Leaf Anatomical Adaptation Under Early Drought Stress of Sugarcane Cultivars – KKU-1999-02 and KKU-1999-03

Anatomical adaptation is an important feature that allows plants to mitigate drought stress. A comparative leaf anatomy of two drought-tolerant sugarcane cultivars, KKU-1999-02 and KKU-1999-03, was studied in early drought stress between 30 and 90 days after planting using peeling and freehand sectioning methods. KKU-1999-02 and KKU-1999-03 showed different anatomical adaptation features, such as increase in cuticle thickness, bulliform cell size, vascular bundle, and stomatal density, and decreases in leaf thickness and stomatal size. KKU-1999-02 showed more remarkable anatomical changes than KKU-1999-03. The results provide important information that can be applied in combination with other agronomic traits in sugarcane breeding programs to expand the adaptation devices of tolerant cultivars under preliminary drought stress.

Mycorrhizal impact on Ocimum basilicum grown under drought stress

Background Ocimum basilicum was grown under three levels of drought stress (100% Field capacity, 70% Field capacity, and 40% Field capacity). Half of the plants were inoculated with Arbuscular mycorrhiza and the other half was not inoculated. Arbuscular mycorrhizal fungi (AMF) were applied to improve plant growth and to alleviate drought stress on sweet basil. Results Drought Couse inhibition in the colonization of Arbuscular mycorrhiza, reduction in plant growth, decrease stomatal size increase stomatal density, a decline in soluble carbohydrates, accumulation of amino acids, proline, and glycine betaine, and reduction in some minerals such as P, K, and Na. Conclusions The effect of drought was alleviated by the application of inoculation with Arbuscular mycorrhiza.

Assessment of the Value of Stomatal Size and Density as Hallmarks of Nonaploid Kiwifruit Plants

In vitro-derived plants with elevated ploidy levels can display distinguishing features from the plants they are derived from, especially owing to their indirect regeneration. Genome size affects cell size and, thus, affects plant morphological characteristics. Therefore, stomata traits may be used as a diagnostic feature allowing identification of ploidy. Actinidia chinensis var. deliciosa A. Chev. (A. Chev.), known as kiwifruit, is successfully cultured in vitro and redifferentiated into plants via endosperm-derived calli. To identify differences between hexaploids obtained from seeds and confirmed nonaploids obtained from endosperm-derived calli, we analyzed the stomata. Our results confirmed that ploidy coincides with mean stomatal length, width, and density. Despite this correlation, this method cannot be used to distinguish individual hexaploid kiwifruit plants from nonaploid ones because samples with different ploidy yielded overlapping measurements.

Particulate Matter Removal of Three Woody Plant Species, Ardisia crenata, Ardisia japonica, and Maesa japonica

In this study, we investigated the physiological responses and particulate matter (PM) abatement and adsorption of three plants: Ardisia crenata, Ardisia japonica, and Maesa japonica, to determine their effectiveness as indoor air purification. When compared to control (without plants), PM was significantly and rapidly decreased by all three plants. The reduction in PM varied by species, with A. crenata being the most effective, followed closely by A. japonica, and finally M. japonica. M. japonica showed the highest rate of photosynthesis and transpiration, generating the greatest decrease in CO2 and a large increase in relative humidity. We hypothesize that the increased relative humidity in the chamber acted in a manner similar to a chemical flocculant, increasing the weight of PM via combination with airborne water particles and the creation of larger PM aggregates, resulting in a faster sedimentation rate. A. crenata had a stomatal size of ~20 μm or larger, suggesting that the PM reduction observed in this species was the result of direct absorption. In the continuous fine dust exposure experiments, chlorophyll fluorescence values of all three species were in the normal range. In conclusion, all three species were found to be suitable indoor landscaping plants, effective at reducing indoor PM.

