The role of aquaporin RWC3 in drought avoidance in rice

Although the discovery of aquaporins in plants has resulted in a paradigm shift in the understanding of plant water relations, the relationship between aquaporins and drought resistance still remains elusive. From an agronomic viewpoint, upland rice is traditionally considered as showing drought avoidance. In the investigation of different morphological and physiological responses of upland rice (Oryza sativa L. spp indica cv. Zhonghan 3) and lowland rice (O. sativa L. spp japonica cv. Xiushui 63) to water deficit, we observed young leaf rolling and the remarkable decline of cumulative transpiration in the upland rice. The expression of water channel protein RWC3 mRNA was increased in upland rice at the early response (up to 4 h) to the 20% polyethylene glycol (PEG) 6000 treatment, whereas there was no significant expression changes in lowland rice. Protein levels were increased in upland rice and decreased in lowland rice at 10 h after the water deficit. The up-regulation of RWC3 in upland rice fits well with the knowledge that upland rice adopts the mechanism of drought avoidance. The physiological significance of this RWC3 up-regulation was then explored with the over-expression of RWC3 in transgenic lowland rice (O. sativa L. spp japonica cv. Zhonghua 11) controlled by a stress-inducible SWPA2 promoter. Compared to the wild-type plant, the transgenic lowland rice exhibited higher root osmotic hydraulic conductivity (Lp), leaf water potential and relative cumulative transpiration at the end of 10 h PEG treatment. These results indicated that RWC3 probably played a role in drought avoidance in rice.     

Divergent selection as revealed by P(ST) and QTL-based F(ST) in three-spined stickleback (Gasterosteus aculeatus) populations along a coastal-inland gradient

Three measures of divergence, estimated at nine putatively neutral microsatellite markers, 14 quantitative traits, and seven quantitative trait loci (QTL) were compared in eight populations of the three-spined stickleback (Gasterosteus aculeatus L.) living in the Scheldt river basin (Belgium). Lowland estuarine and polder populations were polymorphic for the number of lateral plates, whereas upland freshwater populations were low-plated. The number of short gill rakers and the length of dorsal and pelvic spines gradually declined along a coastal-inland gradient. Plate number, short gill rakers and spine length showed moderate to strong signals of divergent selection between lowland and upland populations in comparison between P(ST) (a phenotypic alternative for Q(ST)) and neutral F(ST). However, such comparisons rely on the unrealistic assumption that phenotypic variance equals additive genetic variance, and that nonadditive genetic effects and environmental effects can be minimized. In order to verify this assumption and to confirm the phenotypic signals of divergence, we tested for divergent selection at the underlying QTL. For plate number, strong genetic evidence for divergent selection between lowland and upland populations was obtained based on an intron marker of the Eda gene, of which the genotype was highly congruent with plate morph. Genetic evidence for divergent selection on short gill rakers was limited to some population pairs where F(ST) at only one of two QTL was detected as an outlier, although F(ST) at both loci correlated significantly with P(ST). No genetic confirmation was obtained for divergent selection on dorsal spine length, as no outlier F(ST)s were detected at dorsal spine QTL, and no significant correlations with P(ST) were observed.     

The populations, characterization and activity of suspended bacteria in the Welsh River Dee

In a 29 month study of bacterial populations at three sites on the Welsh River Dee, the aerobic heterotrophic bacteria increased from an average basal level of about 1.2 times 10⁴ colony-forming units (cfu)/ml near the source of the river, to 2 times 10⁵ cfu/ml in the lower reaches. The ratio, total bacterial cell count: viable count, decreased from 70 in the upland reaches to 10 in the lower parts of the river. There was no apparent seasonal variation in bacterial numbers but on occasions the bacterial populations in both upland and lowland reaches of the river increased simultaneously. Fluctuations in bacterial numbers over a 50-fold range were observed in this study. Bacterial isolates from both upland and lowland sites were predominated by two groupings of bacteria, the Pseudomonas—Agrobacterium—Alcaligenes group and the Flavobacterium—Cytophaga—Flexibacter group. Results suggested that the latter group may have been part of the autochthonous population. Seasonal variation in heterotrophic potential ( V _max) for acetate uptake was shown to occur over a 30-fold range in the lowland reaches of the River Dee. Peaks in activity at the lowland site occurred during the summer months, the range of V _max values for acetate ranged from 0.2 to 30 μg/1/h. Fluctuations in V _max values from the upland site were not seasonal but were instead linked to faecal pollution, V _max values from this site range from 0.04 to 3 μg/1/h.     

