ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb01957.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A brief review of the photosynthetic apparatus of higher plants is given, followed by a consideration of the modifications induced in this apparatus by changes in light intensity and light quality. Possible strategies by which plants may optimize photosynthetic activity by both long‐ and short‐term modifications of their photosynthetic apparatus in response to changing light regimes are discus

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb01958.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The effects of environmental factors on stomatal behaviour are reviewed and the questions of whether photosynthesis and transpiration eontrol stomata or whether stomata themselves control the rates of these processes is addressed. Light affects stomata directly and indirectly. Light can act directly as an energy source resulting in ATP formation within guard cells via photophosphorylation, or as a stimulus as in the case of the blue light effects which cause guard cell H+extrusion. Light also acts indirectly on stomata by affecting photosynthesis which influences the intercellular leaf CO2concentration (Ci). Carbon dioxide concentrations in contact with the plasma membrane of the guard cell or within the guard cell acts directly on cell processes responsible for stomatal movements. The mechanism by which CO2exerts its effect is not fully understood but, at least in part, it is concerned with changing the properties of guard cell plasma membranes which influence ion transport processes. TheCimay remain fairly constant for much of the day for many species which is the result of parallel responses of stomata and photosynthesis to light. Leaf water potential also influences stomatal behaviour. Since leaf water potential is a resultant of water uptake and storage by the plant and transpirational water loss, any factor which affects these processes, such as soil water availability, temperature, atmospheric humidity and air movement, may indirectly affect stomata. Some of these factors, such as temperature and possibly humidity, may affect stomata directly. These direct and indirect effects of environmental factors interact to give a net opening response upon which is superimposed a direct effect of stomatal circadian rhythmic activity.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb01959.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Despite 100 years of research, involving many noted experimentalists, our understanding of the importance and mechanisms of phototropism is sadly incomplete. However, a renewed interest in the area has brought new minds and new approaches to the subject and there are encouraging signs of progress.

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb01960.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The evolution of air‐breathing in land crabs is associated with a progressive shift in the primary site of respiratory gas exchange from the diffusion‐limited gills used for water‐breathing, via a simple ‘cutaneous’ lung surface to the perfusion‐limited, invaginated lung described in the mountain crab,Pseudothelphusa garmani.The reduced diffusion limitation over the lungs facilitates oxygen transfer from air to the tissues at lower ventilation rates but is associated with accumulation of carbon dioxide. A potential respiratory acidosis is buffered by the respiratory pigment haemocyanin and by elevation of haemolymph bicarbonate levels. These changes parallel those described in vertebrates but air‐breathing crustaceans maintain relatively low carbon dioxide levels in the haemolymph, either by retaining an aquatic route for its elimination over the reduced gills or by blowing it off across the lung. Maintenance of low carbon dioxide levels may be associated with a limited capacity to buffer against an acidosis due to low levels of circulating haemocyanin (i.e. crustaceans lack red blood cells). This may ultimately limit their survival in air as an acidosis will reduce oxygen transport due to a marked Bohr effect on haemocyanin. The primary role of an invaginated lung may be to reduce rates of wate

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb01961.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Peptide regulators are probably the most widely distributed signalling agents in the animal kingdom. They are found in both invertebrates and vertebrates where they are produced in endocrine, neuroendocrine and neuronal tissues. As more of these ubiquitous messengers have been characterized it has become evident that they may be grouped into families with clearly defined relationships. Amino acid sequences of the mature, final product indicate relationships between for example cholecystokinin (CCK) and gastrin. More detailed examination of peptide precursors can give further insights into family trees and in the case of the secretin‐vasoactive intestinal polypeptide family result in the identification of a novel co‐coded peptide. Such dual coding has led to the hypothesis of gene‐duplication in peptide evolution, a phenomenon admirably exemplified by the glucagon family and the opioid family.A further example of peptide diversity is evident when mRNA processing is examined. Here a single gene encoding two (or more) structural sequences can produce multiple mRNAs, each encoding a unique peptide sequence. The mRNA produced varies according to the tissue site. The calcitonin and Tachykinin family are fine examples with different peptides produced in neurones and endocrine tissues.A remarkable conservatism of peptide sequences is found in the insulin family where distinct relationships are evident between insulin, insulin‐related growth factors (IGF) and insect prothoracicotrophic hormone. Such relationships are supported by examination of the genes for insulin and IGF.Peptide regulators do not evolve in isolation and it is clear that their receptors are also exposed to adaptive pressures. Receptor classes for the Tachykinin family are well characterized, with receptors being identified as falling into two categories, SP‐P type and SP‐E type. Similar situations obtain for the opioids. Much of this information is based on mammalian studies, however recent work on gastrin/CCK receptors in a range of vertebrates indicates a phylogenetic diversity between brain and gu

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb01962.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Flight–defined as the ability to produce useful aerodynamic forces by flapping the wings–is one of the most striking adaptations in vertebrates. Its origin has been surrounded by considerable controversy, due in part to terminological inconsistencies, in part to phylogenetic uncertainty over the sister groups and relationships of birds, bats and pterosaurs, and in part to disagreement over the interpretation of the available fossil evidence and over the relative importance of morphological, mechanical and ecological specializations. Study of the correlation between functional morphology and mechanics in contemporary birds and bats, and in particular of the aerodynamics of flapping wings, clarifies the mechanical changes needed in the course of the evolution of flight. This strongly favours a gliding origin of tetrapod flight, and on mechanical and ecological grounds the alternative cursorial and fluttering hypotheses (neither of which is at present well‐defined) may be discounted. The argument is particularly strong in bats, but weaker in birds owing to apparent inconsistencies with the fossil evidence. However, study of the fossils of the Jurassic theropod dinosaurArchaeopteryx, the sister‐group of the stem‐group proto‐birds, supports this view. Its morphology indicates adaptation for flapping flight at the moderately high speeds which would be associated with gliding, but not for the slow speeds which would be required for incipient flight in a running cursor, where the wingbeat is aerodynamically and kinematically considerably more complex. Slow flight in birds and bats is a more derived condition, and vertebrate flapping flight apparently evolved through a gl

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb01963.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

ISSN:0024-4066    

DOI:10.1111/j.1095-8312.1988.tb01964.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY