Low root zone temperature favours shoot B partitioning into young leaves of oilseed rape (Brassica napus)

In previous studies with tropical plant species, low root zone temperature (RZT) induced boron (B) deficiency, but it is not known if the same response to RZT will be expressed in temperate species, like oilseed rape, that are more tolerant of low temperature. The present experiments investigated the effect of RZT (10 and 20°C) on oilseed rape ( Brassica napus L. cv. Hyola 42) response to B in solution culture, in summer and winter. Regardless of canopy growth conditions, low RZT (10°C) promoted the partitioning of shoot B to the actively growing leaves, especially when B supply was low. However, low RZT did not significantly alter net B uptake rates or plant biomass. Low RZT decreased the shoot-to-root ratio, countering the effects of low B which increased it, leading to a decreased demand for B in the shoot at low RZT. At low B supply, B-deficiency symptoms appeared later at 10 than at 20°C, corresponding with higher B concentrations in the youngest fully opened leaves (YOLs) at 10°C RZT. Thus 10°C RZT increased the tolerance to low B supply. As a result, it is concluded that the effect of decreasing RZT on the responses of the temperate species, oilseed rape, to low B supply depends on whether the low RZT is above or below the optimal root temperature for growth.     

Response of genetic dwarf apple plants to GA3

High temperature has been implicated as the major factor responsible for dwarfing of selected apple ( Malus domestica Borkh.) trees of a hybrid population of cv. Goldspur Delicious x cv. Redspur Delicious. Dwarf plants grew only 2.2 cm in 63 days under a ramped temperature regime (night 15°C, day ramped up to 38°C, held for 2 h and ramped down to 15°C—14 h daylength), whereas semi-dwarf plants grew 26.3 cm. At a constant 27°C (14 h daylength), both dwarf and semi-dwarf plants grew 26.3 cm. At a constant 27°C (14 h daylength), both dwarf and semi-dwarf plants grew nearly 50 cm. The gibberellin biosynthesis inhibitor, paclobutrazol, retarded growth of semi-dwarf plants in both ramped and constant environments and dwarf plants in the constant 27°C environment. It did not further reduce the size of dwarf plants growing under the ramped regime. Gibberellin (GA₃) treatment reversed the inhibition of growth caused by paclobutrazol for all plants except it did not restore growth of dwarf plants in the ramped environment. These data suggest that neither pacobutrazoltreated nor untreated dwarf plants growing in the ramped environment (or in the orchard during hot summer months) are able to respond to GA₃. In constrast, GA₃ was utilized by the paclobutrazol-inhibited dwarf plants growing at constant 27°C, enabling shoot elongation to take place. It appears that high temperature may have caused alterations in GA target tissues in dwarf plants so that they no longer had the capacity to respond to GA.     

The effect of photoperiod and temperature on growth and frost resistance of winter rye root systems

Root growth, development and frost resistance were examined in winter rye ( Secale cereale L. cv. Puma) plants grown under 6 combinations of temperature and photoperiod (20/16°C or 5/3°C, day/night; 8, 16- or 24-h days). Overall root system growth is influenced by the interaction of temperature and photoperiod. Maximum shoot growth occurs at a 24-h photoperiod in 20°C plants and at a 16-h photoperiod in 5°C plants, and is correlated in both treatments with a high root:shoot ratio. Frost resistance of rye roots is affected by short photoperiods in 2 ways. First, short photoperiod and low temperature delay production of new adventitious roots so that newly developing roots are not exposed to freezing temperatures. Second, short photoperiod alone can induce several degrees of frost tolerance in existing roots during the lag phase of growth. Low temperature alone does not decrease the rate of dry weight accumulation in rye root systems, but cold temperature does retard developmental processes within the roots. Rye roots grown at 5°C develop first order lateral roots, differentiate metaxylem vessels and suberize endodermal cell walls more slowly than roots grown at 20°C.     

