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The enhancement in both frequency and intensity of high temperature, besides its large variability will result in up to 40% yield reduction in rice by the end of 21st century. Vegetative growth in rice continues with day time temperature up to 40 °C but development of florets is extremely sensitive to temperature higher than 35 °C. The effect of night time temperature stress is even more adverse than day. Heat stress results in deprived anther dehiscence, impaired pollination and abnormal pollen germination that cause floret sterility. The decrease in pollen viability is presumably caused by imbalance in proteins expression, abandoned biosynthesis, partitioning and translocation of soluble sugars, imbalance in phytohormones release, and loss of pollen water content. Rice responds to heat stress by adjusting various physiochemical mechanisms viz., growth inhibition, leaf senescence and alteration in basic physiological processes. Antioxidant enzymes, calcium and iron also play an important role in managing heat stress. Response of rice to heat stress varies with plant ecotype, growth stage, heat intensity and time of stress application. High temperature stress can be managed by developing heat-tolerant genotypes. Rice breeding and screening may be based on anther dehiscence, pollen tube development and pollen germination on stigma.
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Archives of Agronomy and Soil Science
ISSN: 0365-0340 (Print) 1476-3567 (Online) Journal homepage:
Consequences of high temperature under
changing climate optima for rice pollen
characteristics-concepts and perspectives
Shah Fahad, Muhammad Zahid Ihsan, Abdul Khaliq, Ihsanullah Daur, Shah
Saud, Saleh Alzamanan, Wajid Nasim, Muhammad Abdullah, Imtiaz Ali Khan,
Chao Wu, Depeng Wang & Jianliang Huang
To cite this article: Shah Fahad, Muhammad Zahid Ihsan, Abdul Khaliq, Ihsanullah Daur, Shah
Saud, Saleh Alzamanan, Wajid Nasim, Muhammad Abdullah, Imtiaz Ali Khan, Chao Wu, Depeng
Wang & Jianliang Huang (2018): Consequences of high temperature under changing climate
optima for rice pollen characteristics-concepts and perspectives, Archives of Agronomy and Soil
Science, DOI: 10.1080/03650340.2018.1443213
To link to this article:
Accepted author version posted online: 21
Feb 2018.
Published online: 06 Mar 2018.
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Consequences of high temperature under changing climate
optima for rice pollen characteristics-concepts and perspectives
Shah Fahad*
, Muhammad Zahid Ihsan*
, Abdul Khaliq
, Ihsanullah Daur
, Shah Saud
Saleh Alzamanan
, Wajid Nasim
, Muhammad Abdullah
, Imtiaz Ali Khan
, Chao Wu
Depeng Wang
and Jianliang Huang
National Key Laboratory of Crop Genetic Improvement, MOA Key Laboratory of Crop Ecophysiology and Farming
System, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, China;
of Agronomy, The University of Swabi, Swabi Kyber Paktunkhwa, Pakistan;
Cholistan Institute of Desert Studies,
The Islamia University of Bahawalpur, Pakistan;
Department of Agronomy, University of Agriculture Faisalabad,
Department of Arid Land Agriculture, King Abdulaziz University, Jeddah, Saudi Arabia;
College of
Horticulture, Northeast Agricultural University, Harbin, China;
Department of Environmental Sciences, COMSATS
Institute of Information Technology, Vehari, Pakistan;
College of Life Science, Linyi University, Linyi, China;
Collaborative Innovation Center for Grain Industry, Yangtze University, Hubei, China
The enhancement in both frequency and intensity of high temperature,
besides its large variability will result in up to 40% yield reduction in rice
by the end of 21
century. Vegetative growth in rice continues with day
time temperature up to 40°C but development of orets is extremely
sensitive to temperature higher than 35°C. The eect of night time
temperature stress is even more adverse than day. Heat stress results
in deprived anther dehiscence, impaired pollination and abnormal pollen
germination that cause oret sterility. The decrease in pollen viability is
presumably caused by imbalance in proteins expression, abandoned
biosynthesis, partitioning and translocation of soluble sugars, imbalance
in phytohormones release, and loss of pollen water content. Rice
responds to heat stress by adjusting various physiochemical mechanisms
viz., growth inhibition, leaf senescence and alteration in basic physiolo-
gical processes. Antioxidant enzymes, calcium and iron also play an
important role in managing heat stress. Response of rice to heat stress
varies with plant ecotype, growth stage, heat intensity and time of stress
application. High temperature stress can be managed by developing
heat-tolerant genotypes. Rice breeding and screening may be based on
anther dehiscence, pollen tube development and pollen germination on
Received 15 August 2017
Accepted 16 February 2018
Anther dehiscence; ROS;
heat stress; rice pollen
development; calcium
Rice (Oryza sativa L.) is a primary source of food for approximately 3 billion people and accounts for
3575% of daily calories intake, globally (Fitzgerald et al. 2009). World population is expected to rise up to
10 billion people by the end of 2050, which will exponentially increase the demand for rice in coming
decades. Globally, rice is cultivated on around 153 million hectares that accounts for 11% of the total
world arable lands (FAOSTAT 2011). Rice production is facing multiple challenges viz., extremities of water
CONTACT Jianliang Huang National Key Laboratory of Crop Genetic Improvement, MOA
Key Laboratory of Crop Ecophysiology and Farming System, College of Plant Science and Technology, Huazhong Agricultural
University, Wuhan, Hubei, China
*These authors contributed equally to this work
© 2018 Informa UK Limited, trading as Taylor & Francis Group
stress, salinity, heat and insect pest infestation which had endangered its sustainable production (Ihsan
et al. 2014; Fahad et al. 2016a,2016b). Increase in temperature with changing climatic scenario posed a
serious threat to rice production due to its unwelcomed consequences on kernel development.
Experimental evidences have recurrently exposed the severity of short episodes of high temperature
for greater negative impacts over continuous mild stress (Schlenker and Roberts 2009). A 25-year weather
data report from International Rice Research Institute (IRRI), Philippines has indicated greater increase in
night time temperature (1.13°C) over day time temperature (0.35°C) (Peng et al. 2004). Most of the rice is
currently grown in regions where existing temperature is already close to the optimum range for rice
production. Therefore, any further rise in mean temperature or short episode of high temperature during
sensitive growth stages, will be catastrophic. A reduction of 41% in rice yield is estimated with current rate
of global temperature change by the end of 21
Century (Ceccarelli et al. 2010). To encounter this issue,
rice is increasingly cultivated on marginal environments thus, experiencing above-optimum temperature
stress (28/22°C) (Prasad et al. 2006; Das et al. 2014). Increase in day/night temperature above critical limits
is not uncommon in marginal environment, and hence it impaired seed set, spikelet sterility and grain
yield of rice.
Eects of heat stress vary with the duration, intensity and uctuation of temperature above
optimal limits, and the stage of crop development (Alghabari et al. 2015)(Table 1). Likewise
other cereals, rice crop is tolerant to heat stress at vegetative stage but extremely sensitive at
reproductive stage, particularly at the anthesis stage (Jagadish et al. 2010:Ihsanetal.2016). The
temperature above 35°C at reproductive stage lasting for more than an hour resulted in
maximum spike sterility (Jagadish et al. 2007;Rangetal.2011). Irregular anther dehiscence
was the major reason for heat induced spikelet sterility. Impaired pollination and abnormal
pollen germination might be some of the other possible reasons (Matsui et al. 2005;Jagadish
et al. 2010).
Pollen quality is an important trait in determining the kernel yield and quality (Fahad et al.
2016b,2016c). Under heat stress, oral abnormalities (stamen hypoplasia and pistil hyperplasia)
lead to spikelet sterility. Major eect of heat stress during oral initiation was recorded on kernel
number. The estimated decline in kernel number with each degree increase in temperature was 4%
for temperature stress applied at 30 days preceding anthesis (Fischer 1985). Heat stress limited
photo-assimilation to the grain and increased grain lling rate with a shortening in an eective
grain lling period. Reduced endosperm cell division and elongation under heat stress has
decreased the grain plumpness (Morita et al. 2005).