Annual cycle in female Three-spined sticklebacks (Gasterosteus aculeatus L.) from an upland and lowland population

The annual cycles in female Three-spined sticklebacks from an upland (275 m) and a lowland (25 m) population were compared. The average length and weight of the lowland females were greater, but in both populations growth was checked in winter and again in the breeding season. Both populations also showed a winter decline in condition followed by a sharp increase in spring associated with the maturation of the ovaries. The hepato-somatic index of the females also increased during the spring, but the dry matter content of the liver declined during the spring and early summer. Lowland females had larger livers than the upland fish. In both populations average gonadosomatic index increased steadily throughout the winter, then abruptly in spring. The lowland population bred from May to early August, but the upland population bred only in May.
The energy content of the carcases of females was lowest in winter and again during the breeding season whereas the ash content showed maxima at these two periods. Lipid and glycogen analyses of the carcase, liver and ovaries also suggested that winter and the breeding season were periods of depletion from the carcase and liver, but not from the ovaries.
The observations indicate that the ovaries are to some extent insulated from fluctuations in resource availability. This supports experimental studies which indicate that egg production in the female stickleback can be subsidised by depletion from the carcase and liver when necessary.     

水、旱条件下稻米蒸煮和营养品质性状与土壤水分环境互作分析及其QTL定位

以旱稻品种IRAT109与水稻品种越富杂交构建的DH群体的116个株系及其亲本为材料,在水、旱2种栽培条件下种植,研究了稻米蒸煮和营养品质性状的变化规律,在水、旱2个土壤水分环境下对直链淀粉含量(AC)、胶稠度(GC)、碱消值(GT)和蛋白质含量(PC)4个蒸煮和营养品质性状进行QTL定位及QTLs与环境互作分析。结果表明,以上4个品质性状在水、旱2种不同栽培条件下差异较大,说明这些性状受水分条件影响较大,旱栽条件下稻米蒸煮和营养各品质性状均有不同程度的升高,其中蛋白质含量平均提高37.9%。QTL分析结果表明,4个稻米品质性状在2个环境中的表现型值都为连续分布,均存在超亲遗传类型,共检测到7个加性效应QTL与稻米蒸煮和营养品质性状4项指标有关,分别位于第1、2、3、6、8、11染色体上,单个QTLs对性状的贡献率在1.91%～19.77%之间。位于第3染色体上控制碱消值的QGt3,第6染色体上控制直链淀粉含量的QAc6,在2个不同土壤水分条件下均与环境存在显著互作,对环境互作的贡献率分别为8.99%和47.86%。控制直链淀粉含量的2对上位性QTLs与土壤水分环境显著互作,贡献率较大,分别为32.54%和11.82%。并筛选到5个主效QTL(QGt6b、QGt8、QGt11、QGc1和QPc2)在抗旱育种中可用于蒸煮和营养各品质性状MAS改良。     

The reproductive biology of Common frog (Rana temporaria) populations from different altitudes in northern England

The study investigated the ecophysiological differences between populations of the Common frog( Rana temporaria L.) from different altitudes in northern England. Frog embryos in upland northern ponds experience very low temperatures during the period of embryonic development. These embryos were found to have a lower lethal limit for 50% normal development of2–8 °C, compared with3–8 °C for lowland embryos. These values are below most of the lower limiting temperature estimates previously obtained for R. temporaria . Embryos from upland ponds developed faster at low temperatures than embryos from lowland ponds. This may be an adaptation to the shorter growing season and lower temperatures at higher altitudes. Upland female frogs were found to be shorter and produced fewer eggs than lowland females. The differences found between lowland and upland frogs are discussed in terms of their potential adaptive significance.     

