B U L L E T IN OF N A T IO N A L A C A D E M Y OF SCIEN CES OF TH E R EPU B LIC OF K A ZA K H STA N
ISSN 1991-3494
V olum e 3, N um ber 367 (2017), 47 - 53
UDC 633.853.55
A. K o ig e ld in a 1, A. N iko lova2, A. V assilev2 1 Shakarim State University of Semey, Kazakhstan,
A gricultural University of Plovdiv, Bulgaria.
E-mail: [email protected], [email protected], [email protected]
DROUGHT-INDUCED ACCLIMATION CHANGES IN YOUNG CASTOR (RICINUS COMMUNIS L.) PLANTS
A bstract. Castor (Ricinus communis L., cv. Donskaya krupnolistnaya) plants were grown as pot-soil culture in a greenhouse of the Agricultural University of Plovdiv, Bulgaria. Young plants (4 leaves stage) were grown for next 15 days at three different soil moisture regimes: optimal - 65-70% field water capacity (FWC) as well as soil moisture deficient regimes, provoking moderate and severe plant water stress. The water regimes were maintained by daily pot weighting and irrigation. The amount of the irrigated water for the plants at optimal water regime was equal to full pot evapotranspiration from the previous day (100% ET), while those for the plants at deficient regimes were equal to 75% ET (moderate water stress) or 50% ET (severe water stress). Both physiological and anatomical parameters were measured at the end of the experiment. It was found the castor plants reacted to drought by deve
lopment of clearly distinguished xeromorphic traits, which decreased water loss and contributed the optimization of plant water balance at water-deficient conditions. The drought provoked moderate and severe water stress in castor plants, indicated by strong enhancement of leaf GPOD activity. The photosynthetic apparatus of castor plants at drought conditions was preserved. Both photosynthetic pigments content and the apparent electron transport rate (ETR) were slightly diminished and the maximal quantum yield of photosystem II (Fv/Fm) was not affected. The sharp decrease of leaf gas exchange parameters in drought-stressed plants may be considered as a mechanism to avoid possible structural and functional damages.
Key words: castor, drought, growth, leaf lamina, photosynthesis.
In tro d u c tio n . C astor (Ricinus com m unis L.) is im portant oilseed crop, cultivated in both tropical and sem i-tropical regions o f the w orld (W eiss, 2000). C astor oil is nonedible and has been u sed alm ost entirely for industrial and pharm aceutical applications. It is also an im portant row m aterial fo r the chem ical and polym er industries, and a prom ising candidate for biofuel production (Ram os et al., 1984; O gunniyi, 2006;
M utlu and M eier, 2010). W orld consum ption o f castor oil has increased m ore than 50% during the last 25 years.
A s far as castor oil seeds production does no t m eet the current industrial dem and, diversification o f castor production regions is necessary. It is know n th at castor has relatively high level o f drought to le
rance; therefore its cultivation in d rier zones could be a rational option. In this view point, castor has been recently considered as a prom ising new crop fo r the South and South-East regions o f R epublic o f K azakh
stan (Н азарбаев, 2014).
P lant tolerance to drought usually is based on m any different m echanism s. Sow m ya et al. (2016) has recently reported th at drought tolerant castor genotypes have high er w ater use efficiency (W UE) due to relatively low transpiration rate. This observation corresponds to the early stom atal closure in the leaves o f drought-exposed castor plants and its ability to m aintain efficient stom atal control w hile keeping a high level o f net C O2 fixation (Sausen and R osa, 2010). The low transpiration rate could be partly due to increased abscisic acid concentration in the phloem sap o f this species at d rought (Zhong et al., 1996).
B abita et al. (2010) reported th at osm otic adjustm ent is another im portant m echanism for drought tolerance in castor. N ine genotypes o f castor subjected to drought dem onstrated osm otic adjustm ents in the leaves, bu t w ith a w ide variability in the intensity o f the effect.
