Chalermpol Kirdmanee

Comparative Effects of Salt Stress and Extreme pH Stress Combined on Glycinebetaine Accumulation, Photosynthetic Abilities and Growth Characters of Two Rice Genotypes

Glycinebetaine (Glybet) accumulation, photosynthetic efficiency and growth performance in indica rice cultivated under salt stress and extreme pH stress were investigated. Betaine aldehyde dehydrogenase (BADH) activity and Glybet accumulation in the seedlings of salt-tolerant and salt-sensitive rice varieties grown under saline and acidic conditions peaked after treatment for 72 h and 96 h, respectively, and were higher than those grown under neutral pH and alkaline salt stress. A positive correlation was found between BADH activity and Glybet content in both salt-tolerant (r^2=0.71) and salt-sensitive (r^2=0.86) genotypes. The chlorophyll a, chlorophyll b, total chlorophyll and total carotenoids contents in the stressed seedlings significantly decreased under both acidic and alkaline stresses, especially in the salt-sensitive genotype. Similarly, the maximum quantum yield of PSII (F√F(subscript m)), photon yield of PSII (Ф(subscript PSII)), non-photochemical quenching (NPQ) and net photosynthetic rate (P(subscript n)) in the stressed seedlings were inhibited, leading to overall growth reduction. The positive correlations between chlorophyll a content and F√F(subscript m), total chlorophyll content and Ф(subscript PSII), Ф(subscript PSII) and P(subscript n) as well as P(subscript n) and leaf area in both salt-tolerant and salt-sensitive genotypes were found. Saline acidic and saline alkaline soils may play a key role affecting vegetative growth prior to the reproductive stage in rice plants.

Remediation of salt-affected soil by the addition of organic matter: an investigation into improving glutinous rice productivity

Soil salinity may limit plant growth and development, and cause yield loss in crop species. This study aimed at remediating saline soil using organic matter (OM) treatment, before the cultivation of RD6 rice (Oryza sativa L. spp. indica). Physiological and morphological characters of rice plants, as well as crop yield, were evaluated from salt-affected soil with varying levels of salinity. The chlorophyll a and total chlorophyll pigments of rice plants grown in salt-affected soil (2% salt level) with the application of OM were maintained better than in plants grown without OM treatment. The degree of reduced photosynthetic pigments in rice plants was dependent on the level of salt contamination. Pigment content was positively related to maximum quantum yield of PSII (Fv/Fm) and quantum efficiency of PSII (ΦPSII), leading to reduced net photosynthetic rate (Pn) and reduced total grain weight (TGW). Photosynthetic abilities, including chlorophyll a and total chlorophyll pigments and ΦPSII, in rice plants grown with OM treatment were greater than in those cultivated in soil without the OM treatment, especially in high salt levels (1-2% salt). The remediation of salt-affected soil in paddy fields using OM should be applied further, as an effective way of enhancing food crop productivity.

Expression and functional analysis of putative vacuolar Ca2+-transporters (CAXs and ACAs) in roots of salt tolerant and sensitive rice cultivars

Vacuolar Ca2+-transporters could play an important role for salt tolerance in rice (Oryza sativa L.) root. Here, we compared the expression profiles of putative vacuolar cation/H+ exchanger (CAX) and calmodulin-regulated autoinhibited Ca2+-ATPase (ACA) in rice roots of salt tolerant cv. Pokkali and salt sensitive cv. IR29. In addition to five putative vacuolar CAX genes in the rice genome, a new CAX gene (OsCAX4) has been annotated. In the present study, we isolated the OsCAX4 gene and showed that its encoded protein possesses a unique transmembrane structure and is potentially involved in transporting not only Ca2+ but also Mn2+ and Cu2+. These six OsCAX genes differed in their mRNA expression pattern in roots of tolerant versus sensitive rice cultivars exposed to salt stress. For example, OsCAX4 showed abundant expression in IR29 (sensitive) upon prolonged salt stress. The mRNA expression profile of four putative vacuolar Ca2+-ATPases (OsACA4-7) was also examined. Under control conditions, the mRNA levels of OsACA4, OsACA5, and OsACA7 were relatively high and similar among IR29 and Pokkali. Upon salt stress, only OsACA4 showed first a decrease in its expression in Pokkali (tolerant), followed by a significant increase. Based on these results, a role of vacuolar Ca2+ transporter for salt tolerance in rice root was discussed.