Structure and Spatial‐Temporal Dynamics of Chironomidae Fauna (Diptera) in Upland and Lowland Fluvial Habitats of the Chocancharava River Basin (Argentina)

Structure of benthic Chironomidae assemblages and their spatial‐temporal dynamic were analyzed in upland and lowland habitats from the Chocancharava River basin (Córdoba, Argentina). Sampling was performed in three tributary streams and in three lowland reaches of the river during high and low rainfall periods. Characteristic taxa of upland and lowland reaches and of the different habitats in these reaches were identified using the IndVal method. Chironomidae assemblages were different between upland and lowland reaches and among habitats in each reach, as assessed by Multiresponse Permutation Procedure and Canonical Correspondence Analyses. Substrate type and current velocity were the major explanatory variables structuring the assemblages in upland reaches whereas in lowland reaches current velocity and aquatic vegetation were the most important variables. The highest richness was found in the most complex habitat units in both upland and lowland stretches as assessed by Analyses of Variance. Chironomidae larvae responded to longitudinal changes of hydraulic variables and to local variations of fluvial habitats at different reaches. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Comparison of growth and performance in upland and lowland switchgrass types to water and nitrogen stress

The objective of the study was to examine lowland (Alamo and Kanlow) and upland (Blackwell and Caddo) cultivars of switchgrass (Panicum virgatum L.) for differences in response to water deficit and nitrogen fertilizer. Cultivars were grown in pots with fritted clay at two water levels: well watered and deficit conditions (-0.1 and -1.0 MPa) and two nitrogen levels (10 and 100 kg ha(-1)). Nitrogen determined growth potential of the cultivars more than water availability. The lowland cultivars produced greater biomass yields than upland cultivars. However, upland cultivars showed a smaller response to drought stress. Under water stress conditions all cultivars exhibited a higher leaf percentage of total dry matter (DM), with the upland cultivars having the highest leaf percentage of total DM. Nitrogen proved to have more of an effect on single-leaf photosynthesis rates than water. Alamo demonstrated the greatest biomass production among all cultivars. The differences found between the two lowland cultivars suggest that Alamo would be better suited for forage and biomass production in central Texas, being a higher producer under drought and non-drought conditions than Kanlow as well as upland cultivars.     

Upland rice and lowland rice exhibited different PIP expression under water deficit and ABA treatment

Aquaporins play a significant role in plant water relations. To further understand the aquaporin function in plants under water stress, the expression of a subgroup of aquaporins, plasma membrane intrinsic proteins （PIPs）, was studied at both the protein and mRNA level in upland rice （Oryza sativa L. cv. Zhonghan 3） and lowland rice （Oryza sativa L. cv. Xiushui 63） when they were water stressed by treatment with 20% polyethylene glycol （PEG）. Plants responded differently to 20% PEG treatment. Leaf water content of upland rice leaves was reduced rapidly. PIP protein level increased markedly in roots of both types, but only in leaves of upland rice after 10 h of PEG treatment. At the mRNA level, OsPIP1,2, OsPIP1,3, OsPIP2;1 and OsPIP2;5 in roots as well as OsPIP1,2 and OsPIP1;3 in leaves were significantly up-regulated in upland rice, whereas the corresponding genes remained unchanged or down-regulated in lowland rice. Meanwhile, we observed a significant increase in the endogenous abscisic acid （ABA） level in upland rice but not in lowland rice under water deficit. Treatment with 60 μM ABA enhanced the expression of OsPIP1;2, OsPIP2;5 and OsPIP2;6 in roots and OsPIP1;2, OsPIP2;4 and OsPIP2;6 in leaves of upland rice. The responsiveness of PIP genes to water stress and ABA were different, implying that the regulation of PIP genes involves both ABA-dependent and ABA-independent signaling oathways during water deficit.     

