Effect of Gibberellic Acid on Seed Germination. The tomato mutants 'Lateral Suppressor' (ls), 'Blind' (bl) and its allele 'Blind^2' (bl^2) (the last one formerly referred to as 'Torosa^2' [to^2]) have been found valuable for research on the control of lateral shoot growth (see Mapelli and Lombardi, 1982; Sossountzov et al., 1988; Tucker, 1976). A serious practical problem with their use--especially for ls--has been impaired reproductive capacity due to limited seed yield and low rate of seed germination.
We report now that germination in some of these mutants can be stimulated significantly with gibberellic acid (GA3) treatment. When ls seeds were germinated in the presence of 1 mM GA3, the rate was 30 to 50 percent compared to 0 to 10 percent in the untreated controls (Table 1). Stimulation of germination by GA3 treatment was much less in bl, and little or no increase was observed in the normal line. Therefore, GA3 treatment enhances the efficiency of seed germination in these mutants, and especially in ls plants.
Effect of Indoleacetic Acid on Axillary Bud Growth. Tissue culture techniques have been shown recently to provide a simple and sensitive assay of axillary bud growth in beans (Tamas et al., 1989). In the present work we tested whether differences can be observed among genetic lines of tomato in their rate of axillary bud growth, and in their growth response to applied indoleacetic acid (IAA).
Bud-bearing stem explants of tomato plants were surface sterilized in ten percent Clorox for ten minutes, rinsed in sterile distilled water, and the apical end was inserted in a solid culture medium containing varying levels of IAA (Tamas et al., 1989). Within a few days, outgrowth of axillary buds could be observed on stem explants of normal plants (cv Sutton's Best of All) inserted in a medium without IAA (Fig. 1). After about two weeks of culture, the average length of the resulting axillary shoots was 38 mm. The corresponding values for Blind and Blind^2 plants were four and eleven mm respectively. Therefore, the growth capacity of axillary buds in these mutants appears to be impaired even when the buds are not under the influence of the dominant shoot apex.
When stem segments were inserted with their apical end in IAA-containing medium, bud growth on normal explants was significantly inhibited. At concentrations of 1 and 100 uM IAA, the average length of axillaries was 29 and 10 mm respectively after about two weeks of culture. In bl and bl^2 plants, the difference in axillary bud growth between IAA-treated and untreated plants appeared to be insignificant. This result could be due to diminished IAA sensitivity of these mutants. Alternatively, the growth capacity of axillary buds in these mutants may be impaired to such a degree that no further inhibition by exogenous IAA could be observed.
Therefore, our results suggest that decreased axillary bud growth in bl and bl2 plants is due to the impaired growth capacity of the axillary buds themselves, rather than to increased growth repression by the dominant shoot apex.
Literature cited:
Mapelli, S. and L. Lombardi 1982 A comparative auxin and cytokinin study in normal and to-2 mutant tomato plants. Plant Cell Physiol. 23:751-757.
Sossountzov, L., R. Maldiney, B. Sotta, I. Sabbagh, Y. Habricot, M.Bonnet, and E. Miginiac 1988 Immunocytochemical localization of cytokinins in Craigella tomato and a sideshootless mutant. Planta 175:291-304.
Tamas, I.A., J.L. Schlossberg-Jacobs, R. Lim, L.B. Friedman and C.C. Barone 1989 Effect of plant growth substances on the growth of axillary buds in cultured stem segments of Phaseolus vulgaris L. Plant Growth Regul. 8:165-183.
Tucker, D.J. 1976 Endogenous growth regulators in relation to side shoot development in the tomato. New Phytol. 77:561-568.
Table 1. Effect of GA3 on seed germination in cv. Ailsa Craig and two of its isogenic lines, Blind and Lateral Suppressor. Seeds, sterilized in 10% commercial bleach (Clorox), were placed on filter paper moistened with sterile distilled water or 1 mM GA3.
____________________________________________________________
Genetic % Germination*
______________________________
Line Genotype GA3 Conc. Experiment 1 Experiment 2
mM Day 13 Day 27 Day 13 Day 22
____________________________________________________________
Normal -- 0 80 100 30 80
Normal -- 1 90 100 80 100
Blind bl,bl 0 50 90 20 30
Blind bl,bl 1 50 90 80 80
Lateral ls,ls 0 10 10 0 0
Suppressor
Lateral ls,ls 1 20 30 30 50
Suppressor
_____________________________________________________________
*n=10Figure 1. Effect of indoleacetic acid on axillary bud growth in bud-bearing, cultured stem explants of normal (cv. Sutton's Best of All), Blind (bl) and Blind2 (bl2) tomato mutants. IAA concentration in the medium was: