Interaction of gibberellic acid and photoperiod on leaf sheath elongation in normal and gibberellin-insensitive genotype of wheat

Effect of gibberellic acid (GA₃) on leaf sheath elongation in a normal (cv. Møystad) and a gibberellin(GA)-insensitive (cv. Siete Cerros) genotype of wheat ( Triticum aestivum L.) were studied at 18 and 12°C under short (SD, 12 h) or long (LD, 24 h) photoperiod. Leaf sheath length in cv. Møystad was signficantly increased by exogenous GA₃ both under SD and LD. LD alone stimulated leaf sheath elongation and the combined effect of LD and GA₃ was additive, and there was no statistically signficant interaction between photoperiod and GA₃ concentrations. Leaf sheath length in cv. Siete Cerros was not significantly affected by GA₃ under any conditions. However, there was a highly significant stimulation of leaf sheath elongation by LD in cv. Siete Cerros as well. These results indicate that stimulation of elongation growth in wheat leaves by LD is not mediated by gibberellin.     

Feruloyl- and caffeoylputrescine in stem explants from photoperiodically determined Nicotiana species

The distribution and formation of hydroxycinnamoyl amides (HCA) in in vitro grown stem explants from day-neutral Nicotiana tabacum L. var. Xanthi no were investigated using [¹⁴C]-labelled precursors. Feruloylputrescine (FP) (labelled from [¹⁴C]-putrescine) was continually formed with a decreasing formation rate during a culture period of 35 days. The specific radioactivity, however, remained constant. In contrast, caffeoylputrescine (CP) was labelled in the second part of culture only. [UC]-Label from putrescine, spermidine, spermine, and cinnamic acid was incorporated into FP and p -coumaroylspermidine. CP was labelled from [¹⁴C]-putreseine and [¹⁴C]-spermidine only, while diferuloylputrescine (diFP) failed to be labelled by any of the precursors used. Tissue investigations showed that FP is dominant in cortex during formation of cortical callus, while CP showed a sequential gradient from pith to cortical callus to floral buds. Experiments with photoperiodical Nicotiana species were used to investigate the pattern of HCAs in induced and non-induced plants. The origin of explants had no influence on the pattern of FP and CP but resulted in different growth responses. FP is a marker of cortical callus formation in all explants. CP does not trigger the growth processes observed in the expants since CP also increased in photoperiodically non-induced explants of tobacco, which stopped growing after the formation of cortical callus.     

Effects of thermoperiod on photoperiodic determination of larval diapause in Ostrinia nubilalis

Some effects of thermoperiods on the photoperiodic determination of larval diapause in the European corn borer, Ostrinia nubilalis are reported. Thermoperiods and photoperiods were shown to interact to a highly significant degree in the induction of diapause. Diapause determination was found to be sensitive to the duration and temperature of the cryoscotophase of the thermophotoperiod; the thermophotophase characteristics exerted only minor influence. Cryoscotophase temperatures of 10°C or lower caused an unexpected increase in the apparent critical nightlength for diapause determination. A 0°C cryoscotophase effectively prevented the photoperiodic determination of diapause. Experimental investigation of the effects of 0°C cryoscotophases produced evidence that such low-temperature cryoscotophases may suppress the biological clock functions regulating the determination of diapause. Photoperiodic regimes in which 0°C pulses were inserted at successive points in 24-h cycle evoked responses suggesting that the early scotophase (saturation phase) was more strongly influenced by the low temperature pulse than was the later scotophase (scotonon); low temperature had little effect on the light-dependent processes (photonon) associated with the photophase.     

LIGHT,TEMPERATURE AND PHOTOPERIOD AS FACTORS CONTROLLING REPRODUCTION IN ULOTHRIX ZONATA (ULVOPHYCEAE)1

In many lakes in the northern United States and Canada the filamentous green alga Ulothrix zonata (Weber and Mohr) Kütz grows abundantly in early spring in shallow waters. Asexual reproduction occurs by formation of quadriflagellate zoospores which disrupt, the integrity of the cells upon release causing the filament to disintegrate. Study of the effects of 100 different combinations of irradiance, temperature and photoperiod revealed that zoospore formation is favored by high temperatures near 20°C, high light levels of 520 μE·m^?2·s^?1 and photoperiods of either short day (8:16 h light-dark) or long day cycles (16:8 h light-dark). Zoospore formation is minimal under conditions of low temperature (5°C), low irradiance (32.5 μE·m^?2·s^?1) and neutral day-lengths (12:12 h light-dark). These observations explain the decline in U. zonata biomass when water temperatures rise above 10° C. The combined effect of rising water temperatures and increasing daylengths causes progressively more filaments to switch from vegetable growth to zoospore production resulting in an increasing loss of biomass.     

Gibberellin substitution for long day secondary induction of flowering in Poa pratensis

Plants of Poa pratensis cv. Holt initiate inflorescence primordia when exposed to short days (SD) and low temperature, but require a secondary induction by at least 4 long days (LD) for further inflorescence development and stem elongation. Single or double applications of 10 µg per plant of gibberellins A₁, A₃, A₅ and 16,17‐dihydro A₅ (DHGA₅) induced inflorescence development in a high proportion of plants in SD, but only if the plants were detillered to a single stem. Exposure to 2 LD cycles did not cause heading and flowering alone but enhanced the effect of exogenous gibberellins (GAs), bringing flowering to 100%. GA₅ and DHGA₅ were less effective than GA₁ and GA₃ in SD, especially with double applications, but were more effective than GA₁ and GA₃ when given together with 2 LD. The GAs had differential effects on vegetative growth and flowering, GA₅ and DHGA₅ causing much less leaf and stem growth than the other two GAs. Marginal induction, whether by LD or GA application, resulted in a high proportion of spikelets with viviparous proliferation. Thus, whereas GAs are inhibitory to the primary induction by SD, they can replace secondary induction by LD when vegetative growth is limited.     

Photoperiodic control of growth, development and phytohormone balance in Solanum tuberosum

Some lines of Solanum tuberosum ssp. andigena are strictly photoperiodic, forming tubers only in short days and flowers only in long days. We used this advantageous phenomenon to study phytohormone involvement in the development of the plants, mainly that of tuber formation. Plants grown for 2 months under short days (SD) of 14 h darkness, night break (1 h white light in the middle of the 14‐h dark period) and continuous light (LD) were compared. Short day‐grown plants formed tubers, while plants in LD flowered. Night break prevented tuber formation, but caused flowering, although it was weaker than in LD. Plants grown under night break displayed many growth characteristics intermediate between SD and LD. Under LD and night break regimes ABA levels in all organs were about one‐fourth of those under SD. An opposite trend was found for gibberellin content: it was very low in SD‐grown plants and 4‐10 times higher under both other conditions with the exception of roots and stolons in night break. Thus, the ratio of ABA/GA, known to be important for tuber formation, was high in SD and low in night break and LD. The level of free indoleacetic acid (IAA) was high in LD‐ and night break‐grown plants and it was much lower in SD‐grown plants, including tubers. Cytokinin (CK) levels were also high in LD‐ and night break‐grown plants. In SD, leaves had slightly decreased and stems and roots + stolons had more pronouncedly decreased cytokinin levels. The CK/IAA ratio was thus higher in SD in stems and roots + stolons; it was also high in tubers and no difference was found in leaves. These results indicate that the effect of photoperiod on tuber formation and development may be mediated by photoperiod‐induced changes in hormone levels.     

Abscisic acid involvement in the induction of summer‐dormancy in Poa bulbosa, a grass geophyte

Summer‐dormancy occurs in geophytes that inhabit regions with a Mediterranean climate (mild, rainy winters and hot, dry summers). The environmental control of summer‐dormancy and the involvement of phytohormones in its induction have been little studied. Poa bulbosa L. is a perennial grass geophyte in which summer‐dormancy is induced by long days and by high temperature. Prolonged treatment with ABA (0.1‐1.0 m M ) under non‐inductive 8‐h short days (SD) resulted in cessation of leaf and tiller production and in the development of typical features of dormancy: bulbing at the base of the tillers and leaf senescence. Short‐term applications of ABA had similar effects but dormancy was transient, i.e. after a short while, leaf growth from the formed bulbs was resumed. ABA treatment of plants growing under an inductive 16‐h photoperiod (LD) enhanced the onset of dormancy. Endogenous levels of ABA in leaf blades and at the tiller base (where the bulb develops) increased markedly after the plants were transferred from SD to LD. This increase was greater in the tiller base, and concomitant with bulb maturation. High temperature (27/22 vs 22/17°C) accelerated both bulb development and ABA accumulation in leaf blades.
These results suggest that ABA plays a key role in the photoperiodic induction and development of summer‐dormancy in P. bulbosa .     