Adaptations of skin peptide defences and possible response to the amphibian chytrid fungus in populations of Australian green‐eyed treefrogs,Litoria genimaculata

Aim Rapidly evolving pathogens may exert diversifying selection on genes involved in host immune defence including those encoding antimicrobial peptides (AMPs). Amphibian skin peptides are one important defence against chytridiomycosis, an emerging infectious disease caused by the chytrid fungus Batrachochytrium dendrobatidis (Bd). We examined the population‐level variation in this innate immune defence to understand its relationship with disease dynamics. Location Queensland, Australia. Methods We examined skin peptide defences in five geographically distinct populations of Australian green‐eyed treefrogs, Litoria genimaculata. Skin peptide samples were collected from 52 frogs from three upland populations that previously declined as chytridiomycosis emerged, but subsequently recovered, and from 34 frogs in two lowland populations that did not decline. Historical samples of skin peptides preceding Bd emergence were not available from any population. Results In general, lowland populations had more effective peptide defences than upland populations. Peptide profiles were similar among populations, although relative amounts of peptides expressed differed significantly among populations and were more variable in the uplands. Infected frogs in upland populations carried a significantly higher infection burden compared to lowland populations. The presence of effective AMPs in the skin of L. genimaculata does not eliminate infection; however, more effective peptide defences may limit infection intensity and the progression of disease. Main conclusions The population bottleneck in upland populations caused by chytridiomycosis emergence did not appear to produce responses to selection for more effective peptide defences against chytridiomycosis compared to lowland populations of L. genimaculata. This does not exclude the possibility that current peptide defences have adapted in response to disease emergence. A suggestive (P < 0.10) interaction between infection status and population indicates that in lowland populations, infected individuals tend to be those with lower relative intensities of AMPs, whereas in the upland populations, infected and uninfected individuals are similar. Thus, both the AMPs and the environment may act to mediate resistance to Bd infection.     

The effect of environmental factors on the suspended bacteria in the Welsh River Dee

Water samples collected every 8 d from three sites on the Welsh River Dee over 29 months were examined chemically and morphologically and their heterotrophic activities assessed. Bacterial population estimates were regressed on 21 independent environmental variables using multiple linear regression analysis. Prediction equations calculated from 1975–1976 data accounted for 70% of the total variation from an upland site but only 40% for a lowland site. The validity of the prediction equations was examined by correlating the predicted and observed count data of 1977–1978. The correlations of plate count values were significant for the upper ( r = 0.64, P < 0.001) and middle reach ( r = 0.62, P < 0.01) sites but not significant for the lowland site. The direct count correlation was significant for all three sites. The permanganate value, a measure of organic matter, was the most dominant variable in the prediction equations and was shown by principal component analysis (PCA) to be linked to particulate matter and river flow. Prediction equations constructed from the PCA data accounted for less variation than the original equations but, in general, there was an agreement between the two methods of multivariate analysis. The logarithm of the heterotrophic potential ( V _max) from the lowland site was shown to be a linear function of temperature ( r = 0.7, P < 0.001). A specific activity index calculated for the lowland site data gave a median value of 8.4 times 10^-10μg/h/bacterial cell and was highly sensitive to temperature change ( r = 0.74, P < 0.001) whereas the median value for the upland site was 2.6 times 10^-10μg/h/bacterial cell and did not respond significantly to temperature change ( r = 0.44, P > 0.05).     

