摘要:

Sixteen genera of cacti were discovered to have polymorphic wood, that is, the plants produce one type of wood while young but a different type when older. The polymorphisms are: fibrous wood (with vessels and scanty paratracheal parenchyma) followed by parenchymatous wood (with vessels but few or no fibers) (Hylocereus venezuelensis, Dendrocereus nudiflorus, Borzicactus humboldtii, Haageocereus australis, Morawetzia sericata, Stephanocereus leucostele, Trichocereus schickendantzii); WBT wood (with wide‐band tracheids, vessels, and apotracheal parenchyma but few or no fibers) followed by fibrous wood (Buiningia aurea, Oreocereus celsianus, Vatricania guentheri); WBT wood followed by parenchymatous wood (Echinopsis tubiflora, Gymnocalycium marsoneri, G. oenanthemum, Notocactus warasii, Parodia maassii); trimorphic wood in which WBT wood is followed by fibrous wood, which is followed by parenchymatous wood (Melocactus intortus, Arrojadoa braunii). The different phases within each plant may differ in vessel cluster size, percentage of the vessels that are solitary, diameter of vessels, and lignification of ray cells. Several of these genera are not closely related to the others, so wood polymorphism may have arisen several times.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12652.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Formation of the cuticle from components of the secretory cavity and subcuticular wall was studied by transmission electron microscopy of glandular trichomes ofCannabisprepared by high pressure cryofixation‐cryosubstitution. Secretory vesicles in the secretory cavity resembled those localized in the subcuticular wall as well as the vesicle‐related material associated with the irregular inner surface of the cuticle and appeared to provide precursors for thickening of the cuticle. Some contiguous vesicles in the secretory cavity and subcuticular wall lacked a surface feature at their point of contact, supporting an interpretation of vesicle fusion. Fibrillar matrix from the secretory cavity contributed fibrillar matrix to the subcuticular wall, and persisted as residual fibrillar matrix associated with secretory materials coalesced to the thickened inner surface of the cuticle. Elongated fibrils arranged in uniformly spaced parallel pairs contributed to the organization of fibrillar matrix in the subcuticular wall. Striae were evident in the outer portion of the cuticle, and appeared to represent sites of degraded residual fibrillar matrix associated with secretory materials coalesced to the inner cuticular surface. This study supports an interpretation that contents of secretory vesicles from the secretory cavity contribute to formation of glandular cuticle.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12653.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Ultrastructural observations have revealed that plastids are present in orchid pollen tubes, but the DNA‐binding fluorochrome 4',6‐diamidino‐2‐phenylindole (DAPI) does not localize any DNA in the pollen tube plastids at optimum binding and flourescence conditions. However, the plastids do contain DNA since the gene coding for the large subunit of rubisco (ribulose‐1,5‐bisphosphate carboxylase/oxygenase,rbcL) has been amplified by the polymerase chain reaction from orchid pollen tubes. It is therefore concluded that DAPI is an unreliable fluorochrome for detecting plastid DNA.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12654.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Sorghum [Sorghum bicolor(L.) Moench] and sunflower (Helianthus annuusL.) were grown in a greenhouse with roots divided between sand irrigated with nutrient solution (–0.097 MPa) or nutrient solution containing polyethylene glycol (PEG) (–0.570 MPa) to compare the effect of unequal root zone stress on plant water relations of a C4(sorghum) and a C3(sunflower) plant. Roots also were divided between two pots of sand irrigated only with nutrient solution (controls) or only with PEG in nutrient solution. In addition to plant water‐status measurements, photosynthetic rate, growth (height, root, and shoot dry weights), and evolution of ethylene (a gaseous hormone indicative of stress) were measured. Under all three split‐root treatments, sunflower had a lower leaf water potential and produced more ethylene than sorghum. Sunflower was able to survive the PEG stress if half of its root system was under nonstressed conditions. Sunflower with half its root system irrigated with PEG usually had values of leaf water potential, osmotic potential, stomatal resistance, transpiration rate, photosynthetic rate, ethylene evolution, height, and dry weights that were close to those of the control plants. Sunflower with all roots exposed to PEG was wilted severely. Sorghum was little affected by PEG stress applied either to half or all the root system. Growth of sorghum was the same under all treatments. Apparently because stomata of sorghum were more closed in the partial stress test than those of sunflower, sorghum conserved water and had a higher leaf water potential, which might have permitted growth with stress.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12655.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

