Fluorescence Properties Indicate that Photosystem II Reaction Centers and Light-Harvesting Complex Are Modified by Low Temperature Growth in Winter Rye

Thylakoids isolated from winter rye (Secale cereale L. cv Puma) grown at 20°C (nonhardened rye, RNH) or 5°C (cold-hardened rye, RH) were characterized using chlorophyll (Chl) fluorescence. Low temperature fluorescence emission spectra of RH thylakoids contained emission bands at 680 and 695 nanometers not present in RNH thylakoids which were interpreted as changes in the association of light-harvesting Chl a/b proteins and photosystem II (PSII) reaction centers. RH thylakoids also exhibited a decrease in the emission ratio of 742/685 nanometers relative to RNH thylakoids.

Room temperature fluorescence induction revealed that a larger proportion of Chl in RH thylakoids was inactive in transferring energy to PSII reaction centers when compared with RNH thylakoids. Fluorescence induction kinetics at 20°C indicated that RNH and RH thylakoids contained the same proportions of fast (α) and slow (β) components of the biphasic induction curve. In RH thylakoids, however, the rate constant for α components increased and the rate constant for β components decreased relative to RNH thylakoids. Thus, energy was transferred more quickly within a PSII reaction center complex in RH thylakoids. In addition, PSII reaction centers in RH thylakoids were less connected, thus reducing energy transfers between reaction center complexes. We concluded that both PSII reaction centers and light-harvesting Chl a/b proteins had been modified during development of rye chloroplasts at 5°C.

     

Effects of Low Temperature on Growth and Nutrient Accumulation in Rye (Secale cereale) and Wheat (Triticum aestivum)

Rye (Secale cereale cv. Rheidol) and wheat (Triticum aestivumcv. Mardler) were grown at shoot/root temperatures of 20/20°C (warm grown, WG plants), 8/8 °C (cold grown, CG plants)and 20/8 °C (differential grown, DG plants). Plants fromcontrasting growth temperature regimes were standardized andcompared using a developmental timescale based on accumulatedthermal time (°C d) at the shoot meristem. Accumulationof dry matter, nitrogen and potassium were exponential overthe time period studied (150–550 °C d). In rye, therates of plant dry matter and f. wt accumulation were linearlyrelated to the temperature of the shoot meristem. However, inwheat, although the rates of plant dry matter and f. wt accumulationwere temperature dependent, the linear relationship with shootmeristem temperature was weaker than in rye. The shoot/rootratio of rye was stable irrespective of growth temperature treatment,but the shoot/root ratio of wheat varied with growth temperaturetreatment. The shoot/root ratio of DG wheat was 50% greaterthan WG wheat. In both cereals, nutrient concentrations anddry matter content tended to be greater in organs exposed directlyto low temperatures. The mean specific absorption rates of nutrientswere calculated for the whole period studied for each species/temperaturecombination and were positively correlated with both plant shoot/rootratio and relative growth rate. The data suggest that nutrientuptake rates were influenced primarily by plant demand, withno indication of specific nutrient limitations at low temperatures. Nutrient accumulation, relative growth rate (RGR), rye, Secale cereale cv. Rheidol, temperature, thermal time, Triticum aestivum cv. Mardler, wheat     

Solute Accumulation and Compartmentation during the Cold Acclimation of Puma Rye

During cold acclimation of Puma rye (Secale cereale L. cv Puma), the intracellular osmotic potential nearly doubles. During this period, the accumulation of glycinebetaine, proline, and soluble sugars was monitored. The amount of glycinebetaine increased from 290 to 1300 micrograms per gram fresh weight during the 4-week acclimation period. Proline content did not change during the first 3 weeks of acclimation but then increased from 27 to 580 micrograms per gram fresh weight during the next 3 weeks. The total soluble sugar content more than doubled by the second week of cold acclimation, increasing from 11 to 26 milligrams per gram fresh weight. Most of this increase can be attributed to the accumulation of sucrose and raffinose, whose levels increased from 2.4 and 0 to 11 and 5 milligrams per gram fresh weight, respectively. The content of monosaccharides, predominantly glucose, remained at a constant 10 milligrams per gram fresh weight throughout the acclimation period. A comparison of the sugar content of protoplasts versus vacuoles isolated from cold-acclimated leaves revealed that the extravacuolar volume contained monosaccharides, sucrose, and raffinose. Thus, the increased amounts of sucrose and raffinose that occur during cold acclimation are present in compartments external to the vacuole and may contribute to cryoprotection.     

