Effect of salinity stress on growth and carbohydrate metabolism in three rice (<i>Oryza sativa </i>L.) cultivars differing in salinity tolerance

736-742 Rice seedlings cv. Khao Dawk Mali 105 (salt-sensitive), Luang Anan (moderately salt-tolerant) and Pokkali (salt-tolerant) were exposed to 0, 50, 100 and 150 mM NaCl for 9 d. Salinity stress caused reduction in leaf relative water contents in all cultivars. Shoot length of cv. Pokkali was least affected by salinity stress whereas increased root length in response to salinity stress was apparent in cvs. Khao Dawk Mali 105 and Luang Anan. Increased salinity level also caused reduction in fresh and dry weights in cvs. Khao Dawk Mali 105 and Luang Anan, but had no effect in cv. Pokkali except at 150 mM. Accumulation of total soluble sugars and sucrose in mature leaves were observed in cv. Khao Dawk Mali 105 exposed to high level of salinity whereas their concentrations in cvs. Luang Anan and Pokkali remained the same as control plants. Accumulation of sucrose in cv. Khao Dawk Mali 105 was suggested to be resulted from the alteration of photosynthate partitioning since the activities of sucrose phosphate synthase were not affected by salinity in this cultivar. On the contrary, salinity stress induced an accumulation of starch in cv. Pokkali. It is suggested that partitioning sugars into starch may involve in salinity tolerance by avoiding metabolic alterations. </smarttagtype

How rice Glycogen Synthase Kinase-like 5 (OsGSK5) integrates salinity stress response to source-sink adaptation: A proposed model.

We have previously shown that overexpression of GSK3-like kinase 5 in rice (OsGSK5) was associated with higher starch accumulation and better growth under severe salinity stress. Short-term 14CO2 feeding experiments suggested that OsGSK5 promoted higher flux to starch accumulation in the roots under this condition and that this mechanism may help to underscore the better growth characteristics observed. Here, we expand upon this hypothesis and consider (1) how OsGSK5 action could fit into a signaling model that integrates salinity stress to changes in starch metabolism, and (2) how this would facilitate whole plant physiological adaptations in source-to-sink partitioning. We also discuss additional functions of OsGSK5, necessary to support this adaptive mechanism

Yield, Grain Quality, and Starch Physicochemical Properties of 2 Elite Thai Rice Cultivars Grown under Varying Production Systems and Soil Characteristics

Rice production systems and soil characteristics play a crucial role in determining its yield and grain quality. Two elite Thai rice cultivars, namely, KDML105 and RD6, were cultivated in two production systems with distinct soil characteristics, including net-house pot production and open-field production. Under open-field system, KDML105 and RD6 had greater panicle number, total grain weight, 100-grain weight, grain size, and dimension than those grown in the net-house. The amounts of reducing sugar and long amylopectin branch chains (DP 25&ndash;36) of the RD6 grains along with the amounts of long branch chains (DP 25&ndash;36 and DP &ge; 37), C-type starch granules, and average chain length of the KDML105 were substantially enhanced by the open-field cultivation. Contrastingly, the relative crystallinity of RD6 starch and the amounts of short branch chains (DP 6&ndash;12 and DP 13&ndash;24), B- and A-type granules, and median granule size of KDML105 starch were significantly suppressed. Consequently, the open-field-grown RD6 starch displayed significant changes in its gelatinization and retrogradation properties, whereas, certain retrogradation parameters and peak viscosity (PV) of KDML105 starches were differentially affected by the distinct cultivating conditions. This study demonstrated the influences of production systems and soil characteristics on the physicochemical properties of rice starches

Overexpression of GSK3-like Kinase 5 (OsGSK5) in rice (Oryza sativa) enhances salinity tolerance in part via preferential carbon allocation to root starch

