Pieruschka, Roland; Schurr, Ulrich; Jensen, Manfred; Wolff, Wilfried F.; Jahnke, Siegfried:

Lateral diffusion of CO2 from shaded to illuminated leaf parts affects photosynthesis inside homobaric leaves.

In: New phytologist : international journal of plant science, Jg. 169 (2006), S. 779–788
ISSN: 0028-646X
Zeitschriftenaufsatz / Fach: Biologie
Abstract:
Gas exchange is generally regarded to occur between the leaf interior and ambient
air, i.e. in vertical (anticlinal) directions of leaf blades. However, inside homobaric
leaves, gas movement occurs also in lateral directions. The aim of the present study
was to ascertain whether lateral CO
2
diffusion affects leaf photosynthesis when
illuminated leaves are partially shaded.
• Measurements using gas exchange and chlorophyll fluorescence imaging
techniques were performed on homobaric leaves of
Vicia faba
and
Nicotiana tabacum
or on heterobaric leaves of
Glycine max
and
Phaseolus vulgaris
.
• For homobaric leaves, gas exchange inside a clamp-on leaf chamber was affected
by shading the leaf outside the chamber. The quantum yield of photosystem II (
Φ
PSII
)
was highest directly adjacent to a light/shade border (LSB).
Φ
PSII
decreased in the
illuminated leaf parts with distance from the LSB, while the opposite was observed
for nonphotochemical quenching. These effects became most pronounced at low
stomatal conductance. They were not observed in heterobaric leaves.
• The results suggest that plants with homobaric leaves can benefit from lateral
CO
2
flux, in particular when stomata are closed (e.g. under drought stress). This may
enhance photosynthetic, instead of nonphotochemical, processes near LSBs in such
leaves and reduce the photoinhibitory effects of excess light.

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