In vitro flowering of indica rice (Oryza sativa L. spp. indica)

Nodal explants of rice cultivar Pathumthani 1 (PT1; short-day photoperiod insensitive) were collected, surface-disinfected, and cultured on modified MS medium under in vitro conditions for 90 d. A total of 60% nodal explants generated flowering plantlets (with one inflorescence per cluster). The net photosynthetic rate was greater, and soluble sugars (including glucose, fructose, and sucrose) accumulated to higher levels in the leaves of flowering as compared to non-flowering plants. In contrast, chlorophyll a, chlorophyll b, total chlorophyll, and total carotenoid content were enriched to a greater degree in the leaves of non-flowering as compared to flowering plants. Also, growth performance parameters, including plant height, number of leaves per plant, leaf area, fresh weight, and dry weight of plantlets derived from seedlings were superior to those of plantlets derived from nodal explants. In addition, the protocol proved to successfully induce flowering in KDML 105, a short-day photoperiod-sensitive rice cultivar.     

Photoautotrophic shoot and root development for triploid melon

The aim of this investigation was to establish environmental factors which promote growth and photosynthesis of melon (Cucumis melo L.) shoot buds, in vitro, and determine if photoautotrophic shoots had superior root forming ability in photoautotrophic environments. Buds from the triploid melon clone ‘(L-14×B)×L-14’ were observed for 21 days after transfer from a multiplication MS medium with 3% sucrose and 10 μM benzyladenine (BA) to a shoot development medium with 1 μM BA at three levels of sucrose in the medium (0, 1 and 3%), and light (50, 100 and 150 PPF) and CO₂ (500, 1000 and 1500 ppm) in the culture chamber. More shoot buds were observed with 3% sucrose in the medium. Increased light and CO₂ had a positive interaction with shoot proliferation. Fresh and dry weights were greatest at 3% sucrose, 150 PPF light and 1500 ppm CO₂. Shoot buds grew more slowly in sugar-free medium, but fresh and dry weight still doubled over 21 days of culture. Net photosynthetic rates (NPR) of buds were negative after four days in treatment conditions, but became positive after transfer to fresh, sugar-free medium. Two triploid genotypes of melon were (1) grown in vitro with sugar (photomixotrophic) and without sugar (photoautotrophic), (2) rooted in sugar-free media, both in a laboratory controlled environment chamber (in vitro) and a greenhouse acclimatization unit (ex vitro), and (3) compared for subsequent nursery growth in the greenhouse unit. The genotype ‘(L-14×B)×L-14’ produced more shoots than ‘(L-14×B)×Mainstream’ in both photomixotrophic or photoautotrophic conditions. ‘(L-14×B)×L-14’ rooted as well from either photoautotrophic and photomixotrophic shoots but ‘(L-14×B)×Mainstream’ rooted less frequently from photoautotrophic shoots. Seventy-six percent of the shoots in the laboratory controlled environment chamber were able to root photoautotrophically, whereas 47% of the shoots in the greenhouse acclimatization unit were rooted. Between 77% and 88% of plantlets from all treatment combinations survived transfer to the nursery. After growth in the nursery, the sizes of plants (fresh weight, dry weight, leaf area) were the same for either genotype, from either photoautotrophic or photomixotrophic shoots. Nursery plants that had been rooted in the laboratory controlled environment chamber were larger than those rooted in the acclimatization greenhouse chamber. This revised version was published online in June 2006 with corrections to the Cover Date.     

Effects of CO2 enrichment and supporting materialin vitro on photoautotrophic growth ofEucalyptus plantletsin vitro andex vitro

Summary Eucalyptus camaldulensis shoots were cultured photoautotrophicallyin vitro for 6 wk with four different types of supporting materials (agar matrix, Gelrite matrix, plastic net, or vermiculite) under CO₂-nonenriched or CO₂-enriched conditions. Plantlets from each treatmentin vitro were then grownex vitro in a greenhouse for 4 wk. The growth and net photosynthetic rate of plantletsin vitro, as well as subsequent growth, survival percentage, transpiration rate, and net photosynthetic rate of plantletsex vitro were evaluated. CO₂ enrichment significantly increased growth (total dry weight and number of primary roots) and net photosynthetic rate of plantletsin vitro, as well as the growth and survival percentage of plantletsex vitro regardless of the type of supporting materials. The growthin vitro was greatest in the vermiculite, followed by the plastic net, Gelrite matrix, and agar matrix (in descending order) under either the CO₂-nonenriched or CO₂-enriched conditions. The growth and survival percentage of plantletsex vitro were highest in the vermicultie under the CO₂-enriched condition. The extensive root system producedin vitro was necessary for growth and survival of plantletsex vitro.     

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.     

