The Effect of Temperature upon Translocation of C 14 in Sugarcane

Abstract

The author's work with translocation of ra(lio active photosynthate in sugarcane plants grown under normal conditions of climate and nutrition has been reported previously (13). The amounts and rates of translocation in sugarcane are affected by the temperature of the air or roots, by light, by moisture, an(l by deficiencies in potassium, nitrogen, or phos-phorus. Our investigations were undertaken both for practical reasons an(l in an atteml)t to elucidate the factors responsible for energizing the transloca-tory process. Both temperature and light are closely involved (11, 12). The results front studies of in-tensity and quality of light which suggest a photocon-trol theory of translocation (9) will be reporte l Shortly. This paper deals with the effects of temnpera-ture of air and roots, regulated separately, upon the translocati on of C'4 photosynthate, already reported briefly (2,4, 9, 10), and with the direct effect of air temperature upon translocation in detached blades. The experiments were conducted front 1956 to 1963. Methods The variety of sugarcane used, H 37-1933, wxas the samve as previously reportedly (13). The plants were grown singly in 8-liter crocks in a complete nutrient solution. To regulate root tem-perature, the crocks were set in troughs of water with the temperature of the water thermostatically controlled. Air temperatures were not maintainedl at uniform levels throughout the day, because that is not the normal way of growing sugarcane. In-stead, the daily range in temperature of 1 glasshouse was higher than outdoors, and the daily range in temperature of the other glasshouse was lower than outdoors (fig 1). The air temperature of the con-trol plants was the normal outdoor temperature at this station. The air in the glasshouse was contin-uously changed; the CO2 content of the air within the houses was equal to that of the outside air. Mleth-ocls of application of C1402, harvesting, sampling, and counting, were the same as reported previously (13). Briefly, equal aliquots of previously prepared C140.2 were supplied to a portion of a single blade, either the upper half enclosed in a 1-liter graduate or a central portion enclosed in a specially constructed chamber made of wood and plastic. The duration of 1 Received June 22, 1964. 2 Published with the approval of the Director as Paper No. 145 of the Journal Series of the Experiment Station Hawaiian Sugar Planters' Association. exposure was 5 to 15 minutes after which the chamber was remove(l and translocation continued in air. Further details of the methods are descril)e(l in the legencls. All translocation tests were carried out With high light intensities (full sun) except as noted. The directt effect of temperature upon transloca-tion was studied at 5 to 60 and 21 to 230 by the (le-tached blade method (11). FIG. 1. Climate houses for growing sugarcane plants with air and root temperatures regulated separately. Air temperature in the house at the left was maintained bhlo\x outdoor temperature; center, above outdoor temperature. Outdoor control plants were at the right. The shed he-hind the outdoor controls, for the purpose of darkening the plants, was not used in these temperature tests. Results 7Tcmnpcrahtrc of Air; Plants Growni (a1(1 7icse/d linder EXrpcrinicn0tal Coniditions. Translocation was measured in a, plant from the control series which had been grown at the outdoor air temperature at this station and in a plant grown in the cold house with the air averaging 8" lower than outdoor air, this average temperature being for the entire growth period of the plants. Figure 2 shows the tempera-tures during the experimental period of feeding the C1402, and subsequent translocation; figure 3 shows the disappearance of radioactivity from the fed blade (considered to be translocation). Translocation in both plants was most rapid the first 6 hours, and leveled off after 30 hours. The plant in the cold air always retained a. higher percentage of radlioactivitv in the fed blade than did the control, indicating less translocation in cold air than in warnmer air. HARTT-TEMPERATURE AND TRANSLOCATION IN SUGARCANE The temperatures from 8 AM to 4 PM the first day were averaged. The Q10 for translocation out of the fed blade, when calculated for either 13 to 230 or for 15 to 250, was 1.2. FZIG. 2. Air temperatures in the cold house and out-dloors, in 2-hr averages, during the experimental period of feeding the C1402 and translocation (fig 3). 100 90 80 70 60 50 40 30 20 10 0 M N M N M N M N Jan. 24 Jan. 25 Jan. 26 Jan. 27 DAYS (M -Midnight; N -Noon) FIG. 3. Effect of air and root temperature, regulated separately, upon translocation of C14 photosynthate from the fed blade. C1402 (225 lac) was fed to the upper portion of blade 5 enclosed in a 1-liter graduate, the blade passing through a split cork, for 15 min in sunlight. Immediately after removing the graduate, the initial punch samples were taken near the apex of the fed part. The samples were dried, weighed, ground in a mortar with alcohol, plated, and the radioactivity recorded and plotted as 1009o. Subsequent samples, taken below the