Temperature dependent redistribution of organic nitrogen during 'dry' storage of tulip bulbs cv. Apeldoorn

Tulip bulbs cv. Apeldoorn are dry stored at 5°C for 12 weeks to ensure subsequent optimal flowering when planted in the greenhouse at higher temperatures of 17–20°C. Both temperature and duration of the cold treatment determine the subsequent rate of the shoot elongation, the time until anthesis and the flower size, pigmentation and water content. In search for cold-specific physiological changes, possibly related to the development of the potential of proper flowering (flowering preparation), we studied the redistribution of organic nitrogen in both cooled (5°C) and non-cooled (17°C) bulbs.
During 12 weeks of dry storage, the total protein- and free amino acid-nitrogen content decreased in the scales, whereas the opposite was found in the basal plate (with root primordia) and the shoot. In the shoot, this occurred significantly more at 17°C than at 5°C. At the same time, there was a tissue-specific change in the free amino acid composition in both cooled and non-cooled bulbs. Changes specific for the 5°C treatment were only found for the alanine content, in both the basal plate (with root primordia) and the shoot, and for the proline, asparagine, threonine, glycine and isoleucine content, in the shoot only. These changes are, for the greater part, completed within the first 6–8 weeks of dry storage. Bulbs stored for such a short period of time at 5°C still show flowering disorders. Thus, flowering preparation is only partly accompanied by changes in free amino acid contents.     

Effect of low temperature on dormancy breaking and growth after planting in lily bulblets regenerated in vitro

Lilies regenerating on scale segments may develop dormancy in vitro depending on the culture conditions. The dormancy is broken by storage for several weeks at a low temperature (5 °C). The effect of the low temperature on sprouting, time of leaf emergence and further bulb growth was studied. Dormant and non-dormant bulblets were regenerated in vitro on bulb scale segments cultured at 20 °C or 15 °C, respectively. The low temperature not only affected the number of sprouted bulblets but also the time of emergence. The longer the cold storage, the faster and more uniform leaf emergence occurred. Both dormant and non-dormant bulblets grew faster after a low temperature treatment of six weeks. Thus, during dormancy breaking the tissue is prepared not only for sprouting but also for subsequent bulb growth. These processes are rather independent as low temperature stimulates growth in non-dormant bulblets whereas these bulblets sprout also without treatment at low temperature. Moreover, the hormone gibberellin induces rapid sprouting but has no influence on further bulb growth. Good growth in bulblets exposed to the low temperature coincided with production of an increased leaf weight. However, the relationship is not absolute as bulblets that were cold-treated for six weeks grew larger than bulblets cold-treated for four weeks but the formation of leaf biomass was similar. During storage at low temperature starch was hydrolyzed in the bulb scales and sugars accumulated. This indicates that during this period, preparation for later bulb growth involves mobilization of carbohydrate reserves which play a role in leaf growth and development of the photosynthetic apparatus. Starch hydrolysis proceeded in the outer scales after planting. Approximately six weeks later, the switch from source to sink took place in the bulblet, which became visible as a deposition of starch in the middle scales.     

The effect of low temperature and GA3 treatments on dormancy breaking and activity of antioxidant enzymes in Fritillaria meleagris bulblets cultured in vitro

We investigated the effect of low temperature and gibberellic acid (GA₃) treatment on dormancy in Fritillaria meleagris L. bulbs. Also, we studied the effect of dormancy breaking on the antioxidant enzymes activity. To overcome dormancy, bulbs require a period (4–8 weeks) of exposure to low temperature. Bulbs regenerated in vitro were grown in the dark on medium without growth regulators at the standard (24 °C) or at low temperatures (4 and 15 °C) for 4, 6, 8 and 10 weeks. Bulbs were collected after 3, 4 and 5 weeks of cooling at 4 °C. To investigate the influence of GA₃ on dormancy, bulbs were treated for 24 h with GA₃ solutions with 1, 2 and 3 mg l^?1 concentrations. During the period of growth of bulbs at 4 °C, regeneration of bulbs was very weak, while at 15 °C the number of regenerated bulbs increased significantly. Improved bulb sprouting was achieved by a short treatment with gibberellin. Low temperature also represents a kind of oxidative stress for the plant. The activity of superoxide dismutase, catalase (CAT) and peroxidase (POX) in bulbs of F. meleagris L. grown in vitro and ex vitro increased with decreasing temperature in contrast to glutathione reductase. POX showed generally lower activity than CAT which indicates that major role in the breaking dormancy and preparing bulbs for sprouting have catalases.     

