光对马来良姜花柱运动和花药开裂的影响

以马来良姜(Alpinia mutica)花柱为研究对象,研究光对花柱卷曲运动和花药开裂的影响.结果表明下垂型花柱的两次运动在光下和暗处都能进行,花药的开裂也不受光照影响.上举型花柱的第一次运动在暗处时向下进行,在光下时向上进行;暗处的花药不开裂,光下的花药开裂.第二次运动的方向和幅度取决于第一次运动期间的光照条件,第一次运动在暗处时,若第二次也在暗处,第二次运动不会发生且花药不开裂;若在光处,花柱向上运动.第一次运动在光下时,第二次运动无论光下或暗处,都向下运动.本研究表明,在不同光照条件下,两种表型的花柱与花药状态的组合使柱头接触不到同花的花粉,从而保证了雌雄异位与雌雄异熟.尽管两种表型的花柱运动和花药开裂行为相似,却受不同的机制调控.     

Effects of light and low temperature on the reciprocal style curvature of Flexistylous Alpinia Species (Zingiberaceae)

The style curvature (flexistyly) of Alpinia species in ginger family is a unique plant organ movement because the style of each flower curves twice during its 1-day anthesis and styles of two phenotypes of each Alpinia species in the same population synchronously curve in opposite directions at the same time. In this study, we investigated the effects of low temperature and light conditions on these reciprocal style movements. Our results indicate that low temperature cannot change the direction of each curvature movement, but can slow down these movements and decrease the curve degrees. Light did not affect the upward curvature of the cataflexistylous morph, but the degrees of downward curvature decreased in darkness. For the anaflexistylous morph, the downward curvature only occurred in darkness, but curved directly upward in light condition; after the first (downward) curvature, the second (upward) movement only occurred in light, but did not occur if styles maintained in darkness. These results suggest that low temperature does not stimulate style curvature; light is the necessary condition for the upward movement of the anaflexistylous morph. The stimuli that induced curvature movements in the two morphs were different. Both two curvatures of the cataflexistylous style and downward movement of the anaflexistylous style were controlled via an endogenous program, while the upward movement of the anaflexistylous style was controlled by light.     

Effects of indole-3-acetic acid and auxin transport inhibitors on the style curvature of three Alpinia species (Zingiberaceae)

The effects of indole-3-acetic acid (IAA) and the auxin transport inhibitors 2, 3, 5-triiodobenzoic acid (TIBA) and 1-N-naphthylphthalamic acid (NPA) on the style curvature of Alpinia platychilus, A. blepharocalyx, and A. mutica were studied. Exogenous IAA stimulated the style curvature movement of the anaflexistylous morph (ana-morph) and cataflexistylous morph (cata-morph) of three Alpinia species in light, but had no effect in the dark. Treatment with auxin efflux inhibitors (NPA and TIBA) before flower opening did not affect the first curvature of the two morphs in darkness; however, the subsequent second movement of the ana-morph was enhanced by NPA or TIBA, while the second movement of the cata-morph was completely inhibited. After the first curvature, NPA and TIBA treatments at 06:00?hours (before significant illumination) and 11:00?hours (after the styles were illuminated for 4?h) increased the second curvature of the ana-morph, but significantly decreased that of the cata-morph. The effect at 06:00?hours was more significant than the effect at 11:00?hours. These results suggested that auxin and auxin transport affected the style curvature in a different way in the two morphs, and two morphs had distinct mechanisms for style movement at different times.     

Development of distylous flowers and investment of biomass in male and female function in Palicourea padifolia (Rubiaceae)

Knowledge of developmental pathways for achieving differences in style and anther heights, in concert with those of ancillary features accompanied with data in regard to biomass investment to male and female function, provide an excellent opportunity for examining the developmental correlations between primary and ancillary floral traits so as to understand the evolution of heterostyly. The ontogenetic relationships between bud length and anther height and between bud length and style height, and between bud length versus bud width, anther length, and number of pollen grains per anther for long-styled (LS) and short-styled (SS) morphs of P. PADIFOLIA are described. We also described the ontogenetic biomass allocation to male and female function and to corolla with elongation of buds harvested at regular intervals. We observed an early termination of stylar growth in SS buds, whereas LS styles steadily increased in size. Morph differences for relative growth rates were significant for anther height, anther length, and pollen number but not for bud width. Bud width and anther length had a negative allometric relationship with bud elongation. The relationship between bud length and number of pollen grains per anther was positive and morph differences in pollen number were detected at later stages of development. An increase in corolla mass involved a disproportionate allocation to the female function in SS flowers and male allocation was similar for the two morphs over the course of development. Our results are consistent with theoretical and empirical data for distylous species with an approach herkogamous ancestor, and with the more general hypothesis of ontogenetic lability of heterostyly, in which morph differences in style and anther heights are achieved in various ways. Variations observed in sexual investment between floral morphs suggest differences in sex expression during flower development.     

