Chlorophyll and light gradients in sun and shade leaves of Spinacia oleracea

Abstract

Abstract. Light gradients were measured and correlated with chlorophyll concentration and anatomy of leaves in spinach (Spinacia oleracea L.). Light gradients were measured at 450, 550 and 680 nm within thin (455 μm) and thick (630 μm) leaves of spinach grown under sun and shade conditions. The light gradients were relatively steep in both types of leaves and 90% of the light at 450 and 680 nm was absorbed by the initial 140 μm of the palisade. In general, blue light was depleted faster than red light which, in turn was depleted faster than green light. Light penetrated further into the thicker palisade of sun leaves in comparison to the shade leaves. The distance that blue light at 450 nm travelled before it became 90% depleted was 120 μm in sun leaves versus 76 μm in shade leaves. Red light at 680 nm and green light at 550 nm travelled further but the trends were similar to that measured at 450nm. The steeper light gradients within the palisade‐of shade leaves were caused by increased scattering of light within the intercellular air spaces and/or cells which were less compact than those in sun leaves. The decline in the amount of light within the leaf appeared to be balanced by a gradient in chlorophyll concentration measured in paradermal sections. Progressing from the adaxial epidermis, chlorophyll content increased through the palisade and then declined through the spongy mesophyll. Chlorophyll content was similar in the palisade of both sun and shade leaves. Chloroplast distribution within both sun and shade leaves was relatively uniform so that the chlorophyll gradient appeared to be caused by greater amounts of chlorophyll within chloroplasts located deeper within the leaf. These results indicate that the anatomy of the palisade may be of special importance for controlling the penetration of photo‐synthetically active radiation into the leaf. Changing the structural characteristics of individual palisade cells or their arrangement may be an adaptation that maximizes the absorption of light in leaves with varying mesophyll thickness due to different ambient light regimes.

Measurement of gradients of absorbed light in spinach leaves from chlorophyll fluorescence profiles

“…In spinach there is qualitative agreement between the depth of penetration of light, measured with a fibre-optic probe (Cui et al 1991), and corresponding chlorophyll fluorescence profiles (Fig. 12).…”

“…Despite leaf anatomical adaptations such as palisade tissue that facilitate the penetration of light (Vogelmann & Martin 1993), light gradients within leaves are relatively steep (Vogelmann, Bornman & Josserand 1989;Cui, Vogelmann & Smith 1991) implying that there may be relatively steep gradients in absorbed quanta within the mesophyll. This would lead to departure from the ideal situation where there are minimal gradients in light and CO 2 .…”

Sun-shade variation in bamboo (Poaceae: Bambusoideae) leaves

“…Leaves grown in direct sunlight are usually smaller and thicker with closer vein spacing compared to shaded leaves that are larger and thinner with more widely separated veins (e.g., Wylie 1949, 1951, Esau 1977, Cui et al 1991, Ashton & Berlyn 1994, Yano & Terashima 2004, Terashima et al 2006. Epidermal layers, especially the adaxial epidermis, are thicker in sun leaves than in shade leaves.…”

Profiles of photosynthetic oxygen‐evolution within leaves of Spinacia oleracea

“…In order to examine relationships between leaf structure and whole-leaf photosynthetic performance, it is necessary to be able to measure light, CO # and photosynthesis at the tissue level. Using microscopic light sensors inserted into leaves, it has been shown that light declines rapidly and exponentially within the leaf (Vogelmann et al, 1989 ;Cui et al, 1991 ;Vogelmann & Martin, 1993 ;Vogelmann et al, 1996). In spinach, light within the blue and red parts of the spectrum is absorbed almost completely by the initial palisade cell layers and it is primarily green light that remains for photosynthesis in tissues located deeper within the leaf (Cui et al, 1991 ;Sun et al, 1998).…”

“…Using microscopic light sensors inserted into leaves, it has been shown that light declines rapidly and exponentially within the leaf (Vogelmann et al, 1989 ;Cui et al, 1991 ;Vogelmann & Martin, 1993 ;Vogelmann et al, 1996). In spinach, light within the blue and red parts of the spectrum is absorbed almost completely by the initial palisade cell layers and it is primarily green light that remains for photosynthesis in tissues located deeper within the leaf (Cui et al, 1991 ;Sun et al, 1998). Correspondingly, the distribution of absorbed quanta across the mesophyll tissues is very steep, implying that there could be steep gradients in photosynthetic performance within the leaf (Evans, 1995).…”