Tuberization in Potato at High Temperatures: Responses to Gibberellin and Growth inhibitors

The responses of potato plants (Solanum tuberosum L., cv. Sebago)to high temperatures (32 day/28 C night or 32/18 °C) andgibberellin are similar, in that they promote haulm growth andsuppress tuber production, whereas low temperatures (22/18 °C)abscisic acid and CCC have the opposite effect, promoting tuberproduction and reducing the growth of the haulms. The inhibitoryeffect of the high temperatures on tuber production, under aphotoperiod of 14 h, was almost completely reversed in theseexperiments by the application of CCC, and partly reversed byABA. Single-leaf cuttings from plants grown at the various temperaturesand chemical treatments responded in the same way as the wholeplant. It is suggested that both haulm growth and tuber initiationare influenced by a common hormonal control, and that temperatureexerts its influence by altering the balance between the levelsof endogenous gibberellins and inhibitors. These substancesapparently act directly on the stolon tip, rather than throughtheir general influence on haulm growth. Solanum tuberosum L., potato, tuberization, temperature response, gibberellin, abscisic acid, 2-chloroethyltrimethylammonium chloride (CCC)     

Changes in Tissue Freezing in Senecio vulgaris infected by Rust (Puccinia lagenophorae)

Freezing of healthy and rust (Puccinia lagenophorae) infectedleaves of Senecio vulgaris was compared calorimetrically bythermal analysis. In fully expanded leaves the threshold freezingtemperature was in the range –6.8 to –8.4 °Cin controls but –3.0 to –5.1 °C in leaves withsporulating rust sori. Comparable values in expanding leaveswere –5.0 to –8.9 °C and –3.9 to –6.7°C for healthy and rusted tissues, respectively. The bulktissue freezing point was between –1.0 and –4.0°C in both fully expanded and expanding healthy leaves,and was increased by infection by between +0.2 and 2.5 °C.Whereas healthy leaves supercooled by 3.1–5.8 °C,rusted leaves supercooled by only 1.8–4.9 °C Supercoolingof control leaves was reduced by dusting with aeciospores, particularlywhen leaves were wounded to simulate the rupture of the surfacecaused by sporulation, but wounding alone had no significanteffect. Supercooling of distilled water was also significantlyreduced by aeciospores, suspended at a concentration of 10⁵spores ml^–1. It is concluded that rust-induced changes in leaf freezing inS. vulgaris grown in controlled environments were due to anincrease in the number of sites for ice nucleation, caused bythe presence of the aeciospores, and increased penetration ofice into internal tissues, resulting from damage to the cuticleand epidermis. Although data for frost resistance obtained inthe growth-room are similar to previous field observations,the role of the above mechanisms under field conditions remainsunproven. Senecio vulgaris (groundsel), Puccinia lagenophorae (rust), low temperature, freezing resistance     

The Freezing Response of an Arctic Cushion Plant, Saxifraga caespitosa L.: Acclimation, Freezing Tolerance and Ice Nucleation

Cold hardiness in actively growing plants of Saxifraga caespitosaL., an arctic and subarctic cushion plant, was examined. Plantscollected from subarctic and arctic sites were cultivated ina phytotron at temperatures of 3, 9, 12 and 21 °C undera 24-h photoperiod, and examined for freezing tolerance usingcontrolled freezing at a cooling rate of 3–4 °C eitherin air or in moist sand. Post-freezing injury was assessed byvisual inspection and with chlorophyll fluorescence, which appearedto be well suited for the evaluation of injury in Saxifragaleaves. Freezing of excised leaves in moist sand distinguishedwell among the various treatments, but the differences werepartly masked by significant supercooling when the tissue wasfrozen in air. Excised leaves, meristems, stem tissue and flowerssupercooled to –9 to –15 °C, but in rosettesand in intact plants ice nucleation was initiated at –4to –7 °C. The arctic plants tended to be more coldhardy than the subarctic plants, but in plants from both locationscold hardiness increased significantly with decreasing growthtemperature. Plants grown at 12 °C or less developed resistanceto freezing, and excised leaves of arctic Saxifraga grown at3 °C survived temperatures down to about –20 °C.Exposure to –3 °C temperature for up to 5 d did notsignificantly enhance the hardiness obtained at 3 °C. Whenwhole plants of arctic Saxifraga were frozen, with roots protectedfrom freezing, they survived –15 °C and –25°C when cultivated at 12 and 3 °C, respectively, althougha high percentage of the leaves were killed. The basal levelof freezing tolerance maintained in these plants throughoutperiods of active growth may have adaptive significance in subarcticand arctic environments. Saxifraga caespitosa L., arctic, chlorophyll fluorescence, cold acclimation, cushion plant, freezing stress, freezing tolerance, ice nucleation, supercooling     

