The effect of heat stress on tomato pollen characteristics is associated with changes in carbohydrate concentration in the developing anthers

Continuous exposure of tomato 'Trust' to high temperatures (day/night temperatures of 32/26 degrees 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 degrees 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 degrees 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.     

Effects of high-temperature stress on microsporogenesis in heat-sensitive and heat-tolerant genotypes of Phaseolus vulgaris

High ambient temperature (32/27 °C, day/night, 12 h photoperiod) applied prior to anthesis to Phaseolus vulgaris plants results in abnormal pollen and anther development during microsporogenesis. Scanning and transmission electron microscopy were used to examine anther and pollen morphology and pollen wall architecture after heat stress was applied to two genotypes that differ with respect to yield potential under high‐temperature field conditions: one, a heat‐sensitive, Mesoamerican genotype, A55, the second, a heat‐tolerant, Andean genotype, G122. High‐temperature treatment of both genotypes was applied 1–13 d before anthesis. Under heat stress, the heat‐tolerant genotype showed anther and pollen characteristics that were generally similar to the low temperature controls. In contrast, after 9 d of heat treatment before anthesis, the anthers of the heat‐sensitive genotype were indehiscent and contained abnormal pollen. Pollen wall architecture was also affected in the 12 and 13 d treatments. In addition to the morphological changes, the heat‐sensitive genotype also experienced reduced pollen viability and reduced yield in high‐temperature experiments conducted in both the greenhouse and field.     

Ultrastructural study of rice tapetum under low-temperature stress

The development of male reproductive organs in rice is very sensitive to various environmental stresses. For example, exposing plants to low temperatures during the heading stage leads to a reduction in grain yield. Here, we grew rice under normal conditions and also at three different temperatures -- 16, 18, and 20°C. Treatment at a low temperature significantly decreased pollen viability and grain production. Cytological observations of the anther showed that the tapetum was the most sensitive to low-temperature stress, resulting in male sterility due to functional loss of the tissue. Detailed observations by transmission electron microscopy suggested that this abnormality was restricted primarily to the ER structures. The endoplasmic reticulum, a highly vulnerable sub-cellular organelle, showed two typical morphological aberrations, one in its pattern of arrangement, the other in the formation of ER bodies. Of our three experimental chilling temperatures, the most severe abnormalities were observed in tapetal cells exposed to 16°C.     

Physiological factors limit fruit set of tomato (Lycopersicon esculentum Mill.) under chronic, mild heat stress

The effects of chronic, mild heat stress on fruit set, fruit production, release of pollen grains, photosynthesis, night respiration and anther dehiscence were examined in tomatoes (Lycopersicon esculentum Mill.) differing in high‐temperature sensitivity. Plants were grown under three temperature regimes: (1) 28/22 or 26/22 °C (optimal temperature); (2) 32/26 °C (high temperature); and (3) 32/26 °C day/night temperatures relieved at 28/22 °C for 10 d before anthesis, then returned to 32/26 °C (relieving treatment). FLA 7156 was the only cultivar with fruit set at 32/26 °C. All five cultivars, however, had fruit set under the relieving treatment (RT). The longer the relief, the higher the percentage of fruit set. Longer periods of relief also increased the number of pollen grains released, and linear regression analysis showed a significant relationship between the number of pollen grains released and the percentage of fruit set. Germination of pollen grains was also lowered in high‐temperature‐grown plants. The number of pollen grains produced, photosynthesis and night respiration did not limit fruit set under chronic, mild heat stress, however. This suggested that cultivar differences in pollen release and germination under heat stress are the most important factors determining their ability to set fruit.     

Temperature stress interferes with male reproductive system development in clementine (Citrus clementina Hort. ex. Tan.)

