JA but not JA‐Ile is the cell‐nonautonomous signal activating JA mediated systemic defenses to herbivory in Nicotiana attenuata

The whole‐plant activation of defense responses to wounding and herbivory requires systemic signaling in which jasmonates (JAs) play a pivotal role. To examine the nature of the slower cell‐nonautonomous as compared to the rapid cell‐autonomous signal in mediating systemic defenses in Nicotiana attenuata, reciprocal stem grafting‐experiments were used with plants silenced for the JA biosynthetic gene ALLENE OXIDE CYCLASE (irAOC) or plants transformed to create JA sinks by ectopically expressing Arabidopsis JA‐O‐methyltransferase (ovJMT). JA‐impaired irAOC plants were defective in the cell‐nonautonomous signaling pathway but not in JA transport. Conversely, ovJMT plants abrogated the production of a graft‐transmissible JA signal. Both genotypes displayed unaltered cell‐autonomous signaling. Defense responses (17‐hydroxygeranyllinalool diterpene glycosides, nicotine, and proteinase inhibitors) and metabolite profiles were differently induced in irAOC and ovJMT scions in response to graft‐transmissible signals from elicited wild type stocks. The performance of Manduca sexta larvae on the scions of different graft combinations was consistent with the patterns of systemic defense metabolite elicitations. Taken together, we conclude that JA and possibly MeJA, but not JA‐Ile, either directly functions as a long‐distance transmissible signal or indirectly interacts with long distance signal(s) to activate systemic defense responses.     

光周期对春石斛开花及多胺含量的影响

以春石斛为试材,研究光周期对其开花及多胺（腐胺、亚精胺和精胺）含量的影响,以期了解春石斛开花的光周期特性以及期间能源物质多胺的变化规律。结果显示,春石斛短日照处理植株开花较长日照处理的提前约18d,为称量性短日照植物;同时,短日照处理植株的花芽多,开花量犬,花径较长日照大。不同光周期诱导开花过程中,春石斛叶片内腐胺含量最高,波动较大,短日照处理下基本维持比长日照高的水平。亚精胺含量其次,且随生长发育逐渐升高,短日照处理下一直保持比长日照高的水平。精胺含量最低,变化不大,短日照下保持与长日照相同或略高的水平。由此推测,春石斛为称量性短日照植物,高水平的腐胺和亚精胺可能与春石斛花芽的形成有关。     

Changes in organ growth ofChenopodium rubrum due to suboptimal and multiple photoperiodic cycles with and without flowering effect

The growth changes of cotyledons, leaves, hypocotyls and roots due to photoperiodic induction in short day plantChenopodium rubrum were investigated in relation to flowering. Six-day old plants were induced by photoperiods with a different number of dark hours. We found that the degree of inhibition which occurred during induction in the growth of leaves, cotyledons and roots similarly as the stimulation of hypocotyl is proportional to the length of dark period. The photoperiods with 12, 16 and 20 dark hours bring about marked inhibition of growth and at the same time induce flowering in terminal and axillary meristems. The inhibitory effect of critical period for flowering,i.e. 8 dark hours, is not apparent in all criteria used and even the flower differentiation is retarded. The photoperiods of 4 and 6 dark hours did not affect growth and were ineffective in inducing flowering even if their number has been increased. The experiments with inductive photoperiod interrupted by light break have clearly shown that growth pattern characteristic for induced plants can be evoked in purely vegetative ones. Such statement did not exclude the possible importance of growth inhibition as a modifying factor of flower differentiation. We demonstrated that the early events of flower bud differentiation are accompanied by stimulation of leaf growth. The evaluation of growth and development of axillary buds at different nodes of insertion enabled us to quantify the photoperiodic effect and to detect the effects due to differences in dark period length not exceeding 2 hours.     

