Stomata Profile Comparisons in Abaxial and Adaxial Zones of Dendrobium aphyllum and Arachnis flos-aeris Leaves

Stomata play an essential role in transpiration and metabolism. Orchids are Crassulacean Acid Metabolism (CAM) plants which are generally succulent leaf type. Orchids have several types of stomata, depending on habitat and environmental parameters that affect them. This study aimed to compare the stomata, including the anatomical structure, activity, and density of the orchids Dendrobium aphyllum and Arachnis flos-aeris. The method used was printing the surface of the leaves using glue and observed with a microscope. Data obtained were analyzed with the help of Image raster 3.0 and MS. Excel. In the present study, the stomata of D. aphyllum and A. flos-aeris are characterized by anomocytic type. The highest stomata density was obtained on the abaxial part of D. aphyllum 09.00 am 1177.78 um2. The adaxial leaves of both species are classified as low, or no stomata are found at all. The distance between the stomata on the abaxial leaves of D. aphyllum and A. flos-aeris is denser than the leaves' adaxial side. Stomata activity in orchids is related to orchids' adaptation process to the environmental parameters of their habitat. Stomata activity affects the transpiration process and CO2 fixation in orchid CAM metabolism.

Light Stress Is Not Effective to Enhanced Crassulacean Acid Metabolism

Clusia minor L., a C3-CAM intermediate, and Clusia multifl ora H. B. K., a C3 obligate, present two physiotypes of a similar morphotype occurring sympatrically in the fi eld. Both species, exposed 2 days to high light, show similar responses to this kind of stress: (i) the level of xanthophyll pigments in tested plants during the daycourse adapts to stress, (ii) the levels of antheraxanthin and zeaxanthin clearly increase during the afternoon showing increased de-epoxidation, (iii) the changes in the xanthophyll cycle are similar. Exposure to high light increases the malate levels in C. minor during the afternoon while decreases the day/night changes of the malate levels, and hence the Crassulacean Acid Metabolism (CAM) expression. It can be concluded that strong light applied as a single stress factor to well-watered plants is not effective in strengthing the CAM metabolism in a C3-CAM intermediate plant but rather suppresses the CAM activity despite exposure to high light energy. It is suggested that, when water supply is not limiting and other stresses do not prevail, C3 allows to use up the citrate pool, especially in the afternoon and enables a superior daily photon utilization.

Do Circadian Rhythms Accentuate K Deficiency in Geranium?

Geranium (Pelargonium ×hortorum) typically follows the C3 metabolic pathway. However, it switches to CAM metabolism under certain abiotic stress environments. This switch may affect the nutritional requirement and appearance of visible deficiency symptoms of these plants. Because potassium (K) plays a key role in stomatal function, K-deficiency was studied in geranium. Plants were grown hydroponically in a glass greenhouse. The treatments consisted of a complete, modified Hoagland's solution with millimolar concentrations of macronutrients, 15 NO3-N, 1.0 PO4-P, 6.0 K, 5.0 Ca, 2.0 Mg, and 2.0 SO4-S and micromolar concentrations of micronutrients, 72 Fe, 9.0 Mn, 1.5 Cu, 1.5 Zn, 45.0 B, and 0.1 Mo, and an additional solution devoid of K. It took longer to develop the classic K deficiency symptoms than other bedding plant species commonly require. The K-stress plants' dry weight was 10% and 37% of control at incipient and advanced stage, respectively. When portions of geranium leaves were covered, symptomology on leaves with K stress developed rapidly (within 2 days) compared to the uncovered portion of the leaf blade. Control plants contained an abundance of marble-shaped K crystals in the adaxial surface of leaf mesophyll, but were lacking in the K-deficient plants. Geranium is more prone to K stress during short days than long days and an additional supply of K would be needed for normal growth in short days.

Malate Accumulation in Different Organs of Mesembryanthemum crystallinum L. Following Age-dependent or Salinity-triggered CAM Metabolism

Different organs of Mesembryanthemum crystallinum exhibit differing levels of CAM (Crassulacean acid metabolism), identifiable by quantification of nocturnal malate accumulation. Shoots and also basal parts of young leaves were observed to accumulate high concentrations of malate. It was typically found in mature leaves and especially prominent in plants subjected to salt stress. Small amount of nocturnal malate accumulation was found in roots of M. crystallinum plants following age-dependent or salinity-triggered CAM. This is an indication that malate can be also stored in non-photosynthetic tissue. Measurements of catalase activity did not produce evidence of the correlation between activity of this enzyme and the level of malate accumulation in different organs of M. crystallinum although catalase activity also appeared to be dependent on the photoperiod. In all material collected at dusk catalase activity was greater than it was observed in the organs harvested at dawn.