Factors affecting the adhesion and uptake of an oculo-genital strain of Chlamydia trachomatis to McCoy cells

Abstract We have studied adhesion and uptake of C. trachomatis serovar E in McCoy cells under various infection conditions. Adhesion and uptake of chlamydiae was completed about 3 h after the initiation of stationary infection at 37°C, but ingestion of cell membrane-attached organisms was finished within 0.5 h at 37°C. Reincubated chlamydiae, not attached after 3 h at 37°C, attached readily to fresh McCoy cell monolayers, but to a lesser extent than the original inoculum. Our results indicate that the lack of further attachment after 3 h incubation at 37°C under stationary infection conditions has complex causes, involving both host cell and parasite. Centrifugation did not affect the uptake of chlamydiae already bound to the cell membrane, suggesting that the uptake phase of C. trachomatis serovar E by McCoy cells is unaffected by centrifugation.     

A comparison of low temperature growth vs low temperature shifts to induce resistance to photoinhibition in spinach (Spinacia oleracea)

Plants of Spinacia oleracea L. cv. Savoy grown under cold-hardening (5°C) and nonhardening (16°C) conditions were exposed to a photoinhibitory irradiance of 1300 μmol rrr^: m-² S-¹ 5°C for 12 h. Plants grown at 5°C exhibited a greater resistance to photoinhibition at low temperature in comparison to plants grown at 16°C as measured by the photochemical efficiency of photosyslem II. In contrast, tuily expanded leaves of plants grown at 16°C and then shifted to 5°C for 10 days did not exhibit increased resistance to photoinhibition. This was observed irrespective of the phoioperiod experienced during the shift to a lower temperature. Furthermore, spinach grown at 16°C and subsequently exposed to a stepped, daily decrease in temperature from 16 to 1°C over 10 days w ith a concomitant reduction in photoperiod. also did not exhibit any change in susceptibility to photoinhibition. Thus, a decrease in photoperiod accompanied by either an abrupt or stepped low temperature shift cannot induce increased resistance to photoinhibition. This confirms the hypothesis that growth and development at cold-hardening temperature are absolute requirements for the acquisition of resistance to photoinhibition at low temperature.     

Dormancy and germination of olive embryos as affected by temperature

Olive seeds do not germinate promptly when placed under favourable conditions, which is a problem in raising young plants for breeding or experimental purposes. In a series of experiments an investigation of the role of temperature in the germination of olive embryos was conducted. Naked, unchilled olive embryos ( Olea europaea L. cv. Chalkidikis), cultured in vitro at 20°C, had a germination capacity of 73%, whereas that of embryos which had previously been chilled at 10°C for 2 or more weeks reached 96%. Intact seeds did not germinate at 20°C unless they had previously been subjected to 10°C for 3 or 4 weeks. Embryos chilled while in the intact seed and excised just before transfer to 20°C, reacted in a similar way to naked embryos, but reached their maximum germination capacity after 4 weeks at 10°C. Under constant temperature conditions the highest germination percentage of embryos was observed at 10 and 15°C and the highest germination rate at 15°C, while a moderate capacity and rate of germination occurred at 20°C, and a very low percentage and rate at 25 and 30°C. Prechilling at 10°C did not affect germination at 15°C, but improved the percentage and the rate of germination at 20, 25 and 30°C. The germination percentages of embryos chilled for 1 or 2 weeks at 10°C and then transferred to 25°C were lower than those of similarly chilled embryos transferred to 20°C. The chilling effect could not be reversed at 25°C when the embryos had been chilled for 3 or more weeks. The results show that olive seeds exhibit a state of dormancy that is caused by factors residing partly in the endosperm and partly within the embryo.     