Diapause‐inducing signals prolong nymphal development in the two‐spotted spider mite Tetranychus urticae

Female two‐spotted spider mite Tetranychus urticae are grown under different photoperiods and the photoperiodic regulation of diapause is examined. The photoperiodic response curve for diapause induction was of the long day–short day type, with critical day lengths (CDLs) of 2 and 12.5 h; diapause was induced between these CDLs. The preimaginal period is significantly longer in diapausing females than in non‐diapausing females; moreover, a significant positive correlation is detected between diapause incidence and deutonymphal period. Diapause incidence is high when long‐night photoperiods are applied against a background of continuous darkness in the stages including the deutonymph; this stage appears to be the most sensitive to photoperiod. These observations suggest that diapause‐inducing conditions inhibit nymphal development, particularly in the deutonymphal stage when photoperiodic time measurement for determination of reproduction or diapause is carried out.     

The interactive effects of photoperiod and future climate change may have negative consequences for a wide‐spread invasive insect

Increasing global temperatures may affect many ectotherms, including insects, although increasing temperatures are thought to benefit future populations through effects on adult size, fecundity, or populations. However, the way that temperature may interact with photoperiod is not well understood. We study this problem using the Asian tiger mosquito Aedes albopictus, an important worldwide invasive whose future spread is thought to be affected by changes in climate. We investigated how mass at maturity varied with temperature (21°C, 25°C) across short and long photoperiods, using laboratory populations from the extreme ends of this species’ current US range (Florida, New Jersey). These values were used to parametrize a model to predict optimal mass based on development times; the results of a second laboratory experiment under the same treatments were compared to model predictions. Warmer conditions shortened development times in females from all locations leading to either higher or lower mass depending on the photoperiod. We then used published mass–fecundity relationships to determine the consequences of mass on fecundity under our conditions. Under the majority of scenarios warming decreased predicted fecundity under long photoperiods, but proved beneficial under short photoperiods because the costs of fast development were offset by increased survival in the face of late‐season freezing risk. However, fecundity was always low under short photoperiods, so the marginal benefit of warming appears negligible given its cost under long photoperiods when the majority of reproduction occurs. Thus, with northern range expansion, where colder weather currently limits this species, detrimental effects of warming on fecundity are likely, similar to those identified for mass. Unlike previous work that has shown benefits of a warming planet to insects like Aedes albopictus, our work predicts lower performance under warming conditions in summer across the current range, a prediction with implications for range expansion, disease dynamics and populations.     

Differentiation of Photoperiod-Induced ABA and Soluble Sugar Responses of Two Quinoa (Chenopodium quinoa Willd.) Cultivars

Adaptation of quinoa (Chenopodium quinoa Willd.) to new regions demands acclimation to day-length, in addition to a host of other abiotic factors. To further elucidate the effects of photoperiod on development of quinoa, two differently adapted cultivars, Achachino (short day) from Bolivia and Titicaca (day-length neutral), were subjected to continuous long (17.5 h) and short (10 h) photoperiod conditions as well as a shift between the two to trigger possible adaptive mechanisms initiated by changes in leaf soluble sugar and ABA concentration. Our findings show both cultivars responding to an increase in photoperiod with significant increases in soluble sugar concentrations and a simultaneous increase in ABA. However, Titicaca exhibited a much stronger ABA response to increase in photoperiod, whereas the increase for Achachino falls within the range of natural diurnal variation. Achachino also showed increasing sensitivity to long photoperiods throughout all reproductive growth stages, resulting in continued flowering, stem elongation and disruption of seed formation, whereas Titicaca was capable of maintaining full seed set under all the photoperiod conditions. Discernible photoperiod-dependent chlorosis of the lower leaves of Titicaca was observed under long photoperiods compared to short photoperiods, implying multi-faceted adaptive responses to changes in photoperiod which may also involve nitrogen and carbon dynamics. Both ABA and sugar signals are possibly involved in regulating the photoperiod-adaptive capability of each cultivar, leading to pronounced differences in growth and reproductive development patterns between the contrasting cultivars.     