Rice responds to heat stress by adjusting various physiochemical mechanisms viz., growth
inhibition, leaf rolling, leaf senescence, alteration in basic physiological processes (respiration,
photosynthesis, membrane permeability and ROS) that helps to decrease pollen sterility. Plants
experiencing heat stress at reproductive stage have to keep their male and female organs
functioning especially at meiosis stage, pollen germination, pollen tube growth, pollen-pistil
interaction, pre and post fertilization process, endosperm and embryo development (Erickson
and Markhart 2002). Rice yield reduction through decreased pollen viability is associated with
changes in several metabolites that play a signicant role in pollen development by both con-
tributing to the pollen nutrition and by oering protection against heat stress (Paupière et al.
2014). Nevertheless, there is an urgent need to address high-temperature-induced pollen charac-
terizations in rice under current climatic conditions and more so in the face of a changing climate
This review accentuates the enlarging adversities of high temperature stress and their
substantial impacts on rice pollen characteristics. Furthermore, an attempt has been made to
provide an overview of oret sterility, anther dehiscence, apical and basal pore length, pollen
fertility, pollen count per stigma, pollen germination on stigma, and pollen physiological bases.
Some strategies are also discussed for genetic improvement of rice for enhancing the tolerance
to heat stress.
High temperature and rice pollen characteristics
Floret sterility
Vegetative growth in rice continues with day time temperature up to 40°C but development of
orets is extremely sensitive to temperature higher than 33°C (Figure 1). Predicted global warming
has exacerbated the chances of occurrence of rice oret sterility (Matsui 2009). Booting and
owering are considered as the most heat sensitive developmental stages in rice plant (Shah
et al. 2011; Yang et al. 2017). Temperature exceeding 35°C at anthesis stage may confer 90% oral
sterility (De Datta 1981). Deprived anther dehiscence, lower pollen production, poor pollen germi-
nation on stigma and failure to extend pollen tube are the primary causes of oret sterility (Matsui
et al. 2001; Prasad et al. 2006). The disparity in pollen germination actually occurred in those
pollens that failed to signicantly accumulate iron in their pollen tubes or microspores. The
additional hypothesized explanations might be the abnormal ribosome assembly and proteins
expression specically heat and cold shock proteins (Jagadish et al. 2010).
Inuence of heat stress on oret sterility also varied among rice genotypes. A comparative
analysis of 14 rice genotypes reported cultivar dierence for applied levels of heat stress depend-
ing upon their ecotype (indica and japonica) and origin (temperate and tropical) for oret sterility
Table 1. Some pronounced eects of applied high temperature stresses and durations initiated at dierent plant growth stages
on some pollen characteristics.
Temperature Duration Eect Plant growth stage References
Above 35/
3 days Adverse eects on panicle extrusion, spikelet anthesis,
pollen viability, pollen tube length, anther dehiscence
and pollen reception on stigma.
Panicle initiation Das et al.
Above 35°C 1 h High spikelet sterility Anthesis Jagadish et al.
201038°C 5 days Heat susceptible genotypes showed only 18% spikelet
fertility. Pronounced dierence was noticed in anther
length, width, apical and basal pore length.
37°C - Resulted in 50% spikelet sterility Flowering Matsui et al.
29, 33 and
< 1 h Spikelet fertility was reduced by 7% in heat susceptible
Anthesis Jagadish et al.
38°C 48 h By increasing heat stress duration, a linear decline in
spikelet fertility was documented. Collective eect of heat
and water stress was more severe.
Anthesis Rang et al.
Above 28°C // Reported decline in pollen production and pollen reception
on stigma
Flowering Prasad et al.
32°C 20 DAE
Grains located at panicle base presented higher decline in
fertility and length compared to those on tip of panicle
// Mohammed
and Tarpley
Above 37°C 6 d By increasing heat stress, tightness in locule by closure of
cell layers delayed locule opening and reduced fertility
Middle heading
Matsui and
39°C/30°C 24 d Impaired pollen fertility and poor attachment demonstrated
partial germination on stigma
Microspore stage Endo et al.
Above 32°C/
3 d Expected increase in temperature will reverse stimulatory
eect of elevated carbon dioxide on rice production in
near future
Reproductive stage Cheng et al.
Above 37°C // Signicantly decreased seed set Pollen germination Matsui et al.
2732°C 20 d Extent of spikelet sterility was varied from few empty
glumes to complete sterility with increasing heat stress
intensity and duration
After heading Ohe et al.
35°C/30°C 2 weeks Signicant variation in number of fertile spikelets, anther
length and pollen production
Before heading Inaba 2005
10 d Documented structural abnormalities leading to premature
degeneration of tapetum. Abnormal anther development
and slower provision of metabolites to pollen resulted in
poor pollen nutrition
Anthesis Suzuki et al.,
(Prasad et al. 2006). Cultivar dierences to applied heat stress were manifested by inconsistent
pollen production and reception on stigma that resulted in fewer lled grains and lower 1000 grain
weight (Prasad et al. 2006). A temperature stress of 35°C applied at anthesis stage even for an hour
induced oret sterility (Jagadish et al. 2010) but same stress level when applied for an hour at pre-
and post-anthesis stage failed to induce sterility (Yoshida et al. 1981). Rang et al. (2011) later on
conrmed a complete oret sterility of rice plants exposed to temperature above 35°C for 5
consecutive days at owering stage. Eect of day time temperature of 29°C on oret sterility
were non-signicant while same level of night time temperature increased rice susceptibility to
sterility and subsequently curtailed the seed set (Table 2).
Temperature eect varies among oral parts. The male gametophyte is more susceptible to heat
stress and responsible for spikelet sterility while pistil was unaected at elevated temperature
stress (Yoshida et al. 1981). The spikelets inside the ag leaf sheath exhibited complete sterility
after high temperature stress that might be due to the extra heat trapped under leaf sheath that
limited free air ow (Das et al. 2014). Pollen grains swelling in the locules are the leading force for
anther dehiscence (Matsui et al. 1999). High temperature resulted in poor pollen grains swelling
and subsequently poor anther dehiscence (Matsui et al. 2000). Pollen grains exposed to high
temperature stress presented uniform shape but some of the important functions as pollen
adhesion and germination on the stigma were severely hindered (Endo et al. 2009). Cluster analysis
of microarray data has identied localization of some temperature responsive genes in the anther.
Expression of genes responsible for imbalance in hormonal release, abandoned biosynthesis,
partitioning and translocation of photosynthates have been ascribed the major causes for oret
sterility (Afuakwa et al. 1984). Thus, we can conclude that multiple factors contribute in orets
sterility under heat stress leading to aborted kernel production.
Figure 1. Eects of high temperature stress on young panicle growth and oret degradation at 10 days after treatments
application. (a, b) indicate young panicles of cultivar LYPJ and SY63, (c, d) indicate oret degradation in cultivar LYPJ and SY63.
ADT, high whole-day temperature treatment; CK, control; HDT, high daytime temperature treatment; HNT, high nighttime
temperature treatment (Adapted from Wu et al. 2016).
Table 2. Eect of dierent ranges of high day and tight time temperature stress on pollen characteristics.
