Photoperiod and Temperature Effects on Late Developmental Stages of Stylosanthes guianensis

Seedlings of Stylosanthes guianensis var. guianensis cv. Cookand S. guianensis var. pauciflora cv. Bandeirante were defoliatedand placed in a naturally lit glasshouse at 23/18 °C, 28/23°C or 33/28 °C (day/night). After exposure to 14 h daysand after floral induction with 30 cycles of 11 h, plants wereallocated to 11, 12, 13 or 14 h during flowering and seed formation. Floral initiation occurred after 10–15 short-day cycles.Flower appearance was hastened by warm temperatures and spikenumber per plant at 20 d after flower appearance was negativelyrelated to temperature and greater in Cook than in Bandeirante.Exposure to 13- and 14-h days reduced the continued differentiationof inflorescences in Bandeirante, and in Cook in warm temperatures.Floret number per spike was greatest at 23/18 °C and a higherproportion of florets aborted in Bandeirante at 33/ 28 °C.Variations in seed setting of the bi-articulate loment of Bandeiranteare described. Highest potential seed yield occurred if afterfloral induction 11 or 12 h days were maintained with 23/18°C or 28/23 °C temperatures. Photoperiod, temperature, development, Stylosanthes guianensis, flowering     

Temperature response and flowering of white clover (Trifolium repens) varieties in controlled environments and the field

Floral initiation of 10 white clover varieties growing in three controlled day/night temperature regimes, 22“/10°C, 20°/10°C, 17°/10°C, was recorded. Effects of artificial soil heating on floral initiation of the same plants subsequently transferred to the field were also examined. In the controlled environments only a slight increase in day temperature (2–5°C) was necessary to significantly increase flowering. Defoliation at the three temperatures had contrasting effects on subsequent flower production. Results from the soil heating experiment suggested that increased temperature might compensate for short daylengths, by bringing forward reproductive bud initiation by 1 month. Soil heating increased the total number of inflorescences produced.     

Effect of Diurnally Fluctuating vs. Constant Temperatures on Flower Induction and Sex Expression in the Olive (Olea europaea)

Olive trees must be exposed to a period of winter chilling temperatures in order to form inflorescences the following spring. The effects of diurnally fluctuating and constant temperatures on flower induction and sex expression in the olive were compared under controlled environment conditions. The effect on flowering of diurnally fluctuating temperatures depends upon the length of time at the higher temperatures. While daily exposure to the high temperatures (21° to 26°C) for a short period (four hours) intensified the effectiveness of the low temperatures (7° to 12.5°C), when the high temperature duration was 12 hours it counteracted the low temperature action. Possibly, daily low temperatures act to stimulate reactions leading to floral hormone synthesis, while daily short exposures to high temperatures act to maintain metabolic activity, promote energy-yielding reactions, and possibly stimulate cell-division activity. In the olive, an intermediate constant temperature (12.5°C) favors both types of reactions and induces flowering; however, in this case, the pistils fail to develop. The olive has very specific temperature requirements for flowering and neither the mean temperature nor the accumulated number of hours below a given value, e.g. 7°C, adequately characterizes these requirements.     

Flowering of Contrasting White Clover Varieties in Relation to Temperature in Controlled Environments

Effects of temperature on floral initiation of ten white clovervarieties growing in controlled environments are described.Plants grown under long days (16 h) were subjected to constanttemperatures of 26, 18 and 10 ^°C. Relationships betweenmorphological and physiological traits and flowering were examined. Most plants flowered at the two higher temperatures but only10 per cent of plants flowered at 10 ^°C. Larger leaved typestended to produce more reproductive buds per stolon at the highertemperatures than did smaller leaved varieties. Of the floral characters studied, floret number was least affectedby temperature. Ovule number and peduncle length were greatestat 18 ^°C. Variation in, and absolute level of nectar secretionwas greatest at the highest temperature. Trifolium repens, white clover, flowering, temperature     

Floral Initiation of Upland Cotton Gossypium hirsutum L. in Response to Temperatures

