The role of ABA in freezing tolerance and cold acclimation in barley

The role of ABA in freezing resistance in nonacclimated and cold‐acclimated barley ( Hordeum vulgare L.) was studied. Eleven nonacclimated cultivars differed in their LT₅₀, ranging from −10.8 to −4.8°C. Sugars, free proline, soluble proteins and ABA were analyzed in nonacclimated cultivars and during cold acclimation of one cultivar. There was an inverse correlation between LT₅₀ and both ABA and sucrose contents. Exogenous ABA caused a decrease in the freezing point of leaf tissue in the cultivar with the lowest level of endogenous ABA, but not in the cultivar with the highest level, suggesting that ABA in the latter may be near the optimum endogenous level to induce freezing tolerance. Plants of cv. Aramir treated with ABA or allowed to acclimate to cold temperature increased their soluble sugar content to a similar level. The LT₅₀ of leaves of cold‐acclimated cv. Aramir decreased from −5.8 to −11.4°C, with biphasic kinetics, accumulating proline and soluble sugars with similar kinetics. The biphasic profile observed during cold acclimation could be a direct consequence of cryoprotectant accumulation kinetics. ABA and soluble protein accumulation showed a single step profile, associated mainly with the second phase of the LT₅₀ decrease. Thus, a significant increase in endogenous ABA is part of the response of barley to low temperature and may be required as a signal for the second phase of cold acclimation. Endogenous ABA contents in the nonacclimated state may determine constitutive freezing tolerance.     

An α-galactosidase with an essential function during leaf development

The putative α-galactosidase gene HvSF11 of barley, previously shown to be expressed during dark induced senescence, is expressed in the growing/elongating zone of primary foliage leaves of barley. The amino acid sequence deduced from the full length HvSF11 cDNA contains a hydrophobic signal sequence at the N-terminus. Phylogenetic relationship of the HvSF11 encoded barley α-galactosidase to other α-galactosidases revealed high homology with the α-galactosidase encoded by the gene At5g08370 from Arabidopsis thaliana. We have isolated two independent heterozygous At5g08370 T-DNA insertion mutants from Arabidopsis thaliana, both of which have a higher number of rosette leaves with a curly surface leaf morphology and delayed flowering time in comparison to wildtype plants. Localization of the Arabidopsis α-galactosidase protein via GUS-tag revealed that the protein is associated with the cell wall. This result was confirmed by immunological detection of the orthologous barley protein in a protein fraction derived from cell walls of barley leaves. It is concluded that the α-galactosidase proteins from barley and Arabidopsis might fulfill an important role in leaf development by functioning in cell wall loosening and cell wall expansion.

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Analysis of simple sequence repeats (SSRs) in wild barley from the Fertile Crescent: associations with ecology,geography and flowering time

Wild barley, Hordeum spontaneum C. Koch, is the progenitor of cultivated barley, Hordeum vulgare. The centre of diversity is in the Fertile Crescent of the Near East, where wild barley grows in a wide range of conditions (temperature, water availability, day length, etc.). The genetic diversity of 39 wild barley genotypes collected from Israel, Turkey and Iran was studied with 33 SSRs of known map location. Analysis of molecular variance (AMOVA) was performed to partition the genetic variation present within from the variation between the three countries of origin. Using classification tree analysis, two (or three) specific SSRs were identified which could correctly classify most of the wild barley genotypes according to country of origin. Associations of SSR variation with flowering time and adaptation to site-of-origin ecology and geography were investigated by two contrasting statistical approaches, linear regression based on SSR length variation and linear regression based on SSR allele class differences. A number of SSRs were significantly associated with flowering time under four different growing regimes (short days, long days, unvernalised and vernalised). Most of the associations observed could be accounted for by close linkage of the SSR loci to earliness per se genes. No associations were found with photoperiodic and vernalisation response genes known to control flowering in cultivated barley suggesting that different genetic factors may be active in wild barley. Novel genomic regions controlling flowering time in wild barley were detected on chromosomes 1HS, 2HL, 3HS and 4HS. Associations of SSRs with site-of-origin ecological and geographic data were found primarily in genomic regions determining plant development. This study shows that the analyses of SSR variation by allele class and repeat length are complementary, and that some SSRs are not necessarily selectively neutral.     

Effects of Soil Drought and Atmospheric Humidity on Yield,Gas Exchange,and Stable Carbon Isotope Composition of Barley

The combined effects of water status, vapour pressure deficit (VPD), and elevated temperature from heading to maturity were studied in barley. Plants growing at high VPD, either under well-watered or water deficit conditions, had higher grain yield and grain filling rate than plants growing at low VPD. By contrast, water stress decreased grain yield and individual grain dry matter at any VPD. Water regime and to a lesser extent VPD affected ¹³C of plant parts sampled at mid-grain filling and maturity. The differences between treatments were maximal in mature grains, where high VPD increased ¹³C for both water regimes. However, the total amount of water used by the plant during grain filling did not change as response to a higher VPD whereas transpiration efficiency (TE) decreased. The net photosynthetic rate (P _N) of the flag leaves decreased significantly under water stress at both VPD regimes. However, P _N of the ears was higher at high VPD than at low VPD, and did not decrease as response to water stress. The higher correlation of grain yield with P _N of the ear compared with that of the flag leaf support the role of ear as the main photosynthetic organ during grain filling under water deficit and high VPD. The deleterious effects of combined moderately high temperature and drought on yield were attenuated at high VPD.     