Uptake of ammonium and nitrate by carob (Ceratonia siliqua) as affected by root temperature and inhibitors

Seedlings of carob ( Ceratonia siliqua L. cv. Mulata) were grown in nutrient solution culture for 5 weeks, with or without nitrogen at different root temperatures (10, 16, 22, 30, 35 or 40deg;C) and with the air temperature kept between 20 and 24°C. The nitrogen was given as either ammonium or nitrate. At all root temperatures studied, nitrogen-depleted plants developed higher net uptake rates for nitrogen than plants grown in the presence of nitrogen. Temperature affected the kinetic parameters of nitrate uptake more than those of ammonium uptake. With increasing root temperature, the K_m of ammonium uptake decreased, but to a lesser extent than the K_m for nitrate. The increase in V_max of ammonium uptake with temperature was also less noticeable than that for nitrate uptake. Ammonium and nitrate uptakes were inhibited in a similar way by respiratory or protein synthesis inhibitors. It may be noted that ammonium uptake in the presence of inhibitors at 40°C was higher than uptake at 10°C without inhibitors. Some similarities between the transport mechanisms for nitrate and ammonium are underlined in the present work. Components of both transport systems displayed saturation kinetics and depended on protein synthesis and energy. The following components of nitrate uptake were distinguished: (a) a passive net influx into the apparent free space; (b) a constitutive active uptake and (c) active uptake dependent on protein synthesis. We may similarly define three ammonium uptake systems: (a) a passive influx into the apparent free space; (b) passive diffusion uptake at high temperature and (c) active uptake dependent on protein synthesis. The possible role of the ratio between mechanism (c) and mechanism (b) as determinant of ammonium sensitivity is discussed.     

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.     

Adenine nucleotide contents in callus-forming potato tuber discs with different respiratory characteristics

ATP content (per g fresh weight) and energy charge were higher during incubation at 8°C than at 28°C in the early stages of callus induction of potato tuber discs ( Solanum luberosum L. cv. Bintje). After a transfer from 28°C to 8°C, ATP content increased while a sharp decline in ATP content was observed after a transfer from 8°C to 28°C. ADP and AMP pools did not increase correspondingly. When the callus discs had entered the logarithmic growth phase, the energy charge was maintained within relatively narrow limits (0.77–0.80) at all culture temperatures.     

Does grafting provide tomato plants an advantage against H2O2 production under conditions of thermal shock?

Non-grafted tomato plants ( Lycopersicon esculentum L. cv. Tmknvf₂) and grafted tomato plants ( L. esculentum L. cv. Tmknvf₂ ×  L. esculentum L. cv. RX-335) were grown for 30 days at three different temperatures (10°C, 25°C and 35°C). In the leaves of these plants, the enzymatic activities of SOD, GPX, CAT, APX, DHAR and GR were analysed, as were the concentrations of total H₂O₂, ascorbate and glutathione as well as foliar DW. Regardless of whether the plant was grafted or not, our results indicate that the thermal stress occurred mainly at 35°C, with the following effects: (1) high SOD activity; (2) H₂O₂ accumulation; (3) foliar-biomass reduction; (4) low GPX, CAT, APX, DHAR and GR activities; and (5) high concentrations of ascorbate and glutathione. In addition, our data show these effects to be much weaker in grafted than in non-grafted plants, directly reflected in greater biomass production. Therefore, the use of grafted plants under excessively high temperatures may offer an advantage over non-grafted plants in terms of resistance against thermal shock.     

Senescence in oat leaf segments under hypobaric conditions

The physiological effects of storing plants under hypobaric conditions were studied using oat ( Avena sativa L. cv. Victory) leaf segments as a test system. The segments from seven day old plants were floated on water and stored in darkness at 12°C, 1.6 kPa or at 25°C, 6 kPa. Low temperature or hypobaric conditions delayed senescence, whereas the combination arrested the syndrome at an early stage. One of the effects of low pressure was to force the stomata open. The hormones abscisic acid and kinetin, which affect the stomatal aperture and also senescence, did not show any effect in hypobarically stored plant material. The stomata were forced open in darkness when the pressure was lower than 77 kPa and opening time was 8 h. The senescence syndrome in hypobarically stored segments developed similar to those treated with kinetin at 101 kPa.     