Research articleTwo galacturonosyltransferases function in plant growth, stomatal development, and dynamics

The mechanical properties of guard cell (GC) walls are important for stomatal development and stomatal response to external stimuli. However, the molecular mechanisms of pectin synthesis and pectin composition controlling stomatal development and dynamics remain poorly explored. Here, we characterized the role of two Arabidopsis (Arabidopsis thaliana) galacturonosyltransferases, GAUT10 and GAUT11, in plant growth, stomatal development, and stomatal dynamics. GAUT10 and GAUT11 double mutations reduced pectin synthesis and promoted homogalacturonan (HG) demethylesterification and demethylesterified HG degradation, resulting in larger stomatal complexes and smaller pore areas, increased stomatal dynamics, and enhanced drought tolerance of plants. In contrast, increased GAUT10 or GAUT11 expression impaired stomatal dynamics and drought sensitivity. Genetic interaction analyses together with immunolabeling analyses suggest that the methylesterified HG level is important in stomatal dynamics, and pectin abundance with the demethylesterified HG level controls stomatal dimension and stomatal size. Our results provide insight into the molecular mechanism of GC wall properties in stomatal dynamics, and highlight the role of GAUT10 and GAUT11 in stomatal dimension and dynamics through modulation of pectin biosynthesis and distribution in GC walls.

Developmental integration cannot explain major features of stomatal anatomical evolution in seed plants

Developmental integration can cause traits to covary over macroevolutionary time and in some cases prevent populations from reaching their adaptive optima. Developmental integration between stomatal size and density may contribute to two major features of stomatal anatomical evolution: inverse size-density scaling and bimodal stomatal ratio. If these patterns result from developmental integration, we predicted that in amphistomatous leaves 1) stomatal size and density should covary similarly on both abaxial and adaxial surfaces and 2) stomatal traits (size and density) on each surface should covary isometrically. We synthesized data on stomatal density and length from amphistomatous leaves of 711 terrestrial seed plant taxa mostly from the literature. We estimated the covariance in divergence between stomatal traits from 327 phylogenetically independent contrasts using a robust Bayesian model. Adaxial stomatal density, but not length, is evolutionarily labile and not strongly integrated with stomatal length or abaxial stomatal density. Hence, developmental integration alone cannot explain inverse size-density scaling nor bimodal stomatal ratio. Quasi-independent evolution of stomatal anatomical traits facilitates largely unfettered access to fitness optima. If stomatal anatomical traits are near their current fitness optimum, this implies that limits on trait (co)variance result from selective rather than developmental constraints. However, we cannot rule out that developmental integration is important in some lineages. Future research should identify the mechanistic basis of(dis)integration in stomatal development.

Morphological Characterization of Tetraploids of Limonium sinuatum (L.) Mill. Produced by Oryzalin Treatment of Seeds

Limonium sinuatum (L.) Mill. (2n = 2x = 16) is a popular ornamental plant with dimorphism of pollen grains (type A and type B) and stigmas (papilla and cob-like). We applied polyploidy breeding to this species in order to introduce desirable traits. Tetraploid and mixoploid L. sinuatum plants were successfully obtained with oryzalin treatment of L. sinuatum ‘Early Blue’ seeds. All three tetraploids had increased leaf width, stomatal size, flower length, and pollen width compared to those of the diploid, and tetraploids had four germinal pores of pollen grains, whereas the diploid had three. All tetraploids had type A pollen grains and cob-like stigmas. Furthermore, the growth of cultivated tetraploid plants was slow, with later bolting and flowering times. Mixoploids Mixo-1 and Mixo-3 were estimated to be polyploidy periclinal chimeric plants consisting of a tetraploid L1 layer and diploid L2 layer, and Mixo-2 was estimated to be a polyploidy periclinal chimeric plant consisting of the diploid L1 layer and tetraploid L2 layer. Mixo-4 had tetraploid L1 and L2 layers. Mixoploids, except Mixo-4, had type A pollen grains and cob-like stigmas, whereas Mixo-4 had type B pollen grains and papilla stigmas. These polyploids will be useful as polyploidy breeding materials.