This study describes the specialized brood‐site‐based pollination system ofPeltandra virginicaKunth (Araceae) with the chloropid flyElachiptera formosaLoew and provides experimental evidence that gender‐related changes in floral odor composition synchronize pollinator behavior with the blooming sequence.P. virginicais protogynous and does not self‐pollinate because of a strong temporal separation in sexual function, and it is dependent upon insects for pollination because the spathe completely surrounds the spadix during the pistillate stage. Field observations conducted in central New Jersey and southeastern Pennsylvania showed thatE. formosais closely associated withP. virginicainflorescences. Within the floral chamber,E. formosaadults feed on pollen, mate, and find oviposition sites while the larvae complete their development. Although drosophilid and syrphid flies were collected and reared from inflorescences of both sexual stages, onlyE. formosaemerged from pistillate‐stage inflorescences and adultE. formosarapidly transferred fluorescent dye particles between inflorescences of both sexual stages in laboratory enclosures. These findings indicate that this fly species is the primary pollinator at our study locations. Field censuses demonstrated that althoughE. formosavisitedP. virginicainflorescences of both sexual stages with equal frequency, the female flies preferentially oviposited within pistillate‐stage inflorescences. Analysis of floral volatiles with gas chromatography‐mass spectrometry showed that only the spathes emit the floral fragrance and that the composition of the floral volatiles changed during the transition from pistillate to staminate stage. A particularly noticeable change occurred in the emission ratio of the two primary floral odor components, 4,5,7‐trimethyl‐6,8‐dioxabicyclo[3.2.1.]octane and an unidentified chemical analog with molecular weight of 142. The relationship between floral volatile composition and fly oviposition behavior was evaluated using sham inflorescences placed in theP. virginicastudy population. The sham inflorescences were constructed by covering spadices dissected from mature inflorescence buds with spathes excised from different‐age inflorescences. After a 2‐hr‐long exposure period, sham inflorescences fitted with pistillate‐stage spathes contained moreE. formosaeggs than the sham inflorescences with staminate‐stage spathes. However, the highest number of ovipositions occurred in sham inflorescences fitted with spathes excised from mature inflorescence buds. The fragrance emitted by these spathes was composed almost entirely of the two principal odor components. The decline in ovipositions observed in both real and sham inflorescences corresponded to an increase in the emission ratio of 4,5,7‐trimethyl‐6,8‐dioxabicyclo[3.2.1.]octane to the molecular weight 142 analog. This suggests that gravid flies searching for oviposition sites used the ratio of the two primary floral volatile components as an inflorescence gender or age recognition cue.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12656.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Two field experiments were designed to evaluate the importance of competition, fire, repeated disturbance, and their interactions on the vegetative and reproductive performance of the Mediterranean shrubErica multifloraover a 2.5‐yr period. In a burn experiment, fire was applied to the ground‐level stumps of previously clipped 13‐yr‐old plants with a propane torch and competition was diminished by removal of neighboring plants. Fire resulted in a reduction of sprout vigor and biomass of flowers; mature neighbors also reducedE. multiflorasprout vigor and flowering. The interaction between fire and competition was nonsignificant. In a stand burned by a wildfire we studied the effects of regenerating neighbors on target plants by removing all neighbors or onlyQuercus coccifera, the most dominant species in the burned stand. In this stand we also simulated herbivory by repeatedly clipping the sprouts ofE. multiflora.Regenerating neighbors did not affect target plant sprout vigor after the wildfire, but did cause a decrease in the biomass of flowers per plant. Survival decreased after repeated clipping but was not affected by neighborhood treatment. The results suggest that the importance of competition on resprouting vigor was temporally variable. Variables related to plant size rather than species determined competitive superiority: resprouting neighbors did not affect resprouting performance of target plants, but mature neighbors did. In nature, fire may directly reduce vegetative and reproductive biomass by the heating effect. But it may have an indirect positive effect on biomass, by reducing competition among plants. Frequent disturbances that removed aboveground biomass ofE. multiflorahad a detrimental effect on target plant survival independent of neighborhood effect.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12657.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Seasonal patterns of photosynthesis and carbon allocation were determined forTipularia discolor, a summer‐deciduous wintergreen orchid of the southeastern United States, to assess the effects of environmental conditions and leaf age on carbon acquisition and allocation patterns. There was no shift in the optimum temperature for photosynthesis (Topt) on a seasonal basis andTopt(≈26 C) was at least 10 C higher than daily maximum air temperature during most of the growing season. Lack of photosynthetic adjustment inTipulariato seasonal fluctuations in temperature and light suggested that the photosynthetic characteristics of this wintergreen were more similar to those of spring ephemerals than to those of evergreens and summer‐active herbs. The decline in photosynthetic capacity during the winter growing season forTipularia, largely due to leaf age effects, gradually reduced net photosynthetic rates in the field despite more favorable light and temperature conditions. Photosynthesis in the field was primarily limited by environmental conditions in early‐ and mid‐season and by photosynthetic capacity in late‐season. A14CO2labelling experiment demonstrated that patterns of carbon allocation to vegetative structures were affected by the season of photosynthetic carbon fixation, whereas reproductive structures received 21% of the recovered labelled carbon regardless of the period of labelling. Carbon acquired and stored during all periods of the growing season was used to produce new vegetative and reproductive structures.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12658.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Leaf optical properties (400–1,100 nm) were compared for four species of rain forest trees with crowns in understory, mid‐canopy, and canopy positions to test whether optical properties change with light environment. The species tested represent a spectrum of regeneration patterns ranging from shade tolerant to light demanding. Overall, leaf optical properties of the four species were similar. Differences in absorptance were small, but statistically significant among the species and positions along the canopy gradient. Species absorptance differences corresponded somewhat to shade tolerance; two of the shade species showed higher absorptance in lower light environments, while the sun species showed the reverse pattern. Specific leaf mass (leaf weight per unit area) and chlorophyll content per unit leaf weight also changed along the canopy gradient. Specific leaf mass was positively correlated and chlorophyll per unit leaf weight was negatively correlated with increasing light environment. Consequently, the efficiency of absorption, as represented by the absorptance per unit leaf weight, increased as light level decreased, largely due to changes in specific leaf mass. In contrast, efficiency of absorption per unit leaf chlorophyll was relatively constant with light environment for the two species measured for chlorophyll.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12659.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