Curd Initiation in the Cauliflower: I. JUVENILITY

Hand, D. J. and Atherton, J. G. 1987. Curd initiation in thecauliflower. I. Juvenility.—J. exp. Bot. 38: 2050–2058. Four cauliflower (Brassica oleracea var. botrytis L.) cultivarswere screened for differences in juvenility, measured as thephase of insensitivity to vernalization. Juvenility persisteduntil the initiation of a critical number of leaves which sharplydefined transition to the sensitive, mature form at 13 to 15leaves in cv. Perfection and at 17 to 19 leaves in cv. WhiteFox. Preliminary investigation showed transition in cv. AlphaCliro to occur between 9 and 18 leaves initiated and in cv.Dole after 19 leaves. Leaf number was a stable marker of theend of juvenility in plants grown under different light conditions,whereas time, leaf area and leaf dry weight were not. Leaf numberwas linearly related to log whole shoot dry weight. The rateof leaf initiation in plants of cv. Perfection growing duringthe juvenile phase was approximately one third that of plantsin the mature phase, when measured on a thermal time base. Chilling mature, vegetative plants at 5 °C for 28 d advancedcurd initiation by up to 35 leaves in cv. Perfection; 27 leavesin cv. White Fox; 27 leaves in cv. Alpha Cliro and 21 leavesin cv. Dok, compared with plants grown continuously at 20 °C. Key words: Cauliflower, vernalization, juvenility     

Soybean nitrate reductase activity influenced by manganese nutrition

Nitrate assimilation by soybeans [Glycine max (L.) Merrill cvv.Lee and Bragg] was investigated in plants grown in solutionculture at manganese concentrations of 0, 1.8 and 275 µMand at day-night temperatures of 33–28° and 22–17°C.Manganese deficiency occurred in plants of both cultivars grownat 0 µM Mn; under these conditions, leaf nitrate concentrationincreased in both cultivars and nitrate reductase activity invivo but not in vitro was reduced. High solution Mn (275 µM)produced symptoms of manganese toxicity and reduced nitratereductase activity of both cultivars in vitro but only of Bragggrown at 22–17°C in vivo. A significant interactionbetween cultivars and solution Mn concentration was found forin vitro assays for plants grown at both temperatures; thisinteraction occurred in the in vivo assays for plants grownat 22–17° only. (Received March 20, 1980; )     

The Responses of Leaf Water Potential and Leaf Diffusive Resistance to Abscisic Acid, Water Stress and Low Temperature in Hibiscus esculentus: The Effect of Water Stress and ABA Pre-Treatments

