Controlled-Temperature Studies of Growth, Enzymology, and Sucrose Production by Two Sugarcane Varieties in Puerto Rico

Abstract

Initial sugarcane studies were completed with controlled-climate facilities at Río Piedras, Puerto Rico. The phytotron is designed to provide a broad range of controlled temperature, light and humidity. Employing the sand-culture technique, a high-tonnage variety (P.R. 980) and a high-sucrose variety (P.R. 1059) was exposed to continually warm and cool temperatures for 10 weeks. Treatments were initiated when the plants were 12 weeks of age. The objective was to evaluate growth, sugar production, and enzymology of the two varieties at 55 to 60° F., and at 80° to 85° F. The following results were obtained: 1. Fresh-weight measurements indicated a more rapid growth rate by plants exposed to warm temperature. Growth by P.R. 980 exceeded that of P.R. 1059. Cool temperature induced a general stockiness and equal growth of both varieties. The warm treatment resulted in a spindly condition in both varieties and frequent lodging for P.R. 980. 2. Both sucrose and total ketose production was much higher at 80- 85° F. than at 55-60° F. in each variety, as evidenced by leaf-sugar values. At both temperature ranges P.R. 1059 was clearly superior to P.R. 980 as a sucrose producer. Fructose content was extremely low under warm conditions, suggesting a rapid utilization of inverted sucrose for growth. 3. Sugar content of storage tissues varied greatly in response to both temperature and variety treatments. Although sucrose was rapidly synthesized at 80 to 85° F. neither variety was able to accumulate the sugar in immature storage tissue at that temperature range. At 55 to 60° F., P.R. 1059 accumulated high sucrose in the immature storage tissue but P.R. 980 failed to do so. Brix and polarization data showed that in millable stalk tissues P.R. 980 responded far more readily than P.R. 1059 to the cold treatment. It is suggested that high-tonnage varieties such as P.R. 980 may require a cold stimulus for maximum sucrose accumulation, whereas the cool exposure may not be essential for high sucrose producers such as P.R. 1059. 4. Numerous enzyme variations were encountered with leaf and meristem preparations. The greatest differences were found in leaves where varietal effects outweighed those of temperature. All leaf enzymes measured, including phosphatase, ATP-ase, amylase, peroxidase, and tyrosinase, were significantly less active in P.R. 980 than in P.R. 1059. Low temperature further lowered the enzyme values. It is believed that insufficient enzyme potential was available in cold-treated P.R. 980 to acheive either normal growth or sugar synthesis. 5. Only traces of invertase were detected in meristem of P.R. 1059 exposed to cold temperature. This accounts for high sucrose accumulation in that tissue while supporting the concept of a temperature-sensitive, invertase-synthesizing mechanism. 6. Amylase content varied greatly in response to temperature and varietal treatments. Amylase activity was about three times greater in P.R. 1059 than in P.R. 980. Within variety treatments, amylase values were about two times greater in plants exposed to 80-85° F., as compared with 55-60° F. Amylase roles in determining varietal and temperature control over sucrose level is discussed from the standpoint of sucrose and starch interconversion.