Nativa, Sinop, v. 10, n. 4, p. 547-553, 2022.
Pesquisas Agrárias e Ambientais
DOI: https://doi.org/10.31413/nativa.v10i4.13874 ISSN: 2318-7670
Growth, development, and photosynthetic performance of two soybean lineages
in response to drought
Vanessa do Rosário ROSA1, Allan de Marcos LAPAZ1, Adinan Alves da SILVA1,
José Domingos PEREIRA JUNIOR1, Maximiller DAL BIANCO2, Cleberson RIBEIRO3
1Departamento de Biologia Vegetal, Universidade Federal de Viçosa, Viçosa, MG, Brasil.
2Departamento de Bioquimica e Biologia Molecular, Universidade Federal de Viçosa, Viçosa, MG, Brasil.
3Departamento de Biologia Geral, Universidade Federal de Viçosa, Viçosa, MG, Brasil.
*E-mail: cleberson.ribeiro@ufv.br
(ORCID: 0000-0001-5887-4921; 0000-0003-4798-3713; 0000-0002-1589-6773; 0000-0002-2742-4036;
0000-0002-7001-4841; 0000-0001-7063-1068).
Submitted on 05/13/2022; Accepted on 12/07/2022; Published on 12/xx/2022.
ABSTRACT: Drought stress is a common environmental factor that constrains plants from expressing their
ecophysiological potential, disrupting various physiological and biochemical processes. Hence, the objective of
this work was to evaluate the growth, development and photosynthetic performance under drought in the
vegetative phenological stage of soybean in two lineages with potential difference tolerance to this abiotic stress,
lineages (‘Vx-08-10819’ and ‘Vx-08-11614’. For this purpose, biometric traits of development, relative water
content in leaves, photosynthetic pigments, gas exchange, and chlorophyll a fluorescence were evaluated. The
experimental design was a randomized block design with 4 replications and arranged in a 2 × 3 factorial scheme,
comprising of two soybean lineages (Vx-08-10819 and Vx-08-11614) in combination with three water
availability [100% (control), 60%, and 40% of field capacity]. Relative water content in leaves, total leaf area,
and shoot dry weight of lineage Vx-08-10819 were not changed after exposure to drought. Besides that,
photosynthetic capacity of lineage Vx-08-10819 was less affected than lineage Vx-08-11614 to drought, showing
that this lineage is tolerant to this abiotic stress in at vegetative stage V4.
Keywords: chlorophylls; gas exchange; Glycine max (L.) Merr; water relations.
Crescimento, desenvolvimento e desempenho fotossintético de duas linhagens de
soja em resposta à seca
RESUMO: O estresse hídrico é um fator ambiental comum que impede as plantas de expressarem seu
potencial ecofisiológico, interrompendo vários processos fisiológicos e bioquímicos. Portanto, o objetivo deste
trabalho foi avaliar o crescimento, o desenvolvimento e o desempenho fotossintético sob seca na fase
fenológica vegetativa da soja em duas linhagens com potencial diferença na tolerância a este estresse abiótico,
as linhagens Vx-08-10819 e Vx-08-11614. Para tanto, foram avaliadas características biométricas de
desenvolvimento, teor relativo de água nas folhas, pigmentos fotossintéticos, trocas gasosas e fluorescência da
clorofila a. O delineamento experimental foi em blocos casualizados com 4 repetições e dispostos em esquema
fatorial 2 × 3, composto por duas linhagens de soja (Vx-08-10819 e Vx-08-11614) em combinação com três
disponibilidades hídricas [100% (controle), 60% e 40% da capacidade de campo]. O conteúdo relativo de água
nas folhas, a área foliar total e o peso seco da parte aérea da linhagem Vx-08-10819 não foram alterados após a
exposição à seca. Além disso, a capacidade fotossintética da linhagem Vx-08-10819 foi menos afetada do que
a linhagem Vx-08-11614 à seca, mostrando que esta linhagem é tolerante à este estresse abiótico no estágio
vegetativo V4.