The Effect of Storage Temperature on Shoot Growth, Flowering, and Carbohydrate Metabolism in Tulip Bulbs

Dry bulbs of the cvs. ‘Apeldoorn’ and ‘Paul Richter’ at stage G of flower development were stored at 5° or 21°C for 2, 4, 6, 8, 10, 12, and 14 weeks, respectively before being planted and forced at 18°C. Samples from each treatment were taken for carbohydrate analysis. The low temperature treatment (5°C) was necessary to obtain satisfactory shoot growth and flowering after planting. The rate of shoot growth and the percentage of flowering bulbs increased with increasing duration of the 5°C treatment. Time of flowering was also precipitated. 12–14 weeks of low temperature treatment seemed optimal. High temperature (21°C), or a short period at 5°C (2–6 weeks), resulted in many non-flowering bulbs, and a very slow shoot elongation when flowering occurred. In the latter case the tips or large areas of the perianths became white, the red pigmentation being prevented. Paper chromatographic analysis of oligosaccharides revealed a substantially increased content of sucrose and fructosyl sucrose (DP ≤ 5) during the first 2–4 weeks of cooling. At the end of 12 weeks at 5°C, the content of oligosaccharides decreased. The increase in the oligosaccharide content was accompanied by a corresponding starch decrease. High temperature storage (21°) led to comparatively slight changes in the sucrose and fructosyl sucrose content of the bulbs. The significance of carbohydrate metabolism in relation to shoot elongation and flowering is discussed.     

Respiration Rate and Mitochondrial Activity in Iris Bulbs

The oxygen uptake of iris bulbs (Iris×hollandica‘Wedgwood’) which had been stored dry at 30 C (“retarded’ bulbs) was low (10 μmol O₂ per h and bulb), the oxygen uptake of the intact bulb, the three outer fleshy scales and the remaining central part of the bulb increased three- to fourfold, nearly twofold and fourfold, respectively. Mitochondria were isolated from the scales of retarded and activated bulbs and their oxygen consumption with succinate, l -malate (plus pyruvate). x-ketoglutarate and NADH as substrate was measured polarographically. The oxidative capacity of mitochondria isolated from the scales of activated bulbs was only slightly higher than that from retarded bulbs when calculated on a tissue basis. No difference was found between the phosphorylation efficiency, respiratory control, cytochrome c deficiency, succinate dehydrogenase, malate dehydrogenase, succinate-cytochrome c rductase, NADH-cytochrome c reductase and cytochrome oxidase activity of the retarded and activated bulbs. The increase in the in vitro oxygen uptake of the scales after transition from 30 to 13 C was not accompanied by an equal increase in the oxidative capacity of their mitochondria suggesting that they are not responsible for this rise in oxygen uptake.     

Neoseiulus paspalivorus,a predator from coconut,as a candidate for controlling dry bulb mites infesting stored tulip bulbs