Development of upland rice introgression lines and identification of QTLs for basal root thickness under different water regimes

Introgression lines (ILs) are valuable materials for identifying quantitative trait loci (QTLs),evaluating genetic interactions,and marker assisted breeding.A set of 430 ILs (BC5F3) containing segments from upland tropical japonica cultivar IRAT109 in a lowland temperate japonica cultivar Yuefu background were developed.One hundred and seventy-six polymorphic markers were used to identify introgressed segments.No segment from IRAT 109 was found in 160 lines.Introgressed segments of the other 270 lines covered 99.1％ of the donor genome.The mean number of introgressed donor segments per individual was 3.3 with an average length of 14.4 cM.QTL analysis was conducted on basal root thickness (BRT) of the 270 ILs grown under irrigated lowland,upland and hydroponic conditions.A total of 22 QTLs affecting BRT were identified,six QTLs (qBRT3.1,qBRT3.2,qBRT6.1,qBRT8.2,qBRT9.1,and qBRT9.2) were consistently expressed under at least two environments (location and water regime),and qBRT7.2 was a new BRT QTL identified under lowland conditions.IL255 containing qBRT9.1 showed an increase of 10.09％ and 7.07％ BRT over cultivar Yuefu when grown under upland and lowland conditions,respectively.Using a population of 304 F2:3 lines derived from the cross IL255 × Yuefu,qBRT9.1 was validated and mapped to a 1.2 cM interval between RM24271 and RM566.The presence of qBRT9.1 explained 12％ of BRT variation.The results provide upland rice ILs and BRT QTLs for analyzing the genetic basis of drought resistance,detecting favorable genes from upland rice,and rice drought resistance breeding.     

The effects of size, age and a cost of early breeding on reproduction in female mountain hares

Both age and size may influence female reproductive performance in mammals, and successful early reproduction may lead to reduced success at later attempts. The effects of age, size and early reproduction on distribution of reproductive effort throughout a single breeding season was examined in female mountains hares Lepus timidus L. Hind foot length was used as an index of body size, because, unlike body weight, it did not fluctuate with reproductive status. Fifty-six female carcasses were collected from March to October 1984, and their litters were assigned to one of three chronologically equal'litter periods'(1–3) of equal length. Whereas number of ova shed was always independent of age, large females shed more ova than did smaller females in litter periods 1 and 2. Prenatal mortality of ova and embryos was highest during litter period 1, when it was independent of age and size. Although prenatal mortality remained high in first year females in litter period 2, there was an overall decline through to the final litter period when it was negligible. Total number of young produced through the season increased with skeletal size in old females (age > 1), but not significantly in first year females. It is concluded that large size, rather than age, favours early reproduction in mountain hares. Every additional offspring produced in litter periods 1 and 2 reduced that female's production in period 3. After correcting for this cost of early reproduction the number of young produced in the final litter period also increased with maternal size.     

Use of river-wetland habitats in a declining population of the terrapin (Mauremys rivulata) along the Strymon River, northern Greece

A declining population of the freshwater turtle Mauremys rivulata (Chelonia, Geoemydidae) living in a human-impacted area along the Strymon River, just upstream from Kerkini Lake (Prefecture of Serres, northern Greece), was investigated by capture–recapture and radio-tracking. Fyke nets placed along the river and in ponds lying on the riparian lowland gave about 2000 catches in 6 years, permitting us to assess major inter-habitat movements during ontogenesis and throughout the seasons. Annual intensive radio-tracking of 15 females and 10 males gave finer details of movement patterns between different river-wetland habitats. Younger specimens, including yearlings, inhabited the ponds almost exclusively, whereas the adult population shifted seasonally from the ponds during the mating season to a marsh area lying on the opposite side of the river for aestivation and overwintering. The river served mainly as a corridor for transit between the two habitats. Moreover, longitudinal movements along the river were observed, particularly in the males, which probably allow dispersal and gene flow between subpopulations living in the area. One major threat to the viability of M. rivulata in the study area is the diversion of water for irrigation during the summer, drying up the Strymon completely, which reduces the water level in the ponds. Livestock crossing the area for grazing and watering in the ponds is also of impact, as turtles in the ponds are trampled on and nests are disturbed.     

