Studying the thermal stress effect on sucrose-metabolizing enzymes in sugarcane is of great importance for understanding acclimation to thermal stress. In this study, two varieties, S2003-US-633 and SPF-238, were grown at three different temperatures ( ± 2°C): 30°C as a control, 45°C for various episodes of high temperature treatments and recovery conditions at 24, 48 and 72 hours. Data showed that reducing sugar content increased until the grand growth stage but sharply declined at the maturity stage in both cultivars. On the other hand, sucrose is enhanced only at the maturity stage. The expression of all invertase isozymes declined prominently; however, the expression of SPS was high at the maturity stage. Hence, the sucrose accumulation in mature cane was due to increased SPS activity while decreased invertase isozymes (vacuolar, cytoplasmic and cell wall) activities at maturity stage in both cultivars. Heat shock decreased the sucrose metabolizing enzymes, sucrose content and sugar recovery rate in both cultivars. In contrast, heat-shock treatments induced maximum proline, MDA, H₂O₂ and EC in both cultivars. Notably, this is the first report of diverse invertase isozyme molecular weight proteins, such as those with 67, 134 and 160 kDa, produced under heat stress, suggesting that these enzymes have varied activities at different developmental stages. Overall, S2003-US-633 performs better than the cultivar SPF-238 under heat stress conditions at all development stages, with increased sucrose content, enzyme expression, proline and sugar recovery rate. This work will provide a new avenue regarding sugarcane molecular breeding programs with respect to thermal stress.

Sugarcane (Saccharum officinarum L) is a valuable cash crop which plays an imperative role in the worldwide economy. However, high temperature has significantly retarded the crop growth and yield by alteration of biochemical pathways. Therefore, the biochemical activities of two sugarcane varieties were explored under heat stress condition. The sugarcane cultivars S2003-US-633 (high sucrose accumulation) and SPF-238 (low sucrose accumulation) were cultivated and subjected to different temperature regimes i.e. control at 30±2 °C, heat stress at 45±2 °C and recovery at 30±2 °C for 24, 48 and 72 hours at formative stage. Detailed profiling of physiochemical attributes, sugar analysis linked with sucrose metabolism enzymes and thermotolerance indicators were investigated. S2003-US-633 exhibited better response in terms of sugar accumulation regulated by sucrose synthase, sucrose phosphate synthase and invertase activities along with more proline accumulation, total soluble protein contents with response to high temperature exposure. While S2003-US-633 is ranked as tolerant variety due to less MDA, H₂O₂ content and electrolytes leakage exhibiting its efficient tolerance mechanism, giving high sugar recovery rate despite harsh environmental conditions. Thus, these findings can be helpful in providing information for engineering sugar improvement along with thermotolerance in sugarcane varieties and providing new avenues towards the economic development of the country.