Palavras-chave: clorofilas; troca gasosa; Glycine max (L.) Merr; relações hídricas.
1. INTRODUCTION
Soybean (Glycine max (L.) Merrill) is grown worldwide,
with several industrial applications and great importance in
human and animal nutrition, as an important source of
protein meal and vegetable oil (VOLLMANN et al., 2000;
BEZERRA et al., 2015). Soybean provides more than half of
the world’s vegetable oil and two-thirds of its protein meal
(LAPAZ et al., 2020).
Currently, several Brazilian soybean producing regions
suffer from drought, mainly in sandy soils and under high air
temperatures, where the risk of yield losses due to water and
nutrient deficits is higher (FRANCHINI et al., 2017). This
situation could become worse with climate change.
According to Hlaváčová et al. (2018), an increase in the
occurrence of extreme weather events is expected, such as
short periods of high temperatures and periods of drought,
with negative impacts on agricultural production.
Drought stress is a common environmental factor that
constrains plants from expressing their ecophysiological
potential (KRON et al., 2008; HAGHIGHI et al., 2020),
disrupting various physiological and biochemical processes,
such as membrane integrity, pigment content, osmotic
adjustments, water relations, primary metabolism, stomatal
closure, and photosynthetic activity (HLAVÁČOVÁ et al.,
2018; TANKARI et al., 2021), which can limit yield (SINGH;
REDDY, 2011).
Growth, development, and photosynthetic performance of two soybean lineages in response to drought
Nativa, Sinop, v. 10, n. 4, p. 547-553, 2022.
548
Depending on lineages traits, soybeans need about 450 to
700 mm of water during cultivation (MANAVALAN et al.,
2009), reaching maximum demand at the reproductive stage
that is the most drought sensitive (ROSA et al., 2020).
However, the drought during the early vegetative stage can
influence pod development by the delay of node
development (KIM et al., 2021), since soybean plants under
drought commonly show reduced net photosynthesis due to
the decrease in stomatal conductance (MESQUITA et al.,
2020), resulting in a reduction in the intercellular CO2
concentration, and also affecting electron transport and
photophosphorylation (CATUCHI et al., 2011; MESQUITA
et al., 2020).
In this way, the objective of this work was to evaluate the
growth, development and photosynthetic performance under
drought in the vegetative phenological stage V4 (Fehr;
Caviness, 1971) of soybean in two lineages with potential
difference tolerance to this abiotic stress, lineages ‘Vx-08-
10819’ and ‘Vx-08-11614’, tolerant and sensitive to drought,
respectively (ROSA et al., 2020). For this purpose, biometric
traits of development, relative water content in leaves,
photosynthetic pigments, gas exchange, and chlorophyll a
fluorescence were evaluated.
2. MATERIAL AND METHODS
2.1. Plant growth conditions
Seeds of soybean lineages Vx-08-10819 and Vx-08-11614
were obtained from the Soybean Breeding Program for
Quality Traits of the Agricultural Biotechnology Research
Institute (Bioagro) at the Federal University of Viçosa, Brazil.
The experiments were conducted in a greenhouse
covered with transparent polyethylene and protected on the
sides with 50% shading. During the experiment, the average
temperature and humidity of the greenhouse were 27°C and
67%, respectively. Seeds of the Vx-08-10819 and Vx-08-
11614 lineages were germinated in a Bioplant substrate
(Bioplant Agrícola Ltda., Nova Ponte, MG, Brazil). Four
seedlings were grown per 9-kg pot in a mixture of soil and
sand, in the ratio 2:1. Fertilization was carried out with 10 g
of the formulation 4-14-8 (N-P-K). All pots were weighed
and hydrated to maintain field capacity at 100%. When the
plants reached the V4 growth stage, the irrigation was
interrupted, except in the control. Then, for three days, the
weight of the pots was monitored daily to maintain 60 and
40% field capacity. The control was maintained at 100% field
capacity.
