A comparative transcriptomic analysis of the extremely boron tolerant plant Puccinellia distans with the moderately boron tolerant Gypsophila arrostil.

UNLABELLED: The Turkish ecotype of Puccinellia distans displays exceptional boron (B) tolerance, >1,250 mg B L⁻¹, compared to <50 mg B L⁻¹ for Gypsophila arrostil. In the present study, we compare the molecular basis for the difference in B tolerance between the two species by constructing high B-responsive suppression subtractive hybridization libraries to identify the upregulated genes. A total of 219 and 113 unique non-redundant expressed sequence tags (ESTs) were identified and functionally classified in P. distans and G. arrostil, respectively. In addition, 63 ESTs were down-regulated in P. distans in response to high B. The majority of the high B upregulated genes belong to four categories: metabolism, protein synthesis, cellular organization, and stress/defense. We hypothesize that the superior B tolerance exhibited by P. distans may be due to its ability to restrict the accumulation of B in plant tissues through the upregulated expression of efflux transporters comparable to the Bot1 transporter of barley. In addition, our results are consistent with the view that other molecular mechanisms involved in stress/defense, such as detoxification, anti-oxidative, and signaling pathways, are needed to tolerate B-toxicity stress. KEY MESSAGE: The molecular basis of boron tolerance of two plant species (Puccinellia distans and Gypsophila arrostil) that differ greatly in their boron tolerance was studied in this manuscript.

Mechanisms of boron tolerance and accumulation in plants: a physiological comparison of the extremely boron-tolerant plant species, Puccinellia distans, with the moderately boron-tolerant Gypsophila arrostil.

The physiological characteristics of the extremely boron (B)-tolerant plant species, Puccinellia distans, were compared with those of the moderately tolerant Gypsophila arrostil, two species collected from a B-mining area of Eskisehir, Turkey. Boron was supplied to plants hydroponically at B concentrations ranging from 0.5 to 50 mg B/L for G. arrostil, and from 0.5 to 2000 mg B/L for P. distans. The results show that P. distans has a strikingly greater tolerance to B than G. arrostil. While G. arrostil was unable to survive B supply concentrations greater than 50 mg B/L, P. distans grew at B supply concentrations exceeding 1250 mg B/L. Our research supports the conclusion that from 0.5 to 50 mg B/L, P. distans is better able to restrict the accumulation of B in the whole plant, and the transport of B from root to shoot, than G. arrostil. We propose that P. distans uses several strategies to achieve B tolerance including the ability to restrict the accumulation of B relative to its accumulation of biomass, the ability to restrict the transport of B from root to shoot, and, to a lesser extent, the ability to tolerate high concentrations of B in its shoot and root tissues.

Transcriptomic analysis of boron hyperaccumulation mechanisms in Puccinellia distans.

Puccinellia distans, common alkali grass, is found throughout the world and can survive in soils with boron concentrations that are lethal for other plant species. Indeed, P. distans accumulates very high levels of this element. Despite these interesting features, very little research has been performed to elucidate the boron tolerance mechanism in this species. In this study, P. distans samples were treated for three weeks with normal (0.5 mg L-1) and elevated (500 mg L-1) boron levels in hydroponic solution. Expressed sequence tags (ESTs) derived from shoot tissue were analyzed by RNA sequencing to identify genes up and down-regulated under boron stress. In this way, 3312 differentially expressed transcripts were detected, 67.7% of which were up-regulated and 32.3% of which were down-regulated in boron-treated plants. To partially confirm the RNA sequencing results, 32 randomly selected transcripts were analyzed for their expression levels in boron-treated plants. The results agreed with the expected direction of change (up or down-regulation). A total of 1652 transcripts had homologs in A. thaliana and/or O. sativa and mapped to 1107 different proteins. Functional annotation of these proteins indicated that the boron tolerance and hyperaccumulation mechanisms of P. distans involve many transcriptomic changes including: alterations in the malate pathway, changes in cell wall components that may allow sequestration of excess boron without toxic effects, and increased expression of at least one putative boron transporter and two putative aquaporins. Elucidation of the boron accumulation mechanism is important in developing approaches for bioremediation of boron contaminated soils.

Gap junction expression and the effects of gap junction inhibitors in overactive bladder models: does ovariectomy have a role?

PURPOSE: In this study, gap junction expression and the effects of estrogen deficiency and gap junction inhibitors were investigated in overactive bladder models which were created by bladder outlet obstruction. METHODS: In our study, we created four groups as control, ovariectomy, bladder outlet obstruction (BOO), and ovariectomy + BOO. We investigated the effects of oxybutynin and 18-alpha glycyrrhetinic acid (18-α-GA) which is a gap junction blocker on isolated detrusor strips. Western blot method was used to measure the level of connexin-43 in detrusor. RESULTS: Bladder weights were significantly increased in the BOO and ovariectomy + BOO groups (p < 0.05). There was no statistically significant difference in the maximal contraction responses to carbachol between ovariectomy and control groups. In BOO and ovariectomy + BOO groups, contractile responses were significantly prominent with higher doses of carbachol. Oxybutynin-induced relaxant responses of BOO and ovariectomy + BOO groups were significantly higher than control group (p < 0.05). The relaxation effect of 18-a-GA was more effective in the obstruction groups. Among those two groups, the relaxation observed in BOO group was higher than ovariectomy + BOO group in higher doses of 18-a-GA. Connexin-43 expression was increased in BOO group compared with the control group (p = 0.006). Ovariectomy did not change connexin-43 expression alone; however, when combined with BOO, connexin-43 expression decreased significantly (p = 0.023). CONCLUSIONS: Ovariectomy had no effect on the gap junctions in the bladder and bladder overactivity alone. Therefore, obstruction is the main factor that increases the amount of gap junctions, and gap junction blockers are thus more effective in obstruction. However, ovariectomy was shown to decrease the expression of gap junctions and relaxation effect of gap junction blockers, when combined with BOO.

Callus induction and plant regeneration of the endemic Astragalus nezaketae in Turkey

A callus induction and plant regeneration protocol was developed from leaf and petiole explants of the endemic Astragalus nezaketae. Explants were cultured on Murashige and Skoog medium (MS) supplemented with different plant growth regulators (PGRs) [a-naphthaleneacetic acid (NAA), benzyladenine (BA), 2,4-dichlorophenoxyacetic acid (2,4-D), kinetin (Kin), thidiazuron (TDZ)]. The combinations and concentrations of PGRs were shown significant variations for the frequency of callus formation, appearence of callus and the potential of callus differentiation. NAA x BA have been found highly affective in callusing and plant regeneration. Other PGRs have not resulted in callus differentiation for shoot formation. The highest number of shoots (6/explants) was obtained from leaf explants cultured on MS with 0.5 mg/l NAA and 4 mg/l BA. The regenerated shoots transferred to rooting medium (MS with 0.5 mg/l indole-3-butyric acid) were successfully rooted (100 percent) and showed rapid elongation. Rooted plantlets were acclimatized in pots containing 1:1 mixture of peat and perlite.