Journat ofApplied Bottny and Food Quality 81'26 ' 28 (2007)
IDepartment of Horticulture, University of Khartoum, Sudan 2lnstitute for Ho icultural Sciences, Humboldt University of Berlin, Germany
Influence of heat shock pretreatment on growth and deYelopment of tomatoes under controlled heat stress conditions*
A'H'A. Abdelmageedr, N. Grudaz (Received January 25, 2007)
Summary
The eflect ofa previous heat shock (HS) on growth and development ol diftbrent tomato (L)'colersicon esa e ta, Mill,) cultivars under delined heat stress (HSt) conditions were investigated Plants were grown under two day/night temperature regimes (26120 "C and 37127 'C, respectively) in growth chambers at the Department of Vegetable Crops, Institute tbr Horticultural Sciences, Faculty of Agriculture and Horticulture, Humboldt University of Berlin The experirnents were conducted twice and were set up in a randomized desigrl with flve replicates. The reproductive processes in tomato wcre more sensitive to higlr tempcratures than the vegetative ones Tlre numbcr of pollen grains, mtmber of fruits and iiuit lresh masses produced by the heat tolerant cultivars wcre higher than those ofthe heat sensitive cuitivars. However, HS pretreatments had no positive effects on tomato growth and development.
Introduction
Tonlnrto (fl'colrzr.rico n esculentun Mill.) is usually produced during
\!,inter in Sudan. It js grown throughout the country where irrigation rvatc| and arable land are available rnd is mainly grown by small holdcrs who use relatively poor crop management practices.
Heil stress (HSt) is one of the most important constraints on crop production that adversely af'f'ects the vcgetative and reproductive processes ol tomato and ultimately reduces yield and fruit quality (ABDUL-B^KI, I99I; GRUDA, 2OO5).
Plants respond to HSt by changing rheir metabolic pathways to acclimatize to high temperature. Under HSt, synthesis of many proteins is repressed and some of them, which are called heat slrock proteiDs (HSPS), start to be synthesized (VIERLING, 1991). HSPs synthesis is induced by a rapid rise in temperature of approximately l0 'C or more above thc optimal growth temperature (NovER and SCHARF, 199?). The nuthors reportcd that HSPS plays a major role in nritigating the deleterious elTects of beat-induced protein de- naturation. Moreover, physiological responses ofplants to HSt, suclr as the darnage of structure and the disorder of physiological metabolism, havc been documented (VIERLIN6, 1991;BLUM et al.,
2 0 0 r ) .
Although the damage and deAth of cells are caused by extremc HSt, many plants can survive in otherwise lethal high-temperature regimes if they are tirst subjected to a pretreatment at non-lethal high temperatures (VIERLING, l99l).
Exposure ofplants to elevated tcmperatures fbrshort term,lreat shock (HS), results in a complcx set ofgene expressions selective translation of nrRNA-encoding HS proteins, tlrereby enhancing the.motolcrance and improving cellular survival to subsequent HSt (NovER et al.,
1 9 8 9 : G O N G e t a l . , 2 0 0 1 ) .
'i The resulls of this poper were partly presented at the International Con- ferenceon Tropical and Subropic d AgricIltural Research forDevelopment, , , D e r t s c h e r T r o p e ' r t c g , 2 0 0 3 " , O c t o b e r 8 - 1 0 , C d t t i n g e D .
Heat shock can beused as alternative to chemical control ofvegetable seeds diseases and in the post lrarvest to improve the quality of vegetables (LoAIZA-VELARDE and SALTVEIT, 2001 ; LoAlzA-VELARDE et al., 1997). Moreover, YARwooD (1961) demonstrated that leaves subjected to high temperatures (50 "C) for short periods (15-30 s) tolerated high temperatures (55 'C) longer than untreat€d leaves. In addition, LtN et al. (1984) reported that soybean seedlings exposed to 40 'C for 2 h produced HSPS and tolerate temperature of 45 "C.
However, plants transferred directly from 28 to 45 "C did not produce HSPs. CHEN et al. (1982) mentioned that tomato leaftissues of plants grown in temperature regimes below 30 'C were killed in aboul 15 min at 50 "C, while totnato plants increased significant tolerance when exposed to temperatures above 30 "C lbr 24 h.
The results of the above researclrers led to the assumption that HS treatments on tomato plants would be ofbenefit for tomato production under high temperature conditions. Thus, this study was carried out to investigate whether or not any positive elTects of HS on tlre vegetative growth and productive development jn tomato plants cultivated under high temperature occur in order to mitjgate the effect of HSt conditions. On this basis, the production of tomatoes in arid tropic areas should be possible even during the summer.
