Heat-tolerant Cultivars Research Articles

Small heat shock protein responses in leaf tissues of wheat cultivars with different heat susceptibility

The effect of heat stress on soluble proteins extracted from leaf tissues of bread (Triticum aestivum cv. Gonen-98, tolerant; cv. Cumhuriyet-75, susceptible; genome ABD) and durum (Triticum durum cv. Ege-88, tolerant; cv. Ankara-98, susceptible; genome AB) wheat cultivars differing in sensitivity to high temperature was examined by two-dimensional gel electrophoresis. At acclimation (37°C) and acclimation→high temperature (37°C→50°C) treatments compared to control (25°C), evaluation of gels revealed 31 proteins to be differentially expressed in first leaves as a result of heat stress in heat-susceptible and heat-tolerant cultivars of bread and durum wheats. All of the increased or decreased proteins in amount, newly synthesized and/or disappeared were in low-molecular-weight (LMW, 16.1–24.0 kDa) and generally acidic character (pI 4.8–6.9). The responses of the four cultivars were compared: Twenty-two of 31 proteins were detected as newly synthesized LMW heat shock proteins (LMW HSPs = small HSPs). The number of these sHSPs was different in cultivars which have the same genome. In addition, the number of the sHSPs in heat-tolerant cultivars was higher than in heat-susceptible cultivars. Some of the sHSPs were specific to cultivar. Most of the sHSPs synthesized at 37°C were also detected at 37°C→50°C treatment. It is suggested that sHSPs have special importance in two points: Firstly, sHSPs in cultivars showed abundance and diversity. Secondly, these proteins may play an important role in the acquiring of thermal tolerance.

Phenotyping Parents of Mapping Populations of Rice for Heat Tolerance during Anthesis

Seed set of rice (Oryza sativa L.) is highly sensitive to short episodes of high temperature at anthesis events that are likely to be more frequent in future climates. Breeding for tolerance is therefore an essential component of adaptation to climate variability and change. Experiments were conducted in 2003 and 2004 at optimum (30°C daytime) and high (35 and 38°C) air temperature using parents of some prominent mapping populations (i) to determine whether there were differences in the daily flowering pattern and hence a potential heat avoidance mechanism, and (ii) to identify rice genotypes having true heat tolerance during anthesis, that is, high seed set in spikelets exposed to high temperature. Rice cultivar CG14 (O. glaberrima) reached peak anthesis earlier in the morning (1.5 h after dawn) under both control (30°C) and high (38°C) temperature conditions than O. sativa genotypes (≥3 h after dawn). Exposure to high temperature (centered on the time of peak anthesis) for 6 h reduced spikelet fertility more than exposure for 2 h, and fertility was lower at 38°C than at 35°C. Genotypic ranking for spikelet fertility at 35 and 38°C was highly correlated in both 2003 and 2004. Fertility was also highly correlated across years, suggesting a consistent and reproducible response of spikelet fertility to temperature. The check cultivar N22 was the most heat tolerant genotype (64–86% fertility at 38°C) and cultivars Azucena and Moroberekan the most susceptible (<8%).

Lisianthus 'Double Joy' -- Five Colors of Double-Flowering and Heat-Tolerant Cultivars Released by the University of Florida's Lisianthus Breeding Program

ENH-1067, a 5-page fact sheet by Brent K. Harbaugh and Zhanao Deng, reports the release of these cultivars appropriate for flowering potted plants of intermediate height. Published by the UF Department of Environmental Horticulture, February 2007.

