Temperature and Light Requirements for the Sprouting of Chilled and Unchilled Tubers of the Purple Nutsedge, Cyperus rotundus

Mature and immature tubers of purple nutsedge (Cyperus rotundus L.) chilled at 0°C in dry and wet conditions, were sprouted along with fresh, unchilled tubers over a range of temperatures (10°C-45°C) in light and darkness. Fresh immature tubers showed a high sprouting percentage at all temperatures between 20°C and 40°C, while the mature ones did so only at 30°C and 35°C. Chilling of dry tubers stimulated early sprouting and increased the maximum sprouting percentage of both the mature and immature tubers. Dry chilling also lowered the limit of favourable temperatures to 15°C in the case of mature tubers. Chilling of wet tubers had a depressing effect and no sprouting occurred below 30°C. At all temperatures, light apparently favoured the sprouting of both the mature and immature tubers (except mature wet-chilled ones at 35°C and 40°C). Immature tubers showed relatively higher sprouting percentage than the mature ones, both in light and darkness. Alteration of temperature requirements due to dry and wet chilling of the tubers is regarded as significant and functional in relation to the ecology of the species.     

The inhibition of potato sprout growth by light.

When potato seed tubers (Solanum tuberosum cv. Pentland Javelin) were stored in darkness or diffuse daylight at 9°C and transferred at intervals to conditions suitable for sprouting, their capacity for sprout growth was unaffected by the presence or absence of light during previous storage. When similar tubers were stored at 10°C, 18°C or 25°C, sprout growth commenced earliest at 25°C, but the date was unaffected by fluorescent light. It was concluded that light did not affect the length of the dormant period, but only the rate of sprout elongation after that period had ceased. When tubers with growing sprouts at 10°C or 18°C were transferred from darkness into fluorescent light, sprout growth virtually ceased. Transfer from light into darkness resulted in immediate sprout growth, at a rate comparable with tubers stored continuously in the dark. Tubers of three Peruvian cultivars, stored in farm-scale diffuse-daylight stores, grew progressively shorter sprouts with increasing daily exposure to light from 30 min to 12 h. Storage of cv. Wilja under 21 Wm^-2 (total) of white fluorescent light for 10 h per day maintained the sprouts at the same length as ten times this light intensity for 1 h per day. In a subsequent experiment with cv. Bintje the 10 h, low-intensity light regime gave slightly shorter sprouts. It appeared that the total light energy falling on the tubers was the dominant factor controlling sprout growth.     

The inhibition of potato sprout growth by light.

The effect of light intensity on sprout growth in seed potato tubers (Solanum tuberosum) was examined using diffuse daylight in Peru and diffuse artificial light at Glasgow. Mean temperatures below 20 °C produced strong sprout growth that was inhibited by both daylight and artificial light, at visible irradiances above 0.01 Wm^-2. The percentage inhibition of sprout growth increased linearly with the logarithm of the irradiance, 50% inhibition being at 0.04 - 0.1 Wm^-2 provided that the temperature was suitable for substantial sprout growth in the absence of light. Cultivar and temperature had very little effect on the 50% inhibition point. At high irradiances growth inhibition was up to 95%, but the sprout length was never reduced to zero; short, robust green sprouts remained. Sprout numbers were increased by daylight, but not by artificial light. Diffuse daylight also reduced the total weight loss from seed tubers during a storage season of 180 days. At mean temperatures above 20 °C., sprout growth in the absence of light was much reduced and the effect of light on sprout elongation was less obvious.     