The dry bulb mite, Aceria tulipae, is the most important pest of stored tulip bulbs in The Netherlands. This tiny, eriophyoid mite hides in the narrow space between scales in the interior of the bulb. To achieve biological control of this hidden pest, candidate predators small enough to move in between the bulb scales are required. Earlier experiments have shown this potential for the phytoseiid mite, Neoseiulus cucumeris, but only after the bulbs were exposed to ethylene, a plant hormone that causes a slight increase in the distance between tulip bulb scales, just sufficient to allow this predator to reach the interior part of the bulb. Applying ethylene, however, is not an option in practice because it causes malformation of tulip flowers. In fact, to prevent this cosmetic damage, bulb growers ventilate rooms where tulip bulbs are stored, thereby removing ethylene produced by the bulbs (e.g. in response to mite or fungus infestation). Recently, studies on the role of predatory mites in controlling another eriophyoid mite on coconuts led to the discovery of an exceptionally small phytoseiid mite, Neoseiulus paspalivorus. This predator is able to move under the perianth of coconuts where coconut mites feed on meristematic tissue of the fruit. This discovery prompted us to test N. paspalivorus for its ability to control A. tulipae on tulip bulbs under storage conditions (ventilated rooms with bulbs in open boxes; 23 °C; storage period June–October). Using destructive sampling we monitored predator and prey populations in two series of replicated experiments, one at a high initial level of dry bulb mite infestation, late in the storage period, and another at a low initial dry bulb mite infestation, halfway the storage period. The first and the second series involved treatment with N. paspalivorus and a control experiment, but the second series had an additional treatment in which the predator N. cucumeris was released. Taking the two series of experiments together we found that N. paspalivorus controlled the populations of dry bulb mites both on the outer scale of the bulbs as well as in the interior part of the bulbs, whereas N. cucumeris significantly reduced the population of dry bulb mites on the outer scale, but not in the interior part of the bulb. Moreover, N. paspalivorus was found predominantly inside the bulb, whereas N. cucumeris was only found on the outer scale, thereby confirming our hypothesis that the small size of N. paspalivorus facilitates access to the interior of the bulbs. We argue that N. paspalivorus is a promising candidate for the biological control of dry bulb mites on tulip bulbs under storage conditions in the Netherlands.     

Bulbil production in Narcissus: the effect of temperature and duration of storage on bulb unit development and subsequent propagation by twin-scaling

The growth of bulb components and carbohydrate content of Narcissus bulbs was followed during storage at 5–30 ^oC, and the productivity of twin-scale propagules cut from bulbs after these storage treatments was studied. Growth of daughter bulb unit components was greatest during storage at 9–15 ^oC, and greatly inhibited at 30 ^oC. Concentrations of soluble sugars were highest following 30 ^oC storage, and higher in intermediate bulb scales than in outer or inner scales. Bulbil production on twin-scales was greatest on propagules cut from the intermediate scales, and in bulbs previously stored at 15 or 30 ^oC.     

Energy metabolism of Plantago lanceolata, as affected by change in root temperature

The long and short term metabolic effects of a shift in root temperature was investigated in Plantago lanceolata L. with special reference to the role of the cyanide resistant alternative pathway in root respiration. After a 10-day period of growth at a 13°C root temperature, a decrease in root as well as shoot growth was observed, compared to control plants grown continuously at 21°C. Apart from an increase in shoot soluble and insoluble sugar level, no changes in metabolism were found, neither in root respiration, shoot photosynthesis, nor in root sugar and plant protein level.
Decreasing the root temperature from 21 to 13°C gave several clear short term changes in metabolism. Within one hour a decrease in cytochrome chain activity of the roots was found together with an increase in activity of the alternative chain. After 24 h a recovery to the initial level of both chains was observed. An increase in root temperature from 13 to 21°C gave an immediate increase in activity of both respiratory chains that was still present 24 h after the switch.
It is concluded that the activity of the alternative respiratory pathway in the root is strongly affected by a sudden temperature change in the root environment. This pathway acts in a way which is described by 'the energy overflow model'. The presence of the alternative electron transport pathway should be taken into account in determinations of the respiratory Q₁₀. Moreover, the length of time between the temperature change and respiration measurements is an important factor.     

Mitochondrial Activity and Carbohydrate Levels in Tulip Bulbs in Relation to Cold Treatment

Changes in mitochondrial activity and in the levels of variouscarbohydrates were followed in tulip bulbs (cv. Apeldoorn) keptin the dark at low and high temperatures (9 and 18 ?C respectively)from the time of flower differentiation until anthesis. Afterthe first 10 weeks at either temperature, the activity of themitochondria, measured by their ability to oxidize succinate,malate, or 2-oxoglutarate, was at a minimum. Thereafter oxidationrates improved up to about the 26th week when mitochondria fromcooled (9 ?C) bulbs were usually more active than those fromuncooled (18 ?C) bulbs. Subsequently, rates for both treatmentsfell rapidly. In contrast, levels of total alcohol-soluble carbohydratesand of sucrose in the cooled bulbs were at a maximum after 10weeks and were falling rapidly by the 26th week. Statisticallysignificant inverse correlations between mitochondrial activity,typified by the succinate oxidation rate, and these carbohydrateswere established. No such relationships were found for uncooledbulbs, however, and carbohydrate levels in such bulbs tendedto increase slowly throughout the growing period. In addition,transfer of carbohydrates to the growing shoot was slow, andthe flowers either failed to develop normally or were of poorquality. The mechanism whereby the bulb controls the activityof its mitochondria is at present unknown, but the rise in sucroselevels and its subsequent redeployment to the shoot broughtabout by cold treatment appear essential for normal flowering.     

