INDETERMINATE GROWTH OF LEAVES IN GUAREA (MELIACEAE): A TWIG ANALOGUE

Leaves of seed plants are generally characterized as organs of determinate growth. In this regard, Guarea and related genera seem unusual in that the pinnately compound leaves of these plants contain a bud at their tip from which new pinnae expand from time to time. Previous studies (based upon superficial examinations of leaf-tip buds) have produced contradictory conclusions regarding how long the leaf apex remains meristematic and produces new pinna primordia. In order to determine whether leaf development in Guarea is truly indeterminate, we microscopically examined leaf-tip buds of G. guidonia and G. glabra. In both species, the leaf apex remains meristematic and continues to produce new pinna primordia as the leaf ages. Unexpanded leaves of G. guidonia contained an average of 23 pinna primordia, while the oldest leaves we examined had initiated an average of 44 total pinnae. In G. glabra, unexpanded leaves contained 8 pinnae, whereas an average of 28 pinnae had been initiated on the oldest leaves. These results indicate that leaf development in Guarea is truly indeterminate. Periodic examination of individual intact leaves indicated that the leaves commonly continue their growth for 2 or more years (observed maximum = 51 months). As new leaflets are initiated at the shoot apex (and subsequently expand in rhythmic flushes), older (basal) leaflets may abscise. In addition, the petiole and rachis of the leaf thicken and become woody as a result of the activity of a vascular cambium. Guarea leaves therefore seem to function as the analogue of a typical twig (stem) in general habit as well as in their indeterminate apical growth and secondary thickening.     

TheAfGene Regulates Timing and Direction of Major Developmental Events during Leaf Morphogenesis in Garden Pea (Pisum sativum)

The wildtype leaf of the garden pea possesses proximal pairsof leaflets and distal pairs of tendrils in the blade region.Theafila (af) mutation causes leaflets to be replaced by compound(branched) tendrils. We characterized the morphological variationin leaf form along the plant axis and leaf development in earlyand late postembryonic leaves onafilaplants to infer the roleof theAfgene. Leaf forms are more diverse early in shoot ontogenyonafilaplants.Afinfluences pinna length and pinna branchingin addition to pinna type. Pinna initiation in the proximalregion ofafilaleaf primordia is basipetal and delayed comparedto wildtype plants. In addition, pinna development in the proximalregion ofafilaleaves occurs for a longer period of time thanon wildtype leaf primordia. Therefore,Afregulates the timingand direction of leaf developmental processes in the proximalregion of the leaf, but has little effect on the distal region.These data support the heterochronic model of pea leaf morphogenesisproposed by Luet al. (International Journal of Plant Science157:311–355, 1996).Copyright 1999 Annals of Botany Company. afila,Fabaceae, garden pea, heterochrony, leaf morphogenesis,Pisum sativum.     

Indeterminate leaves of Chisocheton (Meliaceae): survey of structure and development

Pinnately compound leaves in the Malesian genus Chisocheton (Meliaceae) have leaf-tip buds that continue to produce new pinnae (leaflets) periodically for many years. Juvenile leaves form a terminal pinna in place of the leaf-tip bud found in adult leaves. The histology of an old leaf-tip bud is similar to the entire leaf primordium in other species of Meliaceae with large pinnate leaves (e.g. Chukrasia and Dysoxylum ) which serve as examples of more typical leaves. Pinna initiation from this meristem continues after the first stage of leaf expansion as seen in the relatively constant number of pinna primordia in a large sampling of leaf-tip buds of varying ages. Structure and development are compared in leaves of nine species of Chisocheton , out of a total of approxiamtely 50 species in the genus. Species having small leaves (e.g. C. pentandrus ) show more branch-like, indeterminate leaf growth as compared with species with large leaves (e.g. C. macranthus ). The structure and development of leaves of Chisocheton are like the similar indeterminate leaves of the American and African genus Guarea . Some authors have used the indeterminate leaves of Chisocheton and Guarea as examples of intermediate organs showing 'fuzzy morphology' or 'partial homology.' Nevertheless, these unusual organs are considered here as being homologous with leaves of other Meliaceae based on their position, histology and ontogeny. © 2002 The Linnean Society of London, Botanical Journal of the Linnean Society , 2002, 139 , 207–221.     