Nature of enhanced respiration during sprouting of aged potato seed-tubers

Respiration of 18-month-old Solarium tuberosum L. tubers was about 53% greater than that of 6-month-old tubers during sprouting at 23°C; yet, a significant loss of sprout vigor in the older tubers was apparent. Involvement of alternative oxidase (AO) in the age-induced difference in tuber respiration was assessed. AO was only detected in immunoblots if tissue disks from tubers were pre-incubated for 24 h prior to isolation of submitochondrial membrane particles (SMPs). No AO¹ was detected in SMPs from nonincubated tuber tissue of either age, indicating that it was not contributing to tuber respiration during sprouting as previously thought. Respiratory control and ADP/O ratios indicated that oxidative phosphorylation was fully coupled to electron transport in mitochondria isolated from 6- and 18-month-old tubers. Cytochrome c oxidase (EC 1.9.3.1) activities of intact mitochondria were also not affected by tuber age. The difference in respiration during sprouting was unique to whole tubers, as oxygen consumption by mitochondria from young and oid tubers was equal on a milligram protein basis. Sprouting 18-month-old tubers had 15% more mitochondrial protein per gram fresh weight than did 6-month-old tubers. Older tubers also produced more ATP than younger tubers prior to and during sprouting, through a fully coupled, Cyt-mediated respiratory pathway, reduced sprout vigor notwithstanding. From 5 to 10 days of sprouting, coinciding with development of the age-induced difference in whole-tuber respiration, ATP concentration in 18-month-old tubers increased to become 52% higher than that in 6-month-old tubers. ATP synthase (EC 3.6.1.34), assessed by SDS-PAGE and immunoblots of β- and oligomycin-sensitivity conferring protein-subunits, also increased as a proportion of SMP protein in older tubers during this period. Relative to 6-month-old tubers, the increased respiration and associated oxidative phosphorylation of 18-rnonth-old tubers during sprouting were probably in response to a lower adenylate energy charge (AEC) prior to sprouting (from 0 fo 5 days). From 5 to 10 days of sprouting, AEC of 18-rnonth-old tubers increased to equal that of 6-month-old tubers and the two tuber ages maintained the same AEC for the remainder of the 20-day sprouting interval. Higher respiration and lower AEC of older tubers in storage at 4°C, along with the fact that older tubers respired at a higher rate to achieve the same AEC as younger tubers during sprouting, indicate greater utilization of ATP by older tubers.     

Coiled-sprout in the potato: the effect of various storage and planting conditions

The incidence of coiled-sprout was determined in Scotch and local-grown Arran Pilot and Duke of York seed tubers which had been stored at 10°, 4° and 15° C. and in a farm store with no temperature control. All four tuber types were planted in the field and, in addition, the two types of Duke of York were planted in Perlite at 7°, 10° and 15° C. In the field, and when maintained at 7° and 10° C, the percentage of sprouts coiling and the intensity of coiling was greater in tubers stored at 10° and 15° C. than at 4° C. There was no coiling when the Duke of York tubers were planted at 15° C. In a further experiment tubers were stored at 20° C. in the light and dark and samples were planted monthly for 3 months at temperatures of 7°, 10° and 15° C. During the following 3-month period only light-stored were planted because of the excessive amount of tip-death in the tubers stored in the dark. There was very little coiling in the dark-stored tubers. In the first two plantings of the light-stored tubers there was virtually no coiling of those planted at 15° C. There was some, however, at 7° and 10° C. In subsequent plantings there was more coiling and no effect of planting temperature. Attempts to isolate Verticiculum nubilum from sprouts were successful in only a small percentage of attempts and it was not possible to demonstrate any difference between its distribution on coiled and normal sprouts. It was not possible to induce coiling by infection of sprouts with spores of V. nubilum. Over a wide range of sprout sizes the amount of coiling was a function of sprout size at planting. However, the parts which coiled were those in the apical bud of the sprout at the time of planting and hence contributed only a small amount to the total sprout size. It is likely, therefore, that the correlation between coiling and sprout size reflects the changing metabolism of the elongating regions of sprouts with their increase in length, these regions developing in such a way as to produce a greater tendency to coiling. The internal reactions concerned in these changes, however, are not known.     

