The geometry of the compound leaf plays a significant role in the leaf movement of Medicago truncatula modulated by mtdwarf4a

Mechanism of the Pulvinus-Driven Leaf Movement: An Overview

Leaf movement is a manifestation of plant response to the changing internal and external environment, aiming to optimize plant growth and development. Leaf movement is usually driven by a specialized motor organ, the pulvinus, and this movement is associated with different changes in volume and expansion on the two sides of the pulvinus. Blue light, auxin, GA, H+-ATPase, K+, Cl-, Ca2+, actin, and aquaporin collectively influence the changes in water flux in the tissue of the extensor and flexor of the pulvinus to establish a turgor pressure difference, thereby controlling leaf movement. However, how these factors regulate the multicellular motility of the pulvinus tissues in a species remains obscure. In addition, model plants such as Medicago truncatula, Mimosa pudica, and Samanea saman have been used to study pulvinus-driven leaf movement, showing a similarity in their pulvinus movement mechanisms. In this review, we summarize past research findings from the three model plants, and using Medicago truncatula as an example, suggest that genes regulating pulvinus movement are also involved in regulating plant growth and development. We also propose a model in which the variation of ion flux and water flux are critical steps to pulvinus movement and highlight questions for future research.

Effect of leaf phenology and morphology on the coordination between stomatal and minor vein densities

Leaf phenology (evergreen vs. deciduous) and morphology (simple vs. compound) are known to be related to water use strategies in tree species and critical adaptation to certain climatic conditions. However, the effect of these two traits and their interactions on the coordination between minor vein density (MVD) and stomatal density (SD) remains unclear. In this study, we examined the leaves of 108 tree species from plots in a primary subtropical forest in southern China, including tree species with different leaf morphologies and phenologies. We assessed nine leaf water-related functional traits for all species, including MVD, SD, leaf area (LA), minor vein thickness (MVT), and stomatal length (SL). The results showed no significant differences in mean LA and SD between either functional group (simple vs. compound and evergreen vs. deciduous). However, deciduous trees displayed a significantly higher mean MVD compared to evergreen trees. Similarly, compound-leaved trees have a higher (marginally significant) MVD than simple-leaved trees. Furthermore, we found that leaf morphology and phenology have significantly interactive effects on SL, and the compound-leafed deciduous trees exhibited the largest average SL among the four groups. There were significant correlations between the MVD and SD in all different tree groups; however, the slopes and interceptions differed within both morphology and phenology. Our results indicate that MVD, rather than SD, may be the more flexible structure for supporting the coordination between leaf water supply and demand in different leaf morphologies and phenologies. The results of the present study provide mechanistic understandings of the functional advantages of different leaf types, which may involve species fitness in community assembly and divergent responses to climate changes.

Patterns of compound-leaf form and deciduous-leaf habit across forests in China: Their association and key climatic factors

Leaf form (compound vs. simple) and habit (evergreen vs. deciduous) are key functional traits of trees to adapt to various climates and are vital in determining plant response to climate change. However, their association and climatic determinants remain uncertain, especially in East Asian forests in the largest monsoon region on earth. To fill these knowledge gaps, we compiled a dataset comprising 42 intact forests and over 2200 angiosperm tree species across China (spanning 30 latitudes and 47 longitudes). The geographical and climatic patterns of leaf form and habit were analyzed. The association between compound leaf and deciduousness was tested for tropical, subtropical and temperate climatic zones. We found that both the percentage of compound leaf (CT%) and deciduous tree species (DT%) increased with latitude and decreased with mean annual precipitation (MAP). For all forests, DT% was negatively related to mean annual temperature (MAT), whereas CT% was not. Nevertheless, both DT% and CT% increased with increasing MAT in the tropics, possibly owing to the high vapor pressure deficits (VPD) and canopy water deficits associated with high temperatures. A positive linear relationship between CT% and DT% was found across all forests and within different climatic zones except for temperate, and the intercept of the regression line was significantly higher in the tropics than in the subtropics. Overall, as supported by principal component analysis, deciduousness was negatively associated with both temperature and precipitation, while CT negatively with precipitation only across zones and positively with temperature in the tropics. Different relationships in different climatic zones suggest potentially different selective forces. Our findings provide novel insights into the linkage between leaf form and habit, as well as how climate shapes the landscape of broadleaf forests, which has important implications regarding the response of forest composition to climate change.

Mechanics of Reversible Deformation during Leaf Movement and Regulation of Pulvinus Development in Legumes

Plant cell deformation is a mechanical process that is driven by differences in the osmotic pressure inside and outside of the cell and is influenced by cell wall properties. Legume leaf movements result from reversible deformation of pulvinar motor cells. Reversible cell deformation is an elastic process distinct from the irreversible cell growth of developing organs. Here, we begin with a review of the basic mathematics of cell volume changes, cell wall function, and the mechanics of bending deformation at a macro scale. Next, we summarize the findings of recent molecular genetic studies of pulvinar development. We then review the mechanisms of the adaxial/abaxial patterning because pulvinar bending deformation depends on the differences in mechanical properties and physiological responses of motor cells on the adaxial versus abaxial sides of the pulvinus. Intriguingly, pulvini simultaneously encompass morphological symmetry and functional asymmetry along the adaxial/abaxial axis. This review provides an introduction to leaf movement and reversible deformation from the perspective of mechanics and molecular genetics.

