Leaflet Angle Research Articles

Light‐Induced Leaflet Orientation in Phaseolus vulgaris L.1

The effect of light on change of leaflet angle of attached and detached leaves of four cultivars of dry beans (Phaseolus vulgaris L.) was measured. Light receptor and response site were both found to be the pulvinule at the base of each leaflet. All three pulvinules of the trifoliolate leaf responded. Light impinging on the top of pulvinules of all varieties caused them to bend upward, i.e. toward the light. This rotated attached leaflets upward, orienting them more parallel to the overhead source‐direction of the light. Light from the side also caused the pulvinules of all four varieties to bend toward the light. However, the more prominent response to light impinging upon the side of pulvinules was a twisting of the pulvinule which, with reference to the light source, rotated the far side of the leaflet upward and the near side downward. This positioned the leaflets more perpendicular to the horizontal source‐direction of the light. Thus, light from the side caused the leaflets to orient themselves so that they would intercept more light energy, whereas light from above oriented them so that they would intercept less. The four varieties differed in amount and type of leaf orientation under a given light intensity. For one variety only, in addition to causing the pulvinule to bend toward the light, light impinging upon the top of the pulvinule also caused it to twist. With this variety, both responses oriented leaflets more parallel to the overhead source‐direction of the light, with the result that the leaflets would intercept less light energy.It is hypothesized that leaf characters maximizing both pulvinule exposure to light and the leaf‐orientation response would maximize light penetration into the leaf canopy and lead to higher photosynthetic rates, especially at close spacings with high leaf area index.

Rhythmic Leaflet Movement in Albizzia julibrissin

The rhythmic movement of darkened Albizzia leaflets is accompanied by K(+) flux in pulvinule motor cells whose turgor changes control opening and closing. The azide-sensitive open phase is promoted by an increase in temperature from 16 to 33C (Q(10) = 3), implying active transport of K(+) ions during this period. The azide-insensitive closed phase is less temperature-sensitive and has a Q(10) less than 1, implying diffusion or some other physical process as the predominant pathway of K(+) flux at this time. Thus rhythmic leaflet movement is probably due to oscillation in active K(+) transport or membrane permeability or both. External electrolytes (0. 1 n) alter leaflet angle during the open, but not the closed, phase of the rhythm. All chlorides except NH(4) (+) promote opening, with divalent more effective than monovalent ions. Some anions promote and others inhibit opening; activity is not correlated with charge. It is likely that electrolytes alter leaflet movement by altering K(+) flux, accomplishing this by interacting with key macromolecules in motor cell membranes.Pfr phytochrome dampens the amplitude of rhythmic leaflet movement; this process is temperature sensitive (Q(10) = 2) and unaltered by 0.1 n salt solutions. Although K(+) flux is a common basis for phytochrome and rhythmic control of leaflet movement, different mechanisms are clearly involved.

Phytochrome-controlled Nyctinasty in Albizzia julibrissin

Indole-3-acetic acid, alpha-naphthylacetic acid, and 2,4-dichlorophenoxyacetic acid (0.001 to 1.0 mm) inhibit the nyctinastic closure of excised Albizzia leaflet pairs; antiauxins and auxin analogs are ineffective, and the auxin effects seem not to be mediated by ethylene. Indoleacetic acid (0.001 to 0.1 mm) also promotes rhythmic opening in the dark, but is ineffective during that phase of rhythmic closure ("leaky phase") which is insensitive to azide. At these concentrations, all of the indoleacetic acid effects are reversible upon transfer of the tissue to water and are linked to alteration of potassium flux in pulvinule motor cells.A supraoptimal concentration of indoleacetic acid (1 mm) inhibits rhythmic opening as well as nyctinastic closure, although it has little or no effect on potassium flux in motor cells. These inhibitions cannot be completely reversed by transferring the leaflets to water.Although indoleacetic acid (0.01 to 1.0 mm) inhibits leaflet opening and potassium flux in dorsal and ventral motor cells when leaflets are transferred from darkness to light, it has no effect during other portions of the light period, implying that changes in endogenous auxin do not control leaflet angle in the light. Neither does auxin seem to be involved in the phytochrome-regulated process, since it does not alter phytochrome control of leaflet movement or potassium flux. However, endogenous auxin probably plays an important role in controlling potassium flux into ventral motor cells during the opening phase of rhythmic leaflet movement in the dark.