The Effect of Growth in D2O on the Metabolism of Winter Rye

The metabolism of winter rye seedlings (Secale cereale, L. ev.Winter) cultured in 99.8 per cent D₂O was investigated. Comparedwith water-grown seedlings, the protein content was much lowerin the D₂O-cultured seedlings and the pattern of incorporationof [³H]leucine and [³H]phenylalanine into protein was substantiallydifferent. Seedlings cultured in D₂O incorporated [³H]thymidineinto DNA, but did not take up [³H]uridine. The results suggestthat some of the toxic effects of D₂O culture on higher plantscan be attributed to a partial block of protein synthesis.     

The Effect of Restricted Germination during Vernalization on First Leaf Length of Winter Rye

Winter rye grain was vernalized, using the restricted moisturetechnique, at various temperatures and moisture levels and therelation between first-leaf blade length and the degree of vernalizationanalysed. There was an inverse relation between these two factors,but leaf length was influenced by both temperature and moisturelevel in a manner quite different from the effect on the vernalizationtemperatures and the major requirement for short-leaf productionproved to be the period of restricted germination normally imposedduring vernalization. Cell counts of the epidermis of the firstleaf blade showed that the reduction in length was due to inhibitionof the earliest phase of leaf extension growth. It is suggested that some growth-promoting substance in theembryo, possibly IAA, is broken down during the restricted germinationperiod. When grain is sown this shortage impedes early leafextension until the level is restored by synthesis or translocation.     

Root Growth of Bulbous Species during Winter

Bulbs of Allium moly, Scilla siberica, Triteleia uniflora, Tulipakaufmanniana and Narcissus lobularis were planted in a rhizotronand root growth was monitored weekly for an 18 week period.All the genera produced roots until the soil temperature droppedto 3 °C. Root outgrowth from the bulbs and growth of emergedroots then ceased or was strongly inhibited in N. lobularis,S. siberica and T. uniflora but not in the other genera. Mostbulbs resumed root elongation when the soil temperature hadwarmed to 4 °C. Root emergence and continued growth occurredfor a longer period during the winter than has generally beenassumed. Allium moly, Scilla siberica, Triteleia uniflora, Tulipa kaufmanniana, Narcissus lobularis, rhizotron, bulb, root growth     

Winter Climate Limits Subantarctic Low Forest Growth and Establishment

Campbell Island, an isolated island 600 km south of New Zealand mainland (52°S, 169°E) is oceanic (Conrad Index of Continentality  = −5) with small differences between mean summer and winter temperatures. Previous work established the unexpected result that a mean annual climate warming of c. 0.6°C since the 1940''s has not led to upward movement of the forest limit. Here we explore the relative importance of summer and winter climatic conditions on growth and age-class structure of the treeline forming species, Dracophyllum longifolium and Dracophyllum scoparium over the second half of the 20^th century. The relationship between climate and growth and establishment were evaluated using standard dendroecological methods and local climate data from a meteorological station on the island. Growth and establishment were correlated against climate variables and further evaluated within hierarchical regression models to take into account the effect of plot level variables. Winter climatic conditions exerted a greater effect on growth and establishment than summer climatic conditions. Establishment is maximized under warm (mean winter temperatures >7 °C), dry winters (total winter precipitation <400 mm). Growth, on the other hand, is adversely affected by wide winter temperature ranges and increased rainfall. The contrasting effect of winter warmth on growth and establishment suggests that winter temperature affects growth and establishment through differing mechanisms. We propose that milder winters enhance survival of seedlings and, therefore, recruitment, but increases metabolic stress on established plants, resulting in lower growth rates. Future winter warming may therefore have complex effects on plant growth and establishment globally.     

Effects of Low Temperature on Winter Wheat and Cabbage Leaves

Contents of soluble proteins, proline and chlorophyll in winter wheat (Triticum aestivum cv. Doğu-88) and cabbage leaves (Brassica oleracea convar. acephala) during acclimation to low temperature were investigated. When both of the plants species were cold acclimated, soluble proteins, proline and chlorophyll contents were higher than in the controls (non-acclimated). Also protein patterns differed between the plants at control and cold conditions. This revised version was published online in July 2006 with corrections to the Cover Date.     