Intact plants of okra (Hibiscus esculentus) were chilled at6°C in the light, and leaf diffusion resistance (LDR) andleaf water potential measured. The response of the LDR of excisedleaves to fresh weight loss and, separately, exogenous abscisicacid (ABA) supply, was also studied at 6°C and 30°C.The influence of two pre-treatments upon these measurementswas studied. The two pre-treatments consisted of the impositionof a period of water stress at 30°C prior to measurement(followed by re-watering) or the spraying of the leaves withABA. It was found that plants that had been grown in a highhumidity environment continuously (designated control plants)had stomata that were very unresponsive to both water loss fromthe leaves and to exogenous ABA at both temperatures (6°Cand 30°C). Chilling the control plants resulted in rapidwilting and concomitant decline in leaf water potential. A pre-treatmentof water stress prior to chilling did not alter or reduce therate of development of chilling injury, nor did the pre-treatmentincrease the responsiveness of stomata at 6°C to water lossor exogenous ABA. However, spraying the leaves with ABA priorto chilling reduced the severity and delayed the onset of chillinginjury. Stomatal response to water stress and exogenous ABAwas increased by the spraying pre-treatment. These results arediscussed in relation to previous studies of the phenomenonof stomatal locking open at low temperature and the effect ofpre-treatments upon the development of chill-resistance. Key words: Water stress, chilling, stomata     

Changes in Auxins in Expanding and Senescent Primary Leaves of Dwarf French Bean (Phaseolus vulgaris)

A bound, unextractable auxin, or auxin precursor, in the primaryleaves of dwarf French bean was converted to a form, probablyindol-3yl-acetic acid, extractable in ethyl acetate, by maceratingleaves in pH 7.5 phosphate buffer and incubating them at 37–38°C for 2 days in the presence of toluene or hibitane. Boilingthe leaves before macerating and incubating them prevented therelease of bound auxin. This bound auxin was also released whenmacerated leaves were hydrolysed with normal potassium hydroxideat 100° C for 2 hours. The amounts of free auxin and tryptophanin senescent primary leaves increased as their bound auxin andchlorophyll decreased. Removing the apical growing region immediatelyabove the node bearing the primary leaves delayed their senescenceand the conversion of their bound to free auxin.     

Shoot--root Plasticity and Episodic Growth in Red Pine Seedlings

Red pine seedlings of a half-sib seed source were grown in growthchambers under thermoperiodic regimes of 30/20 °C, 25/15°C and 20/10 °C day/night temperatures. Classical growthanalyses based on weekly harvests of leaves, stem and rootswere employed to study the first 3 to 15 weeks of seedling development.Leaf and root growth were inversely related and episodic. Significantshort term surges in growth of either organ were effective inreversing periodic imbalances that occurred, thus maintaininga long term dry weight equilibrium between above and below groundseedling parts. Adaptive plasticity in the leaf-root balanceat different temperatures gave plants grown at 25/15 °Ca larger proportion of leaves relative to roots and a greatersize compared to seedlings grown under other regimes. Episodicfluctuations in leaf and root growth occurred simultaneouslywith depressions in net assimilation rate. Apparently, balancedgrowth is maintained at an assimilatory cost to the plant, periodic‘corrections’ of shoot—root imbalances requiringcarbohydrate conversion and energy expenditure. Pinus resinosa Ait., red pine, episodic growth, shoot—root balance, plasticity, net assimilation rate, growth analysis     

Temperature Response of Vernalization in Wheat: A Developmental Analysis

The vernalization response of wheat ( Triticum aestivum L.)was reinterpreted from a developmental perspective, using currentconcepts of the developmental regulation of wheat morphologyand phenology. At temperatures above 0 °C, the effects ofthe process of vernalization per se in wheat are confoundedby the effects of concurrent vegetative development. These effectsare manifested by differences in the number of leaves initiatedby the shoot apex prior to floral initiation, which in turnaffects the subsequent rate of development to ear emergenceand anthesis. Leaf primordia development during vernalizationand total leaf number at flowering were used to develop criteriato define both the progress and the point of saturation of thevernalization response. These criteria were then used to reinterpretthe results of Chujo ( Proceedings of the Crop Science Societyof Japan 35 : 177–186, 1966), and derive the temperatureresponse of vernalization per se for plants grown under saturatinglong day conditions. The rate of vernalization increased linearlywith temperature between 1 and 11 °C, such that the timetaken to saturate the vernalization response decreased from70 d at 1 °C to 40 d at 11 °C. The rate declined againat temperatures above 11 °C, and 18 °C was apparentlyineffective for vernalization. Total leaf number at saturation,however, increased consistently with temperature, as a resultof the balance between the concurrent processes of leaf primordiuminitiation and vernalization. Total leaf number at saturationincreased from 6 at 1 °C to 13.3 at 15 °C, which inturn influenced the time taken to reach ear emergence. The advantagesof using this developmental interpretation of vernalizationas the basis for a mechanistic model of the vernalization responsein wheat are discussed. Triticum aestivum L.; wheat; vernalization; rate; temperature; primordia; leaf number; flowering     