Susceptibility of quagga mussels (Dreissena rostriformis bugensis) to hot-water sprays as a means of watercraft decontamination

The recent spread of dreissenid mussels to various bodies of water in the western US has sparked interest by many state and federal agencies to develop protocols to stop further expansion. Quagga mussels (Dreissena rostriformis bugensis) are of particular importance as they are currently the most widespread dreissenid species in the region. This project examined the susceptibility of quagga mussels to hot-water sprays at different temperatures and durations of spray contact at Lake Mead (Nevada-Arizona, USA). Emersed adult quagga mussels were exposed to hot-water sprays at 20, 40, 50, 54, 60, 70, and 80°C for 1, 2, 5, 10, 20, 40, 80, and 160 s. Sprays at ≥60°C for 5 s were shown to be 100% lethal. Sprays of 54°C for 10 s, 50°C for 20 s, and 40°C for 40 s also resulted in 100% mortality. A spray temperature of 60°C for 5 s is recommended for mitigating fouling by quagga mussels.     

In-season heat stress compromises postharvest quality and low-temperature sweetening resistance in potato (Solanum tuberosum L.)

Key message

High soil temperature during bulking and maturation of potatoes alters postharvest carbohydrate metabolism to attenuate genotypic resistance to cold-induced sweetening and accelerate loss of process quality.

Abstract

The effects of soil temperature during tuber development on physiological processes affecting retention of postharvest quality in low-temperature sweetening (LTS) resistant and susceptible potato cultivars were investigated. ‘Premier Russet’ (LTS resistant), AO02183-2 (LTS resistant) and ‘Ranger Russet’ (LTS susceptible) tubers were grown at 16 (ambient), 23 and 29 °C during bulking (111–164 DAP) and maturation (151–180 DAP). Bulking at 29 °C virtually eliminated yield despite vigorous vine growth. Tuber specific gravity decreased as soil temperature increased during bulking, but was not affected by temperature during maturation. Bulking at 23 °C and maturation at 29 °C induced higher reducing sugar levels in the proximal (basal) ends of tubers, resulting in non-uniform fry color at harvest, and abolished the LTS-resistant phenotype of ‘Premier Russet’ tubers. AO02183-2 tubers were more tolerant of heat for retention of LTS resistance. Higher bulking and maturation temperatures also accelerated LTS and loss of process quality of ‘Ranger Russet’ tubers, consistent with increased invertase and lower invertase inhibitor activities. During LTS, tuber respiration fell rapidly to a minimum as temperature decreased from 9 to 4 °C, followed by an increase to a maximum as tubers acclimated to 4 °C; respiration then declined over the remaining storage period. The magnitude of this cold-induced acclimation response correlated directly with the extent of buildup in sugars over the 24-day LTS period and thus reflected the effects of in-season heat stress on propensity of tubers to sweeten and lose process quality at 4 °C. While morphologically indistinguishable from control tubers, tubers grown at elevated temperature had different basal metabolic (respiration) rates at harvest and during cold acclimation, reduced dormancy during storage, greater increases in sucrose and reducing sugars and associated loss of process quality during LTS, and reduced ability to improve process quality through reconditioning. Breeding for retention of postharvest quality and LTS resistance should consider strategies for incorporating more robust tolerance to in-season heat stress.     

Age of potato seed-tubers influences protein synthesis during sprouting

The effect of seed-tuber age on the ability of tuber tissue to synthesize protein during sprouting was examined. As seed-tuber age advanced from 4 to 32 months (at 4°C, 95% relative humidity), soluble protein concentration of tubers decreased linearly, with a concomitant increase in free amino acid concentration. The age-induced loss of tuber protein may thus be due to increased proteolysis, decreased protein synthesis, or both. Five- and 17-month-old seed-tubers were compared for their ability to incorporate radiolabeled amino acids into soluble protein at equivalent stages of sprout development. Tuber respiration was profiled through each sprouting stage to characterize the physiological status of the seed-tubers prior to incorporation studies. Five-month-old seed-tubers maintained a constant rate of respiration during sprouting. In contrast, respiration of 17-month-old tubers increased as sprout dry matter increased, resulting in a 2- to 3-fold greater respiratory rate from the older tubers, relative to the younger tubers, at similar stages of sprout development. Prior to sprouting, the rate of incorporation of amino acids into trichloroacetic acid-precipitable protein of tissue from 5-month-old tubers was 2. 9-fold higher than that from 17-month-old tubers. More importantly, protein-synthetic capacity of tissue from younger tubers increased about 1. 7-fold during sprout development. Despite the higher respiratory activity and faster total sprout dry matter accumulation from older seed-tubers, protein synthesis remained at a low and constant level through all stages of sprouting. Protein-synthetic capacity thus declines with advancing tuber age, and this may contribute to reduced growth potential during the latter stages of establishment by affecting the ability of seed-tubers to synthesize enzymes involved in mobilization and translocation of tuber reserves to developing plants.     

