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Influence of night humidityon the distribution ofcalcium and sap flow intomato plantsJae Hee Choi a , Gap Chae Chung a & SeongHee Lee aa Department of Horticulture, Instituteof Biotechnology, College of Agriculture ,Chonnam National University , Kwangju,500–757, South KoreaPublished online: 21 Nov 2008.

To cite this article: Jae Hee Choi , Gap Chae Chung & Seong Hee Lee(1999) Influence of night humidity on the distribution of calcium and sapflow in tomato plants, Journal of Plant Nutrition, 22:2, 281-290, DOI:10.1080/01904169909365626

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JOURNAL OF PLANT NUTRITION, 22(2), 281-290 (1999)

Influence of Night Humidity on theDistribution of Calcium and Sap Flow inTomato Plants

Jae Hee Choi, Gap Chae Chung,1 and Seong Hee Lee

Department of Horticulture, Institute of Biotechnology, College of Agriculture,Chonnam National University, Kwangju 500-757, South Korea

ABSTRACT

Dry or humid night conditions were imposed to determine the distribution ofcalcium (Ca) and sap flow in tomato (Lycopersicon esculentum Mill.) plants.Radioisotopic 45Ca was fed to assess the Ca distribution in a tomato planttreated with different night humidities on different branches. The amount ofsap transported from root to shoot was measured by a heat-balance sap-flowgauge. More than 95% of the sap was transported to the shoots during thedaytime for 12 hours, while only negligible amount were transported at night.High nigh-time humidity considerably enhanced sap flow during the nightdue presumably to generated root pressure. However, high night-time humidityreduced the distribution of 45Ca compared to low night-time humidity imposedin tomato branches.

1 Corresponding author.

281

Copyright © 1999 by Marcel Dekker, Inc. www.dekker.com

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INTRODUCTION

High humidity may reduce the transpiration rate which in turn may decrease thetransport of nutrient elements (Adams, 1991), and Ca in particular (Stebbins andDewey, 1972), causing the incidence of Ca-related disorders (Bakker, 1984). Althoughthe shoot dry weight and leaf area of tomato plants are increased by high night-time humidity (Choi et al., 1997a), blossom-end rot in tomato fruits occurred whenthe relative humidity was high (Adams, 1988). According to Bangerth (1979) andMarschner (1983), high night-time humidity usually affects immature tissues ororgans which have low transpiration rates. In contrast, the response of strawberryplants under high night-time humidity differed from tomato plants. There were fewdifferences in leaf area and dry weight between dry and humid night plant groups,but the concentration of major nutrient elements in strawberry plants were increasedby high night-time humidity (Choi et al., 1997a) which may be due to the rootpressure generated by high night-time humidity (Palzkill and Tibbits, 1977; Bradfieldand Guttridge, 1979). However, guttation is usually seen in tomato leaves as instrawberry leaves when night humidity is high, indicating that the presence of rootpressure may not necessarily guarantee the transport of Ca to less transpiringorgans.

In general, the transport of Ca along the apoplastic and xylem vessel pathwaysmay be affected by the Ca exchange binding sites as well as transpiration rate (BellandBiddulph, 1963; Van deGeijn and Petit, 1979;Hanson, 1984). Calcium exchangeat negatively charged binding sites in the xylem cell walls is not dependent on asimple mass flow (Bell andBiddulph, 1963; Atkinson, 1991). According to Clarkson(1984), transpiration gives rise to simple mass flow and constitutes the main drivingforce for Ca transport into the mature leaves. Considering the suggestion byTanner and Beevers (1990), however, transpiration may not be an absoluterequirement for the long distance transport of nutrient elements in plants. Atkinsonet al. (1992) have suggested that the uptake and transport of Ca has no closerelation with transpiration. Choi et al. (1997b) also showed that the restriction oftomato root growth by culturing in small containers strongly suppressed thetransport of 45Ca2+ ions to new leaves and apices, while water transport, expressedon a leaf area basis, was only marginally reduced, indicating the independence ofCa transport from water transport. In the present experiment, we tried to determinewhether any differences exist in the transport of Ca when tomato plants weregrown under high or low night-time humidity conditions.

MATERIALS AND METHODS

Tomato seeds {Lycopersicon esculentum Mill. cv. Young-Kwang) were sown invermiculite in a temperature-controlled glasshouse (night 17±2°C and day 25±2°C).The photoperiod was about 12 hours and the highest irradiance about 350 uErrrV on clear sunny day. When the second true leaves were just visible, tomatoseedlings of similar sizes were transferred into 20-L containers filled with a nutrient

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DISTRIBUTION OF Ca AND SAP FLOW IN TOMATO PLANTS

Lowhumiditv High Humidity

283

Polyethylene bag J V US3

polyethylene bag

^0 Cotyledon

FIGURE 1. Part of tomato plant used for the measurement of radioisotopic activity of45Ca (L: leaves, S: stem portion below particular leaves). One axillary bud was left to growand low or high night humidity was applied to each branch. Abbreviations used areexplained in Materials and Methods.

solution and grown for another two weeks. All flowers were removed when theyappeared. Uniform plants were allocated to different experiments as describedbelow. The aerated nutrient solutions (Cooper, 1975) were maintained at a constantelectrical conductivity of 2 mS cm-' and at a pH of 6.0.