Morph-specific patterns of variation in stigma height in natural populations of distylous Jasminum fruticans

The purpose of this study was to describe morph-specific patterns of stigma–anther separation and style curling in the distylous Jasminum fruticans . We also examined whether variation in floral traits is correlated with variation in seed production. Stigma–anther separation is more variable in short-styled plants than in long-styled plants. In all populations studied, some plants bear flowers that lack any stigma–anther separation. These plants have the pollen characteristics (size and number) and compatibility relations of short-styled plants. Comparison with other distylous species illustrates that the variability of stigma–anther separation in short-styled plants is a novel finding for a distylous species. Long-styled plants have greater stigma–anther separation than short-styled plants, styles are often curled and protrude from the corolla, and anthers are placed well within the corolla tube. The frequency of long-styled plants with curled styles and the mean degree of style curling were significantly correlated with style length. Short-styled plants have larger corollas than long-styled plants and never have curled styles. Morph ratios are always 50:50 in natural populations. Mean values of each floral trait in the two morphs were significantly correlated among populations. There were no consistent differences in fecundity of the two morphs nor any correlation between floral traits and seed set for each morph in natural populations. We discuss the potential causes and significance of the two morph-specific patterns we describe; reduced stigma–anther separation in short-styled plants and the presence of curled styles in long-styled plants.     

DEVELOPMENT OF TRISTYLY IN PONTEDERIA CORDATA (PONTEDERIACEAE). I. MATURE FLORAL STRUCTURE AND PATTERNS OF RELATIVE GROWTH OF REPRODUCTIVE ORGANS

Pontederia cordata is a tristylous, self-incompatible emergent aquatic. Measurements of reproductive organs in mature flowers and developing buds and analysis of relative growth rates of the styles, filaments, and floral tube were used to analyze the developmental processes that result in reciprocal positioning of reproductive parts among the style morphs. Flowers are trimerous with two series of three tepals, two series of three stamens, and a tricarpellate ovary with a single ovule. Each flower has stamens of two lengths, but the two lengths correspond to upper vs. lower position in the zygomorphic flowers, not to the two series initiated in the primordium. Morph-dependent variation in stigma height depends on differences in style length, not ovary length. Differences among morphs in anther height result from differences in the position of filament insertion on the floral tube and differences in filament length. Styles of the three morphs develop to different lengths as a result of two distinct processes. Styles of L and M morphs develop at different rates with the L style growing more rapidly than the M style, whereas styles of the S morph have a brief period of rapid growth followed by early inhibition. Stamen growth in the S morph also differs qualitatively from that in the L and M morphs, which are distinguished from each other by quantitative differences in growth rates. Results indicate that the developmental processes that result in the complementary arrangements of organs in different morphs are morph-specific. An attempt is made to integrate the findings of this study with the model for genetic control of tristyly.     

温度和湿度对草果花柱卷曲的影响

草果（Amomum tsaoko）为姜科植物,有花柱卷曲机制。研究表明温度和湿度均影响草果上举型花和下垂型花的花柱卷曲,相对恒定的低温和高湿可促使花柱的同步卷曲。当8∶00-19∶30期间的平均温度小于18℃、平均湿度大于90%时,花柱卷曲没有滞后现象,卷曲的同步性较好。当平均温度大于18℃、平均湿度小于90%时,随着温度的升高和湿度的降低,花柱卷曲滞后愈加明显。和上举型花相比,下垂型花的花柱卷曲对湿度变化更为敏感;可能两种花型之间存在一定的分化。居群初花期19.17~19.52℃的平均温度和51.00%~51.44%的平均湿度,导致单朵下垂型花的寿命由1d延长为2d。温度和湿度变化对花柱卷曲的影响导致在居群水平上没有完全形成功能上的雌雄异株,可能影响草果的繁育和降低其适合度。从不同角度对花柱卷曲机制的深入研究,有助于更好的探索其起源和进化。     

