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, 97 (4), 611-21

Leaf Vascular Systems in C(3) and C(4) Grasses: A Two-Dimensional Analysis

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Leaf Vascular Systems in C(3) and C(4) Grasses: A Two-Dimensional Analysis

Osamu Ueno et al. Ann Bot.

Abstract

Background and aims: It is well documented that C(4) grasses have a shorter distance between longitudinal veins in the leaves than C(3) grasses. In grass leaves, however, veins with different structures and functions are differentiated: large longitudinal veins, small longitudinal veins and transverse veins. Thus, the densities of the three types of vein in leaves of C(3) and C(4) grasses were investigated from a two-dimensional perspective.

Methods: Vein densities in cleared leaves of 15 C(3) and 26 C(4) grasses representing different taxonomic groups and photosynthetic subtypes were analysed.

Key results: The C(4) grasses had denser transverse veins and denser small longitudinal veins than the C(3) grasses (1.9 and 2.1 times in interveinal distance), but there was no significant difference in large longitudinal veins. The total length of the three vein types per unit area in the C(4) grasses was 2.1 times that in the C(3) grasses. The ratio of transverse vein length to total vein length was 14.3 % in C(3) grasses and 9.9 % in C(4) grasses. The C(3) grasses generally had greater species variation in the vascular distances than the C(4) grasses. The bambusoid and panicoid C(3) grasses tended to have a denser vascular system than the festucoid C(3) grasses. There were no significant differences in the interveinal distances of the three vein types between C(4) subtypes, although the NADP-malic enzyme grasses tended to have a shorter distance between small longitudinal veins than the NAD-malic enzyme and phosphoenolpyruvate carboxykinase grasses.

Conclusions: It seems that C(4) grasses have structurally a superior photosynthate translocation and water distribution system by developing denser networks of small longitudinal and transverse veins, while keeping a constant density of large longitudinal veins. The bambusoid and panicoid C(3) grasses have a vascular system that is more similar to that in C(4) grasses than to that in the festucoid C(3) grasses.

Figures

F<sc>ig</sc>. 1.
Fig. 1.
Paradermal view of cleared leaf blades of C3 and C4 grasses. (A) Digitaria sanguinalis, an NADP-ME C4 species. (B) Eleusine indica, an NAD-ME C4 species. (C) Panicum bisulcatum, a panicoid C3 species. (D) Briza minor, a festucoid C3 species. LLV, large longitudinal vein; SLV, small longitudinal vein; TV, transverse vein. The magnification of the four photomicrographs is the same. Scale bars = 250 µm.
F<sc>ig</sc>. 2.
Fig. 2.
Relationship of the distance between large longitudinal veins and that between small longitudinal veins in leaf blades of C3 and C4 grasses. Slopes of dotted lines show the ratio of the distance between small longitudinal veins (y) to that between large longitudinal veins (x). LV, longitudinal vein.
F<sc>ig</sc>. 3.
Fig. 3.
Relationship of the distance between transverse veins and that between small longitudinal veins in leaf blades of C3 and C4 grasses. Slopes of dotted lines show the ratio of the distance between small longitudinal veins (y) to that between transverse veins (x). LV, longitudinal vein; TV, transverse vein; Br, Bromus rigidus; Hi, Hymenachne indica; Os, Oryza sativa.
F<sc>ig</sc>. 4.
Fig. 4.
Comparison of the areolar area (the minimum photosynthetic tissue area surrounded by veins) in leaf blades of C3 and C4 grasses. The values were calculated from the distances between small longitudinal veins and the distances between transverse veins. The mean and s.e. are shown for the respective subgroups. Values followed by the same lower case letter are not significantly different at P < 0·05. Dg, Dactylis glomerata; Hi, Hymenachne indica.
F<sc>ig</sc>. 5.
Fig. 5.
Comparison of total vein length per unit leaf area in leaf blades of C3 and C4 grasses. The mean and s.e. are shown for the respective subgroups. Values followed by the same lower case letter are not significantly different at P < 0.05.
F<sc>ig</sc>. 6.
Fig. 6.
Comparison of the ratio of transverse vein length to total vein length per unit leaf area in leaf blades of C3 and C4 grasses. The mean and s.e. are shown for the respective subgroups. Values followed by the same lower case letter are not significantly different at P < 0·05.
F<sc>ig</sc>. 7.
Fig. 7.
Comparison of the number of transverse veins per unit leaf area in leaf blades of C3 and C4 grasses. The mean and s.e. are shown for the respective subgroups. Values followed by the same lower case letter are not significantly different at P < 0·05.

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