Som e plants develop th icker lam ina u nd er conditions o f w ater deficiency, allow ing them to prom ote m ore efficient w ater use and low er transpiration rate (L akshm am m a et al., 2009). There is luck o f inform ation fo r the drought-induced anatom ical changes in the leaves o f casto r plants, and it is unknow n w hat kind o f adaptation patterns they develop. This inform ation is im portant, because there is close relationship betw een the anatom y adaptations and the efficiency o f physiological processes. Therefore, we decided to carry out a study aim ing to clarify young castor plants responses and m echanism s o f acclim a
tion to drought stress using both physiological and anatom ical param eters.
M a te r ia l a n d m e th o d s. Pot-soil experim ents w ere carried out in the greenhouse o f the D epartm ent o f P lant Physiology and B iochem istry o f the A gricultural U niversity o f Plovdiv, B ulgaria. C astor cultivar
“D onskaya krupnolistnaya” w as used in the study. The seeds w ere sow n in pots filled w ith 4 kg dry soil taken from the experim ental field o f the U niversity. W hen plants reached 4 leaf-stage, an experim ental design including three variants w as set up. Each v ariant consisted three pots and each p o t 4 plants. During the next 15 days plants w ere grow n at different soil m oisture regim es - (1) optim al (65-70% field w ater capacity, FW C ) as w ell as deficient regim es provoking (2) m oderate and (3) severe plant w ater stress. The w ater regim es w ere m aintained by daily irrigation. The am ount o f the irrigated w ater for the plants at optim al w ater regim e w as equal to full p o t evapotranspiration for previous day (100% ET), w hile those for plants at deficient regim es w ere equal to 75% E T (m oderate w ater stress) and 50% E T (severe w ater stress). A t the end o f the experim ent, follow ing m easurem ents o f grow th, physiological, and anatom ical param eters w ere m ade.
P lant grow th determ ination. Fresh w eights o f the plants as w ell as th eir le a f area w ere determ ined at the end o f experim ent. The le a f area w as m easured by an electronic area m eter (N EO -2, TU -Sofia, Bulgaria).
G uaiacol peroxidase determ ination. The activity o f the antioxidative enzym e guaiacol peroxidase (G PO D ) in the leaves w as m easured by m ethods o f B ergm eyer (1974).
A natom ical analysis. Sam ples from roots and leaves w ere collected at the end o f the experim ent, fixed in FA A for 24 hours, and transferred for storage in 70% ethyl alcohol. Sem i-lasting glycerin slides o f epiderm al peels and free hand transvers sections w ere prepared. The observations, m easurem ents, and photographs o f the slides w ere m ade w ith a digital light m icroscope M otic D M B A 210 (M otic Incorpo
ration Ltd., C hina), using the im age analysis softw are M otic Im ages Plus version 2.0., w ith a general m agnification o f X400. The follow ing param eters w ere exam ined and analyzed: lam ina thickness, palisade and spongy parenchym a height, upper and low er epiderm is height, stom atal index (SI), stom ata and ordinary epiderm al cells (OEC) size, diam eter o f the root biggest xylem vessel elem ents. F o r each exam i
ned param eter 30 m easurem ents w ere m ade (H endry et al., 1993).
L e a f gas exchange. L e a f gas exchange (net photosynthetic rate-A , transpiration rate-E, stom atal conductance-gs and internal CO2 concentration-ci) w as m easured on the fully developed leaves (closest to the top) at the end o f the experim ental period w ith an open photosynthetic system LC pro+ (AD C, E ng
land). The m easurem ents w ere done after one hour adaptation at 550 ^m ol m-2 s-1 and 30 °C tem perature.
P hotosynthetic pigm ents content. P hotosynthetic pigm ents (chlorophyll a, chlorophyll b and total carotenoids) w ere extracted in 80 % acetone, m easured spectrophotom etrically and calculated according to the form ulae o f L ichtenthaler and W elburn (1983).