Germinação e vigor de sementes de cenoura sob condições de altas temperaturas

Em decorrência do desenvolvimento de cultivares tolerantes ao calor e com resistência às principais doenças de folhagem, o cultivo de cenoura vem expandindo-se também para outras regiões, como Norte e Nordeste. Altas temperaturas por ocasião da semeadura podem reduzir a germinação de sementes de cenoura e comprometer o estabelecimento da cultura. Avaliou-se o efeito de altas temperaturas na germinação e no vigor de sementes de cenoura de diversas cultivares comercializadas no Brasil bem como em progênies de meio-irmãos de uma polulação de cenoura 'Brasília'. Sementes da cv. Brasília foram colocadas para germinar em temperaturas constantes de 20; 24; 28; 32 e 36ºC por um período de 14 dias. Sementes provenientes de umbelas primárias e secundárias de 120 progênies de meio-irmãos de uma população de cenoura 'Brasília' foram também avaliadas quanto à viabilidade (germinação a 20ºC) e temperaturas elevadas (35ºC), vigor (primeira contagem de germinação) e massa de 100 sementes. Finalmente, sementes de 28 lotes comerciais de cenoura foram avaliadas quanto à germinação a 20 e 35ºC. Houve decréscimo na germinação à medida que a temperatura aumentou, sendo que a 36ºC apenas 27% das sementes germinaram. O teste de germinação a 20ºC mostrou que existem variações entre os lotes comerciais, e que, em condições de alta temperatura (35ºC), a germinação foi bastante reduzida para a maioria deles. As progênies de meio-irmãos apresentaram-se com alta germinação e vigor a 20ºC. Entretanto, à temperatura de 35ºC, somente algumas progênies apresentaram germinação superior a 60%. Em adição, as sementes provenientes das umbelas primárias germinaram melhor a 35ºC que aquelas provenientes das umbelas secundárias. Para a obtenção de melhor estande no campo, principalmente em condições adversas de altas temperaturas, a seleção e desenvolvimento de cultivares mais tolerantes, bem como a utilização de sementes provenientes de umbelas primárias seria altamente recomendado.

Heat stress induced ethylene production in developing wheat grains induces kernel abortion and increased maturation in a susceptible cultivar

In this work we present evidence that the heat stress induced kernel abortion and suppression of grain maturation in a representative heat susceptible hard red winter wheat ( Triticum aestivum L.) cultivar is regulated by heat stress induced ethylene production. Exposure to heat stress (38 °C) during early kernel development (10 DAP) resulted in a 6-fold increase in ethylene production in developing kernels of the heat susceptible hard red winter wheat cultivar ‘Karl 92’. A similar 7-fold increase in ethylene production in embryos and 12-fold increase in ethylene production in the flag leaf of heat stressed plants of ‘Karl 92’ was also found. In contrast, no change in ethylene production was observed in the heat tolerant hard white spring wheat cultivar ‘Halberd’. In an effort to link the heat stress induced ethylene production to the observed increase in kernel abortion and reduced kernel weight in the heat susceptible ‘Karl 92’, plants were treated with the ethylene receptor inhibitor 1-methylcyclopropane (1-MCP) prior to exposure to heat stress. Inhibiting ethylene perception in the heat susceptible ‘Karl 92’ in this manner blocked heat stress induced kernel abortion and reduction in kernel weight and demonstrated a clear link between ethylene in regulating susceptibility to heat stress or perception of high temperatures as a timing signal for transitioning to developmental arrest and senescence in certain wheat genotype classes.

Influence Of Temperature Shift After Flowering on Dry Matter Partitioning In Two Cultivars of Snap Bean (Phaseolus Vulgaris)That Differ In Heat Tolerance

