RESUMO
Abscisic acid (ABA) is a stress-related plant hormone, which is reported to confer drought tolerance. A key enzyme in ABA biosynthesis is 9-cis-epoxycarotenoid dioxygenase. In this study, changes in morphological, physiological response, HbNCED3, and ABA accumulation of RRIM 623 and PB 5/51 rubber clones were observed at different time points of water deficit conditions (0, 3, 5, 7, and 9 days of withholding water). During water deficit, the relative water content (RWC), photosynthetic rate (Pn), and stomatal conductance (Gs) decreased, whereas the electro leakage (EL) increased. The magnitudes of the changes in these parameters were greater for PB 5/51 than for RRIM 623. Therefore, RRIM 623 was designated as representative of drought-tolerant clone and PB 5/51 as a drought-sensitive clone. The HbNCED3 transcription level of RRIM 623 showed lower expression compared with that of PB 5/51, which corresponded to the accumulation of ABA. RRIM 623 accumulated less ABA than PB 5/51. The ABA in RRIM 623 gradually increased, especially on the 7th day of withholding water, whereas that in PB 5/51 rapidly increased during the early periods of drought conditions. Additionally, the sensitivity of stomatal response to ABA showed that RRIM 623 had a higher sensitivity than PB 5/51. These results demonstrate that the drought-tolerant rubber clone, RRIM 623, was characterized by lower ABA accumulation during drought stress than the drought-sensitive clone, PB 5/51. The drought tolerance mechanism of the RRIM 623 might be associated with stomatal sensitivity to ABA accumulation under drought stress.
RESUMO
BACKGROUND AND OBJECTIVE: Pathogenesis-related (PR) proteins are dramatically accumulated after pathogen infection. Innate defense response through increasing PR-proteins is important for rubber rootstock selection that is tolerant to the white root disease caused by Rigidoporus microporus. This study was aimed to investigate the expression levels of PR-1 and PR-3 genes in tolerant (PB5/51) and susceptible (BPM24 and RRIM600) rubber clones after R. microporus infection. MATERIALS AND METHODS: The mRNA of HbPR-1b and HbPR-3 was isolated and characterized from rubber leaves. Gene expression levels of HbPR-1b and HbPR-3 were compared among three rubber clones (PB5/51, BPM24 and RRIM600) after R. microporus infection at 0, 12, 24, 48, 72 and 96 h using quantitative real-time PCR. The relative transcript abundances between inoculated and control plants were compared using the means of gene expression between time points and by Tukey's HSD test. A probability value (p<0.05) was used to determine the significance of difference between time points. RESULTS: The open reading frame of HbPR-1b is 492 bp with deduced 163 amino acid residues and the phylogenetic analysis showed it shared significant evolutionary history and clustering into group I of PR-protein. Moreover, the partial HbPR-3 was isolated with 390 bp. Gene expression levels of HbPR-1b and HbPR-3 showed marked differences in both transcripts depending on the rubber clones. Two genes demonstrated up-regulation of both tolerance and susceptibility in response to attack by R. microporus. The highest expression levels were found in seedlings of PB5/51 after inoculation. In RRIM600, low expression levels of HbPR-1b and HbPR-3 were initially observed but gradually increased at 24 h post inoculation. The transcription profile of HbPR-1b was stable expression in BPM24. CONCLUSION: The results demonstrated that the level ofHbPR-1b and HbPR-3 transcription can distinguish between tolerant and susceptible clones. The candidate defense genes to the white root disease were observed in PB5/51 seedlings, particularly HbPR-1b.
Assuntos
Clonagem Molecular/métodos , Fungos/patogenicidade , Hevea/genética , Hevea/microbiologia , Doenças das Plantas/genética , Doenças das Plantas/microbiologia , Proteínas de Plantas/genética , Evolução Molecular , Regulação da Expressão Gênica de Plantas , Hevea/crescimento & desenvolvimento , Interações Hospedeiro-Patógeno , Filogenia , Folhas de Planta/genética , Folhas de Planta/microbiologia , RNA Mensageiro/genética , RNA Mensageiro/metabolismo , RNA de Plantas/genética , RNA de Plantas/metabolismo , Plântula/genética , Plântula/microbiologia , Fatores de TempoRESUMO
Thailand is the world leader in the production of latex extracted from the rubber tree (Hevea brasiliensis). However, the most cultivated clone RRIM 600, is highly susceptible to diseases, and there is economic incentive to develop new rubber tree clones. Four rubber tree clones (T2, SK1, NK1 and SK3) that have high latex yield potential from plantations in Southern Thailand were selected for this study. Yield performance, latex biochemical parameters and anatomical characteristics of bark were monitored for two years, using RRIM 600 clones in the same fields as paired controls. The average yields of the clones SK1, NK1 and SK3 were 129.3, 74.2 and 53.9 g per tree per tapping, respectively, surpassing the paired RRIM 600 controls (94.3, 49.9 and 43.9 g per tree per tapping in matching order). There was a difference in girth increment of SK1, SK3 and T2 clones when compared with RRIM 600, whereas the clones SK1 and T2 had higher renewed bark thickness than the paired RRIM 600. The anatomical measurements showed that the diameter of the latex vessels and density of latex vessels mm2 were the highest in clone NK1, which also had the best latex biochemical parameters. This indicates NK1 is superior, and supports its use in Hevea breeding programs to improve latex yield. Our genetic characterization and assessment of the four clones selected used Random Amplified Polymorphic DNA (RAPD) and Simple Sequence Repeats (SSR). Seventeen recommended rubber clones were included as references. The clones SK3 and SK1 were closely related to RRIM 600 with similarity coefficients of 0.891 and 0.809, while NK1 and T2 were closely related to RRIT 250 (0.836) and RRIC 110 (0.864), respectively.
Assuntos
Células Clonais , Hevea/fisiologia , Hevea/genética , Látex , TailândiaRESUMO
Thailand is the world leader in the production of latex extracted from the rubber tree (Hevea brasiliensis). However, the most cultivated clone RRIM 600, is highly susceptible to diseases, and there is economic incentive to develop new rubber tree clones. Four rubber tree clones (T2, SK1, NK1 and SK3) that have high latex yield potential from plantations in Southern Thailand were selected for this study. Yield performance, latex biochemical parameters and anatomical characteristics of bark were monitored for two years, using RRIM 600 clones in the same fields as paired controls. The average yields of the clones SK1, NK1 and SK3 were 129.3, 74.2 and 53.9 g per tree per tapping, respectively, surpassing the paired RRIM 600 controls (94.3, 49.9 and 43.9 g per tree per tapping in matching order). There was a difference in girth increment of SK1, SK3 and T2 clones when compared with RRIM 600, whereas the clones SK1 and T2 had higher renewed bark thickness than the paired RRIM 600. The anatomical measurements showed that the diameter of the latex vessels and density of latex vessels mm2 were the highest in clone NK1, which also had the best latex biochemical parameters. This indicates NK1 is superior, and supports its use in Hevea breeding programs to improve latex yield. Our genetic characterization and assessment of the four clones selected used Random Amplified Polymorphic DNA (RAPD) and Simple Sequence Repeats (SSR). Seventeen recommended rubber clones were included as references. The clones SK3 and SK1 were closely related to RRIM 600 with similarity coefficients of 0.891 and 0.809, while NK1 and T2 were closely related to RRIT 250 (0.836) and RRIC 110 (0.864), respectively.(AU)