Carbohydrate Status of Tulip Bulbs during Cold-Induced Flower Stalk Elongation and Flowering

The effect of a cold treatment on the carbohydrate status of the scales and flower stalk of Tulipa gesneriana L. cv Apeldoorn bulbs during growth after planting was studied and compared with bulbs not given cold treatment. Bulbs were stored dry for 12 weeks at 5[deg]C (precooled) or 17[deg]C (noncooled). Only the 5[deg]C treatment led to rapid flower stalk elongation and flowering following planting at higher temperatures. Precooling enhanced mobilization of starch, fructans, and sucrose in the scales. The cold-stimulated starch breakdown was initially accompanied by increased [alpha]-amylase activity per scale. In noncooled bulbs, [alpha]-amylase activity slightly decreased or remained more or less constant. Cold-induced flower stalk elongation was partially accompanied by a decrease in the sucrose content and an increase in the glucose content and invertase activity per g dry weight. The starch content in internodes initially decreased and subsequently increased; [alpha]-amylase activity per g dry weight of the lowermost internode showed a peak pattern during starch breakdown and increased thereafter. The internodes of noncooled bulbs, on the contrary, accumulated sucrose. Their glucose content and invertase activity per g dry weight remained low. Starch breakdown was not found and [alpha]-amylase activity per g dry weight of the lowermost internode remained at a low level. Precooling of tulip bulbs thus favors reserve mobilization in the scales and flower stalk and glucose accumulation in the elongating internodes.     

Gibberellin levels and cold-induced floral stalk elongation in tulip

To investigate the role of gibberellins (GAs) in the cold requirement of tulip ( Tulipa gesneriana L. cv. Apeldoorn), bulbs were dry-stored at 5°C or at 17°C for 12 weeks prior to planting at 20°C. Only precooled bulbs showed rapid sprout growth and developed a full-grown flower. Endogenous GA levels were measured in sprouts and basal plates at the time of planting and in the second week after planting, by combined gas chromatography-mass spectrometry using deuterated internal standards. GA₄ was the major gibberellin. while GA₁, GA₉ and GA₃₄ were present in lower amounts. At the time of planting, sprouts from non-cooled bulbs contained significantly more GA₄ and GA₁, per sprout than those from precooled bulbs. Hence, there is no direct correlation between rapid sprout growth after planting and high GA levels at planting. In the second week after planting, floral stalks of precooled bulbs contained 2 to 3 times more GA₄ and its metabolite GA₃₄ per floral stalk and per g fresh weight than those of non-cooled bulbs. The results are discussed with regard to the role of gibberellins in the cold-induced floral stalk elongation of tulip.     

Effect of temperature on the growth of individual cucumber fruits

In order to study the effect of temperature on the growth of individual fruits in cucumber (cucumis sativus L. cv. Corona), fruits were grown at 17. 5. 20,25 and 30°C continuously or the fruit temperature was changed from 17. 5 to 27.5°C or vice versa. Fruit development appeared to be closely related to the temperature sum. When the growth of a fruit was not constrained by assimilate supply, a decrease in growing period with increasing temperature was more than compensated for by a strong increase in growth rate, resulting in an increase in final fruit weight. However, when the growth of a fruit was constrained by assimilate supply, the increase in growth rate with increasing temperature was small and did not compensate for the decrease in growing period, resulting in a decrease in final fruit weight. Determinations of cell number and size showed that the effect of temperature on fruit growth was due to effects on cell expansion rather than on cell division. When growth was not constrained by assimilate supply. However, when assimilate supply did constrain fruit growth the number of cells per fruit decreased with increasing temperature, while the effect on cell size was negligible. In all stages of fruit development, the growth rate of a cucumber fruit responded within one day to a change in temperature. It was not irreversibly impaired by a low temperature (17. 5°C) during the early development of a fruit. A high temperature treatment (27. 5°C), however, had a great effect on the growth rate of a fruit after the temperature treatment had terminated. At all stages of fruit development (even before anthesis) a period of four days at 27. 5°C resulted in a pronounced stimulation of the growth rate afterwards at 17. 5°C.     