Male gametophyte development is a critical phase of the plant life cycle due to its high sensitivity to environmental stresses. The rise in the average global temperature, often accompanied by extreme fluctuations, has an important impact on biological processes. Among those, male gametophytes are particularly sensitive to temperature stress during flower bud development and anthesis. Male gametophyte development was extensively studied in several plant species, but little information is available about the effects of temperature stress on male gametophyte development in the genus Citrus. We evaluated the effects of cold and hot temperatures during microsporogenesis and microgametogenesis on one of the most economically valuable citrus species, the “Comune” clementine (Citrus clementina Hort. ex. Tan.). The effect of constant temperature on the androecium was evaluated by a time course histological analysis performed on the anthers and by monitoring in vitro pollen germination. The results revealed how suboptimal hot and cold temperatures induce drastic alterations on the morphology of the tapetal cells, microspores and mature pollen grains. Shifting from the optimal temperature affected the timing of starch depletion in the anther walls, such as epidermis, endothecium and middle layer, influencing the pollen germination rate and pollen tube growth. To the best of our knowledge this is the first study attempting to assess how temperature stress affects male reproductive development in citrus. A better understanding of the mechanisms underlining male sterility will provide novel insights to elucidate the physiology of this agronomical important quality trait.     

Chemical agents that inhibit pollen development: effects of the phenyl-cinnoline carboxylates SC-1058 and SC-1271 on the ultrastructure of developing wheat anthers (Triticum aestivum L. var Yecora rojò)

Summary Phenylcinnoline carboxylate compounds SC-1058 and SC-1271 cause complete male sterility in wheat when applied at suitable dosages at the pre-meiotic stage of anther development. Anthers from treated and untreated plants were compared using light and electron microscopy from the pre-meiotic stage through the formation of nearly mature pollen. Overall anther development is gradually slowed in treated plants and pollen development is generally arrested in the late prevacuolate or early vacuolate microspore stage, although the first pollen mitosis does sometimes occur. The sporopollenin-containing exine walls are thinner, and show abnormally developed foot and tectum layers with sparse connecting baculi. Microspore cytoplasm degenerates and the cells eventually collapse. At the early, prevacuolate, free microspore stage treated tapetal cells hypertrophy, expanding into the locule. They contain abnormally large vacuoles that appear to form from the fusion of secretory vesicles, and some vacuoles contain electrondense deposits. The sporopollenin-containing orbicular wall and Ubisch bodies are retarded in their development and are structurally deformed. Acetolysis of whole anthers and of thick sections shows that the sporopollen-in-containing structures of treated materials are greatly reduced in thickness and are less rigid than in the control. We conclude that application of these compounds causes interference with the secretory function of tapetal cells which supplies sporopollenin cell-wall polymers to the exine of the microspores and to the tapetal orbicular wall and associated Ubisch bodies. Interference with the tapetal secretion of other nutrients required for microspore development is strongly suggested.     

Heat Shock Stress Causes Stage-specific Male Sterility in Arabidopsis thaliana

Arabidopsis during flower development, floral organs such as sepals, petals, stamens, and carpels developed normally. However, the development of pollen inside the anther was disrupted in a stage-specific manner, with floral stage 9 primordia failing to produce any pollen grains. Morphological analyses suggested that heat shock causes a failure of separation of pollen mother cells followed by microspore differentiation and/or inhibition of male meiotic processes. Heat shock also caused sterility in floral stage 12 flowers but the sterility was due to the failure of pollen release from the pollen sacs. Received 12 December 2000/ Accepted in revised form 4 April 2001     

水稻花期高温胁迫研究进展与展望

水稻花期高温引起的不育危害,具有发生可预测性低、作用局限于特定部位、致害程度严重等特点.本文就水稻花期高温不育问题,在发生时间、致害温度、品种反应差异、作用机制、鉴定方法以及抗性性状遗传等方面作了综述.并结合在日本的相关研究及对中国江汉平原杂交中稻花期高温危害发生的气候条件、品种差异等的初步分析,提出了该领域研究目前存在的关键问题和主要解决途径.     