Eect studied
Day temperature stress (°C)
2730 3134 3538 3942 4346
Decrease/Increase with temperature change
Pollen tube length µm 1300 1180 - 1160 780 Das et al. 2014
Dia. of pollen grain µm 520 480 - 240 34
Pollens on stigma 37 29 - 8 2
Pollen germination % 32 12 - 6 0
Anther dehiscence % 82 46 - 20 2
Spikelet fertility % 93 - 18 - - Jagadish et al. 2010
Total number of pollen 64 - 9 - -
Germinated pollen 41 - 2 - -
Pollen tube length mm 62 - 0 - -
Anther length mm 2.19 - 2.22 - -
Anther width mm 0.68 - 0.70 - -
Basal pore area µm
4929 - 5992 - -
Basal pore length µm 495 - 539 - -
Apical pore area µm
10,318 - 12,132 - -
Apical length µm 581 - 638 - -
Stigma length mm 0.96 - 0.94 - -
Pistil length mm 2 - 2 - -
No. of anthesing spikelets 20 - 12 - - Jagadish et al. 2007
Anther dehiscence % 88 - 32 - - Rang et al. 2011
Number of germinated pollen on stigma 51 - 3 - -
Spikelet fertility % 84 - 1 - -
Pollen production (number anther
) 1177 151 - - - Prasad et al. 2006
Pollen reception (number stigma
) 17.6 3.8 - - -
Pollen viability (%) 92 74 - - -
Pollen viability (%) - - 76.08 - 68.70 Poli et al. 2013
Spikelet fertility (%) - - 91.00 - 69.23
Spikelet fertility (%) I 78 - - 61 - Endo et al. 2009
Spikelet fertility (%) II 78 - - 59 -
Spikelet fertility (%) III 78 - - 0 -
Spikelet fertility % 78 - 75 - - Shah et al. 2014
Grain length mm 5.47 5.48 - - - Morita et al. 2005
Grain width mm 3.12 3.05 - - -
Grain thickness mm 2.12 2.21 - - -
Endosperm cross section mm
5.32 5.42 - - -
Cells in endosperm 748 888 - - -
Avg. cell area (×10mm
) 717 614 - - -
Spikelet sterility% 40 - 60 - - Ohe et al. 2007
Night temperature stress (°C)
2528 2932 3336 3740 4144
Decrease/Increase with temperature change
Spikelet fertility % - 75 10 - - Mohammed and Tarpley 2009
Pollen germination % - 30 14 - -
Spikelet sterility (%) 24 88 - - - Mohammed and Tarpley 2011
Panicle length (cm) 22.5 21.6 - - -
branches per panicle 16 17 - - -
Pollen germination % - 49 - - - Mohammed and Tarpley 2014
Spikelet fertility % 62 43 - - -
Unlled grains Panicle
38 33 - - -
Pollen germination % 58 28 - - -
Pollen germination % 30 27 - - - Mohammed and Tarpley 2011
Spikelets fertility % 78 16 - - -
Fertilized spikelet % 84 70 - - - Cheng et al. 2009
Spikelets fertility % 77 70 - - - Shah et al. 2014
Grain length mm 5.47 - 5.54 - - Morita et al. 2005
Grain width mm 3.12 - 3.00 - -
Grain thickness mm 2.12 - 2.07 - -
Endosperm cross section mm
5.32 - 4.84 - -
Cells in endosperm 748 - 915 - -
Avg. cell area (×10mm
) 717 - 530 - -
DAE; days after emergence, Dia; diameter, I; early panicle development, II; glumous ower primordium dierentiation, III; early
microspore following meiosis
Anther dehiscence
Anther dehiscence is the nal step of anther development and results in the release of pollen
grains to permit pollination, fertilization and seed set. Anther is a specialized organ of the stamen
where development of the male gametophyte takes place. It consists of four maternal cell layers
i.e., epidermis, endothecium, tapetum and connective tissues surrounding the inner sporogenous
cells (Feng and Dickinson 2007).
A complex mechanism is involved in the development and release of the pollens. Cracking of
septa followed by locule wall expansion, pollen swelling and rupturing of the stomium are series of
events required for successful anther dehiscence (Liu et al. 2006). These events must synchronize
with the pollen development for the successful release of anthers and pollination (Zhu et al. 2004).
Fahad et al. (2016a) observed that both high day time (HDT) and night time temperatures (HNT)
aected the anther dehiscence of two rice varieties (IR64 and HHZ). Heat tolerant genotype HHZ
anther dehiscence was 6154% and heat sensitive genotype IR64 was 3322% under HDT and HNT
respectively (Figure 2). Pollen grains swelling exert pressure on anther walls that rupture and free
pollen grains (Matsui et al. 1999). High temperature treatment applied at anthesis stage increased
vapor pressure decit thus enhanced evaporative losses from anther and thereby reduced moisture
availability required for pollen grain swelling and subsequently aected anther dehiscence that is
required for pollination (Matsui et al. 2000). A loss of 3050% of pollen water content negatively
aected not only cell dierentiation but also spikelet fertility (Liu et al. 2006).
Disparity in protein expression (dirigent and subtilisin-like proteins) is mainly responsible for
anther dehiscence under high temperature stress (Jagadish et al. 2010). These proteins play crucial
role in lignin biosynthesis to repair damaged cell wall (Johansson et al. 2000). Increased lignication
of anther walls delayed the breakdown of tissues that disturbed the regular process of anther
Cultivar dierence (susceptible or tolerant) for applied heat stress has been discussed for a
number of reasons. Well-developed cavities and thick locule walls in anther of tolerant cultivars
allowed easy rupture in reaction to pollen swelling and led to improved anther dehiscence and
pollen shed (Matsui et al. 2001). Heat stress not only hinders normal anther dehiscence process but
abnormal pollen developments in anther and oret deformity have been examined that headed
towards abnormal fertilization (Shi et al. 2008)(Figure 3). Usually, complete anther dehiscence
produces higher pollen interception on stigma, but in heat sensitive genotypes (Moroberekan)
even higher anther dehiscence resulted in fewer pollen reception and germination on the stigma
(Jagadish et al. 2010). Such disparity could be attributed to asynchrony between male and female
reproductive organs. Length of basal dehiscence under normal conditions is another indication for
measuring varietal tolerance to heat stress (Matsui 2005). Future research must focus on anther
dehiscence as a major trait in heat tolerant variety development programs.
Apical and basal pore length
Very little is known about the involvement of anther apical and basal pore length in pollination and
the consequent restrictions under heat stress. Basal pores are positioned just above stigmata and at
the bottom of theca, and open at the time of ower opening when the anthers stand erect.
Consequently, pollen grains in the anthers with large basal pores would readily drop out of the
basal pores on to the stigma. Signicant contribution towards pollination was assessed for anther
basal pore length because of its close proximity to the stigmatic surface but knowledge regarding
apical pore length is lacking (Matsui and Kagata 2003). Thus, the basal pore length is a key
morphological trait that inuences the pollen count on stigma (Matsui and Omasa 2002). Heat
stress applied for ve consecutive days at owering stage increased both apical and basal pore
length/area. Cold stress applied at anthesis stage was encountered by cold resistant genotypes
through producing bigger anthers (Suzuki 1981) and longer stigmas (Suzuki 1982) compared to
cold susceptible genotypes. Involvement of same morphological adaptation is considered for heat
tolerant genotypes. After successful pollination, pollen tube takes almost 30 minutes to reach
embryo sac (Cho 1956). Pollen grains with longer basal pores are readily dropped out of the pores
on the stigmata surface while anthers with smaller basal pores remain stacked to anther walls at
the time of oret splitting (Matsui and Kagata 2003). Thus apical and basal pore length along with
Figure 2. Comparison of two rice cultivars, Huanghuazhan (heat tolerant), IR-64 (heat susceptible) for dierent pollen
characteristics to applied high night temperature (HNT), high day temperature (HDT) and ambient temperature (AT) treat-
ments. The HDT of 35°C ± 2, HNT of 32 °C ± 2 and AT 28°C ± 2 throughout the day were provided. The HDT started at 7 am
while HNT started at 7 pm and lasted for 12 hours daily (7 pm to 7 am). Control (AT) plants were grown at 28°C (12 h-day/12
h-night cycles). The heat treatments were employed from booting stage to physiological maturity of plants. Round circles with
dashed lines indicate response curve of Huanghuazhan cultivar while triangles with dotted dashed lines represent IR-64
cultivar. Eect of HNT stress was more severe compared to HDT stress for all studied pollen characteristics for both cultivars.
anther length can increase the probability of successful pollination by facilitating pollen release
under high temperature stress that decreases the chance of pollen reception and synchronization.
