- [Show abstract] [Hide abstract] ABSTRACT: Previous studies have shown that Cucumber-FLO-LFY (CFL) overexpression significantly promotes early flowering without a gibberellin (GA3) supplement in gloxinia (Sinningia speciosa), suggesting that CFL can serve functionally as a LEAFY homolog. In the present study, different sucrose concentrations were applied to the culture medium to investigate the effects of sucrose on the development of excised flower buds and the regeneration of floral buds from sepals in wild-type and 35S::CFL gloxinia lines. The results showed that floral buds were formed directly from sepal explants without prior formation of shoots and leaves in 35S::CFL gloxinia lines when 2% w/v sucrose was added. Conversely, 0% or 5% w/v sucrose inhibited the generation of flower buds from sepals and the opening of flowers. Semi-quantitative PCR also showed that a medium with 5% w/v sucrose significantly inhibited MADS-box gene expression in wild type and much less significantly in 35S::CFL gloxinia. These data indicate that sucrose, as the main carbohydrate transported in floral organs, is a significant promoter of flower induction and maturity.
- [Show abstract] [Hide abstract] ABSTRACT: Leafy (LFY) and LFY-like genes control the initiation of floral meristems and regulate MADS-box genes in higher plants. The Cucumber-FLO-LFY (CFL) gene, a LFY homolog in Cucumis sativus L. is expressed in the primordia, floral primordia, and each whirl of floral organs during the early stage of flower development. In this study, functions of CFL in flower development were investigated by overexpressing the CFL gene in gloxinia (Sinningia speciosa). Our results show that constitutive CFL overexpression significantly promote early flowering without gibberellin (GA(3)) supplement, suggesting that CFL can serve functionally as a LFY homolog in gloxinia. Moreover, GA(3) and abscisic acid (ABA) treatments could modulate the expression of MADS-box genes in opposite directions. GA(3) resembles the overexpression of CFL in the expression of MADS-box genes and the regeneration of floral buds, but ABA inhibits the expression of MADS-box genes and flower development. These results suggest that CFL and downstream MADS-box genes involved in flower development are regulated by GA(3) and ABA.
- [Show abstract] [Hide abstract] ABSTRACT: Ultraweak luminescence (UL) changes and sister-chromatid exchanges (SCEs) induced by Al toxicity were investigated in root tip cells of barley (Hordeum vulgare L.). A low positive correlation between relative UL rates and root relative elongation rates (RERs) was observed in 30 barley cultivars. During 1.5–24 h exposure to 20 μM Al solution, the UL value in cv Humai 16 (Al-tolerant) was higher than that in cv 2000-2 (Al-sensitive), suggesting that UL is a possible mechanism by which Al-tolerant cultivars avoid reactive oxygen species (ROS) toxicity. Upon raising Al levels (>50 μM), the increase for UL in Al-tolerant and sensitive cultivars possibly involved cell death. A significant increase in the SCE rate was observed in cv 2000-2 but not in cv Humai 16 at 20 μM Al level, suggesting that mechanisms of Al-tolerance might block the occurrence of Al-induced SCEs. With raising Al levels (0–640 μM), SCE rates first increased and then decreased in the two cultivars, but their Al levels inducing the highest SCE rate were 10 μM in cv 2000-2 and 320 μM in cv Humai 16. In cv 2000-2, SCEs reached saturation status after 4 h treatment with 10 μM Al, suggesting that SCEs can be considered as a sensitive indicator for Al phytotoxicity. Ascorbic acid (ASA) pretreatment could significantly inhibit Al-induced SCE occurrence, indicating that Al indirectly induces SCEs via Al-triggered ROS formation. To our knowledge, this is the first report demonstrating that Al can induce UL changes and SCEs in root tip cells, and that may serve as possible indicators and thereby provide new insights into the mechanisms of Al toxicity and tolerance in barley.
- [Show abstract] [Hide abstract] ABSTRACT: In vivo and in vitro experiments showed that border cell (BC) survival was dependent on root tip mucigel in barley (Hordeum vulgare L. cv. Hang 981). In aeroponic culture, BC development was an induced process in barley, whereas in hydroponic culture, it was a kinetic equilibrium process during which 300-400 BCs were released into water daily. The response of root elongation to temperatures (10-35 degrees C) was very sensitive but temperature changes had no great effect on barley BC development. At 35 degrees C, the root elongation ceased whereas BC production still continued, indicating that the two processes might be regulated independently under high temperature (35 degrees C) stress. Fifty microM Al could inhibit significantly BC development by inhibiting pectin methylesterase activity in the root cap of cv. 2000-2 (Al-sensitive) and cv. Humai 16 (Al-tolerant), but 20 microM Al could not block BC development in cv. Humai 16. BCs and their mucigel of barley had a limited role in the protection of Al-induced inhibition of root elongation, but played a significant role in the prevention of Al from diffusing into the meristems of the root tip and the root cap. Together, these results suggested that BC development was a temperature-insensitive but Al-sensitive process, and that BCs and their mucigel played an important role in the protection of root tip and root cap meristems from Al toxicity.