An official website of the United States government
The superior photosynthetic efficiency of C 4 leaves over C 3 leaves is owing to their unique Kranz anatomy, in which the vein is surrounded by one layer of bundle sheath (BS) cells and one layer of mesophyll (M) cells. Kranz anatomy development starts from three contiguous ground meristem (GM) cells, but its regulators and underlying molecular mechanism are largely unknown. To identify the regulators, we obtained the transcriptomes of 11 maize embryonic leaf cell types from five stages of pre-Kranz cells starting from median GM cells and six stages of pre-M cells starting from undifferentiated cells. Principal component and clustering analyses of transcriptomic data revealed rapid pre-Kranz cell differentiation in the first two stages but slow differentiation in the last three stages, suggesting early Kranz cell fate determination. In contrast, pre-M cells exhibit a more prolonged transcriptional differentiation process. Differential gene expression and coexpression analyses identified gene coexpression modules, one of which included 3 auxin transporter and 18 transcription factor (TF) genes, including known regulators of Kranz anatomy and/or vascular development. In situ hybridization of 11 TF genes validated their expression in early Kranz development. We determined the binding motifs of 15 TFs, predicted TF target gene relationships among the 18 TF and 3 auxin transporter genes, and validated 67 predictions by electrophoresis mobility shift assay. From these data, we constructed a gene regulatory network for Kranz development. Our study sheds light on the regulation of early maize leaf development and provides candidate leaf development regulators for future study.
more »
« less
A fossil dicranid moss from the Late Cretaceous of Antarctica
An anatomically preserved moss gametophyte has been discovered in a marine carbonate concretion from the Baculites Hill locality, James Ross Island, Antarctica. The concretion is derived from the Late Cretaceous Beta Member of the Santa Marta Formation, dated as early to middle Campanian (ca. 80 Ma). The moss has actinomorphic stems with alternate branching, spiral, patent leaf arrangement and large numbers of attached rhizoids. The largest stem is 210 mm in diameter with the largest branch measuring up to 3.7 mm long and 90–100 mm wide. Most stems appear to contain a distinct conducting strand. Cross sections show that the leaves are strongly plicate with a simple D-shaped costal anatomy and unistratose laminae typically with bistratose margins. Leaves range from 650–700 mm wide and at least 700 mm long. The costa appears percurrent, 90 mm wide and 55 mm thick. Laminar cells are elongate, rhomboidal, L/W ¼ 5:1. No ornamentation or papillae have been observed on the upper medial cells of the leaf. These fossils show leaf morphology and costal anatomy similar to several orders of acrocarpous mosses, in the Dicranidae including species of the family Rhabdoweisiaceae. While the combination of characters does not fit into any known genus, it suggests that this moss represents a fossil member of the Dicranales s.l. To date, this represents the most completely preserved moss gametophyte from Gondwana.
more »
« less
- PAR ID:
- 10552219
- Publisher / Repository:
- The American Bryological and Lichenological Society
- Date Published:
- Journal Name:
- The Bryologist
- Volume:
- 127
- Issue:
- 3
- ISSN:
- 0007-2745
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract BackgroundPlant dispersal units, or diaspores, allow the colonization of new environments expanding geographic range and promoting gene flow. Two broad categories of diaspores found in seed plants are dry and fleshy, associated with abiotic and biotic dispersal agents, respectively. Anatomy and developmental genetics of fleshy angiosperm fruits is advanced in contrast to the knowledge gap for analogous fleshy structures in gymnosperm diaspores. Improved understanding of the structural basis of modified accessory organs that aid in seed dispersal will enable future work on the underlying genetics, contributing to hypotheses on the origin of angiosperm fruits. To generate a structural framework for the development and evolution of gymnosperm fleshy diaspores, we studied the anatomy and histochemistry ofEphedra(Gnetales) seed cone bracts, the modified leaves surrounding the reproductive organs. We took an ontogenetic approach, comparing and contrasting the anatomy and histology of fleshy and papery-winged seed cone bracts, and their respective pollen cone bracts and leaves in four species from the South American clade. ResultsSeed bract fleshiness inEphedraderives from mucilage accumulated in chlorenchyma cells, also found in the reduced young leaves before they reach their mature, dry stage. Cellulosic fibers, an infrequent cell type in gymnosperms, were found inEphedra, where they presumably function as a source of supplementary apoplastic water in fleshy seed cone bracts. Papery-winged bract development more closely resembles that of leaves, with chlorenchyma mucilage cells turning into tanniniferous cells early on, and hyaline margins further extending into “wings”. ConclusionsWe propose an evolutionary developmental model whereby fleshy and papery-winged bracts develop from an early-stage anatomy shared with leaves that differs at the pollination stage. The ancestral fleshy bract state may represent a novel differentiation program built upon young leaf anatomy, while the derived dry, papery-winged state is likely built upon an existing differentiation pattern found in mature vegetative leaves. This model for the evolution of cone bract morphology in South AmericanEphedrahence involves a novel differentiation program repurposed from leaves combined with changes in the timing of leaf differentiation, or heterochrony, that can further be tested in other gymnosperms with fleshy diaspores.more » « less
