Effects of pod removal on the transport and accumulation of abscisic Acid and indole-3-acetic Acid in soybean leaves

Concentrations of abscisic acid (ABA) and indole-3-acetic acid (IAA) in the second most recently expanded trifoliolate leaf were determined during reproductive development of soybean (Glycine max [L.] Merr cv `Chippewa 64'). The concentration of ABA in leaves was constant during most of the seed filling period until the seeds began to dry. The concentration of IAA in the leaves decreased throughout development. Removal of pods 36 hours prior to sampling resulted in increased concentrations of ABA in leaves during the period of rapid pod filling but had little effect on the concentration of IAA in leaves. ABA appears to accumulate in leaves after fruit removal only when fruits represent the major sink for photosynthate.

ABA and IAA moving acropetally and basipetally in petioles of soybean were estimated using a phloem exudation technique. ABA was found to move mostly in the basipetal direction in petioles (away from laminae). IAA, primarily in the form of ester conjugate(s), was found to be moving acropetally (toward laminae) in petioles. The highest amount of IAA ester(s) was found in petiole exudate during the mid and late stages of seed filling. Removal of fruits 36 hours prior to exudation reduced the amount of IAA ester recovered in exudate, suggesting that fruits were a source of the IAA conjugate in petiole exudate.

     

Ethylene and growth control in the fringed waterlily (Nymphoides peltata): Stimulation of cell division and interaction with buoyant tension in petioles

The effect of ethylene on petiole growth of the Fringed Waterlily (Nymphoides peltata (S.G. Gmelin) O. Kuntze) changes during leaf ontogeny. During early development (before expansion of laminae), ethylene causes an increase in both cell number and cell size; later in development, promotion of rapid cell expansion is the dominant effect. The early effects may contribute to the accommodation of new leaves to water columns of different depth. The later effects on cell expansion only are shown to contribute to the rapid accommodation of floating leaves when changes in water level submerge the laminae. This kind of accommodation results from an interaction between accumulated ethylene, which increases wall extensibility, and the tension in petioles due to natural buoyancy which, it is suggested, supplements the driving force for cell expansion. Cell age (position) within a petiole and age of the whole petiole influence the growth response to ethylene alone and the amount of extra growth produced by applying tension when ethylene is present. In young petioles, apical cells are highly sensitive to ethylene and tension causes little further growth; older cells in both immature and mature petioles show little response to ethylene unless the petiole is under tension. Young (but not mature) petioles respond slowly to applied tension even in the absence of ethylene. It is concluded that as cells age the driving force for expansion limits increasingly their capacity to respond to the wall-loosening effects of ethylene. Dual sensitivity to ethylene and buoyant tension facilitates rapid accommodation responses but sensitivity of young petioles to tension alone may exclude Nymphoides from habitats where current velocity is appreciable.     

Genomic fingerprinting of Frankia strains by PCR-based techniques. Assessment of a primer based on the sequence of 16S rRNA gene of Escherichia coli

Submergence stimulates elongation of the leaves of Rumex palustris and under laboratory conditions the maximum final leaf length (of plants up to 7 weeks old) was obtained within a 9 day period. This elongation response, mainly determined by petiole elongation, depends on the availability of storage compounds and developmental stage of a leaf. A starch accumulating tap root and mature leaves and petioles were found to supply elongating leaves with substrates for polysaccharide synthesis in expanding cell walls. Changes in the composition of cell wall polysaccharides of elongated petioles suggest a substantial cell wall metabolism during cell extension. Reduced starch levels or removal of mature leaves caused a substantial limitation of submerged leaf growth. From the 5th leaf onward enough reserves were available to perform submerged leaf growth from early developmental stages. Very young petioles had a limited capacity to elongate. In slightly older petioles submergence resulted in the longest final leaf lengths and these values gradually decreased when submergence was started at more mature developmental stages. Submerged leaf growth is mainly a matter of petiole elongation in which cell elongation has a concurrent synthesis of xylem elements in the vascular tissue. Mature petioles still elongated (when submerged) by cell and tissue elongation only: the annular tracheary elements stretched enabling up to 70% petiole elongation.     

