The single gene, homozygous recessive, "stamenless-2" (sl-2/sl-2) mutant of tomato (Lycopersicon esculentum Mill.) is male sterile and exhibits abnormal stamen development under normal greenhouse conditions. Stamenless-2 mutant is both temperature- and hormone-sensitive. Gibberellic acid (GA3) treatment (Sawhney and Greyson, 1973) or low temperatures (Sawhney, 1983) restore fertility in mutant flowers. Conversely, indole-3-acetic acid (IAA) treatment (Sawhney and Greyson, 1973) or high temperatures (Sawhney, 1983) cause carpellization of stamens which do not undergo microsporogensis. We have now analyzed the endogenous levels of gibberellins (GAs) (especially GA1 and GA3) and IAA in leaves of the normal (+/+) and mutant (sl-2/sl-2) plants grown under low (LTR) and high temperature regimes (HTR).
Gibberellin activity was determined by dwarf rice bioassay (Murakami, 1968) of GA fractions purified by reversed phase high performance liquid chromatography (HPLC) followed by the methods of Koshioka et al. (1983). IAA content was analyzed by HPLC and gas chromatography-mass spectrometry-selected ion monitoring (Cohen et al., 1986).
The results indicate lower levels of GA1 and GA3 in leaves of the mutant than normal tomato plants in both LTR and HTR (Table 1). In an earlier study, Sawhney (1974) also found lower gibberellin-like activity in the vegetative and floral parts of the stamenless-2 mutant than normal tomato plants. Low temperature grown normal and mutant leaves exhibited higher GA1 plus GA3 levels than the corresponding plants in HTR. On the contrary, in LTR and HTR, the mutant leaves had 10 and 20 times higher IAA contents than the normal leaves under the same temperature conditions (Table 1). The concentrations of IAA in the normal leaves had two times higher IAA content in HTR than LTR.
Low GA1 + GA3 levels in the leaves of sl-2/sl-2 mutant appear to be related to the male sterility whereas high IAA content (especially at HTR) may be associated with carpellization of stamens in this mutant. We suggest that the effect of temperature on the stamen development and male sterility is mediated through the endogenous plant hormones.
Literature cited:
Cohen, J.D., B.G. Baldi and J.P. Slovin. 1986. Plant Physiol. 80:14-19.
Koshioka, M., J. Harada, K. Takeno, M. Noma, T. Sassa, K. Ogiyama, J.S. Tayler, S.B. Rood, R.L. Legge and R.P. Pharis. 1983. J. Chromatogr. 256:101-115.
Murakami, Y. 1968. Bot. Mag. Tokyo 81:33-43.
Sawhney, V.K. 1974. J. Exp. Bot. 25:1004-1009.
Sawhney, V.K. 1983. J. Hered. 74:51-54.
Sawhney, V.K. and R.I. Greyson 1973. Can. J. Bot. 51:2473-2479.
Table 1. Endogenous levels of GA1 + GA3 and IAA in leaves of the normal (+/+) and the 'stamenless-2' (sl-2/sl-2) mutant of L. esculentum Mill., grown in LTR and HTR.
___________________________________________________________
Genotype Temperature Hormone content (ng per g dry wt.)
__________________________________
*Ga1 + GA3 IAA
___________________________________________________________
+/+ LTR 3.7 33.6
sl-2/sl-2 LTR 1.8 338.7
+/+ HTR 2.0 36.1
sl-2/sl-2 HTR 1.1 712.1
___________________________________________________________
*Determined by dwarf rice bioassay as GA3 equiv. per g dry wt.