Leaf rosette closure in the alpine rock species Saxifraga paniculata Mill.: significance for survival of drought and heat under high irradiation

The significance of leaf rosette closure for survival of drought and heat under high irradiation on alpine rock sites was investigated in the cushion forming rosette plant, Saxifraga paniculata Mill. With decreasing water content the leaves fold over the rosette centre reducing reversibly the evaporative leaf surface area by 80%. Internal water redistribution driven by an osmotic gradient from older to younger leaves occurs. The oldest leaves dry out to promote the survival of the individual. Leaf temperatures above 45 °C (which match heat tolerance limits 45–57 °C; LT₅₀) co-occurred with low substrate water potentials (less than – 0·5 MPa) on 11·3% of summer days. Shading by leaves can be crucial to surviving high temperatures as it keeps the rosette centre up to 10 °C colder. Mutual shading prevented sustained drought-induced photoinhibition in upper leaf surfaces at relative water contents below 60%. In exposed lower leaf surfaces restoration of photosystem II took several days. Leaf temperatures above 40 °C (21·3% of summer days) induced photoinhibition in situ. Periods with sufficient water supply can be fully utilized as rehydration is fast ( < 12 h) and exposes the upper leaf surfaces that showed only minor photoinhibition. By reversible leaf rosette closure environmental extremes that otherwise could exceed tolerance are efficiently avoided.     

Heat and smoke pre‐treatment of seeds to improve restoration of an endangered Mediterranean climate vegetation type

Invasive alien plants impact ecosystems, which often necessitates their removal. Where indigenous species recovery fails following removal alone, an active intervention involving reintroduction of seed of native species may be needed. This study investigated the potential for a combination of the fire cues of smoke and heat as a pre‐treatment of seeds in breaking dormancy and facilitating increased germination. Species were selected to represent different functional types within Cape Flats Sand Fynbos; a fire‐prone, critically endangered vegetation type in South Africa. Seeds were exposed to either a heat pulse (temperatures between 60 and 300°C for durations of between 30 s and 20 min) or dry after‐ripening (1 or 2 months at milder temperatures of 45°C or less). Thereafter, seeds were soaked in smoke solution for 18 h and subsequently placed on agar at 10/20°C for germination. Most species fell into one of two main groups: Seed germination in the first group was greatest following a lower temperature (60°C) heat pulse, an extended period of mild temperature (20/40°C or 45°C) exposure, or no pre‐treatment with heat. Seed germination in the second group was promoted after brief exposure to higher (100°C) temperatures. No germination occurred in any species following heat treatments of 150°C or higher. Species which responded better to higher temperatures were mainly those possessing physical dormancy, but seed morphology did not correlate with germination success. This study showed that heat stimulation of seeds is more widespread in fynbos plant families than previously known and will enable the development of better seed pre‐treatment protocols before large‐scale sowing as an active restoration treatment after alien plant clearing.     

