often been concerned largely with mechanisms in the stem which would account for the data obtained there. With the exception of Geiger and Swanson's work (10), experimental data for tracer kinetics in the leaf were not utilized in the models, which relied to varying degrees on hypothetical rates of tracer efflux from the leaf (or, in the case of Spanner and Prebble's experiments [17], from a "3'Cs source applied directly to the stem) to solve equations for the