Morphological development of anthers induced by the dimorphic smut fungus<Emphasis Type="Italic"> Microbotryum violaceum</Emphasis> in female flowers of the dioecious plant<Emphasis Type="Italic"> Silene latifolia</Emphasis>

When inoculated with the dimorphic smut fungus Microbotryum violaceum (Pers.) G. Deml and Oberwinkler, the female flower of the dioecious plant Silene latifolia (Miller) E.H.L. Krause develops anther-like structures filled with spores instead of pollen grains. Using natural scanning electron microscopy, Nomarski interference microscopy, and fluorescence microscopy, we investigated the morphological modifications of the host plant resulting from this parasitism and the localization of smut hyphae in the flower bud. Flowers of infected plants lasted significantly longer than those of healthy plants, probably because the infection strengthened floral organs, such as the flower base and the anther filaments. Smut hyphae were observed throughout all organs of the young flower buds of infected plants, including sepals, petals, stamens, and pistil primordia. In healthy female flowers, anthers initiated sporogenous cell formation, but lacked parietal cell layers. By contrast, the parietal cell layers of infected female flowers differentiated into tapetal tissue, middle cell layers, and endothecial layers, as in the anthers of healthy male flowers. Smut spore formation in the infected anther was initiated in intercellular regions between the sporogenous cells, resulting in degeneration of premature sporogenous cells, tapetal tissue, and middle cell layers. The development of the endothecial layers and epidermis in the infected anther were morphologically normal.Abbreviations DAPI 4,6-diamidino-2-phenylidole - i infected - PMC pollen mother cell     

Anther response to high-temperature stress during development and pollen thermotolerance heterosis as revealed by pollen tube growth and in vitro pollen vigor analysis in upland cotton

Main conclusion

Pollen tube growth in styles was strongly inhibited by temperature above 35 °C, and the yield of cotton decreased because of the adverse effect of high temperatures during square development. High-temperature stress during flowering influences the square development of upland cotton (Gossypium hirsutum L.) and cotton yield. Although it is well known that square development is sensitive to high temperature, high-temperature sensitive stages of square development and the effects of high temperature on pollen tube growth in the styles are unknown. The effect of high temperature on anther development corresponding to pollen vigor is unknown during anther development. The objectives of this study were to identify the stages of square development that are sensitive to high temperatures (37/30 and 40/34 °C), to determine whether the abnormal development of squares influenced by high temperature is responsible for the variation in the in vitro germination percent of pollen grains at anthesis, to identify the effect of high temperature on pollen germination in the styles, and to determine pollen thermotolerance heterosis. Our results show that the stages from the sporogenous cell to tetrad stage (square length <6.0 mm) were the most sensitive to high temperature, and the corresponding pollen viability at anthesis was consistent with the changes in the square development stage. Pollen tube growth in the styles was strongly inhibited by temperature above 35 °C, and the yield of cotton decreased because of the effect of high temperature during square development. The thermotolerance of hybrid F₁ pollen showed heterosis, and pollen viability could be used as a criterion for screening for high-temperature tolerance cultivars. These results can be used in breeding to develop new cotton cultivars that can withstand high-temperature conditions, particularly in a future warmer climate.

     

An overview of heat stress in tomato (Solanum lycopersicum L.)