Effect of high temperature treatment on disinfestation and quality characteristics of sorghum

Sorghum grain (two varieties) was modified to different water contents (12% to 16% wet weight basis) and heated to 60°C, 70°C and 80°C for periods of 4, 8 and 12 min. Germination, seedling vigour, seedling dry matter, free fatty acid (FFA) content, fungal contamination and infestation with the insect pest Rhyzopertha dominica (F.) were all markedly affected by heat treatment. The effectiveness of the heat treatment was also influenced by the size of the sample used. Heat treatment at 60°C and 70°C resulted in germination being unaffected or stimulated while at 80°C and the higher water contents significantly reduced, when compared to untreated controls. The dry matter of seedlings, and seedling vigour was positively correlated with germination and heat treatment. Heat treatment had no effect on FFA. All stages of the insect pest, R. dominica, were destroyed at 70°C and an 8 min exposure time. However, the water content of the sorghum was critical in determining the efficacy against this pest. The percentage fungal contamination of grain was reduced from 90% to about 25% by heat treatment. However, some grain fungi, particularly Eurotium spp., Aspergillus niger and Penicillium spp. could still be isolated from sorghum grain treated at 80°C for up to 12 minutes.     

Synergistic effects of heat and diatomaceous earth treatment for the control of Plodia interpunctella (Lepidoptera: Pyralidae)

Plodia interpunctella is a major economic pest that commonly infests most stored and processed agricultural products. Currently, heating at 50–60°C for at least 48 h is applied in facilities for disinfestation. However, this condition requires a great deal of time and expense. To improve the control efficiency of this system, we conducted combined treatments with heating and diatomaceous earth (DE), which is known to be toxic to pest insects. The DE effect was compared to heating at 25°C or 40°C to wandering fifth instar larvae, which is the stage most tolerant to heat. When larvae were brushed with DE powder, mortality was only 15.0–18.3% at 25°C for 10 days, but rapidly increased to 100% at 40°C within 4 h post‐treatment. In addition, when larvae were kept in a plastic cage with DE [4 mg/L (w/v)], their mortality was 100% in 24 h at 40°C post‐treatment; otherwise mortality was only 8.8% without DE. Thus, the control efficiency of heating significantly improved with the combination of DE. These effects increased further at higher temperatures and with longer exposure. Our results clearly showed that DE treatment showed synergistic effects with heating systems for the control of P. interpunctella.     

The effect of temperature on the rate of sprout growth and development within stored onion bulbs

In order to understand better the effects of storage temperature on the time to visible sprouting in stored onions, sprout growth was measured by regularly dissecting samples from bulbs stored at 1, 10, 15 or 25°C for 243 days. The dry-weight of the shoot or sprout within stored onion bulbs increased exponentially with time. The rate of increase of sprout dry weight, as well as the rate of leaf initiation by the shoot apex was faster at 17° than at 10 or 25°C, and almost zero at 1°C. The rate of loss of dry weight from storage tissue was similar at 17°C and 25°C but slower at 10°C and slower still at 1°C.     

Effects of delaying fungicide treatment of wounded potatoes on the incidence of Fusarium dry rot in store

Potato tubers artificially inoculated with Fusarium solani var. coeruleum or F. sulphureum 3 months after harvest were uniformly wounded and held at 5, 10 or 15°C for up to 21 days before immersion in fungicide suspensions. Holding tubers for 14 days at 15°C (curing conditions) or at 5°C did not alter the incidence of dry rot subsequently developing on tubers stored at 10°C, and holding tubers for up to 21 days at 15°C slightly increased disease caused by both pathogens. Thiabendazole, imazalil and prochloraz applied to tubers immediately after wounding almost completely prevented dry rot. Treatment after 3 days was less effective and the amount of disease increased with further delay; fungicides were more effective on tubers held at 5°C than at 10 or 15°C before treatment and storage, and efficacy of the fungicide was decreased by increasing the amount of inoculum on tubers. Wounds became less susceptible to infection by F. solani var. coeruleum and F. sulphureum when tubers were held at 15°C before inoculation, and the incidence of rots was decreased by 70–80% by delaying inoculation for 7 days. Treating tubers with dichlorophen immediately after wounding slightly increased the disease. The effects of fungicide treatment, curing conditions and wound healing are discussed.     

