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How does timing, duration and severity of heat stress influence pollen-pistil interactions in angiosperms?
Plant Signaling & Behavior
Abstract and Figures
Reproductive development in sexual plants is substantially more sensitive to high temperature stress than vegetative development, resulting in negative implications for food and fiber production under the moderate temperature increases projected to result from global climate change. High temperature exposure either during early pollen development or during the progamic phase of pollen development will negatively impact pollen performance and reproductive output; both phases of pollen development are considered exceptionally sensitive to moderate heat stress. However, moderately elevated temperatures either before or during the progamic phase can limit fertilization by negatively impacting important pollen pistil interactions required for successful pollen tube growth toward the ovules. This minireview identifies the impacts of heat stress on pollen-pistil interactions and sexual reproduction in angiosperms. A special emphasis is placed on the biochemical response of the pistil to moderately high temperature and the resultant influence on in vivo pollen performance and fertilization.
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... Plant reproductive development, particularly male gametophyte (i.e. pollen) development and performance are the most sensitive development stages to heat stress [14,20,24,[35][36][37]. When extreme heat occurs during floral development, maturation and/or dehiscence, it can have compounding adverse consequences, including degradation of the tapetum, failure to release microspores, altered metabolism and transport of nutrients in pollen, reduced pollen viability, poor anther dehiscence and failure to release pollen [24,36,[38][39][40]. ...
... pollen) development and performance are the most sensitive development stages to heat stress [14,20,24,[35][36][37]. When extreme heat occurs during floral development, maturation and/or dehiscence, it can have compounding adverse consequences, including degradation of the tapetum, failure to release microspores, altered metabolism and transport of nutrients in pollen, reduced pollen viability, poor anther dehiscence and failure to release pollen [24,36,[38][39][40]. When heat inhibits nutrient sequestration in developing pollen, concentrations of carbohydrates, proteins, lipids and amino acids can be reduced or altered [24,38,39,41,42]. ...
... Brief heat exposure can cause abiotic stress in white clover [77], resulting in fewer inflorescences [78] or vegetative tissue loss and mortality [79]. While crop plants have received greater attention, many plants enduring high temperatures (>35°C) during floral development, even for a few hours, experience adverse repercussions on pollen quality, performance and subsequent plant functioning [20,24,[35][36][37]. ...
Extreme heat poses a major threat to plants and pollinators, yet the indirect consequences of heat stress are not well understood, particularly for native solitary bees. To determine how brief exposure of extreme heat to flowering plants affects bee behaviour, fecundity, development and survival we conducted a no-choice field cage experiment in which Osmia lignaria were provided blueberry (Vaccinium corymbosum), phacelia (Phacelia tanacetifolia) and white clover (Trifolium repens) that had been previously exposed to either extreme heat (37.5°C) or normal temperatures (25°C) for 4 h during early bloom. Despite a similar number of open flowers and floral visitation frequency between the two treatments, female bees provided with heat-stressed plants laid approximately 70% fewer eggs than females provided with non-stressed plants. Their progeny received similar quantities of pollen provisions between the two treatments, yet larvae consuming pollen from heat-stressed plants had significantly lower survival as larvae and adults. We also observed trends for delayed emergence and reduced adult longevity when larvae consumed heat-stressed pollen. This study is the first to document how short, field-realistic bursts of extreme heat exposure to flowering host plants can indirectly affect bee pollinators and their offspring, with important implications for crop pollination and native bee populations.
... Climate change affects the reproductive phase of plants much more than vegetative phase and must be studied urgently especially for global species. Temperature stress causes: morphological disorders in flower development (Albertos et al. 2019 (Albertos et al. 2019), reduced embryo sac size (Bykova et al. 2012), pollen and pistil abortion (Snider and Oosterhuis 2011;Bykova et al. 2012), disturbed anther dehiscence (Qi et al. 2022), reduced pollen tube growth (Snider and Oosterhuis 2011;Karabıyık 2022), improper effective pollination period (EPP) (Hedhly et al. 2005), abnormal embryo or endosperm development (Cuevas et al. 1994) and lower fruit or seed formation (Carpenedo et al. 2017). Like in most species, fruit set in the Citrus genus also depends on flower formation and the development of an ovarium and for the species that should form seed in order to set fruits, the (EPP), is a very important phenomenon (Karabıyık 2022). ...