Study of the Geometry and Folding Pattern of Leaves of Mimosa pudica

Many structural and functional properties possessed by plants have great potentials to stimulate new concepts and inno-vative ideas in the field of biomimetic engineering. The key inputs from biology can be used for creation of efficient and op-timized structures. The study of the geometry and folding pattern of leaves of Mimosa pudica,referred as Sensitive Plant,reveals some of the peculiar characteristics during folding and unfolding. When the leaf is touched,it quickly folds its leaflets and pinnae and droops downward at the petiole attachment. With the help of experiments on simulation model,the variations in angle of leaflets and degree of compaction after folding are investigated.     

PROCERA encodes a DELLA protein that mediates control of dissected leaf form in tomato

Leaves of seed plants can be described as simple, where the leaf blade is entire, or dissected, where the blade is divided into distinct leaflets. Mechanisms that define leaflet number and position are poorly understood and their elucidation presents an attractive opportunity to understand mechanisms controlling organ shape in plants. In tomato (Solanum lycopersicum), a plant with dissected leaves, KNOTTED1-like homeodomain proteins (KNOX) are positive regulators of leaflet formation. Conversely, the hormone gibberellin (GA) can antagonise the effects of KNOX overexpression and reduce leaflet number, suggesting that GA may be a negative regulator of leaflet formation. However, when and how GA acts on leaf development is unknown. The reduced leaflet number phenotype of the tomato mutant procera (pro) mimics that of plants to which GA has been applied during leaf development, suggesting that PRO may define a GA signalling component required to promote leaflet formation. Here we show that PRO encodes a DELLA-type growth repressor that probably mediates GA-reversible growth restraint. We demonstrate that PRO is required to promote leaflet initiation during early stages of growth of leaf primordia and conversely that reduced GA biosynthesis increases the capability of the tomato leaf to produce leaflets in response to elevated KNOX activity. We propose that, in tomato, DELLA activity regulates leaflet number by defining the correct timing for leaflet initiation.     

The mutant crispa reveals multiple roles for PHANTASTICA in pea compound leaf development

Pinnate compound leaves have laminae called leaflets distributed at intervals along an axis, the rachis, whereas simple leaves have a single lamina. In simple- and compound-leaved species, the PHANTASTICA (PHAN) gene is required for lamina formation. Antirrhinum majus mutants lacking a functional gene develop abaxialized, bladeless adult leaves. Transgenic downregulation of PHAN in the compound tomato (Solanum lycopersicum) leaf results in an abaxialized rachis without leaflets. The extent of PHAN gene expression was found to be correlated with leaf morphology in diverse compound-leaved species; pinnate leaves had a complete adaxial domain of PHAN gene expression, and peltate leaves had a diminished domain. These previous studies predict the form of a compound-leaved phan mutant to be either peltate or an abaxialized rachis. Here, we characterize crispa, a phan mutant in pea (Pisum sativum), and find that the compound leaf remains pinnate, with individual leaflets abaxialized, rather than the whole leaf. The mutant develops ectopic stipules on the petiole-rachis axis, which are associated with ectopic class 1 KNOTTED1-like homeobox (KNOX) gene expression, showing that the interaction between CRISPA and the KNOX gene PISUM SATIVUM KNOTTED2 specifies stipule boundaries. KNOX and CRISPA gene expression patterns indicate that the mechanism of pea leaf initiation is more like Arabidopsis thaliana than tomato.     

