The instantaneous rate of photosynthetic CO2 assimilation in C3 plants has generally been studied in model systems such as isolated chloroplasts and algae. From these studies and from theoretical analyses of gas exchange behavior it is now possible to study the biochemistry of photosynthesis in intact leaves using a combination of methods, most of which are nondestructive. The limitations to the rate of photosynthesis can be divided among three general classes: (1) the supply or utilization of CO2, (2) the supply or utilization of light, and (3) the supply or utilization of phosphate. The first limitation is most readily studied by determining how the CO2 assimilation rate varies with the partial pressure of CO2 inside the leaf. The second limitation can be studied by determining the quantum requirement of photosynthesis. The third limitation is most easily detected as a loss of O2 sensitivity of photosynthesis. Measurement of fluorescence from intact leaves can give additional information about the various limitations. These methods are all non-destructive and so can be observed repeatedly as the environment of a leaf is changed. In addition, leaves can be quick-frozen and metabolite concentrations then measured to give more information about the limitations to intact leaf photosynthesis rates. In this review the physics and biochemistry of photosynthesis in intact C3 leaves, and the interface between physiology and photosynthesis—triose phosphate utilization—are discussed.

Photosynthesis in intact leaves of C3 plants: Physics, physiology and rate limitations

Simulations using a biochemically-based model of leaf photosynthesis make it possible to predict the distribution of leaf nitrogen contents that maximizes photosynthetic carbon gain over the canopy of an entire plant. In general, the optimal nitrogen content increased with increasing daily photosynthetically active photon irradiance.

Allocating leaf nitrogen for the maximization of carbon gain: Leaf age as a control on the allocation program.

The hydraulic conductance of the leaf lamina (Klamina) substantially constrains whole-plant water transport, but little is known of its association with leaf structure and function. Klamina was measured for sun and shade leaves of six woody temperate species growing in moist soil, and tested for correlation with the prevailing leaf irradiance, and with 22 other leaf traits. Klamina varied from 7.40 × 10−5 kg m−2 s−1 MPa−1 for Acer saccharum shade leaves to 2.89 × 10−4 kg m−2 s−1 MPa−1 for Vitis labrusca sun leaves. Tree sun leaves had 15–67% higher Klamina than shade leaves. Klamina was co-ordinated with traits associated with high water flux, including leaf irradiance, petiole hydraulic conductance, guard cell length, and stomatal pore area per lamina area. Klamina was also co-ordinated with lamina thickness, water storage capacitance, 1/mesophyll water transfer resistance, and, in five of the six species, with lamina perimeter/area. However, for the six species, Klamina was independent of inter-related leaf traits including leaf dry mass per area, density, modulus of elasticity, osmotic potential, and cuticular conductance. Klamina was thus co-ordinated with structural and functional traits relating to liquid-phase water transport and to maximum rates of gas exchange, but independent of other traits relating to drought tolerance and to aspects of carbon economy.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.0016-8025.2003.01058.x

The ‘hydrology’ of leaves: co‐ordination of structure and function in temperate woody species

The design and function of leaf venation are important to plant performance, with key implications for the distribution and productivity of ecosystems, and applications in paleobiology, agriculture and technology. We synthesize classical concepts and the recent literature on a wide range of aspects of leaf venation. We describe 10 major structural features that contribute to multiple key functions, and scale up to leaf and plant performance. We describe the development and plasticity of leaf venation and its adaptation across environments globally, and a new global data compilation indicating trends relating vein length per unit area to climate, growth form and habitat worldwide. We synthesize the evolution of vein traits in the major plant lineages throughout paleohistory, highlighting the multiple origins of individual traits. We summarize the strikingly diverse current applications of leaf vein research in multiple fields of science and industry. A unified core understanding will enable an increasing range of plant biologists to incorporate leaf venation into their research.

https://nph.onlinelibrary.wiley.com/doi/pdf/10.1111/nph.12253

Leaf venation: structure, function, development, evolution, ecology and applications in the past, present and future