... Climate change affects the reproductive phase of plants much more than vegetative phase and must be studied urgently especially for global species. Temperature stress causes: morphological disorders in flower development (Albertos et al. 2019 (Albertos et al. 2019), reduced embryo sac size (Bykova et al. 2012), pollen and pistil abortion (Snider and Oosterhuis 2011;Bykova et al. 2012), disturbed anther dehiscence (Qi et al. 2022), reduced pollen tube growth (Snider and Oosterhuis 2011;Karabıyık 2022), improper effective pollination period (EPP) (Hedhly et al. 2005), abnormal embryo or endosperm development (Cuevas et al. 1994) and lower fruit or seed formation (Carpenedo et al. 2017). Like in most species, fruit set in the Citrus genus also depends on flower formation and the development of an ovarium and for the species that should form seed in order to set fruits, the (EPP), is a very important phenomenon (Karabıyık 2022). ...
It is important to know the effects of extreme temperatures on reproductive biology within the scope of climate change. Polyamines play significant roles against stress conditions that are related to abiotic stress responses. For this reason, polyamines take an important role in terms of growing, development and stress tolerances by coping with the negative effects of several ecological conditions. In this research, Citrus limon cv. ‘Meyer’ was used. The aim of this study was to determine the effects of different doses and treatment periods of putrescine on pollen germination, in vivo pollen tube growth, ovule longevity, fruit yield and some fruit quality parameters. As a result of the study, it was determined that putrescine treatment increased in vitro pollen germination level, accelerated in vivo pollen tube growth for 2 days and prolonged ovule viability by at least 10 days. At the same time, especially 8 ppm putrescine treatment at the beginning of flower bud formation increased fruit set 70% by increasing fruit number on the tree without any dimensional reduction. Fruit juice acidity was increased as much as 2% with putrescine, which is an important fruit quality parameter for lemons. The germination of the obtained seeds was also increased via putrescine treatments from 52.0% to 71.3%. In conclusion, 8 ppm putrescine treatment at the beginning of flower bud formation resulted in faster pollen tube growth and longer ovule viability, which in turn provide a longer effective pollination period (EPP).
... Fahim et al. [15], revealed that environmental factors (temperature at day & night and soil moisture content) effect the growth and yield of vegetable (tomato). High temperatures and low moisture condition inhibit the growth and production of chili [16], resulting in poor fertilization and fruit set reviewed in [17]. Development of plant is highly linked to temperature [18]. ...
... In T3 was statistically higher than T2, where T1 and T2 showed statistically same result. High temperatures and low moisture condition inhibit the growth and production of chili [16], resulting in poor fertilization and fruit set as a result late fruiting reviewed in (Snider et al. 2011). High temperature inhibits the development of pollen grains and reduces the pollen viability lead to late fruit setting of sweet pepper [45]. ...
... Fahim et al. [15], revealed that environmental factors (temperature at day & night and soil moisture content) effect the growth and yield of vegetable (tomato). High temperatures and low moisture condition inhibit the growth and production of chili [16], resulting in poor fertilization and fruit set reviewed in [17]. Development of plant is highly linked to temperature [18]. ...
... In T3 was statistically higher than T2, where T1 and T2 showed statistically same result. High temperatures and low moisture condition inhibit the growth and production of chili [16], resulting in poor fertilization and fruit set as a result late fruiting reviewed in (Snider et al. 2011). High temperature inhibits the development of pollen grains and reduces the pollen viability lead to late fruit setting of sweet pepper [45]. ...
In urban agriculture, rooftop gardening is a remarkable part which is practiced to overcome the food crisis and climate change; if it is not economically viable on the basis of productivity, then rooftop
garden will not enhance and sustain. So, a pot experiment was conducted during November 2021 to April 2022 on the rooftop of different height of buildings and Agroforestry research field at Shere-Bangla Agricultural University, Dhaka-1207 to study the productivity of chili (BARI Morich 3). The experiment was laid out in a Completely Randomized Design with four replications. The treatments of this experiment were T1= Control (Ground, 0.0 m), T2= Rooftop of three storied building (11.28 m), T3 = Rooftop of six storied building (21.34 m) and T4 = Rooftop of ten storied building (34.75 m).Results indicated that soil moisture content, plant height, stem diameter, number of (leaf, branch and fruit), fresh and dry weight of plant, single fruit (weight, length and diameter), fresh and dry weight of yield per plant were significantly decreased with the increased of building height (T1>T2>T3>T4) and air temperature, soil temperature and light intensity were significantly increased
with the increased of building height (T4> T3> T2> T1). As gradually increased the height of building
rooftop, sequentially decreased the growth, yield and yield contributing characteristics of chili plant.
Although ground performed the best productivity, up to rooftop of three storied building can be
selected as an appropriate height for chili (BARI Morich-3) cultivation to increase the rooftop
gardening.
... Fahim et al. [15], revealed that environmental factors (temperature at day & night and soil moisture content) effect the growth and yield of vegetable (tomato). High temperatures and low moisture condition inhibit the growth and production of chili [16], resulting in poor fertilization and fruit set reviewed in [17]. Development of plant is highly linked to temperature [18]. ...
... In T3 was statistically higher than T2, where T1 and T2 showed statistically same result. High temperatures and low moisture condition inhibit the growth and production of chili [16], resulting in poor fertilization and fruit set as a result late fruiting reviewed in (Snider et al. 2011). High temperature inhibits the development of pollen grains and reduces the pollen viability lead to late fruit setting of sweet pepper [45]. ...
In urban agriculture, rooftop gardening is a remarkable part which is practiced to overcome the food crisis and climate change; if it is not economically viable on the basis of productivity, then rooftop garden will not enhance and sustain. So, a pot experiment was conducted during November 2021 to April 2022 on the rooftop of different height of buildings and Agroforestry research field at Sher-e-Bangla Agricultural University, Dhaka-1207 to study the productivity of chili (BARI Morich 3). The experiment was laid out in a Completely Randomized Design with four replications. The treatments of this experiment were T1= Control (Ground, 0.0 m), T2= Rooftop of three storied building (11.28 m), T3 = Rooftop of six storied building (21.34 m) and T4 = Rooftop of ten storied building (34.75 m). 105 Results indicated that soil moisture content, plant height, stem diameter, number of (leaf, branch and fruit), fresh and dry weight of plant, single fruit (weight, length and diameter), fresh and dry weight of yield per plant were significantly decreased with the increased of building height (T1>T2>T3>T4) and air temperature, soil temperature and light intensity were significantly increased with the increased of building height (T4> T3> T2> T1). As gradually increased the height of building rooftop, sequentially decreased the growth, yield and yield contributing characteristics of chili plant. Although ground performed the best productivity, up to rooftop of three storied building can be selected as an appropriate height for chili (BARI Morich-3) cultivation to increase the rooftop gardening.
... The stigma, serving as the primary interface for the initial interaction between the pistil and pollen grains, plays a pivotal role in pollination, influencing reproductive success and subsequent fruit production [51][52][53]. Moreira et al. found that more pollen deposition on the stigma resulted in higher rates of fruit setting and seed production [54]. Crosspollination has been identified as a contributing factor to increase fruit size [55]. ...
... The stigma, serving as the primary interface for the initial interaction between the pistil and pollen grains, plays a pivotal role in pollination, influencing reproductive success and subsequent fruit production [51][52][53]. Moreira et al. found that more pollen deposition on the stigma resulted in higher rates of fruit setting and seed production [54]. Crosspollination has been identified as a contributing factor to increase fruit size [55]. ...
Elucidation of the genetic foundation governing crucial traits in pitaya flowers is imperative for enhancing both the ornamental and economic values. In this study, the dynamic variation in flower genetics, segregation variation patterns, and a mixed inheritance model of the major and multigene flower traits of ‘Dahong’ and ‘Honghuaqinglong’ pitayas and their progenies were explored. The results showed that the main traits of flowers exhibited varying degrees of variation among the reciprocal F1 hybrids, with the data exhibiting the characteristics of quantitative traits. The betalain content, petal number, and stigma number exhibited values below the median values of the parents, suggesting a genetic inclination towards lower values. Perianth width, calyx tube width, petal number, and stigma number had the same genetic effects and significant correlation. Stigma-related traits had a clear maternal inheritance tendency. The heritability of flower length, stigma relative to anther distance, and petal betalain content was governed by two pairs of additive-dominant major genes. Perianth width, calyx tube width, petal number, and stigma number all conformed to the model of two pairs of equal-additive-dominant major genes. This study provides valuable information for parental selection, cross-breeding, and the enhancement of pitaya varieties to meet market preferences and environmental conditions.