Control of Postharvest Diseases of Sweet Cherry with Ethanol and Hot Water

Complete inhibition of the germination of spores of Penicillium expansum occurred after 10 s exposure to 40% ethanol or more at ambient temperature, while spores of Botrytis cinerea were completely inhibited by 30% ethanol or more. Mortality of the spores of P. expansum and B. cinerea in heated 10% ethanol was higher than in water at the same temperatures. Immersion of naturally inoculated fruit in 20, 30, 40, or 50% ethanol reduced the decay present after storage for 10 days at 20°C similarly and by approximately 60–85%. Immersion of fruit that had been inoculated with the spores of P. expansum and B. cinerea reduced decay by both pathogens after storage for 30 days at 0°C and 5 days at 20°C when 30% or higher concentrations of ethanol were used. The incidence of decay after immersion in water alone for 30 s at 24, 50, 55, or 60°C was 57.7, 44.7, 46.2, and 35.7%, respectively, while 10% ethanol at these temperatures the decay incidence to 52.2, 33.9, 32.8, or 14.7%, respectively. Water treatments at 50, 55, or 60°C alone were not effective against P. expansum, while their efficacies were significantly increased by the addition of 10% ethanol. The most effective treatment was immersion in 10% ethanol at 60°C. Ethanol treatments at 20, 30, 40, or 50% and water treatments at 55 or 60°C significantly reduced natural fungal populations on the surfaces of fruit in all of the experiments. Addition of 10% ethanol to water significantly increased the efficacy of water in reducing the fungal populations at elevated temperatures. None of these treatments caused surface injuries to the fruit or adversely affected stem colour.     

Predicting patterns of post-fire germination in 35 eastern Australian Fabaceae

Germination in 35 species from 15 legume genera of southeastern Australia was promoted by a heat treatment which broke the seed coatcaused dormancy. Once the critical temperature was reached, most seeds had their dormancy broken, independent of the duration of heating. Species fell into three classes according to whether their dormancy was broken by a temperature of 40, 60 or 80°C. Highest germination in all species was achieved by heating in the temperature range 80–100°C, although long durations (120 min) at 100°C caused seed death in several species. At 120°C, seeds of most species were killed at all but one minute's duration. A proportion of seeds from 7 species (Acacia myrtifolia, Pultenaea daphnoides, P. incurvata, P. linophylla, P. polifolia, Dillwynia floribunda and Sphaerolobium vimineurn) was not killed at 120°C and had their dormancy broken. This proportion varied markedly and resultant germination levels were significantly less than those at 80 and 100°C, except in S. vimineum. Between-site variations in the 4 species tested (A. myrtifolia, A. suaveolens, A. terminalis and A. ulicifolia) were small. These variations concerned: (i) the minimum temperature required to break seed dormancy in 2 species: 60°C in one population of A. myrtifolia and A. suaveolens, and 80°C in the other; and (ii) the intensity of the germination response. Duration of heating was less important than temperature as a determinant of germination. Ordination techniques revealed that results from one duration across temperatures were comparable with data from multiple durations. This has significant applications in studying rare species, where seed may be in short supply. Predicted germination levels after a moderate intensity fire should far exceed those after a low intensity fire. Little germination was predicted for many species after a low intensity fire and for one species, A. elongata, no germination was predicted. The potential role of indicator species in relation to the maintenance of species in a community is suggested.     