2.2. Relative water content and crop development
Leaf discs (6 mm diameter) were collected from fully
expanded leaves, weighed, and placed in water for saturation
to analyse the relative water content (RWC), which was
obtained by the formula: Leaf RWC (%) = ((FW-DW)/(TW-
DW)) × 100, where FW is fresh weight, DW is dry weight,
and TW is turgid weight. The hydrated discs were then
weighed again and dried to determine dry weight (Turner
1981). Subsequently, total leaf area (LA) and specific total leaf
area (SLA) were evaluated using the LI-3100C area meter (LI-
COR Biosciences, Lincoln, NE, USA). The shoot height
(SH) was evaluated with the aid of a ruler. Lastly, the shoot
was oven dried at 65 °C for 72 h and the shoot dry weight
(SDW) was determined.
2.3. Photosynthetic pigments
Leaf discs (6 mm diameter) from fully expanded leaves
were immersed in dimethyl sulfoxide saturated with calcium
carbonate. Then, the absorbance of the samples was
evaluated at 665.1, 649.1, and 480 nm to calculate the content
of chlorophyll a (Chl a), b (Chl b), and of total chlorophyll
(Total Chl) and carotenoids (CAR) (WELLBURN, 1994).
2.4. Gas exchange and chlorophyll
a
fluorescence
Gas exchange traits were determined on fully-expanded
leaves at the same time that chlorophyll a fluorescence was
measured using an open-flow infrared gas exchange analyzer
system equipped with the LI-6400-40 leaf chamber
fluorometer (LI-COR Biosciences, Lincoln, NE, USA). The
net CO2 assimilation rate (A), stomatal conductance (gs),
internal CO2 concentration (Ci), and transpiration rate (E)
were measured from 8:00 to 10:00 a.m. (solar time), when A
was at its maximum, under artificial photosynthetically active
radiation (i.e., 1,000 μmol photons m-2 s-1 at the leaf level and
400 μmol CO2 mol-1 air), at 25°C, with vapor pressure deficit
maintained at ≈1.0 kPa and amount of blue light set to 10%
of the photosynthetic photon flux density to optimize
stomatal aperture. Intrinsic water use efficiency (intWUE) was
calculated as A/gs ratio.
The slow phase of chlorophyll a fluorescence induction,
fluorescence of a light-adapted sample measured briefly
before the application of a saturation pulse (F), and
maximum fluorescence of a light-adapted sample (Fm’) were
obtained sequentially by applying a saturation pulse of actinic
light (>3,000 μmol photons m-2 s-1). The minimal
fluorescence traits of the illuminated plant tissue (F0’) and
the fraction of open PSII centres (qP) were calculated from
F and Fm’. The effective quantum yield of photosystem II
photochemistry (ΦPSII) was used to estimate the apparent
electron transport rate (ETR). The photochemical quenching
coefficient was calculated as qP = (Fm’ - Fs)/(Fm’ - F0’) and
the quantum efficiency of open PSII reaction centres (Fv' /
Fm') was calculated as (Fm’- Fo’)/Fm’.
2.5. Experimental design and statistical analysis
The experimental design was a randomized block design
with 4 replications and arranged in a 2 × 3 factorial scheme,
comprising of two soybean lineages (Vx-08-10819 and Vx-
08-11614) in combination with three water availability [100%
(control), 60%, and 40% of field capacity].
Normality and homoscedasticity of the data were
analyzed using the Shapiro-Wilk and Bartlett tests,
respectively, both at 0.05 probability. Then, the data were
subjected to analysis of variance (ANOVA) using the F test
(p ≤ 0.05). When significant, the traits were subjected to the
Scott-Knott test (p < 0.05). As supplementary analysis,
principal component analysis (PCA) was performed using
‘FactoMineR,’ ‘factoextra,’ and ‘ggplot2’ packages. All
statistical analysis of the data was performed using protocols
developed in the R software (R DEVELOPMENT CORE
TEAM, 2019).
