Inclination of sun and shade leaves influences chloroplast light harvesting and utilization

Abstract

1997. Inclination of sun and shade leaves influences chloropiast light harvesting and utilization. -Physiol. Plant. 99; 395-404.Light harvesting and utilization by chloroplasts located near the adaxial vs the abaxial surface of sun and shade leaves were examined by fluorometry in two herbaceous perennials that differed in their anatomy atid leaf inclination. Leaves of Thermopsis montana had well-developed palisade and spongy mesophyl! whereas the photosynthetic tissue of Smiladna stellata consisted of spongy mesophyll only. Leaf orientation depended upon the irradiance during leaf development. When grown under low-light levels, leaves of S. stellata and T. montana were nearly horiiontal, whereas under high-light levels, S. stellata leaves and T. montana leaves were inclined 60° and 30°, respectively. Leaf inclination increased the amount of light that was intercepted by the lower leaf surfaces and affected the photosynthetic properties of the chloroplasts located near the abaxial leaf surface. The slowest rates of quinone pool reduction and reoxidation were found in chloroplasts located near the adaxial le^ surface of T. montana plants grown tmder high light, indicating large quinone pools in these chloroplasts. Chloroplasts near the abaxia! surface of low-light leaves had lower light utilization capacities as shown by photochemical quenching measurements. The amount of photosystem D (PSII) down regulation, measured bom each leaf surface, was also found to be influenced by irradiance and leaf inclination. The greatest difference between down regulation monitored from the adaxial vs abaxial surfaces was fotind in plants with horizontal leaves. Different energy dissipation mechanisms may be employed by the two species. Values for down regulation in S. stellata were 2-3 times higher than those in T. montana, while the portion of the PSII populadoB which was found to be QB nonreducing was 4-6 times lower in high light S. stellata leaves than in T. montana. All values of Stem-Volmer type nonphotochemical quenching (NPQ) from S. stellata leaves were similar when quenching analysis was performed at actinic irradiances that were higher thaji the iiradiance to which the leaf surface was exposed during growth. In contrast, with T. montana, NPQ values from the abaxial leaf surface were up to 45% higher than those from the adaxial leaf surface regardless of growth conditions. The observed differences in chloroplast properties between species and between the adaxia! and abaxia! leaf surfaces may depend upon a complex interaction among light, leaf anatomy and leaf isclination.

From thallus to communities: scale effects and photosynthetic performance in macroalgae communities

“…5). This finding corresponds closely to the theories from terrestrial ecology where erectophile canopies utilise light more efficiently than planophile canopies (Russel et al 1990, Myers et al 1997. The high community photosynthesis of Ahnfeltia compared to its low thallus photosynthesis can only be caused by a better distribution and utilisation of light, which accords with the fact that Ahnfeltia has a rigid structure that can keep the individual thallus parts well apart, create penumbras and, thus, prevent direct shading (Stenberg 1998).…”

“…Changes in the P-I curves are caused by the complex distribution of irradiance in the foliage that influences light interception and can vary depending on the size, density and especially inclination of leaves (McMillen & McClendon 1979, Oker-Blom & Kellomäki 1983, Myers et al 1997. This is well documented for terrestrial plants, but has received only little attention in aquatic plant communities.…”

Importance of structure and density of macroalgae communities (Fucus serratus) for photosynthetic production and light utilisation

“…The arrangement of leaves in terrestrial canopies makes them more efficient in converting incident photons to oxygen evolution and carbon assimilation than aquatic canopies. High efficiencies are attained in dense terrestrial canopies of broad-leaf canopies with a vertical orientation of leaves in the upper canopy and a horizontal orientation in the lower canopy (Myers et al 1997, Smith et al 1997 and in canopies of conifers with slender needles placed in clumps in a complex spatial pattern (Oker-Blom & Kellomäki 1983, Ceulemans & Saugier 1991. The relatively even distribution of light with depth in many terrestrial communities means that most leaves are exposed to low light, and can absorb and utilise photons at high efficiency on the light-limited part of the production-light response curve.…”

“…A common canopy structure in terrestrial plants conducive to efficient light utilisation and high community production is a vertical leaf orientation at high light in the upper part of the canopy and a horizontal leaf orientation at low light in the lower part of the canopy (Russell et al 1990, Myers et al 1997. A vertical leaf orientation, characterised by a high leaf angle (␦, angle between the sun and the normal to the leaf surface) relative to the incoming photon flux density (I 0 ), will markedly reduce the photon flux density received per unit of leaf surface area (I L = I 0 cos␦) by distributing incident light at the planar surface over a large leaf surface.…”

Variabilidade fenotípica de Rumohra adiantiformis (G. Forst) Ching (Dryopteridaceae)

“…A inclinação vertical das folhas também se relaciona com a redução do excesso de luz incidida na face adaxial, principalmente nas horas mais quentes do dia, além de permitir maior incidência de luz na superfície abaxial (DeLucia et al 1991, Myers et al 1997. No entanto, folhas com esta inclinação, geralmente, apresentam mesofilo isobilateral ou homogêneo, formado por parênquima paliçádico bem desenvolvido e/ou parênquima lacunoso compacto, além de apresentarem estômatos em ambas as faces (Poulson & DeLucia 1993).…”