The Partitioning of Dry Matter (Ratio of Dry Weight of Individual Parts To That of Total Dry Matter) Was Analyzed In Snap Bean Cultivars, Haibushi, A Heat-Tolerant Cultivar, and Kentucky Wonder, A Heat-Sensitive Cultivar, At Four Temperatures After Flowering on The Subtropical Island of Ishigaki, Japan. The Temperature Regimes Included 27/23ºC (Day/Night) As Normal, 24/20ºC As Low, 30/26 As High, and 33/29ºC As Extremely High. Most Growth Traits Increased After Flowering Time (35 Das), Displaying A Plateau At 68-75 Das. The Total Dry Matter Was Similar Under All Temperature Conditions, But Differed With The Cultivar. Haibushi Had A Higher Value of Total Dry Matter Than Kentucky Wonder, Which Was Mainly Due To Higher Pod Dry Weight Although Stem and Root Dry Weights Were Lower In Haibushi. A Sharp Decline of Dry Matter Partitioning To Pods Was Observed At 33/29 ºC. In The Temperature Range of 24/20 To 30/26ºC, Haibushi Showed Higher Partitioning To Pods Than Kentucky Wonder, Independent of Temperature. on The Other Contrary, Kentucky Wonder Showed Higher Partitioning To Pods At 27/23ºC Than At 24/20ºC. These Results Showed That The Partitioning of Dry Matter, Which Varied With The Cultivar and Temperature, Played An Important Role In Achieving Higher Harvest Index In The Heat-Tolerant Than In The Heat-Sensitive Cultivars.

Field screening for heat tolerant common bean cultivars (Phaseolus vulgaris L.) by measuring of chlorophyll fluorescence induction parameters

Abstract The temperature induced changes in chlorophyll fluorescence induction parameters (F0, Fm, Fv and their ratios) measured by a PEA analyzer were used to screen for heat-tolerance 12 cultivars and lines of common bean (Phaseolus vulgaris L.) available in the germplasm collections of Maritsa Vegetable Crops Research Institute, Plovdiv, and Institute of Plant Genetic Resources, Sadovo, Bulgaria. The experiments were carried out in a selection field of Maritsa Institute. The measurements were made on six different dates during the bean reproductive period (in June–July) when the temperatures were approximately 26 °C in the morning to and 42 °C at noon. Two lines, known earlier as heat-tolerant were used as controls. We found that most of studied cultivars and lines were heat-sensitive because upon day-course increase of temperatures from 26 °C to 42 °C they revealed statistically significant increase in initial fluorescence (F0), simultaneous decreases in maximum fluorescence (Fm), and in Fv/F0 ratio. Only two cultivars: Ranit and Nerine RS like the heat-tolerant lines preserved F0, Fm and Fv values and Fv/F0 ratio at 42 °C similar to those values at 26 °C. We have considered these two cultivars as heat-tolerant. They have good productivity and been quality and will be used as parental lines in bean breeding program.

Pollen grains of heat tolerant tomato cultivars retain higher carbohydrate concentration under heat stress conditions

Abstract Exposure to high temperatures (heat stress) causes reduced yield in tomatoes (Lycopersicon esculentum), mainly by affecting male gametophyte development. Two experiments were conducted where several tomato cultivars were grown under heat stress, in growth chambers (day/night temperatures of 31/25 °C) or in greenhouses (day/night temperatures of 32/26 °C), or under control (day/night temperatures of 28/22 °C) conditions. In heat-sensitive cultivars, heat stress caused a reduction in the number of pollen grains, impaired their viability and germinability, caused reduced fruit set and markedly reduced the numbers of seeds per fruit. In the heat-tolerant cultivars, however, the number and quality of pollen grains, the number of fruits and the number of seeds per fruit were less affected by high temperatures. In all the heat-sensitive cultivars, the heat-stress conditions caused a marked reduction in starch concentration in the developing pollen grains at 3 days before anthesis, and a parallel decrease in the total soluble sugar concentration in the mature pollen, whereas in the four heat-tolerant cultivars tested, starch accumulation at 3 days before anthesis and soluble sugar concentration at anthesis were not affected by heat stress. These results indicate that the carbohydrate content of developing and mature tomato pollen grains may be an important factor in determining pollen quality, and suggest that heat-tolerant cultivars have a mechanism for maintaining the appropriate carbohydrate content under heat stress.