The effect of germination temperature, duration of high-intensitylight, and day temperature in modifying the influence of nighttemperature on the flowering process of the M-8 strain of Uplandcotton was examined. In general, night temperatures above 28°C caused the first floral branch to be formed at a higher node.The magnitude of the reaction was conditioned by the other environmentalfactors studied. Germination temperature had a slight but significanteffect on subsequent floral responses to night temperature.Plants given eight-hour periods of high-intensity light eachday were delayed more by high night temperature than those exposedto 14 or 24 hours of high light. At high day temperatures (28–32°C) the inhibiting influence of the high night temperature wasgreatly increased. High day temperatures delayed floral initiationif the night temperature was high (28–32°C) but causeda lowering of position of first floral branch when the nighttemperature was low (20–22°C). The enhancement offlowering by 32°C days and 22°C nights was expressednot only in the low node of first floral branch, but also inthe shorter time from planting to floral initiation.     

Photoperiod and Temperature Regulation of Floral Initiation and Anthesis in Soya Bean

Floral development includes initiation of floral primordia andsubsequent anthesis as discrete events, even though in manyinvestigations only anthesis is considered. For ‘Ransom’soya bean [Glycine max (L.) Merrill] grown at day/night temperaturesof 18/14, 22/18, 26/22, 30/26, and 34/30 °C and exposedto photoperiods of 10, 12, 14, 15, and 16 h, time of anthesisranged from less than 21 days after exposure at the shorterphotoperiods and warmer temperatures to more than 60 days atlonger photoperiods and cooler temperatures. For all temperatureregimes, however, floral primordia were initiated under shorterphotopenods within 3 to 5 days after exposure and after notmore than 7 to 10 days exposure to longer photoperiods. Onceinitiation had begun, time required for differentiation of individualfloral primordia and the duration of leaf initiation at shootapices increased with increasing length of photoperiod. Whileproduction of nodes ceased abruptly under photoperiods of 10and 12 h, new nodes continued to be formed concurrently withinitiation of axillary floral primordia under photoperiods of14, 15 and 16 h. The vegetative condition at the main stem shootapex was prolonged under the three longer photoperiods and issuggestive of the existence of an intermediate apex under theseconditions. The results indicate that initiation and anthesisare controlled independently rather than collectively by photoperiod,and that floral initiation consists of two independent steps—onefor the first-initiated flower in an axil of a main stem leafand a second for transformation of the terminal shoot apex fromthe vegetative to reproductive condition. Apical meristem, intermediate apex, floral initiation, anthesis, photoinduction, Glycine max(L.) Merrill, soya bean, photoperiod, temperature     

Differential responses of Arabidopsis ecotypes to cold, chilling and freezing temperatures

Arabidopsis plants show an increase in freezing tolerance in response to exposure to low nonfreezing temperatures, a phenomenon known as cold acclimation. In the present study, we evaluated the physiological and morphological responses of various Arabidopsis ecotypes to continuous growth under chilling (14°C) and cold (6°C) temperatures and evaluated their basal freezing tolerance levels. Seedlings of Arabidopsis plants were extremely sensitive to low growth temperatures: the hypocotyls and petioles were much longer and the angles of the second pair of true leaves were much greater in plants grown at 14°C than in those grown at 22°C, whereas just intermediate responses were observed under the cold temperature of 6°C. Flowering time was also markedly delayed at low growth temperatures and, interestingly, lower growth temperatures were accompanied by longer inflorescences. Other marked responses to low temperatures were changes in pigmentation, which appeared to be both ecotype specific and temperature dependent and resulted in various visual phenotypes such as chlorosis, necrosis or enhanced accumulation of anthocyanins. The observed decreases in chlorophyll contents and accumulation of anthocyanins were much more prominent in plants grown at 6°C than in those grown at 14°C. Among the various ecotypes tested, Mt‐0 plants markedly accumulated the highest levels of anthocyanins upon growth at 6°C. Freezing tolerance examination revealed that among 10 ecotypes tested, only C24 plants were significantly more sensitive to subzero temperatures. In conclusion, Arabidopsis ecotypes responded differentially to cold (6°C), chilling (14°C) and freezing temperatures, with specific ecotypes being more sensitive in particular traits to each low temperature.     