Uptake and distribution of potassium in tomato plants

Summary The uptake and distribution of potassium was examined in tomato plants, cv. Amberley Cross and Moneymaker, grown in peat/loam and given a nutrient feed either adequate or deficient in potassium.Detailed studies were also made of the distribution of potassium in various parts of tomato plants, cv. Amberley Cross, grown in sand and supplied with nutrient feeds containing four and seven concentrations of potassium. In these plants the concentration of potassium in stem, petiole and laminar tissue increased from the base to the apex of plants, irrespective of the potassium concentration in the nutrient feed. There was also a gradient of decreasing potassium concentration along leaves, from proximal to distal laminae. The concentration of potassium in all plant parts increased with increasing nutrient supply of potassium, petioles showing a greater response to nutrient potassium than laminar tissue.Marginal chlorosis and/or necrosis were observed when the potassium concentration in fully expanded leaves fell below 1.2 per cent of the dry weight for cv. Amberley Cross or 1.5 per cent for cv. Moneymaker. A 50 per cent incidence of chlorosis and/or necrosis occurred in leaf laminae containing 0.74 per cent potassium.Leaves rarely showed deficiency symptoms when the concentration of potassium in the petioles was higher than that in adjacent laminar tissue. However, chlorosis and/or necrosis occurred when the potassium concentration in petioles fell below that in laminae. In the diagnosis of the potassium status of tomato plants, the most suitable tissue for sampling for potassium analysis is considered to be the petioles of young fully expanded leaves.     

GRAVITY-INDUCED EFFECTS ON MATERIAL PROPERTIES AND SIZE OF LEAVES ON HORIZONTAL SHOOTS OF ACER SACCHARUM (ACERACEAE)

The influence of gravity on the size and mechanical properties of mature leaves on horizontal shoots and etiolated seedlings of Acer saccharum Marsh. (Aceraceae) was examined. Leaves were grouped into three categories regarding their location on shoots (dorsal or “top” T, lateral or “left/right” L/R, and ventral or “bottom” B). Young's modulus E, petiole length L, lamina surface area A and weight P, and the cross-sectional areas of different tissues within petioles were measured for each leaf and were found to be correlated with leaf location (T, L/R, and B): T leaves were smaller and had lower E than their B counterparts; the size and material properties of L/R leaves were intermediate between those of T and B leaves. In general, A, P, and E decreased from the base to the tip of shoots. In addition to anisophylly, the influence of gravity induced petiole bending and torsion and resulted in the horizontal planation of laminae. This was observed for field-grown mature plants and etiolated seedlings. Petiole bending and torsion were interpreted as gravimorphogenetic phenomena. Anatomically, L, E, and petiole deflection angle Fv measured from the vertical were highly correlated with the combined cross-sectional areas of phloem fibers and xylem in petioles of B leaves and when data from all leaves were pooled. It is tentatively advanced that the correlation of E with the transverse areas of phloem fibers and xylem is evidence that either the pattern or the extent of lignification of petiole tissues is influenced by petiole position with respect to gravity.     

A mechanical perspective on foliage leaf form and function

The mechanical behaviour of large foliage leaves in response to static and dynamic mechanical forces is reviewed in the context of a few basic engineering principles and illustrated in terms of species drawn from a variety of vascular plant lineages. When loaded under their own weight or subjected to externally applied forces, petioles simultaneously bend and twist, and thus mechanically operate as cantilevered beams. The stresses that develop in petioles reach their maximum intensities either at their surface or very near their centroid axes, where they are accommodated either by living and hydrostatic tissues (parenchyma and collenchyma) or dead and stiff tissues (sclerenchyma and vascular fibres) depending on the size of the leaf and the species from which it is drawn. Allometric analyses of diverse species indicate size-dependent variations in petiole length, transverse shape, geometry and stiffness that accord well with those required to maintain a uniform tip-deflection for leaves with laminae differing in mass. When dynamically loaded, the laminae of many broad-leaved species fold and curl into streamlined objects, thereby reducing the drag forces that they experience and transmit to their subtending petioles and stems. From a mechanical perspective, the laminae of these species operate as stress-skin panels that distribute point loads more or less equally over their entire surface. Although comparatively little is known about the mechanical structure and behaviour of foliage leaves, new advances in engineering theory and computer analyses reveal these organs to be far more complex than previously thought. For example, finite-element analyses of the base of palm leaves reveal that stresses are decreased when these structures are composed of anisotropic as opposed to isotropic materials (tissues).     