These traits are easy to identify, and in combination with some other traits, can be used as
breeding and screening tool for heat resistant germplasm selection.
Pollen tube growth rate vary with the susceptibility or tolerance level of genotypes under
varying intensity and duration of heat stress. For non-stressed conditions, pollen tube length of
heat susceptible (Moroberekan), medium tolerant (IR-64) and highly tolerant (N-22) genotypes
were between 1.42 mm to 1.85 mm and it was equivalent to 0.750.79% of the pistil length
(Jagadish et al. 2010). Under severe heat stress, susceptible genotype failed to produce pollen
germination on stigma while the pollen tube length of medium tolerant cultivar decreased up to
1.42 mm, while pollen tube length of heat tolerant genotype decreased up to 1.35 mm.
Pollen fertility
Pollen is the male gametophyte and most sensitive organ to heat stress that delivers genetic
material to embryo sac through double fertilization. Pollen is formed in the specialized organ
(stamen) that comprises of broader upper region called anther that holds pollens, and lower
stalked region containing the vasculature-the lament that extends to ensure pollen release to
stigmata surface (Goldberg et al. 1993). Mature pollen contains fructose, glucose, sucrose and
starch as major soluble sugars. Pollen is a sink for these sugars that are required for development,
growth, and protection against environmental stresses.
Figure 3. Illustration of pollen grains retained within the anthers of dierent cultivars under high temperature treatments.
(ad) N22, (eh) HHZ, (il) LYPJ, and (mp) SY63. ADT, high whole-day temperature treatment; CK, control; HDT, high
daytime temperature treatment; HNT, high nighttime temperature treatment. Scale bar = 100μm (Adapted from Wu et al.
Tang et al. (2008) described a lower rate of pollen activity at higher temperature. Several physiolo-
gical and morphological adaptations in heat avoidance plants contribute to pollen fertility and rate of
grain setting. Heat stress sensitivity of pollens are attributed to failure of male gametophyte to respond
and produce signicant quantity of heat shock proteins as compared to vegetative tissues
(Mascarenhas and Crone 1996). Pollen abortion was linked with imbalance in polyamine content
while pollen germination and pollen tube growth rate decrease was associated with spermine and
spermidine content under high temperature stress (Song et al. 2002). Endo et al. (2009) studied the
eect of heat stress (39/30°C) applied at microspore stage for 24 days on pollen viability. Pollen grains
displayed normal round shape when stained with Alexander reagent however, they exhibited poor
attachment and germination on the stigma surface. It was due to heat stress induced disruption in
tapetum functioning that is required for adhesion and germination on the stigma.
Heat stress caused reduction in pollen production, their release, interception, viability and
germination. Pollen quality is a crucial indicator of male fertility and health. Tapetum development
is very sensitive to heat stress. Its a key organ that provides metabolites to the pollen. Heat
induced abnormalities in tapetum development resulted in reduced provision of metabolites to the
pollen thus displaying poor pollen nutrition. Matsui et al. (2000) connected poor pollen fertility
with the opening of anther loculi that decreased under heat stress. The eect of heat stress on
pollen fertility was dependent on several complex factors (genotype, growth stage, duration of
stress, time of stress day/night, moisture level, radiation, wind velocity and ambient recovery
conditions) that aect it individually or in an interactive way (Morita et al. 2005). Eect of heat
stress was more severe on pollens of low land genotype compared to upland genotypes. Both
quantitative and qualitative variations in pollen proteins of these genotypes were present that
possibly headed towards dierential loss in viability (Jagadish et al. 2007). Nonetheless, heat stress
induced changes in physiology demonstrated adverse eects on pollen meiosis, germination, ovule
development and viability of embryo. Pressman et al. (2002) illustrated that at optimum tempera-
ture, concentration of soluble sugars gradually increased in pollen. Heat stress prevented the rise in
starch content and decreased the concentration of soluble sugars in mature pollen. The decrease in
pollen viability is presumably caused by this decrease in soluble sugars.
Pollen dehydration to increased heat intensity has been studied but information on the water
content of pollen and coping mechanism is scarce. On contrary, heat stress might have conned
soluble sugars into the locular uid and restrict their transfer to the pollen. Low temperature stress
diluted the tapetal cell layer that led to starch-less pollen grain causing immature pollen develop-
ment (Mamun et al. 2006). Similar mechanism might be involved under high temperature stress. In
future research, there is a strong need to explore the actual mechanisms responsible for sugar
partitioning and translocation in pollens under heat stress.
Pollen count per stigma
Stigma must receive at least 20 healthy pollen grains to ensure successful pollination (Matsui and
Kagata 2003). Accordingly, half of them have to germinate on stigma. Heat stress severely
inuences the number of pollens on stigma (Figure 4). Matsui et al. (2001) noted only 20% spikelet
fertility with 10 germinated pollen grains on stigma under mild stress while no fertility was noticed
at 40°C. Declined pollen reception and viability on stigma under heat stress is a direct cause of yield
reduction in rice (Fahad et al. 2015). Matsui and Omasa (2002) postulated that in heat tolerant
genotypes, larger anther size played a crucial role in inducing tolerance and compensated for the
lower number of pollen grains germinating on stigma under high temperature stress. Pollen
dispersal pattern and stickiness also contributed towards pollen reception and count on stigma.
A pollen count of less than 5, recorded 13% spikelet fertility while pollen count of more than 20
showed almost 100% spikelet fertility (Matsui et al. 1997). Although little is known about post
pollen germination processes, yet it has been reported that the processes after pollen germination
were also highly sensitive to heat stress. Liu et al. (2006) reported increased pollen stickiness that
prevented pollen shedding. Relative position of style to anther and time of dehiscence to spikelet
opening were also important. Developmental escape (exposure of anther and stigma to ambient
temperature prior to pollination) was expected as a major contributor towards pollen shedding and
count on stigma under heat stress.
Pollen germination on stigma
Multiple explanations for decline in pollen germination with heat stress have been reported
previously. For instance, altered hormonal balance in the oret (Michael and Beringer 1980),
Ambient temperature High night temperature
Pollen fertilityAnther dehiscenceNo of pollen on stigma
Figure 4. Eect of high night temperature on (a) pollen fertility (b) anther dehiscence and (c) number of pollens on stigma in
rice crop (Fahad et al. 2015b).
disturbance in availability of photosynthates (Afuakwa et al. 1984), lack of oral buds ability to
mobilize sugars and changes in starch biosynthesis enzymes (Keeling et al. 1994) were the main
reasons for reduced pollen germination under heat stress. Pollen germination on stigma is a
physiological factor responsible for yield reduction (Table 3). Poor germination of pollen grains
heavily caused spikelet sterility (Prasad et al. 2006). Tolerant genotype N22 presented the minimum
variation to heat stress and percentage of germinated pollen was the associated trait in this regard
(Lan et al. 2004).
Physiology of rice pollen for heat stress tolerance
Growth hormones
At high temperature stress, anther quantitative analysis displayed a decreased level of some
phytohormones (indole-acetic acid (IAA), gibberellic acid (GA
)), free proline and soluble proteins.
Unexpectedly, an increase was observed in abscisic acid (ABA) under heat stress (Tang et al. 2008;
Wu et al. 2016,2017; Fahad et al. 2016a). Involvement of auxin in oret sterility has been reported
by Sakata et al. (2010) as plants treated with auxin compensated for heat stress by increasing
pollen fertility over control. Auxin was supposed to alter endothecium thickening with changing
levels of heat stress. Various physiological traits such as oxidation activity, RNA content, ethylene
evolution rate, and malondialdehyde content have been reported to be involved in heat tolerance
(Zhao et al. 2018). Higher activity of roots under heat stress was due to stronger antioxidant
defense system, greater RNA content and lesser ethylene synthesis along with lower malondialde-
hyde content during meiosis (Yun-Ying et al. 2009).