Materials and methods
Two heat tolerant and one heat sensitive cultivars of dift-erent origin were selected for this study, namely: 'Drd85 F,', 'Kervic F,' and 'UC 82-B', respectively. The plants were grown in the greenlrouse of the Department of Vegetable Crops, Institute lbr Horticultural Sciences, Faculty oi Agriculture and Horticulture, Humboldt University ofBerlin (Latitude 52'30' N, Longitude 13" 25' E). For more details concerning the plant cultivation, see ABDELMACEED et al. (2003).
35 days after sowing th€ transplants were subjected to HS treatments by immersing the shoot system in a hot-water bath at 50'C tbr 30 s.
Another set fiom each cultivar was left as control (without HS treatment). Thereafter, the plants were divided into two sets. One set was transferred in one plant growth chamber under normal temperature (NT), 26120 'C for l3/l I h (day/night). Another set was transferred in a s€cond plant growth chamber under HSt conditions, 31121 "C fot ll/l I h rday/nighl). During thc dry. 550 pmol m: s I irradiance from a combination offluorescent and incandescent lights were provided for each set, on the top ofthe plants. Temperature and relative humidity were continuously recorded using ltygrothenno- graplrs (Beltbrt Instrument, Baltimore, MD).
The experiments were conducted twice and were set up in a ran- rdomized design with five replicates. Plants were rotated within dre _ plant growth chamber every week to avoid any potential positional
effects.
The following piramelers were recorded: leal allei lcmT). meisured with an electronic leafarea meter, type LI-COR Model 3100 (Lincoln, NE-USA), fresh and dry mass (g pl^nf') of different plant parts, number of truits and fruit fresh mass (g plant-r) Number of pollen grains per llower was recorded according to SATO et al. (2000) and
lnfluence of heat stress on tomatoes
ALONI et al. (2001). Leaf area ratio (1"4R), specific leaf area (SIA), and leaf weight ratio (LllR) were calculated according to RADFoRD 0 967).
Statistical analysis
Collected data were analysed using the statistical software SPSS version 10.0. One-way analysis of variance (ANOVA) was used to deteflnine the signilicance of variation among the diff'erent treat- ments. Mean separation was done by Duncan's multiple range test.
A combined analysis of variance was performed. The same con- clusions were drawn from each experiment and the data are presented as mean values of l0 replicates across the two experiments.
Results
Systematic and consistent diftbrences between the plants subjected or not subjected to HS pretreahnent at both temperature regimes were noticed. However, no positive effects of HS pretreatment on tomato plants under both temperatures regimes were shown.
Leaf area was generally reduc€d for the plants that were subjected to HS prerreatment compared to that not pretreated (Tab. l). Sinila(
results were tbund for leaf lieslr and dry rnass as well as stem fresh and dry mass (data not shown). At both temperature regimes, there were signiticant differences among the cultivars when subjected or not subjected to HS pretreatment. 'Kervic F,'and 'Drd85 F,'showed the better results in all plant parameters measured. Moreover, there was no signiticant d ift'e rence it LAR, SLA and LIVR (data not shown) among the different cultivars when the plants were subjected or not to HS pretreatment at both temperature regimes except for the cultivar 'UC 82-B' (Tab. l).
Numbers of po]len grains produced and released by the plants under NT regime were higher than that produced and released under HSt cdnditions. However, among the cultivars at HSt conditions th€re were no signiticant differences when the plants were not subjected to HS pretreatment. 'Kervic F,' had tl'te highest number of pollen grains when the plants were subjected to HS pretreatment. At NT there were significant differences among the cultivars when not subjected to HS pretreatment, while 'UC 82-B'produced the lowest number of pollen grains per flower The number of fruits per plant, and fruits t'resh mass per plant showed the same trend as described above tbr the number of pollen grains (Tab. l).
Discussion
High temperatures alTected the vegetative and reproductive organs and tissues of tomato plants for all investigated cultivars. 'Kervic Fr' and 'Drd85 Fr' were more tolerant to high temperatures than
'UC 82-B'. This confirms earlier findings of ABDUL-BAKI (1991) and PEET et al. (1997) who reported the adverse elfect of HSt on the vegetative and reproductive development in tomato plants.
The effectofHSt on reproductive developmenf was more pronounced than on vegetative growth. Reduction in pollen production is an example of this in all cultivars at HSt conditions. Kuo et al. (1986) suggested as mechanism that proline accumulation in tomato leaf tissue at high temperature leads to the depletion in the reproductive tissue, tlrereby seriously reducing pollen lbrmation or viability.
ln agreement with the results of SATo et al. (2000) fte number of fruits per plant and fruits fiesh mass in tomatoes were also reduced at high temperature regimes (Tab. 1). Flower abortion and delay of growth ofnewly formed fruits acted as a feedback control mechanism to prevent too generative growth of tonatoes due to a high sink- source ratio, intluenced by high air temperature (DE KoNING, 1989;
GRUDA.2005).