Environmental Engineering for Transplant Production

Environmental engineering provides several tools and techniques needed to alter the environmental management in vitro. Development and application of methods in vitro for plant micropropagation, selection and improvement are encouraging. In past two decades, most of researchers focused on chemical environmental factors rather than physical environmental factors in order to promote the plantlet growth and to exhibit their hereditary characteristics. In this decade, the researches on physical environment under photoautotrophic condition (without an artificially supplied carbon source) have been extensively conducted. A system for photoautotrophic culture has been developed for various species and utilized to decrease the production cost. The photoautotrophic growth is utilized for in vitro plant micropropagation, selection, and improvement. The various applications of environmental engineering under photoautotrophic condition Refslect the thrust and confidence in using such tools to improve transplant production.

Physio-Biochemical Responses of Oil Palm (Elaeis guineensis Jacq.) Seedlings to Mannitol- and Polyethylene Glycol-Induced Iso-Osmotic Stresses

References The aim of this investigation was to comparatively examine the physio-biochemical responses of oil palm seedlings to mannitol- and PEG-induced iso-osmotic stresses. The water content of osmotically stressed oil palm seedlings decreased, but the proline content and the electrolyte leakage of the seedlings increased with decreasing water potential (Ψw). However, the responses varied with the strength of osmotic stress and type of osmotic agent. Relative electrolyte leakage (REL) was negatively correlated to chlorophyll content in the osmotically stressed leaves. Chlorophyll a (Chla), chlorophyll b (Chlb), total carotenoids (Cx+c) and total chlorophyll (TC) in the seedlings were significantly reduced by osmotic stress, subsequently reducing maximum quantum yield of PSII (Fv/Fm) and photon yield of PSII (Φpsii), thereby lowering net-photosynthetic rate (Pn) and inhibiting growth. Physio-biochemical parameters, including REL, Fv/Fm, and Φpsii in oil palm seedlings were reduced more greatly by PEG-induced osmotic stress than by mannitol-induced stress. A deterioration in morphological characters, including leaf chlorosis, leaf burn, and green leaf area reduction were demonstrated in oil palm seedlings under osmotic stress induced by either mannitol or PEG. However, the toxic symptoms in oil palm seedlings under PEG-induced stress were severer than in those under mannitol-induced iso-osmotic stress, especially under severe osmotic stress.

Physio-biochemical and morphological characters of halophyte legume shrub, Acacia ampliceps seedlings in response to salt stress under greenhouse

Acacia ampliceps (salt wattle), a leguminous shrub, has been introduced in salt-affected areas in the northeast of Thailand for the remediation of saline soils. However, the defense mechanisms underlying salt tolerance A. ampliceps are unknown. We investigated various physio-biochemical and morphological attributes of A. ampliceps in response to varying levels of salt treatment (200–600 mM NaCl). Seedlings of A. ampliceps (25 ± 2 cm in plant height) raised from seeds were treated with 200 mM (mild stress), 400 and 600 mM (extreme stress) of salt treatment (NaCl) under greenhouse conditions. Na+ and Ca2+ contents in the leaf tissues increased significantly under salt treatment, whereas K+ content declined in salt-stressed plants. Free proline and soluble sugar contents in plants grown under extreme salt stress (600 mM NaCl) for 9 days significantly increased by 28.7 (53.33 μmol g–1 FW) and 3.2 (42.11 mg g–1 DW) folds, respectively over the control, thereby playing a major role as osmotic adjustment. Na+ enrichment in the phyllode tissues of salt-stressed seedlings positively related to total chlorophyll (TC) degradation (R2 = 0.72). Photosynthetic pigments and chlorophyll fluorescence in salt-stressed plants increased under mild salt stress (200 mM NaCl). However, these declined under high levels of salinity (400–600 mM NaCl), consequently resulting in a reduced net photosynthetic rate (R2 = 0.81) and plant dry weight (R2 = 0.91). The study concludes that A. ampliceps has an osmotic adjustment and Na+ compartmentation as effective salt defense mechanisms, and thus it could be an excellent species to grow in salt-affected soils.