3. RESULTS
3.1. Relative water content and crop development
The relative water content in the leaves of lineage Vx-08-
11614 was reduced after exposure to both drought
conditions, which resulted in lower values when compared to
the plants of lineage Vx-08-10819 (Figure 1). Conversely, in
Rosa et al.
Nativa, Sinop, v. 10, n. 4, p. 547-553, 2022.
549
Vx-08-10819, there were no differences in RWC between the
different water availabilities (Figure 1).
The values of LA, SDW and SH decreased in line Vx-08-
11614 after exposure to both drought conditions, with
greater reductions observed after 40% of field capacity
(Figure 2A, 2C–D). After to drought, Vx-08-10819 reduced
SLA (40% of field capacity) and SH (60% and 40% of field
capacity) (Figure 2B, 2D).
Figure 1. Relative water content in leaves – RWC in leaves of two
soybean lineages, ‘Vx-08-10819’ and ‘Vx-08-11614’, during vegetative
stage V4 after exposure to different water availability: 100% (control),
60%, and 40% of field capacity. Different letters indicate significant
differences according to the Scott-Knott test (p < 0.05). Uppercase
letters compare the different soybean lineages in the same water
availability, while lowercase letters compare each soybean lineage
between different water availability. Vertical bars represent the standard
error.
Figura 1. Conteúdo relativo de água – RWC nas folhas em folhas de
duas linhagens de soja, Vx-08-10819 e Vx-08-11614, durante o estágio
vegetativo V4 após exposição a diferentes disponibilidades hídricas:
100% (controle), 60% e 40% da capacidade de campo. Letras diferentes
indicam diferenças significativas de acordo com o teste de Scott-Knott
(p < 0,05). Letras maiúsculas comparam as diferentes linhagens de soja
na mesma disponibilidade hídrica, enquanto letras minúsculas
comparam cada linhagem de soja entre diferentes disponibilidades
hídricas. As barras verticais representam o erro padrão.
3.2. Photosynthetic performance
Reductions in Chl a and Total Chl content were observed
in Vx-08-11614 after exposure to 60% of field capacity
(Figure 3A, 3C). Conversely, Chl b content was not modified
after exposure to both drought conditions (Figure 3B).
Between the two soybean lineages, Vx-08-10819 had the
highest Chl a content (60% of field capacity) and the highest
Total Chl content (60% and 40% of field capacity), while Vx-
08-11614 showed higher Chl a content after exposure to 40%
of field capacity (Figure 3A, 3C). Regarding CAR content,
there was an increase in Vx-08-10819 after exposure to 40%
of field capacity (Figure 3D). Among the tested lineages, Vx-
08-10819 showed higher CAR values in both drought
conditions.
After water restriction, both lineages had a decreased A,
but it remained higher in Vx-08-10819 (Figure 4A). The
values of gs, E and Ci were reduced in both lineages after
exposure to both drought conditions, with greater reductions
in Vx-08-11614 (Figure 4B–D). Intrinsic water use efficiency
increased similarly in both lineages after exposure to water
restriction (Figure 4E).
In Vx-08-10819, there were no differences in ΦPSII,
ETR, qP, and Fv'/Fm' between the different water
availabilities (Figure 5A–D). In contrast, Vx-08-11614
showed the opposite response, reducing these traits after
water restriction. Thus, among the lineages, Vx-08-11614
presented the lowest values for these traits in both drought
conditions (Figure 5A–D).
3.3. PCA analysis
The first two principal components explained 63.3% of
the total variation among traits. Soybean lineages were
separated into two groups by their responsiveness to both
drought conditions. The Vx-08-10819 was strongly linked to
a range of photosynthetic traits, RCW, and SH (Figure 6).
