Photosynthesis - beyond the leaf

Abstract

Although leaves are considered the main site for photosynthesis, other green nonfoliar tissues can carry out considerable amounts of photosynthetic carbon assimilation. With photosynthesis, a potential target for improving crop productivity, physiology and contribution of nonfoliar tissues to overall plant carbon acquisition is gaining increasing attention. This review will provide an overview of nonfoliar photosynthesis, the role of stomata in these tissues and methodologies for quantification and the contribution to overall carbon gain.

Keywords: net CO2 assimilation rate (A); nonfoliar photosynthesis; stomatal conductance (gs); stomatal density; wheat ears.

Fig. 1

Chlorophyll fluorescence images of awned and nonawned wheat ears of (a, b) photosystem II (PSII) operating efficiency ($F_{\mathrm{q}}^{\prime }$/$F_{\mathrm{m}}^{\prime }$); (c, d) $F_{\mathrm{q}}^{\prime }$/$F_{\mathrm{v}}^{\prime }$ (PSII photochemical quenching factor); and (e, f) maximum PSII operating efficiency ($F_{\mathrm{v}}^{\prime }$/$F_{\mathrm{m}}^{\prime }$). Colour scale bar represents 0.4–0.6 for $F_{\mathrm{q}}^{\prime }$/$F_{\mathrm{m}}^{\prime }$ and 0.5–0.85 for $F_{\mathrm{q}}^{\prime }$/$F_{\mathrm{v}}^{\prime }$ and $F_{\mathrm{v}}^{\prime }$/$F_{\mathrm{m}}^{\prime }$.

Fig. 2

Example of photosynthetic activity in Cameor pea pods and leaves. Mean (a) pod and (b) leaf assimilation (A), (c) pod and (d) leaf stomatal conductance (g _s) was measured in response to a step in light intensity from 100 to 1000 μmol m⁻² s⁻¹ photosynthetic photon flux density (PPFD), at 400 ppm CO₂ and 23°C within a bespoke pod chamber. Grey shaded areas represent when the light source is at 100 μmol m⁻² s⁻¹ PPFD. Error bars represent mean ± SE (n = 3). All measurements are normalized to an illuminated projected area (typically used for leaves). (e) Chlorophyll fluorescence image of photosystem II operating efficiency ($F_{\mathrm{q}}^{\prime }$/$F_{\mathrm{m}}^{\prime }$) was used to demonstrate differences in efficiency between the two tissue types. Colour scale bar represents an $F_{\mathrm{q}}^{\prime }$/$F_{\mathrm{m}}^{\prime }$ of 0.5–0.8. Example of a (f) pod and (g) leaf epidermal impression at a 200× magnification.

Fig. 3

Example of epidermal impressions showing stomata from a barley (a) lemma and (b) awn and a wheat (c) awn and (d) glume.

Fig. 4

Thermal images of wheat ears which demonstrate functional difference due to variation in stomatal density (SD): (a) SD of 12 mm⁻² and (b) 35 mm⁻². Measurements were made following 1 h exposure to 27°C. Colour scale bar represents a difference in temperature from 15°C to 29°C.