PHYSIOLOGICAL-ASPECTS IN TUXPENO MAIZE WITH IMPROVED DROUGHT TOLERANCE

Tuxpeno maize has been selected in eight successive cycles under droug ht conditions. We studied three cycles (0, 4, and 8) to know how physi ological parameters such as stomatal conductance (gs), leaf photosynth esis rate CPS) and detectable abscisic acid (ABA) levels changed in cy cle 8 compared to the earliest generations under drought or well-irrig ated conditions. Four-week old plants, grown under greenhouse conditio ns, were exposed to drought until relative water content was reduced t o approximately 60% (water potential = -1.7 MPa), Neither under well-i rrigated or water stressed conditions did significant differences in l eaf ABA levels among the three cycles occur under drought conditions, gs and PS were almost zero; however, under well-irrigated conditions, plants from cycle 0 had values for gs of 197 mmol m(-2) s(-1), while p lants in cycle 4 and 8 had higher values of 257 and 255 mmol m(-2) s(- 1), respectively PS showed a pattern similar to gs, where cycle 0 had the lowest value of 19 mu mol m(-1) sl, while cycles 4 and 8 had highe r values with 26 mu mol m(-2) s(-1), respectively. The chlorophyll con tent of well-irrigated plants did not show significant differences and the seedlings under drought conditions showed lower values of chlorop hyll than weil-watered conditions.