The Receptor-Like Kinase ERECTA Confers Improved Water Use Efficiency and Drought Tolerance to Poplar via Modulating Stomatal Density

Poplar is one of the most important tree species in the north temperate zone, but poplar plantations are quite water intensive. We report here that CaMV 35S promoter-driven overexpression of the PdERECTA gene, which is a member of the LRR-RLKs family from Populus nigra × (Populus deltoides × Populus nigra), improves water use efficiency and enhances drought tolerance in triploid white poplar. PdERECTA localizes to the plasma membrane. Overexpression plants showed lower stomatal density and larger stomatal size. The abaxial stomatal density was 24–34% lower and the stomatal size was 12–14% larger in overexpression lines. Reduced stomatal density led to a sharp restriction of transpiration, which was about 18–35% lower than the control line, and instantaneous water use efficiency was around 14–63% higher in overexpression lines under different conditions. These phenotypic changes led to increased drought tolerance. PdERECTA overexpression plants not only survived longer after stopping watering but also performed better when supplied with limited water, as they had better physical and photosynthesis conditions, faster growth rate, and higher biomass accumulation. Taken together, our data suggest that PdERECTA can alter the development pattern of stomata to reduce stomatal density, which then restricts water consumption, conferring enhanced drought tolerance to poplar. This makes PdERECTA trees promising candidates for establishing more water use efficient plantations.

Abscisic acid implicated in differential plant responses of Phaseolus vulgaris during endophytic colonization by Metarhizium and pathogenic colonization by Fusarium

Metarhizium robertsii is an insect pathogen as well as an endophyte, and can antagonize the phytopathogen, Fusarium solani during bean colonization. However, plant immune responses to endophytic colonization by Metarhizium are largely unknown. We applied comprehensive plant hormone analysis, transcriptional expression and stomatal size analysis in order to examine plant immune responses to colonization by Metarhizium and/or Fusarium. The total amount of abscisic acid (ABA) and ABA metabolites decreased significantly in bean leaves by plant roots colonized by M. robertsii and increased significantly with F. solani compared to the un-inoculated control bean plant. Concomitantly, in comparison to the un-inoculated bean, root colonization by Metarhizium resulted in increased stomatal size in leaves and reduced stomatal size with Fusarium. Meanwhile, expression of plant immunity genes was repressed by Metarhizium and, alternately, triggered by Fusarium compared to the un-inoculated plant. Furthermore, exogenous application of ABA resulted in reduction of bean root colonization by Metarhizium but increased colonization by Fusarium compared to the control without ABA application. Our study suggested that ABA plays a central role in differential responses to endophytic colonization by Metarhizium and pathogenic colonization by Fusarium and, we also observed concomitant differences in stomatal size and expression of plant immunity genes.

Diverse Physiological and Physical Responses among Wild, Landrace and Elite Barley Varieties Point to Novel Breeding Opportunities

Climate change from elevated [CO2] may reduce water availability to crops through changes in precipitation and higher temperatures. However, agriculture already accounts for 70% of human consumption of water. Stomata, pores in the leaf surface, mediate exchange of water and CO2 for the plant. In crops including barley, the speed of stomatal response to changing environmental conditions is as important as maximal responses and can thus affect water use efficiency. Wild barleys and landraces which predate modern elite lines offer the breeder the potential to find unexploited genetic diversity. This study aimed to characterize natural variation in stomatal anatomy and leaf physiology and to link these variations to yield. Wild, landrace and elite barleys were grown in a polytunnel and a controlled environment chamber. Physiological responses to changing environments were measured, along with stomatal anatomy and yield. The elite barley lines did not have the fastest or largest physiological responses to light nor always the highest yields. There was variation in stomatal anatomy, but no link between stomatal size and density. The evidence suggests that high photosynthetic capacity does not translate into yield, and that landraces and wild barleys have unexploited physiological responses that should interest breeders.