Calcium and sugars
Macronutrients such as calcium (Ca
) and sulfur (S) play crucial role in attaining heat stress
tolerance in plants. Calcium is known to regulate antioxidant activity rather than osmotic adjust-
ment under heat stress (Jiang and Huang 2001). Increased level of Ca
modulated the heat
tempted adversities in potato crop. Kolupaev et al. (2005) reported that in heat stressed plants,
calcium improved the lipid peroxidation rate, guaiacol peroxidase, superoxide dismutase and
catalase activity. Mach (2012) reported that calcium signals might play an important role in thermo
tolerance and selection of heat tolerant varieties.
Carbohydrates availability during heat stress represents an important physiological trait asso-
ciated with high temperature stress tolerance. At low concentration sugars act as signaling
molecule while at higher concentration they become reactive oxygen species (ROS) scavenger
(Sugio et al. 2009). Normal pollen development accumulates the highest level of starch content
three days before the start of anthesis stage and, from this point onwards, converts it into soluble
Table 3. Eect of high temperature stress on rice production.
Stress level Stage of crop growth Yield reduction References
36°C whole growth period A yield reduction of 22% Ohe et al. 2007
32°C Whole growth period A decrease of 86% in grain weight Mohammed and
Tarpley 2009
32°C Reproductive A decrease of 5% in nal grain yield Cheng et al. 2009
Above 33°C Heading A yield reduction of 28% Yun-Ying et al.
3139°C Early reproductive
A yield reduction of 3040% Wu et al. 2016
32°C and 35°C Booting 36% decrease in high night temperature stress and 25%
decrease in high day temperature stress
Fahad et al.
sugars (Paupière et al. 2014). On contrary, in heat stressed plants, starch accumulation did not
reach to its peak and results in decreased level of soluble sugars in established pollen grains. Mild
heat stress led to a signicant alteration in sugar transport, metabolism and distribution over
various anther tissues (Paupière et al. 2014). Higher activity of acid invertase also played critical role
in manufacturing hexoses under high temperature stress (Li et al. 2012). In conclusion, decreased
carbohydrates supply would have probably lowered energy ow to the pollen and subsequently
produced infertile pollens.
Calcium pretreatment increased total sugars and reducing sugars in wheat seedlings under heat
stress. While under non stress conditions, calcium has non-signicant eect on acid invertase
activity. Thus, at high temperature stress, the elevated calcium might be having a role in sucrose
and starch metabolism (Bhatia and Asthir 2014). Further study is needed to explore the role of
calcium in sugar transport in developing pollens of rice crop.
Involvement of reactive oxygen species and antioxidant enzymes
High temperature exposure signicantly increases ROS production in rice anther. This high
temperature induced overproduction of ROS is responsible for a decline in pollen viability and
oret fertility (Zhao et al. 2018). The increased extent of ROS concentration under high
temperature stress is extremely variable, depending upon heat intensity, duration of plant
exposure, plant growth stage and studied cultivar. At the time of pollen tube development,
pollen and tapetum cells accumulate twenty times higher mitochondria that shows faster
respiration (Selinski and Scheibe 2014). Under high temperature stress, this great amount of
accumulated mitochondria dramatically increased ROS production and suppressed the ROS
scavenging machinery (Kumar et al. 2014). Zhang et al. (2014) reported that a number of ROS
genes in rice are heat responsive. Cell keeps extensive ROS scavenging machinery to detoxify
ROS negative eects. This machinery consists of enzymes such as catalase, ascorbate peroxidase
and superoxide dismutase as well as antioxidants like ascorbic acid, avonoids etc., (Mittler et al.
2004). The tight regulation of ROS under high temperature is very important for viable pollen
production. Exogenous application of antioxidants may increase pollen viability under heat
stress by ROS scavenging (Fahad et al. 2016a).
Genetic basis for heat stress tolerance
Clustering of microarray data has identied various genes responsible for heat stress tolerance in
rice crop. Among these studied genes, thirteen were localized in the anther. Expression analysis has
revealed that these genes were specically expressed in immature anthers especially in tapetum at
microspore stage and a minimum of 24 hours of heat stress was required to down regulate these
tissue specic genes (Endo et al. 2009). The tapetum specic genes (Osc6, OsRAFTIN and TDR) were
unaected to long exposure of heat stress. This indicates the inhibition of selective genes by the
heat stress. Gene ontological studies revealed an impaired activity of genes important for pollen
development under heat stress. Minor reduction in functionality was noted after 3 and 4 days of
applied stress. It further conrmed that not all genes were involved in down-regulation/degrada-
tion of tapetum except for some specic ones (Endo et al. 2009).
Cellular membranes are primarily composed of proteins and lipids. Disorganization in lipid and
protein content in matured pollen were studied to applied levels of heat stress that inuenced
membrane structure, integrity and pollen viability (Das et al. 2014). Two of the genes, expressed in
tapetal cells, were suppressed by heat stress indicating the involvement in lipid metabolism. The
plant specic c cytochrome P450 (CYP703) was an expression of gene AK106843 while AK106946
encoded a GDSL lipase. The CYP703 catalyzed the conversion of saturated fatty acid and has major
part in sporopollenin synthesis (Morant et al. 2007). Mayeld et al. (2001) reported GDSL involve-
ment in pollen coat formation in A. thaliana. The exact biological activity in rice anther of these two
genes is still unclear. The possible mechanism may include heat induced alteration in the pollen
wall lipid composition.
Conclusions and future prospective
High temperature stress is the major upcoming challenge for successful rice production. The
adversity of the eect depends upon crop growth stage, duration and intensity of the applied
stress. Pollen is more heat sensitive over stigma. Therefore, understanding and management of
anthesis stage is vital for rice heat tolerance. The responses of rice plant to heat stress have been
studied intensively in recent years; however, a complete understanding of thermo tolerance
mechanisms remains elusive. The role of osmoprotectants and phytohormones also remains
unclear under mild and extreme heat stress conditions. A little progress has been made in
developing heat tolerant genotypes through traditional breeding and genetic engineering
approaches. The above discussed rice pollen characteristics can be exploited as screening tools
for varietal development but selection must focus for those germplasm sources which can tolerate
temperature above 38°C.
Further study is needed to nd out the physiological basis of osmotic adjustment, assimilate
partitioning and protein denaturation for heat stress tolerance. Exact role of sugars and calcium in
pollen fertility needs to be studied in detail. Involvement of roots in heat stress management and
root-shoot signaling mechanisms also needed exploration in future research. Knowledge at mole-
cular level about heat tolerance mechanisms will pave the ways for engineering plants that can
tolerate heat stress and might be the source for crop production under heat stress conditions. For
better understanding of plant heat stress tolerance, application of genomics, proteomics and
trascriptomics is imperative.
We thank the funding provided by the Major International Joint Research Project of NSFC (No. 31361140368).
Disclosure statement
No potential conict of interest was reported by the authors.
This work was supported by the Major International Joint Research Project of NSFC [31361140368];
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Rice (Oryza sativa L.) is one of the most significant staple foods worldwide. Carbohydrates, proteins, vitamins, and minerals are just a few of the many nutrients found in domesticated rice. Ensuring high and constant rice production is vital to facilitating human food supplies, as over three billion people around the globe rely on rice as their primary source of dietary intake. However, the world’s rice production and grain quality have drastically declined in recent years due to the challenges posed by global climate change and abiotic stress-related aspects, especially drought, heat, cold, salt, submergence, and heavy metal toxicity. Rice’s reduced photosynthetic efficiency results from insufficient stomatal conductance and natural damage to thylakoids and chloroplasts brought on by abiotic stressor-induced chlorosis and leaf wilting. Abiotic stress in rice farming can also cause complications with redox homeostasis, membrane peroxidation, lower seed germination, a drop in fresh and dry weight, necrosis, and tissue damage. Frequent stomatal movements, leaf rolling, generation of reactive oxygen radicals (RORs), antioxidant enzymes, induction of stress-responsive enzymes and protein-repair mechanisms, production of osmolytes, development of ion transporters, detoxifications, etc., are recorded as potent morphological, biochemical and physiological responses of rice plants under adverse abiotic stress. To develop cultivars that can withstand multiple abiotic challenges, it is necessary to understand the molecular and physiological mechanisms that contribute to the deterioration of rice quality under multiple abiotic stresses. The present review highlights the strategic defense mechanisms rice plants adopt to combat abiotic stressors that substantially affect the fundamental morphological, biochemical, and physiological mechanisms.