Effects of leaf blade narrowness and petiole length on the light capture efficiency of a shoot

Effects of the length: width ratio of a leaf blade and petiole length on shoot light capture were studied with computer simulation. Both a larger length: width ratio and longer petiole contributed to larger light capture per unit leaf area due to a reduced aggregation of leaf area around the stem. Other conditions being equal, shoots with narrow leaves and no petioles and those with wide leaves with petioles showed similar light capture as long as the mean distance of the leaf blade from the stem was the same. In shoots with a short internode and/or distichous phyllotaxis, however, narrow leaves contributed more to avoiding mutual shading than wide leaves with petioles. The predominance of light coming from a higher angular altitude also favored narrow leaves. The possible consequences of these results in the adaptive geometry of plant architecture are discussed.     

Changes in soluble carbohydrates during phytochrome-regulated petiole elongation in watermelon seedlings

Changes in soluble carbohydrate composition and concentration in leavesand petioles of watermelon (Citrullus lanatus (Thunb)Matsum and Nakai cv. Sugar Baby) seedlings during early stages ofphytochrome-regulated petiole elongation were investigated. Watermelon seedlingswere grown in a controlled environment with 350 molm^–2 s^–1 photosynthetically activeradiation (PAR) during a 12-h photoperiod. Low intensity end-of-day(EOD) light treatments (for 15 min) of red (R), far-red (FR) and FRfollowed by R (FR/R) were initiated when the seedlings were 14 days old.Seedling growth, and soluble carbohydrate concentration and composition inleaves and petioles were determined after 3 and 6 days of EOD light treatments.The EOD FR increased the petiole length and dry mass partitioned to petioles asearly as 3 days into the treatment. This increased petiole dry mass inFR-treated plants was accompanied with an increase in reducing sugar (glucoseand fructose) concentration in the petioles. Although both leaves and petiolesshowed this effect, the relative increase was greater in petioles than leaves.While the most abundant sugars in petioles were fructose and glucose, thepredominant sugars in leaves were sucrose, raffinose, and stachyose. Thephotoreversion of FR induced changes in growth and sugar concentrations by Rindicates the involvement of phytochrome in these processes.     

冬性植物红菜薹在不同温度处理下花青素积累的分子机制

芸薹属植物红菜薹（Brassica rapa）是一种常见的蔬菜,它的花茎和叶柄表皮中均积累有花青素。为了解红菜薹中花青素合成的分子机制,进行了花青素含量的测定和花青素合成相关基因的表达分析。研究结果表明,叶柄表皮中的花青素含量显著高于叶片（去主脉）的花青素含量。同时,叶柄表皮花青素合成相关基因的表达水平高于叶柄（去表皮）和叶片（去主脉）的表达水平,这表明红菜薹中花青素的合成调控发生在转录水平。BrMYBA1仅在叶柄表皮中表达,但BrbHLH1和BrWD40在叶片和叶柄表皮中均能检测到表达。因此,BrMYBA1的转录激活可能与红菜薹的花青素合成相关。连续低温处理时,红菜薹叶柄表皮中的花青素含量逐渐增加,而该组织中花青素合成的结构基因表达水平逐渐降低。     

The functional morphology of the petioles of the banana, Musa textilis

Bananas are among the largest herbs in the world and their lightweight petioles hold up huge leaves. This study examined how the petioles manage to achieve adequate rigidity to do this, while allowing extensive and reversible reconfiguration in high winds. Morphological and anatomical examination of the petioles and leaves of Musa textilis suggested how these two apparently incompatible abilities are achieved. The hollow U-shaped section of the petiole and the longitudinal strengthening elements in its outer skin give it adequate rigidity, while its ventral curvature help support the leaf without the need for thick lateral veins. These features, however, also allow the petiole to reconfigure by twisting away from the wind, while the leaf can fold away. In addition, two sets of internal structures, longitudinal partitions and transverse stellate parenchyma plates, help prevent dorsoventral flattening, allowing the petiole to flex further away from the wind without buckling. These ideas were tested and verified by a range of mechanical tests. Simple four-point-bending and torsion tests showed that the petioles are indeed far more compliant in torsion than in bending. Axial bending tests and crushing tests showed that petioles could be flexed twice as far and were four times as resistant to dorsoventral flattening when intact than when the internal tissue is removed. The banana petiole, therefore, seems to be an excellent example of natural integrated mechanical design.     