Figure 2. Total leaf area – LA (A), specific total leaf area – SLA (B), shoot dry weight – SDW (C), and shoot height – SH (D) of two soybean
lineages, ‘Vx-08-10819’ and ‘Vx-08-11614’, during vegetative stage V4 after exposure to different water availability: 100% (control), 60%, and 40%
of field capacity. Different letters indicate significant differences according to the Scott-Knott test (p < 0.05). Uppercase letters compare the different
soybean lineages in the same water availability, while lowercase letters compare each soybean lineage between different water availability. Vertical
bars represent the standard error.
Figura 2. Área foliar total – LA (A), área foliar específica total – SLA (B), massa seca da parte aérea – SDW (C) e altura da parte aérea – SH (D) de
duas linhagens de soja, Vx-08-10819 e Vx-08-11614, durante o estágio vegetativo V4 após exposição a diferentes disponibilidades hídricas: 100%
(controle), 60% e 40% da capacidade de campo. Letras diferentes indicam diferenças significativas de acordo com o teste de Scott-Knott (p < 0,05).
Letras maiúsculas comparam as diferentes linhagens de soja na mesma disponibilidade hídrica, enquanto letras minúsculas comparam cada linhagem
de soja entre diferentes disponibilidades hídricas. As barras verticais representam o erro padrão.
Growth, development, and photosynthetic performance of two soybean lineages in response to drought
Nativa, Sinop, v. 10, n. 4, p. 547-553, 2022.
550
Figure 3. Chlorophyll a – Chl a (A), chlorophyll b – Chl b (B), total chlorophyll – Total Chl (C), and carotenoids – CAR (D) contents of two soybean
lineages, ‘Vx-08-10819’ and ‘Vx-08-11614’, during vegetative stage V4 after exposure to different water availability: 100% (control), 60%, and 40%
of field capacity. Different letters indicate significant differences according to the Scott-Knott test (p < 0.05). Uppercase letters compare the different
soybean lineages in the same water availability, while lowercase letters compare each soybean lineage between different water availability. Vertical
bars represent the standard error.
Figura 3. Conteúdo de clorofila a – Chl a (A), clorofila b – Chl b (B), clorofila total – Chl total (C) e carotenóides – CAR (D) de duas linhagens de
soja, Vx-08-10819 e Vx-08-11614, durante o estágio vegetativo V4 após exposição a diferentes disponibilidades hídricas: 100% (controle), 60% e
40% da capacidade de campo. Letras diferentes indicam diferenças significativas de acordo com o teste de Scott-Knott (p < 0,05). Letras maiúsculas
comparam as diferentes linhagens de soja na mesma disponibilidade hídrica, enquanto letras minúsculas comparam cada linhagem de soja entre
diferentes disponibilidades hídricas. As barras verticais representam o erro padrão.
Figure 4. Net CO2 assimilation rate – A (A), stomatal conductance – gs (B), transpiration rate – E (C), internal CO2 concentration – Ci (D), and
intrinsic water use efficiency – intWUE (E) of two soybean lineages, ‘Vx-08-10819’ and ‘Vx-08-11614’, during vegetative stage V4 after exposure to
different water availability: 100% (control), 60%, and 40% of field capacity. Different letters indicate significant differences according to the Scott-
Knott test (p < 0.05). Uppercase letters compare the different soybean lineages in the same water availability, while lowercase letters compare each
soybean lineage between different water availability. Vertical bars represent the standard error.
Figura 4. Taxa de assimilação líquida de CO2 - A (A), condutância estomática - gs (B), taxa de transpiração - E (C), concentração interna de CO2 -
Ci (D) e eficiência intrínseca do uso da água - intWUE (E) de duas linhagens de soja, Vx-08-10819 e Vx-08-11614, durante o estágio vegetativo V4
após exposição a diferentes disponibilidades hídricas: 100% (controle), 60% e 40% da capacidade de campo. Letras diferentes indicam diferenças
significativas de acordo com o teste de Scott-Knott (p < 0,05). Letras maiúsculas comparam as diferentes linhagens de soja na mesma disponibilidade
hídrica, enquanto letras minúsculas comparam cada linhagem de soja entre diferentes disponibilidades hídricas. As barras verticais representam o
erro padrão.