Temperature stress induces notochord abnormalities and heat shock proteins expression in larval green sturgeon (Acipenser medirostris Ayres 1854)

The effects of thermal stress on survival, development and heat shock protein (hsp) expression of green sturgeon (GS) yolk‐sac larvae, from hatching through yolk depletion were investigated to provide insight into effects of highly altered natural river hydrographs. Hatched GS larvae were reared at constant water temperatures 18°C (control) through 28°C at 2°C increments. Larval survival significantly decreased at 26–28°C, with 28°C being lethal. Significant proportions of deformed larvae were found at sub‐lethal (20–26°C) and lethal 28°C rearing temperatures, with kyphosis (i.e. backward flexion of notochord) accounting for >99% of morphological deformities. Histological analysis of larvae preparations indicate that elevated water temperature affects notochord cell function and physiology. At rearing temperatures 20–28°C, thermal stress elicited a quick (24 h) and long lasting (yolk‐sac absorption) significant over‐expression of measured heat shock proteins (hsps), all of which are known components of intracellular protein repair and stabilization mechanism. Thermal sensitivity, as indicated by the incidence of abnormalities and expression of different hsps, varied significantly between crosses. Thermally tolerant progeny exhibited a short but rapid hsp72 (size in kDa) over‐expression, and more pronounced hsp60 and hsp90 over‐expression, than less tolerant progeny which exhibited a prolonged hsp72 and hsp78 over‐expression. At environmentally relevant water temperatures bent larvae exhibited spiral swimming, which in the wild would compromise the ability of emerging larvae to forage, avoid predators, and migrate downstream, ultimately compromising survival and recruitment. Before larvae hsp content can be used as a thermal‐stress biomarker for GS, field validation studies are needed.     

Proteomic characterization and antifungal activity of potato tuber proteins isolated from starch production waste under different temperature regimes

Proteins were obtained from effluent of a starch manufacture by using different isolation temperatures (40, 60, 80, and 100 °C). The proteins, remaining in effluent after treatment of potato juice at 80 and 100 °C differed significantly in composition and in structural stability as well as in trypsin inhibitory and antifungal activities in comparison with the variants of 40 and 60 °C. The protein samples of 80 °C exhibited the highest antifungal activity and its average value of IC₅₀ against five strains of two Fusarium species was determined in average at 0.18 mg ml⁻¹. The 80 °C protein samples consisted predominantly of low-molecular proteins (7–17 kDa) identified as potato tuber protease inhibitors I and II. Predominantly, protease inhibitors II were identified for the protein samples obtained by 100 °C and here we identified 7 spots in comparison with 12 identified for the 80 °C samples. Samples of 40 and 60 °C with low antifungal activities represent high variability of detected and identified proteins. We identified various representatives of aspartic, cysteine, and serine protease inhibitors in both types of samples. These samples also contained Kunitz-type protease inhibitors that were not found in the 80 and 100 °C samples which documented thermal unstableness of Kunitz-type protease inhibitors. Functional stability at high temperatures and antifungal activity of isolated potato protease inhibitors I and II support the potential of this fraction usage in food, feed, pharmaceutical, or agricultural industry and offer new products for starch manufactures. At the same time, utilization of the stable protein fraction of waste deproteinized potato water promotes exploitation of potato starch production resources.

     

Importance of dormancy and sink strength in sprouting of onions (Allium cepa) during storage

In onion ( Allium cepa L.) postponement of sprouting is necessary to achieve long term storage. We studied the factors determining sprouting during dry storage at 16°C. The period to visible sprouting depends on the length of the dormancy period, if present, and on the growth rate of the sprout. In the three cultivars tested, sprouts were initiated within 2 weeks after harvest indicating the absence of a real dormancy period. Sprout length increased linearly during storage. The mitotic activity of the apex decreased before harvest, was low at the transition from scale to leaf formation, and increased again when the sprout was initiated. From a few weeks before harvest, the initially high fructan content of the scales decreased, leading to a large increase in fructose. The sprout always contained enough carbohydrates for growth (between 50 and 60 mg g⁻¹ dry weight, of which 30% was fructan). The activity of sucrose synthase (EC 2.4.1.13) increased as the sprout grew, indicating an increase in sink strength. Invertase (EC 3.2.1.26) was absent in all bulb organs, during the various developmental stages. Although carbohydrates and enzymes were available for fast sprouting, sprout growth was still linear instead of exponential during dry storage at temperatures favorable for growth (16°C). The relative importance of factors determining sprouting are discussed.