Photoperiodism in Relation to Hormones as Factors in Floral Initiation and Development

The regional and geographical adaptation of strawberry varieties is known to be influenced by day-length and temperature. As DARRow and WALDO (3) have shown, the ordinary varieties of strawberries are short-day plants, initiating flower buds when the light period per day approximates 10 hours or less. According to DARROW (2), temperature exerts a modifying influence on the response of the strawberry to the photoperiod.In this investigation the response of the strawberry to certain temperature and day-length treatments was studied under controlled environmental conditions. The strawberry is well adapted for use in studies of this kind as it is known to have definite photoperiodic responses which are influenced by temperature. These responses are judged by criteria that are definite and easily measured; namely, the formation of flower clusters when the plant is in the reproductive state and the production of runners when it is in the vegetative condition. In addition the strawberry can be propagated vegetatively by runners, thereby furnishing plant material of the same genetic constitution for experimental treatment.The equipment used in the present investigation consisted of a set of four environment-control cabinets, described in detail by HARTMANN and Mc- KINNON (5). With these cabinets the temperature could be maintained at desired levels by electric heaters and refrigeration units, both thermostatically controlled. The plants were grown under banks of fluorescent lamps, which maintained a light intensity of about 500 foot-candles at the level of the plants. The day-lenath conditions could be adjusted at will and were automatically maintained by a time switch. Methods and resultsTo test the response of the Missionary strawberry to short and long light periods under the controlled environmental conditions used in this investigation a preliminary experiment was carried out. Twenty plants of this variety, which had been growing in long days and were definitely in a vegetative state, were placed in the cabinets on July 9, 1942. Ten plants were maintained under "short-days" (10 hours) and ten were put under "long days" (15 hours). They

“…A 28-hour photoperiodic cycle (14 hours light and 14 hours darkness) did cause runner production. 4. Flowers were formed under both the 20-and the 28-hour photoperiodic cycle.…”

Section: Strawberrymentioning

confidence: 99%

Some Effects of Temperature and Photoperiod on Flower Formation and Runner Production in the Strawberry

Hartmann

1947

“…Whereas light is often referred to as the most important environmental factor 'setting the clocks' for biorhythmic activities, the length of the dark periods may be equally important in determining if light is to have its maximal effect. This has long been known to be true for the flowering response (18).…”

Section: Resultsmentioning

confidence: 89%

Growth, Pigment Synthesis, and Ultrastructural Responses of Phaseolus vulgaris L. cv. Blue Lake to Intermittent and Flashing Light

Naylor¹,

Giles²

1982

Growing bean plants (Phaseolus vulgaris L. cv. Blue Lake) on cycles of 1 minute light-I minute dark or 5 minutes light-5 minutes dark, providing an integrated 12 hours light-12 hours dark per day for each set of plants, led to production after 21 days of new leaves low or lacking in chloroplast pigments. Subsequently, dry weight increase was sharply cut. Leaf area was affected by the light regimes after the second week of growth. By the fourth week, plants on the 1 minute light-I minute dark cycle showed about one-half the leaf area of the controls. Shoot growth was favored over root growth to the greatest degree on the 1 minute light-I minute dark regimes. Chlorophyll a/b ratios were close to 3.0 in all of the intermittent light regimes, but the total amounts of chlorophyll in milligrams per primary leaf were higher from day 9 to day 23 for the 12 hour light-12 hours dark controls than for other plants.Although they produced chlorophyll, the plants receiving 1 or 2 milliseconds per second of light continued to lose weight at the same rate as the dark controls; thus, it is assumed there was no net photosynthesis. Plants receiving flashing light allocated significantly more food reserves from the seed to roots than did dark controls. Total chlorophyll formation was significantly accelerated by 2 milliseconds per second light. With 1 millisecond per second light, it took 5 days longer to achieve the same level of chlorophyll. After the 18th day, there was a steady decline in chlorophyll, b degrading more rapidly than a.It is thought that several light-driven reactions are involved in the observed pigment synthesis, photosynthesis, food allocation, and growth of bean. Some of these reactions may be cyclic and others linear. Collectively, they must reach-harmonic point for normal metabolism and development to occur. Because fnte courses for each of these reactions are different, the intermittent and flashing-light technique offers the possibility of individually studying some of the key light-diiven renctious.When plants are exposed from shortly after germination to maturity to equal alternations of artificial light and darkness of seconds, minutes, and hours as compared with 12-h alternationsthe integrated total time of illumination remaining constantdramatic differences in height, coloration, and reproductive behavior have been noted (12, 13). Growth was progressively poorer 'This paper is dedicated to the memory of Dr. William S. Hillman, former student of A. W. Naylor and respected colleague.

“…In addition, thin section,s of these iron-treated Xanthium leaves have heavy clusters of ferritin within their plastids (unpublished data). Xanthium pensylvanicuin being a short day plant, can be induced to initiate floral primordia after exposure to one long dark period (7). Biochemical changes of flowering induction are associated with iron demand (18).…”

Section: Discussionmentioning

confidence: 99%

Iron Content and Ferritin in Leaves of Iron Treated Xanthium pensylvanicum Plants

Seckbach

1969

Abstract. Iron administration to iron-starved cocklebur (Xanthium pensylvanicum) plants causes an increase in the iron content of ferritin fractions extracted from mature leaves. Xanthium plants grown under long days (vegetative stage) have more iron and ferritin than similarly iron-treated plants induced to flower under short day regimes. This first demonstration of ferritin in cocklebur (Compositae) leaves suggests that a substantial portion of iron that enters the iron-starved plant appears as this protein-iron macromolecule.Plant ferritin (phytoferritin) is a protein-iron complex closely resembling ferritin from other sources; it is located within the plastids and chloroplasts in regions not occupied by the thylakoid system. Most of the phytoferritin studies and observations in higher plants (3. 12, 15, 19) Recovery of iron-chlorotic plants by application of iron has been known for over a century (6) but as yet the role of iron or its function in deficient plan,ts remains uncertain and vague (14). Seckbach (16) has shown that iron supply to iron-chlorotic bean plants results in the deposition of ferritin in the plastids and chloroplasts of the mature green leaves. The uptake of iron compounds is associated with ferritin formation also in mammalian tissues (4,8, 13 fraction was determined by absorption spectra in the ultraviolet region (Fig. 2) Fig. 3 and 4 respectively. These fractions were extracted from leaves harvested from plants grown under long day regimes in liquid cultures which contained 0 to 20 ug Fe per ml nutrient solution. In general the more iron supplied in the media, the higher the leaf iron content (Fig. 3). The iron level of the iron-treated leaves is higher than the control among all fractions ( Fig. 3 and 4). The amoutnt of iron in the treated plants (Fig. 3 ) is abotit 12 to 15-foldIhigher at lowk,er Fe levels (5 and 10 1ug) in ntutrient solution, tflall in tIle conitrol planlts, and(l only 9-fold higher at 2 ) jug fe/nml level. Fig. 4 represents the iron content of the ferritin fraction. Iron level within the nutrient solution and the ferritin iron detected from leaf extracts are less correlated than the previous fractions (Fig. 3) might have affected this accumulation. Xanthiurn being a short-day plant will flower when the dark period exceeds 8 hr with accompanying light periods of shorter than 15 hr (7). Table I gives the actual amount of iron from Xanthiumit plants grown under 16-hr (long days) and 10-hr (short days) photoperiods from 3 fractions. Both the total and the relative ratios (over the 5 p,g/ml control) of iron content determined from ferritin fraction,s (PPT.-RNase, PPT3) were twice as concentrated in the plants grown under long days (16 hr photoperiods).