Abstract
The Reduced Height (Rht) genes formed the basis for the green revolution in wheat by decreasing plant height and increasing productive tillers. There are two current widely used Rht mutant alleles, Rht-B1b and Rht-D1b. Both reduce plant height by 20% and increase seed yield by 5–10%. They are also associated with decreased seed size and protein content. Here, we tested the degree to which Rht-B1b impacts flag leaf photosynthetic rates and carbon and nitrogen partitioning to the flag leaf and grain during grain fill under field conditions using near isogenic lines (NILs) that were either standard height (Rht-B1a) or semi-dwarf (Rht-B1b). The results demonstrate that at anthesis, Rht-B1b reduces flag leaf photosynthetic rate per unit area by 18% and chlorophyll A content by 23%. Rht-B1b significantly reduced grain protein beginning at 14 days post anthesis (DPA) with the greatest difference seen at 21 DPA (12%). Rht-B1b also significantly decreased individual seed weight beginning at 21 DPA and by 15.2% at 28 DPA. Global expression analysis using RNA extracted from developing leaves and stems demonstrated that genes associated with carbon and nitrogen metabolism are not substantially altered by Rht-B1b. From this study, we conclude that Rht-B1b reduces flag leaf photosynthetic rate at flowering while changes in grain composition begin shortly after anthesis.
Highlights
The introduction of the semi-dwarfing trait into wheat cultivars during the 1960s and 1970s was a defining characteristic of the “Green Revolution”
The genes associated with the green revolution are mutant forms of the Reduced Height-1 (Rht) gene which reduce plant height by decreasing the ability of the plant to respond to gibberellic acid (GA) (Allan et al, 1959; Allan, 1970; Gale and Gregory, 1977)
Incorporation of height reducing (Rht) semi-dwarf genes Rht-B1b and Rht-D1b into wheat cultivars has led to dramatic increases in grain yield (Flintham et al, 1997b)
Summary
The introduction of the semi-dwarfing trait into wheat cultivars during the 1960s and 1970s was a defining characteristic of the “Green Revolution” (reviewed in Hedden, 2003). Due to the impressive yield increases associated with these genes, by the late 1990s more than 70% of wheat cultivars grown globally incorporated one of the original semi-dwarfing genes (reviewed in Evans, 1998). The genes associated with the green revolution are mutant forms of the Reduced Height-1 (Rht) gene which reduce plant height by decreasing the ability of the plant to respond to GA (Allan et al, 1959; Allan, 1970; Gale and Gregory, 1977). A single functional copy of Rht resides on each of the group four chromosomes of wheat (Gale et al, 1975; Gale and Marshall, 1975, 1976; McVittie et al, 1978; Sourdille et al, 1998)
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