... Environmental conditions can have a significant impact on the pollination and fertilization processes. Optimal temperature is essential for different stages of sexual reproduction in flowering plants, such as pollen formation, pollen transfer, the readiness of stigmas for pollen, pollen germination, the growth of pollen tubes, double fertilization, and seed development (Hedhly et al., 2003(Hedhly et al., , 2005Snider and Oosterhuis, 2011;Zulkarnain et al., 2019;Ali-Dinar et al., 2021;Alla et al., 2022). Any form of stress during these stages can result in sterility and, ultimately, reduce crop yields. ...
Introduction: In hot arid regions, the productivity of certain date palm cultivars faces a significant challenge wherein non-fertilized flowers can give rise to parthenocarpic singular or triplet fruit. Aims: The aims of this study, we aimed to investigate the impact of delayed pollination on date palm yield and fruit quality, while also examining the influence of temperature on these processes. Methods: We conducted this research using 10 15-year-old 'Assiane' palm trees, all situated within the Figuig Oasis environment. Pollination was performed on the same day of spathe opening, as well as up to 16 days after the initial opening. Additionally, we utilized 30 palm trees to analyze the effect of daily average temperatures. Results and Discussion: Our findings reveal that the optimal period for achieving maximum yield and fruit quality falls between the sixth and eighth day following the cracking of the female spathe. Furthermore, we observed that relatively lower temperatures, ranging from 5 to 20°C, promote the formation of parthenocarpic fruits while inhibiting the development of normal fruits. Moreover, the insights gained from investigating these issues could have broader implications for date palm cultivation in arid regions and offer valuable lessons for the preservation of oasis ecosystems worldwide.
Soybean is the primary oilseed crop in the United States, with significant industrial value. Understanding the molecular mechanisms of heat stress tolerance in soybean plants is critical for developing stress-resistant cultivars. Current knowledge about the role of fatty acid desaturases (FADs) in modulating membrane fluidity under abiotic stress prompted this investigation into the impact of mutations in the FAD genes on seed germination from heat-stressed plants. In soybean plants, exposure to heat stress during anthesis is known to significantly reduce seed germination. In silico expression analysis indicated high expression levels of the soybean FAD2 and FAD3 genes in the leaves. Therefore, a detailed expression analysis of these genes was conducted using qRT-PCR from leaf tissue. Generally, downregulation of these genes was observed in the mutants; however, two genes, FAD3A and FAD2-3, showed a more than 2-fold increase in expression in six out of ten mutants under heat stress. This upregulation was particularly pronounced (7-fold) in the mutant S17CR-170. Correlation analysis revealed a positive correlation (up to 0.48) between the expression level of FAD3A, FAD3B, FAD3C, and FAD2-3 and the decline in germination from heat-stressed plants. This suggests these FAD genes may act as negative regulators of germination under heat stress conditions.
Soybean is the primary oilseed crop in the United States, with significant industrial value. Understanding the molecular mechanisms of heat stress tolerance in soybean is critical for developing stress-resistant cultivars. Current knowledge about the role of fatty acid desaturases (FADs) in modulating membrane fluidity under abiotic stress prompted this investigation into the impact of mutations in the FAD genes on seed germination from heat-stressed plants. In soybean, exposure to heat stress during anthesis is known to significantly reduce seed germination. In silico expression analysis indicated high levels of expression of the soybean FAD2 and FAD3 genes in leaves. Therefore, a detailed expression analysis of these genes was conducted using qRT-PCR from leaf tissue. Generally, downregulation of these genes was observed in the mutants; however, two genes, FAD3A and FAD2-3, showed a more than 2-fold increase in expression in six out of ten mutants under heat stress. This upregulation was particularly pronounced (7-fold) in mutant S17CR-170. Correlation analysis revealed a positive correlation (0.5) between the expression level of FAD3A, FAD3B, FAD3C, and FAD2-3 and the decline in germination from heat-stressed plants. This suggests these FAD genes may act as negative regulators of germination under heat stress conditions.