Effect of temperature on drought resistance and growth of cotton plants

In cotton plants ( Gossypium hirsutum L. cv. B.J.A.) the temperature of the roots affected both root and shoot growth, as did the temperature of the shoot. Drought resistance increased when the temperature imposed on roots (27°C) was lower than that imposed on shoots (17°C); the result was a decrease in both transpiration and flow of root sap. Stomatal characteristics as measured by density, index and resistance, depended only on shoot temperature. Differences in drought resistance, depended only on shoot temperature. Differences in drought resistance seem to be a result of changes in transpiration flow modulated by the amount of absorbed water.     

Participation of the cyanide-resistant pathway in respiration of winter rape leaves as affected by plant cold acclimation

Leaf slices sampled from winter rape plants ( Brassica napus L., var. oleifera L., cv. GórczaánAski), grown in cold (5°C), showed an increase in the dark respiration rate (measured at 25°C) as compared to slices cut from control plants (grown at 20/15°C). The effect of low temperature was most pronounced after 4 days of plant growth in the cold. Oxygen uptake by control slices was 60% inhibited by 1 m M KCN and was insensitive to 2.5 m M salicylhydroxamic acid (SHAM). On the contrary, respiration of leaf slices from cold-pretreated plants was more resistant to cyanide (35% inhibition after 4 days of cold treatment) and was 30% inhibited by SHAM. The patterns of cold-induced changes in total respiratory activity and in the estimated activity of alternative pathway were similar. It seems that in leaf slices from plants grown in the cold, the cyanide-resistant, alternative pathway participates in oxygen uptake. Cold treatment of plants also brought about a 4-fold increase in the level of soluble sugars, which reached a maximum on day 4 of exposure to cold. Addition of sucrose to the incubation medium resulted in an immediate increase in oxygen uptake by slices with low endogenous sugar level. The respiration stimulated by sucrose addition was more resistant to cyanide than the basal respiration and it was inhibited by SHAM. It is concluded that the operation of the alternative pathway is responsible for the increased oxygen uptake by the cold-grown winter rape leaves and it may be induced by an increased sugar supply for respiratory processes.     

Short-term aluminium uptake by tobacco cells: Growth dependence and evidence for internalization in a discrete peripheral region

Short-term uptake and initial localization of aluminium (Al) were investigated in cultured cells of Nicotiana tabacum L. cv. BY-2. Graphite furnace atomic absorption spectrometry and an in vivo Al-sensitive fluorometric assay, employing morin, yielded similar results in all experiments. Aluminium uptake was critically dependent on cell growth. As opposed to negligible uptake in stationary-phase cells, Al uptake (20 μ M AlCl₃, pH 4.5, 23°C) by actively growing cells was detectable within 5 min, with an initial rate of 16 nmol Al (10⁶ cells)⁻¹ h⁻¹. Increased CaCl₂ levels (up to 20 m M ), low temperature (4°C), and pre-chelation of Al to citrate greatly reduced Al uptake (by 75–90%). A pH-associated permeabilization of cells at pH 4.5, as monitored by trypan blue, was observed in some growing cells. Although permeability to trypan blue was not a requirement for Al uptake, enhanced membrane permeability at pH 4.5, relative to pH 5.6, may contribute to Al uptake. Aluminium was observed to localize mainly in a pronounced and discrete fluorescent zone at the cell periphery (2–30 μm wide), presumably in the cortical cytosol and/or the adjoining plasma membrane section, although the possibility cannot be excluded that some Al resided in the cell wall apposing this discrete region. However, as judged by the Al-morin assay, there were no detectable Al levels in the remaining, larger portion of the cell wall. The potential of the Al-morin method in Al toxicity studies is illustrated.     

