Amount Of Aerenchyma Research Articles

Effects of Water Stress and Auxin Application on Growth and Yield of Two Sugarcane Cultivars under Greenhouse Conditions

Water stress (drought and flood) is one of the major factors that limits sugarcane growth and yield. The two greenhouse experiments were conducted at Khon Kaen University, Thailand. The first experiment investigated the individual and combined effects of droughts and floods on two sugarcane cultivars. The results showed that photosynthetic potential, based on chlorophyll a fluorescence (PSII) and chlorophyll content, exhibited a response to the water regime treatments. However, stomatal conductance in the K93-219 cultivar was higher than the KK3 cultivar. Similarly, plant height, number of tillers, number of stems, fresh stem weight, and sugar quality were not affected by the varying water regime conditions imposed on both of the sugarcane cultivars. However, drought or flood conditions, whether alone or in combination, reduced the fresh stem weight, with regards to the water regimes and cultivars. In general, a combination of drought and flood reduced the fresh stem weight as opposed to drought or flood alone. The KK3 cultivar gave a higher fresh stem weight than the K93-219 cultivar under dual stress conditions. The second experiment investigated the auxin application rates at different growth stages on two sugarcane cultivars under flood conditions. The results revealed that the application of auxin at 10 mg L−1 increased the number, and fresh weight, of adventitious roots over the control (0 mg L−1). The cultivar K93-219 produced a higher number, and fresh weight, of adventitious roots. However, the amount of aerenchyma in the adventitious roots was not affected by auxin application rates, growth stages, or cultivars. Similarly, plant height, leaf width, number of stems, fresh stem weight, and sugar quality were not affected by auxin rates. Auxin application at five months of age increased leaf width and fresh stem weight over the control. The cultivar K93-219 tended to produce a higher fresh stem weight than the KK3 cultivar.

Root Cortex Provides a Venue for Gas-Space Formation and Is Essential for Plant Adaptation to Waterlogging.

Lysigenous aerenchyma, which develops by death and subsequent lysis of the cortical cells in roots, is essential for internal long-distance oxygen transport from shoot base to root tips of plants in waterlogged soil. Although many studies focus on the amounts of aerenchyma in roots, significance of the size of the root cortex in which aerenchyma forms has received less research attention. In the present study, we evaluated the cross-sectional area of each root tissue in adventitious roots of upland crops, wheat (Triticum aestivum) and maize (Zea mays ssp. mays), and the wetland crop, rice (Oryza sativa) under aerated or stagnant deoxygenated conditions; the latter can mimic the changes in gas composition in waterlogged soils. Our analyses revealed that the areas of whole root and cortex of the three species increased under stagnant conditions. In rice roots, cortex to stele ratio (CSR) and aerenchyma to cortex ratio (ACR), which is associated with the areas of gas spaces, were much higher than those in wheat and maize roots, suggesting that these anatomical features are essential for a high capacity for oxygen transport along roots. To test this hypothesis, rates of radial oxygen loss (ROL), which is the diffusive flux of oxygen from within a root to the external medium, from thick and thin adventitious roots of rice were measured using a cylindrical (root-sleeving) oxygen electrode, for plants with shoots in air and roots in an oxygen-free medium. As expected, the rate of ROL from thick roots, which have larger cortex and aerenchyma areas, was higher than that of thin roots. The rate of ROL was highest at the apical part of rice roots, where aerenchyma was hardly detected, but at which cuboidal cell arrangement in the cortex provides tissue porosity. We conclude that high CSR in combination with large root diameter is a feature which promotes oxygen transport from shoot base to root tips of plants. Moreover, we propose that CSR should be a useful quantitative index for the evaluation and improvement of root traits contributing to tolerance of crops to soil waterlogging.

Plant Stress-Tolerance Traits Predict Salt Marsh Vegetation Patterning

It is increasingly acknowledged that stresses can resonate across the boundaries between ecosystems. Salt marshes, vast areas shaped by ocean-shore interactions, constitute prime examples of ecosystems where multiple stress factors arising from one ecosystem act on the local community of another ecosystem. Although it is generally recognized that zonation of plant communities on salt marshes is strongly affected by marine stress factors associated with frequent flooding (salinity, anoxia), it is largely unknown what the isolated and interacting effect are of these different stresses. This calls for experiments to disentangle the relative effects of these single and interacting multiple stresses. In this study, we determined the single and interacting effects of two main abiotic stress factors on salt marshes: salinity and anoxia (as a result of flooding) and one biotic stress factor: soil compaction (as a result of livestock grazing) on the growth of the twelve dominant salt marsh plant species, using a full-factorial experiment. To link the experimental work to distributions of natural plant communities along a natural stress gradient, we related our experimental results to observed plant species distributions on a salt marsh that is exposed to all these three stresses. Whereas salinity strongly affected ten species with two high-marsh species not surviving the highest salinity levels whereas anoxia only consistently affected growth of four species. Interestingly, we observed no synergistic effect of anoxia and salinity in salt marsh plants. Moreover, we observed a trade-off between the amount of aerenchyma and mechanical strength, indicating that species vary in their resistance to soil compaction. Overall, our results suggest that salinity is a major determinant of plant species composition on the salt marsh, followed by anoxia. The importance of soil compaction depends on salt marsh elevation: on the low marsh, increased oxygen supply by aerenchyma seems to outweigh resistance against mechanical stress whereas on the anaerobe low marsh, the reverse applies. Using the experimental data to predict cover of plant species in the field, our results suggest that the combination of plant responses to the various stresses may be a powerful predictor for explaining the plant composition on the salt marsh.