EXOGENOUS APPLICATION OF POTASSIUM NITRATE TO ALLEVIATE SALT STRESS IN RICE SEEDLINGS

□ Overall growth characteristics of many plant species cultivated in soil affected by salinity could be alleviated by the application of potassium nitrate (KNO3) to the soil. The aim of this research was to investigate salt-tolerance in a salt-sensitive rice cultivar, ‘Pathumthani 1’ (PT1), in response to the exogenous application of 11.8 mM KNO3, in comparison to ‘Homjan’ (HJ), a salt tolerant cultivar. Water potential (ψw) in both the roots and leaves of PT1 seedlings under salt stress dropped significantly, while it was maintained in PT1 pretreated with KNO3, and similarly in HJ. The reduction of leaf water potential was positively related to total chlorophyll degradation, leading to diminished chlorophyll fluorescence, directly affecting growth in plants exposed to salt stress. In salt-sensitive PT1, the application of 11.8 mM KNO3 improved salt-tolerance via the conservation of water use efficiency, the maintenance of photosynthetic pigments, enhancement of chlorophyll a fluorescence, and stimulation of growth characters.

Isolation and characterization of proline/betaine transporter gene from oil palm

Oil production from oil palm is adversely affected by drought and salt. Under drought and salt stress, proline content increases in oil palm; the mechanism for this is unknown. Here, an 8319-nucleotide sequence including cDNA, genomic DNA and the promoter region of proline transporter gene from oil palm Elaeis guineensis was determined. The transporter gene exhibited high similarity to Bet/ProT genes from several plants, but the highest homology was found with rice ProT1. The exon-intron structure of genomic DNA was unique, and numerous stress-response cis-elements were found in the promoter region. Expression of cDNA EgProT1 in Escherichia coli mutant exhibited uptake activities for glycinebetaine and choline as well as proline. Under salt-stressed conditions, exogenously applied glycinebetaine was taken up into the root more rapidly than the control. These data indicate that oil palm has a unique Pro/T1 gene. Nucleotide sequence data for the cDNA and genomic DNA of proline transporter gene from Elaeis guineensis are available in the DDJB database under accession numbers AB597035 and AB597036, respectively.

Adjustment of medium composition and iso-osmotic potential in direct-shoot organogenesis produces true-to-type oil palm (Elaeis guineensis Jacq.) plantlets

Clonally propagating elite lines of oil palm via multiple shoot organogenesis is promising due to genetic stability of regenerants. In this study, we tested the effects of medium composition using three basal media types (Murashige and Skoog (MS), woody plant medium (WPM), and Y3) with concentrations of sucrose and different ionic strengths derived from sucrose, sorbitol, or both sucrose and sorbitol on the growth and development of oil palm plantlets derived from direct-shoot organogenesis and zygotic embryo-derived seedlings (control). We used histological assays to better understand the medium formulation’s efficiency for shoot organogenesis. The shoot induction percentage was the highest when plantlets were cultured on ½ MS medium supplemented with 5% sucrose. A minimum osmotic potential of -2.0 MPa is essential to efficiently drive shoot maturation of oil palm. Sorbitol appeared to be less effective than sucrose for shoot formation of oil palms. To determine the rate of somoclonal changes between these two micropropagation methods, we investigated the rate of DNA methylation in oil palm plantlets using the methylation-sensitive amplification polymorphism (MSAP) technique. Our MSAP results showed that polymorphisms between in vitro seedling-derived plantlets and direct-shoot organogenesis-derived plantlets were considerably low. We conclude that regenerated plantlets derived from this established protocol are reliable for trueto- type propagation of elite oil palm clones.