Phenotypic Characterization of Lettuce Dwarf Mutants and Their Response to Applied Gibberellins

Abstract

Four monogenic, recessive dwarf mutants of lettuce (Lactuca sativa L.), previously isolated from a population induced by ethyl methanesulfonate, were compared with the normal genotype (E-1) for plant height, weight, leaf area, as well as hypocotyl length and root length. These nonallelic dwarfs (dwf1, dwf2, and dwf3) exhibited reduced hypocotyl length, smaller, dark green leaves, and reduced stem length. Another mutant, dwf2', allelic with dwf2, exhibited an intermediate phenotype. Epidermal cells on hypocotyls and mature leaves were counted for both normal E-1 and dwf2 plants. The total number of epidermal cells per unit area for hypocotyls and for leaves from these plants was very similar, implying the dwarf's smaller size was due to an inhibition of cell expansion and not due to decreased cell divisions. Both dwarf and normal hypocotyls elongated normally in response to exogenous gibberellin A3 (GA3). In the rosette stage, only E-1 and dwf2' responded similarly to lower concentrations of GA3, while the other dwarfs required higher concentrations to respond. Hypocotyls of dwf2 and E-1 elongated equally with applied entkaurenol, ent-kaurenoic acid, GA53-aldehyde, GA53, GA19, GA20, and GA1 indicating that the biochemical block in dwf2 occurs at a very early step in the GA-biosynthetic pathway.

The Endogenous Gibberellins of Dwarf Mutants of Lettuce

“…In summary, the results presented in this paper and the previous paper (22) are consistent with the operation of the early-1 3-hydroxylation pathway in lettuce shoots and suggest that mutants dwfl, dwf2, and dwf2' are GA biosynthetic mutants of this pathway. Metabolic studies are now required to confirm these conclusions.…”

“…In the preceding paper (22), the characterization of four dwarf mutants of early flowering lettuce (E-1) was reported. These dwarfs responded to applied GA3 and to members of the early-1 3-hydroxylation pathway by elongating at the normal rate, suggesting that the mutants were GA deficient.…”

“…Seeds of Lactuca sativa L. SC 904 (dwfl), SC 367 (dwf2), SC 3670 (dwf2%), SC 352 (E-1, early flowering strain), and cv Salinas (Saladin), were sown in flats containing sterilized field soil and grown in a greenhouse (22). Plant shoots (leaves and stems) were harvested after 3 weeks and immediately frozen at -70°C.…”

Isolation and functional characterization of the FLOWERING LOCUS T homolog, the LsFT gene, in lettuce

“…We reported that bioactive GA 1 increased with the upregulation of LsGA3ox1 expression, which metabolizes GA 20 to GA 1 in the lettuce stem at high temperature (Fukuda et al, 2009). Waycott and Taiz (1991) and Mazier et al (2007) demonstrated the importance of GA in regulating lettuce stem growth with GA mutants of lettuce, but they showed a severe dwarf phenotype. Although some options to control LsGA3ox1 expression or LsGA3ox1 activity and others to reduce GA 1 level only in stems are known, an additional factor related Abbreviations: FT, FLOWERING LOCUS T; GA, gibberellin; LB, left border; LD, long-day; NJ, neighbor-joining; npt II, neomycin phosphotransferase II gene; OE, overexpression; Pnos, nos promoter; RACE, rapid amplified cDNA ends; RB, right border; SAM, shoot apical meristem; Tnos, 3 region of nos; ZT, zeitgeber time.…”

Characterization of a Loss-of-Function Mutant of Gibberellin Biosynthetic GeneLsGA3ox1in Lettuce

“…1) In contrast, loss-offunction mutants of the GA biosynthetic genes in lettuce have not been widely used, although GA-related dwarf lettuce mutants have been reported. 7,8) Recently, gene tagging in lettuce cv. Jessy using the Tnt1 retrotransposon from tobacco (Nicotiana tabacum) was performed.…”