Heat stress has been defined as the rise of temperature for a period of time higher than a threshold level, thereby permanently affecting the plant growth and development. Day or night temperature is considered as the major limiting factor for plant growth. Earlier studies reported that night temperature is an important factor in the heat reaction of the plants. Tomato cultivars capable of setting viable fruits under night temperatures above 21 °C are considered as heat-tolerant cultivars. The development of breeding objectives is generally summarized in four points: (a) cultivars with higher yield, (b) disease resistant varieties in the 1970s, (c) long shelf-life in 1980s, and (d) nutritive and taste quality during 1990s. Some unique varieties like the dwarf “Micro-Tom”, and the first transgenic tomato (FlavrSavr) were developed through breeding; they were distributed late in the 1980s.High temperature significantly affects seed, pollen viability and root expansion. Researchers have employed different parameters to evaluate the tolerance to heat stress, including membrane thermo stability, floral characteristics (Stigma exertion and antheridia cone splitting), flower number, and fruit yield per plant. Reports on pollen viability and fruit set/plant under heat stress by comparing the pollen growth and tube development in heat-treated and non-heat-stressed conditions are available in literature. The electrical conductivity (EC) have been used to evaluate the tolerance of some tomato cultivars in vitro under heat stress conditions as an indication of cell damage due to electrolyte leakage; they classified the cultivars into three groups: (a) heat tolerant, (b) moderately heat tolerant, and (c) heat sensitive.It is important to determine the range in genetic diversity for heat tolerance in tomatoes. Heat stress experiments under field conditions offer breeders information to identify the potentially heat tolerant germplasm.     

Anther wall layers control pollen sugar nutrition inLilium

Summary Anthers ofLilium were for the first time investigated at the ultrastructural level in order to appreciate the possible ways of sugar transport in the microsporangium. Our results have shown that the cells of the outer anther wall layers and the cell of the connective were interconnected by plasmodesmata, thus allowing assimilates to travel through the symplasmic pathway from the vascular bundle to the most internal middle layer (ML 1). ML 1 was devoid of cell communication throughout pollen development. Tapetal cells were also lacking plasmodesmata on their external face towards ML 1, but adjacent tapetal cells developed lateral junctions: the tapetum could represent a syncytium. Sugars destinated to pollen in the loculus have then to cross the ML 1 and the tapetal layers by the apoplasmic pathway; it is suggested that these two envelopes could be involved in the control of sugar transport from the outer anther wall layers to the locular fluid. Before microspore mitosis, the tapetum degenerated but ML 1 remained structurally unchanged. During pollen development, the guard cells of stomata were lacking cell communication, and preserved their starch content, which could be the sign of photosynthesis within the anther wall. In order to check whether these structural disconnections in anther tissues corresponded to physiological barriers, isolated pollen and stamens were cultivated during the anther maturation phase, on a medium containing increasing concentrations of sucrose (0 M, 1/6 M, 1/2 M, 1 M). After 7 days of culture, isolated pollen was engorged with starch grains and was unable to germinate, whereas in cultivated stamens, pollen did not contain any starch grain: sporophytic tissues, however, accumulated abnormal amylaceous reserves. These results strongly suggest that the anther wall layers, in particular ML 1, starve pollen with sugars during its maturation. They are acting as a physiological buffer storing nutriment surplus in starch grains.Abbreviations ML 1 middle layer 1 - ML 2 middle layer 2 - PAS periodic acid Schiff - PATAg periodic acid thiosemicarbazide silver nitrate     

Comparing heat stress effects on male-fertile and male-sterile tomatoes

To separate the effects of heat stress on male and female reproductive tissues, male-sterile (MSs) and male-fertile tomatoes (MFs) were placed in growth chambers at 12 h day/12 h night temperatures of 28/22, 30/24 or 32/26 °C from flower appearance to seed maturation (daily mean temperatures of 25, 27 or 29 °C). Pollen from MFs was applied individually to MS flowers. As MFs were self-pollinated, heat stress was experienced by both male and female tissues. At growth temperatures of 29 °C fruit number, fruit weight per plant, and seed number per fruit were only 10%, 6·4% and 16·4%, respectively, compared with those at 25 °C. Heat stress also adversely affected fruitset in MSs, especially when experienced by donor pollen. No fruit at all developed on MSs receiving pollen produced at 29 °C, even when ovule development, pollen germination and subsequent embryo development all took place at 25 °C. Effects on fruitset in MSs were reduced if donor pollen had not experienced heat stress. MSs grown at 29 °C but receiving pollen developing at 25 °C produced 73% as much fruit (both on number and weight basis), had 40% as high fruitset and produced 87% of the seed per fruit as MSs grown at 25 °C. This use of male-sterile and male-fertile lines of tomato provides new evidence that impairment of pollen and anther development by elevated temperature will be an important contributing factor to decreased fruit set in tomato, and possibly other crops, with global warming.     