Water Use Efficiency of Field-grown Maize during Moisture Stress

Theoretical analysis of the CO₂ assimilation and water loss by single leaves suggests that the water use efficiency of C₄ species decreases as stomatal resistance increases. To confirm this hypothesis for a complete maize crop, results from computer simulations and a field experiment were compiled for varying stomatal resistances. A soil-plant-atmosphere model allowed simulations of the many simultaneous interactions between a crop canopy and its environment. The simulations for varying stomatal resistances clearly indicated that as stomatal resistance increased, water use efficiency of the maize crop decreased. The field experiment data also confirmed that water use efficiency was significantly decreased under water stress conditions when stomatal resistance increased. We concluded that management practices for maize, which induce moisture stress conditions resulting in increased stomatal resistance, reduce both crop photosynthetic productivity and water use efficiency.     

Root Formation on Petioles of Detached Primary Leaves of Dwarf Bean (Phaseolus vulgaris) Pretreated with Gibberellic Acid, Triiodobenzoic Acid, and Cytokinins

Rooting experiments carried out with isolated primary leavesof dwarf bean demonstrated the effect of GA on increasing theIAA level and IAA synthesis. Pretreatment of the lamina of isolatedleaves with GA, especially when tryptophane was added at thesame time, strikingly increased the rooting of petioles. Enhancedroot formation on the petiole of GA-pretreated leaves can beattributed to increase of IAA level by GA in the lamina, i.e.in IAA biosynthesis the utilization of tryptophane releasedfrom the proteins of isolated leaves is promoted by GA. Application of TIBA on the upper part of petiole suppressedthe stimulatory effect of GA on root initiation presumably becauseTIBA inhibits the transport of IAA into the petiole, which resultsin failure of rooting. Pretreatment of the leaves with cytokinins also results in failureof root production. These substances retard protein decompositionin isolated leaves so that the quantity of TPP available forauxin synthesis is less. Simultaneously, this treatment increasesthe cytokinin concentration in the leaf tissues so that theauxin/cytokinin ratio alters and mainly callus forms on thebase of the petioles and differentiation of root primordia cannottake place.     

Uptake and translocation of paclobutrazol by shoots of M.26 apple rootstock

When ¹⁴C-paclobutrazol, a gibberellin synthesis inhibitor, was applied to different parts of actively-growing M.26 apple rootstock shoots it was translocated acropetally when applied to the young stem and, to a lesser extent, from the youngest unrolled leaf. Paclobutrazol was not translocated out of leaf laminae, shoot tips or from one-year-old wood but translocation occurred out of a treated petiole into the attached leaf. No basipetal translocation was detected. This translocation pattern suggested movement through the xylem.Localised application of paclobutrazol caused a reduction in shoot extension and leaf production when the young stem or shoot tip were treated; the effect decreased as older parts of the stem were treated. Treatment of laminae or petioles had only a slight effect on shoot extension and treatment of one-year-old wood was ineffective. Combined treatment of the shoot tip plus young stem was similar in effect to treatment of the complete shoot.It is suggested that paclobutrazol exerts its effects on shoot growth by inhibiting gibberellin biosynthesis in the shoot tip and the expanding leaves.The findings contribute to an understanding of the requirements for efficient orchard application of foliar sprays of paclobutrazol.     

土壤水分胁迫对燕麦叶片渗透调节物质含量的影响

以旱棚内盆栽的'内农大莜一号'燕麦品种为材料,测定了其不同水分胁迫下各生育期叶片的脯氨酸、可溶性糖含量和细胞膜相对透性,分析土壤含水量对燕麦叶片渗透调节物质的影响,以明确燕麦不同生育时期的抗旱特性.结果表明:(1)随着土壤相对含水率的下降,燕麦各生育期叶片脯氨酸含量、可溶性糖含量、细胞膜相对透性均呈上升趋势.(2)随着生育期的推进,燕麦叶片脯氨酸含量在30%和45%土壤含水量下呈持续上升趋势,而在含水量 60%、75%、90%处理下则于生育前期上升,灌浆期略有下降;随着生育期的延续,可溶性糖的含量呈先升后降的抛物线型变化,且其最大值随水分胁迫强度增加而提前,含水量 30%和45%处理的最大值均出现在拔节期,含水量60%和75%处理则分别出现在孕穗期和开花期;随着生育期的延续,各处理燕麦叶片的细胞膜相对透性均呈持续上升趋势.可见,水分胁迫能诱导燕麦叶片渗透调节物质的积累,且增幅随着胁迫强度的增加而上升,从而使燕麦表现出较强的抗旱性.     