FLORAL VARIATION AND DISTYLY IN GUETTARDA SCABRA (RUBIACEAE)

Controversy exists as to whether the tropical shrub Guettarda scabra (Rubiaceae) is distylous. Variations in stigma and anther position and floral morphology of G. scabra were studied in a population in south Florida. Stigma and anther height have unimodal distributions, but stigma-anther separation is bimodally distributed and can be used to identify a long-styled and a short-styled morph. Stigma width varies between morphs, but anther length, pollen diameter, and stigma papillae length do not. The morphs occur in a 1:1 ratio in the two populations studied. G. scabra is self-compatible and can pollinate itself. Styles of the two morphs have similar relative growth rates in early development. Stylar growth is inhibited in the short-styled morph when buds are approximately 12 mm long. Anther height differs between morphs because of different relative growth rates and because the long-styled morph corolla tube, where the anthers are attached, stops growth before the tube of the short-styled morph. Reciprocity between morphs for average stigma and anther height falls within the range of reciprocity found in other distylous Rubiaceae. Thus G. scabra is morphologically distylous but unusual among distylous species in the variation within morphs and overlap between morphs in stigma and anther heights.     

草豆蔻传粉生物学的研究

比较研究了花柱卷曲性植物草豆蔻 Alpinia hainanensis两种表型(上举型和下垂型)的传粉生物学特性。结果表明:草豆蔻的花柱卷曲运动节律与其他已报道的山姜属Alpinia植物基本一致,而下垂型花的花柱卷曲运动明显滞后于上举型花约2 h。草豆蔻的花柱卷曲运动中存在一些不同步的现象,甚至在同一花序上的两朵花的花柱运动节律亦会表现出不一致的现象,但上举型花的花药开裂时间却严格同步,都发生在同类型个体的柱头全部位于花药上方之后进行。草豆蔻上举型花的花蜜分泌量、单花花粉量、花粉/胚珠比率(P/O)均明显比下垂型花多,而两种表型的胚珠数、花蜜糖含量、氨基酸含量无显著差异。在草豆蔻的单花期内不同时间段进行人工授粉,上举型花在其柱头位于花药下方时进行人工授粉,其结实率明显比柱头位于花药上方时人工授粉的处理高,下垂型花则没有显著差异。在自然居群中,草豆蔻的主要传粉者是无垫蜂Ameglla sp.和两种木蜂Xylocopa sp.,但存在传粉者不足而影响结实率的现象。完全套袋、去雄和去雌(去柱头)处理的均不结实,表明草豆蔻中不存在无融合生殖、主动自花授粉和滞后自交的生殖保障现象。而人工自交和异交均具有较高的结实率,表明草豆蔻为自交亲和植物。草豆蔻的繁育系统是具花柱卷曲性运动的异花授粉的交配系统。     

二型花柱植物海仙花报春花部性状随地理梯度的变异

植物的花部性状在异质环境中表现出不均一的适应性进化, 其自然变异可能在时空格局上呈现一定的规律性。选择同一物种的不同地理居群进行花部表型变异分析, 能揭示花部性状随地理梯度的变异模式。海仙花报春(Primula poissonii)属于典型的二型花柱植物, 依赖昆虫传粉实现严格的型间异交。该物种广布于横断山地区亚高山-高山草甸, 其分布海拔跨度大且花部性状在种内具有较高变异, 但这些变异在不同地理梯度(海拔梯度和经纬度梯度)的特定选择因子作用下的变化规律尚不清楚。本研究选择海仙花报春16个居群, 对8个花部关键性状和二型花柱繁殖器官的互补度与海拔和经纬度的关系进行研究, 探究花部性状随地理梯度变异的模式及其潜在的选择因素。研究表明, 海仙花报春两种花型的花冠管开口大小、花药高度以及短柱花柱头高度与海拔均呈正相关, 但两种花型的花冠大小, 长柱花的花瓣长度、柱头到花冠管开口的距离, 以及短柱花的花冠管长度与海拔高度间均呈负相关, 其余性状与海拔无显著相关性。除短柱花中柱头高度以外的性状均随着纬度升高而逐渐减小。长柱花中除花药和柱头间的距离以及柱头到开口的距离外, 其余性状均随着经度的增加而减小; 短柱花的花瓣长度、花药高度以及花药和柱头间的距离随着经度的增加而变大, 其余性状均随着经度的增加而减小。繁殖器官间的互补度并不随地理环境的变化而变化。花部性状的地理变异可能受访花昆虫组成的地理变化驱动。繁殖器官间互补程度的高度保守表明非选型交配在居群二态性的维持和稳定过程中起关键作用。本研究为进一步深入开展报春花属(Primula)花部性状及其选择压力的地理变异研究奠定了基础。     