Long term regeneration by somatic embryogenesis in barley (Hordeum vulgare L.) tissue cultures derived from apical meristem explants

Callus cultures were initiated from apical meristem explants of one to four-week-old aseptically-grown barley (Hordeum vulgare L. cv. Atlas 57) plants. Embryogenic callus and plants were produced in three separate experiments; the cultures have retained regenerative capacity for three years after initiation. Our results demonstrate that explants other than immature embryos are embryogenically competent in barley and that regeneration occurs by both somatic embryogenesis and organogenesis.     

Methods for estimating gene numbers for quantitative characters using doubled haploid lines

Summary Three methods of estimating the numbers of genes segregating for quantitative characters using doubled haploid lines are presented. The first uses estimates of the range and genetical variance of an F₁ or F₂ derived population. The second adapts the genotype assay method of Jinks and Towey (1976) to F₂ derived lines. The third uses the variances of an F₂ derived population. Statistical problems of obtaining meaningful estimates using these methods are discussed and it is concluded that genotype assay is the best method for distinguishing between few and many genes. These methods are illustrated using data from an experiment containing doubled haploid lines of barley developed using the H. bulbosum system.     

鹅观草与大麦属间杂种的形态和细胞遗传学研究

用活体/离体幼胚培养法成功地获得了鹅观草(Roegneria kamooji,2n=12,SSHHYY)与大麦(Hordeum vulgare,2n=14,11)间的属间杂种。杂交结实率为31.4％,胚培成苗率60.9％。杂种表现一年生,具有很强的生活力,形态上偏向鹅观草。F_1自交不孕,用大麦回交亦不结实。杂种具有预期的2n=28(SHYI)条染色体,花粉母细胞减数分裂中期Ⅰ平均形成26.38个单价体,0.67个棒状二价体,0.12个环状二价体和0.02个三价体。本文对双亲染色体组间的同源性以及在大麦育种中利用鹅观草种质的可能性进行了讨论。     

Accumulation of pathogenesis-related proteins in barley leaf intercellular spaces during leaf senescence

Accumulation of the pathogenesis-related (PR) proteins localised in intercellular spaces of barley primary leaves, chlorophyll content, structure of chloroplasts, and photosynthesis were examined during natural and in vitro induced leaf senescence (cultivation of whole plants in the dark or detached leaves under nutrient deficiency). Some of PR proteins accumulated during natural senescence, but their accumulation pattern was different from those of pathogen-induced as well as during in vitro-induced senescence, which indicate different molecular bases of these processes. Photosynthetic rate and chlorophyll content indicate that natural senescence of barley primary leaves began from 15th day after sowing. In 35-d-old first leaves, the chloroplasts showed typical characteristics of senescence as significant decrease of size, greater grana, and prominent plastoglobuli. The chloroplasts contained more grana under in vitro induced senescence and they had reduced length in the dark. Correspondingly, accumulation of PR proteins was detectable on about the 15th day but the content of some PR proteins increased in later stages of senescence. This revised version was published online in July 2006 with corrections to the Cover Date.     

Mapping QTLs and candidate genes for iron and zinc concentrations in unpolished rice of Madhukar×Swarna RILs

Identifying QTLs/genes for iron and zinc in rice grains can help in biofortification programs. 168 F(7) RILs derived from Madhukar×Swarna were used to map QTLs for iron and zinc concentrations in unpolished rice grains. Iron ranged from 0.2 to 224ppm and zinc ranged from 0.4 to 104ppm. Genome wide mapping using 101 SSRs and 9 gene specific markers showed 5 QTLs on chromosomes 1, 3, 5, 7 and 12 significantly linked to iron, zinc or both. In all, 14 QTLs were identified for these two traits. QTLs for iron were co-located with QTLs for zinc on chromosomes 7 and 12. In all, ten candidate genes known for iron and zinc homeostasis underlie 12 of the 14 QTLs. Another 6 candidate genes were close to QTLs on chromosomes 3, 5 and 7. Thus the high priority candidate genes for high Fe and Zn in seeds are OsYSL1 and OsMTP1 for iron, OsARD2, OsIRT1, OsNAS1, OsNAS2 for zinc and OsNAS3, OsNRAMP1, Heavy metal ion transport and APRT for both iron and zinc together based on our genetic mapping studies as these genes strictly underlie QTLs. Several elite lines with high Fe, high Zn and both were identified.