The Effects of Low Growth and Measurement Temperature on the Respiratory Properties of Five Temperate Species

Five temperate ruderal species, Epilobium glandulosum, Matricariamatricariodes, Melilotus alba, Sonchus asper and Taraxacum officinale,were grown under controlled conditions at both 10 °C and20 °C. Respiration was measured at 10 °C and 20 °C.Total dark respiration rates of plants grown at 10 °C wereconsistently higher than the rates of plants grown at 20 °C.This was due to greater respiratory activity along both thecytochrome (KCN-sensitive) and alternative (SHAM-sensitive)pathways in the cold grown plants. The capacity to use the alternativepathway was also greater in the 10 °C grown plants. Theincrease in the relative contribution of each pathway was speciesspecific. At a given growth temperature the activity of thealternative pathway varied little between measurements at 10°C and 20 °C. In contrast, the activity of the cytochromepathway was greater when measured at 20 °C than when itwas measured at 10 °C. The capacity of the alternative pathwaywas lower when measured at 10 °C. These results suggestthat the cytochrome pathway is more sensitive to temperaturestress than is the alternative pathway. Alternative pathway, cyanide resistance, cytochrome pathway, respiration, temperature     

Effects of Low Temperature on the Development and Morphology of Rye (Secale cereale) and Wheat (Triticum aestivum)

Seedlings of Secale cereale cv. Rheidol and Triticum aestivumcv. Mardler were grown at shoot/root temperatures of 20/20 °C,20/8 °C and 8/8 °C. During vegetative growth both cerealsproduced leaves, tillers and roots in a defined pattern, ata species-specific rate which was linearly related to the temperatureof the shoot meristem. Thus, plant development could be standardizedon a temperature x time (°C d) basis despite contrastinggrowth-temperature treatments. When compared at a similar developmentalstage, the cooling of whole plants or of plant roots resultedin an increase in the d. wt: f. wt ratio of both shoot and roottissues, a decrease in the length of both the longest shootand root, and the development of broader and thicker leaves.Although the effects of temperature on developmental characteristicscould be accurately predicted by an empirical relationship,the effects on morphological characteristics could not. Development, phyllochron, rye, Secale cereale cv. Rheidol, temperature, thermal time, Triticum aestivum cv. Mardler, wheat     

The Effect of Low Temperature on Ethylene Production by Leaf Tissue of Phaseolus vulgaris L.

When leaf discs cut from primary leaves of Phaseolus vulgarisL. cv. Masterpiece plants grown at 25°C were incubated attemperatures below 25 °C, basal and wound ethylene productioncontinued at reduced rates. In both cases detectable levelsof ethylene were produced at 25 °C. When the rates of ethyleneproduction were plotted according to the Arrhenius equationa marked discontinuity was found at 11.4 °C which is consistentwith a membrane phase-transition at the critical chilling temperatureof the plant. Activation energies for the rate-limiting enzymereaction in ethylene production above and below the criticaltemperature have been calculated and the data interpreted asindicating the involvement of membrane-bound enzyme systemsin the biosynthesis of basal and wound ethylene. ethylene, temperature, Arrhenius plot, activation energy, Phaseolus vulgaris L., bean     

High Temperature Sensitivity of Auxin-induced Ethylene Production in Mung Bean Hypocotyl Sections