The determination of pea leaves,leaflets, and tendrils

Pea leaf determination was examined by culturing excised leaf, leaflet, and tendril primordia of different ages on a nutrient medium. Pinna primordia were designated as 1) determined, if they grew normally in culture; 2) undetermined, if they grew into differentiated structures that were morphologically and anatomically different from either leaflet or tendril; or 3) partially determined, if the two pinnae of an opposite pair developed unequally in isolation, or for leaflet pinnae only, if laminae were initiated but did not develop completely. The compound pea leaf as a whole is determined over four plastochrons of development. Proximal pinnae are determined during the second leaf plastochron, approximately 0.8 plastochron after their initiation. The second most proximal pair of pinnae is determined during the third plastochron, and the terminal portion of the rachis is determined last, during the fourth plastochron. Determination of leaflet dorsiventrality is gradual, requiring a critical minimum period with the leaf in physiological contact with the shoot system. The rachis primordium, when isolated from the shoot, does not affect determination of its pinnae as leaflets or tendrils. Afila and tendril-less homeotic mutations do not alter the timing of pinna determination.     

Storage ability of overwintering leaves and rhizomes in a semi-evergreen fern, <Emphasis Type="Italic">Dryopteris crassirhizoma</Emphasis> (Dryopteridaceae)

Dryopteris crassirhizoma is a rhizomatous semi-evergreen fern growing in the understory of deciduous forests. Although the top portion of the overwintering leaves began to wither in early winter, intensive senescence occurred in the spring, concurrently with new leaf development. Dry weight comparisons between organs revealed that the rhizome occupied the largest proportion of the total mass, followed by the pinnae. To assess the storage ability of overwintering leaves and the rhizome, seasonal changes in nitrogen content and the dry mass of pinnae and the rhizome were measured. Nitrogen (36.6%) was resorbed from winter-withering pinnae, but not from spring-withering pinnae. In contrast, a similar decrease in dry mass per unit area occurred between winter- and spring-withering pinnae (15%). These results indicate that overwintering leaves serve as a carbohydrate storage organ, but do not serve as a nitrogen storage organ. Nitrogen was not translocated from the rhizome during the early growing season, but translocation did occur in late summer and autumn. The dry mass of the rhizome decreased by 18.4% in spring, at the time of new leaf expansion. The amount of exported dry matter from the rhizome was threefold larger than that from senescent pinnae. Therefore, the rhizome is a major carbohydrate storage organ in this species, although overwintering leaves also act as a carbohydrate storage organ.     

14C Translocation pathways in honeylocust and green ash: Woody plants with complex leaf forms

Long-distance transport in plants requires precise knowledge of vascular pathways, and these pathways differ among species. This study examines the ¹⁴C translocation pathways in honeylocust (Gleditsia triacanthos L.) and green ash (Fraxinus pennsylvanica Marsh.), species with compound leaves, and compares them with those of cottonwood (Populus deltoides Bartr. ex Marsh.), a species with simple leaves. The stem vasculature of honeylocust conforms to a 2/5 helical phyllotaxy and that of green ash to a decussate phyllotaxy. The plastochron is relatively long in both species – 2.5+ days in honeylocust and 4.5+ days in green ash. Consequently, the transition from upward to downward translocation from mature source leaves is abrupt and occurs close to the apex. Export of ¹⁴C from localized treatment positions within a leaf was found to vary both quantitatively and spatially. To determine export patterns, ¹⁴CO₂ was administered to either individual leaflets of once-pinnate or pinnae of bipinnate leaves of honeylocust, and to either individual veins of simple or leaflets of compound leaves of green ash. Transections of either the petiole or rachis base were then examined for ¹⁴C by micro-autoradiography. In all cases, as treatment positions advanced acropetally in the leaves, the bundles translocating ¹⁴C were situated more dorsally in the basal petiole and rachis vasculatures. ¹⁴C was confined to the right side of the vasculature when structures on the right side of a leaf were treated. Compound leaves of both species mature acropetally. Thus, mature basal pinnae of honeylocust and basal leaflets of green ash translocate acropetally to younger leaf parts that are still rapidly expanding. All translocation pathways, both in the stem and leaf, conformed with vascular organization previously determined by anatomical analyses.     

