Sugarcane is one of the most efficient 1plants for producing carbohydrates by photosynthesis (12); it is therefore of great interest to compare its photosynthetic cycle with that of other plants. Our preliminary experiments (not reported here), in which sections of sugarcane blades were exposed to C1402 for periods up to 15 seconds showed that the radioactivity in 3-phosphoglyceric acid (PGA) was never over 34 % of the total activity incorporated. In no case was this as much as the sum of the activities in malic plus aspartic acids. As a check on our methods of analysis, we exposed a soybean leaf to C1402 for 15 seconds; PGA accounted for 80 % of the total radioactivity.The experiments reported here are part of a continuing study of sucrose synthesis in the sugarcane plant. Materials and MethodsLeaves were selected from 1-year old, field-grown plants of variety H 37-1933. This is a complex interspecific hybrid involving Saccharurn officinarum L., S. spontaneum L., and S. robustum Brandes and Jeswiet ex Grassl (13). Leaf No. 3 or No. 4 (the youngest fully expanded leaves) was cut off, and sections were cut under water from the middle part of the leaf.Tungsten light, filtered through water to reduce heat, gave an illumination of 2000 ft-c at the surface of the leaf. This is well below light saturation for sugarcane (10) and about the same intensity used by many other investigators (1,2,3,4 CO2 was injected to raise the concentration to 0.10 %. Ten minutes later, 500 juc of C1402 were injected. At each scheduled time 1 leaf section was withdrawn and dropped into boiling alcohol; this operation required 1 to 2 seconds.3. The dip method. The procedure was to inject C1402 into a closed glass chamber with a narrow, cellophane-tape-covered slit in the top. The tape was removed, a leaf quickly lowered through the slit, and withdrawn after the selected time.Extractions. Leaf sections were boiled in 95 % ethanol for 5 minutes. Whereas a leaf such as soybean is completely extracted and colorless after this treatment, the sturdier sugarcane leaf appears unchanged although some green color can be seen in the alcohol. Blending with the further addition of alcohol to 50 ml in a Waring blendor resulted in the extraction of most of the sugars and chlorophyll.After filtration, the alcohol-insoluble material was twice boiled for 3 minutes with 20 ml of water and filtered. The residue was again washed with alcohol to facilitate drying. Aliquots of each solution were counted on planchets at infinite thinness. The resiwww.plantphysiol.org on May 11, 2018 -Published by Downloaded from

Abstract. A dzfic!ency in potassium decreased the translocation of labeled photosvnthate frcm the leaf to the rest of the plant. Translocaticn was inhibited in blades which exhibited no visible symptoms of potassium deficiency and in which no decrease in photosvnthesis was detected. In more severe deficiency both the rate of photosynthesis and the conversion of intermediates to end products decreas:d. The rate of respiration in deficient blades increased. The decrease in translocation caused by potassium deficiency is considered to be a primary erfect and not secondary to the developmznt of the well-known symptoms of potassium deficiency.

No abstract

No abstract

Summa111101ryA. Low moistuire suLpply, controlledl by 3 methods (addiing NaCl to a complete nuttrieint soluition, allowing a cuit stalk to wilt, or withholding irrigation in the fiekl), decreased the -elocity and percentage rate of translocation of 14C-photosynthate. The suirpluis suicrose not use(d in growth movedl more slowly in the phloem ani(d was stored in the stalk.Low moistuire stipply depressed translocationi of 14C-photosynthate more severely thanl it cuirtailed formation of 14C-photosNvnthate in the same leaf: therefore, the effect of moisture supply ulpoII translocation was primary.Low moistuire stupply retarded profile (levelopment in the stem, anid a loss in moistuire gradieint was associated with a steepened slope of the profile. These resuilts inclicate a flow mechanism of translocatioin rather than d(ifflusion.Resuilts reported now aild previouisly point to the operatioil of a slow pressulreflow mechanism particuilarl) duiring the night buit also during the day; suiperimpose(I upoIn this geineral mass tranisport is the more rapid process of phototranslocation which is indepenldent of suigar gra(lients anid which cani cauise the accuimuilationi of suIcrose at the storage-siink.DuIring ripeniing, storage of stucrose in the stalk may be increase(l by withholdlilng water because less sucrose is hydrolyzed in transit, less is uised in growth, and the slowly moving sucrose has more time for pa renchyma. (28,34,36,37,38