Growth Analysis of Solution Culture-grown Winter Rye, Wheat and Triticale at Different Relative Rates of Nitrogen Supply

At low nitrogen (N) supply, it is well known that rye has ahigher biomass production than wheat. This study investigateswhether these species differences can be explained by differencesin dry matter and nitrogen partitioning, specific leaf area,specific root length and net assimilation rate, which determineboth N acquisition and carbon assimilation during vegetativegrowth. Winter rye (Secale cereale L.), wheat (Triticum aestivumL.) and triticale (X Triticosecale) were grown in solution cultureat relative addition rates (R_N) of nitrate-N supply rangingfrom 0.03–0.18 d^-1and at non-limiting N supply under controlledconditions. The relative growth rate (R_W) was closely equalto R_Nin the range 0.03–0.15 d^-1. The maximalR_W at non-limitingnitrate nutrition was approx. 0.18 d^-1. The biomass allocationto the roots showed a considerable plasticity but did not differbetween species. There were no interspecific differences ineither net assimilation rate or specific leaf area. Higher accumulationof N in the plant, despite the same relative growth rate atnon-limiting N supplies, suggests that rye has a greater abilityto accumulate reserves of nitrogen. Rye had a higher specificroot length over a wide range of sub-optimal N rates than wheat,especially at extreme N deficiency (R_N=0.03–0.06 d^-1).Triticale had a similar specific root length as that of wheatbut had the ability to accumulate N to the same amount as ryeunder conditions of free N access. It is concluded that thebetter adaptation of rye to low N availability compared to wheatis related to higher specific root length in rye. Additionally,the greater ability to accumulate nitrogen under conditionsof free N access for rye and triticale compared to wheat maybe useful for subsequent N utilization during plant growth.In general, species differences are explained by growth componentsresponsible for nitrogen acquisition rather than carbon assimilation.Copyright 1999 Annals of Botany Company Growth analysis, nitrogen, nitrogen productivity, partitioning, specific root length, Secale cereale L.,Triticum aestivum L., X Triticosecale, winter rye, winter wheat, winter triticale.     

Resistance to Ergot in Self-incompatible Germplasm Resources of Winter Rye

The poor progress in breeding for resistance to ergot ( Claviceps purpurea [Fr.] Tul.) in rye ( Secale cereale L.) is attributed to the lack of appreciable genotypic variation for this trait. The present study was, therefore, undertaken to evaluate 52 indigenous and exotic genetic resources and 13 open-pollinated cultivars for ergot resistance. These 65 self-incompatible populations were evaluated in four environments with each entry plot surrounded by wheat plots on four sides. Inoculation with a pathogen mixture was done thrice during flowering and harvesting was done early by hand. Resistance traits were ergot incidence and severity. Logit-transformed data were subjected to analyses of variance. The lowest disease severity in any environment was 0.18%, and that was still higher than the official threshold of 0.1% for feed. In the pooled analysis across environments, significant genotypic differences as well as genotype × environment interaction were present. The correlation between ergot severity and pollen shedding was not significant indicating that genotypic differences were not affected by pollen shedding. Broad-sense heritability ( h ² ) estimates were moderate (0.54–0.65). 'Halo', an old German cultivar, and the genetic resources 'Schmidt-Roggen' and 'Dukat', had low ergot severity (Halo having the lowest severity) as well as low disease incidence. The results document a significant, but moderate genotypic variance for ergot resistance among self-incompatible rye that can be exploited to breed ergot-resistant rye.     

Studies in Vernalisation: XII. The Reversibility by High Temperature of the Vernalised Condition in Petkus Winter Rye

The reversibility of vernalisation in Petkus winter rye hasbeen studied in detail, by using alternating periods, duringgermination, of low and high temperature of varying durations.The degree of devernalisation by exposure to subsequent hightemperature varies with the initial duration of vernalisationand becomes progressively less as vernalisation proceeds. Aquantitative method of studying these effects is described,and a revised schema of the dynamic aspects of vernalisationput forward.     

Differential Inhibition of Shootvs.Root Growth at Low Temperature and its Relationship with Carbohydrate Accumulation in Different Wheat Cultivars

Shoot and root growth rate, carbohydrate accumulation (includingfructan), reducing sugar content and dry matter percentage weremeasured in six wheat cultivars, ranging from winter to springtypes, grown at either 5 or 25 °C. At 5 °C (comparedwith 25 °C), the relative growth rate (RGR) of shoots wassimilarly reduced in all cultivars, but the RGR of shoots wasmore affected in winter wheats. This difference resulted insmaller root:shoot ratios than in spring wheats, which alsodeveloped more first-order lateral roots. A direct relationshipbetween carbohydrate accumulation at low temperatures and reductionin root growth was established. These results suggest that differentialshootvs.root growth inhibition at low temperature may play akey role in carbohydrate accumulation at chilling temperatures.This differential response might lead to improvements in survivalat temperatures below 0 °C, regrowth during spring, andwater and nutrient absorption at low temperatures.Copyright1997 Annals of Botany Company Wheat; Triticum aestivum; low temperatures; root growth; root: shoot ratio; sugar accumulation     

