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D R Geiger

Publications and source records attributed to D R Geiger.

43 records · Page 3Linked to original sources
PubMed1969

Leaf structure and translocation in sugar beet.

Anatomical and ultrastructural details of a translocating 10-cm leaf of sugar beet (Beta vulgaris L. var. Klein Wanzleben) were correlated with translocation rate data. The minor veins were found to be 13 times as extensive as the major veins and measure 70 cm/cm(2) leaf lamina. Measurements disclosed that a 33-mu length of minor vein services 29 mesophyll cells with the result that translocate moves an average of 73 mu or 2.2 cell diameters during transport from mesophyll cells to a minor vein. High-resolution, freeze-dry autoradiography revealed that assimilates accumulate in organelle-rich cells of the minor vein phloem. Correlation of phloem volume and loading rate for minor veins yielded an uptake rate of 735 mumoles of sucrose per g fresh weight of phloem. The arrangement and structural features of minor veins appeared to be consistent with the concept that vein loading precedes translocation.

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PubMed1969

Translocation and accumulation of translocate in the sugar beet petiole.

Accumulation of translocate during steady-state labeling of photosynthate was measured in the source leaf petioles of sugar beet (Beta vulgaris L. monogerm hybrid). During an 8-hr period, 2.7% of the translocate or 0.38 mug carbon/min was accumulated per cm petiole. Material was stored mainly as sucrose and as compounds insoluble in 80% ethanol. The minimum peak velocity of translocation approached an average of 54 cm/hr as the specific activity of the (14)CO(2) pulse was progressively increased. The ratio of cross sectional area required for translocation to actual sieve tube area in the petiole was 1.2. A regression analysis of translocation rate versus sieve tube cross sectional area yielded a coefficient of 0.76. The specific mass transfer rate in the petiole was 1.4 g/hr cm(2) phloem or 4.8 g/hr cm(2) sieve tube. Histoautoradiographic studies indicated that translocation occurs through the area of phloem occupied by sieve tubes and companion cells while storage occurs in these cells plus cambium and phloem parenchyma cells. The ability of the petiole to act as a sink for translocate is consistent with the concept that storage along path tissue serves to buffer sucrose concentration in the translocate during periods of fluctuating assimilation.

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PubMed1967

Translocation of C Sucrose in Sugar Beet during Darkness.

The time-course of arrival of (14)C 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 (14)C 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 CO(2). 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 CO(2). 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 CO(2) from the source leaf appears to be derived from a pool which, unlike sucrose, remains at a uniform specific activity.

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PubMed1967

Time course of low temperature inhibition of sucrose translocation in sugar beets.

Further studies are presented characterizing the time-course response of sucrose translocation in sugar beet (Beta vulgaris L. cv Klein Wanzleben) to low temperature inhibition. Only the temperature of a 2 cm zone of the source-leaf petiole was varied (1 degrees vs 25 degrees , approximately). The half-time of inhibition, defined as the time required for 50% inhibition of the control or pre-cooling rate, varied from 4 to 15 minutes, and the half-time of recovery from 30 to 100 minutes. Maximum inhibition varied from 68 to 92%. Possible uncertainties in evaluating these parameters are discussed. When the duration of the low temperature period was sufficient to permit essentially full recovery, subsequent re-warming of the petiole zone to 25 degrees to 30 degrees effected little or no increase in the translocation rate. It is evident that the interposition between source and sink of a 2 cm petiole zone maintained at a temperature generally inhibitory to physiological processes resulted in little or no impairment to the translocation process, after a suitable thermal adaptation period. Thermally adapted petiole systems de-adapted after periods as short as 1 hour at 25 degrees .

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PubMed1966

Effect of sink region cooling on translocation of photosynthate.

The effect of metabolic inhibition of the sink tissues on translocation of (14)C-labeled photosynthate was studied by cooling part or all of the sink region in a translocating sugar beet plant (Beta vulgaris L. var Klein Wanzleben).When the sink region was cooled, 4 phases were observed: a temporary decline, a period of translocation at the pre-treatment rate, a period of decline, and a new steady rate at 35 to 45% of the original rate. The new rate persisted throughout 26 hours of cooling.Cooling half the blade of a developing leaf caused a decline in translocation to the uncooled half. When a portion of the beet was cooled, translocation 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 (14)C as sucrose in the cooled portion of the sink leaf as compared with the corresponding warm side indicated that sucrose is the chief species of translocate molecule arriving in the sink.The data suggest that the translocation process includes active uptake into storage and growing areas.

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