A TEN-YEAR RECORD OF ABOVEGROUND BIOMASS IN A KANSAS TALLGRASS PRAIRIE: EFFECTS OF FIRE AND TOPOGRAPHIC POSITION

Measurements of mid-season live and dead aboveground biomass are reported for a 10-yr period (1975–84) in a northeast Kansas tallgrass prairie. Study sites included shallow, rocky upland and deep, non-rocky lowland soils in annually burned (April) and unburned watersheds. Lowland sites had significantly greater live biomass than upland sites for both burned and unburned prairie for the 10-yr period. Moreover, live biomass was greater on burned than unburned lowland sites, but was not significantly increased by fire on the upland sites. Averaged across upland and lowland sites, mid-season live biomass was 422 g m^–2 on annually burned and 364 g m^–2 on unburned sites for the 10-yr period. Each site had its lowest live biomass value during the severe drought year of 1980 (range = 185–299 g m^–2). During the study period, live biomass was most strongly correlated with seasonal pan water evaporation (r = –0.45 to –0.82), whereas dead biomass was correlated with the previous yr's precipitation (r = 0.61 and 0.90 for upland and lowland sites, respectively). When aboveground biomass was sampled throughout the 1984 season and separated into several components, biomass of the graminoids was 40% lower, whereas that of forbs and woody plants was 200–300% greater in the unburned than in the annually burned site.     

Longitudinal changes in δ13C of riffle macroinvertebrates from mountain to lowland sections of a gravel‐bed river

Summary 1. To understand longitudinal changes in the trophic base of benthic macroinvertebrates from mountain to lowland river sections, we investigated carbon stable isotopic compositions (δ¹³C) of macroinvertebrates and their food resources in riffles for four seasons at 14 sites along the main stem of the Toyo River, Japan. 2. At each site, δ¹³C was usually highest or nearly highest for periphyton (epilithic biofilm) and was lowest for transported leaf materials. Among macroinvertebrate groups, grazers usually had higher δ¹³C values than filterers or predators. 3. During all seasons, δ¹³C of periphyton and all macroinvertebrate groups increased downstream from mountain to upland sections, but decreased downstream from upland to lowland sections. In addition, the difference between grazer δ¹³C and filterer δ¹³C decreased from mountain to upland sections, but increased from upland to lowland sections. 4. The observed changes in δ¹³C of periphyton and macroinvertebrates from mountain to upland sections agree with previous reports: the δ¹³C of periphyton and consumers increased with stream size and productivity. The decrease in δ¹³C of periphyton and macroinvertebrates from upland to lowland sections has not been reported previously, and this may have resulted from an increased importance of terrestrial detritus relative to periphyton production in the lowland section, where riffles were infrequent and pools dominated the reach. 5. A simple mixing model of δ¹³C showed that grazers rely mostly on periphyton at all sites, whereas the importance of periphyton for filterers changed longitudinally increasing from mountain to upland sections and decreasing from upland to lowland sections. This longitudinal trend for filterers is possibly associated with the changes in the availability or quality of terrestrial detritus in transported particulate organic matter. 6. Longitudinal changes in the relative importance of autochthonous production and allochthonous detritus appear to be reflected in δ¹³C of riffle benthic communities. The longitudinal changes were not monotonic, and specific reach characteristics may be responsible for the greater importance of allochthonous detritus in mountain and lowland sections.     

Factors affecting the distribution of genetic variability in the guppy, Poecilia reticulata

Previous studies on Trinidadian guppies have shown an apparent association of genetic variability, expressed as mean heterozygosity (Ho) at allozyme loci, with river order: fish from lowland sites exhibit higher mean Ho than their upland counterparts. Detailed genetic and behavioural observations were undertaken in the present study by repeated sampling throughout two river courses to examine population heterogeneity. Results show that the predation regime mediated mating behaviour of upland and lowland populations in the wild is not as divergent as previous laboratory observations have suggested. Furthermore, genetic variation at the eight loci variable in Trinidadian populations (p₁₀₀=0·13–O·88, H₀=O·03–0·23) appears to bear little association with predation regime, but is related to sub-structuring of populations by habitat features and geographic isolation. We therefore conclude that the observed patterns of genetic variability arise primarily as a consequence of stochastic as opposed to deterministic factors.     