Climate change is the main reason for the different abiotic and biotic stresses in agriculture, and it adversely affects crop production and yield. Fluctuating climate conditions such as rainfall, drought, and temperature can cause global changes in atmospheric carbon dioxide levels and sea level rise. These alarming global events have attracted the attention of agronomists because of the detrimental impacts of climate change on the agriculture sector and food security under increasing global food demand. Therefore, climate-resilient agriculture is the only possible and most appropriate solution to mitigate the negative impacts of climate change. Therefore, it is imperative to focus on global food production and its security under changing climatic conditions to meet the needs of the fast-growing population. To deal with climatic fluctuations, different global agricultural practices including water, land, crop, and livelihood management strategies are being adopted worldwide to improve climate-resilient agricultural crops. In addition, the modifications in the plant genetic material such as genomics (molecular plant breeding), genetic engineering, and other genome editing approaches are practices to develop climate-resilient transgenic crops to enhance crop productivity and yield. Moreover, conservation agriculture can also be effectively converted into sustainable agriculture through different land management practices and resource utilization. Plants also use various adaptive strategies such as physiological, biochemical, and molecular mechanisms to cope with harsh environmental conditions. However, more research is required to design and develop more climate-resilient management strategies and eco-friendly and resistant agricultural crops under changing climatic conditions.
Although using SDGs in texts is easy, as shown in previous chapters, any contribution to these goals faces unpredictable and unexpected challenges. Lack of experts and implementation hardships such as language barriers and financial barriers are only a few of these challenges. Under these circumstances, deep tech can be a great solution in bringing closer the knowledge gap among stakeholders, removing language barriers, and even lowering the implementation costs.
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At the global and regional scales, green vegetation cover has the ability to affect the climate and land surface fluxes. Climate is an important factor which plays an important role in vegetation cover. This research aimed to study the changes in land cover and relation of different vegetation indices with temperature using multi-temporal satellite data in Sahiwal region, Pakistan. Supervised classification method (maximum likelihood algorithm) was used to achieve the land cover classification based on ground-truthing. Our research denoted that during the last 24 years, almost 24,773.1 ha (2.43%) of vegetation area has been converted to roads and built-up areas. The built-up area increased in coverage from 43,255.54 ha (4.24%) from 1998 to 2022 in study area. Average land surface temperature (LST) values were calculated at 16.6 °C and 35.15 °C for winter and summer season, respectively. In Sahiwal region, the average RVI, DVI, TVI, EVI, NDVI and SAVI values were noted as 0.19, 0.21, 0.26, 0.28, 0.30 and 0.25 respectively. For vegetation indices and LST relation, statistical linear regression analysis indicated that kappa coefficient values were R 2 = 0.79 for RVI, 0.75 for DVI, 0.78 for DVI, 0.81 for EVI, 0.83 for NDVI and 0.80 for SAVI related with LST. The remote sensing (RS) technology can be used to monitor changes in vegetation indices values over time, providing valuable information for sustainable land use management. Even though the findings on land cover provide significant references for reasoned and optimal use of land resources through policy implications.
The alkaline calcareous nature, high pH, salinity, heavy metals pollution, and low organic matter content of soils in many parts of the world have diminished the soil fertility and made essential nutrients unavailable to crops. To cope with the poor availability of soil nutrients, improve soil health, and feed the fast-growing global population, the farming community is using millions of tons of expensive chemical fertilizers in their fields to maintain an adequate level of nutrients for crop sustainability as well as to ensure food security. In this scenario, the exploitation of biofertilizers has become of paramount importance in the agricultural sector for their potential role in food safety and sustainable crop production. Bearing in mind the key importance of biofertilizers, this book examines the role of biofertilizers in sustainable management of soil and plant health under different conditions of the changing climate. Finally, it provides a platform for scientists and academicians all over the world to promote, share, and discuss various new issues, developments, and limitations in biofertilizers, crops, and beneficial microbes.
Both social protection (SP) and climate change (CC) adaptation seek to safeguard the most vulnerable persons as well as to promote resilience. The Sustainable Development Goals (SDGs) are combined to identify that action in an area affects outcomes in others and that development must balance economic, social and environmental sustainability. Developing countries are determined to prioritize progress for those who are furthermost behind. The SDGs are planned to finish the hunger, poverty and discrimination against girls and women. SP needs to pay extra attention to the long-term threats posed by CC. Similarly, social protection can provide such programmatic and policy options which have not been fully taken into consideration by adaptation. Adaptive SP includes a long-term perception that studies the varying nature of CC stresses and shocks. Other characteristics of adaptive SP include giving importance to protecting and transforming productive livelihoods, as well as adapting to CC situations instead of only reinforcing managing mechanisms. However, the adaptive SP structure analysis does allow the identification of various prospects for future work that relates these connected fields together. These include developing tools and resources, e.g., climate risk assessment for use with SP programmes, engagement in international and national conferences and events, funding of adaptive SP and integration of SP with adaptation funding and vice versa.KeywordsSocial protectionClimate changeSustainable Development Goals
Climate change is now seen as an established challenge, and its consequences are being felt across the world. Principally, it affects the people and food chain systems, but its influence would also affect every aspect of the economy. Agriculture is important for food security as a source for food and, more importantly, the primary source of livelihood incorporating about 40% of the world’s total workforce. Overpopulation, especially in developing countries, amplifies the demand for agricultural products. The weather in different parts of the world is becoming increasingly divergent from the norms of the local climate. The temperatures are increasing on a regular basis, and precipitation is becoming more unpredictable. The weather-based extremes, including heavy downpours, flooding, extremes of both heat and cold, storms, and a prolonging of drought are occurring more frequently. In the climate change context, the agricultural sector has been the most badly affected. Climate change effects have been reduced through the application of state-of-the-art forecasting systems and modernized farming technologies. However, those are inaccessible to the underdeveloped or poor states of developed countries. These states have agrarian-based fragile economies and are incapable of bearing any loss due to climatic extremes. In addition, the continuous availability of water throughout a cropping season became a substantial challenge which has enhanced the application of dryland farming on a wider scale. In this scenario, the responsibilities of the stakeholders, from planners and breeders up to the growers, are more pronounced. International partners, such as the Food and Agriculture Organization(FAO) are working on various schemes to cope with these issues.KeywordsSeasonal rainfallAgricultureTemperaturesFood securitySeasonal rainfall
Climate-smart agriculture is the emerging and sustainable option to mitigate the adverse effects of climate change (on crop adaptability) before it significantly influences global crop production. Crop development through modern breeding techniques, effective agronomic practices and exploitation of natural variability in neglected and popular crops are all good ways to meet future food demands. However, the rapidly changing environment requires technological interventions to improve crop climate resilience. Technological advances such as genome-edited transgenic plants, high-throughput phenotyping technologies combined with next-generation sequencing techniques, big data analytics and advances in modern breeding techniques help modern agriculture progress towards robotics or digital conversion to face future environmental adversaries. For example, speed breeding in combination with genomic and phenomic methods can lead to quicker identification of genetic factors and, as a result, speed up crop development programmes.Furthermore, combining next-generation interdisciplinary breeding platforms might open up new opportunities for developing climate-ready crops. Several integrated modern breeding platforms were created in the last few decades and are now employed worldwide. Africa and Asia have adopted these most frequently used crop improvement platforms with advanced techniques like multitrait association studies using genome-wide association studies (GWASs). These have permitted precise exploration of the genetic make-up of agricultural attributes in most crops. This chapter explores various ways to increase crop output by developing climate-resilient superior genotypes. Further, we discussed how combinatorial advanced breeding technologies and biotechnological approaches would be used for managing climate change’s consequences to promote crops with climate resilience.KeywordsBiotechnologyGenomic and phenomic methodsSpeed breedingGenome-wide association studiesNext-generation OMICS techniques
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Rice production is challenged by the asymmetric increases in day and night temperatures. Efforts are required to improve our understanding of the impact of climate change on rice production. To this end, 2-year experiment was conducted to evaluate the response of mid-season rice growth in the central and southern regions of China to elevated temperatures. Four replicates of four widely planted indica rice cultivars (Huanghuazhan: HHZ; Shanyou63: SY63; Yangliangyou6: YLY6; Liangyoupeijiu: LYPJ) were subjected to four elevated-temperature treatments (control: ambient temperature; NW: night-time warming; DW: daytime warming; AW: all-day warming) generated by an open-top hot-blast system under field conditions. This apparatus causes an ∼2 • C increase in the rice canopy temperature. Of all the elevated-temperature treatments, AW was the most devastating treatment for all rice cultivars, negatively affecting nearly all of investigated parameters, including grain yield and its components, dry matter accumulation, biomass, and harvest index (HI). The AW treatment decreased the grain yield by 11-35% and 43-78% in 2015 and 2016, respectively. No significant reduction in the grain yield was observed in the DW and NW treatments in 2015. However, the grain yield was decreased in DW and NW treatments by 20-52% and 18-55%, respectively, in 2016. Furthermore, the temperature-driven degradation of pollen viability, the number of pollen grains adhering to the stigma and pollen germination on the stigma caused spikelet sterility and thereby decreased the grain yield. The YLY6 and SY63 cultivars performed better than the HHZ and LYPJ cultivars with respect to grain yield and its components in all elevated-temperature treatments in both years. However, 42.97 and 61.01% reductions still occurred for the SY63 and YLY6 cultivars, respectively, in the AW treatment in 2016. The above results suggested that the elevated temperature may cause a noteworthy reduction in the productions of these widely planted genotypes in central and southern regions of China. To ensure the security of rice production in this region in an expected global warming environment, currently planted varieties will need to be replaced by heat-resistant varieties in the future.
