Interaction between K‐Deficiency and Light in ¹⁴C‐Sucrose Translocation in Bean Plants

Abstract

The effect of K deficiency on sucrose transport was studied in bean plants from which the cotyledons had been removed soon after germination and which were subsequently grown in culture solution. Labelled sucrose wassupplied to the primary leaf. Mild Kdeficiency depressed translocation. A statistically significant interaction between the presence of K and light was observed. K deficiency had no effect on translocation if the plants had been placed in the dark before the experiment and remained in the dark during the translocationperiod. Maximum correction for differences in the specific activity of the sugar being translocated, as between control and K‐deficient plants (based on sugar analyses in various plant parts), failed to abolish the K effect when the amount of sugar applied was relatively low (high specific activity). On the other hand no effect of K‐deficiency was observed on translocation when the amount of applied sugar was high (low specific activity). In this case 14CO2 fixation was greatly reduced in the controls, but not in the K‐deficient plants. Significant interaction existed between added sugar and K‐deficiency on 14CO2 fixation. All results reported here can be explained on the basis of a scheme whereby K plays a rôle in reversible intermediate steps between sugar formation in the chloroplast and the entry of this photosynthesised sugar into the “translocation pool” where it mixes with exogenous sugar.

Biochemical Basis for Effects of K-Deficiency on Assimilate Export Rate and Accumulation of Soluble Sugars in Soybean Leaves

“…It is interesting to note that in soybean plants, translocation was not inhibited by K-stress before adverse effects on CER occurred, as has been reported for bean (1) and sugarcane (9). …”

Potassium Nutrition and Translocation in Sugar Beet

“…Several studies have shown that increased K+ supply to source leaves promotes transfer of products of photosynthesis to minor vein sieve tubes (1,5,11). Increased arrival of K+ in source leaves did not appear to increase translocation of newly assimilated carbon over a 6-to 8-h period (Fig.…”

“…Various studies provide evidence that K+ promotes the translocation of products of photosynthesis in plants (1,2, 5,9,10,12,13,16,17). This promotion will occur if a higher level of K+ nutrition causes one or more of the following to increase: (a) net carbon exchange, (b) phloem loading, (c) transport into cells in sinks, and (d) metabolic conversion of sucrose in sink tissues.…”

Translocation of Labelled Assimilate in Potassium‐deficient Plants

“…Some support for such an argument is given by the work of Amir and Reinhold (1971). They added potassium nitrate to a potassium-deficient culture solution at various periods before giving ^"^002 to the plants growing therein, and were able to demonstrate significant improvement in sugar translocation during 3 h, and continued improvement for the subsequent 48 h. On the other hand.…”

“…In the later paper she also reported a decrease in transport of sugars when nitrogen or phosphorus were deficient. Amir and Reinhold (1971), using 14-or 21-day old Phaseolus vulgaris plants, were able to show depressed export of labelled sucrose supplied by the leaf-flap method to the primary leaf under conditions of mild potassium deficiency, but the effect occurred only in light. In darkness, potassium deficiency had no effect on translocation.…”