Small heat shock protein LimHSP16.45 protects pollen mother cells and tapetal cells against extreme temperatures during late zygotene to pachytene stages of meiotic prophase I in David Lily

Plant meiotic prophase I is a complicated process involving the late zygotene and pachytene stages, both crucial for completing synapsis and recombination. Using David Lily (Lilium davidii var. Willmottiae) as our research material, we performed suppression subtractive hybridization to construct EST library of anthers at various stages of development by the pollen mother cells. From this library, we identified small heat shock protein LimHSP16.45 was highly expressed during the late zygotene to pachytene stages. Our results also showed that LimHSP16.45 was almost specifically expressed in the anther compared with the root, stem, or leaf, and in situ expression of LimHSP16.45 mRNAs showed strong signals in the pollen mother cells and tapetal cells. LimHSP16.45 could be induced by heat and cold in lily anthers, and its ectopic expression enhanced the viability of E. coli cells under both high and low temperatures. In vitro, it acted as molecular chaperone and could help luciferase refolding after heat shock stress. All of these data suggest that LimHSP16.45, working as molecular chaperone, possibly protects pollen mother cells and tapetal cells against extreme temperatures during late zygotene to pachytene stages of meiotic prophase I in David Lily.     

Effects of Temperature on Pollen Viability in Mango cv. 'Kensington'

The response of pollen development to low or high temperatureregimes was studied to determine the conditions suitable forthe formation of fertile pollen in the mango cv. 'Kensington'.The phase most sensitive to the degree and duration of temperaturestress was that from meiosis to the pre-vacuolate microspore(about 3 d duration at 25/20 °C) though vacuolated microsporeswere also sensitive to low temperature. Night temperatures below10 °C resulted in pollen grains with a low viability (<50%). A temperature between 15 and 33 °C during the phasefrom meiosis to the pre-vacuolate microspore was optimum forpollen development (70-85% pollen viability). Analysis of field records showed a linear negative correlationbetween percentage of pollen viability and number of days whichhad a mean night temperature lower than 10 °C during theperiod from meiosis to early mature stage (y = 77·7-3·4x,r² = 0·60). The temperature sensitive phase was estimatedto begin 155 degree days D = [(T_max + T_min)/2 - 10] before anthesisand to end 78 degree days before anthesis. This equation maybe useful as a means of predicting pollen viability in the fieldfrom temperature records and thus fruit set, date of maturityand yield. It may also aid in the selection of areas for growingmangoes in marginal climates.Copyright 1994, 1999 Academic Press Mangifera indica L. mango, microsporogenesis, pollen development, viability, sterility, temperature     

Effects of relative humidity and temperature stress on pollen viability of Cistus incanus and Myrtus communis

Cistus incanus and Myrtus communis are two species commonly found in Mediterranean shrublands, flowering respectively in spring and summer. Pollen of single flowers of C. incanus is available for dispersal for 8-10 hours, during which time viability decreases from 91% to 61%. Field measurements of the variation in the percent pollen viability during the anthesis of single flowers of M. communis shows that, immediately after anthesis, pollen viability is very high; by the end of the first day it significantly declines and 36 hours after anthesis almost all grains are unviable. Experiments carried out under controlled environment showed that, in C. incanus, the greatest loss of viability occurs at 100% humidity and high temperatures, while under dry conditions pollen viability remains high throughout a wide temperature range. Similarly, pollen viability of M. communis remains high for several hours at high temperature and dry conditions, while it rapidly decreases at high humidity. In conclusion, the temperature experiments indicate that in C. incanus and M. communis, pollen viability does not appear to be drastically reduced if the relative humidity of the environment is low. Therefore, humidity is a far more important factor determining pollen viability loss in both species.     