Exogenous GA<Subscript>3</Subscript> overcomes bud deterioration in tulip (<Emphasis Type="Italic">Tulipa gesneriana</Emphasis> L.) bulbs during dry storage by promoting endogenous IAA activity in the internodes

Endogenous free IAA was examined with an immunohistochemical method for its involvement in the reduction of bud deterioration after GA₃ was injected into the bulbs. We found that tulip bulbs stored at 20°C constantly developed severe bud deterioration, whereas the symptoms of deterioration was lighter in the bulbs with GA₃ injection and not observed in the bulbs with 4°C treatment. 73% success in overcoming bud deterioration was achieved in 20°C with GA₃ treatment after 8 weeks of bulb storage, and the success rate was 7% after 12 weeks of storage. IAA was detected in the parenchyma cells in the internodes of the shoot after the bulbs were stored at 4°C or at 20°C with GA₃ injection for 4 weeks, but little was detected in the bulbs stored at 20°C constantly. Moreover, a weak IAA signal was present in between the cells of the internodes irrespective of bulb treatment. After planting, the bulbs that had been treated differently exhibited different flowering ability. The bulbs stored at 4°C for 4, 8 and 12 weeks attained high flowering percentage, which was lower in the 20°C with GA₃ treatment and lowest in the 20°C treatment. It may be concluded that GA₃ injection decreases bud deterioration of tulip bulbs during dry storage at 20°C by promoting the endogenous IAA in the internodes.     

The development of dormancy in bulblets of Lilium speciosum generated in vitro. II. The effect of temperature

Upon harvest, lily ( Lilium speciosum Thunb. cv. Rubrum) bulblets generated in vitro under standard conditions (11 weeks at 20°C) were dormant and needed a cold treatment prior to planting. During culture in vitro at 20°C, the bulblets proceeded through three phases: (1) at first they were non–viable and non-dormant (up to 5 weeks), (2) then viable and non-dormant (5–9 weeks) and (3) finally viable and dormant (from 9 weeks onwards). At 15°C, the bulblets became viable but did not develop dormancy, even after protracted culture. The results suggest that the development of dormancy depends upon an accumulation of'heat units'occurring at temperatures higher than 15°0. At 25°C, the succession of the three phases occurred more rapidly than at 20°C and heat units were accumulated more rapidly. During the third period, the chilling requirement increased showing that heat units continued to be accumulated during this period.
Dormancy connotes an arrest of growth. In lily bulblets, however, the number of scales continued to increase after the induction of dormancy at 20 or 25°C. Many of the scales initiated before the onset of dormancy were formed by swelling of a petiole, whereas, after the onset of dormancy, all scales were formed directly from a primordium. We conclude that the development of dormancy corresponds to a switch in the development of the primordium. Thus, after the induction of dormancy the primordium lost the ability to become a leaf and always developed into a scale.     

Abscisic acid controls dormancy development and bulb formation in lily plantlets regenerated in vitro