The Effects of Increased Illumination and Shading on the Low-Light-Induced Decline in Photosynthesis in Cotton Leaves

An experiment was carried out to study whether low-light-induced damage to the photosynthetic system in leaves of cotton (Gossypium hirsutum cv. Deltapine) which are below the compensation point in the canopy can be arrested and reversed by increased illumination. In addition it was intended to find out whether the photosynthetic system in leaves of shade plants show a greater resistance to low-light-induced damage than leaves of plants from more exposed habitats. The plants were grown at high density, and increased illumination to the shade leaves in the canopy was achieved by thinning the stand. Thinning was carried out at two stages and its effects on the decline in the photosynthetic capacity of the 4th leaf were followed. An early thinning was carried out shortly after the 4th leaf dropped below the compensation point and a late thinning 2 weeks later. Comparison was also made between the low-light-induced damage to the photosynthetic capacity of the 4th leaf in plants grown under two light regimes during the progressive increase in self-shading of the 4th leaf within the canopy. It was observed that both types of thinning arrested the low-light-induced damage to the photosynthetic system in shade leaves. The decline in photosynthetic capacity of the 4th leaf was stopped after both early and late thinning. The dry weight of the shoot system in the early and late thinned plants was not significantly different. It was double that of the control plants. The plants thinned early did not have higher shoot weight than the late thinned plants since there was a rapid shedding of flowers and fruits after early thinning. The 4th leaf in the early thinned plants showed a 30% increase in chlorophyll content and dry weight per unit leaf area. It is suggested that shedding of flowers and fruits, and increases in chlorophyll and dry weight per unit leaf area in the early thinned plants were caused by a change in the hormonal balance of the plants. The photosynthetic system in leaves of shade plants showed a greater resistance to damage by low light intensity than the photosynthetic system in leaves of plants grown at higher light intensities.     

HETEROPHYLLY AND NEOFORMATION OF LEAVES IN SUGAR MAPLE (ACER SACCHARUM)

Variation in leaf form and timing of leaf initiation were investigated in vigorous leader shoots of open-grown saplings and larger forest trees of sugar maple (Acer saccharum Marsh.). Winter buds of leader shoots usually contained 6 or 8 leaf primordia and embryonic leaves, whereas 12 to 18 leaves typically expanded along the shoots each year. Preformed (early) leaves differ in form from neoformed (late) leaves. As in some other Acer species, the first-formed late leaves have large angles of secondary lobe divergence and deeply indented sinuses. This pattern of heterophylly contributes to the multilayered nature of open-grown saplings and leader shoots of forest trees of sugar maple.     

The rates of shoot and root growth in intact plants of pea mutants in leaf morphology

Isogenic lines of pea (Pisum sativum L.) with the genetically determined changes in leaf morphology, afila (af) and tendril-less (tl), were used to study the relationship between shoot and root growth rates. The time-course of shoot and root growth was followed during the pre-floral period in the intact plants grown under similar conditions. The af mutation produced afila leaves without leaflets, whereas in the case of the tl mutations, tendrils were substituted with leaflets, and acacia-like leaves were developed. Due to the changes in leaf morphology caused by these mutations, pea genotypes differed in leaf area: starting from day 7, the leaf area was lower in the af plants and larger in the tl plants as compared to the wild-type plants. Such divergence was amplified in the course of plant development and reached its maximum immediately before the transition to flowering. Plants of isogenic lines did not notably differ in stem surface areas. In spite of significant difference in total leaf area, the wild type and tl plants did not differ in leaf dry weight. Starting from leaf 9, the af plants lagged behind two leaflet-bearing genotypes (wild type and tl) in leaf dry weight, whereas stem dry weight was similar in the wild type and tl forms and slightly lower in the af plants. Root dry weights were practically similar in the wild type and tl plants until flowering. The reduction of leaf area in the af plants drastically reduced root dry weight. In other words, the latter index was related to the total weight and total area of leaves and stems. The correlation analysis demonstrated an extremely low relationship between leaf and stem area and dry weight and those of roots early in plant development (when plants develop five to seven leaves). Later, immediately before flowering (nine to eleven leaves), root weight was positively related to leaf weight and area; however, stem area and root weight did not correlate. Thus, in three genotypes (wild type, af, and tl), at the end of their vegetative growth phase, leaf and root biomass accumulated in proportion, independently of leaf area expansion.     