Evolution and Function of Leaf Venation Architecture: A Review

THE MORE CONSPICUOUS differences between sun and shade leaves are well known and references in this field are numerous. Many papers have dealt more or less critically with the structural features shown by cross sections of the lamina; several of these consider environmental factors and a few take into account the vascularization of the blade. A recent paper by the writer (Wylie, 1949) summarizes briefly some related papers in this field in connection with a comparative study of leaf organization at four stations in the crown of a single tree (Acer platanoides). The general structural concept of the foliage leaf has been largely based upon the study of transections of the blade. Early students had only freehand sections and later workers, with modern histological methods available, have based most of their findings on transections. These show favorably the blade thickness and the depth of its several layers as well as the form of individual palisade cells but afford little information about the spongy mesophyll or the general relations of its cells. Paradermal sections, cut in the plane of the blade, supplement by showing the size and shape of epidermal cells, stomatal distribution and the inter-relations of palisade cells, together with critical information on the structure of the spongy mesophyll. These sections also favor study of the minor venation, which is closely associated with the spongy mesophyll, and permit measurement of the vascularization. The present paper summarizes a survey of the blade tissues for ten species of deciduous woody dicotyledons, using leaves from three widely spaced stations in the crown of each tree. The purpose of the study, in addition to obtaining information on the structure and relative volume of the several tissues at the different stations, was to review their tissuemodifications and shifts in vascularization in relation to problems of foliar organization. MATERIALS AND METHODS.-Of these ten species, listed in table 1, six are native to Iowa; two, Liquidamber styracifiua and Catalpa,speciosq, are of southern range, while Acer platanoides and Lonicera tatarica are introduced north temperate plants. This series is a heterogeneous assemblage, selected in part because of problems presented by the structure of their sun leaves. Catalpa, and several others in lesser degree, have a vertical trend among their spongy mesophyll cells. Others, including the oaks, Acer platanoides, and Catalpa, have a dominant palisade, and a majority of them have patterns of spongy mesophyll differing from that of typical mesophytic foliage. Ulmus americana was included for various reasons primarily to learn more about the puzzling leaf of this widely distributed tree. While Acer platanoides had been previously sur-

Principles of foliar organization shown by sun-shade leaves from ten species of deciduous dicotyledonous trees

The role of the epidermis in foliar organization and its relations to the minor venation

IN LEAVES of many dicotyledons, vertical layers of colorless cells are often closely associated with certain of the lesser veins. These are obvious in transections of the blade and appear as columns or sheets of cells depending upon their angle to the plane of the section. While lacking in many species they are found in leaves of both herbaceous and woody plants of temperate and tropical regions and are most common in leaves of northern deciduouis trees. More or less similar specializations are often associated with the veins in other broadleaved vascular plants.

The bundle sheath extension in leaves of dicotyledons

THIS PAPER deals with certain relations between leaf structure and the distribution of minor veins in the blade. In connection with work on the wound responses of foliage leaves the writer built up several series of slides which were equally favorable for the study of normal leaf tissues. It seemed from reviewing these preparations that vein spacing was often related to mesophyll organization. A careful analysis of leaves of three series of plants seemed to confirm this generalization and revealed a fairly close correlation between the photosynthetic and conductive tissue of the blade in these species. Several investigations have dealt quantitatively with the development of the minor venation in the leaf blade. Zalenski (1902), using leaves cleared in chloral hydrate and mounted in glycerin, called attention to variations in total length of vein per unit area in plants of given species even in similar habitats. This led to his later paper (1904), which is discussed at length by Maximov. He demonstrated a wide range in the structure of leaves distributed vertically along a single stem. On shrubby or herbaceous plants of moderate size he found leaves of higher insertion successively more xeromorphic with progressively greater vein length per unit area than those lower on the same stem. While this feature was associated with several other structural differences in the leaves investigated, he considered these vein specializations as most closely correlated with cell size in the different leaves. Schuster (1908) surveyed a considerable number of plants, giving attention to differences between sun and shade leaves. With few exceptions, shade leaves were larger than sun leaves of the same species, but the shaded leaves had reduced venation, in terms of total vein length per unit area of blade, compared with those in the sun. Benedict (1915) made an intensive vein study of a few plants but concerned himself particularly with ritis vulpina. He held that vein spacing (which he termed the vein-islet) for leaves of this species was correlated closely with the plant's age, diminishing regularly through successive years after the launching of a new plant from an embryo started by fertilization. His records were made photographically by transmitted light, using untreated living leaves, which method probably failed to record some of the lesser veinlets. While he noted the earlier work of Zalenski (1902), he does not include the very important paper by that writer published in 1904. Strain (1933) recently made a study of the types of vascular elements in the vein endings of a large number of species, by clearing whole leaves, cotyledons, and petals. He finds type patterns of tracheal organization rather than variations due to environ-

Robert B. Wylie

Papers

Principles of foliar organization shown by sun-shade leaves from ten species of deciduous dicotyledonous trees

The role of the epidermis in foliar organization and its relations to the minor venation

The bundle sheath extension in leaves of dicotyledons

Relations between tissue organization and vein distribution in dicotyledon leaves

The major veins of mesomorphic leaves