Leucine uptake by tomato leaf tissue under low temperature: Preincubation dependence of uptake reduction

The uptake of ³H-leucine by leaf fragments of Lycopersicon esculentum Mill. cv. Rutgers and L. hirsutum Humb. & Bonpl., a wild tomato, was studied. Two altitudinal races of L. hirsutum were used which differed in chilling tolerance. The temperature dependence of uptake was initially similar for all plant varieties. However, at temperatures below about 11°C, uptake progressively decreased in the more chilling-sensitive varieties ( L. esculentum , Low-altitude L. hirsutum ), but not in the more chilling-tolerant (high-altitude L. hirsutum ) with increasing preincubation time. More than 60 min preincubation was required for this effect, and it was greatest at the lower temperatures. When leaf fragments, chilled for short periods of time (>22 h), were returned to 22°C, initial rates of uptake were recovered within 2 h. The relationship between membrane lipid changes and membrane protein activity under chill stress is discussed.     

Putrescine uptake and translocation in higher plants

Putrescine uptake and translocation were studied by feeding [³H] putrescine to roots of tomato seedlings ( Lycopersicon esculentum Miller, cv. Earlypak 7) at the stage of expanded cotyledons, of maize seedlings ( Zea mais L.) at the coleoptile stage, and of one year old pines ( Pinus pinea L.). Putrescine translocation was rapid as radioactivity appeared in the upper part of the seedlings within 30 min, continuing to increase up to 24 h, while it decreased in roots. The putrescine supplied was partly metabolized to spermidine and spermine in the course of 24 h. The transport was temperature-dependent as it increased with increasing temperature from 4°C to 30°C. In plants kept in 100% relative humidity the transport decreased by 27% compared to controls kept in 50% relative humidity. The existence of basipetal transport was assessed by feeding labeled putrescine to cotyledons or to a primary leaf of tomato plants at different stages of growth. The influence of ringing at the hypocotyl level on polyamine translocation in pine plants was studied in order to exclude cortical parenchyma and phloem from transport. Radioactivity decreased in the hypocotyl just above the ring and in the upper parts (epicotyls with needles), but long-distance transport was low affected indicating xylem transport. It is suggested that polyamine transport is not polar, and that it occurs mainly through xylem vessels.     

Boron uptake and translocation in some cotton cultivars

Aims

Boron (B) is the most deficient micronutrient in cotton (Gossypium hirsutum L.). It is generally accepted that B is immobile in cotton phloem, but some cultivars could remobilize the nutrient. In order to further understand B uptake and mobility in various cotton cultivars two experiments were conducted.

Methods

In experiment-1, cotton cultivars were grown in ¹⁰B enriched or natural abundance nutrient solutions for 4 weeks and transferred to nutrient solutions ranging from deficient to sufficient in B. In experiment-2 ¹⁰B enriched boric acid was applied to cotton leaves and B mobilization was determined.

Results

In deficient plants, B previously supplied to roots was remobilized from older to younger plant tissues, but the amount was insufficient to maintain growth. Boron deficiency symptoms appeared and progressed with time. Boron applied to leaves was taken up and remobilized within 24 h. Boron mobilization was higher to plant parts above the treated region.

Conclusion

Boron uptake and mobilization was similar among cotton cultivars. Boron applied to cotton leaves shows a preferential translocation to younger tissues. Foliar sprays of B to cotton may be used to cope with a temporary deficiency, but to achieve full growth and development B must be available to cotton throughout the plant cycle.     

