Number Of Short Days Research Articles

Comparison of Photoperiodic Sensitivity of Green-Leafed and Red-Leafed Perilla

The flowering responses of Perilla frutescens (L.) Britt. (green-leafed Perilla) and P. crispa (Thunb.) Tanaka (red-leafed Perilla) to different 24-hour photoperiodic regimes were compared quantitatively. Although both taxa are short-day plants, P. frutescens was less strict in its short-day requirement, forming macroscopically visible inflorescence primordia and open flowers even in continuous light after 77 to 85 and 132 days, respectively, compared to 12 and 22 days in 8-hour days. P. crispa took only 4 days longer to reach the same stages in 8-hour short days, but exhibited a sharply defined critical day-length between 14 and 16 hours. Two-hour light-breaks in the middle of a 16-hour night were more effective in inhibiting floral development in P. crispa than in P. frutescens, for which they had a small effect compared to true long-days, particularly on the formation of inflorescence primordia. The number of short days needed to obtain the flowering in P. frutescens plants raised in continuous light decreased in a linear manner with the age of the plants upon transfer to short days.

Effect of Number of Photoperiodic Cycles on Flowering and Fruiting in Early and Late Varieties of Okra (Abelmoschus esculentus (L.) Moench.)

Early and late varieties of the short day plant, Abelmoschus esculentus (L.) Moench. (= Hibiscus esculentus L.), were subjected to various numbers of short days (SD; 10 h natural daylight) before transfer to 16 h long days. Short day treatments were started at the time of cotyledon release following seed germination, and their effects on the induction and development of flowers and fruits were recorded. While early okra required 6 SD cycles for the induction of flowering in all plants, late okra required 14. However, both varieties needed more than 20 SD cycles for flower opening; flower buds produced by plants given fewer SD cycles abscinded with little or no development. In both varieties, the number of flower buds produced on each plant increased as the number of short day cycles was increased from 5 to 20; flower buds were initiated at more axillary bud sites on the main stem. Three fruits were formed on each plant of both varieties subjected to more than 30 SD cycles but, while the last formed fruit abscinded without development, the other two developed and became filled with seeds. However, the greatest yield in fruit dry weight was from plants kept under SD throughout and also in late okra plants given 55 SD. In general, the total number of seeds per plant increased as a larger number of SD cycles were imposed.

Shoot, Stolon, and Tuber Formation on Potato (Solanum tuberosum L.) Cuttings in Response to Photoperiod

The intensity of "tuberization stimulus" in potato shoots (Solanum tuberosum L.) can be assessed from cuttings containing one or more leaves. Cuttings maintained in a mist chamber under long days will form tubers from underground buds if prior to taking the cutting the leaves received sufficient exposure to photoperiods less than the critical photoperiod. The greatest tendency to tuberize was found in cuttings that consisted of a single, fully expanded leaf and its subtended bud. Grafts showed that genetical differences in critical photoperiod resided in properties of the leaf. Short days before cutting tended to shift growth from above ground buds of two-node cuttings to below ground buds, even if the number of short days was insufficient for tuber induction. As few as 6 short days reduced growth of shoots at the upper bud and increased underground growth of shoots and stolons.

Selection for wide temperature adaptation in Chrysanthemum morifolium (Ramat.) Hemsl.

Rooted cuttings of commercial cvs were grown to flowering at five temperatures and the the number of short days to flowering was recorded. The optimum temperature for rapid flowering varied between cvs. The number of days to flowering at the optimum temperature was not related to the delay in flowering caused by either high or low temperature. In many cvs the delay in flowering at low temperature was accompanied by a similar delay at high temperature. It was concluded that for the character 'time to flowering' genotypes should preferably be selected at low temperatures. If low temperature cannot be realized, only rapidly flowering genotypes should be selected. (Abstract retrieved from CAB Abstracts by CABI’s permission)

Stolon Formation in Chlorophytum1

Abstract Daylengths ≤ 12 hours greatly reduced the time required to form visible stolons in Chlorophytum. Three weeks of 8 hour daylengths were the minimum number of short days required to reduce the days to visible stolon formation. The all-green plant (Chlorophytum capense (L.) Voss) was less responsive to photoperiod than the variegated plant (Chlorophytum comosum (Thunb.) Jacques cv. Vittatum).

The role of short days in the termination of photorefractoriness in female canaries (Serinus canarius).

