Translocation of Assimilates and Phosphate in Detached Bean Leaves

Abstract

A bstract. 14C-assimilates were accumulated by the veins in the blades and transported hasipetaltly into the petioles of detached leaves of Red Kidney bean (Phaseolus vulgaris L.).Neither process was greatly affected by mild moisture stress, age of fully enlarged leaves, or period in the dark prior to exposure to 14CO,. However, both vein loading and transport into petioles were greatly reduced by oxygen deficiency. The basipetal tranisport of 32PO4 also did not appear to be greatly reduced by 6 or 8 days of darkness prior to the application of phosphate-32P, followed by a trans,port period of 1 day in the dark. Endothall at 5 X 10-3 Ni was effective in stopping basipetal fow of <9P. It is oonsidered that ttansport in leaves may be powered by forces in the plasmodesmata of the cell walls between the border parenchyma and phloem.Twventy-nine years ago the senior author ( 12) observed that sugars were translocated in detached sugar beet leaves from the laminae into the petioles. The su,gars accumulated rather uniformly in different parts of the petioles, with no indication of any special accumulation in the basal section. It wvas suggested that the basipetal flow in the petioles was due to a polarity originating in the border parenchyma of the veins of the blades. Barrier and Loomis (1) later described vein loading in detached leaves using 'LC-2,4-D and 32po4. Mfore recently Hartt and Kortschak (6), Nakata and Leopold (18) Materials and MethodsSeeds of Red Kidney bean (Phaseolus vulgaris L.) were planted in 4-inch pots and later thinned 1 This research was supported in part hy National Sctience Foundation(Grant GB-6437, to 1 plant per pot. \Vhen the primary leaves were well expanded they were exposed in a polyethylene or plexiglass chamber in sunlight to 50 c 14CO.,. The petioles were wrapped with aluminum foil to prevent photosynthetic incorporation of 14CO., by the petioles. In some tests, the detached leaves or whole plants were subjected to various dark periods before being exposed to 14C02. When whole plants were used, the leaves were detached inmmediately following the exposure. Some leaves were freezedried directly following their exposure to 14CO.. while others were placed in moist chambers for varying periods to allow transport to go on. In most instances, transport occurred while the leaves were in the dark, with the petioles either in water Or in air.In other tests, 5 to 25 ,uc of phosphoric acid-39}' neutralized with NH4O0I' was applied per leaf in 5 ,ul of water. The applications wvere made in the laboratory Nvith the overhead lights turne(l off anid the leaves returneed to the (lark mloist chambers withini a fewr miitnutes following treatmiielnt. Otlherasl)ects of explerimeiltatioil \\ere the same as for '+CM_ Some experiMlental details \\ill be described alowig wVith the resilts silnce several types of exl)eriilmets were conducted.Specific activity measurenmenit, chromatograplhy, and autoradiography were conducted by methods described by Hull and Leonard (9) and Crafts and Yamaguchi (4). In all ins...

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

“…The autoradiographs in Figure 1 indicate no vein loading occurred in the 2-hr period for the younger leaves, while vein loading is clearly apparent in the older leaves. In other tests, a transport period of 5 hr resulted in greater labeling of veins and petioles of exporting leaves than after 2 hr (5 hr transport autoradiographs are not presented), while even greater differences were shown after 24 hr (15). The younger leaf in Figure 1 (A) was extracted with 80% ethanol, the extract was concentrated, and about 1 % Tween 20 was added to the concentrate.…”

“…The petioles of detached leaves incorporated a much higher amount of label into ethanol-insoluble compounds than the petioles of attached leaves. Leonard and Glenn (15) found in addition to this that partial inversion of sucrose occurred in the petioles of detached bean leaves, which suggests that sucrose was taken out of the sieve tubes and inverted in the surrounding tissues. Investigations by Leonard and Glenn (15) and Bieleski (4) suggest that the bundle parenchyma cells act as sinks in detached leaves and thus maintain a mass flow of assimiflates from the leaf veinlets into the petioles.…”

“…Leonard and Glenn (15) found in addition to this that partial inversion of sucrose occurred in the petioles of detached bean leaves, which suggests that sucrose was taken out of the sieve tubes and inverted in the surrounding tissues. Investigations by Leonard and Glenn (15) and Bieleski (4) suggest that the bundle parenchyma cells act as sinks in detached leaves and thus maintain a mass flow of assimiflates from the leaf veinlets into the petioles. Bean blades without a petiole accumulate label strongly in the main veins, suggesting that parenchyma of the major veins of the blade as well as that of the petiole bundles may function as a sink.…”

“…The radioactivity of plant material was determined by a Tracerlab Geiger-Muller counter with a tube of the type TGG 14. Autoradiographic studies were done on freeze-dried material, following methods of Crafts and Yamaguchi (8).…”

“…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.…”