Tomato plants were grown under different night humidities for seven days anda heat-balance sap-flow gauge (Dynagage Flow 32, Dynamax, Houston, TX) wasused to measure sap flow through their main stems (Steinberg et al., 1990). Briefly,15 mm stem gauges were attached to the stem just above the cotyledons andgauge signals, measured with a 'datalogger' (21X; Campbell Scientific, Logan,UT), were collected every one minute and averaged over 15 minutes.

For tomato plants designated for radioisotopic Ca feeding, all axillary budsexcept one from the fourth internode on the main shoot were removed when they

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284 CHOI, CHUNG, AND LEE

LDW humidity

High humidity

Low humidity

High humidity

Low humidity

High humidity

72Calendar day

FIGURE 2. Effect of night humidity on the sap flow rate of tomato plants after 7 days oftreatment. Signals were collected every 1 minute and averaged over 15 minutes to givehourly mean values. Measurement was carried out for 72 hours from 0:00 on the 71stcalendar day of 1997 to 24:00 on the 73rd calendar day of 1997. Quanta and humidity werealso recorded by sensors. Note that humidity is almost at saturation during the night whenhumidity was raised. Shaded and unshaded bars indicate night-time ad day-time, respectively.

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DISTRIBUTION OF Ca AND SAP FLOW IN TOMATO PLANTS 285

appeared. When two shoots were similar in size, low and high night relativehumidity (50-55%/90-95%) was applied to the main and lateral shoots on the sameplant for 15 days. The designated night humidity was achieved by covering thebranch with an opaque polyethylene bag and attaching a humidifier to it. Lowhumidity was achieved by ventilation and placing calcium chloride (CaCl2) in thesecompartments. The polyethylene bags were removed to maintain common humiditylevels during the daytime after night humidity treatments. Average day and nighttemperatures were 25±2°C/17±2°C. Three plants receiving low and high humiditytreatments were arranged in a completely randomized design. To determine Cadistribution within tissues, plants were fed with 2 mS cm*1 nutrient solutioncontaining 45Ca (3.7 kBq ml/1 as 45CaCl2, Amersham, UK) on the 16th day at thebeginning of the dark period. The distribution of 45Ca in each sample was examined12 hours later. After feeding, two tomato shoots were divided into the followingsections; apex, first leaf (Ll-1) and second leaf (Ll-2) from apices, the 2 cm-portionofstemjustbelowLl-2 (SI), lowest leaf between the apices and branching node(L2), the 2 cm-portion of stem just below L2 (S2), the lowest leaf between thecotyledon and branching node (L3), the 2 cm-portion of stem just below L3 (S3)and the root system as shown in Figure 1. These plant sections were each oven-dried at 80°C for three days, powdered, and ashed at 550°C. An acid extract [1Mhydrochloric acid (HCl)] of the ash was dried at 60°C in order to remove the acidand the residue was redissolved in 1 mL of distilled water. A 0.2 mL aliquot of the1 mL suspension was mixed with a cocktail (Ultima Gold, UK) for scintillationcounting (Ehret and Ho, 1986).

RESULTS AND DISCUSSION

Amount of sap transported from root to shoot was continuously measured witha sap-flow gauge for 72 hours from 0:00 on the 71 st calendar day of 1997 to 24:00 onthe 73rd calendar day of 1997, after seven days of night-time humidity treatment(Figure 2). The sap flow rate during the daytime was clearly dependent on thequantum regardless of the night-time humidity level. On a sunny day (calendarday 72), the maximum rate of sap transport was about 590 g h1 at midday. Incontrast, only 40 g h"1 was transported on calendar day 73, when the highestquantum was about 125 uE n r V . It is clear from Figure 2 that night-time humiditydid not affect the amount of sap transported during the daytime. The total amountof sap transported from tomato roots to shoots on calendar day 72 was 1,222 g,among which 98.5% was transported during the daytime while only 1.5% wastransported during the 12 hour night. However, high night humidity considerablyenhanced sap transport during the night as shown in Figure 3 which may be mostlikely due to the root pressure generated. Virtually no sap was transported whennight humidity was low, whereas about 10-15 g h1 of sap transport was evidentunder high night-time humidity (19:00-07:00 at calendar day 71-72). It is interestingto note that sap flow started from 03:30 when night-time humidity was low,

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286 CHOI, CHUNG, AND LEE

Low humidity —»-Hlgh humidity

Calendar day 71 - 72

Low humidity • High humidity

24Time of day (h)

07

FIGURE 3. Effect of night humidity on the sap flow rate of tomato plant during the twonights (19:00-07:00) of calendar day 71 -73,1997. Experimentals are the same as in Figure2.

suggesting that sap flow during the night may be affected by environmentalconditions during the daytime. When quantum was low due to rain on calendarday 72-73, sap flow during the night occurred much faster than on the sunnycalendar day 71-72.

