Last year we reported evidence of HSP variability in a limited sample of maize genotypes. The screening has been continued on a larger scale. In vivo-synthesized proteins (control and heat-shock) from 35 unrelated inbred lines and some F1's were analyzed by 1D SDS PAGE in a linear 5-20% gradient gel. The results allow maize HSPs to be divided into two major groups.
The first group includes HSPs expressed by the vast majority of the lines examined, namely HSPs 240, 94, 84, 82, 72, 70, 27, 22, and 18kD in molecular weight. This set, which includes exclusively high (over 70kD) and low (under 30kD) polypeptides, corresponds to HSPs generally reported in the literature, except for HSP 240kD which, to our knowledge, was never detected before. Genetic variability in this group is limited. HSPs 240, 72 and 18kD were invariant and mainly quantitative differences were detected for the others. Nearly 70% of the inbreds analyzed showed this "standard" pattern with only minor variations (at most 1 or 2 additional bands).
To the second group belong HSPs expressed only in a small number of genotypes. With the exception of HSPs 93 and 91kD (detected in 1 and 2 inbreds respectively), all HSPs of this group are in the medium (60-40kD) and low (34-17kD) molecular weight range. HSPs 52kD (9 inbreds), 44kD (12 inbreds) and 40kD (11 inbreds) were the most frequently found in this survey. Four inbreds showed a prominent 17kD HSP in addition to the standard 18kD. Analysis of F1's for this and other HSPs showed an additivity pattern.
Few lines exhibited a large variation in HSP pattern -4 to 6 different bands compared to standard lines. However, until now precise data are available with regard to in vivo thermotolerance of the inbreds considered. Analysis of this important aspect is in progress.
Carla Frova and Giorgio Binelli
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