Induction of a β-phaseolin promoter by exogenous abscisic acid in tobacco: developmental regulation and modulation by external sucrose and Ca2+ ions

Using degenerate oligonucleotides that correspond to conserved amino acid residues of known 1-aminocyclopropane-1-carboxylic acid (ACC) synthases, we cloned a genomic fragment that encodes ACC synthase in Stellaria longipes. Southern analysis suggests that ACC synthase is encoded by a small gene family comprising about 4 members. We isolated four unique ACC synthase cDNA clones under different growth conditions from alpine and prairie ecotypes of S. longipes. Northern analyses suggest that ACC synthase genes are differentially and synergistically regulated by photoperiod and temperature. Such differential regulation of ACC synthase genes positively correlate with the levels of ACC and ethylene. Since ethylene has previously been shown to partly control the stem elongation plasticity in S. longipes, we propose that differential regulation of ACC synthase genes may represent one of the underlying molecular mechanisms of phenotypic plasticity in S. longipes.     

Life history plasticity in the satyrine butterfly Lasiommata petropolitana: investigating an adaptive reaction norm

This study addresses the general hypothesis that insects living in seasonal environments should shorten development times at progressively later dates in the growth season, and that insects living outside equatorial areas should use daylength as a cue to determine the date. Diapause strategies and reaction norms relating the duration of larval development to daylength was investigated in a French population of the butterfly, Lasiommata petropolitana. The results are compared with those of an earlier study of the species in Sweden. Because of the diapausing strategy and phenology of the population, it was expected that an adaptive reaction norm relating larval time to daylength should have a positive slope, i.e. relatively shorter daylengths induce faster growth and development. This prediction was supported, and the reaction norm was qualitatively similar to the one found in Swedish populations. In the French population it was, however, shifted to a range of shorter photoperiods which corresponds to the regime of shorter daylengths in southern Europe. Shorter larval development times and high growth rates were associated with a reduction in pupal size, suggesting a trade off between time and size at pupation. There was no evidence of a trade off between growth rate and starvation endurance. The results suggests that the daylength-dependent decision of what growth trajectory an individual larva will follow, is not made continuously but rather at one or a few occasions during larval development. It is clear that larvae of L. petropolitana make developmental decisions in relation to the daylength they experience during larval growth. The result is a reaction norm that agrees closely to what is predicted by some life history models, suggesting that it is an adaptation for optimising life history traits in a seasonal environment.     

Involvement of abscisic acid (ABA) in bulb dormancy of Allium wakegi Araki I. Endogenous levels of ABA in relation to bulb dormancy and effects of exogenous ABA and fluridone

Allium wakegi plants exposed to long days (LD, 14 h-photoperiod) developed bulbs, which were dormant from the 30th to the 125th day of LD, but those grown under natural short days (SD) did not develop bulbs. The contents of abscisic acid (ABA) in both whole bulbs and buds of the bulbs increased in LD, reaching a maximum at the 60th day of LD and decreasing thereafter, but those in basal leaf sheaths (this part corresponds to a bulb after bulb development) and buds did not increase in SD. The ABA content was related to the depth of bulb dormancy. Application of 500 M ABA to bulbs for 24 h significantly delayed sprouting, but that of 5 or 50 M ABA had little or no effect. Application of 25 or 125 M fluridone to the soil just before exposure to LD bleached new expanding leaves and reduced bulb size, but had no effect on the development of bulb scales that characterize bulb formation. The bulbs formed under such conditions sprouted earlier than those of control plants. The levels of endogenous ABA in bulbs, buds of the bulbs, leaf blades, and roots were reduced by fluridone application. These results indicate that ABA plays an important role in bulb dormancy of Allium wakegi.