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Calcium (Ca ²⁺ ) may be involved in plant tolerance to heat stress by regulating antioxidant metabolism or/and water relations. This study was designed to examine whether external Ca ²⁺ treatment would improve heat tolerance in two C 3 , cool‐season grass species, tall fescue ( Festuca arundinacea L.) and Kentucky bluegrass ( Poa pratensis L.), and to determine the physiological mechanisms of Ca ²⁺ effects on grass tolerance to heat stress. Grasses were treated with CaCl 2 (10 mM) or H 2 O by foliar application and then exposed to heat stress (35/30 °C) in growth chambers. Some of the Ca ²⁺ ‐untreated plants were maintained at 20/15 °C as the temperature control. Heat stress reduced grass quality, relative water content (RWC), and chlorophyll (Chl) content of leaves in both species, but Ca ²⁺ treatment increased all three factors under heat stress. The Ca ²⁺ concentration in cell saps increased with heat stress and with external Ca ²⁺ treatment in both species. Osmotic potential increased with heat stress, but external Ca ²⁺ treatment had no effect. Osmotic adjustment increased during short‐term heat stress, but then decreased with a prolonged period of stress; it was not influenced by Ca ²⁺ treatment. The activity of superoxide dismutase (SOD) in both species increased transiently at 12 d of heat stress and then remained at a level similar to that of the control. External Ca ²⁺ treatment had no effect on SOD activity. The activities of catalase (CAT), ascorbate peroxidase (AP), and glutathione reductase (GR) of both species decreased during heat stress. Plants treated with Ca ²⁺ under heat stress had higher CAT, GR and AP activities than untreated plants. Lesser amounts of malondialdehyde (MDA) accumulated in Ca ²⁺ ‐treated plants than in untreated plants during extended periods of heat stress. The results suggested that exogenous Ca ²⁺ treatment enhanced heat tolerance in both tall fescue and Kentucky bluegrass. This enhancement was related to the maintenance of antioxidant activities and a decrease in membrane lipid peroxidation, but not to the regulation of osmotic potential and osmotic adjustment.
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Cytokinins (CTKs) regulate panicle size and mediate heat tolerance in crops. To investigate the effect of high temperature on panicle CTK expression and the role of such expression in panicle differentiation in rice, four rice varieties (Nagina22, N22; Huanghuazhan, HHZ; Liangyoupeijiu, LYPJ; and Shanyou63, SY63) were grown under normal conditions and subjected to three high temperature treatments and one control treatment in temperature-controlled greenhouses for 15 days during the early reproductive stage. The high temperature treatments significantly reduced panicle CTK abundance in heat-susceptible LYPJ, HHZ, and N22 varieties, which showed fewer spikelets per panicle in comparison with control plants. Exogenous 6-benzylaminopurine application mitigated the effect of heat injury on the number of spikelets per panicle. The high temperature treatments significantly decreased the xylem sap flow rate and CTK transportation rate, but enhanced cytokinin oxidase/dehydrogenase (CKX) activity in heat-susceptible varieties. In comparison with the heat-susceptible varieties, heat-tolerant variety SY63 showed less reduction in panicle CTK abundance, an enhanced xylem sap flow rate, an improved CTK transport rate, and stable CKX activity under the high temperature treatments. Enzymes involved in CTK synthesis (isopentenyltransferase, LONELY GUY, and cytochrome P450 monooxygenase) were inhibited by the high temperature treatments. Heat-induced changes in CTK transportation from root to shoot through xylem sap flow and panicle CTK degradation via CKX were closely associated with the effects of heat on panicle CTK abundance and panicle size. Heat-tolerant variety SY63 showed stable panicle size under the high temperature treatments because of enhanced transport of root-derived CTKs and stable panicle CKX activity. Our results provide insight into rice heat tolerance that will facilitate the development of rice varieties with tolerance to high temperature.
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Heat stress causes morphological and physiological changes and reduces crop yield in rice (Oryza sativa). To investigate changes in phytohormones and their relationships with yield and other attributes under heat stress, four rice varieties (Nagina22, Huanghuazhan, Liangyoupeijiu, and Shanyou 63) were grown in pots and subjected to three high temperature treatments plus control in temperature-controlled greenhouses for 15 d during the early reproductive phase. Yield reductions in Nagina22, Huanghuazhan, and Liangyoupeijiu were attributed to reductions in spikelet fertility, spikelets per panicle, and grain weight. The adverse effects of high temperature were alleviated by application of exogenous 6-benzylaminopurine (6-BA) in the heat-susceptible Liangyoupeijiu. High temperature stress reduced active cytokinins, gibberellin A1 (GA1), and indole-3-acetic acid (IAA), but increased abscisic acid (ABA) and bound cytokinins in young panicles. Correlation analyses and application of exogenous 6-BA revealed that high temperature-induced cytokinin changes may regulate yield components by modulating the differentiation and degradation of branches and spikelets, panicle exsertion, pollen vigor, anther dehiscence, and grain size. Heat-tolerant Shanyou 63 displayed minor changes in phytohormones, panicle formation, and grain yield under high temperature compared with those of the other three varieties. These results suggest that phytohormone changes are closely associated with yield formation, and a small reduction or stability in phytohormone content is required to avoid large yield losses under heat stress.