Effects of temperature and photoperiod on flowering in Hyptis brevipes

Few tropical species have been tested for their flowering response under controlled conditions. Hyptis brevipes Poit, is an annual herb, commonly found in wet margins of streams and ponds, being considered a weed for some perennial plantations in Brazil. Under experimental glasshouse conditions, this species proved to be an obligate short-day plant. Flowering was delayed when photoperiods longer than 8 h were given, the critical photoperiod being between 12 and 13 h. When both temperature and photoperiod were controlled, at 20°C a longer protoperiod (by almost 1 h) is still inductive compared to 25 and 30°C. The number of short-day cycles required for full induction is relatively high and dependent upon temperature; at 20°C or above, 10 cycles are adequate, but at 15°C, more short-day cycles are needed. The number of inflorescences formed as well as the floral index vary according to daylength × temperature × inductive cycle number, allowing flowering to be assessed quantitatively. Long days are inhibitory to flowering, either suppressing it completely (when symmetrically intercalated among 24 inductive cycles) or preventing the floral index from increasing.     

Inflorescence commitment and subsequent development differ in their responses to temperature and photoperiod in Osteospermum jucundum

Although Osteospermum is a species which is known to require a period of chilling to induce flowering, the precise form of the relationships between temperature and photoperiod on the phases of flowering has not been quantified. This study aimed to investigate the effects of temperature and photoperiod on time to inflorescence commitment and on the rate of subsequent floral development in Osteospermum jucundum cv. Zulu. To assess how temperature and photoperiod affected the number of days needed for inflorescence commitment, plants were transferred from a range of photothermal environments to a non‐inductive environment. The effect of temperature and photoperiod on subsequent inflorescence development was examined by transferring plants with initiated inflorescences to a range of photothermal environments. Inflorescence commitment occurred first in plants grown at a low average diurnal temperature (10.6°C), but no evidence was found to suggest that photoperiod affected the duration of this phase. Once initiated, high temperatures and long days hastened inflorescence development. The rate of progress to flowering from initiation increased linearly with photoperiod and temperature (up to an optimum of 23.5°C).     

Is the threshold size for flowering in Cynoglossum officinale fixed or dependent on environment?

In the monocarpic perennial Cynoglossum officinale L. the probability of flowering is related to the size of the plant. In previous work it was observed that this relation varies between years. We hypothesized that variable conditions during the winter, the period of vernalization, explain this variation.
We collected plants from the field in autumn and placed these under different simulated winter conditions in a climate room. In contrast to our hypothesis, the probability of initiating flowering at a given size was not affected by: ( a ) the temperature during the cold period, ( b ) the duration of the cold period, or ( c ) the application of a plant hormone (GA₃) or an inhibitor of gibberellin synthesis (paclobutazol) during the cold period. Winter cold is not necessary for floral initiation, and is only required for elongation of the inflorescence. It is unlikely that winter temperature affects the fraction of plants flowering.
Subsequent morphological investigation of flower development in material collected in the field showed that large plants had primordial inflorescences well before vernalization, sometimes as early as August. In plants grown from seeds under constant conditions in a climate room, the probability of initiating the inflorescence differed for plants grown at various temperatures (34·1% at 15°C, 100% at 20°C, and 95% at 25°C). Our results suggest that environmental conditions in August and September, up to 10 months before actual flowering, could affect the fraction of flowering plants.     