A leaf-derived signal is a quantitative determinant of floral form in Impatiens

The completion of flower development in Impatiens balsamina requires continuous inductive (short-day) conditions. We have previously shown that a leaf-derived signal has a role in floral maintenance. The research described here analyzes the role of the leaf in flower development. Leaf removal treatments, in which plants were restricted to a specified number of leaves, resulted in flowers with increased petal number, up to double that of the undefoliated control. Similar petal number increases (as well as changes in bract number or morphology) were recorded when plants began their inductive treatment at a late developmental age or when plants of a nonreverting line (capable of floral maintenance in the absence of continuous short days) were transferred from short days to long days. Our data imply that the increased petal number was neither a response to stress effects associated with leaf removal nor a result of alterations in primordium initiation rates or substitutions of petals for stamens. Rather, the petal initiation phase was prolonged when the amounts of a leaf-derived signal were limiting. We conclude that a leaf-derived signal has a continuous and quantitative role in flower development and propose a temporal model for the action of organ identity genes in Impatiens. This work adds a new dimension to the prevailing ABC model of flower development and may provide an explanation for the wide variety and instabilities of floral form seen among certain species in nature.     

EFFECTS OF PHOTOPERIOD AND VERNALIZATION ON THE NUMBER OF LEAVES AT FLOWERING IN 32 ARABIDOPSIS THALIANA (BRASSICACEAE) ECOTYPES

The extent of natural variation among wild type Arabidopsis thaliana L. Heynh for response to environmental stimuli that affect flowering is poorly documented. The effects of photoperiod and vernalization on the number of rosette leaves at the time of anthesis was measured for 32 Arabidopsis ecotypes. All ecotypes were vernalized 24 days at 4 C under continuous illumination. Vernalized and nonvernalized plants were transplanted into 8- (short-day) and 20-hour (long-day) photoperiods in controlled environment growth chambers. Two ecotypes failed to flower after 110 days. Mean leaf number was less for all ecotypes under long day compared to short day. Sixteen ecotypes responded to vernalization; eight had reduced leaf number regardless of photoperiod, and eight had reduced leaf number only under short day. Two ecotypes required vernalization to flower in this study. For three ecotypes, vernalization and short day resulted in a reduction in leaf number whereas vernalization and long day resulted in increased leaf number. Documentation of the effects and interactions of photoperiod and vernalization across many ecotypes provides a broader range of described natural variation for genetic and physiologic study.     

Floral plasticity: Herbivore‐species‐specific‐induced changes in flower traits with contrasting effects on pollinator visitation

Plant phenotypic plasticity in response to antagonists can affect other community members such as mutualists, conferring potential ecological costs associated with inducible plant defence. For flowering plants, induction of defences to deal with herbivores can lead to disruption of plant–pollinator interactions. Current knowledge on the full extent of herbivore‐induced changes in flower traits is limited, and we know little about specificity of induction of flower traits and specificity of effect on flower visitors. We exposed flowering Brassica nigra plants to six insect herbivore species and recorded changes in flower traits (flower abundance, morphology, colour, volatile emission, nectar quantity, and pollen quantity and size) and the behaviour of two pollinating insects. Our results show that herbivory can affect multiple flower traits and pollinator behaviour. Most plastic floral traits were flower morphology, colour, the composition of the volatile blend, and nectar production. Herbivore‐induced changes in flower traits resulted in positive, negative, or neutral effects on pollinator behaviour. Effects on flower traits and pollinator behaviour were herbivore species‐specific. Flowers show extensive plasticity in response to antagonist herbivores, with contrasting effects on mutualist pollinators. Antagonists can potentially act as agents of selection on flower traits and plant reproduction via plant‐mediated interactions with mutualists.     