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A 2-year experiment was conducted to ascertain the effects of exogenously applied plant growth regulators (PGR) on rice growth and yield attributes under high day (HDT) and high night temperature (HNT). Two rice cultivars (IR-64 and Huanghuazhan) were subjected to temperature treatments in controlled growth chambers and four different combinations of ascorbic acid (Vc), alpha-tocopherol (Ve), brassinosteroids (Br), methyl jasmonates (MeJA), and triazoles (Tr) were applied. High temperature severely affected rice morphology, and also reduced leaf area, above-, and below-ground biomass, photosynthesis, and water use efficiency, while increased the leaf water potential of both rice cultivars. Grain yield and its related attributes except number of panicles, were reduced under high temperature. The HDT posed more negative effects on rice physiological attributes, while HNT was more detrimental for grain formation and yield. The Huanghuazhan performed better than IR-64 under high temperature stress with better growth and higher grain yield. Exogenous application of PGRs was helpful in alleviating the adverse effects of high temperature. Among PGR combinations, the Vc+Ve+MejA+Br was the most effective treatment for both cultivars under high temperature stress. The highest grain production by Vc+Ve+MejA+Br treated plants was due to enhanced photosynthesis, spikelet fertility and grain filling, which compensated the adversities of high temperature stress. Taken together, these results will be of worth for further understanding the adaptation and survival mechanisms of rice to high temperature and will assist in developing heat-resistant rice germplasm in future.
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Increasing temperature due to global warming has emerged one of the gravest threats to rice production. This study examined the influence of high temperature and exogenously applied plant growth regulators on pollen fertility, anther dehiscence, pollen germination and metabolites synthesis in pollens of two rice cultivars (IR-64 and Huanghuazhan (HHZ)). Plants were subjected to high day temperature (HDT), high night temperature (HNT) and control temperature (CT) in controlled growth chambers. Four different combinations of ascorbic acid (Vc), alpha-tocopherol (Ve), brassinosteroids (Br), methyl jasmonates (MeJA) and triazoles (Tr) were used along with a nothing applied control. Our results depicted that high temperature severely reduced the pollen fertility, anther dehiscence, pollen retention, germination and metabolites synthesis in pollens of both rice cultivars. Nonetheless, exogenous application of various plant growth regulators assuaged the adverse effects of high temperature and Vc + Ve + MeJA + Br was found the best combination than the other treatments for every studied characteristic. The HNT posed more negative effects than the HDT. Variations were also apparent between cultivars and HHZ performed better than IR-64 under high-temperature stress, with higher pollen fertility, better anther dehiscence, and greater pollen retention and germination rates. The greater tolerance of HHZ to high temperature was related with the higher synthesis of metabolites in this cultivar.
High temperature (HT) at meiosis stage is one of most important environment constraint affecting spikelet fertility and rice yield. In this paper, the effects of HT exposure at meiosis stage on the ROS (reactive oxygen species) accumulation, various superoxide dismutase (SOD, EC1.15.1.11) isozymes in developing anther, and its relationship with HT-induced decline in pollen viability and floret fertility were investigated by using four rice cultivars differing in heat tolerance under well-controlled climatic condition. Results showed that HT exposure significantly increased ROS level and malondialdehyde (MDA) content in rice anther, and this occurrence was strongly responsible for the HT-induced decline in pollen viability and harmful effect of HT adversity on floret fertility. However, the increased extent of ROS concentration in rice anther under HT exposure was greatly variable, depending on both the intensity and duration of HT exposure and different rice cultivars used. The SOD and CAT activities of HT-sensitive cultivars decreased more profoundly than those of HT-tolerant cultivars under the same HT regimes. Among various types of SOD enzymes, Cu/Zn-SODa expressed highly in rice anther and responded sensitively to HT exposure, while Cu/Zn-SODb expressed weakly in rice anther and preferentially in rice leaves. HT exposure suppressed the expression of Cu/Zn-SODa in developing anther, which was closely associated with the down-regulated transcripts of cCu/Zn-SOD1 gene. Hence, Cu/Zn-SODa may play a central role in the regulation of total SOD activity and ROS detoxification in rice anther as affected by HT exposure at meiosis stage.
This study evaluates the potential for adaptability and tolerance of wheat genotypes (G) to an arid environment. We examined the influence of drought stress (DS) (100%, 75% and 50% field capacity), planting times (PT) (16-November, 01-December, 16-December and 01-January) and G (Yocoro Rojo, FKAU-10, Faisalabad-08 and Galaxy L-7096) on phenological development, growth indices, grain yield and water use efficiency of drip-irrigated wheat. Development measured at five phenological growth stages (GS) (tillering, jointing, booting, heading and maturity) and growth indices 30, 45, 60 and 75 days after sowing (DAS) were also correlated with final grain yield. Tillering occurred earlier in DS plots, to a maximum of 31 days. Days to complete 50% heading and physiological crop maturity were the most susceptible GS that denoted 31-72% reduction in number of days to complete these GS at severe DS. Wheat G grown with severe DS had the shortest grain filling duration. Genotype Fsd-08 presented greater adaptability to studied arid climate and recorded 31%, 35% and 38% longer grain filling period as compared with rest of the G at 100-50% field capacity respectively. December sowing mitigated the drought and delayed planting effects by producing superior growth and yield (2162 kg ha-1) at severe DS. Genotypes Fsd-08 and L-7096 attained the minimum plant height (36 cm) and the shortest growth cycle (76 days) for January planting with 50% field capacity. At severe DS leaf area index, dry matter accumulation, crop growth rate and net assimilation rate were decreased by 67%, 57%, 34% and 38% as compared to non-stressed plots. Genotypes Fsd-08 and F-10 were the superior ones and secured 14-17% higher grain yield than genotype YR for severely stressed plots. The correlation between crop growth indices and grain yield depicted the highest value (0.58-0.71) at 60-75 DAS. So the major contribution of these growth indices towards grain yield was at the start of reproductive phase. It’s clear that booting and grain filling are the most sensitive GS that are severely affected by both drought and delay in planting.
Present study examined the influence of high-temperature stress and different biochar and phosphorus (P) fertilization treatments on the growth, grain yield and quality of two rice cultivars (IR-64 and Huanghuazhan). Plants were subjected to high day temperature-HDT (35˚C ± 2), high night temperature-HNT (32 ˚C ± 2), and control temperature-CT (28 ˚C±2) in controlled growth chambers. The different fertilization treatments were control, biochar alone, phosphorous (P) alone and biochar + P. High-temperature stress severely reduced the photosynthesis, stomatal conductance, water use efficiency, and increased the leaf water potential of both rice cultivars. Grain yield and its related attributes except for number of panicles, were reduced under high temperature. The HDT posed more negative effects on rice physiological attributes, while HNT was more destructive for grain yield. High temperature stress also hampered the grain appearance and milling quality traits in both rice cultivars. The Huanghuazhan performed better than IR-64 under high-temperature stress with better growth and higher grain yield. Different soil fertilization treatments were helpful in ameliorating the detrimental effects of high temperature. Addition of biochar alone improved some growth and yield parameters but such positive effects were lower when compared with the combined application of biochar and P. The biochar+P application recorded 7% higher grain yield (plant-1) of rice compared with control averaged across different temperature treatments and cultivars. The highest grain production and better grain quality in biochar+P treatments might be due to enhanced photosynthesis, water use efficiency, and grain size, which compensated the adversities of high temperature stress.
A japonica rice (cv.Koshihikari) was used to test the effects on blooming and ripening of UV-B radiation treatment combined with high temperature treatments (day/night, 35 / 30°C). Strong UV-B radiation (60.4 kJ/m 2·day) slightly increased sterility. High temperatures and weak UV-B radiation (18.1 kJ/m2·day) applied together from two weeks before heading and from the heading day increased sterility and those applied from two weeks after heading decreased sterility. High temperature combined with strong UV-B radiation applied from two weeks before heading increased sterility and decreased the size of unhulled grain and anther length. The same treatment given from the heading stage greatly increased sterility and decreased anther length and pollen production, and that given two weeks after heading decreased unhulled grain weight. It also decreaed photosynthetic rate in Flag leaves. A high temperature applied together with strong UV-B radiation had a synergistic effect causing poor growth; it increased the harmful effects of a high temperature and sttong UV-B given separately, on the sterility and pollen formation.