Multidimensional Gene Regulatory Landscape of Motor Organ Pulvinus in the Model Legume Medicago truncatula

Nyctinastic leaf movement of Fabaceae is driven by the tiny motor organ pulvinus located at the base of the leaf or leaflet. Despite the increased understanding of the essential role of ELONGATED PETIOLULE1 (ELP1)/PETIOLE LIKE PULVINUS (PLP) orthologs in determining pulvinus identity in legumes, key regulatory components and molecular mechanisms underlying this movement remain largely unclear. Here, we used WT pulvinus and the equivalent tissue in the elp1 mutant to carry out transcriptome and proteome experiments. The omics data indicated that there are multiple cell biological processes altered at the gene expression and protein abundance level during the pulvinus development. In addition, comparative analysis of different leaf tissues provided clues to illuminate the possible common primordium between pulvinus and petiole, as well as the function of ELP1. Furthermore, the auxin pathway, cell wall composition and chloroplast distribution were altered in elp1 mutants, verifying their important roles in pulvinus development. This study provides a comprehensive insight into the motor organ of the model legume Medicago truncatula and further supplies a rich dataset to facilitate the identification of novel players involved in nyctinastic movement.

Combining Fine Mapping, Whole-Genome Re-Sequencing, and RNA-Seq Unravels Candidate Genes for a Soybean Mutant with Short Petioles and Weakened Pulvini

A short petiole is an important agronomic trait for the development of plant ideotypes with high yields. However, the genetic basis underlying this trait remains unclear. Here, we identified and characterized a novel soybean mutant with short petioles and weakened pulvini, designated as short petioles and weakened pulvini (spwp). Compared with the wild type (WT), the spwp mutant displayed shortened petioles, owing to the longitudinally decreased cell length, and exhibited a smaller pulvinus structure due to a reduction in motor cell proliferation and expansion. Genetic analysis showed that the phenotype of the spwp mutant was controlled by two recessive nuclear genes, named as spwp1 and spwp2. Using a map-based cloning strategy, the spwp1 locus was mapped in a 183 kb genomic region on chromosome 14 between markers S1413 and S1418, containing 15 annotated genes, whereas the spwp2 locus was mapped in a 195 kb genomic region on chromosome 11 between markers S1373 and S1385, containing 18 annotated genes. Based on the whole-genome re-sequencing and RNA-seq data, we identified two homologous genes, Glyma.11g230300 and Glyma.11g230600, as the most promising candidate genes for the spwp2 locus. In addition, the RNA-seq analysis revealed that the expression levels of genes involved in the cytokinin and auxin signaling transduction networks were altered in the spwp mutant compared with the WT. Our findings provide new gene resources for insights into the genetic mechanisms of petiole development and pulvinus establishment, as well as soybean ideotype breeding.

The Genetic Control of the Compound Leaf Patterning in Medicago truncatula

Simple and compound which are the two basic types of leaves are distinguished by the pattern of the distribution of blades on the petiole. Compared to simple leaves comprising a single blade, compound leaves have multiple blade units and exhibit more complex and diverse patterns of organ organization, and the molecular mechanisms underlying their pattern formation are receiving more and more attention in recent years. Studies in model legume Medicago truncatula have led to an improved understanding of the genetic control of the compound leaf patterning. This review is an attempt to summarize the current knowledge about the compound leaf morphogenesis of M. truncatula, with a focus on the molecular mechanisms involved in pattern formation. It also includes some comparisons of the molecular mechanisms between leaf morphogenesis of different model species and offers useful information for the molecular design of legume crops.

Leaf Area Calculation Models for Vines Based on Foliar Descriptors

In the case of foliar area studies on vines, with a large number of determinations, a simple, fast, sufficiently accurate and low-cost method is very useful. The typology of leaves on the vine is complex, characterized by several descriptive parameters: median rib; secondary venations of the first and second order; angles between the median rib and the secondary venations; sinuses; length and width of the leaf. The present study aimed to evaluate models for calculating the leaf area based on descriptive parameters and KA (KA as the surface constant used to calculate the leaf area) for six vine cultivars, ‘Cabernet Sauvignon’ (CS), ‘Muscat Iantarnîi’ (MI), ‘Muscat Ottonel’ (MO), ‘Chasselas’ (Ch), ‘Victoria’ (Vi) and ‘Muscat Hamburg’ (MH). The determined KA surface constants had subunit values (0.91 to 0.97), except for the cultivars ‘Muscat Iantarnîi’ and ‘Muscat Ottonel’ where the surface constant KA₂ (in relation to the second-order secondary venations) had supraunitary values (1.07 and 1.08, respectively). The determination of the leaf area was possible under different conditions of statistical accuracy (R² = 0.477, p = 0.0119, up to R² = 0.988, p < 0.001) in relation to the variety and parametric descriptors considered. The models obtained from the regression analysis facilitated a more reliable prediction of the leaf area based on the elements on the left side of the leaf, in relation to the median rib, compared to those on the right. The accuracy of the results was checked on the basis of minimum error (ME) and confirmed by parameters R², p and RMSE.