High temperature sensitivities of IAA-induced and 1-aminocyclopropane-1-carboxylicacid (ACC)-dependent ethylene production in etiolated mung bean(Vigna radiata [L] Wilczek) hypocotyl sections were comparedat 30,40, 42.5°C. When ethylene production at 30°C wastaken as control, IAA-induced production at 40°C was firstenhanced and then suppressed after 3 h, whereas ACC-dependentproduction was enhanced two-fold throughout the 8 h experimentalperiod. However, when hypocotyl sections treated with 1 mM ACCat 30°C for several hours were transferred to 40°C,the ACC-dependent production rate fell below that at 30°C.An initial transient enhancement of IAA-induced ethylene productionat 40°C was supported by increased ACC synthase activityand thus by ACC content. At 42.5°C, both IAA-induced andACC-dependent production were almost completely suppressed.The results indicate that auxin-induced ethylene productionis affected by high temperatures in two different steps: a)at 40°C, the auxin action gradually deteriorates althoughconversion of ACC to ethylene is not affected at all, and at42.5°C, the conversion is nearly completely suppressed. (Received July 8, 1985; Accepted January 24, 1986)     

The Effects of Temperature on Leaf Growth in Cyperus longus, a Temperate C4 Species

Plants of the C₄ sedge Cyperus longus L. were grown at 10, 20and 30 °C. An asymptotic growth curve, the Richards function,was fitted to growth data for successive leaves. The mean rateof leaf appearance was a linear function of temperature with0.014 leaves appearing per day for every 1 °C increase intemperature. The instantaneous relative rate of leaf extensionshowed a marked ontogenetic drift which was most rapid at 30°C and slowest at 10 °C. The mean absolute extensionrate for foliage had a temperature coefficient of 0.16 cm d^–1° C^–1 in the range from 10 to 30 °C. The durationof leaf growth was independent of leaf number at 10 and 20 °Cbut increased linearly with leaf number at 30 °C. The smalldifferences in relative growth rate at the three temperaturesresulted in large differences in foliage area produced at theend of a 30 d growth period. The final foliage areas at 20 and10 °C were 51 and 9% respectively of that at 30 °C. Cyperus longus, temperature, leaf growth, Richards function, growth analysis     

Effect of growth temperature on reserve mobilization and hydrolytic enzyme activities in Vigna mungo cotyledons

Seeds of Vigna mungo were allowed to germinate at 27, 18 and15°C, and time-course changes of hydrolytic enzyme activitiesand the mobilization rate of reserve components in cotyledonswere studied. The seeds germinated at 27 and 18°C grew normally,whereas the growth at 15°C was markedly retarded. In cotyledonsof seedlings grown at 27 and 18°C, amylolytic and proteolyticenzyme activities increased at early stages of growth and therates of starch and protein mobilization changed correspondingto the hydrolytic enzyme activities. At 15°C the enzymeactivities increased gradually during the experimental periodof 16 days, but the reserves in cotyledons remained almost unchangeduntil the end of the experimental period. Changes of zymogram patterns of amylolytic and proteolytic activitiesin cotyledons of seedlings grownat 27, 18 and 15°C wereexamined using polyacrylamide gel electrophoresis. The intensitiesof a main band of a-amylase and at least two bands of protease(gelatin-hydrolyzing activity) increased concurrently with invitro activities of amylolytic and proteolytic enzymes. At leastthree bands of starch phosphorylase were present in cotyledonsat early stages of germination and their intensities decreasedduring the growth of seedlings at 27, 18 and 15°C. (Received June 4, 1980; )     