Photorefractory intact female canaries were exposed to a photoperiod of 8 h light: 16 h darkness (8L: 16D) for 0, 2, 4 or 6 weeks before photostimulation with 14L: 10D for 4 weeks. Photoresponsiveness was measured in terms of plasma immunoreactive LH, ovary and oviduct weights, follicle size and nest-building behaviour. Birds not exposed to 8L: 16D were unresponsive to photostimulation while those exposed for 6 weeks to 8L: 16D were as fully photosensitive as females similarly treated immediately before their first breeding season. Birds exposed for 2 or 4 weeks to 8L: 16D responded to subsequent photostimulation but were not as responsive as birds exposed to short days for 6 weeks. Positive correlations between the two ovarian parameters and between these ovarian parameters and oviductal weight existed in all groups exposed to short days, but not in birds not exposed to short days. It is concluded that the restoration of photosensitivity at the end of the refractory period is a function of the number of short days experienced; about 6 weeks of short days are needed for its completion. In another experiment photorefractory birds exposed for 6 weeks to short days without subsequent photostimulation, although potentially photosensitive, were indistinguishable (in terms of the above parameters) from refractory birds kept on long days for the same period; in these birds refractoriness was not broken.

The effect of photoperiod and temperature on northern Canadian ecotypes of Agropyron trachycaulum var. trachycaulum (slender wheatgrass)

Thirty-five plants of Agropyron trachycaulum from northern Canada were categorized as to the latitude of origin. Categories were 53–55, 55–58, 58–61, and 61–68° north latitude. In field plots at Beaverlodge (latitude 55° N) the plants originating from farthest north had the shortest number of days from heading to maturity and lowest average height and seed yield. Controlled environment studies confirmed that plants from north of 60° latitude have reduced capability of producing seed culms in summer environments with less than continuous light. Seed production of such species would be suspect in the current farming areas at lower latitudes. If large quantities of seed were required, new seed production areas may have to be developed in northern latitudes.

Effect of varying number of short days, gibberellic acid and ascorbic acid on the flowering of soybean

Both the cultivars of soybean, namely E.C. 2579 and Punjab I, studied were found to be qualitative short day plants. Even one SD was sufficient to cause flower bud initiation in E.C. 2579, although flower opening required 3 SDs. Pb. I did not show flower bud initiation with less than 10 SDs. In Pb. I the number of flowers with 20 SDs was higher than continuous SD, indicating the favourable effect of long days prior to induction. Exogenous application of GA3 and AA singly and in combination substituted for the additional photoperiodic requirements of incompletely induced plants of Pb. I, but were ineffective under continuous LDs. Treatment with these regulators of plants having received 8 SDs resulted in initiation of flower buds, which failed to open into flowers. In plants subjected to 10 SDs flower buds were initiated with all these treatments except control. Floral buds did not open into flowers with any treatment or combination not containing GA3.

Effect of decapitation, phosfon D and cycocel on the flowering of <italic>Impatiens balsamina</italic> exposed to varying numbers of short days

Impatiens balsamina L., a qualitative short day plant, requires more short days for the development of floral buds into flowers than for their initiation. Phosfon D and cycocel reduce the number of short days required for flowering, increase the number of floral buds and flowers and delay their reversion to vegetative growth when transferred to noninductive conditions. The effect of decapitation of the main shoot subsequent to the emergence of floral buds resembles that of retardants indicating that the effect of the latter in flower promotion in this plant may be by virtue of their effect on cessation of apical dominance as a consequence of which reserve food materials may be channeled to axillary floral buds enabling them to develop into flowers.

Development of the gibberellin-induced ovulate strobilus of western red cedar: quantitative requirement for long-day → short-day → long-day

The induction of flowering in western red cedar (Thuja plicata Donn.) by gibberellin (GA3) has a quantitative requirement for long-day (LD). However, the strobilus does not develop fully under LD. Full development does occur though, if the photoperiod sequence of short-day (SD) → LD is given after an initial period of 3+ months under LD for induction. For the male, continued development entails a slight expansion and the shedding of pollen. For the female, it involves expansion from a tight 2-mm bud to a 15-mm cone, even without pollination. Cold increased the number of developing strobili, although it did not affect the date of first expansion. GA3 concentration had little effect on continued strobilus development under SD or LD. The present study indicates that continued development of the strobilus has a photoperiodic requirement that can be likened to the requirement of SD → LD of some flowers for anthesis. The requirement for SD is quantitative rather than qualitative, an increasing number of short-days will increase the number of expanding strobili, and eventually (18 to 30 months) some strobili will develop even under continuous LD. Continued development of the strobilus will not take place under SD alone, LD must follow. Therefore, the LD requirement in the sequence SD → LD appears to be qualitative in nature. This does not appear to be true for another conifer, Arizona cypress (Cupressus arizonica Greene). These strobili will develop under SD, but their development is enhanced by the sequence SD → LD.

PHOTOCONTROL OF GROWTH AND FLOWERING OF CARYOPTERIS

Piringer, A. A., R. J. Downs, and H. A. Borthwick. (U. S. Dept. of Agriculture, ARS, Belts ville, Md.) Photocontrol of growth and flowering of Caryopteris. Amer. Jour. Bot. 50(1): 86–90. Illus. 1963.—Flower buds were initiated on plants of Caryopteris × clandonensis A. Simmonds (C. incana [Houtt.] Miq. × C. mongholica Bunge) on all photopcriods but developed to anthesis only when daily dark periods exceeded 8 hr. Anthesis occurred in not less than 22 days after the beginning of 11 or more short photoperiods. Treatments with short days could be interrupted by as many as 30 non‐inductive long days without significant increase in the minimum number of short days required for anthesis. Anthesis, like floral initiation of many plants, was reversibly controlled by red and far‐red radiation acting through phytochrome. The inductive effectiveness of long dark periods was nullified by 1 min of red light or about 1 hr of far red. It was modified by night temperature in the range 45–70.F and filament lengths of stamens were shorter at night temperatures of 60 than at 70 F.