镜湖长三肢轮虫的有性生殖

2004年5—11月,对芜湖市镜湖大、小湖区水体中长三肢轮虫(Filinia longiseta)的有性生殖及其与种群密度、水温、水体透明度、水体叶绿素a含量和轮虫总密度等环境因子间的关系进行了研究.结果表明:当水温低于22℃或水体透明度大于一定值(小湖区SD>95cm,大湖区SD>100cm)时,长三肢轮虫不进行有性生殖;而当其本身的种群密度达到一定值(小湖区种群密度>122ind·L-1,大湖区种群密度>113ind·L-1)时才进行有性生殖.长三肢轮虫的混交雌体密度仅与其本身的种群密度以及水体中轮虫总密度之间呈正相关关系(P<0·01),而与水温、叶绿素a含量、水体透明度之间均无明显的相关关系;长三肢轮虫种群的混交率和受精率与水温、水体透明度、叶绿素a含量、轮虫总密度和长三肢轮虫种群密度之间也无明显的相关性.长三肢轮虫的有性生殖发生在种群增长的早期阶段,混交雌体以间断的、多循环的方式产生;最大混交率与最大种群密度同时出现,但最大受精率出现在种群即将消失时.     

Natural variation in the promoter of rice calcineurin B‐like protein10 (OsCBL10) affects flooding tolerance during seed germination among rice subspecies

Rice (Oryza sativa L.) has two ecotypes, upland and lowland rice, that have been observed to show different tolerance levels under flooding stress. In this study, two rice cultivars, upland (Up221, flooding‐intolerant) and lowland (Low88, flooding‐tolerant), were initially used to study their molecular mechanisms in response to flooding germination. We observed that variations in the OsCBL10 promoter sequences in these two cultivars might contribute to this divergence in flooding tolerance. Further analysis using another eight rice cultivars revealed that the OsCBL10 promoter could be classified as either a flooding‐tolerant type (T‐type) or a flooding‐intolerant type (I‐type). The OsCBL10 T‐type promoter only existed in japonica lowland cultivars, whereas the OsCBL10 I‐type promoter existed in japonica upland, indica upland and indica lowland cultivars. Flooding‐tolerant rice cultivars containing the OsCBL10 T‐type promoter have shown lower Ca²⁺ flow and higher α‐amylase activities in comparison to those in flooding‐intolerant cultivars. Furthermore, the OsCBL10 overexpression lines were sensitive to both flooding and hypoxic treatments during rice germination with enhanced Ca²⁺ flow in comparison to wild‐type. Subsequent findings also indicate that OsCBL10 may affect OsCIPK15 protein abundance and its downstream pathways. In summary, our results suggest that the adaptation to flooding stress during rice germination is associated with two different OsCBL10 promoters, which in turn affect OsCBL10 expression in different cultivars and negatively affect OsCIPK15 protein accumulation and its downstream cascade.     

Metabolic adaptation to flooding stress in upland and lowland rice seedlings

Ability of metabolic adaptation in upland and lowland rice (Oryza sativa L.) seedlings to flooding stress was compared. Flooding stress increased alcohol dehydrogenase (ADH) activity and ethanol concentration in shoots and roots of the upland and lowland rice seedlings. The difference in ADH activity and ethanol concentration in shoots between the upland and lowland rice was not apparent. However, both ADH activity and ethanol concentration in roots of the lowland rice were 2-fold greater than those in roots of the upland rice, suggesting that flooding-induction of ethanolic fermentation in lowland rice roots may be significantly greater than that in the upland rice roots. Since flooding often causes the anaerobic conditions in rooting zone than aerial part of plants and ethanolic fermentation is essential to survive in the anaerobic conditions, the ability of metabolic adaptation in lowland rice seedlings to flooding stress may be greater than that in upland rice seedlings.