Winterhardiness in cereals is the consequence of a number of complex and interacting component characters: cold tolerance, vernalization requirement, and photoperiod sensitivity. An understanding of the genetic basis of these component traits should allow for more-effective selection. Genome map-based analyses hold considerable promise for dissecting complex phenotypes. A 74-point linkage map was developed from 100 doubled haploid lines derived from a winter x spring barley cross and used as the basis for quantitative trait locus (QTL) analyses to determine the chromosome location of genes controlling components of winterhardiness. Despite the greater genome coverage provided by the current map, a previously-reported interval on chromosome 7 remains the only region where significant QTL effects for winter survival were detected in this population. QTLs for growth habit and heading date, under 16 h and 24 h light, map to the same region. A QTL for heading date under these photoperiod regimes also maps to chromosome 2. Contrasting alleles at these loci interact in an epistatic fashion. A distinct set of QTLs mapping to chromosomes 1, 2, 3, and 5 determined heading date under 8 h of light. Under field conditions, all QTLs identified under controlled environment conditions were determinants of heading date. Patterns of differential QTL expression, coupled with additive and additive x additive QTL effects, underscore the complexity of winterhardiness. The presence of unique phenotype combinations in the mapping population suggests that coincident QTLs for heading date and winter survival represent the effects of linkage rather than pleiotropy.

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Winterhardiness has three primary components: photoperiod (day length) sensitivity, vernalization response, and low temperature tolerance. Photoperiod and vernalization regulate the vegetative to reproductive phase transition, and photoperiod regulates expression of key vernalization genes. Using two barley mapping populations, we mapped six individual photoperiod response QTL and determined their positional relationship to the phytochrome and cryptochrome photoreceptor gene families and the vernalization regulatory genes HvBM5A, ZCCT-H, and HvVRT-2. Of the six photoreceptors mapped in the current study (HvPhyA and HvPhyB to 4HS, HvPhyC to 5HL, HvCry1a and HvCry2 to 6HS, and HvCry1b to 2HL), only HvPhyC coincided with a photoperiod response QTL. We recently mapped the candidate genes for the 5HL VRN-H1 (HvBM5A) and 4HL VRN-H2 (ZCCT-H) loci, and in this study, we mapped HvVRT-2, the barley TaVRT-2 ortholog (a wheat flowering repressor regulated by vernalization and photoperiod) to 7HS. Each of these three vernalization genes is located in chromosome regions determining small photoperiod response QTL effects. HvBM5A and HvPhyC are closely linked on 5HL and therefore are currently both positional candidates for the same photoperiod effect. The coincidence of photoperiod-responsive vernalization genes with photoperiod QTL suggests vernalization genes should also be considered candidates for photoperiod effects.

Chilling tolerance was increased in suspension‐cultured cells and seedlings of maize (Zea mays L. cv ‘Black Mexican Sweet’) grown in media containing glycinebetaine (GB). A triphenyl tetrazolium chloride (TTC) reduction test indicated that after a 7 d chilling period at 4 °C, cells treated with 1 mm GB at 26 °C for 1 d had a survival rate (30%) that was twice as high as that of untreated controls. The addition of 2·5 m M GB to the culture medium resulted in maximum chilling tolerance (40%). The results of a cell regrowth assay were consistent with viability determined by the TTC method. In suspension‐cultured cells supplemented with various concentrations of GB, accumulation of GB in the cells was proportional to the GB concentration in the medium and was saturated at a concentration of 240 μmol (g DW)−1. The degree of increased chilling tolerance was positively correlated with the level of GB accumulated in the cells. The increased chilling tolerance was time‐dependent; i.e. it was first observed 3 h after treatment and reached a plateau after 14 h. Feeding seedlings with 2·5 m M GB through the roots also improved their chilling tolerance, as evidenced by the prevention of chlorosis after chilling for 3 d at 4 °C/2 °C. Lipid peroxidation, as expressed by the production of malondialdehyde, was significantly reduced in GB‐treated cells compared with the untreated controls during chilling. These results suggest that increased chilling tolerance may be due, in part, to the reduction of lipid peroxidation of the cell membranes in the presence of GB.

Poplars (Populus deltoides Bartr. ex Marsh) accumulate a 32-kD bark storage protein (BSP) i n phloem parenchyma and xylem ray cells during autumn and winter. Accumulation of poplar BSP is associated with short-day (SD) photoperiods. Poplar BSP shares sequence similarity with the product of the wound-inducible poplar gene win4. The influence of nitrogen availability and photoperiod on the levels of BSP, BSP mRNA, and win4 mRNA was investigated. In long-day (LD) plants BSP, BSP mRNA, and win4 mRNA levels were correlated with the amount of NH,N03 provided to the plant. BSP mRNA and BSP were detected only in bark, whereas win4 mRNA was detected only in leaves. In LD plants treated with NH,NO,, BSP mRNA levels were significantly greater than those of win4. In nitrogen-deficient plants exposed to SD conditions, the accumulation of BSP mRNA and BSP was delayed for 2 weeks. This delay was eliminated by further SD exposure, and after 6 weeks of SD treatment similar levels of BSP and BSP mRNA were detected in the bark of SD plants regardless of the leve1 of NH,NO3 treatment. win4 mRNA levels declined to undetectable levels in young leaves of SD plants but increased in mature leaves. These results indicate that BSP accumulation in both LD and SD plants is influenced by nitrogen availability. Although both BSP and win4 appear to be involved in nitrogen storage, our data suggest that BSP is probably the primary protein involved in both seasonal and shortter" nitrogen storage in poplar. These results also suggest that nitrogen cycling and storage in poplar could involve a twocomponent system. In this system the win4 gene product may modulate accumulation and mobilization of leaf nitrogen, whereas BSP is involved in seasonal and short-term nitrogen storage during periods of excess nitrogen availability.