Compensating for climate change–induced cue‐environment mismatches: evidence for contemporary evolution of a photoperiodic reaction norm in Colias butterflies

Anthropogenic climate change alters seasonal conditions without altering photoperiod and can thus create a cue‐environment mismatch for organisms that use photoperiod as a cue for seasonal plasticity. We investigated whether evolution of the photoperiodic reaction norm has compensated for this mismatch in Colias eurytheme. This butterfly’s wing melanization has a thermoregulatory function and changes seasonally. In 1971, Hoffmann quantified how larval photoperiod determines adult wing melanization. We recreated his experiment 47 years later using a contemporary population. Comparing our results to his, we found decreased melanization at short photoperiods but no change in melanization at long photoperiods, which is consistent with the greater increase in spring than summer temperatures recorded for this region. Our study shows that evolution can help correct cue‐environment mismatches but not in the same way under all conditions. Studies of contemporary evolution may miss important changes if they focus on only a limited range of conditions.     

GIBBERELLIN-INDUCED INHIBITION OF FLORAL INITIATION IN FUCHSIA

The ‘Lord Byron’ cultivar of Fuchsia hybrida is a long day plant for which GA acts as an inhibitor of flower initiation. At the dosages required to inhibit initiation (0.025 μg per plant) GA also promotes increased stem elongation but causes no other departures from normal development. Similar tests with auxins, antiauxins, kinins, and other substances showed no effect on flower initiation at dosages equivalent to that for GA. At 10- to 100-fold greater dosages, auxins, kinins, and anti-auxins inhibit not only flower initiation but also vegetative development. Thus the effect of GA on flower initiation appears to be unique, although other hormonal substances, such as abscisin, have not been tested. GA-induced inhibition is directly proportional to the dosage applied and inversely to the strength of long day induction (as measured by the number of long days). GA is most effective when applied to the terminal bud rather than to the mature leaves, suggesting that it is active at the site of flower initiation rather than in the leaves. If it is applied after translocation of the floral stimuli from the leaves, GA does not prevent flower initiation. Regardless of the dose applied, GA is less effective if applied later rather than earlier during LD induction. The inhibitory effect persists for several days. For example, an 0.85 μg dosage causes an 8–10-day delay in initiation; lower dosages have reduced effects. GA inhibits flower initiation but has no effect upon flower development. The rate of bud development is the same in GA-treated and control plants. Apparently no more than one to two axillary buds immediately below the apical meristem are receptive to long day-induced floral stimuli from the leaves. Regardless of the daylength conditions axillary buds more basal do not initiate flowers but develop into branch axes. The effect of a long day treatment persists for a very short time, perhaps no longer than the inhibition caused by minimal GA dosage. Thus flower initiation continues for a very short time following the end of long day induction. The significance of these findings is discussed in relation to the many reports of GA-induced inhibition as well as promotion of flower initiation. In particular, the discussion concerns the nation that flower initiation in fuchsia may be controlled by a gibberellin-like transmissible inhibitor.     

REVERSION AND REINDUCTION OF FLOWERING IN PERILLA

Lam , S. L., and A. C. Leopold . (Purdue U., Lafayette, Indiana.) Reversion and reinduction of flowering in Perilla. Amer. Jour. Bot. 48(4): 306–310. Illus. 1961.—Plants of Perilla crispa (Thunb.) Tanaka ultimately revert to the vegetative state provided that they have received not more than about 20 cycles of short photoperiods. Reversion is markedly promoted by repeated debudding of plants induced with 35 cycles or less. Reverted plants of Perilla could be reinduced twice by photoperiodic treatment of the originally induced leaves. Timing experiments to measure the flow of flower stimulus from induced leaves suggest a gradual loss of the stimulus, as indicated by increased time to appearance of flowers and decreased flower number. It is concluded that after the inductive treatment is withdrawn, the effectiveness of the flower stimulus coming from the leaf declines with time. It is suggested that reversion is made possible by the decline of effective flower stimulus coming from the induced leaves.     