C hlorophyll fluorescence. C hlorophyll fluorescence m easurem ents w ere perform ed on the fully developed leaves w ith a pulse m odulation fluorom eter (M IN I-PA M , H einz W alz, G erm any) in dark and light-adapted leaves. The castor plants w ere k ep t in the dark fo r at least 30 m in before the start o f the m easurem ent. By sw itching on the m easuring beam (0.02 - 0.20 ^m ol m-2 s-1), the m inim al level o f fluorescence (F0) w as recorded. Im m ediately thereafter, a saturating light pulse o f 5500 ^m ol m-2 s-1 w ith 0.8 s duration w as sent out to record the m axim al level o f fluorescence in the dark-adapted state (Fm), from w hich the m axim al quantum yield o f PSII (Fv/Fm) w as calculated (w ith Fv = Fm - F 0).
A fter 30 m in light adaptation at 550 ^m ol m-2 s-1 the steady-state level o f photosynthesis w as achieved and a saturating pulse w ith the same characteristics w as applied. Fluorescence yield before triggering w ith the saturation pulse (F), m axim al (Fm') fluorescence reached during the saturation pulse, effective yield o f photochem ical energy conversion (Y), Y = (Fm'-F)/Fm') as w ell as apparent electron transport rate (ETR) calculated as E T R = Y *P A R *0.5*0.84 (W hite and C ritchley, 1999) w ere deter
m ined.
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Statistics. Statistical analysis w as perform ed using a one-w ay A N O V A (for P < 0.05). B ased on the A N O V A results, a T ukey test fo r m ean com parison w as perform ed fo r a 95% confidential level, in order to test for significant differences am ong treatm ents. In the tables, different letters (a, b, c) express signi
ficant differences. L etter “a” is representing the highest value.
R e su lts a n d discussion. C astor plants, grow n for 15 days at deficient w ater m oisture regim es, grew slow ly and form ed significantly low er fresh m ass (FM ) and le a f area (LA ) (Таble 1). The decrease o f FM o f plants from the variants 75% Е Т и 50% Е Т w ere 32 and 42.6% and those o f LA - 31.9 and 36.9% , respectively. It is im portant to m ention th at the dim inished values o f these param eters in drought-exposed castor plants w ere m ostly due to falling o f the low er leaves, w hich could be considered as a m echanism for w ater balance optim ization.
The results, presented in Table 1, show ed sharp increase o f G PO D activity in casto r plants grow n at deficient soil m oisture regim es - from over 2 to m ore than 4-fold. It is w ell know n th at G PO D is key enzym e in cell antioxidative netw ork preventing m acrom olecule oxidation from hydrogen peroxide and other active oxygen species. The enhanced G PO D activity gave evidence th at the applied deficient soils m oisture regim es provoked m oderate (2-fold) and severe (4-fold) w ater stress in the castor plants.
Table 1 - Effect of different soil moisture regimes on fresh mass,
leaf area formation and leaf guaiacol peroxidase activity of the leaves of young Ricinus communis plants Variants Fresh mass (FM, g/plant) Leaf area (LA, cm2 plant) GPOD activity (U/g FM)
100% ET 5.15“ 108.2a 4.5c
75% ET 3.51* 74.8* 10.1*
50% ET 2.96 * 68.3* 21.8a
Different letters (a, b, c) indicate statistically differences (P < 0.05), letter “a” representing the highest value.
Plants experiencing drought stress try to acclim ate by developing different anatom ical and m orpho
logical changes and physiological m echanism s. C astor possesses alternate, sim ple, palm ately lobed leaves, w ith 5 -1 2 deep lobes. The le a f blade is am phistom atous, w ith uniseriate epiderm is, w ith barrel-shaped ordinary epiderm al cells, sm all anisocytic stom ata and high er stom atal frequency on the low er epiderm is (M aiti, et al., 2012). The upper epiderm is has w ell developed cuticle, especially in drought-resistant gen o types. C astor plants grow n at optim al w ater regim es have bifacial leaves, w ith a single layer o f palisade parenchym a and 3-5 layers o f spongy parenchym a (Figure 1). Cells o f the palisade parenchym a are
Figure 1 - Bifacial leaf structure of Ricinus communis plant, grown at optimal water regime (transverse section, X400)
colum nar, thin-w alled, w ith num erous chloroplasts, perpendicularly oriented to the up per epiderm is. The cells o f the spongy parenchym a are small, thin w alled, isodiam etric w ith large intercellular spaces (Tyagi, et al., 2013).
