摘要:

Impatiens pallida, a succulent annual herb of moist temperate forests, typically wilts on summer days after several minutes of direct sunlight. Time courses of gas exchange and leaf water potential were measured to determine if wilting resulted in substantially reduced photosynthesis, stomatal conductance, or leaf internal CO2concentrations. Leaves quickly wilted with the onset of high‐light, but photosynthesis and stomatal conductance increased markedly. Photosynthetic rates and stomatal conductance declined slightly after several hours of high‐light, and from morning to late afternoon shade conditions. Leaf internal CO2declined with increased photosynthesis, but there was no evidence that stomatal conductance limited photosynthesis through the day. We propose that rapid wilting is an adaptation that facultatively limits heat loading and extreme water loss under high‐light. Further whole plant studies in natural settings are needed to fully evaluate the quantitative significance of wilting in relation to water use and photosynthesis.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb13813.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

The relationships between photosynthesis, flowering, and growth temperatures were examined experimentally in four populations of the C4grass genusBouteloua.Field‐collected plants were grown under two temperature regimes, cool (20 C day/6 C night) and warm (30/16), representative of the extreme populations. Populations collected from the warm climates had significantly lower photosynthetic capacity when grown in the cool chamber relative to the warm chamber, while photosynthetic capacity in the cool climate populations did not differ between the growth conditions. Additionally, exposure to a 2‐day cold temperature treatment (10/‐2), representative of late‐season frosts in high altitude sites, resulted in further reductions in photosynthesis in the warm climate plants, but not in the cool climate plants. This effect was greater for plants grown in the cool growth chamber. Flowering was reduced by 70% in the warm climate plants grown in the cool chamber, and was correlated with photosynthetic inhibition following the short‐term cold temperature treatment. These results indicate that genetic differentiation for photosynthetic temperature sensitivity has occurred in the cool climate populations, and that long‐term exposure to cool temperatures coupled with short‐term relatively extreme low temperatures results in greater photosynthetic inhibition in nontolerant populations.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb13814.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Culm (ramet) demography of two bamboos,Fargesia robustaandBashania fangiana, was studied over 7 yr in southwest China to determine if: 1) ramet numbers remain relatively constant; 2) ramet mortality was constant; 3) density response was greater in spreading vs. compact clones; 4) extrinsic factors (e.g., predation, climate) influenced ramet dynamics; and 5) ramets that die are smaller than ones that live. Culm numbers remained relatively constant (±20%) in most plots, but culm numbers increased (>;20%) on some sites. Mortality of culms>;6 mo old over 7 yr was low and constant, but mortality of younger culms (≤6 mo) was high and variable due to predation. Spreading clones had greater recruitment response to density than compact clones, but predation and climate may have diminished or amplified the observed demographic patterns. Predators and perhaps climate influenced culm demography, and culms that died were smaller than remaining live culms. The demography of the two bamboos we studied is compared to other clonal plants, including bamboos, to identify common processes controlling ramet demography.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb13815.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Germination of spores of the fernAnemia phyllitidisin red light or in the dark in the presence of gibberellic acid in the medium is accompanied by the synthesis of chlorophyll. Spores incubated in the dark in the absence of the hormone neither germinate nor accumulate the pigment. mRNA levels of plastid‐encoded photosynthetic genes (rbcL andpsbA) increase maximally in photo‐induced spores and at intermediate to low levels in hormone‐induced and dark‐incubated spores. On the other hand, transcripts for the nuclear‐encodedrbcS gene appear only in photo‐induced spores. The results show that light and hormonal signals promote differential gene expression at the mRNA level during germination of spores.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb13816.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Underwater cross pollination (hypohydrophily) represents a markedly divergent form of pollination in seed plants; reproductive structures are functionally wet during pollination.Callitriche(Callitrichaceae) is the only genus in which both aerial pollination systems and hypohydrophily are reported. This diversity in pollination types would not be predicted based on the general uniformity in floral structure in the genus. Logistic difficulties in conducting experimental pollination studies inC. hermaphroditicahave plagued actual confirmation of hypohydrophily. Evidence from paternity exclusion analysis using random amplified polymorphic DNA markers is presented that confirms hypohydrophily inC. hermaphroditica.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb13817.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Cephalanthus occidentalisL. is protandrous and presents pollen secondarily on the stigma surface. Because self‐pollen is present on the stigma, the degree of selling vs. outcrossing in this species will depend on 1) the phenology of pollen presentation and stigma receptivity; 2) whether the species is self‐incompatible; and 3) the rates of self vs. crossed pollen tube growth. This study describes floral morphology and phenology, self‐incompatibility, and pollen tube growth rates in self‐ and crosspollinations ofC. occidentalis.Light and scanning electron microscopy were used to study stigma morphology after flower opening, while controlled pollinations tested for incompatibility. Stigmas were unreceptive initially but became receptive by the second day after flower opening. Ninety‐two percent of cross‐pollinated flowers set fruit, compared to 12% fruit set in self‐pollinations. Pollen tubes from selfed and out‐crossed pollen initially had similar growth rates. Out‐crossed pollen tubes began to grow rapidly ca. 5 hr after pollination of a receptive stigma, whereas selfed pollen tubes ceased growth or grew slowly after this time. Pollen tubes from out‐crossed pollen grew the length of the style within 24 hr after pollination, while selfed pollen tubes were inhibited at the stigma‐style junction. Our results indicate thatC. occidentalishas selfincompatibility, in addition to protandry and secondary pollen presentation. Protandry allows removal of self‐pollen from the unreceptive stigma, while self‐incompatibility prevents fertilization by unremoved self‐pollen.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb13818.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