Prolonged high-temperature exposure differentially reduces growth and flowering of 12 Viola × wittrockiana Gams. cvs

Many cool season garden crops, including Viola × wittrockiana Gams. (pansy), exhibit reduced flowering outdoors during the warm summer months. Twelve pansy cultivars varying in summer garden performance were grown under either 20 ± 1.5 or 30 ± 1 °C (air temperature) to determine growth and flowering responses to prolonged high-temperature exposure and to identify selection criteria to screen pansies for flowering heat tolerance. Increasing temperature from 20 to 30 °C increased leaf number below the first flower on ‘Crystal Bowl Primrose’ and ‘Skyline White’ only. Flower bud number reduction at 30 °C versus 20 °C varied from 20% for ‘Crystal Bowl Purple’ to 77% for ‘Majestic Giants Red and Yellow’. Flower diameter reduction at 30 °C versus 20 °C ranged from 14% for ‘Skyline Beaconsfield’ to 44% for ‘Super Majestic Giants Ocean’. The percentage reduction in total color (flower number × estimated flower area) ranged from 60% for ‘Crystal Bowl Primrose’ to 88% for ‘Majestic Giants Rose Shades’. Based on a weighted base selection index, ‘Super Majestic Giants Canary’ and ‘Delta Yellow’ were identified as the most heat-tolerant cultivars, while ‘Super Majestic Giants Ocean’ and ‘Majestic Giants Rose Shades’ were identified as the most heat-sensitive. In a second experiment, root and shoot dry mass were determined after 10, 20, or 30 d when grown at 20 or 30 °C. Relative growth rate and root:shoot ratio were also calculated. After 30 d, ‘Crystal Bowl Primrose’, ‘Crystal Bowl Sky Blue’ and ‘Skyline White’ relative growth rates were lower at 30 °C versus 20 °C. Root:shoot ratio on day 30 was lower at 30 °C compared to 20 °C for six cultivars, but similar across temperature for five cultivars and higher for ‘Crystal Bowl Primrose’. Flower bud number at first flower was positively correlated with branch number, shoot dry mass at flowering, but not correlated with root dry mass at flowering, and negatively correlated with flower diameter and root:shoot ratio (either at flowering, or after 10, 20 or 30 d at 30 °C), suggesting that these traits may be useful when screening pansies for flowering heat tolerance.

Influence of High Temperature on Morphological Characters, Biomass Allocation, and Yield Components in Snap Bean (Phaseolus vulgaris L.)

High temperature in summer is a major limiting factor for the growth of snap bean in the subtropical islands of Okinawa, Japan. The effect of temperature on biomass production, yield components, and morphological characters were studied in five snap-bean cultivars and strains in the phytotron. Plants were initially grown at 24/20ºC (day/night temperature, 12/12hr) and transferred to 24/20ºC, 27/23ºC (control) or 30/26ºC at the onset of flowering (34 days after sowing). High temperature (30/26ºC) increased single pod weight and the number of flowers and branches, but reduced the number of pods/plant, pod set ratio, and plant weight. ‘Haibushi’, a heat-tolerant cultivar, had higher pod weight/plant, number of pods/plant, pod weight/pod, pod set ratio, number of branches, and rate of biomass allocation to pods, but lower rates of biomass allocation to leaves, stems, and roots than ‘Kentucky Wonder’, a heat-sensitive cultivar, in all temperature regimes. The number of flowers, biomass, and accumulative temperature affected both the yield components (number of pods/plant, single pod weight) antithetically. The yield components were estimated by a stepwise multiple regression analysis. The number of pods/plant was estimated from the number of flowers, leaf weight, pod set ratio per branch, and plant weight with a reasonable precision (R2=0.78). Single pod weight was determined (R2=0.69) from pod set ratio, number of branches, root weight, and accumulative temperature. The results indicated that higher biomass allocation to pods and higher pod set in branches, which were observed in heat-tolerant cultivars at all temperature regimes, were most effective for the estimation of heat tolerance in snap bean.