Plantlets of lily regenerated in vitro from scale explants consist of scales and leaves from which the base of the petiole has swollen to a scale. Fluridone, an inhibitor of ABA-synthesis, applied during culture in vitro, inhibited the swelling of the petioles and promoted leaf formation. At high fluridone concentrations (10 or 33μ M ), swelling was completely blocked, and plantlets consisted of leaves only. Addition of ABA during the regeneration in vitro had the opposite effect and resulted in plantlets with scales only. When applied simultaneously with fluridone, ABA nullified the effect of fluridone. This demonstrates that bulb formation in lily is under the control of ABA. Lily plantlets regenerated in vitro on scale explants at 20 or 25°C were harvested after 11 weeks, and the leaves were removed from the bulblets. The bulblets were dormant and required a cold treatment to achieve rapid emergence after planting in soil. Fluridone added during the culture in vitro prevented the development of dormancy, and the bulblets did not require a cold treatment. The effect of fluridone was nullified by simultaneous addition of ABA. Bulblets harvested after 6 weeks of culture at 20°C had not yet developed dormancy. Bulblets regenerated at 15°C were only slightly dormant. In both types of bulblets, it is unlikely that the lack of dormancy was due to low ABA-levels since addition of ABA did not affect the dormancy status. These data indicate that the level of endogenous ABA and an unknown additional factor play major roles in the development of dormancy.     

兰州百合鳞茎发育及低温解除休眠过程中内源激素的变化

以兰州百合为试材,研究了鳞茎发育过程中以及2、6、10℃条件下保湿贮藏101 d内母鳞茎与新鳞茎中内源激素的变化。结果表明：鳞茎发育过程中内源ABA含量以及母鳞茎的GA₃与ZR含量增加,而内源IAA含量以及新鳞茎的GA₃与ZR含量下降。低温贮藏期间,母鳞茎与新鳞茎的GA₃、IAA含量均有升高过程,而ABA含量呈下降趋势;新鳞茎的ZR含量呈下降趋势,母鳞茎的ZR含量也有升高过程。低温处理初期的34 d内,内源激素变化最为显著。不同贮藏温度相比较,ABA含量差异不大,GA₃含量随温度升高而下降。在富含淀粉的新鳞茎中,GA₃和ABA表现出极显著的负相关关系,而在淀粉含量较低的母鳞茎中GA₃和ABA无相关性。通径分析结果表明,母鳞茎与新鳞茎的物质代谢机制不同,母鳞茎的物质变化受内源GA₃的调控,新鳞茎主要是ABA作用的结果。     

The dynamics of indole-3-acetic acid in Acer platanoides seeds during stratification and germination

During stratification at 5°C indole-3-acetic acid (IAA) levels in embryos of Acer platanoides decreased during the early stages but subsequently increased again throughout the remainder of a 144 day period. The reduction in IAA levels in embryos of fruits stored at 17°C was even more pronounced, and in addition, no increase was observed after longer storage periods at this temperature, the levels of IAA remaining very low. Germination in seeds maintained at 5°C was not observed until after 120 days or longer, but germination potential increased at an earlier stage, as shown by the fact that seeds transferred to 20°C gave appreciable increases in germination after much shorter chilling periods. Endogenous IAA levels in embryos from seeds transferred to 20°C after a chilling period, long enough to break dormancy, increased within 24 h, i.e. before visible germination, to levels similar to those observed in embryos from seeds chilled continuously for 144 days. Embryos from seeds chilled for 120 days, i.e. when the samples already showed visible germination and when the endogenous IAA content was already high, showed no further increase in endogenous IAA during a three day incubation at 20°C. None of the treatments employed was effective in inducing germination of seeds or embryos from fruits stored at 17°C.     

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 .     

Influence of temperature,ethylene and cyanide on the occurrence of alternative respiration in mitochondria from iris bulbs

Mitochondria, isolated from iris (Iris hollandica cv. Ideal) bulbs that have been treated for early flowering with high temperatures (14 days at 35°C followed by 3 days at 40°C) or with ethylene (10–500 ppm), show an induction of alternative respiratory capacity and a rise in state III respiration. Mitochondria from untreated bulbs (stored at 30°C) do not have an alternative pathway capacity and state III respiration is low. Induction of the alternative respiration by ethylene is maximal after 24 h, while induction by high temperature (> 36°C) is much slower. In the temperature range from 36–40°C, the extent of the induced alternative respiratory capacity increases with higher temperatures. A temperature of 42°C is lethal within 5 days. Bulbs stored at 30°C and 35°C before 40°C treatment reach the same values for alternative respiratory capacity. A treatment of the bulbs with 2.2 mM HCN (30°C) leads to an induction of alternative respiration concomitant with a decrease in state III respiration, after a lag time of 2–3 days. A treatment of 5 days with 2.2 mM HCN or longer is lethal.