Time of sowing and temperature effects on the flowering of Stylosanthes guianensis

Seedlings of Stylosanthes guianensis var. guianensis cv. Cook and of two selections of S. guianensis var. pauciflora (CIAT 1280 and CIAT 1062) were grown at day/night temperatures of 20°/25°, 30°/25°, and 35°/30°C in a naturally-lit glasshouse at latitude 27°30'S. Sowings were made in decreasing daylength at 30-day intervals from 22 January to 21 May. Cv. Cook and the CIAT 1280 selection did not flower fully if sown after 22 January and the CIAT 1062 selection did not flower if sown after 22 March. This is interpreted as a long-short day flowering response. Usually, flowers were initiated earlier and at a lower node at 25?/20°C than at the warmer temperatures. At 25?/20°C the first flowers to appear were produced predominantly at the terminal apex of the main stem in cv. Cook and the CIAT 1062 selection, but not in the CIAT 1280 selection. At the two warmer temperatures first flowers were more commonly produced at the terminal apex of primary, secondary and tertiary branches. There were more inflorescences per plant on earlier than later sown plants when measured 21 days from appearance of the first flower and the most inflorescences were produced by cv. Cook at 25?/20°C, by selection CIAT 1062 at 30°/25°C, and by CIAT 1280 at 35°/30°C.     

Dual induction control of flowering in Leucanthemum vulgare

The perennial herb Leucanthemum vulgare (oxeye daisy) has a dual induction requirement for flowering. The primary induction is a typical low temperature vemalization response. Temperatures up to 15°C are effective, and the optimum is 6–9°C. Short days (SD) during low temperature exposure enhanced primary induction, but SD could not fully substitute for low temperature in primary induction. At optimum temperatures about 6 weeks exposure were required for 100% flowering, but the flowering response increased with increasing exposure up to 12 weeks, especially at higher temperatures. Seedling have a short juvenile phase of about 4 weeks. Populations with origin ranging from 59 to 69°N in Norway did not vary in their primary induction requirements. Long days (LD) were required for inflorescence initiation and stem elongation at 9°C. At 21 and 15°C some plants initiated and developed inflorescences in SD, but the inflorescences were sessile and their development strongly delayed. More than 16 LD cycles were required for normal stem elongation (bolting).     

Influence of day length and temperature on number of main stem leaves and time to flowering in lupin

A growth chamber experiment was carried out to investigate the influence of day length and temperature on the development of flowering in eight varieties of the three grain lupin species Lupinus albus (Wat and C3396), L. angustifolius (Gungurru, Polonez and W26) and L. luteus, (Juno, Radames and Teo). The plants were grown at two temperatures, 10°C and 18°C, in combination with five daylength regimes: 10, 14, 18, 24 h day at full light intensity and 10 h full light extended with 8 h low intensity light. Increased daylength decreased days from sowing to flowering in all varieties, but had little effect on thermal time to flowering in most varieties. However, C3396, W26 and Radames had a significantly longer thermal time to flowering at high, non‐vernalising temperature (18°C) at short daylengths. Low light intensity daylength extension did not significantly influence thermal time to flowering. For flower initiation, measured as number of leaves on the main stem three types of response were found. All varieties formed fewer leaves on the main stem at 10°C than at 18°C, although the two thermo‐neutral varieties of L. luteus, Juno and Teo, gave only a small response to temperature and daylength. In Polonez, Gungurru and Wat, low temperature decreased leaf number, but there was only a small response to changes in daylength. Three varieties, C3396, W26 and Radames, showed longer thermal time to flowering at 18°C with short daylengths. This could be explained by a greater number of main stem leaves formed at short daylength at non‐vernalising temperatures. Increased daylength decreased leaf number in these varieties, but never to a smaller number than for plants grown at 10°C. In these varieties, low intensity extension of the daylength had a similar (W26, Radames) or decreased (C3396) effect compared to full light extension. The hastening of time to flowering by long days could be separated into two effects: a high light energy effect hastened development by increasing the rate of leaf appearance in all varieties, while low light energy in thermo‐sensitive varieties was able to substitute for vernalisation by decreasing leaf number.     