MORPHOANATOMY OF Garcinia madruno (KUNTH) HAMMEL (CLUSIACEAE) UNDER WATERLOGGED CONDITIONS

ABSTRACT Garcinia madruno (Kunth) Hammel is a neotropical tree that naturally occurs in terra firme forests and is important as a source of income and medicine for Amazonian populations. This study describes and compares the morphoanatomical responses of plants under conditions of stress and normoxia. Young plants of Garcinia madruno were subjected to two water regimes: daily controlled irrigation and waterlogged for 84 days. Hypertrophic lenticels, adventitious roots and anatomical characteristics of the roots and leaves were evaluated on days 0, 21, 42, 63 and 84. There were no changes in leaf structure, but cracks and hypertrophic lenticels appeared on the stems, there was an increase in blackness of the roots and the plants formed adventitious roots to adapt to the flooded environment. The anatomical changes in the roots of the flooded plants were thickening of the exodermis in the main root and of the pericycle in the lateral roots, and a large increase in the amount of aerenchyma. Histochemical tests detected starch in the midrib, mesophyll, stem and root of flooded plants, and in the petiole of control plants. In the waterlogged plants, phenolic compounds were found in the petiole and alkaloids were found in the midrib, petiole and root.

Anatomy And Morphology Of Rhizophora Stylosa In Relation To Internal Airflow And Attim's Plant Architecture

Abstract The purpose of this research was to: (1) document the path of internal airflow, (2) describe and quantify tissues of internal airflow, and (3) determine if the amounts of aerenchyma in leaves, stems, and roots are relatively constant among plants of Rhizophora stylosa. Cork warts of leaves (average of 10.1 cork warts per mm2 of leaf surface) are sites of air uptake. Cork warts deliver air to aerenchyma tissues near adaxial leaf surfaces (30% of total leaf volume). Air becomes pressurized within illuminated leaf blade aerenchyma by hygrometric pressurization and this air enters the petiole aerenchyma. In turn, the petiole aerenchyma joins the stem aerenchyma (5.5% of total stem area). Air descends the stem aerenchyma and then passes to the inner aerenchyma of stilt roots (about 15% of root cross-sectional area). Air descends in the inner aerenchyma of roots and eventually enters the smallest roots growing in anoxic substrates. From these terminal portions of roots, air ascends the outer aerenchyma...

Aerenchyma development and oxygen transport in the estuarine cordgrasses Spartina alterniflora and S. anglica

Spartina alterniflora and Spartina anglica are intertidal cordgrasses that have the capacity to develop extensive aerenchyma systems. Aerenchyma may supply submerged portions of the plant with atmospheric oxygen as well as lower metabolic demands of the plant. These physiological benefits help to make Spartina grasses formidable invasive species in areas where they have been introduced. Aerenchyma development was investigated in S. alterniflora and S. anglica maintained in greenhouse experiments under flooded and drained soil conditions. Amounts of aerenchyma along the lengths of roots were calculated from digital images of serial root cross-sections using image analysis software. Maximal aerenchyma formation occurred in S. alterniflora following exposure to flooded conditions, while aerenchyma in S. anglica did not increase under the same conditions. Aerenchyma function was investigated by testing individual Spartina plants for their ability to transport oxygen from leaves to roots. Oxygen transport capacities provided information about the plants’ oxygen demands and the overall effectiveness of their aerenchyma systems. S. anglica plants were able to transport substantial oxygen to their roots, but no oxygen transport was detected in S. alterniflora plants under the same conditions. Increased aerenchyma formation in flooded S. alterniflora did not enhance oxygen transport and may function primarily in reducing metabolic oxygen demands.

Flooding tolerance of Carex species in relation to field distribution and aerenchyma formation.

The flooding tolerance of Carex species was studied in relation to their field distribution and their capacity to form root aerenchyma under controlled conditions. In an alpine meadow, six Carex species were selected which were distributed in a clear zonation correlating with water content of the soil. Carex sempervirens and C. ferruginea were only found on nonflooded soil, the latter species preferring moister conditions. Carex davalliana and C. nigra were both associated with water-saturated soil, whereas C. limosa and C. rostrata preferred partially submerged conditions. Carex davalliana and C. limosa were bound to flooded soils with a relatively high redox potential and horizontally flowing groundwater. Carex rostrata and C. nigra grew in stagnant soil-flooded conditions with low soil redox potentials. The amount of aerenchyma in the roots of all species increased when grown in oxygen-deficient stagnant agar. This increase in root porosity, combined with increased root diameter, presumably improved internal aeration of the roots. Although all species survived experimental soil flooding, partial submergence was lethal to C. sempervirens and, surprisingly, also to the wetland species C. davalliana. Carex ferruginea showed a reduced growth rate during partial submergence. The three other species, all wetland plants, reached highest biomass production under soil-flooded and partially submerged conditions, with slower growth on free-draining soil. It is concluded that aerenchyma is not constitutive in the Carex species under study, and is best developed in Carex species from wetlands. Species with less aerenchyma perform poorly when soil-flooded, but conditions of partial submergence could even affect species with a considerable amount of root aerenchyma.