One of the reasons of poor nutritive value of sorghum grain is resistance of its seed storage proteins (kafirins) to protease digestion. To reveal sorghum entries with increased kafirin digestibility, the sodium dodecyl sulfate -polyacrylamide gel electrophoresis (SDS-PAGE) of endosperm proteins of 10 lines [cytoplasmic male sterility (CMS)-lines and fertility restorers] and five F 1 hybrids before and after pepsin digestion was carried out. For quantitative estimation of kafirin digestibility the SDS-PAGE banding patterns were scanned by laser densitometer. Significant variability for both individual fractions and total kafirin digestibility was found. The line KVV-45, fertility restorer for the Indian ÔM35-1AÕ type of CMS, had the highest level of kafirin digestibility (30% and 25% of undigested c-and a 1 -kafirins, respectively), while in some entries 80-90% of kafirins remained undigested. Increased a 1 -kafirin digestibility coincided with relatively high c-kafirin digestibility. High-molecular weight kafirins (HMWK) (45 kDa and 66 kDa) resistant to pepsin digestion were found in some lines, the F 1 hybrids had the same HMWK as parental lines. These data demonstrate possibility for isolation of sorghum genotypes with increased nutritive value by screening their flour for in vitro protein digestibility.
Male fertility restoration in new types of sorghum cytoplasmic male sterility-inducing cytoplasms (A4, Ô9EÕ, ÔM35Õ), characterized by the formation of non-dehiscent anthers, is difficult. Lines with fertilityrestorer genes for these unique cytoplasms do occur, but rarely, and when found tend to be unstable in their inheritance and expression. The aim of this research was to explore reasons for this instability. Seven lines in three unique cytoplasms, Ô9EÕ, A4 and ÔM35Õ, and six lines that restore with these cytoplasms were grown at the Agricultural Research Institute for South-East Region in Saratov, Russia from 1993 to 2004. Levels of male fertility restoration and various environmental factors were recorded. It is reported that for sorghum hybrids in the A4, Ô9EÕ and ÔM35Õ male-sterile cytoplasms, the level of plant male fertility is determined by the level of water available to plants during anther and pollen formation that which Ôswitches onÕ the expression of fertility-restoring genes, and is possibly involved in an unusual type of male fertility inheritance in these cytoplasms. The creation of reliable line-fertility restorers capable of the restoration of male fertility of F 1 hybrids in ÔM35Õ cytoplasm under conditions of water stress is also reported. Current research explore mechanisms involved possible in responses to water levels at various growth stages and their influence on fertility within these cytoplasms.
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