Diurnal cycles of embolism formation and repair in petioles of grapevine (Vitis vinifera cv. Chasselas)

The impact of water deficit on stomatal conductance (g(s)), petiole hydraulic conductance (K(petiole)), and vulnerability to cavitation (PLC, percentage loss of hydraulic conductivity) in leaf petioles has been observed on field-grown vines (Vitis vinifera L. cv. Chasselas). Petioles were highly vulnerable to cavitation, with a 50% loss of hydraulic conductivity at a stem xylem water potential (Ψ(x)) of -0.95?MPa, and up to 90% loss of conductivity at a Ψ(x) of -1.5?MPa. K(petiole) described a daily cycle, decreasing during the day as water stress and evapotranspiration increased, then rising again in the early evening up to the previous morning's K(petiole) levels. In water-stressed vines, PLC increased sharply during the daytime and reached maximum values (70-90%) in the middle of the afternoon. Embolism repair occurred in petioles from the end of the day through the night. Indeed, PLC decreased in darkness in water-stressed vines. PLC variation in irrigated plants showed the same tendency, but with a smaller amplitude. The Chasselas cultivar appears to develop hydraulic segmentation, in which petiole cavitation plays an important role as a 'hydraulic fuse', thereby limiting leaf transpiration and the propagation of embolism and preserving the integrity of other organs (shoots and roots) during water stress. In the present study, progressive stomatal closure responded to a decrease in K(petiole) and an increase in cavitation events. Almost total closure of stomata (90%) was measured when PLC in petioles reached >90%.     

Translocation pathways in the petioles and stem between source and sink leaves of Populus deltoides Bartr. ex Marsh.

Microautoradiography was used to follow the translocation pathways of ¹⁴C-labeled photosynthate from mature source leaves, through the stem, to immature sink leaves three nodes above. Translocation occurred in specific bundles of the midveins and petioles of both the source and sink leaves and in the interjacent internodes. When each of six major veins in the lamina of an exporting leaf was independently spot-fed ¹⁴CO₂, label was exported through specific bundles in the petiole associated with that vein. When the whole lamina of a mature source leaf was fed ¹⁴CO₂, export occurred through all bundles of the lamina, but acropetal export in the stem was confined to bundles serving certain immature sink leaves. Cross-transfer occurred within the stem via phloem bridges. Leaves approaching maturity translocated photosynthate bidirectionally in adjacent subsidiary bundles of the petiole. That is, petiolar bundles serving the lamina apex were exporting unlabeled photosynthate while those serving the lamina base were simultaneously importing labeled photosynthate. The petioles and midveins of maturing leaves were strong sinks for photosynthate, which was diverted from the export front to differentiating structural tissues. The data support the idea of bidirectional transport in adjacent bundles of the petiole and possibly in adjacent sieve tubes within an individual bundle.Abbreviations C central leaf trace - L left leaf trace - LPI leaf plastochron index - R right leaf trace     

Development of plant cuticles: occurrence and role of non-ester bonds in cutin of Clivia miniata Reg. leaves

The effect of BF₃-methanol treatment on the mass and fine structure of isolated Clivia leaf cuticles at different stages of development has been investigated. BF₃-methanol cleaves ester linkages in cutin; however, the cuticles are not completely depolymerized. With increasing age, the residue left after BF₃-methanol treatment increases in mass. In very young cuticles, 10% of the total cutin resisted BF₃-methanol and the fraction of nonester cutin increased up to 62% in mature leaves. Transmission electron microscopy shows that fine structure of the cuticle proper is severely distorted but not destroyed. The internal cuticular layer, which exhibits a heavy contrast when fixed with KMnO₄, is completely depolymerized, while the external cuticular layer is hardly affected. The results are discussed in relation to cuticle development and to the function of cuticles as transpiration resistances.Abbreviation CP cuticle proper - ECL external cuticular layer - E cutin ester bonded cutin - ICL internal cuticular layer - MX-membrane polymer matrix membrane - NE-cutin non-ester bonded cutin - TEM transmission electron microscopy     