Many evolutionary and ecological studies of plants with seed dormancy are plagued by design problems related to seed germination. On the one hand, traits of interest, especially life history traits like early growth rate or time to flowering, may not be independent of dormancy phenotype. On the other hand, germination‐inducing treatments are likely to affect these traits of interest. Consequently, researchers often have had to use confounded designs without information about the consequences. To examine this problem, we studied how early growth in California poppy (Eschscholzia californica) is affected by treating seeds with giberellic acid (GA) to stimulate germination. The dose used was sufficient to slightly but significantly advance emergence time in treated seeds, but it appeared to cause variable growth responses among treated seeds. Experiments using GA to stimulate germination may thus be misleading, at least for the populations and dose studied. Perhaps more importantly, the experimental and statistical approach we used can be employed to study the effects of this confounded design for other doses and species.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12660.x

出版商:Wiley    

年代:1995

数据来源: WILEY

摘要:

As part of a continuing study of the effects of leaf surface wetness on gas exchange, the occurrence of leaf surface wetting by dewfall and associated effects on photosynthesis were evaluated for floating and aerial leaves of the pond lilyNuphar polysepalumEngelm. Because of nighttime radiation exchange with a cold sky, high humidity, and the presence of adaxial stomata, we predicted that pond lily leaves would be particularly susceptible to wetting events such as dewfall. A substantial reduction in net photosynthesis (up to 20%) occurred for leaves that were experimentally misted to simulate leaf wetting by dewfall. Aerial leaves remained below dewpoint temperatures for long periods on clear nights. However, floating leaves rarely approached dewpoint temperatures at night because minimum nighttime temperatures of leaves were up to 10 C warmer than air temperature. Thus, floating leaves ofN. polysepalumdid not experience dew formation primarily because of strong thermal coupling to a substrate (water) that was much warmer than air temperature at night. This coupling to a warmer substrate prevented a potentially strong inhibition of photosynthetic CO2exchange the following morning.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1995.tb12661.x

出版商:Wiley    

年代:1995

数据来源: WILEY