The severe and m oderate w ater stress affected the size o f the epiderm al cells (Table 2) reducing the height o f the u p p er epiderm is w ith 19% and 8% respectively, and the height o f the low er epiderm is w ith 12% and 5% respectively. The w ater stress did n o t cause changes in stom ata frequency on the upper epiderm is, bu t increased significantly the SI (up to 38% ) o f the low er epiderm is. Increased num ber o f stom ata, positioned on the low er le a f surface aw ay from direct sunlight, contributes to a reduction in the rate o f loss o f absorbed w ater (D ickison, 2000). A reduction o f the size o f the stom ata and ordinary epiderm al cells o f the upper and low er epiderm is w as also observed.
Table 2 - The effect of different soil moisture regimes on Ricinus communis leaf anatomical structure
Variants
Leaf lamina Upper
epidermis height ц
Lower epidermis height ц
Palisade parenchyma height ц
Spongy parenchyma height ц
Lamina width ц
100% ET 26.29a 22.17a 67.88a 73.44a 191.19a
75% ET 24.22* 21.23a 60.04* 66.51* 171.27*
50% ET 21.30c 19.65* 55.0c 60.96c 159.16c
Variants Upper epidermis
Stomata length ц Stomata width ц OEC length ц OEC width ц SI %
100% ET 28.01a 19.80a 32.89* 19.23a 11.30
75% ET 28.35a 19.23a 35.95a 19.65a 11.23
50% ET 26.46* 17.55* 34.44b 17.62* 10.03
Variants Lower epidermis
Stomata length ц Stomata width ц OEC length ц OEC width ц SI %
100% ET 25.74a 19.69a 35.50a 20.85a 14.87*
75% ET 25.66a 18.01* 33.27* 18.96* 20.58a
50% ET 25.35a 17.39* 33.16* 17.83* 19.70a
Different letters (a, b, c) indicate statistically differences (P < 0.05), letter “a” representing the highest value.
The plants grow n un der severe and m oderate w ater stress show ed statistically significant reduction o f the height o f the palisade (w ith 19% and 12% respectively), and spongy m esophyll (w ith 17% and 10%
respectively), w hich reflected to a reduced size o f the lam ina (w ith 17% and 11% respectively). The w ater stress did no t affect the num ber o f the layers com posing the palisade and spongy m esophyll bu t instead reduced the intercellular spaces betw een the m esophyll cells and m ade the lam ina m ore com pact. It is observed th at in some species, a thicker lam ina prom otes m ore efficient w ater use and low er transpiration rates under conditions o f w ater deficiency (D ickison, 2000).
The results show ed th at castor plants grow n u n d er m oderate and severe w ater stress on a histological level reacted to these conditions by developing com pact lam ina, reduced size o f the root xylem vessels (data n o t show n), ordinary epiderm al cells and stom ata, palisade and spongy m esophyll, and lam ina, and increased stom atal frequency on the low er epiderm is - patterns typical fo r xerom orphic plants. Sim ilar changes in the anatom ical structure o f the le a f and root o f castor plan t grow n un der the influence o f industrial effluent w ere observed by Tyagi et al. (2013). The results o f the le a f anatom ical studies show ed th at w ater stress causes developm ent o f clearly distinguished xerom orphic adaptations at a histological level.
D rought stress influenced the perform ance o f casto r plants, at physiological level, too. The applied soil m oisture deficient regim es reduced significantly le a f gas exchange param eters in drought-stressed plants. The n et photosynthetic rate (A) o f these plants decreased by 44.1 (m oderate stress) and 74.9%
50
(severe stress), respectively. Transpiration rate show ed the same trend, b u t to a sm aller degree.