The effect of high temperature and high atmospheric CO2 on carbohydrate changes in bell pepper (Capsicum annuum) pollen in relation to its germination

Pollen viability and germination are known to be sensitive to high temperature (HT). However, the mode by which high temperature impairs pollen functioning is not yet clear. In the present study, we investigated the effect of high temperature on changes occurring in carbohydrate of bell pepper (Capsicum annuum L. cv. Mazurka) pollen in order to find possible relations between these changes and pollen germination under heat stress. When pepper plants were maintained under a moderate HT regime (32/26 degrees C, day/night) for 8 days before flowers have reached anthesis, pollen count at anthesis was similar to that found in plants grown under normal temperatures (NT 28/22 degrees C). However, the in vitro germination, carried out at 25 degrees C, of pollen from HT plants was greatly reduced. This effect matched the marked reduction in the number of seeds per fruit in the HT plants. Maintaining the plants at high air CO2 concentration (800 &mgr;mol mol-1 air) in both temperature treatments did not affect the in vitro germination of pollen from NT plants, but restored germination to near the normal level in pollen from HT plants. Under NT conditions, starch, which was negligible in pollen at meiosis (8 days before anthesis, A-8) started to accumulate at A-4 and continued to accumulate until A-2. From that stage until anthesis, starch was rapidly degraded. On the other hand, sucrose concentration rose from stage A-4 until anthesis. Acid invertase (EC 3.2.1.26) activity rose parallel with the increase of sucrose. In pollen from HT plants, sucrose and starch concentrations were significantly higher at A-1 pollen than in that of NT plants. Under high CO2 conditions, the sucrose concentration in the pollen of HT plants was reduced to levels similar to those in NT pollen. In accordance with the higher sucrose concentration in HT pollen, the acid invertase activity in these pollen grains was lower than in NT pollen. The results suggest that the higher concentrations of sucrose and starch in the pollen grains of HT plants may result from reduction in their metabolism under heat stress. Elevated CO2 concentration, presumably by increasing assimilate availability to the pollen grain, may alleviate the inhibition of sucrose and starch metabolism, thereby increasing their utilization for pollen germination under the HT stress. Acid invertase may have a regulatory role in this system.     

大白菜新型细胞质雄性不育系6w-9605A的育性鉴定和花药败育的细胞学观察

采用石蜡切片技术,研究了大白菜(Brassica campestris L.ssp.pekinensis)细胞质雄性不育系6w-9605A及其保持系6w-9605B的花药发育过程的细胞形态学特征,确定不育系花药败育时期及方式,并对不育系6w-9605A进行花器官观察和育性鉴定.结果表明:保持系6w-9605B花药发育正常;不育系6w-9605A花药发育受阻于孢原分化时期,占总败育花药的66.7％,不形成花粉囊和花粉粒,属于无花粉囊型败育;另外33.3％的败育花药可形成花粉囊,小孢子均受阻于单核靠边期或者二胞期,败育特点为绒毡层细胞异常肥大,挤压小孢子,导致小孢子和绒毡层解体;6w-9605A的不育性稳定、彻底,不育株率和不育度均为100％.     

枸杞花药发育过程中脂滴和淀粉粒的分布特征

宁夏枸杞(Lycium barbarurn L．)花药发育过程中,淀粉粒和脂滴两种营养物质的积累和分布具有一定的特点：在造孢细胞时期,药隔薄壁细胞,表皮和药室内壁细胞中开始积累淀粉粒,而造孢细胞、绒毡层细胞和中层细胞中则没有淀粉粒。在四分体时期,绒毡层细胞开始积累脂滴并且数量逐渐增加。到小孢子晚期,绒毡层细胞降解,内含脂滴流入药室中。在小孢子发育过程中既没有淀粉粒也没有脂滴积累,直到二胞花粉的大液泡消失后花粉粒中才开始积累脂滴,然后又开始出现淀粉粒。枸杞成熟花粉中的营养储存物是脂滴和淀粉粒。