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81.
The ability of leaves to acclimate photosynthetically to low temperature was examined during leaf development in winter rye plants ( Secale cereale L. cv. Puma) grown at 20°C or at 6°C. All leaves grown at 6°C exhibit increased chlorophyll (Chl) levels per leaf area, higher rates of uncoupled, light-saturated photosystem I (PSI) electron transport, and slower increases in photosystem II (PSII) electron transport capacity, when compared with 20°C leaves. The stoiehiometry of PSI and PSII was estimated for each leaf age class by quantifying Chl in elcctrophorctic separations of Chl-protein complexes. The ratio of PSII/PSI electron transport in 20°C leaves is highly correlated with the ratio of core Chl a -proteins associated with PSII (CPa) to those associated with PSI (CP1). In contrast, PSII/PSI electron transport in 6°C leaves is not as well correlated with CPa/CP1 and is related, in part, to the amount and organization of light-harvesting Chl a/b -proteins associated with PSII. CPa/CP1 increases slowly in 6°C leaves, although the ratio of CPa/CP1 in mature 20°C and 6°C leaves is not different. The results suggest that increased PSI activity at low temperature is not related to an increase in the relative proportion of PSI and may reflect, instead, a regulatory change. Photosynthetic acclimation to low environmental temperature involves increased PSI activity in mature leaves shifted to 6°C. In leaves grown entirely at 6°C, however, acclimation includes both increased PSI activity and modifications in the rate of accumlation of PSII and in the organization of LHCII. 相似文献
82.
The gas exchange properties of whole plant canopies are an integral part of crop productivity and have attracted much attention
in recent years. However, insufficient information exists on the coordination of transpiration and CO2 uptake for individual leaves during the growing season. Single-leaf determinations of net photosynthesis (Pn), transpiration
(E) and water use efficiency (WUE) for field-grown cotton (Gossypium hirsutum L.) leaves were recorded during a 2-year field study. Measurements were made at 3 to 4 day intervals on the main-stem and
first three sympodial leaves at main-stem node 10 from their unfolding through senescence. Results indicated that all gas
exchange parameters changed with individual main-stem and sympodial leaf age. Values of Pn, E and WUE followed a rise and
fall pattern with maximum rates achieved at a leaf age of 18 to 20 days. While no significant position effects were observed
for Pn, main-stem and sympodial leaves did differ in E and WUE particularly as leaves aged beyond 40 days. For a given leaf
age, the main-stem leaf had a significantly lower WUE than the three sympodial leaves. WUE's for the main-stem and three sympodial
leaves between the ages of 41 to 50 days were 0.85, 1.30, 1.36 and 1.95 μmol CO2 mmol−1 H2O, respectively. The mechanisms which mediated leaf positional differences for WUE were not strictly related to changes in
stomatal conductance (gs·H2O) since decreases in gs·H2O with leaf age were similar for the four leaves. However, significantly different radiant environments with distance along
the fruiting branch did indicate the possible involvement of mutual leaf shading in determining WUE. The significance of these
findings are presented in relation to light competition within the plant canopy during development. 相似文献
83.
When pea (Pisum sativum L.) embryos were cultured on low osmotica, with or without added abscisic acid (ABA), there was very little change in the
total mRNA translation products resolved by one-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE).
The only marked alteration was an increase in production of two low-molecular-weight proteins. The purification and partial
characterisation of these two ABA-responsive seed proteins (ABR17 and ABR18) is described. Both proteins were purified to
homoeneity, as judged by SDS-PAGE, from embryos cultured in the presence of ABA. Antisera were raised against both proteins.
Each serum cross-reacted with the other protein, indicating that the proteins are closely related. Their apparent molecular
masses (Mrs) were estimated to be 17200 (ABR17) and 18100 (ABR18) by SDS-PAGE, and 26000 by gel filtration. Both proteins were heterogeneous
on isoelectric focusing. Neither protein was detected (by immunoblotting or immunoprecipitation of cell-free translation products)
in embryos grown in vivo at early to mid-development stages but both were present in embryos late in development. These proteins
appear to be produced late in seed development but are capable of being induced early in development by culturing embryos
in vitro and are markedly enhanced by ABA. 相似文献
84.
Shape variations in the dentition and the cranium were analyzed for sevenSaguinus forms of the hairy-face tamarin by applying the factor analysis method. The results obtained for the dental and cranial measurements
were almost consistent with each other.
The magnitude of the difference in shape factors between theS. nigricollis group and theS. midas group is appreciably larger than that between the former group and theS. mystax group. If the ancestral geographic centre of origin is postulated as being within the region which is inhabited by the livingS. nigricollis group, the morphological distances between any pairs of groups correlate well with the geographic distances between them.
Concerning the dental and cranial morphologies, the physical changes in the three species group probably took place in two
directions; that is, from theS. nigricollis group to theS. mystax group, and from theS. nigricollis group to theS. midas group.
The forms belonging to each species group are more closely related to each other, with the exception ofS. imperator in theS. mystax group. The uniqueness ofS. imperator was clearly demonstrated by factor analysis and distance analysis. In theS. mystax group, although still hypothetical,S. imperator may have been related only through the basic ancestral stock toS. labiatus andS. mystax. 相似文献
85.