Soybean [Glycine max (L.) Merr.] reproduction is sensitive to temperatures > 35°C. Two studies were conducted to determine temperature effects on soybean pollen germination (PG) and to detect genotypic differences. Pollen collected from 44 genotypes (Maturity Groups III to VI) grown outdoors was subjected to in vitro temperatures from 15 to 50°C at 5°C intervals. Genotypes differed significantly for in vitro PG percentage (mean of 81%) and tube length (mean of 437 μm). Mean cardinal temperatures (Tmin, Topt, and Tmax) were 13.2, 30.2, and 47.2°C for PG and 12.1, 36.1, and 47.0°C for pollen tube growth. Genotypes differed for leaf cell membrane thermostability (CMTS), but CMTS did not correlate with pollen parameters. Cumulative temperature response index, CTRI (unitless), of each genotype calculated as the sum of eight individual stress responses (ISRs) derived from maximum PG, maximum pollen tube length (PTL), and the maximum (Tmax), minimum (Tmin), and optimum (Topt) temperatures for PG and for PTLs was used to group genotypes for temperature tolerance. Heat-tolerant genotype (DG 5630RR) was less sensitive to high temperature (38/30°C) compared with heat-intermediate (PI 471938) and heat-sensitive (Stalwart III) genotypes that had deformed pollen, with reduced apertures and collumelae heads. Hence, pollen can be used as a screening tool for heat tolerance. Most sensitive to temperature was D88-5320 with a CTRI of 6.8, while AG 4403RR was most tolerant with a CTRI of 7.5. Elevated [CO 2] did not modify reproductive parameters or CTRL The study also revealed that heat tolerance of vegetative tissue had little or no relationship with the heat tolerance of reproductive tissue. Maturity groups lacked a specific trend for tolerance to high temperature. The identified high temperature-tolerant genotypes and temperature-dependent pollen response functions might be useful in soybean breeding and modeling programs, respectively.
High night temperatures during floral development induce male sterility in cowpea (Vigna unguiculata [L.] Walp.). The objectives of this study were to determine: the possible causes of the male sterility; the stage of floral development when damage due to heat stress occurs; and whether specific tissues are damaged during the period of sensitivity to heat. Plants were grown under controlled temperatures in both greenhouses and growth chambers in separate experiments. Floral development was normal under a night temperature of 20 C, whereas flowers developed under high night temperature (30 C) set no pods due to low pollen viability and anther indehiscence. Anthers developed under 33/30 C day/night temperatures did not exhibit endothecial formation, whereas anthers developed under 33/20 C day/night temperatures exhibited normal development of the endothecial layer. Reciprocal transfers of plants between chambers with high or optimum night temperature demonstrated that the stage of floral development most sensitive to heat stress occurs 9 to 7 d before anthesis. Anthers developed under either optimal or high night temperatures were compared cytologically. Development was similar through meiosis, but after tetrad release, which occurred 8 d before anthesis, the tapetal layer degenerated prematurely under high night temperature. Premature degeneration of the tapetal layer and lack of endothecial development may be responsible for the low pollen viability, low anther dehiscence, and low pod set under high night temperatures.
Continuous exposure of tomato ‘Trust’ to high temperatures (day/night temperatures of 32/26 °C) markedly reduced the number of pollen grains per flower and decreased viability. The effect of heat stress on pollen viability was associated with alterations in carbohydrate metabolism in various parts of the anther during its development. Under control, favourable temperature conditions (28/22 °C), starch accumulated in the pollen grains, where it reached a maximum value 3 d before anthesis; it then diminished towards anthesis. During anther development, the concentration of total soluble sugars gradually increased in the anther walls and in the pollen grains (but not in the locular fluid), reaching a maximum at anthesis. Continuous exposure of the plants to high temperatures (32/26 °C) prevented the transient increase in starch concentration and led to decreases in the concentrations of soluble sugars in the anther walls and the pollen grains. In the locular fluid, however, a higher soluble sugar concentration was detected under the high‐temperature regime throughout anther development. These results suggest that a major effect of heat stress on pollen development is a decrease in starch concentration 3 d before anthesis, which results in a decreased sugar concentration in the mature pollen grains. These events possibly contribute to the decreased pollen viability in tomato.
Wheat plants (cv. Gabo) otherwise grown at 20°C were subjected to a temperature of 30°C for 3 days at the onset of meiosis in the anthers. Control plants were maintained at 20°C throughout development. Serial sections through the heat-stressed ovaries just prior to anthesis showed that a third contained abnormal embryo sacs. Abnormalities ranged from the complete absence of an embryo sac accompanied by reduced nucellus development, to small embryo sacs that contained the full complement of cells. No abnormalities were observed in control ovaries.
Following pollination with fertile pollen, heat-stressed stigmas had similar numbers of germinated pollen grains to non-stressed controls but there were fewer tubes reaching the ovary. In 7% of the stressed pistils, no pollen tube reached the ovary. Callose was deposited in some of the inhibited pollen grains and tubes that showed abnormal growth.
It is concluded that heat stress during meiosis in wheat can reduce yield by causing abnormal ovary development, which results in reduced pollen tube growth and seed set.