C onsequently, w ater use efficiency (W U E = A /E)) in drought-stressed plants also w as dim inished - from 28 to 25.6% . W hen stom ata lim itation prevails o v er m esophyll constrains, n et photosynthetic rate (A) is retarded by low internal CO2 concentration (ci). In our study, the ci values in drought-exposed castor plants did no t vary significantly, w hich is an indicator for the presence o f nonstom atal lim itations.
The integral photosynthetic process includes several sub-processes, nam ely light perception, photosynthetic electron transport, CO2 assim ilation, short and long photoassim ilates transport and all o f them m ay be negatively affected by drought. The results, presented in Table 3, show ed th at the content o f photosynthetic pigm ents w as dim inished only in plants und er severe w ater stress. The values o f both chlorophylls and carotenoids decreased, in average by 25% . The low er degree o f drought im pact on pigm ents as com pared w ith n et assim ilation rate (A) could be partly explained by the fact, th at low er and m ore affected leaves w ere not used for this analysis as th ey w ere fall dawn.
Table 3 - Effect of different soil moisture regimes on leaf gas exchange, photosynthetic pigment content and selected chlorophyll fluorescence parameters of young Ricinus communis plants
Variants Leaf gas exchange
A E gs ci WUE
100% ET 17.20a 8.12a 0.37a 232a 2.11a
75% ET 9.61* 6.31* 0.21* 254 a 1.52*
50% ET 4.32c 2.80c 0.07 c 239a 1.57 c
Variants Photosynthetic pigments content and chlorophyll fluorescence parameters
Chl.a Chl.b Car 4Fv m ETR
100% ET 1.15a 0.43a 0.45a 0.81a 85.1a
75% ET 1.03a 0.37a 0.46a 0.82a 83.1a
50% ET 0.89* 0.32* 0.35* 0.81a 65.2*
A - net photosynthetic rate ^m ol CO2/m2/s); E - transpiration rate (mmol H2O/m2/s); gs - stomatal conductance (mol/m2/s); ci - internal CO2 concentration (vpm); WUE - water use efficiency (A/E; цmol CO2/mmol H2O);
Chl.a,b - chlorophyll content (mg/g FM); Car - carotenoids (mg/g FM); Fv/Fm - maximal quantum yield of photosystem II;
ETR - apparent electron transport rate ^m ol m-2 s-1).
Different letters (a, b, c) indicate statistically differences (P < 0.05), letter “a” representing the highest value.
The severe w ater stress did not influence the m axim al quantum yield o f photosystem II (Fv/Fm) in castor plants. The m easured Fv/Fm values (0.81-0.82) w ere in the range typical for healthy leaves (0.75 - 0.83). This m eans th at reduced chlorophyll content reflexed the antennae chlorophyll, b u t n o t the reaction centers. N evertheless, the apparent electron transport rate (ETR) w as slightly dim inished, by 23%.
C onsidering the relatively stable light-dependent photosynthetic processes, as w ell as the alm ost equal ci values am ong the variants, w e m ay conclude th at other lim iting factors (C alvin cycle biochem ical reac
tions, photosassim ilate transport, etc.) m ay have big ger im pact on the photosynthesis o f drought-exposed castor plants.
C o n c lu sio n . B ased on the results obtained we m ay conclude th at young casto r plants responded to drought by efficient acclim ation at, both, histological and physiological levels. The castor plants reacted to drought by developing clearly distinguished xerom orphic traits, such as com pact lam ina, reduced size o f the root xylem vessels, ordinary epiderm al cells and stom ata, palisade and spongy m esophyll, and lam ina, as w ell as increased stom atal frequency on the low er epiderm is. All these changes decreased w ater loss and contributed the optim ization o f plant w ater balance at w ater-deficient conditions. The drought provoked m oderate and severe w ater stress in castor plants. U nder stress conditions the le a f gas exchange param eters sharply decreased to preserve the castor photosynthetic apparatus from structural and functional dam ages. The enhanced le a f G PO D after 15 days o f drought exposure indirectly indicated the presence o f efficient control on the production o f the active oxygen species. Subsequently, both photosynthetic pigm ents content and the apparent electron tran sport rate (ETR) w ere slightly dim inished
and the m axim al quantum yield o f photosystem II (Fv/Fm) w as n o t affected. Therefore, w e m ay conclude th at young castor plants are capable o f efficient acclim ation to drought. This observation confirm ed previous reports concerning drought tolerance o f this species and is a good initial point for further agronom ic investigation fo r its behavior and productivity in rainfed conditions.