`Maurine Dawn'—A Heat-tolerant Lisianthus with Pink/White Bicolored Flowers

Seedlings of most commercial cultivars of lisianthus [Eustoma grandifl orum (Raf.) Shinners; Gentianaceae Juss.] form rosettes when grown at or above 25 to 28 °C (Harbaugh, 1995; Harbaugh et al., 1992; Ohkawa et al., 1991; Ohkawa et al., 1994; Pergola, 1992). ‘Maurine Blue’ was released in 1995 as a blue fl owering, heat-tolerant cultivar of lisianthus developed at the University of Florida’s Gulf Coast Research and Education Center, Bradenton, Fla. (Harbaugh and Scott, 1996). In 1998, six other heat-tolerant cultivars with either pink, pinklilac, white, light blue, or lilac fl ower colors but similar vegetative and fl owering characteristics were released in the Maurine cultivar group (Harbaugh and Scott, 1998). In 2003, ‘Maurine Daylight’ and ‘Maurine Twilight’ were released as blue-white bicolored fl owering cultivars in the Maurine cultivar group. ‘Maurine Dawn’ plants also are heat-tolerant with vegetative and fl ower characteristics that are similar to ‘Maurine Blue’, and add a pink-white bicolor fl ower color to the Maurine cultivar-group (Fig. 1).

`Florida Blue Frill' and `Florida Pink Frill'—Semi-dwarf Heat-tolerant Lisianthus with Bicolored Flowers

‘Florida Blue’ was released in 1995 as a blue fl owering, semi-dwarf, and heat-tolerant cultivar of lisianthus [Eustoma grandifl orum (Raf.) Shinners; Gentianaceae Juss.] developed at the University of Florida’s Gulf Coast Research and Education Center, Bradenton, Fla. (Harbaugh et al., 1996). It was the fi rst semi-dwarf cultivar whose seedlings could be grown at 28 to 31 °C without rosetting. Seedlings of most commercial cultivars of lisianthus form rosettes when grown at or above 25 to 28 °C (Harbaugh et al., 1992; Ohkawa et al., 1991). Rosetted plants have a basal cluster of leaves, very short internodes typical of biennials, and do not bolt or fl ower for 3 to 6 months unless exposed to <15 to 18 °C for 3 to 4 weeks (Ohkawa et al., 1994; Pergola, 1992). Thus, commercial production of lisianthus for late spring or summer sales is limited by high temperatures in many areas of the United States and other countries. Also, rosetting of plugs caused by the interaction of high temperatures and short days makes fall plug production to produce fl owering plants for early spring sales diffi cult (Harbaugh, 1995). ‘Florida Pink’ and ‘Florida Light Blue’ released in 1998 (Harbaugh and Scott, 1999) and ‘Florida Silver released in 2001 (Harbaugh and Scott, 2001) were F1 semi-dwarf, heat-tolerant, low rosette-forming lisianthus similar to ‘Florida Blue’. These cultivars provided different fl ower color selections in the Florida cultivar group. ‘Florida Blue Frill’ and ‘Florida Pink Frill’ plants also are semi-dwarf and heat-tolerant. They have vegetative and fl ower characteristics that are similar to ‘Florida Blue’ and provide blueand pink-bicolor fl ower selections to the Florida cultivar-group (Fig. 1).

Species, ecotype and cultivar differences in spikelet fertility and harvest index of rice in response to high temperature stress