ABA Levels and Effects in Chilled and Hardened Phaseolus vulgaris

Leaf abscisic acid (ABA) levels of chilled P. vulgaris weremeasured after 18 h chilling at 5°C, at a saturation deficitof 1.24 g m^–3 (SD), and after chilling in a water-saturatedatmosphere. Changes were also followed during a chill hardeningperiod of 4 d at 12°C, 2.1 g m^–3 SD. It was foundthat hardening resulted in an almost 5. fold increase in ABAlevels after 3 d at 12°C, and this decreased to approximatelycontrol levels on the fourth day. Subsequent chilling of hardenedplants produced no change in ABA levels from that of controlplants (22° C). In contrast, non-hardened plants chilledat 1.24 g m^–3 SD had ABA levels almost 3 times the levelof control plants. However, chilling in a water-saturated atmosphereresulted in a decrease in ABA levels. In addition, the response of leaf diffusion resistance (LDR)to exogenous ABA fed via the transpiration stream was measuredat 5 ° C and 22° C in hardened and non-hardened plants.Use of tritium-labelled ABA was made to calculate the stomatalsensitivity to ABA. It was found that exogenous ABA caused anincreased in LDR at 22°C in both hardened and non-hardenedplants. However, the sensitivity of the hardened plants to ABAwas greater in terms of rate of closure and amount of ABA requiredto close the stomata. At 5°C, however, ABA caused stomatalopening and the maintainance of open stomata in non-hardenedplants. In hardened plants, ABA caused stomatal closure at 5°C.These results are discussed in relation to the locking-openresponse of chilled P. vulgaris stomata. Key words: Chilling, Stomata, ABA, Phaseolus vulgaris     

Growth Hormone Changes in Chrysanthemum morifolium: Effects of Environmental Factors Controlling Flowering

Simultaneous quantitative analyses have been made of the endogenouslevels of auxin- and gibberellin like substances, growth inhibitors,and auxin-oxidizing enzyme activity in the cold-requiring Chrysanthemummorifolium cv. Sunbeam subjected to different daylength, lightintensity and temperature regimes known to affect flowering.While little hormone or enzyme activity was found in extractsfrom unvernalized plants, a striking rise in auxin-oxidizingenzyme activity occurred rapidly after the end of cold treatment.Increased auxin activity was also recorded shortly after vernalization.At 28 °C both enzyme and auxin activity declined over aperiod of 3–4 weeks; at 20 °C this response was delayed.Gibberellin activity at 28 °C rose steeply about 2 weeksfrom vernalization and declined several weeks later; at 20 °Ca similar response was less marked. Low light intensity treatment,which may have increased endogenous auxin levels, or exogenousauxin application reduced gibberellin-like substance levelsand cause d devernalization.Phosphon D treatment also loweredgibberellin levels and prevented flowering. An extract fromvernalized plants containing gibberellin-like substances intensifiedthe flowering of partially vernalized test plants. Persistenceof high auxin activity in vernalized plants on long days wasassociated with failure to form normal flower buds. Stem elongationrates correlated in general with levels of endogenous auxin-and gibberellin-like substances. Significant amounts of an abscisin-likeinhibitor were found in extracts of flower buds. The mechanismof natural devernalization is discussed in relation to theseobservations.     

Low Temperature-induced Accumulation of Protein is Sustained both in Root Meristems and in Callus in Winter Wheat but not in Spring Wheat

Plant growth was assessed and cellular protein per nuclear DNAamount measured in root meristems and in callus derived fromembryos of a spring (‘Katepwa’) and a winter variety(‘Beaver’) of allohexaploid wheat exposed to lowtemperature treatment. The data obtained were used to test whetherthese genetically distinct varieties of wheat responded differentiallyto cold treatment. Seedlings were grown for 14 d at 20°Cand then transferred to 4°C for 14 d before returning themto 20°C, or else were maintained continuously at 20°C.In winter wheat, root growth at 4°C was significantly greaterover the first 7 d following transfer to 4°C compared withplants retained at 20°C, whereas in spring wheat it wasreduced at 4°C. The pattern of accumulation of cellularprotein for both root meristem cells and in callus cells wasalso generally enhanced at 4°C compared with 20°C inwinter wheat but not in spring wheat. Thus, clear inter-varietaldifferences were established both for dry weight accumulationand cellular protein, and the callus data clearly show thatthe low-temperature-induced accumulation of protein is a cellularphenomenon not necessarily linked to development. The extentto which cold-shock proteins are a component of this low temperature-inducedincrease in cellular protein is discussed. Copyright 2000 Annalsof Botany Company Protein, spring wheat, temperature, tissue culture, Triticum aestivum, winter wheat