Light‐induced systemic signalling down‐regulates photosynthetic performance of soybean leaves with different directional effects

• When plants are exposed to a heterogeneous environment, photosynthesis of leaves is not only determined by their local condition, but also by certain signals from other parts of the same plant, termed systemic regulation. Our present study was conducted to investigate the effects of light‐dependent systemic regulation on the photosynthetic performance of soybean (Glycine max L. Merr.) under heterogeneous light conditions.
• Soybean plants were treated with heterogeneous light. Then gas exchange characteristics were measured to evaluate the photosynthetic performance of leaves. Parameters related to photosynthetic pigments, chlorophyll fluorescence, Rubisco and photosynthates were examined to study the mechanisms of light‐dependent systemic regulation on photosynthesis.
• Light‐induced systemic signalling by illuminated leaves reduced the P_n of both upper and lower non‐illuminated leaves on the same soybean plant. The decrease in g_s and increase in C_i in these non‐illuminated leaves indicated restriction of carbon assimilation, which was further verified by the decline in content and activity of Rubisco. However, the activation state of Rubisco decreased only in upper non‐illuminated leaves. Quantum efficiency of PSII (ΦPSII) and ETR also decreased only in upper non‐illuminated leaves. Moreover, the effects of light‐induced systemic signalling on carbohydrate content were also detectable only in upper non‐illuminated leaves.
• Light‐induced systemic signalling by illuminated leaves restricts carbon assimilation and down‐regulates photosynthetic performance of non‐illuminated leaves within a soybean plant. However, effects of such systemic regulation differed when regulated in upward or downward direction.

     

Effect of ínductive photoperiod and gibberellin treatment on peroxidase enzyme system in relation to floral induction inImpatiens balsamina L

Gibberellins A₃ and A₁₃ cause floral induction inImpatiens balsamina, a qualitative short day plant, under non-inductive 24-h photoperiods (continuous illumination). However, the influence of the two inductive factors,i.e. gibberellins and short days (8-h photoperiods) on the peroxidase enzyme system is different. The total peroxidase activity decreases under both inductive and non-inductive photoperiods, with or without gibberellin treatment. The electrophoretic pattern of isoperoxidases changes only in response to gibberellin treatment. Under 24-h photoperiods, treatment with gibberellins A₃ and A₁₃ causes the appearance in the stem of three additional isoenzymes of peroxidase (Rm 0.50, 0.71 and 0.76). These bands do not appear in the leaves, which are non-essential for gibberellin-caused floral induction in this plant. Under 8-h photoperiods also, gibberellins induce the appearance of new isoenzyme bandsi.e. two in the stem (Rm 0.50 and 0.76) and one in the leaves (Rm 0.05). These may be correlated with the synergistic increase in the number of floral buds in these plants in response to simultaneous exposure to two inductive factors.     

不同光周期对西红花开花和花丝品质的效应比较

为筛选促进西红花开花和提高花丝品质的最佳光周期,以3种不同规格(20～25 g、25～30 g、30～35 g)西红花种球为材料,设置4种光周期处理(8 h/16 h、10 h/14 h、12 h/12 h、14 h/10 h),考察光周期对西红花种球鲜重变化、主芽生长、展叶数量、开花后营养物质含量以及花朵性状和花丝品...     

The Role of Leaves as Inhibitors of Flower Induction in Strawberry: With one Figure in the Text

The effects of various defoliation treatments on flower initiationwere studied in the strawberry var. Talisman, which is a facultativeshort-day plant, with particular reference to differences inthe inductive capacity of leaves of differing maturity. Plants from which all mature leaves had been removed to leaveonly two immature leaves flowered in longer photoperiods thanintact controls, and conversely plants bearing only three fullymature and no immature leaves required a shorter photoperiodfor flower initiation than intact plants. Intact plants in constant darkness and totally defoliated plantsin continuous light both initiated flowers, but intact plantsin continuous light failed to flower. It is submitted that these results provide evidence that thephotoperiodic control of flowering in this plant operates througha flower inhibitor produced in the leaves. They also show that although leaves of any maturity are ableto inhibit flower initiation, under some conditions mature leavesare more inhibitory than immature, and that the inhibitory activityof any leaf decreases with decreasing photoperiod.     