Robert M. Netting M. Priscilla Stone Glenn D. Stone 《Human ecology: an interdisciplinary journal》1989,17(3):299-319
Amid discussions of an agricultural crisis and the failure of largescale, mechanized, capitalintensive development schemes in Nigeria, the Kofyar of Plateau State provide a case study of farmers spontaneously expanding food crop production for the market, using indigenous lowenergy technology. Temporary, followed by permanent, migration from the Jos Plateau homeland to frontier settlements on the fertile Benue plains has been accompanied by a change from initial shifting cultivation in forest clearings to permanent, intensively tilled and fertilized homestead fields. Labor is organized primarily in households that have grown in size and complexity. Cooperative and exchange work groups are also important for meeting seasonal bottlenecks and providing the careful, disciplined cultivation that intensive agriculture requires. Kofyar now devote up to 50% of their labor to cash crops, and they purchase considerable quantities of manufactured goods and medical services. Their uncoerced adaptation to an environment of new land resources and market incentives suggests both the advantages of indigenous development with a minimum of state control or interference and the limitations of a conventional dependency theory perspective. 相似文献
86.
Ramon J. Rhine Guy W. Norton Gail M. Wynn Roger D. Wynn 《International journal of primatology》1989,10(4):319-342
Focal-animal feeding data obtained from 64 adult baboons during a 3-year period were used together with equivalent data from
46 infants to evaluate hypotheses predicting selection for a birth peak and to study the baboon’s eclectic/selective feeding
adaptation, with emphasis on differential feeding by sex, developmental trends, and seasonal use of food classes (fruit, leaf,
flower, grass, etc.). The findings suggest that feeding conditions are better in the wet season than in the dry season. Despite
large sexual dimorphism, estimates of total amounts eaten were virtually identical for males and females. Infants used all
of the same plant-food classes as adults, but proportional differences occurred for some food classes in amounts eaten. Foods
eaten proportionately less by infants were probably harder for them to obtain and process or were chosen through inexperience
or for exploration. There was considerable between-year variation in amounts of food classes eaten, but the within-year standard
deviations were similar, as were also the mean amounts eaten per year. An eclectic/selective feeding adaptation has the advantage
of permitting long-run acquisition of adequate nutrition within a context of high feeding variation from season to season
and year to year. Mixed results were obtained from hypotheses about selection for a birth peak. Although a peak occurred in
the early dry season, this was not the optimal time of birth for survival. Survival was highest for individuals born in the
late wet season, when the availability and probably the quality of food for lactating mothers were greatest. 相似文献
87.
88.
Calli of P. argentatum were grown on a newly designed liquid nutrient flow-through system which facilitated the subculturing of calli and delayed
browning for 6 weeks. Friable calli were obtained on half-strength Gamborg B5-medium supplemented with 0.05 mgl−1 2,4-dichlorophenoxyacetic acid. Shoots developed on media supplemented with 0.2 mgl−1 benzylaminopurine but lacking 2,4-dichlorophenocyacetic acid. 相似文献
89.
Summary Two pairs of ganglia are found in the propodial region of the veliger of Onchidoris bilamellata: the anterolateral pair is located at the foremost corners of the propodium, and the frontal pair is located beside the propodial midline. Both sets of ganglia are positioned below the epidermis, and they are joined to the cerebral ganglia by large, common connectives. Each ganglion possesses sensory cells, nerve cells and sheath cells, and the frontal pair contains a complement of secretory cells. Externally, the propodial ganglia are manifested as sensory fields. The fields of the anterolateral pair are elliptical in shape, and each appears as a band of cilia bordering an unciliated zone. The region devoid of cilia is composed of ordinary epidermal cells, whereas the ciliated portion is comprised of dendritic endings originating from cells in the ganglion. Dendrites arise from one type of sensory cell and pass through the epidermis in bundles. Each dendrite terminates as a single cilium at the epidermal surface. Sensory fields of the frontal ganglia are key-shaped and oppose one another on the anterior end of the foot. Each field appears as a flat, circular, unciliated region which extends into a ciliated groove that runs dorsally toward the mouth. The groove contains the terminals of secretory cells, ciliated sensory cells, and the cell bodies of nonciliated sensory cells. The nonciliated sensory cells, characterized by a microvillous apex, are the dominant cells in the flattened circular zone. The space between the frontal ganglia and the epidermis is bridged by bundles of processes which are similar to those of the anterolateral ganglia. However, these tracts contain collections of the apical processes of secretory cells, the dendrites of ciliated sensory cells, and the axons of nonciliated sensory cells. Morphological and behavioral evidence indicates that the propodial ganglia serve a chemosensory function during settlement and metamorphosis. 相似文献
90.
A classification scheme for those population models which allow variation in development rates is proposed, based on two ways of modifying standard age-structured models. The resulting classes of models are termed development index models and sojourn time models. General formulations for the two classes of models are developed from two basic balance equations, and numerous specific models from the literature are shown to fit into the scheme. Concepts from competing risks theory are shown to be important in understanding the interplay between mortality and maturation. Relationships among the classes are investigated both for the most general forms of the models and for the simpler forms often used. The scheme can provide guidance in developing appropriate insect population models for specific modelling situations.Contribution 3878871 相似文献