Rosa et al.
Nativa, Sinop, v. 10, n. 4, p. 547-553, 2022.
551
Figure 5. Effective quantum yield of PSII – ΦPSII (A), electron transport rate – ETR (B), photochemical quenching coefficient – qP (C), and
quantum efficiency of open PSII reaction centres – Fv' / Fm' (D) of two soybean lineages, ‘Vx-08-10819’ and ‘Vx-08-11614’, during vegetative stage
V4 after exposure to different water availability: 100% (control), 60%, and 40% of field capacity. Different letters indicate significant differences
according to the Scott-Knott test (p < 0.05). Uppercase letters compare the different soybean lineages in the same water availability, while lowercase
letters compare each soybean lineage between different water availability. Vertical bars represent the standard error.
Figura 5. Rendimento quântico efetivo do PSII – ΦPSII (A), taxa de transporte de elétrons – ETR (B), coeficiente de extinção fotoquímica – qP
(C) e eficiência quântica de centros abertos de reação PSII – Fv' / Fm' (D) de duas linhagens de soja, Vx-08-10819 e Vx-08-11614, durante o estágio
vegetativo V4 após exposição a diferentes disponibilidades hídricas: 100% (controle), 60% e 40% da capacidade de campo. Letras diferentes indicam
diferenças significativas de acordo com o teste de Scott-Knott (p < 0,05). Letras maiúsculas comparam as diferentes linhagens de soja na mesma
disponibilidade hídrica, enquanto letras minúsculas comparam cada linhagem de soja entre diferentes disponibilidades hídricas. As barras verticais
representam o erro padrão.
Figure 6. Biplot component analysis of the relative water content in leaves, crop development, and photosynthetic performance of two soybean
lineages, ‘Vx-08-10819’ and ‘Vx-08-11614’, under 60% and 40% of field capacity. Relative water content in leaves – RWC, total leaf area – LA,
specific total leaf area – SLA, shoot dry weight – SDW, and shoot height – SH, total chlorophyll – Total Chl, carotenoids – CAR, net CO2 assimilation
rate – A, stomatal conductance – gs, transpiration rate – E, internal CO2 concentration – Ci, intrinsic water use efficiency – intWUE, effective
quantum yield of photosystem II – ΦPSII, electron transport rate – ETR, photochemical quenching coefficient – qP, and quantum efficiency of
open PSII reaction centres – Fv' / Fm'.
Figura 6. Análise de componentes biplot do conteúdo relativo de água nas folhas, desenvolvimento da cultura e desempenho fotossintético de duas
linhagens de soja, Vx-08-10819 e Vx-08-11614, sob 60% e 40% da capacidade de campo. Conteúdo relativo de água nas folhas – RWC, área foliar
total – LA, área foliar específica total – SLA, massa seca da parte aérea – SDW, altura da parte aérea – SH, clorofila total – Chl total, carotenóides –
CAR, taxa de assimilação líquida de CO2 – A, condutância estomática - gs, taxa de transpiração – E, concentração interna de CO2 – Ci, eficiência
intrínseca do uso da água – intWUE, rendimento quântico efetivo do PSII – ΦPSII, taxa de transporte de elétrons – ETR, coeficiente de extinção
fotoquímica – qP e eficiência quântica de centros abertos de reação PSII – Fv' / Fm'.
Growth, development, and photosynthetic performance of two soybean lineages in response to drought
Nativa, Sinop, v. 10, n. 4, p. 547-553, 2022.
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4. DISCUSSION
Different physiological responses were observed between
soybean lineages after exposure to both drought conditions
(Figure 1–6), being the Vx-08-10819 the one that showed the
best drought tolerance responses, with emphasis on the
photosynthetic traits (Figure 4–6). Additionally, the RWC in
the Vx-08-10819 was not changed after the water restriction
(Figure 1), keeping the LA and SDW phenotypic traits
unchanged during both drought conditions (Figure 2A, 2C),
which demonstrates that this lineage has a greater tolerance
to drought in the vegetative stage, as well as observed in the
reproductive stage (ROSA et al., 2020).