The relative importance of age and size as predictors of demographic parameters such as survivorship or reproductive status is generally unknown for herbaceous perennials, due primarily to the difficulty in estimating the age of herbaceous plants. We investigated the relationship between age, size, and reproductive status inTrillium grandiflorum, a rhizomatous perennial herb in which age can be estimated. We measured the leaf area and rhizome volume and estimated the age of plants in a study population that included reproductive and nonreproductive individuals. Reproductive plants were significantly older ( = 22.8 years) than nonreproductive plants ( = 13.3 years). Reproductive plants also had significantly larger total leaf areas and rhizome volumes. Total leaf area, rhizome volume, and age were positively correlated in both groups. Reproduction in this population occurred once plants reached a threshold leaf area or rhizome volume. Both measures of plant size, i.e., total leaf area and rhizome volume, were better predictors of plant reproductive status than was plant age.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb13819.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Structural, autofluorescent, and mechanical characteristics show that the so‐called “collar” of the stamen is an elongated basal portion of the connective inCirsium horridulum.The connective base/filament boundary is precisely demarcated by epidermal cells with thick, autofluorescent walls. In the region of the connective base near the anther lobes, the autofluorescence is less intense and the cells are longer, but wall thickness does not decrease. The autofluorescence can be assayed in fresh, frozen, or rehydrated materials, and is resistant to boiling in water and to acetone. Additional features delineate the connective base from the filament. The abaxial and lateral portions of the connective base surface are relatively flat due to the underlying thick secondary walls. Ultrathin sections taken at various points along the length of the connective base and the filament show that cuticle thickness gradually increases from approximately 30 nm in the connective base to 450 nm in the filament. The connective base/filament junction appears to be a weak mechanical link within the stamen. These data establish several new connective base characteristics inCirsiumand define the connective base/filament boundary.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb13820.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

The positions at which floret primordia arise in developing capitulum buds ofMicroseris pygmaeaD. Don have been mapped by computer‐assisted light microscopy. The primordia can be assigned positions along a basic phyllotactic spiral with a divergence angle of about 137.5°. In addition, there are regular deviations from a spiral arrangement. Typically, the first 26 primordia in phyllotactic sequence are arranged in two concentric circles of 13 primordia with considerable deviations in the divergence angle and in the distances between primordia along a parastichy at positions 13 and 26. This arrangement can be simulated by geometric models that include nearest neighbor packing, together with spiral phyllotaxis. The circular arrangement of peripheral primordia at nearly equal radial distances from the center of the developing capitulum helps to explain the numerical constancy (canalization) of peripheral structures, especially the constant number of 13 inner phyllaries on heads with very different numbers of florets.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb13821.x

出版商:Wiley    

年代:1993

数据来源: WILEY

摘要:

Floral onset in soybean (Glycine maxcv. Ransom) is characterized by precocious initiation of axillary meristems in the axils of the most recently initiated leaf primordium. During floral transition, leaf morphology changes from trifoliolate leaf with stipules, to a three‐lobed bract, to an unlobed bract. Soybean flowers initiated at 26/22 C day/night temperatures are normal, papilionaceous, and pentamerous. Sepal, petal, and stamen whorls are initiated unidirectionally from the abaxial to adaxial side of the floral apex. The median sepal is located abaxially and the median petal adaxially on the meristem. The organogeny of ‘Ransom’ flowers was found to be: sepals, petals, outer stamens plus carpel, inner stamens; or, sepals, petals, carpel, outer stamens, inner stamens. The outer stamen whorl and the carpel show possible overlap in time of initiation. Equalization of organ size occurs only within the stamen whorls. The sepals retain distinction in size, and the petals exhibit an inverse size to age relationship. The keel petals postgenitally fuse along part of their abaxial margins; their bases, however, remain free. Soybean flowers initiated at cool day/night temperatures of 18/14 C exhibited abnormalities and intermediate organs in all whorls. The gynoecium consisted of one to ten carpels (usually three or four), and carpel connation varied. Fusion of keel petals was often lacking, and stamen filaments fused erratically. Multiple carpellate flowers developed into multiple pods that were separate or variously connate. Intermediate type organs had characteristics only of organs in adjacent whorls. These aberrant flowers demonstrate that the floral meristem of soybean is not fixed or limited in its developmental capabilities and that it has the potential to produce alternate morphological patterns.

ISSN:0002-9122    

DOI:10.1002/j.1537-2197.1993.tb13822.x

出版商:Wiley    

年代:1993

数据来源: WILEY