All possible crosses among 5 strains of Gossypium hirsutum were made, and the pollen tubes were grown in vivo for 4 h before being fixed, stained and measured. Temperatures ranging from 18.5 to 40.0 °C were tested for pollen germination and pollen tube growth. The optimal temperature for pollen tube growth was 30.0 °C. Relative humidity levels of 0 to 100% were used as a pre-pollination treatment of the pollen. Significant differences among the mean pollen tube length of the strains occurred due to pollenXstyle interactions. The strains also differed in the number of styles which did not support pollen tube growth. These differences were also due to pollenXstyle interactions. Pollen and style strains could be ranked according to their relative contribution to pollen tube length.
Protein synthesis as well as pollen tube development of pollen of Lilium longiflorum and Nicotiana tabacum, incubated in vitro, are affected by a heat shock applied after germination for 30 min. Pollen tube elongation ceases and a protrusion is formed at the tip. The protein pattern in germinating pollen of lily is slightly changed by heat shock; cordycepin inhibited heat shock-induced de novo synthesis of two proteins, indicating that heat shock-induced regulation occurs at the level of transcription. In tobacco, however, the change in the pattern of protein synthesis is more pronounced, and the production of more heat shock proteins (HSPs) could be established. Some of those HSPs in tobacco are already present before heat shock: their synthesis at the control temperature of 27 °C can be inhibited by cordycepin, indicating that transcriptionally controlled synthesis of HSP-mRNAs occurs during normal pollen tube growth. Furthermore, some of the heat shock induced changes in the overall pattern of protein synthesis in tobacco seem to be similar to those in lily. The alterations in protein synthesis due to heat shock gradually disappear during the subsequent period of 1.5 h following heat shock. This period is characterized both by the recovery of the synthesis of the normal proteins and the restart of pollen tube growth. The recovery of the overall pattern of protein synthesis can be retarted by cordycepin as is the restart of the pollen tube growth. In lily and tobacco, a pre-heat shock of 3 min immediately after imbibition has a similar effect on the protein pattern as cordycepin: no synthesis of the HSPs when the actual heat shock of 30 min is applied.
The pollen-pistil interaction has been examined in kiwifruit (Actinidia deliciosa). In this species a large number of seeds are produced in each fruit and a great many pollen grains germinate and grow to reach the ovules. This growth is assisted by an abundant secretion that is present all along the pistilar tract. At anthesis, the stigma is covered by a secretion where the pollen grains germinate and grow. The stylar transmitting tissue is initially rich in starch reserves, but the starch gradually disappears and, concomitantly, an abundant secretion that stains for carbohydrates appears in all of the intercellular spaces. Pollen tube growth relies on this secretion since it is depleted after pollen tube passage, while in unpollinated flowers it remains unaltered throughout the flower life-span. In the ovary a similar situation occurs. The placental surface, where the pollen tubes grow before reaching the ovules, is covered by a number of obturators. At anthesis, these obturators are rich in starch reserves and have an abundant secretion on their outer surface. As time passes, starch disappears while the secretion increases. It is in this secretion that the pollen tubes grow on their way toward the ovules. These observations are discussed in terms of the support given by the pistil to pollen tube growth to achieve the highly successful reproductive performance of this species.
Discontinuite de la croissance du tube pollinique en fonction des structures traversees le long du pistil. Caractere heterotrophe de la croissance du tube. Processus secretoires lies a la maturation du pistil posterieurement a l'anthese. Role regulateur du pistil. Necessite d'une synchronisation entre le developpement du gametophyte mâle et la maturation du pistil
Methods for measuring pollen viability were compared to determine their relative value in evaluating cotton ( Gossypium hirsutum L.) pollen. Pollen was treated at constant temperature of 30, 33, 35, 37, 40, and 43°C for 15 hours prior to anthesis. Treated and untreated pollen were evaluated using several common techniques. Pollen killed at the highest temperature (43°C) stained readily with a cytoplasmic stain indicating that stains of this type may determine pollen maturity, but not viability. Pollen treated at 33 to 40°C responded positively to vital staining and germinated both on artificial media and on the stigma while pollen treated at 43°C did not. However, pollen fertility (as measured by pollen tubes penetrating the lower style and ovules) was severely reduced at 33°C and absent at 35°C. The best available criterion for pollen fertility appears to be tube penetration into the lower style or ovules. Staining and pollen germination methods are not accurate indicators of pollen fertility in cotton.