Spikelet fertility (seed-set) is an important component of yield that is sensitive to high temperature. The objectives of this research were (a) to quantify the effects of high temperature on spikelet fertility and harvest index of rice; (b) to determine if there were species, ecotype, and/or cultivar differences in response to high temperature; and (c) to understand the reasons for lower and/or differential spikelet fertility and harvest index of rice cultivars at high temperatures. Fourteen rice cultivars of different species ( Oryza sativa and Oryza glaberrima), ecotypes ( indica and japonica) and origin (temperate and tropical) were exposed to ambient and high temperature (ambient + 5 °C) at Gainesville, Florida. High temperature significantly decreased spikelet fertility across all cultivars, but effects varied among cultivars. Based on decreases in spikelet fertility at high temperature, cultivar N-22 was most tolerant, while cultivars L-204, M-202, Labelle, Italica Livorna, WAB-12, CG-14 and CG-17 were highly susceptible and cultivars M-103, S-102, Koshihikari, IR-8 and IR-72 were moderately susceptible to high temperature. There were no clear species or ecotype differences, as some cultivars in each species or within ecotypes of tropical and temperature origin were equally susceptible to high temperature (for example M-202 temperate japonica, Labelle tropical japonica, CG-14 O. glaberrima, and WAB-12 interspecific). Decreased spikelet fertility and cultivar difference at high temperature were due mainly to decreased pollen production and pollen reception (pollen numbers on stigma). Lower spikelet fertility at elevated temperature resulted in fewer filled grains, lower grain weight per panicle, and decreased harvest index. There is a potential for genetic improvement for heat tolerance, thus it is important to screen and identify heat-tolerant cultivars. Spikelet fertility at high temperature can be used as a screening tool for heat tolerance during the reproductive phase.

Diurnal Change in Water Balance of Heat-Tolerant Snap Bean (Phaseolus vulgaris) Cultivar and Its Association with Growth under High Temperature

A snap bean (Phaseolus vulgaris L.) cultivar Haibushi shows high productivity under high-temperature conditions. Together with intensive radiation, high temperature enhances transpiration and causes water deficit in plants even when they are irrigated enough. To characterize daily change in water balance of the heat-tolerant cultivar, we compared parameters of water balance, dry matter production and pod yield among cultivars. Four snap bean cultivars, Haibushi, Kurodane-Kinugasa, Oregon and Kentucky Wonder, were grown under optimal temperature (spring cropping) and high temperature (summer cropping) condition in the field. The daily water balance and gas exchange rate in the heat-tolerant cultivar Haibushi were compared with those in the heat-sensitive cultivar Kentucky Wonder, grown in 0.02 m2 Wagner pots. In the summer cropping in the field, dry matter production, pod yield, stomatal conductance, photosynthetic rate and transpiration rate were higher in Haibushi and Kurodane-Kinugasa than in the other cultivars. In a glasshouse, the sap flow rate was lower than the transpiration rate in the morning when the transpiration rate rapidly increased in both Haibushi and Kentucky Wonder. In spite of the higher transpiration rate, Haibushi showed a higher sap flow rate and smaller cumulative water loss in the morning than Kentucky Wonder. We conclude that better growth of the heat-tolerant snap bean cultivar Haibushi under high temperature was due to higher photosynthetic rate resulting from higher stomatal conductance during the daytime, which had a higher water uptake rate.

Efficacy of hot water drenches of Anthurium andraeanum plants against the burrowing nematode Radopholus similis and plant thermotolerance

SummaryHot‐water drench treatments were evaluated for disinfesting roots of potted anthurium Anthurium andraeanum of the burrowing nematode Radopholus similis. A continuous drench of roots and media in pots with 50°C water for 5 to 20 min eliminated or reduced nematode populations to &lt; 1 g−1 of dry root. A second hot water drench, 2 months after the first drenching, tended to increase the efficacy of the heat treatment. A few survivors persisted in the roots and/or stems of a few plants 2 to 4 months after heat treatment. Non‐treatment of the shoots and possible migration from stem to root tissues are probable causes of nematode survival. Drenching potting media and roots in pot were as effective against R. similis in the roots as hot water dipping bare‐rooted plants. Plant response to hot‐water drenching varied among cultivars, but most exhibited tolerance to the heat treatments. Visual inspection of the plants showed little difference between treated and untreated plants in the heat tolerant cultivars. However, all heat‐treated ‘Marian Seefurth’ plants, especially hot water‐dipped bare‐rooted plants, appeared to suffer some degree of growth reduction as measured by lower root and stem dry weights when compared to untreated plants 3 months after treatment. Conditioning anthurium plants with hot water or hot air prior to hot water drenching did not benefit plant quality when compared to unconditioned, heat‐treated plants.

