Diel Patterns of Water Potential Components for the Crassulacean Acid Metabolism Plant Opuntia ficus-indica when Well-Watered or Droughted

Abstract

Under well-watered conditions, chlorenchyma acidity in ciadodes of Opuntia ficus-indica increased substantially at night, fully accounting for the 0.26-megapascal noctumal increase in osmotic pressure in the outer 2 millimeters. Osmotic pressure in the inner part of the chlorenchyma and in the water-storage parenchyma did not change significantly over 24-hour periods. Three months of drought decreased nocturnal acid accumulation by 73% and essentially abolished transpiration; also, 27% of the chlorenchyma water and 61% of the parenchyma water was lost during such drought, but the average tissue osmotic pressure was little affected. Turgor pressure was maintained in the chlorenchyma after 3 months of drought, although it decreased sevenfold in the water-storage parenchyma compared with the wellwatered condition. Moreover, the nocturnal increases in turgor pressure of about 0.08 megapascal in the outer part of the chlorenchyma was also unchanged by such drought. The water potential magnitudes favored water movement from the parenchyma to the chlorenchyma at the end of the night and in the reverse direction during the late afternoon. Experiments with tritiated water support this pattern of water movement, which is also in agreement with predictions based on electric-circuit analog models for Crassulacean acid metabolism plants. Several and the photosynthetic tissue (chlorenchyma) reduces the distance for water movement between them, with important consequences for the daily water relations of shoot tissues of CAM plants, the focus of this study.Certain aspects of the water relations of CAM plants have not been extensively investigated in detail (18). For instance, both solute accumulation and increased tissue elasticity can lower the V3 at which P becomes zero, a phenomenon that has not been studied in CAM plants. Recently, the effects of acid accumulation rhythms of CAM on individual 1 components have been evaluated (8,19,23,24), although none of these studies simultaneously measured the diel variations in ir and P of different shoot tissues. The increase in the concentration of malic acid and hence in ir at night can create a 'I gradient leading to water acquisition by the chlorenchyma cells (6).The major objective of the present investigation was to determine the diel patterns of T components in photosynthetic and water storage tissue of cladodes of Opuntia ficusindica, a CAM plant cultivated worldwide for its fruits and cladodes ( 1). An understanding of the behavior and interactions of the 'P components in these tissues may help elucidate the diel pattern of water flow for both well-watered and droughted plants. Transpiration, titratable acidity, 3r, P, and T therefore were measured over 24-h periods for both wellwatered plants and plants subjected to drought for 3 months. A radioactive tracer technique was used to assess the water exchange between the wsp and the chlorenchyma. MATERIALS AND METHODS Plant Material

CO2 uptake of Opuntia ficus-indica (L.) Mill. whole trees and single cladodes, in relation to plant water status and cladode age

“…Moreover, the chlorenchyma dw of 1-and 2-year-old cladodes did not change significatively along with the season. Similarly, Goldstein et al (1991) and Nerd and Nobel (1991) reported that, after a 15-week drought period, cladode water content decreased by around 60%, and the water-storage parenchyma lost a greater fraction of water (61%) than the chlorenchyma (27%), which most likely helped maintain nocturnal acid accumulation in the latter tissue. The accumulated C, in absence of fruit, was apparently partitioned, in well-watered cladodes, to the parenchyma of 1-and 2-year-old cladodes and to the current-year growth.…”

Soil water dynamics and evapotranspiration of forage cactus clones under rainfed conditions

“…In low soil water availability conditions, the apical meristem of cactus pear roots dies while the deeper cells continue to divide and increase their length, but at lower rates (Dubrovsky et al, 1998). In addition, forage cactus water loss occurs preferably by parenchyma, allowing higher collenchyma hydration and ensuring continuous productive increment (Goldstein et al, 1991).…”

Activities of carboxylating enzymes in the CAM species Opuntia ficus-indica grown under current and elevated CO2 concentrations

“…Sampling times were based on the maximal activities observed over 24-h periods. In particular, samples for Rubisco were collected 1-2 h after midday and those for PEPCase 2-3 h after sunset, when nighttime CO2 uptake rates were high but C4 acids had not yet built up substantially (Goldstein et al 1991). Discs 1.4 cm in diameter, including the chlorenchyma from both sides of a cladode, were removed with a cork borer.…”