Evolutionary maintenance of stigma-height dimorphism in Narcissus papyraceus (Amaryllidaceae)

Stigma-height dimorphism is a sexual polymorphism in which plant populations are composed of two floral morphs that differ significantly in style length but not anther position. The morphs exhibit approach and reverse herkogamy, floral designs that in most species typically occur as monomorphic conditions. We investigated the floral biology of stigma-height dimorphism in the Mediterranean geophyte Narcissus papyraceus (Amaryllidaceae) in an effort to understand the evolutionary forces maintaining stylar polymorphism. Our survey of 66 populations in Spain, Portugal, and Morocco indicated that 56% were dimorphic with the long-styled morph at an average frequency of 0.79. The remaining 44% of populations sampled were monomorphic for the long-styled morph. In dimorphic populations there was a significant positive relation between population size and the frequency of the short-styled morph. Controlled pollinations demonstrated that N. papyraceus is self-sterile with no significant differences in female fertility between intra- and intermorph crosses. Prior self-pollination reduced seed set in flowers that were subsequently cross-pollinated. Estimates of mating patterns using allozyme markers in eight populations indicated that N. papyraceus is largely outcrossing (mean t(m) = 0.81) with no significant differences between monomorphic and dimorphic populations or style morphs. Stigma-height dimorphism in N. papyraceus is maintained in populations by insect-mediated cross-pollination with biased morph ratios and stylar monomorphism likely resulting from the combined influence of the inheritance of the polymorphism, morph-specific differences in assortative mating and founder effects.     

Effects of prior self-pollination on outcrossed seed set in tristylous Pontederia sagittata (Pontederiaceae)

The potential inhibitory effects of incompatible pollen on outcrossed seed set were investigated in mass-flowering, self-incompatible, tristylous Pontederia sagittata. Prior application of self pollen, followed after 2, 4, or 6 h by compatible pollen, was conducted on five genotypes of each of the three style morphs under uniform glasshouse conditions. The greatest reductions in seed set occurred in pollinations of the long-styled (L) morph at the 6 h time interval. Smaller reductions were also found for this treatment in the mid-styled (M) morph. No significant reductions in seed set were observed in the short-styled (S) morph or in the other morphs at shorter time intervals. Observations of pollen germination and pollen tube growth indicated that the lack of inhibitory effects in the S morph may occur because relatively few pollen grains adhered to stigmas in selfpollinations. In the L and M morphs, early germination of self pollen may cause physical clogging of the stigma and style, resulting in a reduced number of compatible pollen tubes in styles. Observations of the structural integrity of styles indicated that prior germination of self pollen resulted in more rapid onset of pistil senescence, particularly in the L morph. These influences may contribute to the morph-specific differences in seed set observed following prior self-pollination of outcrossed flowers. The negative effects of incompatible pollen are likely to be most evident where ecological factors cause delays in the delivery of outcross pollen to stigmas.     

刺五加花的形态学及雄蕊异长现象的观察

刺五加Eleuthercoccocus senticosus (Rupr．et Maxim．)Maxim．具有花丝长度不同的三种植株类型,本文报道了其花序和花的形态结构,开花式样,异长雄蕊现象及相应的花柱长度。结果表明：长花丝长3．96～4. 44mm ,短花丝长0．45～0．93mm,中花丝长2．16～3．08mm。伴随异长雄蕊特征的其它表现在于花药大小、花药形状和颜色、花粉大小、花粉数量、柱头宽度和雌雄蕊育性。其中,长花丝对应的花药饱满、白色、花粉量大、花柱较短、雌性败育;短花丝对应的花药小、黄褐色、无花粉、花柱较长、雌性可育;中花丝对应的花药中等、花粉粒较大、雄性半不育、雌性可育。据此,刺五加被认为是单全异株的,其长花丝类型是雄性、短花丝类型是雌性、中花丝类型是两性的。另外,对三种性别形态类型的关系进行了讨论,并认为将雌株作为变种“短蕊刺五加”var.brevistaminea 显然是不恰当的。     

Differential foraging success across a light level spectrum explains the maintenance and spatial structure of colour morphs in a polymorphic bird

