Growth and sugar storage in sugarcane grown at temperatures below and above optimum

Sugarcane plants were grown for 10 months in the greenhouse at 27 degrees, considered the optimal temperature, and at low temperature (15 degrees) and high temperature (45 degrees). The growth pattern, biomass production, sug ar levels in leaves and stem, and activity of the enzymes involved in sucro se metabolism were determined on plants grown at each temperature. Plants maintained at 15 degrees were very slow growing, with few and short internodes and few leaves. At 45 degrees the plants had nearly as many inte rnodes and leaves as control plants (27 degrees), but the internodes were s maller and shorter and the leaves became dry earlier; side shoot formation (tillering) was increased. The shoot/root ratio was approximately constant over time and the same for all three growth temperatures. The leaf area per plant increased over time and was highest at 27 degrees. The leaf area per shoot biomass was constant over time, but twice as high at 15 degrees as a t 45 degrees and 2.5 higher than at 27 degrees. Total biomass production wa s half to one third at 45 degrees and one tenth at 15 degrees. The carbohyd rate level in the leaves, especially sucrose and starch, were highest in pl ants grown at 15 degrees and lowest in plants grown at 45 degrees. This res ult together with the growth data was interpreted as indication that sucros e translocation by the phloem is especially strongly inhibited at 15 degree s, whereas at 45 degrees the elevated leaf respiration, which is highest at 45 degrees, reduces the amount of available sugar for translocation. The sucrose concentration in the stalk was the same in internodes for plant s grown at 15 degrees and 27 degrees and lower in internodes of plants grow n at 45 degrees. The hexose concentration in the young internodes was highe r at 27 degrees than at the other temperatures, indicating the higher growt h rate. All four enzymes of sucrose metabolism (acid and neutral invertase, sucrose synthase and sucrose phosphate synthase) were highest in the stalk at 27 degrees and lowest at 15 degrees; the development of activity during internode ripening was the same for all three temperatures. There was a st rong correlation, valid for all three growth temperatures, between the sucr ose concentration in the stalk internodes and the difference between sucros e phosphate synthase and acid invertase, not however for neutral invertase, although the latter may be higher in activity in some cases. The results a re taken as evidence for a decisive role of acid invertase in regulation of sugar storage in sugarcane.