Role of plant growth substances in MS33‐controlled stamen filament growth in Arabidopsis

Abstract

The rapid growth of stamen filaments just before flower anthesis in Arabidopsis thaliana does not occur in the male sterile33 (ms33, formerly known as msZ) mutant. ms33 filaments were approximately 40% shorter than the wild type (WT), and there was corresponding reduction in the epidermal cell length of filaments. This suggests that MS33 controls the final cell‐elongation phase of filament growth. Both low temperatures and gibberellic acid (GA3) restored filament and cell growth in intact ms33 flowers, but these treatments only had a small promotive effect on WT filaments. Decapitation experiments involving the removal of the anther had the opposite effect on WT and ms33 filaments; growth was inhibited in WT, but was increased in ms33 filaments. In young stamen primordia cultured in vitro, filament growth was less in WT, but more in ms33, than in respective in vivo produced filaments. Plant growth substances (PGSs), GA3 and indole‐3‐acetic acid (IAA) were promotive, zeatin had no effect, and abscisic acid (ABA) and ethrel inhibited filament growth in both intact and decapitated WT and ms33 filaments. Together these observations suggest that MS33 is activated immediately before anthesis and that the MS33 product either regulates temporal biosynthesis of gibberellins (GAs) and/or IAA or makes the filament tissue sensitive to these PGSs, which in turn trigger cell elongation and filament growth. The data also suggest that ms33 mutant anthers contain a relatively high ratio of growth inhibitors to promoters, which inhibits epidermal cell elongation and filament growth.

Pleiotropic effects of the male sterile33 (ms33) mutation in Arabidopsis are associated with modifications in endogenous gibberellins, indole-3-acetic acid and abscisic acid

“…2). For stamen length there was a much greater increase in the mutant (74%), compared to only a 10% increase for the WT, and the mutant stamen length at low temperature was similar to that of WT at normal temperatures (see also Fei and Sawhney 1999). In contrast, carpel length was reduced in ms33 flowers by about 8% and increased in WT flowers by 30% (Fig.…”

“…Thus, the MS33 gene function is required for normal growth of all floral organs, not just for stamens. As reported elsewhere, the inhibition of stamen filament growth in ms33 was caused by inhibition of cell elongation prior to anthesis, and this effect could be rescued by low temperature or exogenous GA, suggesting that the mutant may have a defect in GA biosynthesis or signaling (Fei and Sawhney 1999). Similarly, in the ga1-1 mutant in Arabidopsis, the stunted growth of the stamen filament could be restored by exogenous GA (Goto and Pharis 1999).…”

“…A comparison of floral organs at anthesis showed no difference in final petal lengths between ms33 and WT flowers. However, the mutant stamens were significantly shorter, and sepals and gynoecium longer, than the corresponding WT organs (Table 1, see also Fei and Sawhney 1999). The low temperature treatment, i.e., 15°C/11°C, had different effects on the growth of floral organs in ms33 and WT.…”

“…We showed earlier that the inhibition of filament growth in ms33 was related to inhibition of rapid cell elongation immediately before anthesis, and that exogenous GA or low temperature was able to restore normal filament growth (Fei and Sawhney 1999). Pollen development in ms33 is impaired near the maturation stage and this was, in part, related to increased vacuolation of pollen grains, likely as a result of inadequate pollen desiccation (Fei and Sawhney 2001).…”

SPL8, an SBP-Box Gene That Affects Pollen Sac Development in Arabidopsis

“…In this context, it is interesting that SPL8 expression itself was found to be inducible by the phytohormone gibberellin (M. Schmid and D. Weigel, personal communication). Mutants known to be affected in either the biosynthesis or the perception of gibberellin often display severe fertility problems (Koornneef et al, 1985;Jacobsen and Olszewski, 1993;Fei and Sawhney, 1999;Goto and Pharis, 1999). Furthermore, trichome formation, which also was reduced on the sepals of spl8 mutant flowers, is known to be controlled by gibberellin (Chien and Sussex, 1996;Perazza et al, 1998).…”