Heat Stress Responses of Four Herbaceous Ornamentals Differing in Heat Tolerance

The demand for new and/or improved herbaceous annuals and perennials continues to increase, making information on production and viability of these plants a necessity. In Louisiana and the Southern U.S., one of the greatest impediments to production of marketable herbaceous plants and their longevity is high temperature. Herbaceous plants have various stages of vegetative growth and flowering; high temperatures during these developmental stages can have a tremendous impact on plant metabolism, and thus plant growth and development. The goal of this research was to better understand the differences between heat tolerant (HT) and heat sensitive (HS) species and cultivars at various high temperatures in terms of whole plant growth, flowering, photosynthesis, carbohydrate content, electrolyte leakage, chlorophyll content and plant small heat shock proteins (HSP) expression levels. Salvia splendens Vista Series (HT), Sizzler series (HS); Viola witrokiana `Crystal Bowl Purple' (HT), `Majestic Giant Red Blotch' (HS), F1 Nature Series (HT) and F1 Iona Series (HS); Gaillardia × grandiflora `Goblin' (HT) and Coreopsis grandiflora `Early Sunrise' (HS) were grown from seed in growth chambers under 25/18 °C (day/night) cycles. Plants at 4, 6, and 8 weeks after germination were subjected to different high temperature treatments of 25 (control), 30, 35, 40, and 45 °C for 3 h. Results show that there was a significant difference in net photosynthesis, electrolyte leakage, soluble carbohydrate content and HSP levels between HT and HS cultivars. Effects of high temperature on plant growth, chlorophyll content, and number of days to flower, flower size, and marketable quality were also significantly different.

Genotypic differences in the heat-shock response and thermotolerance in four potato cultivars

We have studied the relationship between thermotolerance and heat-shock protein (HSP) expression in potato ( Solanum tuberosum L.), analyzing two reported heat sensitive cultivars (‘Russet Burbank’ and ‘Atlantic’) and two reported heat tolerant cultivars (‘Norchip’ and ‘Désirée’) under prolonged heat-stress conditions. A standard and quantitative assay for heat tolerance, based on electrolyte leakage, revealed that one of the “heat tolerant” cultivars, ‘Désirée’, is not nearly as heat tolerant as the other heat tolerant cultivar, ‘Norchip’. In addition, protein labeling and immunodetection analyses revealed that there were genotypic differences in HSP expression in potato cultivars; at 40 °C, ‘Norchip’, the most heat tolerant cultivar, synthesized small (sm) HSPs for a longer time period, than the other three cultivars. The levels of an 18 kDa smHSP increased up to 24 h in ‘Norchip’ and ‘Désirée’, whereas the levels started to decrease after 4 h in ‘Russet Burbank’ and 12 h in ‘Atlantic’. At 35 °C, a more moderate heat stress, we observed an unusual pattern of accumulation of the 18 kDa smHSP; the level initially increased, then decreased at 12–18 h, and, upon prolonged heat stress up to 40 h, increased again at 18–24 h. The possible mechanism behind this dynamic pattern is discussed. This is the first extensive study on heat-shock protein expression in potatoes using commercially important potato cultivars.

Responses of Cytokinins, Antioxidant Enzymes, and Lipid Peroxidation in Shoots of Creeping Bentgrass to High Root-zone Temperatures

