<p>The present investigation was undertaken to compare the thermotolerance behaviour of maize with its wild progenitor, teosinte on the basis of carbon and nitrogen metabolism. For this study, maize genotypes, viz. PMH 2 (relatively susceptible to heat stress), PMH 10 (relatively tolerant to heat stress) and a wild relative, teosinte were taken into consideration. High sucrose content of teosinte roots due to unaffected sucrose synthase (SS), acid invertase (AI) and alkaline invertase (AKI) activities, under heat stress, might help the wild progenitor in tolerating stress conditions. In contrast, the relatively lower AI activity in its shoots, under control and stress conditions, showed an apparently lesser role of AI in maintaining homeostasis in its shoots. The stress tolerant behaviour of PMH 10 seedlings may be attributed to the unaffected, yet high AKI activity in its roots and the significantly high SS and SPS activities in its roots and shoots under stress conditions. The susceptibility of PMH 2 towards heat stress was due to lesser induction of SS in roots and that of SPS in both roots and shoots as compared to the other genotypes. Besides, the reduced total soluble protein content and the decreased glutamine oxoglutarate aminotransferase (GOGAT), glutamate dehydrogenase (GDH) and glutamine synthetase (GS) activities in its seedlings, under heat stress also contributed to the susceptible behaviour of the genotype. On the contrary, the manifold increase in GOGAT, GS and GDH activities in PMH 10 and teosinte seedlings, under high temperature conditions were responsible for their stress tolerance behaviour.</p>