Photoperiod cues and patterns of genetic variation limit phenological responses to climate change in warm parts of species’ range: Modeling diameter‐growth cessation in coast Douglas‐fir

The phenology of diameter‐growth cessation in trees will likely play a key role in mediating species and ecosystem responses to climate change. A common expectation is that warming will delay cessation, but the environmental and genetic influences on this process are poorly understood. We modeled the effects of temperature, photoperiod, and seed‐source climate on diameter‐growth‐cessation timing in coast Douglas‐fir (an ecologically and economically vital tree) using high‐frequency growth measurements across broad environmental gradients for a range of genotypes from different seed sources. Our model suggests that cool temperatures or short photoperiods can induce cessation in autumn. At cool locations (high latitude and elevation), cessation seems to be induced primarily by low temperatures in early autumn (under relatively long photoperiods), so warming will likely delay cessation and extend the growing season. But at warm locations (low latitude or elevation), cessation seems to be induced primarily by short photoperiods later in autumn, so warming will likely lead to only slight extensions of the growing season, reflecting photoperiod limitations on phenological shifts. Trees from seed sources experiencing frequent frosts in autumn or early winter tended to cease growth earlier in the autumn, potentially as an adaptation to avoid frost. Thus, gene flow into populations in warm locations with little frost will likely have limited potential to delay mean cessation dates because these populations already cease growth relatively late. In addition, data from an abnormal heat wave suggested that very high temperatures during long photoperiods in early summer might also induce cessation. Climate change could make these conditions more common in warm locations, leading to much earlier cessation. Thus, photoperiod cues, patterns of genetic variation, and summer heat waves could limit the capacity of coast Douglas‐fir to extend its growing season in response to climate change in the warm parts of its range.     

Influence of daylength on gibberellin metabolism and stem growth in Silene armeria

Summary When radioactive gibberellin A₅ (³H-GA₅) was applied to the apices and surrounding young leaves of the long-day plant Silene armeria, it was partially converted to at least two other acidic substances. One of them was similar to GA₃ in chromatographic, but not in biological properties. The other metabolite was more polar than GA₃ and inactive in the dwarf d-5 corn assay.The rate of ³H-GA₅ conversion was influenced by the photoperiod under which Silene plants were grown. Exposure to 2 long days significantly increased ³H-GA₅ metabolism over that in control plants kept under short days. The increased conversion of ³H-GA₅ persisted for at least a few days after transferring Silene plants back from long to short days. Likewise, stem growth induced by long photoperiods continued for a considerable period of time under subsequent short days.Application of the growth retardant AMO-1618 to Silene reduced the levels of two endogenous GA-like substances, one of them with GA₅-like properties, more under long than under short days. These results indicate that long photoperiods, which induce flower formation and stem elongation in Silene, increase the turnover of endogenous gibberellins.     

Temperature-dependent internode elongation in vegetative plants of Arabidopsis thaliana lacking phytochrome B and cryptochrome 1

 Vegetative plants of Arabidopsis thaliana (L.) Heynh. form a compact rosette of leaves in which internode growth is virtually arrested. Rapid extension of the internodes occurs after flower buds are present in the reproductive apex. Under natural radiation, continuous light from fluorescent lamps, or short photoperiods of light from fluorescent lamps, plants of the phyB cry1 double mutant (lacking both phytochrome B and cryptochrome 1) did not form normal rosettes because all the internodes showed some degree of elongation. Internode elongation was weak in the phyB single mutant and absent in the cry1 mutant, indicating redundancy between phytochrome B and cryptochrome 1. The absence of phytochrome A caused no effects. The failure to form normal rosettes was conditional because internode elongation was arrested at low temperatures in all the mutant combinations. In contrast, the temperature dependence of phytochrome B and cryptochrome 1 effects on hypocotyl growth was weak. The elongation of the internodes in phyB cry1 was not accompanied by early flowering as showed by the lack of effects on the final number of leaves. Apex dissection indicated that in phyB cry1 double mutants internode elongation anticipated the transition from the vegetative to the reproductive stage. Thus, stem growth in Arabidopsis thaliana is not fully dependent on the program of reproductive development. Received: 2 June 1999 / Accepted: 13 August 1999