An efficient procedure for embryogenic callus induction and double haploid plant regeneration through anther culture of Thai aromatic rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L. subsp. <Emphasis Type="Italic">indica</Emphasis>)

Anther culture is a biotechnology technique that can be used for the production of pure lines. The aims of this investigation were to induce embryogenic callus from major and minor culms of Thai aromatic rice cultivars and to subsequently regenerate double-haploid green plantlets by the application of exogenous polyamines. Embryogenic callus derived from anther culture was successfully induced in varieties KDML105, Homjan (HJ), and Pathumthani 1 (PT1). Production of embryogenic callus from anthers collected from the major culms was greater than those collected from the minor culms, especially in cultivar HJ. Plantlet regeneration in the three rice cultivars was observed from embryogenic callus and was highest, at 12.1%, from variety HJ treated with 0.5 mM spermidine. Plantlet regeneration from anther-derived embryogenic callus was dependent on the plant genotype, the types of exogenous polyamines, and the interactions of these factors. The percentage of haploid plantlets regenerated in PT1, KDML105, and HJ were 68.1%, 70.7%, and 78.5%, respectively. Only haploid plantlets were treated with colchicine for double-haploid production. This investigation has increased the knowledge of both embryogenic callus induction and plantlet regeneration in aromatic rice and has lead to the development of a pure, double-haploid line for the use in rice breeding programs in Thailand.     

Sugar accumulation,photosynthesis and growth of two indica rice varieties in response to salt stress

Sugar, a final product of photosynthesis, is reported to be involved in the defense mechanisms of plants against abiotic stresses such as salinity, water deficiency, extreme temperature and mineral toxicity. Elements involved in photosynthesis, sugar content, water oxidation, net photosynthetic rate, activity of enzyme and gene expression have therefore been studied in Homjan (HJ), salt-tolerant, and Pathumthani 1 (PT1), salt-sensitive, varieties of rice. Fructose-1,6-biphosphatase (FBP) and fructokinase (FK) genes were rapidly expressed in HJ rice when exposed to salt stress for 1–6 h and to a greater degree than in PT1 rice. An increase in FBP enzyme activity was found in both roots and leaves of the salt-tolerant variety after exposure to salt stress. A high level of sugar and a delay in chlorophyll degradation were found in salt-tolerant rice. The total sugar content in leaf and root tissues of salt-tolerant rice was 2.47 and 2.85 times higher, respectively, than in the salt-sensitive variety. Meanwhile, less chlorophyll degradation was detected. Salt stress may promote sugar accumulation, thus preventing the degradation of chlorophyll. Water oxidation by the light reaction of photosynthesis in the salt-tolerant variety was greater than that in the salt-sensitive variety, indicated by a high maximum quantum yield of PSII (F _v/F _m) and quantum efficiency of PSII (Φ_PSII) with low nonphotochemical quenching (NPQ), leading to a high net photosynthetic rate. In addition, the overall growth performances in the salt-tolerant variety were higher than those in the salt-sensitive variety. The FBP gene expression and enzyme activity, sugar accumulation, pigment stabilization, water oxidation and net photosynthetic rate parameters in HJ rice should be further investigated as multivariate salt-tolerant indices for the classification of salt tolerance in rice breeding programs.     

Screening sugarcane (Saccharum sp.) genotypes for salt tolerance using multivariate cluster analysis

Disease-free sugarcane plantlets of 11 cultivars derived from meristem cuttings were photoautotrophically grown on the MS medium and subsequently exposed to 0 (control) or 200?mM NaCl (salt stress) for 14?days. Sodium ion (Na⁺) in all sugarcane varieties was enriched when plantlets were subjected to 200?mM NaCl, except K88-1. Chlorophyll a (Chl_a), chlorophyll b (Chl_b) and total carotenoids (C_x+c), in the salt stressed leaves of all genotypes decreased significantly, but the extent of decrease was variable among different genotypes. In contrast, proline content in salt stressed plantlets of all sugarcane genotypes increased markedly, except in genotypes K95, K92-2 and LK92-4. Maximum quantum yield of PSII (F_v/F_m), photon yield of PSII (??_PSII), quantum efficiency of PSII (qP) and net photosynthetic rate (P_n) in salt stressed plantlets of all genotypes were significantly dropped, whereas ??_PSII and qP in cv. KK88-1 were alleviated, resulting in improved P_n. Moreover, growth parameters including shoot height, root length, fresh weight, dry weight and leaf area in salt stressed plantlets of all genotypes were significantly inhibited. The Na⁺ accumulation, pigment degradation, proline accumulation, photosynthetic abilities and growth inhibition in saline regimes were subjected to Hierarchical cluster analysis. Salt tolerant, K88-1 and UT94-7 and salt susceptible, K92-2 and LK92-4 classes of sugarcane genotypes were classified. The salt tolerant cultivars may be further studied including yield, sugar content and ratoon recovery rate in saline field trials.