Effects of root zone temperature on aluminium toxicity in two cultivars of spring wheat with different resistance to aluminium

Manifestations of aluminium (Al) toxicity in two cultivars of wheat ( Triticum aestivum L. cvs Kadett [relatively Al-resistant] and WW 20299 [relatively Al-sensitive]) were investigated at two root zone temperatures (RZT) that may occur in the field. The plants were grown for 9 days at 10 or 25°C RZT. Mineral nutrients other than CaSO₄ were supplied daily in exponentially increasing amounts to meet the demand of the plants. Al was added as Al₂(SO₄)₃ at the beginning of the culture period at concentrations ranging from 0 to 100 μ M . pH was kept constant at 4.1. Experimental data were analysed for interactions between Al and RZT on a fresh weight basis by the nonlinear Weibull function. Cultivar Kadett, when grown at 25°C RZT, was more resistant to Al than when grown at 10°C RZT. Cultivar WW 20299 was equally sensitive to Al at 10 and 25°C RZT but generally more sensitive to Al than cv. Kadett. It is suggested that cv. Kadett, in contrast to cv. WW 20299, possesses a mechanism for Al resistance that is less effective at 10°C than at 25°C RZT and therefore may be metabolically dependent. In roots, the concentrations of K, P, Mg and Ca were not negatively affected by Al or by RZT. In shoots of both cultivars the concentrations of Ca and Mg became comparatively low when the plants were treated with Al or at low RZT, the effect being larger for Ca than for Mg. At 10°C RZT under Al stress, the Ca concentrations in shoots approached the critical concentration where growth may be inhibited. As no Al was detected in the shoots, it is suggested that Al in the roots inhibits shoot growth by reducing transport of Ca from roots to shoots.     

Adaptation of potassium translocation into the shoot of maize (Zea mays) to shoot demand: Evidence for xylem loading as a regulating step

In order to manipulate the shoot demand for mineral nutrients per unit root weight, maize ( Zea mays L.) seedlings were grown in nutrient solution with different temperatures in the root zone and at the shoot base. The aerial temperature was kept uniform at 24/20°C day/night. At a root zone temperature (RZT) of 24°C, shoot growth was reduced by decreasing the shoot base temperature (SBT) to 12°C; at a RZT of 12°C, shoot growth was increased by raising the SBT to 24°C. At both RZT root growth was not affected by the SBT. Thus, the shoot demand for nutrients per unit root was either increased by raising, or decreased by lowering the SBT. The net uptake rate of potassium (K), as determined from accumulation rates between sequential harvests, was not affected within the first 3 days after lowering the SBT, whereas net translocation rates of K into the shoot and translocation rates in the xylem exudate of decapitated plants were markedly reduced. Obviously, translocation of K into the shoot seems to be regulated independently from K uptake into the root cells. Translocation rates of K in the xylem exudate of decapitated plants were markedly reduced when the nutrient solution was replaced by CaCl₂ solution during exudation. But, depending on the SBT before decapitation, significant differences remained in the translocation rates of K even when K uptake from the nutrient solution was prevented.
From the results it is suggested that xylem loading of K is regulated separately from K uptake from the external solution and that the adaptation of K translocation to shoot demand is coupled with an altered capacity of the root for xylem loading.     

Effect of bacterial suspensions on vascular occlusion in stems of cut rose flowers

A suspension of Pseudomans aeruginosa at 5 × 10⁹ cfu/ml was either left untreated, pasteurized (15 min, 70°C) or autoclaved (15 min, 121°C). Stems of cut rose flowers ( Rosa hybrida L. cv. Sonia) placed in these solutions for 0·5–4·0 h showed decreased water uptake and a reduction of hydraulic conductance of the basal 5·0 cm stem segment. No difference was found between the treatments. When the pasteurized or autoclaved solutions were left at 4°C for 7 days, bacterial cells had autolyzed, and stems placed in these suspensions showed lower water uptake and hydraulic conductance than stems in freshly prepared solutions. The results show that living and non-living bacteria have the same effect on vascular occlusion, and indicate that hydraulic conductance was more reduced when the average size of the particles was smaller than that of bacterial cells. Vascular blockage occurred within 30 min after the start of treatment, apparently due to a physical effect rather than a physiological response of the stem tissue.