Detectability of different colour morphs under varying light conditions has been proposed as an important driver in the maintenance of colour polymorphism via disruptive selection. To date, no studies have tested whether different morphs have selective advantages under differing light conditions. We tested this hypothesis in the black sparrowhawk, a polymorphic raptor exhibiting a discrete white and dark morph, and found that prey provisioning rates differ between the morphs depending on light condition. Dark morphs delivered more prey in lower light conditions, while white morphs provided more prey in brighter conditions. We found support for the role of breeding season light level in explaining the clinal pattern of variation in morph ratio across the species range throughout South Africa. Our results provide the first empirical evidence supporting the hypothesis that polymorphism in a species, and the spatial structuring of morphs across its distribution, may be driven by differential selective advantage via improved crypsis, under varying light conditions.     

Adaptive significance of flexistyly in Alpinia blepharocalyx (Zingiberaceae): a hand-pollination experiment

BACKGROUND AND AIMS: Flexistyly is a sexual dimorphism where there are two morphs that differ in the temporal expression of sexual function and also involve reciprocal movement of the stigmatic surface through a vertical axis during the flowering period. The adaptive significance of flexistyly has been interpreted as a floral mechanism for outcrossing, but it may also function to reduce sexual interference in which styles and stigmas impede the pollen export. Here these two explanations of flexistyly were tested in Alpinia blepharocalyx through a hand-pollination experiment. METHODS: Hand-pollinations were performed in two temporal morphs and consisted of two sequential pollination treatments, namely self-pollination in the morning and inter-morph pollination in the afternoon (treatment 1) or conversely inter-morph pollination in the morning and self-pollination in the afternoon (treatment 2), and two simultaneous self- and inter-morph cross-pollination treatments either in the morning (treatment 3) or in the afternoon (treatment 4). Seed paternity was then determined to assess relative success of self- versus cross-pollen using allozyme markers. KEY RESULTS: In the sequential pollination treatments, whether the stigmas of recipients are receptive in the morning is crucial to the success of the pollen deposited. When the cataflexistylous (protandrous) morph served as pollen recipient, early-arriving pollen in the morning can sire only a very small proportion (<15%) of seeds because the stigmas were then unreceptive. However, when the anaflexistylous (protogynous) morph served as pollen recipient, early pollen did gain a large competitive advantage over the late pollen, particularly when cross-pollen arrived first. Simultaneous self- and inter-morph cross-pollination indicated that outcross-pollen is more competitive than self-pollen on receptive stigmas. CONCLUSIONS: Differential maturing of male and female organs in Alpinia blepharocalyx is sufficient for selfing avoidance, obviating the need for style movements. Instead, the upward style curvature of the cataflexistylous morph in the morning and the anaflexistylous morph in the afternoon most likely represents a means of reducing interference with pollen export.     

Quantitative evaluation of stigma polymorphism in a tristylous weed,Lythrum salicaria (Lythraceae)

Tristyly involves three different forms of flowers that differ reciprocally in the heights of stigmas and anthers within flowers. Apart from the style and stamen lengths, heterostylous species also demonstrate pollen and stigma polymorphisms. We quantified stigma polymorphism in tristylous Lythrum salicaria by measuring the stigma diameters, structure of papillae, and density and distribution of papillae on the stigma from flower samples of 201 individuals belonging to three morphs. The diameter of the stigma and the distribution of papillae were quantified using a scanning electron microscope, and the structure of papillae was determined using a light microscope. The stigma diameter in the long morph was significantly greater than in the mid and short morphs. While the density of stigmatic papillae was significantly greater in the mid and short morphs than in the long morph, the total number of papillae per stigma did not differ across morphs. The length and diameter of papillae at the apex, neck, and base were significantly greater in the long morph followed by the mid and short morphs. A discriminant function analysis separated the long morph from the mid and short morphs based on the canonical scores of measurements of papillae structure. The stigma polymorphism coupled with those of pollen may play a functional role in self-incompatibility mechanisms.     