This low sap transport during the night is not comparable with the results ofCockshull et al. (1988), where transpiration measured at the tomato leaves at nightwas 61-77% of that during the day. Assuming that transpiration provides thedriving force for sap flow through the stem, there seems to be a large discrepancyin the amount of sap transported at night. There are convincing results about theactual amount of water transported when measured with a sap-flow gauge. Devitt

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DISTRIBUTION OF Ca AND SAP FLOW IN TOMATO PLANTS 287

TABLE 1. Specific activity of 45Ca (cpm xlO5) affected by high night humidity intomato plants 12 h after 45Ca was applied to 2 mS cm' nutrient solution (3.7 kBq mL')at the beginning of dark (night-fed) on day 16. Main shoots and lateral shoots on theplants were separately exposed to low and high humidity for 15 days.

Plant Part

ApexLl-1LI-2SIL2S2

Sub total

L3S3Root

Total uptake

Low Humidity

0.014±0.00080.022±0.0021O.OO8±O.O0O50.107±0.00410.007±0.00020.652±0.0284

0.809±0.0360

6.049±0.0362

0.0140.9434.283

High Humidity

0.003±0.00020.004±0.00020.003±0.00020.049±0.0037O.003±O.0O030.264±0.0227

0.326±0.273

5.566±0.0273

et al. (1993) compared the transpiration with a gauge and lysimetry and showedthat an accurate water transport measurement from root to shoot could be obtainedwith a sap-flow gauge.

Calcium as 4SCa was fed to tomato plants having two shoots per plant as explainedin Materials and Methods. Since different night-time humidities were imposed onseparate shoots of the same plant, the variation may be less than in studies usingtwo distinct plant groups. A greater proportion of absorbed 45Ca accumulated inthe stem whether shoots were exposed to low or high humidity (Table 1). However,high humidity considerably reduced the distribution of 45Ca to the upper leavescompared to low humidity. These results are consistent with Ho (1989) in that ahigher proportion of 45Ca accumulated in the stems on humid nights. It is clear thatCa distribution in the leaves of tomato plants was severely limited by high night-time humidity.

It has been generally accepted that high night-time humidity limits transpirationwhich affects the transport of Ca to young leaves and the concurrent leaf growth(Bakker, 1990; Holder and Cockshull, 1990; Armstrong and Kirkby, 1979). Twoassumptions underlie this view. The first assumption is that Ca distribution toyoung developing leaves depends on sufficient water flow. Most of the literatureconcerning the effects of night-time humidity assumed that high night-time humidityprevents transpiration during the night, limiting concurrent Ca distribution. Drynights, therefore, promote Ca transport as suggested by others (Bakker et al.,1987). However, as pointed out earlier, sap transport during a dry night was minimal

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in the present experiment when measured with a sap-flow gauge. In addition, sapflow during the night was enhanced by high night-time humidity, presumably dueto root pressure generated as shown in Figure 3. The second assumption is thatCa transport is carried out by xylem mass flow. However, Atkinson et al. (1992)have suggested that the long distance transport of Ca in the xylem was independentof transpiration. Choi et al. (1997b) also demonstrated that Ca transport from rootto shoot may not be directly related to water transport in tomato plants.

Despite enhanced sap transport by high night-time humidity (Figure 3), theeffects of high night-time humidity on tomato plants were serious, inducing low Caconcentrations (Choi et al., 1997a) and low 45Ca distribution (Table 1) in youngleaves and apices. These results indicate that the rate of transpiration explainsthese Ca levels (Ho, 1989; Adams and Hand, 1993;Bakker, 1990;Bakkeretal., 1987;Clarkson, 1984) which contrasts with results indicating that the uptake anddistribution of Ca is not closely related with transpiration or mass flow (Atkinsonet al., 1992). Tanner and Beevers (1990) have also attempted to demonstrate thattranspiration is not necessary for long-distance ion transport. If the movement ofCa into the xylem were driven by transpirational flow, the amount of Ca in the topparts of shoots should be in proportion to the measurement of transpiration rate(KirkbyandPilbeam, 1984; Marschner, 1995). However, although the transport ofCa mainly occurs by mass flow, the amount of Ca transported may be modified byCa exchange at binding sites (Bell and Biddulph, 1963; Marschner, 1995), by thebinding form of Ca (Marschner, 1995), or the mutual interaction between IAA andCa(BanuolesetaL, 1987).

It appears that plants may have a different or additional mechanism for controllingCa distribution, independent from mass flow in the xylem. This Ca flow may besignificantly affected by high night-time humidity as observed in this experiment,even though water transport is enhanced by the root pressure generated.

ACKNOWLEDGMENTS

Financial support of Korea Research Foundation to G.C.C. made in the programyear of 1997 is greatly appreciated. We thank Professor T. Chen, Department ofHorticulture, Oregon State University, Corvallis, OR for critical review of the paper.

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