Translocation and Accumulation of Translocate in the Sugar Beet Petiole

Abstract

Abstract. 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 #g carbon/min was accumulated per cm petiole. Material was stored mainly as sucrose and as oompounds insoluble in 800% ethanol. The minimum peak velocity of translocion approached an average of 54 cm/hr as the specific aotivity of the 34CO2 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 cm2 phloem or 4.8 g/hr cm2 sieve tube. Histoautoradiographic studies indicated that translocttion occurs through the area of ph,loem occupied by sieve tubes and companion oells 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 conoept that storage along path tissue serves to buffer sucrose ooncentration in the translocate during periods of fluctuating assimilation.

Evidence for the Presence of a Sucrose Carrier in Immature Sugar Beet Tap Roots

“…Both sucrose and F-sucrose accumulated in the root and to a lesser extent in the petiole. Presence of relatively large quantities of radiolabeled sugars in the petiole is consistent with the role of this sink in buffering the flow of sucrose to the root during periods of high or low assimilate export (5).…”

Tansley Review No. 27 The control of carbon partitioning in plants

“…3), which has been shown to result in a fairly uniform rate of specific mass transfer (SMT) of carbon through the sieve tubes in the petiole of a leaf such as sugar beet (Geiger, Saunders & Cataldo, 1969), it has been suggested that the cross-sectional area of the sieve elements (capacity of the transport system) may limit translocation out of a leaf. However specific mass transfer through the phloem varies greatly even within the C4 species (Lush & Evans, 1974) ranging from 4-7 to 14-9 g d. wt cm"^ h~^ in Digitaria sanguinalis and Chloris gay ana respectively.…”

Root and Shoot Respiration of Perennial Ryegrass Are Supplied by the Same Substrate Pools: Assessment by Dynamic 13C Labeling and Compartmental Analysis of Tracer Kinetics

“…Typically, however, the range of tracer exposure (or chase) times has been much narrower, thus capturing only fast or slow pools. In this study, we aimed to characterize all major components of the respiratory supply system by using labeling times ranging from 1 to 600 h. To this end, we labeled all carbon assimilated by individual plants with a known constant 13 C/ 12 C ratio in CO 2 over a period of up to 25 d, when respired CO 2 had reached 95% label saturation (this labeling method is termed "steady-state labeling" in "classical" plant physiology literature [Geiger and Swanson, 1965;Geiger et al, 1969] but is now referred to as "dynamic labeling" [Ratcliffe and Shachar-Hill, 2006]). The 13 C/ 12 C ratio of respiratory CO 2 produced in the root and shoot was measured at various times, and the time course of tracer in respired CO 2 was evaluated with compartmental analysis.…”