The SERRATE locus controls the formation of the early juvenile leaves and phase length in Arabidopsis

The development of the shoot can be divided into a series of distinct developmental phases based on leaf character-istics and inflorescence architecture. The relationship between phase length, defined by the number of organs produced, and the timing of the floral induction (V3-I1 transition) is relatively ill defined. Characterization of the serrate mutant (CS3257; Arabidopsis Biological Research Center) revealed defects in both vegetative and inflores-cence phase lengths, the timing of phase transitions, leaf number, the leaf initiation rate, and phyllotaxy. The timing of floral induction, however, is the same as in wild-type in extended short days as well as in short days, whereas the flowering time response to photoperiod is unaffected. SERRATE is shown to be required for the development of early juvenile leaves (V1) and to promote late juvenile leaf development (V2), while suppressing adult leaf (V3) and inflorescence development (I1 and I2). The se mutation supports the hypothesis that the timing of floral induction is independent of vegetative and inflorescence phase lengths. The role of SERRATE in the regulation of phase length and leaf identity is discussed.     

LEAF DEVELOPMENT IN THE NORMAL AND SOLANIFOLIA MUTANT OF TOMATO (LYCOPERSICON ESCULENTUM)

Leaf development in the normal (lobed margin) and the solanifolia (sf/sf) mutant (entire margin) of tomato (Lycopersicon esculentum) was compared at the light and scanning electron microscope levels. The shoot apices of the mutant plants contained microbodies near the axil of the youngest leaf, which were absent in the normal plants. The structural and morphological events in the initiation of leaf primordia were similar in the two genotypes. The pattern of leaflet emergence was also similar in the two types of plants, but the timing of leaflet production was different. The first pair of leaflet primordia in the normal plants was produced on P₃, whereas in the mutant it was not produced until P₅. The adult leaves of sf/sf plants were larger than those of normal, and the greater leaf area in the mutant was associated with a greater adaxial epidermal cell and areole area. A continuous marginal fimbriate vein (MFV) was present along the margin of each of the normal leaflets. However, a continuous MFV was absent in the mutant leaflets. It is suggested that the absence of a continuous MFV in the mutant might alter the nutritional and hormonal supply to the leaf margin, which ultimately leads to a modified leaf, i.e., with an entire margin.     

Heterochronic Effects of Teopod 2 on the Growth and Photosensitivity of the Maize Shoot

Teopod 2 (Tp2) is a semidominant mutation of maize that prolongs the expression of juvenile vegetative traits, increases the total number of leaves produced by the shoot, and transforms reproductive structures into vegetative ones. Here, we show that Tp2 prolongs the duration of vegetative growth without prolonging the overall duration of shoot growth. Mutant shoots produce leaves at the same rate as wild-type plants and continue to produce leaves after wild-type plants have initiated a tassel. Although Tp2/+ plants initiate a tassel later than their wild-type siblings, this mutant tassel ceases differentiation at the same time as, or shortly before, the primary meristem of a wild-type tassel completes its development. To investigate the relationship between the vegetative and reproductive development of the shoot, Tp2/+ and wild-type plants were exposed to floral inductive short day (SD) treatments at various stages of shoot growth. Tassel initiation in wild-type plants (which normally produced 18 to 19 leaves) was maximally sensitive to SD between plastochrons 15 and 16, whereas tassel branching was maximally sensitive to SD between plastochrons 15 and 18. Tassel initiation and tassel morphology in Tp2/+ plants (which normally produced 21 to 26 leaves) were both maximally sensitive to SD between plastochrons 15 and 18. Thus, the constitutive expression of a juvenile vegetative program in Tp2/+ plants does not significantly delay the reproductive maturation of the shoot.     