-
Summary There is a long‐standing idea that the timing of leaf production in seasonally cold climates is linked to xylem anatomy, specifically vessel diameter because of the hydraulic requirements of expanding leaves.We tested for a relationship between the timing of leaf out and vessel diameter in 220 plants in three common gardens accounting for species’ phylogenetic relationships. We investigated how vessel diameter related to wood porosity, plant height and leaf length. We also used dye perfusion tests to determine whether plants relied on xylem produced during the previous growing season at the time of leaf out.In all three gardens, there was later leaf out in species with wider vessels. Ring‐porous species had the widest vessels, exhibited latest leaf out and relied less on xylem made during the previous growing season than diffuse‐porous species. Wood anatomy and leaf phenology did not exhibit a phylogenetic signal.The timing of leaf out is correlated with wood anatomy across species regardless of species’ geographic origin and phylogenetic relationships. This correlation could be a result of developmental and physiological links between leaves and wood or tied to a larger safety efficiency trade‐off.more » « less
-
null (Ed.)Salinity is a widespread environmental stress that severely limits crop yield worldwide. Cerium oxide nanoparticles (nanoceria) have the unique capability of catalytically reducing levels of stress-induced reactive oxygen species (ROS) including hydroxyl radicals (˙OH) that lack enzymatic scavenging pathways. The underlying mechanisms of how nanoceria ROS scavenging augments plant tolerance to environmental stress are not well understood. Herein, we demonstrate that catalytic ˙OH scavenging by nanoceria in Arabidopsis thaliana leaves significantly improves mesophyll K + retention, a key trait associated with salinity stress tolerance. Leaves with mesophyll cells interfaced with 50 mg L −1 poly(acrylic acid) coated nanoceria (PNC) have significantly higher ( P < 0.05) carbon assimilation rates (85%), quantum efficiency of photosystem II (9%), and chlorophyll content (14%) compared to controls after being exposed to 100 mM NaCl for 3 days. PNC infiltrated leaves (PNC-leaves) under salinity stress exhibit lower ROS levels – including hydroxyl radical (41%) and its precursor hydrogen peroxide (44%) – and one fold higher ( P < 0.05) cytosolic K + dye intensity in leaf mesophyll cells relative to controls. Non-invasive microelectrode ion flux electrophysiological (MIFE) measurements indicated that PNC-leaves have about three-fold lower NaCl-induced K + efflux from leaf mesophyll cells compared to controls upon exposure to salinity stress. The ROS-activated nonselective cation channels (ROS-NSCC) in the plasma membrane of leaf mesophyll cells were identified as the main ˙OH-inducible K + efflux channels. Long term catalytic scavenging of ˙OH in leaves by PNC enhances plant photosynthetic performance under salinity stress by enabling plasma membrane channels/transporters to coordinately retain higher levels of K + in the leaf mesophyll cell cytosol. PNC augmented plant ROS scavenging provides a key tool for understanding and improving plant tolerance against abiotic stresses such as salinity.more » « less
-
null (Ed.)Different microclimates can have significant impact on the physiology of succulents that inhabit arid environments such as the Mojave Desert (California). We investigated variation in leaf physiology, morphology and anatomy of two dominant Mojave Desert monocots, Yucca brevifolia (Joshua tree) and Hesperoyucca whipplei , growing along a soil water availability gradient. Stomatal conductance ( g s ) and leaf thickness were recorded in the field at three different sites (north-western slope, south-eastern slope, and alluvial fan) in March of 2019. We sampled leaves from three individuals per site per species and measured in the lab relative water content at the time of g s measurements, saturated water content, cuticular conductance, leaf morphological traits (leaf area and length, leaf mass per area, % loss of thickness in the field and in dried leaves), and leaf venation. We found species varied in their g s : while Y. brevifolia showed significantly higher g s in the alluvial fan than in the slopes, H. whipplei was highest in the south-eastern slope. The differences in g s did not relate to differences in leaf water content, but rather to variation in number of veins per mm 2 in H. whipplei and leaf width in Y. brevifolia . Our results indicate that H. whipplei displays a higher water conservation strategy than Y. brevifolia . We discuss these differences and trends with water availability in relation to species’ plasticity in morphology and anatomy and the ecological consequences of differences in 3-dimensional venation architecture in these two species.more » « less
- Free Publicly Accessible Full Text
-
Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1639/0007-2745-127.3.342