YARwooD (1961) and Lin et al. (1984) reported positive eff'ects of heat shock treatments on the plants that later on exposed for a short period to higher temperature. Heat shock response has been ex- t€nsively studied in dift'erent plants (VIERLING, 1991). lt has been known that plants induced thermotolerance and can survive under a normally lethal high temperature il they are preconditioned by mild heat shock treatment (HoNG and VIERLING, 2000).
Although heat shock response has been extensively studied in plants, most of the studies have tbcused on the response at the whole plant level. However, the heat shock affects the development ofeach plant organ differently. HoNG and VIERLING (2000) repofied that seedling development during the ve.y early stage shows stronger thermo- tolerance than the late stage.
Heat shock treatment in tlre present study had no positive eff-ect on the vegetative growtlr and reproductive development and the hope that heat shock treatment would be beneticial for tomato plants, particularly for the reproductive development at high temperatures, was not fulfilled. On the other hand, this is in agreement with the results ofABDUL-BAKI (1991), who suggested that heat shock proteins have little to do with fruit set. Frova et al. ( 1991) reported tlrat relative to the heat shockresponsein vegeiative tissues, the response in pollen is weak, the subset of HSPS mad€ aie present in low amounts and mature pollen se€ms incapable of synthesizing HSPS under high
Tab, lt Influence of heat shock pretreatmelt oD some plant and physiological parameters oftomatoes grown under controlled conditions
Parameters Leafarea (cmz)
Treatment/Temp. ('C) 37127 26/20
l-4R (cmz g-r)
37t27 26120
Sl"4 (cm? g-r)
37/21 26t20
Numbe. of pollen Number of fruits grains flowerr plant_l 37/2't 26t20 31t21 26/20
Fftit fresh mass (g plarrr) 3't/27 26/20 K e r v i c F r ( c o D t . ) 8 5 1 . 3 b c 1 5 1 6 . 6 a
8 3 8 . 9 b c I 1 2 6 . 6 b
6 6 . 6 c l O i . 4 a 92.7 b ?9.t bc '74.5
c 12.3 c 63.I c 86.3 abc 130.4 a 83.5 bc
90.7 b 92.4 ab 86.4 85.9
5.03 2.75
1 0 0 . 6 c 1 4 9 . 3 a 5 7 . 0 ^ 7 5 . O ^ 2 0 a b 143.5 b | 13.8 b 69.0 a '72.o ab 2.5 | I 1 8 . 3 c 1 0 8 . 7 b 6 1 . 0 a 6 8 . 0 b 1 . 8 a b
98.9 c 129.9 ab 60.0 a 74.0 ^b 2.3 ^ l 7 l . 7 a { l l l . ? b 3 7 . 0 c 5 7 . 0 c 0 . 0 b 118.5 c 122.3 tr 48.0 b 60.0 c 0.0 b
7.0 a I4.5 a 46.3 a 7.5 a I7.8 fl 50.0 a 6.0 a 10.7 b 40.5 ab 6.5 a I1.5 ab 37.5 ab 6.5 a 0.0 b 22.0 c 6.0 a 0.0 b 30.7 bc 6.58 9.08 3' 7.8 0 . I 8 t . 3 6 t . 8 7 Kervic Fr
Drd85 Fr (coDt.) 910.1 b 1077.5 b Drd85 Fr 678.1 c 1046.9 b UC82-B (cont.) 1266.2 c. 1212.8 b
uc 82-B
Mean
s.E.
125.3 122.6 5.95 4.04 862.8 bc 1238.9 b
90t.2 t203.2 35.68 3t.1' 7
55.3 67.7 |.4 2.05 1.38 0.21
cont. = control (without heat shock pretreatment), L4R = Leaf area ratio, SIA = specific leaf area. Means followed by the same letter(s) within each column arc rot sigrificantly different at P< 0.05, according to Duncan multiple range test.
n = l0 plants
2 8 A . H . A . A b d e l m a g e € d . N . G r u d l r
temperatur€ conditions.
In addition, the plants in the present study were well irrigated. KTMPEL and KEy (1985) reported that HSPS in soybean might accumulate urder hot fleld conditions fbr plants subjected to drought but not for irrigated plants.
Under lield conditions in Sudan other thctors, such as low relative humidity, insect and virus diseases as well as soil properties have to be considered as well. Optimization of microclimate could be very impo ant to ensure a good pertbrmance of new tolerant varieties cultivated during the summer in Sudan.
Acknowledgmenls
The Gennan Academic Exchange Services (DAAD) is acknowledged for providing a scholarship lbr the tlrst author.
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Address of the authors:
Dr Adil H.A. Abdelmageed, Department of Horticultlre, Faculty of Agri cuiture, University of Khartoum, 13314 Shambat, PO. Box 32, Khartornn Nonh, Sudan. Email: aadilhassan@hotmail.com
Dr habil. N- Groda, InstitIte forHonicrltural Sciences, Faculty ofAgricultore and Horticulture, Humboldt University ofBerlin, D-14163 Berlin, cermany.
Email: nazim-gruda@rz.hu-berlin.de