This study was designed to examine whether shoot injury induced by high root-zone temperature is associated with changes in shoot detoxifying metabolism and to determine the level and duration of high root-zone temperatures that would induce physiological changes in two cultivars of creeping bentgrass (Agrostis stolonifera var. palustris Huds) differing in heat tolerance. Plants of `Penn A-4' (heat tolerant) and `Putter' (heat susceptible) were grown in sand and exposed to root-zone temperatures of 20 (control), 21, 22, 23, 25, 27, 31, and 35 °C in water baths while air temperature was maintained at 20 °C in a growth chamber. Turf quality, leaf cytokinin content, and antioxidant enzyme activities declined at increased soil temperatures and the duration of treatment for both cultivars. A decline in turf quality occurred following 40 days of exposure to 35 °C for `Penn A-4' and 26 days of exposure to 31 °C for `Putter'. The root-zone temperature causing the decline of isopentenyl adenosine and zeatin cytokinins was 25 °C at 37 d for `Putter' and 27 °C at 47 days for `Penn A-4'. The temperature causing the decline of superoxide dismutase and catalase activities was 25 °C and 27 °C at 33 days for `Putter' and 27 °C and 31 °C at 43 days for Penn A-4, respectively. Malondialdehyde content increased at 27 °C for `Putter' and 31 °C for `Penn A-4' at 43 days of treatment. The decline in cytokinin content and antioxidant enzyme activity occurred at a lower soil temperature and earlier during the treatment than the decline in turf quality, possibly contributing to turf quality decline. The root-zone temperatures causing the decline in turf quality, cytokinin content, and oxidative damage were higher in the heat-tolerant cultivar than heat-susceptible cultivar.

Water Status of Flower Buds and Leaves as Affected by High Temperature in Heat-Tolerant and Heat-Sensitive Cultivars of Snap Bean (Phaseolus vulgaris L.)

In snap bean {Phaseolus vulgaris L.), flower and pod abscission causes yield reduction under high-temperature conditions. A high temperature enhances transpiration and thus may induce temporal water deficiency in plants in the daytime. The objective of this study was to clarify the effect of a high temperature on the water status of floral organs at their most heat-sensitive stage. We compared the water potential and its components as well as gas exchange between the heat-tolerant cultivar, Haibushi, and heat-sensitive cultivar, Kentucky Wonder, grown under optimal (control) and high-temperature conditions. Haibushi showed higher pollen fertility under high temperature than Kentucky Wonder. Transpiration was enhanced under a high temperature, causing decrease of water potential in leaves and flower buds. The deterioration of water status in floral organs was larger in Kentucky Wonder than in Haibushi. We conclude that temporal deterioration of the water status in flower buds is one of the factors causing pollen damage.

Heat Shock of Wheat During Grain Filling: Proteins Associated with Heat-tolerance

Two complementary approaches were used to determine the effects of heat shock on wheat-grain quality. Heat-susceptible (cv. Wyuna) and heat-tolerant (cv. Fang) cultivars of wheat were compared after heat shock, utilising both dough-quality testing and proteome analysis. Plants were grown at day/night temperatures of 24/18 °C during development, with stressed plants being subjected to heat shock at day/night temperatures of 40/25 °C on 15, 16 and 17 days post-anthesis. Grain samples were taken during development (17 days post-anthesis) and at maturity (45 days post-anthesis). Dough-quality testing of flour indicated that the Wyuna cultivar exhibited a decrease in dough strength after heat shock, whilst the Fang cultivar exhibited an increase. Proteome studies conducted on endosperm (at 17 days post-anthesis) showed that the heat-tolerant Fang cultivar exhibited a stronger and more diverse «heat shock response» than Wyuna. In total, 48 protein spots exhibiting differential expression between control and heat shock treatments were excised from gels and analysed by mass spectrometry. The resultant tryptic-peptide mass fingerprint data was submitted to SWISS-PROT and TrEMBL databases for protein identification. The majority of heat-shock associated proteins had low molecular mass and showed database similarity to previously characterised small heat shock proteins. Several discrete isoforms of the low molecular weight heat shock proteins were observed as differentially expressed between the two cultivars. Furthermore, seven protein spots were expressed in heat shocked Fang but not in heat shocked Wyuna, thus were further characterised utilising tandem mass spectrometry. These possible marker proteins for heat-tolerance may assist breeders in the selection of heat-tolerant cultivars that would not be expected to lose dough strength in such an environment.