Studies in Vernalisation of Cereals: XV. After-effects of Temperature and Drying during Seed Ripening and the Origin of the Vernalisation Requirement in Petkus Winter Rye

Experiments are described which were designed to test whetherthe unvernalised condition of winter rye grain produced by fullyvernalised parent plants is due to de-vernalisation occurringduring maturation and ripening of the seed. The results showclearly that drying of the grain does not account for the un-vernalisedcondition. Parent ears exposed from the time of their emergenceto a range of non-vernalising temperatures (12–20°C), i.e. including ‘neutral’ levels which are neithervernalising nor de-vernalising, still produced unvernalisedgrain. Even plants raised from grain which had been developedat mildly vernalising temperatures (9° C) benefited fromfurther cold treatment applied during their early growth. Itappears, therefore, that the vernalisation requirement in winterrye arises very early in the formation of the seed, i.e. possiblyat meiosis or fertilisation, and that there is no subsequenttransmission of the vernalisation stimulus from the parent plant. Additional observations on plant height, ear size, &c.,also indicate marked effects of temperature and daylength treatments.     

Vernalisation of Winter Rye by Negative Temperatures and the Influence of Vernalisation upon the Lamina Length of the First and Second Leaf in Winter Rye, Spring Barley, and Winter Barley

The lowest effective temperature observed for vernalising PetkuaWinter Rye was –4.5° C., whereas –6° to–10° C. did not induce any hastening of flowering.Seedlings of 20–25 mm. length were as susceptible to –3°C. as seeds in the stage at which the radicle had just brokenthrough the pericarp. Vernalising temperatures alternating between7 days +1° C. and 3 days –3° C. were as effectiveas continuous treatment by +1° C. The lamina length of thefirst and second leaf is shortened by raising the vernalisingtemperatures from –3° C. to +3° C. and also isfurther shortened by prolonging the vernalisation period inwinter rye and winter barley. No progressive shortening of thelamina length, however, was observed in spring barley when treatedlike winter barley. This suggests a direct dependence of thelamina length of the first and second leaf on the degree ofvernalisation reached in the embryo.     

Effect of Microdochium nivale and Low Temperature on Winter Survival of Perennial Ryegrass

Winter survival of perennial ryegrass (Lolium perenne L.) depends mainly on the plant resistance to low freezing temperature and to snow mould fungi (Microdochium nivale). Field evaluation of these plant characters gave irreproducible results. A comparison of field trials with laboratory tests pointed to the close correlation between the yield level of examined varieties and strains and their resistance to Microdochium nivale and frost. A lack of correlation between snow mould resistance and frost tolerance was shown.     

Analysis of Organ Specificity of a Low Temperature Responsive Gene Family in Rye (Secale cereale L.)

The barley (Hordeum vulgare L.) low temperature responsive geneblt14 was used as a probe, to isolate two different cognateclones (rlt1412; rlt1421) from a rye (Secale cereale L.) cDNAlibrary prepared from low temperature-treated (6°C day/2°C night) shoot meristems of the cultivar, Puma. Northernblot analysis revealed that low temperature expression of rlt1412is highest in root tissues whereas, rlt1421 shows greatest mRNAaccumulation in mature leaf tissues. There is a relationshipbetween the steady-state levels of these mRNA species and thefrost hardiness of Puma (North American cultivar) and Rhayader(UK cultivar) such that the expression ofboth genes is higherin the more frost hardy cultivar, Puma, compared with Rhayader. DNA and predicted amino acid sequence analysis indicated thatthe rye and barley clones encode small proteins with consensusN-terminal signal sequences whose biological function is atpresent unknown. The relevant sequences are lodged in the EMBL data base. Key words: Rye, cold, cDNA, organ specificity, low temperature genes     

Levels of Growth Regulating Substances during Vernalization of Winter Wheat

Seeds of winter wheat (Triticum vulgare L.) cultivars Fema and Ferto, were vernalized at 3°C in the dark. Samples were taken 9, 18, 27, 36 and 45 days after the start of vernalization, and extracts were analysed for auxins, gibberellins and growth inhibiting substances. As vernalization progressed the levels of auxins and gibberellins increased whereas the levels of growth inhibitors decreased. The pattern of growth regulator changes was almost similar in both the cultivars. Vernalization seemingly controls the balance between growth promoting and growth inhibiting substances in winter wheat.