Floral inhibition in relation to photoperiodism in Biloxi soybean

Biloxi soybean is a short day plant with a critical photoperiod of about 14y2 hours. It has been demonstrated that if short days are given in direct succession, the number of nodes which produce flowers on a plant is directly proportional to the number of inductive short days between three and approximately ten. If the short day treatments are not given in direct succession, however, there may be no flowering response. Long (11) conducted experiments with Biloxi soybean in which he gave plants alternating short day and long day treatments, and the plants remained vegetative over long periods of time. He also gave varying numbers of short days in succession, alternating varying numbers of long days. His results show that the inductive effect of one or two short days may be cancelled out when followed by one or more long days. Numerous other workers have studied the inhibitory effect of long days when intervened between the short days of an inductive treatment in various short day plants. Results of such experiments have been reported for Kalanchoe blossfeldiana by Harder and Giummer (10); for Perilla ocymoides, Chenopodium amaranticolor, and Biloxi soybean by Schawabe (14); for Chrysanthemum morifolium by Post (13), and for Chenopodium by Carr (7). The above studies indicate that, in short day plants, partial induction by short day treatment may be reversed by subsequent exposure of the plants to long day conditions. A direct relationship is exhibited between the number of short days used in the partially inductive treatments and the number -of long days required to cause inhibition or reduction of the flowering response. In these previous studies long days known to be non-inductive were interspersed between inductive short days. It was inferred that such long day treatments were capable of destroying the flowering stimulus. No previous studies have been made in which varied lengths of photoperiods during the long days were investigated. In the following experiments, both the length and the intensity of the photoperiod during the long days have been investigated to determine the importance of their role in floral inhibition. Biloxi soybean, with an 8 hour photoperiod in each cycle, produces the same magnitude of flowering on both 24 and 48 hour cycles. One may consider that the plants on such a 48 hour cycle are actually being exposed to one short day followed by a day of complete darkness. Such treatments have also been called bidiurnal cycles (6). We have employed the 48 hour period as a unit of experimental treatment. After normal short day (8 hour photoperiod & 16 hour dark period) during the first 24 hours of the treatment, we have varied the photoperiodic conditions of the second 24 hours. Obviously, if the second 24 hour period were a long day, no flowering would result. On the other hand, if the second period were complete darkness, the amount of flowering would be the same as that exhibited by plants which received 7 consecutive short days. Any 48 hour period in which two photoperiods are given shall be considered as two photoperiodic cycles by us regardless of the length of each light treatment used. Differential flowering due to varying lengths of photoperiod during the second 24 hour period provides information concerning the nature of floral inhibition in Biloxi soybean.

Day-Length Control of Inflorescence Initiation in the Grass Rottboellia Exaltata L.F.

R. exaltata is a strict short�day plant with a critical photoperiod of about 13 hr. The number of short days required for inflorescence initiation varies with age, being 6 with plants 5 weeks old. Exposure to additional short days increases the rate of inflorescence development. The expanding leaf is the one most sensitive to short.day induction and removal of the leaves below it accelerates inflorescence development.

Evidence for a Flowering Inhibitor Produced in Long Days in Kalanchoe blossfeldiana

Experiments with Kalanchoe blossfeldiana are described in which periods of short-day treatment were interrupted by intercalated long days or light breaks during long dark periods. The effects of 24-hour dark periods preceding and following such intercalated long days were also investigated. The results of these experiments have shown that: Single long days intercalated between numbers of short days have a positive inhibitory effect on flower initiation and are not merely ineffective. The inhibitory effect expressed as the number of inductive cycles annulled is approximately additive, provided the long days are interspersed with short days, but not if several long days are given consecutively. On the average 1 long day is capable of annulling the flower-promoting effect of about 1⅓ short days. To a first approximation flower numbers in Kalanchoe increase exponentially with the number of inductive cycles given—up to at least 12 short days; the inhibitory effect of long days interspersed with short days also fits an exponential curve; i.e. the inhibition is roughly proportional to the amount of previous photo-periodic induction. A light break of as little as 30 seconds' duration given in the middle of a long dark period is as inhibitory as a long day. If followed by a long dark period the inhibition of an intercalated long day is almost completely neutralized; a long dark period preceding it has no such effect. These results have been interpreted as due to the interaction of a flowering inhibitor with a reaction leading to flowering. A mechanism involving competitive inhibition of an adaptively formed enzyme has been described as a possible example of the kind of reaction which could account for the results presented.