The root system of maize consists of the primary root and a variable number of lateral seminal‐, crown‐ and brace roots. Except for the primary root and some minor roots forming at the mesocotyl, all other roots grow out of nodal regions, namely, the embryogenic scutellar node and the underground—as well as the lower above‐ground stem nodes. Besides their role in water and nutrient uptake, some of these roots (crown‐ and brace roots) are essential for the lodging resistance of the plants. This property of the crown roots has now been successfully used for screening a segregating F2 population of a cross between a flint inbred line and an En transposon line. Two allelic root‐deficient mutants have been isolated and have been designated rtcs‐1 and rtcs‐2 for their complete lack of formation of crown‐ and lateral seminal roots. They survive by the ability of the primary root to support the growth of the developing plant. The monogenic and recessive mutants appear to be affected in an early root‐forming function since no primordia are formed either in the case of embryo‐borne lateral seminal or stem‐derived crown roots. The Rtcs locus could be mapped to the short arm of chromosome 1 with the help of a co‐segregating RAPD marker. The effect of the mutation seems to be highly specific since no pleiotropic effects on other parts of the plants have been observed. The formation of adventitious roots can, however, still be induced in the mesocotyl region of the mutant.
Broadening of the genetic base and systematic exploitation of heterosis in faba bean requires reliable information on the genetic diversity in the germ plasm. Three groups of faba bean inbred lines were examined by means of RAPDs (random amplified polymorphic DNAs) assays: 13 European small-seeded lines, 6 European large-seeded lines, and 9 Mediterranean lines. Out of 59 primers, 35 were informative and yielded 365 bands, 289 of which were polymorphic with a mean of 8.3 bands per primer. Monomorphic bands were omitted from the analyses and genetic distances (GD) were estimated via the coefficient of Jaccard. The mean GD among the European small-seeded lines was significantly greater than those among the lines of the other two groups. Repeatability of GD estimates was high. Cluster (UPGMA) and principal coordinate analyses identified European small-seeded lines and Mediterranean lines as distinct groups with European large-seeded lines located in between. The results are in harmony with published archaeobotanical findings. We conclude that RAPDs are useful for classification of germ plasm and identification of divergent heterotic groups in faba bean.
In this publication we report the effects of cycles of light-dark and high-low temperature on SER of C. rubrum. The basic kinetics of pure photo-and thermoperiodic effects on SER are taken as a system of reference to study the interaction of light and temperature signals. The results are discussed in relation to current hypotheses ofthe nature of the biological clock and light perception in green plants (22,23).In their natural environment, plants develop under photo-and thermoperiodic conditions which change with the seasons. Developmental and behavioral responses of plants clearly demonstrate their potential for measuring the duration and sequence of environmental conditions. It is now generally accepted that time measurement in eukaryotes depends on the interaction of an
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