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A. ^ ш ^ л ь д и н а 1, A. Н иколова2, A. Василев2
1 Семей каласыныц Шэкэрiм атындагы мемлекетпк университет!, Казакстан, 2 Пловдив аграрлык университет^ Болгария
ЖАС М АЙКЕНЕ (RICINU S COMMUNIS L.) 0С1М Д1Г1НЩ ЦУРГАЦ Ш Ы ЛЫ ВДА Т0З1МДШ1Г1, К ЛИМ АТТЬЩ 0ЗГЕРГ1Ш Т1Г1
А ннотация. Майкененщ (Ricinus communis L.,) Донская крупнолистная сорты Пловдив аграрлык университетшщ (Болгария) жылыжайы жагдайында топырак толтырылган ыдыстарда еарш д г Жас еам дш (4 жапырак кезещнде) келеа 15 кун ш ш де топырак ылгалдылыгына байланысты Yш тYрлi жагдайда сыналды: оптимальдi - 65-70% (бакылау), сонымен катар минимум жэне максимум жагдайда. Осы мелшердi ыдыстарды ^ н д е л ж л таразыга елшеу аркылы кстап отырдык. Физиологиялык жэне анатомиялык керсет- кiштерi зерттеу жумысыныц соцында елшендг
Кургакшылык майкенеге эсерш типзед^ оны барлык параметрлершщ езгерушен ацгардык.
Тушн сездер: майкене, кургакшылык, еару , жапырак алаканы, фотосинтез.
52
A. ^ ш ^ л ь д и н а 1, A. Н иколова2, A. Василев2
Государственный университет им. Шакарима города Семей, Казахстан, 2Аграрный университет Пловдив, Болгария
ЗАСУХОУСТО ЙЧИВОСТЬ АКЛИМ АТИЗАЦИОН НЫ Е И ЗМ ЕН ЕНИЯ В М ОЛОДОМ РА СТЕНИИ КЛ ЕЩ ЕВ И Н Е (RICINU S COMMUNIS L.)
А ннотация. Клещевина (Ricinus communis L.,) сорта Донская крупнолистная была выращена в горшках с почвой в теплице аграрного университета г. Пловдив, Болгария. Молодые растения (4 листьев) проращивали в течение следующих 15 дней в трех разных режимах по влажности почвы: оптимальная - 65
70% (контрольный), а также почвы с дефицитом режимов влаги, провоцируя у растений стресс умеренной и тяжелой воды. Режимы воды были сохранены путем ежедневного взвешивания горшков и полив. Количество поливной воды для растений в оптимальных условиях водного режима был равен полному испарению с предыдущего дня (100% ПЭ), в то время как растения в дефицитных режимах были равны 75% (умеренный водный стресс) или 50% (дефицитом воды). Как физиологические, так и анатомические параметры были измерены в конце эксперимента. Клещевина реагируют на засуху, при развитии четко выделяются черты xeromorphic, что снизило потери воды и способствовали оптимизации водного баланса растения в воде-дефи- цитных состояниях. Засуха спровоцировала умеренной и тяжелой воды в касторовом растений, обозначается значительное усиление активности GPOD листьев. Сохранился фотосинтетического аппарата касторового растения в условиях засухи. Содержание фотосинтетических пигментов и явное электронного транспорта показатель (ЭТР) были немного уменьшены и максимального квантового выхода фотосистемы II (FV в/ФМ) не пострадали. Резкое снижение параметров листа газообмен в пострадавших от засухи растения можно рас
сматривать в качестве механизма, чтобы избежать возможных структурных и функциональных повреж
дений.
К лю чевы е слова: клещевина, засуха, выращивание, листовые пластинки, фотосинтез.