Petiole mechanics,light interception by Lamina,and “Economy in Design”

Summary Computer simulations were used to assess the influence of palmate leaf morphology, decussate phyllotaxy, and the elastic moduli of petioles on the capacity of turgid and wilted twigs ofAesculus hippocastanum to intercept direct solar radiation. Leaf size, morphology, orientation, and the Young's and shear moduli (E and G) of petioles were measured and related to leaf position on 8 twigs whose cut ends were placed in water (turgid twigs) and 8 twigs dried for 8 h at room temperature (wilted twigs). Petioles mechanically behaved as elastic cantilevered beams; the loads required to shear petioles at their base from twigs were correlated with the cross-sectional areas of phyllopodia but not with petiole length or tissue volume. Empirically determined morphometric and biomechanical data were used to construct average turgid and wilted twigs. The diurnal capacity to intercept direct sunlight for each was simulated for vertically oriented twigs for 15 h of daylight, 40° N latitude. The daily integrated irradiance (DII) of the wilted twig was roughly 3% less than that of the otherwise comparable twig bearing turgid leaves. Simulations indicated that the orientation of turgid leaves did not maximize DII. More decumbent (wilted) petioles increased DII by as much as 4%. Reduction in the girth, E, or G of petioles, or an increase in petiole length or the surface area of laminae (with attending increase in laminae weight), increased petiolar deflections and DII. Thus, the mechanical design of petioles ofA. hippocastanum was found not to be economical in terms of investing biomass for maximum light interception.     

MOVEMENT AND DISTRIBUTION OF 14C WITHIN PETIOLES OF INTACT COLEUS BLUMEI (LABIATAE) AFTER APPLICATION OF INDOLE-3-(ACETIC ACID-2-14C) TO THE LEAF SURFACE

Auxin transport and immobilization were followed in the petioles of intact plants of Coleus blumei Benth. after application of IAA-2-¹⁴C at a physiological concentration as droplets to the upper surface near the base of the blades of leaves #3 and #5. After 14 hr transportable and immobilized radiocarbon was found all along the petioles. Moreover, about half the total amount of ¹⁴C detected within the plant (= uptake) had moved beyond the petioles. This was true for leaves of both ages although the younger #3 petioles were only about half as long as the older #5 petioles. Because the uptake of radiocarbon by the #3 petioles was roughly half that of the #5 petioles, the absolute amounts immobilized per unit length of section were essentially uniform in the two petioles. On the contrary, the fractions remaining transportable within the #3 petiole sections averaged half those of the #5 petiole sections. The distribution of the transportable and the immobilized radioactive fractions along the petioles was characterized by high values near the apical application point, a decrease toward the middle of the petioles, and an increase to the level of the apical part toward the base of the petioles, which includes the abscission layer. The results have been discussed in connection with measurements of the cross sectional areas and the lengths of the epidermal and subepidermal cells along the petioles. An auxin transport and immobilization model, which assumes there are two different immobilization systems of different strength in the differently aged tissues, is outlined to explain the observations.     

Gravity can induce epinastic bending of isolated leaves

Abstract Isolated leaves of Plectranthus fruticosus were grown in cubic plastic cuvettes, and were supplied via their cut petioles with nutrient solution and indole-3-acetic acid (10^?6m ). Holes bored in the cuvette walls allowed the petioles to be oriented at approximately 60°, 90° or 120° to the vertical. Growth of the leaves initially oriented at angles of 60° and 90°, which simulated the situation in the intact plant, did not result in epinastic bending of the petiole. Inversion of the leaves (adaxial surface of the petiole downwards) and orientation of the adaxial/abaxial surfaces of the horizontal petiole parallel to the gravity vector, however, yielded strong epinastic bending of the petioles. In the latter case, this bending was not in the direction of the gravity vector (evidence for point (iii), below). Furthermore, epinastic bending occurred, when the isolated leaves were rotated on a clinostat (petioles parallel to the rotation axis or inclined to the rotation axis at an angle of 30°; 3 r.p.m.). Since a possible influence of the shoot was excluded, it is concluded that (i) perception and response are restricted to the leaf, (ii) gravity alone is sufficient to induce epinasty, (iii) a gravitropic component of the response can probably be excluded. The clinostat induced epinasty may not have been caused by nullifying the effect of gravity but due to continuous gravistimulation of the leaf.