Inversostyly: a new stylar polymorphism in an oil-secreting plant, Hemimeris racemosa (Scrophulariaceae)

A new kind of stylar polymorphism, provisionally called inversostyly, is described. The polymorphism occurs in Hemimeris racemosa (Scrophulariaceae), a common annual herb of the Cape region of South Africa. Most populations are dimorphic for style orientation: the style alternates with the two stamens and is deflected either upwards or downwards. Thus, there is reciprocal placement of the style and stamens in a vertical plane in zygomorphic flowers. The flowers are symmetrical, and the floral parts do not vary in length. All flowers on a given plant are of the same stylar orientation. Pollination is by specialized oil-collecting bees (Rediviva spp.), which carry the pollen of the two morphs separately in discrete anterior or posterior locations on the underside of the body. Most inversostylous populations have a slightly higher proportion of the style-down morph, and this bias increases with decreasing pollinator abundance. In contrast with inversostylous populations, all individuals in homostylous populations of H. racemosa have the style and the stamens clustered together in the down position and high levels of autogamous seed set. Homostylous populations of H. racemosa, as well as the homostylous species Hemimeris sabulosa, occur where oil-collecting bees are less abundant.     

THE DEVELOPMENTAL BASIS OF TRISTYLY IN EICHHORNIA PANICULATA (PONTEDERIACEAE)

Eichhornia paniculata is a tristylous, self-compatible, emergent aquatic. A given plant produces flowers with either long, mid or short styles and two levels of stamens equal in length to the styles not found in that flower. Flowers of each morph have two whorls of three tepals, six stamens and three fused carpels. The six stamens differentiate into two sets of three stamens each. A relatively short set, having either short- or mid-level stamens, occurs on the upper side of the flower, while a relatively long set, having either mid- or long-level stamens, occurs on the lower side. Stamen level depends on differences among stamens in filament length and position of insertion on the floral tube. Floral parts arise in whorls of three, but the two stamen whorls do not form the two sets of stamens found in each mature flower. Instead, stamens from both whorls make up a given set. Floral differences among morphs are not present at flower origin or floral organ initiation. Morphological differences arise first among stamen sets. The two sets within a flower differ prior to meiosis in the size, number, and timing of comparable developmental events in the sporogenous cells. After these initial differences arise, anther size diverges. In later developmental stages differences in filament and floral tube length, cell size, and cell number, as well as differences in the length, cell size, and cell number of styles, develop among morphs. This sequence of developmental events suggests that the genes controlling development in different morphs do not control flower and floral organ initiation but are first morphologically visible in sporogenous cell differentiation.     

Polychromatism of the scale-eaterPerissodus microlepis (Cichlidae,Teleostei) in relation to foraging behavior

Variation in foraging behavior in a population of the scale-eaterPerissodus microlepis was studied on the northwest coast of Lake Tanganyika. Differences in body coloration were found among adult and subadult individuals, which were classified into 4 color morphs designated as Beige, Dark, Grey and Stripe. These color morphs were not strictly related to either sex or size. Each morph spent much time in specific microhabitats and had a major hunting technique that differed from other morphs. Beige morph. which predominated in number, ambushed prey at open surfaces of the substrate, whereas Dark morph used the shade of rock as an ambush site. Grey morph mixed in schools of fisheds hovering in midwater to attack school members, and Stripe morph cruised in the water column and stooped mainly at bottom-fishes. Prey preference differed among the morphs corresponding to their hunting techniques but successful attack rates were similar among them. Observations of marked individuals demonstrated adherence to particular hunting techniques and, in some cases, to particular hunting sites. Intraspecific foraging specialization is discussed in relation to the function of body color and diversity of life styles of prey fishes.     

Gravitropic response of primary maize rootlets as influenced by light and temperature

Abstract. The gravitropic curvature of primary maize rootlets was measured as a function of temperature, both in the presence and absence of light. In two different cultivars, light strongly increased the downward curvature of roots developing from horizontally-oriented embryos. At 15–20°C, the bending angle was in the range of 70–80° in the light, and 25–50° in the dark, depending on the cultivar. When the temperature was increased above the 15–20°C range, marked differences were found between the two cultivars in their response to light. In one variety tested, JX180, the effect of light was relatively small at 30–35°C. Gravitropic curvature in another variety, Halamish, depended strongly on light throughout the temperature range tested. In both cultivars, gravitropic curvature was only slightly temperature dependent when germination and growth were in total darkness. In the dark, the extent of gravitropic curvature also depended on whether the kernels were oriented with their embryos facing upwards or downwards. Under continuous light, the gravitropic bending of roots of cultivar Halamish did not show a marked temperature dependence. When the seedlings were subjected to only a 15 min illumination, their gravitropic response was partial, and the dependence on temperature somewhat increased. In cultivar JX180, a combination of temperature and light modulates gravitropism. The gravitropic response of different maize cultivars thus differs considerably in its combined dependence on light and temperature.