The reduction in leaf water content can result in low
turgor pressure, leading to decreased gs and limiting cell
expansion (Jaleel et al., 2009), hence causing lessened plant
growth and development (Ullah et al., 2017), as observed in
the Vx-08-11614 (Figure 2A, 2C–D). Similar results in
response to drought were reported in different plant species
such as sweet potatoes (YOSHIDA et al., 2020), chili pepper
(WIDURI et al., 2020), and cabbage (HAGHIGHI et al.,
2020).
The lower Total Chl and carotenoids contents observed
in Vx-08-11614 (Figure 3C, 3D, 6) shows a lower efficiency
in light absorption and, consequently, a lower transfer of
radiant energy to reaction centers under drought (Rosa et al.,
2020), which can negatively impact A. Chlorophyll and
carotenoids contents are a key factor in plant photosynthesis
and closely reflects the photosynthetic capacity of plants
(TALBI et al., 2020). In addition, the lower carotenoids
content decreases the protection of the antenna complex
from oxidative damage (Lapaz et al., 2020; Yoshida et al.,
2020), since these antioxidants scavenge reactive oxygen
species (ROS) to protect the photosynthetic apparatus
(ROSA et al., 2020). However, Mesquita et al. (2020)
observed a more pronounced decrease in photosynthetic
pigments in the tolerant soybean lineage. In fact, reduction in
chlorophyll content is attributed as a typical symptom of
oxidative stress (Iqbal et al., 2019), indicating that the Vx-08-
11614 is more affected by drought stress (ROSA et al., 2020),
as shown in Figure 3.
The gs is responsive to almost all external and internal
factors related to drought, it represents a highly integrative
basis for overall effect of drought on photosynthetic traits
(SINGH et al., 2011). In this context, the decrease in gs
(Figure 4B) was crucial to optimizing the intWUE in both
lineages (Figure 4E). Gulias et al. (2012) also found higher
intWUE in grasses subjected to drought. Additionally, the
lower A (Figure 4A) observed in the Vx-08-11614 under
drought is apparently associated with a marked reduction in
gs (Figure 4B), which resulted in lower Ci (Figure 4D) due to
the limitation stomatal, as well as a photochemical inhibition
(Figure 5A, C–D). Hence, the lower gs reduced Ci, inducing
limitations CO2 assimilation, and causing an imbalance
between photochemical activity at PSII and electron
requirement for photosynthesis, which increases the
susceptibility to photooxidative and oxidative damage to
photosystems (Ohashi et al., 2006); this answer explains the
reduction in the content of Total Chl e carotenoids in the Vx-
08-11614 (Figure 3C, D, 6).
Electron transport rate reduction is a defense strategy
against photooxidative damage in plants whose CO2 fixation
is compromised (Yamori, 2016), indicating cumulative effects
of biochemical limitations (Mesquita et al., 2020), as noted in
the Vx-08-11614 (Figure 5B). Similar results were observed
under the same conditions of drought stress imposition, but
in the reproductive phenological stage R3 (FEHR;
CAVINESS, 1971) by Rosa et al. (2020). In contrast,
although gs has also substantially reduced in the Vx-08-10819
(Figure 4B), there was a moderate reduction in A and traits
of chlorophyll a fluorescence were unchanged (Figure 4A, 5),
suggesting that the PSII structural integrity of the Vx-08-
10819 was not injured by drought (IQBAL et al., 2019).
5. CONCLUSIONS
Relative water content in leaves, LA, and SDW of lineage
Vx-08-10819 were not changed after exposure to drought.
Besides that, photosynthetic capacity of lineage Vx-08-10819
was less affected than lineage Vx-08-11614 to drought,
showing that this lineage is tolerant to this abiotic stress in at
vegetative stage V4.
6. REFERENCES
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plantio à colheita. Viçosa: UFV, 2015. p. 20-85.
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