Diel growth patterns of young soybean (Glycine max) leaflets are synchronous throughout different positions on a plant

Leaf growth is controlled by various internal and external factors. Leaves of dicotyledonous plants show pronounced diel (24 h) growth patterns that are controlled by the circadian clock. To date, it is still uncertain whether diel leaf growth patterns remain constant throughout the development of a plant. In this study, we followed growth from the primary leaves to leaflets of the seventh trifoliate leaf of soybean (Glycine max) on the same plants with a recently developed imaging‐based method under controlled conditions and at a high temporal resolution. We found that all leaflets displayed a consistent diel growth pattern with maximum growth towards the end of the night. In some leaves, growth maxima occurred somewhat later – at dawn – as long as the leaves were still in a very early developmental stage. Yet, overall, diel growth patterns of leaves from different positions within the canopy were highly synchronous. Therefore, the diel growth pattern of any leaf at a given point in time is representative for the overall diel growth pattern of the plant leaf canopy and a deviation from the normal diel growth pattern can indicate that the plant is currently facing stress.     

The origin of postembryonic neuroblasts in the ventral nerve cord of Drosophila melanogaster

Embryonic and postembryonic neuroblasts in the thoracic ventral nerve cord of Drosophila melanogaster have the same origin. We have traced the development of threefold-labelled single precursor cells from the early gastrula stage to late larval stages. The technique allows in the same individual monitoring of progeny cells at embryonic stages (in vivo) and differentially staining embryonic and postembryonic progeny within the resulting neural clone at late postembryonic stages. The analysis reveals that postembryonic cells always appear together with embryonic cells in one clone. Furthermore, BrdU labelling suggests that the embryonic neuroblast itself rather than one of its progeny resumes proliferation as a postembryonic neuroblast. A second type of clone consists of embryonic progeny only.     

Regulation of Leaf Shape in the Solanifolia Mutant of Tomato (Lycopersicon esculentum) by Plant Growth Substances

The solanifolia mutant (sf/sf) of tomato (Lycopersicon esculentum)produces leaves consisting of leaflets with entire margins,unlike the lobed leaflets of normal plants. Normal plants treatedwith gibberellic acid (GA₃) produced leaves with entire marginswhereas mutant plants exposed to 2-chloroethyl-trimethyl ammoniumchloride (CCC)—an inhibitor of gibberellin biosynthesis—producedlobing of leaflets. The leaf area of the mutant was significantlygreater than that of the normal, but was not significantly differentfrom GA₃-treated normal leaves. Similarly, in CCC-treated mutantleaves the leaf area was not different from that of normal untreatedleaves. These observations suggest that the sf/sf mutation affectsthe leaf shape through its effect on endogenous gibberellinsand/or inhibitory substances. Leaf shape, Lycopersicon esculentum, plant growth substances, tomato     

Herbivory in canopy gaps created by a typhoon varies by understory plant leaf phenology

1. Availabilities of light and soil nitrogen for understory plants vary by extent of canopy gap formation through typhoon disturbance. We predicted that variation in resource availability and herbivore abundance in canopy gaps would affect herbivory through variation in leaf traits among plant species. We studied six understory species that expand their leaves before or after canopy closure in deciduous forests. We measured the availabilities of light, soil nitrogen, soil water content, and herbivore abundance in 20 canopy gaps (28.3–607.6 m²) formed by a typhoon and in four undisturbed stands. We also measured leaf traits and herbivory on understory plants. 2. The availabilities of light and soil nitrogen increased with increasing gap size. However, soil water content did not. The abundance of herbivorous insects (such as Lepidoptera and Orthoptera) increased with increasing gap size. 3. Concentrations of condensed tannins, total phenolics, and nitrogen in leaves and the leaf mass per area increased in late leaf expansion species with increasing gap size, whereas none of the leaf traits varied by gap size in early leaf expansion species. 4. Herbivory increased on early leaf expansion species with increasing gap size, but decreased on late leaf expansion species. In these late leaf expansion species, total phenolics and C : N ratio had negative relationships with herbivory. 5. These results suggested that after typhoon disturbance, increased herbivory on early leaf expansion species can be explained by increased herbivore abundance, whereas decreased herbivory on late leaf expansion species can be explained by variation in leaf traits.