Rice (Oryza sativa L.) is very sensitive to soil salinity. To identify endogenous mechanisms that may help rice to better survive salt stress, we studied a rice GSK3-like isoform (OsGSK5), an orthologue of a Medicago GSK3 previously shown to enhance salinity tolerance in Arabidopsis by altering carbohydrate metabolism. We wanted to determine whether OsGSK5 functions similarly in rice. OsGSK5 was cloned and sequence, expression, evolutionary and functional analyses were conducted. OsGSK5 was expressed highest in rice seedling roots and was both salt and sugar starvation inducible in this tissue. A short-term salt-shock (150mM) activated OsGSK5, whereas moderate (50mM) salinity over the same period repressed the transcript. OsGSK5 response to salinity was due to an ionic effect since it was unaffected by polyethylene glycol. We engineered a rice line with 3.5-fold higher OsGSK5 transcript, which better tolerated cultivation on saline soils (EC=8 and 10dSm-2). This line produced more panicles and leaves, and a higher shoot biomass under high salt stress than the control genotypes. Whole-plant 14C-tracing and correlative analysis of OsGSK5 transcript with eco-physiological assessments pointed to the accelerated allocation of carbon to the root and its deposition as starch, as part of the tolerance mechanism

Chemical composition, structural features, and physicochemical properties of starches from Thai indigenous rice varieties

ABSTRACTThai indigenous rice varieties provide valuable genetic resources due to their environmental resilience, but it is yet to be elucidated whether their endosperm starches are suitable for whole grain consumption or industrial applications. Here, 19 Thai indigenous rice starches were explored for compositional, structural, and physicochemical characteristics. Grain reducing sugar, protein, and amylose contents significantly differed among genotypes. Their starches were categorized as waxy, very low-, and low-amylose starches. The varieties with low-amylose starches displayed higher amylose content but lower crystallinity than the varieties with waxy and very low-amylose starches. The largest median starch granule size (d(0.5)) was also observed in most varieties with low-amylose starches. The starch compositional and structural variations contributed to substantial differences in starch physicochemical properties among these genotypes. The partial least squares discriminant analysis revealed that amylose content, setback, swelling power, reducing sugar, C- and A-type granules, d(0.5), and final viscosity could discriminate the low-amylose starches from the waxy and very low-amylose starches. Notably, correlation analyses revealed that amylose content was the most crucial factor determining starch physicochemical properties of these varieties. Starch compositional, structural, and physicochemical variations among the indigenous rice varieties can be adopted as alternative industrial raw materials and as genetic resources for future breeding programs

Ectopic Expression of Arabidopsis thaliana zDof1.3 in Tomato (Solanum lycopersicum L.) Is Associated with Improved Greenhouse Productivity and Enhanced Carbon and Nitrogen Use.

A large collection of transgenic tomato lines, each ectopically expressing a different Arabidopsis thaliana transcription factor, was screened for variants with alterations in leaf starch. Such lines may be affected in carbon partitioning, and in allocation to the sinks. We focused on 'L4080', which harbored an A. thaliana zDof (DNA-binding one zinc finger) isoform 1.3 (AtzDof1.3) gene, and which had a 2-4-fold higher starch-to-sucrose ratio in source leaves over the diel (p &lt; 0.05). Our aim was to determine whether there were associated effects on productivity. L4080 plants were altered in nitrogen (N) and carbon (C) metabolism. The N-to-C ratio was higher in six-week-old L4080, and when treated with 1/10 N, L4080 growth was less inhibited compared to the wild-type and this was accompanied by faster root elongation (p &lt; 0.05). The six-week-old L4080 acquired 42% more dry matter at 720 ppm CO2, compared to ambient CO2 (p &lt; 0.05), while the wild-type (WT) remained unchanged. GC-MS-TOF data showed that L4080 source leaves were enriched in amino acids compared to the WT, and at 49 DPA, fruit had 25% greater mass, higher sucrose, and increased yield (25%; p &lt; 0.05) compared to the WT. An Affymetrix cDNA array analysis suggested that only 0.39% of the 9000 cDNAs were altered by 1.5-fold (p &lt; 0.01) in L4080 source leaves. 14C-labeling of fruit disks identified potential differences in 14-DPA fruit metabolism suggesting that post-transcriptional regulation was important. We conclude that AtzDof1.3 and the germplasm derived therefrom, should be investigated for their 'climate-change adaptive' potential