Reproductive Anatomy of the Grape-vine (Vitis vinifera L.): Origin and Development of the Anlage and its Derivatives

The origin and development of anlagen (undifferentiated primordia),inflorescences, tendrils and flowers in the grape cv. Shirazhas been investigated by scanning electron microscopy. Anlagenarise terminally by bisection of the apex of the so-called latentbud. The axis of the latent bud is continued by the originalapex and anlagen are displaced laterally. Micrographs presentedhere favour the interpretation of the grape-vine shoot as amonopodium. Anlagen formed distal to the 10th node of container grown vinesformed inflorescence primordia when plants were grown at hightemperatures (33°C day-28°C night). At lower temperatures(21°C day, 16°C night or 18°Cday, 13°C night)anlagen formed distal to the 10th node grew into tendril primordia.At basal nodes anlagen gave rise to shoot primordia. Each branchof the highly-divided inflorescence primordium of Shiraz formsfive flower primordia. Flower development is discussed.     

Effects of temperature and nitrogen supply on the growth of timothy (Phleutn pratense L.)

Timothy was grown in controlled environments with day/night temperatures of 18.5/10° C. and 29.5/21° C, with and without extra nitrogen. High temperatures hastened all stages of development after inflorescence initiation. Anthesis occurred after 48 days when N was added and after 52 days without N. Anthesis did not occur until after 68 days at the lower temperatures, with or without N. Largest yields of leaves, stems and stubble were produced at all growth stages at the lower temperatures with N. This treatment gave the highest crop growth rate, which increased almost linearly with time. The lower temperatures with N gave many more and longer stems and more inflorescences than any other treatment. With N and high temperatures, there was no increase in crop growth rate after inflorescence emergence. Temperature had little effect on growth when no N was provided. With no added N, crop growth rate was retarded and increased very little after inflorescence initiation. Herbage produced at high temperatures had the lower percentages of water-soluble carbohydrates and digestible dry matter, but had the higher percentages of most minerals. N increased the percentage content of most minerals. Weights of stubble and of water-soluble carbohydrates in the stubble, and the numbers of stem bases and tillers, were larger at the lower temperatures, and were usually larger with added N in both temperature regimes. Nitrogen decreased the percentage content of carbohydrates in the stubble. Large haplocorms were produced at the low temperatures, but none developed at the high temperatures, indicating less carbohydrate storage. The results partly explain the vigorous growth of timothy in the cool, temperate regions of Europe and North America, and the small dry matter production, lower nutritional value of the herbage, and lack of persistence in the warm southern regions where rainfall is adequate.     

Flowering in Xanthium strumarium: INITIATION AND DEVELOPMENT OF FEMALE INFLORESCENCE AND SEX EXPRESSION

Vegetative plants of Xanthium strumarium L. grown in long days were induced to flower by exposure to one or several 16-hour dark periods. The distribution of male and female inflorescences on the flowering shoot was described, and a scoring system was designed to assess the development of the female inflorescences. The time of movement of the floral stimulus out of the induced leaf and the timing of action of high temperature were shown to be similar for both the apical male and lateral female inflorescences.     

High temperature arrest of inflorescence development in broccoli (Brassica oleracea var. italica L.)

High temperature causes unevenly-sized flower buds on broccoli inflorescences. This deformity limits production of broccoli to areas where summer temperatures rarely exceed 30 C. The stage of development sensitive to heat was determined by exposing plants of 'Galaxy' broccoli at varying developmental states to 35 C day temperature for 1 week, and subsequently analysing the head structure. During the high temperature exposure, the development of certain flower buds was arrested. There was no corresponding cessation of bud initiation at the apex. No injury resulted if heat was applied before the reproductive induction, or was their injury to differentiated flower buds. Meristems were affected only if heat was applied during inflorescence production or the floral initiation process. Shorter heat exposures produced little injury, and longer exposures were lethal. The plant's development at this sensitive period still appeared vegetative externally, but the youngest leaves had just begun to reorientate as a consequence of the reduced stem elongation rate. The meristem was less than 1 mm wide, and floral primordia were just forming, still subtended by leaf primordia. The injury was fully expressed by the time the head was first exposed (approximately 5-10 mm wide), though it became more apparent as the head matured. The buds that were delayed in development by the high temperature developed into normal flowers.Key words: Brassica oleracea, broccoli, flowering, heat injury, developmental arrest      

Effects of extended and repeated exposures to low temperature on mortality of the peach-potato aphid Myzus persicae

Abstract.

