Complementary patterns of stiffness in stem and leaf sheaths of Triticale : Measurements of ultrasound velocity

Capturing High Resolution Plant Movement in the Field

Lodging of small grains due to environmental stresses results in yield loss, quality reduction, and difficulties with mechanical harvesting, which lead to economic consequences. New technological discoveries allow for faster and in situ measurements for determining the mechanics of loading stress and plant movement. The overall measurement of plant movement can be a very sophisticated method to mechanically test and predict the behavior of stems when exposed to wind. We investigated the inertial measurement of plants during different magnitude wind events. This type of analysis captures real time quantitative stem behavior during wind events. Using a 1.5 cm2 inertial measurement sensor attached to the upper panicle of a plant, we recorded the ranges and extremes of instantaneous linear acceleration and rotational velocity. When this technology was applied to historically known varieties of different lodging classification, the measurements were able to distinguish between cereal species and differences between movement of lodging susceptible and resistant plants without physical lodging. This type of technology could be used to improve field based lodging models and quantify movement resulting from micro changes in structural and composition of the stem, and to analyze plant movement in natural conditions with a resolution and specificity that has so far been prohibitively expensive and technologically challenging to achieve.

Sheathing the blade: Significant contribution of sheaths to daytime and nighttime gas exchange in a grass crop

Despite representing a sizeable fraction of the canopy, very little is known about leaf sheath gas exchange in grasses. Specifically, estimates of sheath stomatal conductance, transpiration and photosynthesis along with their responses to light, CO₂ and vapour pressure deficit (VPD) are unknown. Furthermore, the anatomical basis of these responses is poorly documented. Here, using barley as a model system, and combining leaf-level gas exchange, whole-plant gravimetric measurements, transpiration inhibitors, anatomical observations, and biophysical modelling, we found that sheath and blade stomatal conductance and transpiration were similar, especially at low light, in addition to being genotypically variable. Thanks to high abaxial stomata densities and surface areas nearly half those of the blades, sheaths accounted for up to 17% of the daily whole-plant water use, which -surprisingly- increased to 45% during the nighttime. Sheath photosynthesis was on average 17-25% that of the blade and was associated with lower water use efficiency. Finally, sheaths responded differently to the environment, exhibiting a lack of response to CO₂ but a strong sensitivity to VPD. Overall, these results suggest a key involvement of sheaths in feedback loops between canopy architecture and gas exchange with potentially significant implications on adaptation to current and future climates in grasses.

Physiological Mechanism of Internode Bending Growth After the Excision of Shoot Sheath in Fargesia yunnanensis and Its Implications for Understanding the Rapid Growth of Bamboos

The physiological function of bamboo shoot sheaths is still unclear. In the present study, we investigated the anatomical and physiological influences of bamboo shoot sheaths on internode elongation by longitudinally striping parts of sheaths. The internodes would bend toward the bare sides during night. The results showed that amounts of water leaked at the cut of shoot sheaths during night, which impeded the increase of water, water pressure and assimilate transport rates, and decreased starch and soluble sugar catabolism in the bare side of the internodes. A higher level of water pressure and sugar metabolism increased the vacuole expansion and promoted the cell expansion in the outer sides as compared to the bare sides. The bending growth of internodes was mainly due to the significant differences in cell expansion, which was led by the difference in water pressure and sugar hydrolysis levels between the inner and outer sides. Bamboo internode elongation mainly relied on the increase of water pressure and soluble sugar concentration. Shoot sheaths played an important role in the rapid growth of bamboo shoots as a controller in water and assimilate transportation. This study gave a new insight into understanding the rapid growth mechanism of bamboo plants.

Suppression of Leaf Blade Development by BLADE-ON-PETIOLE Orthologs Is a Common Strategy for Underground Rhizome Growth

Rhizomes are modified stems that grow horizontally underground in various perennial species, a growth habit that is advantageous for vigorous asexual proliferation. In Oryza longistaminata, a rhizomatous wild relative of cultivated rice (Oryza sativa), leaves in the aerial shoots consist of a distal leaf blade and a proximal leaf sheath [1]. Leaf blade formation is, however, suppressed in rhizome leaves. In O. sativa, BLADE-ON-PETIOLE (BOP) genes are the main regulators of proximal-distal leaf patterning [2]. During the juvenile phase of O. sativa, BOP expression is maintained at high levels by the small regulatory RNA microRNA156 (miR156), leading to formation of leaves consisting predominantly of the sheath. Here, we show that in O. longistaminata, high expression of BOPs caused by miR156 was responsible for suppression of the blade in rhizomes and that bop loss-of-function mutants produced leaves consisting of the leaf blade only. Rhizome growth in soil was also hampered in the mutants due to a severe reduction in rhizome tip stiffness. Leaf blade formation is also suppressed in the stolons of Zoysia matrella, a monocot species, and in the rhizomes of Houttuynia cordata, a dicot species, indicating that leaf blade suppression is widely conserved. We also show that strong expression of BOP homologs in both rhizome and stolon leaves rather than in aerial leaves is another conserved feature. We propose that suppression of the leaf blade by BOP is an evolutionary strategy that has been commonly recruited by both rhizomatous and stoloniferous species to establish their unique growth habit.

Bamboo sheath-A modified branch based on the anatomical observations

Culm sheath has always been considered a modified leaf. In this study, the anatomical structure of the culm sheath from Fargesia yunnanensis was analyzed to determine whether it originated from the foliage leaf blade or from the branch. The vascular bundles of the culm sheath showed greater similarity to the branches in shape and anatomical structure. In contrast to foliage blades, there are no midribs in culm sheaths. Stomatal density in the culm sheath is greater in the adaxial than it is in the abaxial epidermis, which is the opposite of that found in foliage leaf blades, and that density shows greater similarity to branches than it does to foliage blades. Fusoid cells are distributed on both sites of the vascular bundles in foliage blades, whereas culm sheaths have, instead, a few parenchyma cells that disintegrate and form air cavities when the sheath matures. Additionally, the culm sheath has no bulliform cells or trichome in its epidermis, and the shape of its long cells shows greater similarity to those of branches. Therefore, culm sheath is a modified branch, rather than a modified leaf.