Total Relative Water Content Research Articles

Growth and vase life of gladiolus plants cultivated under different conditions in the semi-arid region of Brazil

Abstract Cultivation conditions are determining factors that affect the quality of cut flowers. The objective of this study was to evaluate the vegetative growth, flowering and vase life of commercial gladiolus cultivars under different shading conditions in the Brazilian semi-arid region. Two cultivars of gladiolus (Jester and Rose Friendship) were grown under two conditions: full sun and 70% shade. Biometrics were evaluated 60 days after planting and the growth rate of the crop was evaluated at 15-30, 30-45 and 45-60 days for the variables: number of tillers, stem diameter, number of leaves and plant height. After 45 days, the fresh weight, dry weight and total relative water content of the area and root parts of the plants were evaluated. After the harvest, the stems were kept at a temperature of 22±3 °C and relative humidity (RH) of 60%. Visual assessment, pH of the solution, variation in the volume of water and loss of fresh mass were measured every two days. Cultivation with 70% shading resulted in greater accumulation of biomass in the aerial part of gladiolus plants, greater neck diameter and height. The Rose Friendship cultivar underwent a greater translocation of dry matter to the aerial part of the plants, resulting in greater height. On the other hand, the gladiolus stems from cultivation under full sun conditions resulted in longer vase life, 10 days under conservation conditions at 22±3 °C and RH 60%.

Natrum muriaticum atenúa el estrés por NaCl en Capsicum annuum L. var. glabriusculum

Soil salinity is a global problem that increases year by year in arid and semi-arid regions, including Mexico where the distribution and extension of salinized soils reduces productivity and causes severe damage to different cultivated species. Homeopathic medicine is compatible with traditional, ecologic, and organic agriculture, and it can increase tolerance to salinity stress conditions and improve soil-plant ratio. Chiltepin chili (Capsicum annuum L. var. glabriusculum) is a species of high commercial value in northern Mexico affected by soil salinity. Thus, the objective of this study was to assess the eff iciency of Natrum muriaticum (NaM) homeopathic medicine for human use, to mitigate NaCl stress in chiltepin chili established in a hydroponic system and subjected to different NaCl concentrations. A completely randomized design (2A × 3B) with factorial arrangement was used with four replicates of nine plants each. The plants were subjected to two NaCl (0 and 200 mM) concentrations, two centesimal NaM (7CH and 13CH) of NaM (NaM-7CH and NaM-13CH) dynamizations and a control treatment without NaM. The variables evaluated were length, aerial and root part fresh and dry weight, leaf area, chlorophyll A, B, total relative water content, and water potential. In general, the plants treated with NaM-13CH showed the highest values for the majority of the morphometric and physiological variables, including the plants subjected to high salinity stress by adding NaCl (200 mM). These results conf irmed that NaM attenuated NaCl stress in chiltepin chili (C. annuum L. var. glabriusculum) plants and that agricultural homeopathy has the potential to increase productivity and yield in hydroponic cultivation of the species.

Coping with gravity: the foliar water relations of giant sequoia.

In tall trees, the mechanisms by which foliage maintains sufficient turgor pressure and water content against height-related constraints remain poorly understood. Pressure-volume curves generated from leafy shoots collected crown-wide from 12 large Sequoiadendron giganteum (Lindley) J. Buchholz (giant sequoia) trees provided mechanistic insights into how the components of water potential vary with height in tree and over time. The turgor loss point (TLP) decreased with height at a rate indistinguishable from the gravitational potential gradient and was controlled by changes in tissue osmotica. For all measured shoots, total relative water content at the TLP remained above 75%. This high value has been suggested to help leaves avoid precipitous declines in leaf-level physiological function, and in giant sequoia was controlled by both tissue elasticity and the balance of water between apoplasm and symplasm. Hydraulic capacitance decreased only slightly with height, but importantly this parameter was nearly double in value to that reported for other tree species. Total water storage capacity also decreased with height, but this trend essentially disappeared when considering only water available within the typical range of water potentials experienced by giant sequoia. From summer to fall measurement periods we did not observe osmotic adjustment that would depress the TLP. Instead we observed a proportional shift of water into less mobile apoplastic compartments leading to a reduction in hydraulic capacitance. This collection of foliar traits allows giant sequoia to routinely, but safely, operate close to its TLP, and suggests that gravity plays a major role in the water relations of Earth's largest tree species.

Solute accumulation and elastic modulus changes in six radiata pine breeds exposed to drought

Drought is one of the main abiotic factors that determine forest species growth, survival and productivity. For this reason, knowledge of plant drought response and the identification of physiological traits involved in stress tolerance will be of interest to breeding programs. In this work, several Pinus radiata D. Don breeds from different geographical origins were evaluated along a water stress period (4 weeks) and subsequent rewatering (1 week), showing different responses among them. Leaf water potential (Ψ(leaf)) and osmotic potential decreases were accompanied by a variation in the total relative water content (RWC, %). The most tolerant breeds presented the lowest leaf water potential and RWC at turgor loss point, and showed the lowest elastic modulus (ε) values. A high ε value was a characteristic of a less-drought-tolerant plant and was related to membrane alterations (high electrolyte leakage percentages) that could favor cell water loss. Of the group of solutes that contributed to osmotic adjustment, soluble carbohydrates were the most abundant, although stressed plants also increased their content of free amino acids [mainly proline (Pro) and glutamic acid (Glu), and γ-aminobutyric acid (GABA)] and free polyamines. In addition, the most sensitive breeds had a higher GABA/Glu ratio. After rewatering, Pro and GABA were higher in rehydrated plants than in controls.