• 1 The survival of adult and first-instar Myzus persicae reared at 20°C and 10°C was investigated after brief (1 min) exposure in the absence of plant material to temperatures between −5°C and −25°C, and extended exposures on plants of 1–10 days at a constant 5°C, 3°C and −5°C and a 24 h cycling regime between 5°C (18 h) and −5°C (6 h).
• 2 Life stage, rearing temperature, period of exposure and temperature regime all had a significant effect on the ability of aphids to survive cold. The effects of life stage and rearing temperature were most noticeable following exposure to cycling temperatures and extended exposures at −5°C, and least apparent after 1 min exposures at lower sub-zero temperatures.
• 3 Mortality following exposure to temperatures cycling between −5°C and 5°C was greater than that at 3°C (the mean of the cycling temperatures) and less than at a constant −5°C, suggesting that when temperatures fluctuate by a few degrees around 0°C the minimum temperature may affect survival to a greater extent than the mean.
• 4 These results suggest that an overwintering population of acclimated M.persicae would persist without significant mortality after a period of 7–10 days with −5°C frosts each night.

     

Factors Affecting Flower Abortion and Malformation in Roses

The formation of blind shoots and malformed flowers in rose plants grown under various temperatures and light intensities, and subjected to different cut back procedures has been studied. Low temperature, low light intensity and low cut back promoted blind shoot formation. Hybrid tea cultivars are more sensitive for unfavourable temperature, light and cut back treatments than Floribunda cultivars. The process of floral abortion is initiated during the early stages of shoot growth before the differentiation of floral parts has been completed. Low temperatures (12–15°C) in this critical stage of development strongly promote blind shoot formation, but have no effect when stamen and pistil primordia had been formed in the apical flower bud. The formation of malformed flowers, so-called “bullheads”, which have significantly more petals than normal flowers, is also promoted by low temperature and low cut back. Light intensity seems to have no effect. Shoots subjected to low temperature (12°C) during the early stages of development, before the differentiation of the floral organs are fully completed, produce malformed flowers to a greater extent than shoots subjected to high temperature (18–24°C) during this period. It is suggested that blind shoot formation in roses is subject to hormonal control.     

Photosynthetic Rates, Gross Patterns of Carbon Dioxide Assimilation and Activities of Ribulose Diphosphate Carboxylase in Marine Algae Grown at Different Temperatures

Studies of the marine green flagellate Dunaliella tertiolecta have confirmed and extended previous observations of Steemann Nielsen and his colleagues. Algae, grown at 12°C, assimilated carbon dioxide under light-saturated conditions more rapidly than did those grown at 20°C; for both, the assimilation rate being higher at 20°C than at 12°C. Cells grown at the lower temperature contained higher concentrations of soluble protein, higher activities of ribulose diphosphate carboxylase and showed an enhanced relative rate of protein synthesis during the photosynthetic assimilation of carbon dioxide. This appears to represent true adaptation since it allowed the growth rate at 12°C to be almost the same as that at 20°C. Studies of the marine diatom Phaeodactylum tricornutum have not revealed the same picture of temperature adaptation. Cultures grown at 5°C had significantly higher rates of photosynthesis than did those grown at 10°C, but the same was not true when algae grown at 10°C were compared with those grown at 20°C. In this organism, growth at the lower temperatures reduced its ability to photosynthesize at 20°C. Cells grown at the lower temperatures contained more protein than did those grown at 20°C; this was particularly marked in cells growing at 5°C, a temperature which reduced the growth rate. The relative rate of protein synthesis was higher in Phaeodactylum grown at lower temperatures; but this difference was most marked when the measurements were made at 20°C.